Compound objective lens having two focal points and apparatus using the lens

Claim 2

A compound objective lens according to claim 1 in which a grating pattern is drawn in the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %.

Claim 3

A compound objective lens according to claim 2 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, and each block of the grating pattern is formed in a step-wise shape to blaze the grating pattern.

Claim 4

A compound objective lens according to claim 1 in which the hologram means is a phase modulation type of diffraction device made of a liquid crystal cell.

Claim 5

A compound objective lens according to claim 1 in which the hologram means is a phase modulation type of diffraction device made of a birefringence material of which a surface part is proton-exchanged.

Claim 6

A compound objective lens according to claim 1 in which the hologram means is partitioned into a pattern region and a no-pattern region surrounding the pattern region, a grating pattern is drawn in the pattern region of the hologram means in a concentric circle shape, and a diameter of the grating pattern is smaller than an aperture of the lens means to transmit the incident light through the no-pattern region of the hologram means without any diffraction.

Claim 7

A compound objective lens according to claim 6 in which the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions in the pattern region, a thickness of the no-pattern region in the hologram means is set to an average value of those of the pattern region, and a phase of the incident light passing through the no-pattern region of the hologram means agrees with an average value of those of the incident light passing through the pattern region of the hologram means.

Claim 8

A compound objective lens according to claim 2 in which the hologram means is partitioned into a pattern region and a no-pattern region, the grating pattern is drawn in the pattern region of the hologram means, a diameter of the grating pattern is smaller than an aperture of the lens means to transmit the incident light through the no-pattern region of the hologram means without any diffraction, the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, a thickness of the no-pattern region is set to a thickness of the pattern region at one of the stairs which is not a top stair or a bottom stair among the stairs, and a phase of the incident light passing through the no-pattern region of the hologram means agrees with an average value of those of the incident light passing through the pattern region of the hologram means.

Claim 9

A compound objective lens according to claim 1 in which a first diffraction efficiency of the hologram means at a first region for the incident light differs from a second diffraction efficiency of the hologram means at a second region for the incident light.

Claim 10

A compound objective lens according to claim 2 in which the height H of the relief in the grating pattern is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the outer direction of the pattern region.

Claim 11

A compound objective lens according to claim 1 in which the transmitted light converged by the lens means passes through a first information medium having a first thickness from its front surface to its rear surface to form the first converging spot on the rear surface of the first information medium, and the diffracted light converged by the lens means passes through a second information medium having a second thickness from its front surface to its rear surface to form the second converging spot on the rear surface of the second information medium, the second thickness differing from the first thickness.

Claim 12

A compound objective lens according to claim 11 in which the hologram means functions as a concave lens for the diffracted light to diverge the diffracted light from the hologram means, and the first thickness of the first information medium is shorter than the second thickness of the second information medium.

Claim 13

A compound objective lens according to claim 12 in which a grating pattern is drawn in a pattern region of the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a difference in phase modulation degree between the incident light transmitting through the bottom portions of the grating pattern and the incident light transmitting through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means for the incident light to a value lower than 100 %, and the diffraction efficiency is gradually lowered toward an outer direction of the pattern region.

Claim 14

A compound objective lens according to claim 12 in which a difference between the first thickness and the second thickness ranges from 50 µm to 1.0 mm.

Claim 15

A compound objective lens according to claim 2 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the outer direction of the pattern region, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the outer direction of the pattern region.

Claim 16

A compound objective lens according to claim 2 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern at a center portion of a pattern region in which the grating pattern is drawn is formed in a first step-wise shape and is composed of a first flight of four stairs, an inclined angle of the first flight is gradually lowered toward an outer direction of the pattern region to gradually lower the height H of the relief in the center portion toward the outer direction of the pattern region, each block of the grating pattern at a peripheral portion of the pattern region is formed in a second step-wise shape and is composed of a second flight of two stairs, an inclined angle of the second flight is gradually lowered toward an outer direction of the pattern region to gradually lower the height H of the relief in the peripheral portion toward the outer direction of the pattern region, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the outer direction of the pattern region.

Claim 17

A compound objective lens according to claim 1 in which the hologram means functions as a convex lens for the diffracted light to converge the diffracted light diffracted by the hologram means, the diffracted light converged by the lens means passes through a first information medium having a first thickness from its front surface to its rear surface to form the second converging spot on the rear surface of the first information medium, the transmitted light converged by the lens means passes through a second information medium having a second thickness from its front surface to its rear surface to form the first converging spot on the rear surface of the second information medium, and the first thickness is shorter than the second thickness.

Claim 18

A compound objective lens according to claim 17 in which a grating pattern is drawn in a pattern region of the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward an outer direction of the pattern region.

Claim 19

A compound objective lens according to claim 17 in which a difference between the first thickness and the second thickness ranges from 50 µm to 0.5 mm.

Claim 20

A compound objective lens according to claim 2 in which the height H of the relief in the grating pattern is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the inner direction of the pattern region.

Claim 21

A compound objective lens according to claim 2 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the inner direction of the pattern region, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the inner direction of the pattern region.

Claim 22

A compound objective lens according to claim 2 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern at a center portion of a pattern region in which the grating pattern is drawn is formed in a first step-wise shape and is composed of a first flight of four stairs, an inclined angle of the first flight is gradually lowered toward an inner direction of the pattern region to gradually lower the height H of the relief in the center portion toward the inner direction of the pattern region, each block of the grating pattern at a peripheral portion of the pattern region is formed in a second step-wise shape composed of a second flight of two stairs, an inclined angle of the second flight is gradually lowered toward an inner direction of the pattern region to gradually lower the height H of the relief in the peripheral portion toward the inner direction of the pattern region, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the inner direction of the pattern region.

Claim 23

A compound objective lens according to claim 17 in which a grating pattern is drawn in a pattern region of the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100%, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward an inner direction of the pattern region.

Claim 24

A compound objective lens according to any one of the preceding claims, additionally including: packaging means for unifying the hologram means and the lens means to fix a relative position between the hologram means and the lens means.

Claim 25

A compound objective lens according to any one of the preceding claims, in which the hologram means is formed on a curved surface of the lens means to integrally form the hologram means and the lens means.

Claim 26

A compound objective lens according to any one of claims 1 to 24, in which the hologram means is formed on a plane surface of the lens means to integrally form the hologram means and the lens means.

Claim 27

A compound objective lens according to any one of the preceding claims, in which a diffraction efficiency of the hologram means defined as an efficiency for changing the incident light to the diffracted light ranges from 30% to 70%.

Claim 28

A compound objective lens according to any one of the preceding claims, in which the hologram means functions as a concave lens for the diffracted light to diverge the diffracted light from the hologram means, and a diffraction efficiency of the hologram means defined as an efficiency for changing the incident light to the diffracted light is equal to or less than 30%.

Claim 29

A compound objective lens according to any one of the claims 1 to 27, in which the hologram means functions as a convex lens for the diffracted light to converge the diffracted light diffracted by the hologram means, and a diffraction efficiency of the hologram means defined as an efficiency for changing the incident light to the diffracted light is equal to or more than 70%.

Claim 30

A compound objective lens according to claim 1 in which a grating pattern is drawn on a flat surface of the hologram means, and a normal line of the flat surface of the hologram means is tilted from an optical axis of the lens means.

Claim 31

A compound objective lens, comprising: lens means for converging a beam of first incident light on a front surface of a first information medium having a first thickness T1 and converging a beam of second incident light on a front surface of a second information medium having a second thickness T2 (T2<T1), the first incident light passing through the first information medium from its rear surface, and the second incident light passing through the second information medium from its rear surface; and aperture limiting means for selectively limiting an aperture of the lens means for the second incident light which is incident on the lens means, a second numerical aperture of the lens means for the second incident light which is incident on the lens means being lower than a first numerical aperture of the lens means for the first incident light which is incident on the lens means.

Claim 32

A compound objective lens according to claim 31 in which the numerical aperture limiting means is formed of a hologram lens to transmit through the first incident light without any diffraction and diffracting the second incident light, the hologram lens functioning as a concave lens for the second incident light to diverge the second incident light from the hologram lens, a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 33

A compound objective lens, comprising: lens means for converging a beam of first incident light on a front surface of a first information medium having a first thickness and converging a beam of second incident light on a front surface of a second information medium having a second thickness, the first incident light passing through the first information medium from its rear surface, and the second incident light passing through the second information medium from its rear surface; and curvature changing means for changing a curvature of spherical waves of a part of incident light to form the first incident light which is incident on the lens means and not changing a curvature of spherical waves of a remaining part of incident light to form the second incident light which is incident on the lens means.

Claim 34

A compound objective lens according to claim 33 in which the curvature changing means is formed of a hologram lens to transmit through the remaining part of the incident light without any diffraction to form the second incident light and diffracting the part of the incident light to form the first incident light, a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 35

An imaging optical system, comprising: a light source for radiating a beam of incident light of which a far field pattern is distributed to decrease intensity of the incident light toward a peripheral portion of the beam; hologram means for transmitting a part of the incident light radiated from the light source without any diffraction to form a beam of transmitted light and diffracting a remaining part of the incident light to form a beam of diffracted light, a grating pattern being formed in relief in the hologram means to concentrically form alternating rows of bottom portions and top portions on condition that a height H of relief in the grating pattern is set to H < λ/(n(λ)-1) where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength λ, a difference in phase modulation degree between the incident light transmitting through the bottom portions of the grating pattern and the incident light transmitting through the top portions of the grating pattern being lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %, the height H of the relief in the grating pattern being gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn, and the diffraction efficiency of the hologram means for the incident light being gradually lowered toward the outer direction of the pattern region to distribute intensity of the transmitted light in a gently-sloping shape; and lens means for converging the transmitted light formed in the hologram means to form a first converging spot at a first focal point and converging the diffracted light formed in the hologram means to form a second converging spot at a second focal point.

Claim 36

An imaging optical system according to claim 35 in which the hologram means functions as a concave lens for the diffracted light to diverge the diffracted light from the hologram means, the transmitted light converged by the lens means passes through a first information medium having a first thickness from its front surface to its rear surface to form the first converging spot on the rear surface of the first information medium, the diffracted light converged by the lens means passes through a second information medium having a second thickness from its front surface to its rear surface to form the second converging spot on the rear surface of the second information medium, the second thickness differing from the first thickness, and the first thickness is shorter than the second thickness.

Claim 37

An imaging optical system according to claim 35 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, and an inclined angle of the stairs is gradually lowered toward the outer direction of the pattern region to gradually lower the height H of the relief in the grating pattern toward the outer direction of the pattern region.

Claim 38

An imaging optical system according to claim 35 in which the hologram means functions as a convex lens for the diffracted light to converge the diffracted light diffracted by the hologram means, the diffracted light converged by the lens means passes through a first information medium having a first thickness from its front surface to its rear surface to form the second converging spot on the rear surface of the first information medium, the transmitted light converged by the lens means passes through a second information medium having a second thickness from its front surface to its rear surface to form the first converging spot on the rear surface of the second information medium, and the first thickness is shorter than the second thickness.

Claim 39

An imaging optical system, comprising: a light source for radiating a beam of incident light of which a far field pattern is distributed to decrease intensity of the incident light toward a peripheral portion of the beam; hologram means for transmitting a part of the incident light radiated from the light source without any diffraction to form a beam of transmitted light and diffracting a remaining part of the incident light to form a beam of diffracted light, a grating pattern being formed in relief in the hologram means to concentrically form alternating rows of bottom portions and top portions on condition that a height H of relief in the grating pattern is set to H < λ/(n(λ)-1) where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength λ, a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern being lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %, the height H of the relief in the grating pattern being gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn, and the diffraction efficiency of the hologram means for the incident light being gradually lowered toward the inner direction of the pattern region to distribute intensity of the diffracted light in a gently-sloping shape; and lens means for converging the transmitted light formed in the hologram means to form a first converging spot at a first focal point and converging the diffracted light formed in the hologram means to form a second converging spot at a second focal point.

Claim 40

An imaging optical system according to claim 39 in which the hologram means functions as a concave lens for the diffracted light to diverge the diffracted light from the hologram means, the transmitted light converged by the lens means passes through a first information medium having a first thickness from its front surface to its rear surface to form the first converging spot on the rear surface of the first information medium, the diffracted light converged by the lens means passes through a second information medium having a second thickness from its front surface to its rear surface to form the second converging spot on the rear surface of the second information medium, the second thickness differing from the first thickness, and the first thickness is shorter than the second thickness.

Claim 41

An imaging optical system according to claim 39 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape composed of a flight of stairs, and an inclined angle of the stairs is gradually lowered toward the inner direction of the pattern region to gradually lower the height H of the relief in the grating pattern toward the inner direction of the pattern region.

Claim 42

An imaging optical system according to claim 39 in which the hologram means functions as a convex lens for the diffracted light to converge the diffracted light diffracted by the hologram means, the diffracted light converged by the lens means passes through a first information medium having a first thickness from its front surface to its rear surface to form the second converging spot on the rear surface of the first information medium, the transmitted light converged by the lens means passes through a second information medium having a second thickness from its front surface to its rear surface to form the first converging spot on the rear surface of the second information medium, and the first thickness is shorter than the second thickness.

Claim 43

An optical head apparatus for recording or reproducing a piece of information on or from a first information medium having a first thickness or a second information medium having a second thickness, comprising: a light source for radiating a beam of incident light; hologram means for transmitting a part of the incident light radiated from the light source without any diffraction on an outgoing path to form a beam of transmitted light and diffracting a remaining part of the incident light radiated from the light source on the outgoing path to form a beam of diffracted light, the hologram means functioning as a lens for the diffracted light to diverge the diffracted light from the hologram means or converge the diffracted light; lens means for converging the transmitted light formed in the hologram means at a first focal length on the outgoing path to form a first converging spot at a front surface of the first information medium or converging the diffracted light formed in the hologram means at a second focal length on the outgoing path to form a second converging spot at a front surface of the second information medium, the transmitted light passing through the first information medium from its rear surface, the transmitted light being reflected at the front surface of the first information medium and again passing through the lens means and the hologram means on an incoming path, the diffracted light passing through the second information medium from its rear surface, and the diffracted light being reflected at the front surface of the second information medium and again passing through the lens means and the hologram means on the incoming path; wavefront changing means for changing a wavefront of the transmitted light or the diffracted light passing through the lens means and the hologram means on the incoming path to form one or more beams of information light; and detecting means for detecting intensities of the information light formed by the wavefront changing means and generating an information signal according to the intensities of the information light, the information signal expressing a piece of information recorded on the first information medium or the second information medium.

Claim 44

An optical head apparatus according to claim 43 in which a grating pattern is drawn in the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %.

Claim 45

An optical head apparatus according to claim 43 in which a far field pattern of the incident light radiated from the light source is distributed to decrease intensity of the incident light toward a peripheral portion of its beam, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward an outer direction of the hologram means to distribute intensity of the transmitted light in a gently-sloping shape.

Claim 46

An optical head apparatus according to claim 43 in which a far field pattern of the incident light radiated from the light source is distributed to decrease intensity of the incident light toward a peripheral portion of its beam, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward an inner direction of the hologram means to distribute intensity of the diffracted light in a gently-sloping shape.

Claim 47

An optical head apparatus according to claim 43 in which the hologram means functions as a concave lens for the diffracted light to diverge the diffracted light from the hologram means, and the first thickness of the first information medium is smaller than the second thickness of the second information medium.

Claim 48

An optical head apparatus according to claim 43 in which the hologram means functions as a convex lens for the diffracted light to converge the diffracted light diffracted by the hologram means, and the first thickness of the first information medium is larger than the second thickness of the second information medium.

Claim 49

An optical head apparatus according to claim 44 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, and each block of the grating pattern is formed in a step-wise shape to blaze the grating pattern.

Claim 50

An optical head apparatus according to claim 43 in which the hologram means is partitioned into a pattern region and a no-pattern region surrounding the pattern region, a grating pattern is drawn in the pattern region of the hologram means in a concentric circle shape, and a diameter of the grating pattern is smaller than an aperture of the lens means to transmit the incident light through the no-pattern region of the hologram means without any diffraction.

Claim 51

An optical head apparatus according to claim 50 in which the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions in the pattern region, a thickness of the no-pattern region in the hologram means is set to an average value of those of the pattern region, and a phase of the incident light passing through the no-pattern region of the hologram means agrees with an average value of those of the incident light passing through the pattern region of the hologram means.

Claim 52

An optical head apparatus according to claim 44 in which the height H of the relief in the grating pattern is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the outer direction of the pattern region.

Claim 53

An optical head apparatus according to claim 44 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the outer direction of the pattern region, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the outer direction of the pattern region.

Claim 54

An optical head apparatus according to claim 44 in which the height H of the relief in the grating pattern is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the inner direction of the pattern region.

Claim 55

An optical head apparatus according to claim 44 in which the grating pattern of the hologram means is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the inner direction of the pattern region, and a diffraction efficiency of the hologram means for the incident light is gradually lowered toward the inner direction of the pattern region.

Claim 56

An optical head apparatus according to claim 43 in which the detecting means comprises a pair of focus error detectors for detecting intensities of two beams of first information light selected among the information light to generate the information signal and a focus error signal, and four tracking error detectors for detecting intensities of four beams of second information light selected among the information light to generate a tracking error signal, a position of the lens means being adjusted according to the focus error signal and the tracking error signal to focus the transmitted light or the diffracted light on the first information medium or the second information medium.

Claim 57

An optical head apparatus according to claim 43 in which a beam of first information light is generated in the wavefront changing means to have a first focal point in the front of the detecting means, a beam of second information light is generated in the wavefront changing means to have a second focal point in the rear of the detecting means, and the detecting means comprises a pair of focus error detectors for detecting an intensity of the first information light and an intensity of the second information light to generate a focus error signal, a position of the lens means being adjusted according to the focus error signal to focus the transmitted light or the diffracted light on the first information medium or the second information medium, and the information signal being detected in the focus error detectors.

Claim 58

An optical head apparatus according to claim 43 in which the wavefront changing means is a hologram having a plurality types of grating patterns, and the transmitted light or the diffracted light passing through one of the grating patterns of the hologram means is changed to one of the information light.

Claim 59

An optical head apparatus according to claim 43 in which the wavefront changing means is an astigmatic aberration generating unit for generating an astigmatic aberration in the information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the information light having the astigmatic aberration to generate the information signal and servo signals such as a focus error signal and a tracking error signal, a position of the lens means being adjusted according to the servo signals to focus the transmitted light or the diffracted light on the first information medium or the second information medium.

Claim 60

An optical head apparatus according to claim 59 in which the astigmatic aberration generating unit is formed of a plane parallel plate of which a normal line is tilted from an optical axis.

Claim 61

An optical head apparatus according to claim 59 in which the astigmatic aberration generating unit is formed of a cylindrical lens.

Claim 62

An optical head apparatus according to claim 43 in which a grating pattern is drawn on a flat surface of the hologram means, and a normal line of the flat surface of the hologram means is tilted from an optical axis of the lens means.

Claim 63

An optical head apparatus according to claim 43, additionally including: a polarized beam splitter for totally transmitting the incident light which is radiated from the light source and is linearly polarized in a first direction and totally reflecting light linearly polarized at a second direction perpendicular to the first direction; and a 1/4-λ plate for forming the transmitted light or the diffracted light linearly polarized in the second direction by passing the incident light transmitting through the polarized beam splitter or a pair of the transmitted light and the diffracted light on the outgoing path and passing the transmitted light or the diffracted light on the incoming path, the transmitted light or the diffracted light linearly polarized in the second direction by the 1/4-λ plate being reflected by the polarized beam splitter on the outgoing path and being incident on the wavefront converging means.

Claim 64

An optical head apparatus according to claim 43, additionally including a wedge-like prism for reshaping the incident light radiated from the light source, the incident light reshaped being incident on the hologram means.

Claim 65

An optical head apparatus according to claim 43 in which the first thickness of the first information medium is smaller than the second thickness of the second information medium, the wavefront changing means comprises a beam splitter for transmitting the diffracted light which transmits through the hologram means without any diffraction on the incoming path to form a beam of first information light having an astigmatic aberration and reflecting the transmitted light which transmits through the hologram means without any diffraction on the incoming path, and a wavefront changing unit for changing a wavefront of the transmitted light reflected by the beam splitter to form a plurality of beams of second information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the first information light transmitting through the beam splitter to generate a first information signal and servo signals such as a first focus error signal and a first tracking error signal, a pair of focus error detectors for detecting intensities of two beams of second information light formed in the wavefront changing unit to generate a second information signal and a second focus error signal, and four tracking error detectors for detecting intensities of four beams of second information light formed in the wavefront changing unit to generate a second tracking error signal, a positional relation between the lens means and the second information medium being adjusted according to the servo signals to focus the diffracted light on the second information medium, a positional relation between the lens means and the first information medium being adjusted according to the second focus error signal and the second tracking error signal to focus the transmitted light on the first information medium, the first information signal expressing the information recorded on the second information medium, and the second information signal expressing the information recorded on the first information medium.

Claim 66

An optical head apparatus according to claim 43 in which the first thickness of the first information medium is smaller than the second thickness of the second information medium, the wavefront changing means comprises a beam splitter having a wavefront changing unit for transmitting the transmitted light which transmits through the hologram means without any diffraction on the incoming path to form a beam of first information light having an astigmatic aberration and diffracting and reflecting the diffracted light which transmits through the hologram means without any diffraction on the incoming path and is incident on the wavefront changing unit to form a plurality of beams of second information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the first information light transmitting through the beam splitter to generate a first information signal and servo signals such as a first focus error signal and a first tracking error signal, a pair of focus error detectors for detecting intensities of two beams of second information light formed in the wavefront changing unit to generate a second information signal and a second focus error signal, and four tracking error detectors for detecting intensities of four beams of second information light formed in the wavefront changing unit to generate a second tracking error signal, a positional relation between the lens means and the first information medium being adjusted according to the servo signals to focus the transmitted light on the first information medium, a positional relation between the lens means and the second information medium being adjusted according to the second focus error signal and the second tracking error signal to focus the diffracted light on the second information medium, the first information signal expressing the information recorded on the first information medium, and the second information signal expressing the information recorded on the second information medium.

Claim 67

An optical head apparatus according to claim 43 in which the first thickness of the first information medium is smaller than the second thickness of the second information medium, the transmitted light converged by the lens means on the outgoing path is also converged at the front surface of the second information medium in defocus and is reflected to again pass through the lens means and the hologram means without any diffraction on the incoming path, the wavefront changing means comprises a beam splitter having a wavefront changing unit for transmitting the diffracted light which transmits through the hologram means without any diffraction on the incoming path to form a beam of first information light having an astigmatic aberration and diffracting the transmitted light which is converged on the second information medium in defocus and is incident on the wavefront changing unit to form a plurality of beams of second information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting in defocus an intensity of the first information light transmitting through the beam splitter to generate a first information signal expressing the information recorded on the second information medium and detecting in focus intensities of the second information light diffracted in the wavefront changing unit to generate a focus error signal, a positional relation between the lens means and the second information medium being adjusted according to the focus error signal to focus the diffracted light on the second information medium.

Claim 68

An optical head apparatus according to claim 43 in which the first thickness of the first information medium is larger than the second thickness of the second information medium, the wavefront changing means comprises a beam splitter for transmitting the diffracted light again diffracted by the hologram means on the incoming path to form a beam of first information light having an astigmatic aberration and reflecting the transmitted light diffracted by the hologram means on the incoming path, and a wavefront changing unit for changing a wavefront of the transmitted light reflected by the beam splitter to form a plurality of beams of second information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the first information light transmitting through the beam splitter to generate a first information signal and servo signals such as a first focus error signal and a first tracking error signal, a pair of focus error detectors for detecting intensities of two beams of second information light formed in the wavefront changing unit to generate a second information signal and a second focus error signal, and four tracking error detectors for detecting intensities of four beams of second information light formed in the wavefront changing unit to generate a second tracking error signal, a positional relation between the lens means and the second information medium being adjusted according to the servo signals to focus the diffracted light on the second information medium, a positional relation between the lens means and the first information medium being adjusted according to the second focus error signal and the second tracking error signal to focus the transmitted light on the first information medium, the first information signal expressing the information recorded on the second information medium, and the second information signal expressing the information recorded on the first information medium.

Claim 69

An optical head apparatus according to claim 43 in which the first thickness of the first information medium is larger than the second thickness of the second information medium, the wavefront changing means comprises a beam splitter having a wavefront changing unit for transmitting the transmitted light diffracted by the hologram means on the incoming path to form a beam of first information light having an astigmatic aberration and diffracting and reflecting the diffracted light which is again diffracted by the hologram means on the incoming path and is incident on the wavefront changing unit to form a plurality of beams of second information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the first information light transmitting through the beam splitter to generate a first information signal and servo signals such as a first focus error signal and a first tracking error signal, a pair of focus error detectors for detecting intensities of two beams of second information light formed in the wavefront changing unit to generate a second information signal and a second focus error signal, and four tracking error detectors for detecting intensities of four beams of second information light formed in the wavefront changing unit to generate a second tracking error signal, a positional relation between the lens means and the first information medium being adjusted according to the servo signals to focus the transmitted light on the first information medium, a positional relation between the lens means and the second information medium being adjusted according to the second focus error signal and the second tracking error signal to focus the diffracted light on the second information medium, the first information signal expressing the information recorded on the first information medium, and the second information signal expressing the information recorded on the second information medium.

Claim 70

An optical head apparatus according to claim 43 in which the hologram means is partitioned into a central region and a peripheral region surrounding the central region, a first grating pattern is drawn in the central region of the hologram means in a concentric circle shape, a second grating pattern is drawn in the peripheral region of the hologram means in a non-concentric shape, the transmitted light transmits through the central region of the hologram means without any diffraction on the outgoing and incoming paths, a part of the incident light radiated from the light source transmits through the peripheral region of the hologram means on the outgoing path to form a beam of noise cancelling light which is converged by the lens means to form a third converging spot surrounding the first converging spot, the noise cancelling light forming the third converging spot passes through the lens means and is diffracted in the peripheral region of the hologram means on the incoming path, the detecting means comprises a first photo detector for detecting an intensity of the transmitted light transmitting through the central region of the hologram means without any diffraction on the incoming path to generate a first information signal component SC1 expressing a piece of information recorded on the first information medium, and a second photo detector for detecting an intensity of the noise cancelling light diffracted in the peripheral region of the hologram means on the incoming path to generate a second information signal component SC2 expressing the information, a noise cancelled information signal Snc being obtained by adding the first information signal component SC1 and a multiplied second information signal component RxSC2 which is obtained by multiplying the second information signal component SC2 by a weighting factor R.

Claim 71

An optical head apparatus according to claim 70 in which the peripheral region of the hologram means is partitioned into a first side peripheral region and a second side peripheral region facing each other with the central region between the first and second side peripheral region, a far field pattern of the incident light radiated from the light source is distributed to decrease intensity of the incident light toward a peripheral portion of its beam, a cross-sectional beam profile of the incident light radiated from the light source is in an elliptic shape in which a beam divergent angle of the incident light in a perpendicular direction is larger than that in a horizontal direction, the incident light placed at one side of its beam in the perpendicular direction passes through the first side peripheral region of the hologram means to form a part of the noise cancelling light, the incident light placed at the other side of its beam in the perpendicular direction passes through the second side peripheral region of the hologram means to form a remaining part of the noise cancelling light, and a cross-sectional beam profile of light defined as the combination of the transmitted light and the noise cancelling light is in a circular shape.

Claim 72

An optical head apparatus according to claim 70 in which the peripheral region of the hologram means is partitioned into a first side peripheral region and a second side peripheral region facing each other with the central region between the first and second side peripheral region, a second photo detector of the detecting means is composed of a first noise cancelling detector for detecting an intensity of the noise cancelling light formed in the first side peripheral region of the hologram means to generate a third information signal component SC3 expressing the information, and a second noise cancelling detector for detecting an intensity of the noise cancelling light formed in the second side peripheral region of the hologram means to generate a fourth information signal component SC4 expressing the information, the noise cancelled information signal Snc being obtained according to an equation: Snc = SC1 + R1×SC3 + R2×SC4, where R1 is a first weighting factor and R2 is a second weighting factor.

Claim 73

An optical head apparatus according to claim 43 in which the light source and the detecting means are placed on a substrate to fix a relative position between the light source and the detecting means, and the light source is placed closely to the detecting means.

Claim 74

An optical head apparatus according to claim 43 in which the incident light radiated from the light source is linearly polarized in a first direction, the wavefront changing means comprises a transparent substrate, a polarizing separation film formed on a front surface of the transparent substrate for reflecting the incident light linearly polarized in the first direction on the outgoing path and refracting the transmitted light or the diffracted light linearly polarized in a second direction perpendicular to the first direction on the incoming path, a hologram formed on a rear surface of the transparent substrate for diffracting the transmitted light or the diffracted light refracted by the polarizing separation film to form the beams of information light, and a 1/4-λ plate for forming the transmitted light or the diffracted light linearly polarized in the second direction by passing the incident light reflected by the polarizing separation film and passing the transmitted light or the diffracted light on the incoming path.

Claim 75

An optical head apparatus for recording or reproducing a piece of information on or from a first information medium having a first thickness T1 or a second information medium having a second thickness T2 (T1<T2), comprising: lens means for converging a beam of first incident light on a front surface of a first information medium having a first thickness T1 or converging a beam of second incident light on a front surface of a second information medium having a second thickness T2 (T2<T1), the first incident light passing through the first information medium from its rear surface, and the second incident light passing through the second information medium from its rear surface; aperture limiting means for selectively limiting an aperture of the lens means for the second incident light which is incident on the lens means, a second numerical aperture of the lens means for the second incident light which is incident on the lens means being lower than a first numerical aperture of the lens means for the first incident light which is incident on the lens means, the first incident light being reflected at the front surface of the first information medium and again passing through the lens means and the aperture limiting means on an incoming path, and the second incident light being reflected at the front surface of the second information medium and again passing through the lens means and the aperture limiting means on the incoming path; a light source for radiating the first incident light and the second incident light to the aperture limiting means; wavefront changing means for changing a wavefront of the first or second incident light passing through the lens means and the aperture limiting means on the incoming path to form one or more beams of information light; and detecting means for detecting intensities of the information light formed by the wavefront changing means and generating an information signal according to the intensities of the information light, the information signal expressing a piece of information recorded on the first information medium or the second information medium.

Claim 76

An optical head apparatus according to claim 75 in which the numerical aperture limiting means is formed of a hologram lens to transmit through the first incident light without any diffraction and diffracting the second incident light, the hologram lens functioning as a concave lens for the second incident light to diverge the second incident light from the hologram lens, a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 77

An optical head apparatus for recording or reproducing a piece of information on or from a first information medium having a first thickness or a second information medium having a second thickness, comprising: lens means for converging a beam of first incident light on a front surface of the first information medium and converging a beam of second incident light on a front surface of the second information medium, the first incident light passing through the first information medium from its rear surface, and the second incident light passing through the second information medium from its rear surface; and curvature changing means for changing a curvature of spherical waves of a part of incident light to form the first incident light which is incident on the lens means and not changing a curvature of spherical waves of a remaining part of incident light to form the second incident light which is incident on the lens means, the first incident light being reflected at the front surface of the first information medium and again passing through the lens means and the curvature changing means on an incoming path, and the second incident light being reflected at the front surface of the second information medium and again passing through the lens means and the curvature changing means on the incoming path; a light source for radiating the incident light to the curvature changing means; wavefront changing means for changing a wavefront of the first or second incident light passing through the lens means and the curvature changing means on the incoming path to form one or more beams of information light; and detecting means for detecting intensities of the information light formed by the wavefront changing means and generating an information signal according to the intensities of the information light, the information signal expressing a piece of information recorded on the first information medium or the second information medium.

Claim 78

An optical head apparatus according to claim 77 in which the curvature changing means is formed of a hologram lens to transmit through the remaining part of the incident light without any diffraction to form the second incident light and diffracting the part of the incident light to form the first incident light, a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 79

An optical disk, comprising: an information recording substrate partitioned into a first region and a second region, the first region having a first thickness, and the second region having a second thickness smaller than the first thickness; a plurality of first recording pits placed at the first region of the information recording substrate for recording pieces of recording information at a high recording density, the first recording pits being formed at narrow intervals; and a plurality of second recording pits placed at the second region of the information recording substrate for recording pieces of distinguishing information at an ordinary recording density of a compact disk, the distinguishing information informing that the recording information are recorded on the information recording substrate having the first thickness, and the recording density of the recording information being higher than that of the distinguishing information.

Claim 80

An optical disk according to claim 79 in which the first thickness of the first region ranges from 0.4mm to 0.8mm, and the second thickness of the second region is 1.2mm.

Claim 81

An optical disk, comprising: an information recording substrate having a thin thickness, the thin thickness of the information recording substrate being thinner than that of a compact disk; a plurality of first recording pits placed at a first region of the information recording substrate for recording pieces of recording information at a high recording density, the first recording pits being formed at narrow intervals; and a plurality of second recording pits placed at a second region of the information recording substrate for recording pieces of distinguishing information at a low recording density, the distinguishing information informing that the recording information are recorded on the information recording substrate having the thin thickness, the recording density of the recording information being higher than that of the distinguishing information, each of the second recording pits being larger than that of a recording pit in the compact disk, and a converging spot of a beam of reproducing light, which is converged to focus on an ordinary recording pit formed on a substrate having an ordinary thickness of the compact disk, being formed in one of the second recording pits to read the distinguishing information.

Claim 82

An optical disk according to claim 81 in which the thin thickness of the information recording substrate ranges from 0.4mm to 0.8mm.

Claim 83

An optical disk apparatus for recording or reproducing pieces of recording information on or from an optical disk in which the recording information are recorded or reproduced at a high density on or from a first substrate having a first thickness and a piece of distinguishing information informing that the recording information are recorded or reproduced on or from the first substrate having the first thickness is recorded at an ordinary density on a second substrate having a second thickness larger than the first thickness, comprising: rotating means for rotating the optical disk at a regular speed; a light source for radiating a beam of incident light; hologram means for transmitting a part of the incident light radiated from the light source without any diffraction on an outgoing path to form a beam of transmitted light and diffracting a remaining part of the incident light radiated from the light source on the outgoing path to form a beam of diffracted light, the hologram means functioning as a lens for the diffracted light to diverge the diffracted light from the hologram means; lens means for converging the transmitted light formed in the hologram means on the first substrate of the optical disk rotated by the rotating means to record or reproduce a piece of recording information on or from the optical disk and converging the diffracted light formed in the hologram means on the second substrate of the optical disk rotated by the rotating means to reproduce the distinguishing information from the optical disk, the transmitted light being reflected by the first substrate of the optical disk and again passing through the lens means and the hologram means on an incoming path, and the diffracted light being reflected by the second substrate of the optical disk and again passing through the lens means and the hologram means on the incoming path; wavefront changing means for changing a wavefront of the transmitted light passing through the lens means and the hologram means on the incoming path to form one or more beams of recording information light and changing a wavefront of the diffracted light passing through the lens means and the hologram means on the incoming path to form one or more beams of distinguishing information light; detecting means for detecting intensities of the recording information light formed by the wavefront changing means to generate a recording information signal according to the intensities of the recording information light and detecting intensities of the distinguishing information light formed by the wavefront changing means to generate a distinguishing information signal according to the intensities of the distinguishing information light, the distinguishing information signal expressing the distinguishing information recorded on the second substrate of the optical disk, and the recording information signal expressing the recording information recorded on the first substrate of the optical disk; and moving means for moving an optical head apparatus comprising the light source, the hologram means, the lens means and the detecting means to converge the diffracted light formed in the hologram means on the second substrate of the optical disk and moving the optical head apparatus, in which the diffracted light formed in the hologram means is converged on the second substrate of the optical disk, to converge the transmitted light formed in the hologram means on the first substrate of the optical disk in cases where the distinguishing information is detected in the detecting means.

Claim 84

An optical disk apparatus according to claim 83 in which a grating pattern is drawn in the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %.

Claim 85

An optical disk apparatus according to claim 83 in which the detecting means comprises a pair of focus error detectors for detecting intensities of two beams of first recording information light selected among the recording information light to generate the recording information signal and a first focus error signal and detecting intensities of two beams of first distinguishing information light selected among the distinguishing information light to generate the distinguishing information signal and a second focus error signal, and four tracking error detectors for detecting intensities of four beams of second recording information light selected among the recording information light to generate a first tracking error signal and detecting intensities of four beams of second distinguishing information light selected among the distinguishing information light to generate a second tracking error signal, a position of the lens means being adjusted according to the first focus error signal and the first tracking error signal to focus the transmitted light on the first substrate of the optical disk, and a position of the lens means being adjusted according to the second focus error signal and the second tracking error signal to focus the diffracted light on the second substrate of the optical disk.

Claim 86

An optical disk apparatus according to claim 83 in which the wavefront changing means is an astigmatic aberration generating unit for generating an astigmatic aberration in the recording information light and the distinguishing information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the recording information light having the astigmatic aberration to generate the recording information signal and first servo signals such as a first focus error signal and a first tracking error signal and detecting an intensity of the distinguishing information light having the astigmatic aberration to generate the distinguishing information signal and second servo signals such as a second focus error signal and a second tracking error signal, a position of the lens means being adjusted according to the first servo signals to focus the transmitted light on the first substrate of the optical disk, and a position of the lens means being adjusted according to the second servo signals to focus the diffracted light on the second substrate of the optical disk.

Claim 87

An optical disk apparatus for recording or reproducing pieces of recording information on or from an optical disk in which the recording information are recorded or reproduced at a high density on or from a first substrate having a thin thickness thinner than that of a compact disk and a piece of distinguishing information informing that the recording information are recorded or reproduced on or from the first substrate having the thin thickness is recorded at a low density on a second substrate having the thin thickness, comprising: rotating means for rotating the optical disk at a regular speed; a light source for radiating a beam of incident light; hologram means for transmitting a part of the incident light radiated from the light source without any diffraction on an outgoing path to form a beam of transmitted light and diffracting a remaining part of the incident light radiated from the light source on the outgoing path to form a beam of diffracted light, the hologram means functioning as a lens for the diffracted light to diverge the diffracted light from the hologram means; lens means for converging in focus the transmitted light formed in the hologram means on the first substrate of the optical disk rotated by the rotating means to record or reproduce a piece of recording information on or from the optical disk and converging in defocus the diffracted light formed in the hologram means on the second substrate of the optical disk rotated by the rotating means to reproduce the distinguishing information from the optical disk, the transmitted light being reflected by the first substrate of the optical disk and again passing through the lens means and the hologram means on an incoming path, and the diffracted light being reflected by the second substrate of the optical disk and again passing through the lens means and the hologram means on the incoming path; wavefront changing means for changing a wavefront of the transmitted light passing through the lens means and the hologram means on the incoming path to form one or more beams of recording information light and changing a wavefront of the diffracted light passing through the lens means and the hologram means on the incoming path to form one or more beams of distinguishing information light; detecting means for detecting intensities of the recording information light formed by the wavefront changing means to generate a recording information signal according to the intensities of the recording information light and detecting intensities of the distinguishing information light formed by the wavefront changing means to generate a distinguishing information signal according to the intensities of the distinguishing information light, the distinguishing information signal expressing the distinguishing information recorded on the second substrate of the optical disk, and the recording information signal expressing the recording information recorded on the first substrate of the optical disk; and moving means for moving an optical head apparatus comprising the light source, the hologram means, the lens means and the detecting means, to converge the diffracted light formed in the hologram means in defocus on the second substrate of the optical disk and moving the optical disk, in which the diffracted light formed in the hologram means is converged on the second substrate of the optical disk in defocus, to converge the transmitted light formed in the hologram means on the first substrate of the optical disk in focus in cases where an intensity of the distinguishing information signal generated in the detecting means is larger than a threshold value.

Claim 88

An optical disk apparatus according to claim 87 in which a grating pattern is drawn in the hologram means in a concentric circle shape, the grating pattern of the hologram means is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the incident light and a symbol n(λ) denotes a refractive index of the hologram means made of a glass material for the incident light having the wavelength λ, and a difference in phase modulation degree between the incident light passing through the bottom portions of the grating pattern and the incident light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram means to a value lower than 100 %.

Claim 89

An optical disk apparatus according to claim 87 in which the detecting means comprises a pair of focus error detectors for detecting intensities of two beams of first recording information light selected among the recording information light to generate the recording information signal and a first focus error signal and detecting intensities of two beams of first distinguishing information light selected among the distinguishing information light to generate the distinguishing information signal and a second focus error signal, and four tracking error detectors for detecting intensities of four beams of second recording information light selected among the recording information light to generate a first tracking error signal and detecting intensities of four beams of second distinguishing information light selected among the distinguishing information light to generate a second tracking error signal, a position of the lens means being adjusted according to the first focus error signal and the first tracking error signal to focus the transmitted light on the first substrate of the optical disk, and a position of the lens means being adjusted according to the second focus error signal and the second tracking error signal to focus the diffracted light on the second substrate of the optical disk.

Claim 90

An optical disk apparatus according to claim 87 in which the wavefront changing means is an astigmatic aberration generating unit for generating an astigmatic aberration in the recording information light and the distinguishing information light, and the detecting means comprises a quadrant photo-detector having four detecting sections for detecting an intensity of the recording information light having the astigmatic aberration to generate the recording information signal and first servo signals such as a first focus error signal and a first tracking error signal and detecting an intensity of the distinguishing information light having the astigmatic aberration to generate the distinguishing information signal and second servo signals such as a second focus error signal and a second tracking error signal, a position of the lens means being adjusted according to the first servo signals to focus the transmitted light on the first substrate of the optical disk, and a position of the lens means being adjusted according to the second servo signals to focus the diffracted light on the second substrate of the optical disk.

Claim 91

A binary focus microscope for simultaneously observing a first image put on a first image plane and a second image put on a second image plane, comprising: an objective lens for refracting a beam of first light diverging from the first image and a beam of second light diverging from the second image, a first distance between the objective lens and the first image of the first image plane differing from a second distance between the objective lens and the second image of the second image plane; a hologram lens for transmitting the first light refracted by the objective lens without any diffraction to form a beam of transmitted light and diffracting the second light refracted by the objective lens to form a beam of diffracted light, the hologram lens functioning as a lens for the second light to pass the diffracted light through the same optical path as the transmitted light passes through, and a beam of superposed light being formed of the transmitted light and the diffracted light; an inner lens for converging the superposed light formed by the hologram lens at an image point of a third image plane to simultaneously form the first image and the second image enlarged on the third image plane; and an ocular lens for converging the superposed light which is converged by the inner lens and diverges from the image point to simultaneously form the first image and the second image moreover enlarged.

Claim 92

A binary focus microscope according to claim 91 in which a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the first and second light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the first and second light having the wavelength λ, and a difference in phase modulation degree between the first or second light passing through the bottom portions of the grating pattern and the first or second light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 93

A binary focus microscope according to claim 92 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, and each block of the grating pattern is formed in a step-wise shape to blaze the grating pattern.

Claim 94

A binary focus microscope according to claim 91 in which the hologram lens is partitioned into a pattern region and a no-pattern region surrounding the pattern region, a grating pattern is drawn in the pattern region of the hologram lens in a concentric circle shape, and a diameter of the grating pattern is smaller than an aperture of the objective lens to transmit the first light through the no-pattern region of the hologram lens without any diffraction.

Claim 95

A binary focus microscope according to claim 94 in which the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions in the pattern region, a thickness of the no-pattern region in the hologram lens is set to an average value of those of the pattern region, and a phase of the first light passing through the no-pattern region of the hologram lens agrees with an average value of those of the first light passing through the pattern region of the hologram lens.

Claim 96

A binary focus microscope according to claim 92 in which the height H of the relief in the grating pattern is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram lens for the second light is gradually lowered toward the outer direction of the pattern region.

Claim 97

A binary focus microscope according to claim 92 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the outer direction of the pattern region, and a diffraction efficiency of the hologram lens for the second light is gradually lowered toward the outer direction of the pattern region.

Claim 98

A binary focus microscope according to claim 92 in which the height H of the relief in the grating pattern is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the second light is gradually lowered toward the inner direction of the pattern region.

Claim 99

A binary focus microscope according to claim 92 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the inner direction of the pattern region, and a diffraction efficiency of the hologram lens for the second light is gradually lowered toward the inner direction of the pattern region.

Claim 100

A binary focus microscope for simultaneously observing a first image put on a first image plane and a second image put on a second image plane, comprising: an objective lens for refracting a beam of first light diverging from the first image and a beam of second light diverging from the second image, a first distance between the objective lens and the first image of the first image plane differing from a second distance between the objective lens and the second image of the second image plane; a hologram lens for transmitting the first light refracted by the objective lens without any diffraction to form a beam of transmitted light and diffracting the second light refracted by the objective lens to form a beam of diffracted light, the hologram lens functioning as a lens for the second light to pass the diffracted light through the same optical path as the transmitted light passes through, and a beam of superposed light being formed of the transmitted light and the diffracted light; an inner lens for converging the superposed light formed by the hologram lens at an image point of a third image plane to simultaneously form the first image and the second image enlarged on the third image plane; and photographing means for photographing a superposed image formed of the first and second images enlarged on the third image plane by converging the superposed light in the inner lens.

Claim 101

A binary focus microscope according to claim 100 in which a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the first and second light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the first and second light having the wavelength λ, and a difference in phase modulation degree between the first or second light passing through the bottom portions of the grating pattern and the first or second light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 102

A binary focus microscope according to claim 101 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, and each block of the grating pattern is formed in a step-wise shape to blaze the grating pattern.

Claim 103

A binary focus microscope according to claim 100 in which the hologram lens is partitioned into a pattern region and a no-pattern region surrounding the pattern region, a grating pattern is drawn in the pattern region of the hologram lens in a concentric circle shape, and a diameter of the grating pattern is smaller than an aperture of the objective lens to transmit the first light through the no-pattern region of the hologram lens without any diffraction.

Claim 104

A binary focus microscope according to claim 103 in which the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions in the pattern region, a thickness of the no-pattern region in the hologram lens is set to an average value of those of the pattern region, and a phase of the first light passing through the no-pattern region of the hologram lens agrees with an average value of those of the first light passing through the pattern region of the hologram lens.

Claim 105

A binary focus microscope according to claim 101 in which the height H of the relief in the grating pattern is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram lens for the second light is gradually lowered toward the outer direction of the pattern region.

Claim 106

A binary focus microscope according to claim 101 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the outer direction of the pattern region, and a diffraction efficiency of the hologram lens for the second light is gradually lowered toward the outer direction of the pattern region.

Claim 107

A binary focus microscope according to claim 101 in which the height H of the relief in the grating pattern is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the second light is gradually lowered toward the inner direction of the pattern region.

Claim 108

A binary focus microscope according to claim 101 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the inner direction of the pattern region, and a diffraction efficiency of the hologram lens for the second light is gradually lowered toward the inner direction of the pattern region.

Claim 109

An alignment apparatus for aligning a first reference image drawn on a photomask with a second reference image drawn on a sample, comprising: a light source for radiating beams of alignment light to illuminate the first and second reference images; an objective lens for refracting both a beam of first alignment light diverging from the first reference image and a beam of second alignment light diverging from the second reference image which are illuminated with the alignment light radiated from the light source, a first distance between the objective lens and the first reference image of the photomask differing from a second distance between the objective lens and the second reference image of the sample; a hologram lens for transmitting the first alignment light refracted by the objective lens without any diffraction to form a beam of transmitted light and diffracting the second alignment light refracted by the objective lens to form a beam of diffracted light, the hologram lens functioning as a lens for the second alignment light to pass the diffracted light through the same optical path as the transmitted light passes through, and a beam of superposed light being formed of the transmitted light and the diffracted light; an inner lens for converging the superposed light formed by the hologram lens at an image point of an image plane to simultaneously form the first and second reference images enlarged on the image plane, an optical axis passing through centers of the objective lens, the hologram lens and the inner lens; photographing means for photographing a superposed image formed of the first and second images enlarged on the image plane by converging the superposed light in the inner lens; and moving means for moving the photomask or the sample according to the superposed image photographed by the photographing means to align the first reference image with the second reference image along the optical axis.

Claim 110

An alignment apparatus according to claim 109 in which a grating pattern is drawn in the hologram lens in a concentric circle shape, the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions, a height H of relief in the grating pattern is set to: H < λ/(n(λ)-1), where a symbol λ denotes a wavelength of the first and second reference light and a symbol n(λ) denotes a refractive index of the hologram lens made of a glass material for the first and second reference light having the wavelength λ, and a difference in phase modulation degree between the first or second reference light passing through the bottom portions of the grating pattern and the first or second reference light passing through the top portions of the grating pattern is lower than 2π radians to set a diffraction efficiency of the hologram lens to a value lower than 100 %.

Claim 111

An alignment apparatus according to claim 110 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, and each block of the grating pattern is formed in a step-wise shape to blaze the grating pattern.

Claim 112

An alignment apparatus according to claim 109 in which the hologram lens is partitioned into a pattern region and a no-pattern region surrounding the pattern region, a grating pattern is drawn in the pattern region of the hologram lens in a concentric circle shape, and a diameter of the grating pattern is smaller than an aperture of the objective lens to transmit the first reference light through the no-pattern region of the hologram lens without any diffraction.

Claim 113

An alignment apparatus according to claim 112 in which the grating pattern of the hologram lens is formed in relief to concentrically form alternating rows of bottom portions and top portions in the pattern region, a thickness of the no-pattern region in the hologram lens is set to an average value of those of the pattern region, and a phase of the first reference light passing through the no-pattern region of the hologram lens agrees with an average value of those of the first reference light passing through the pattern region of the hologram lens.

Claim 114

An alignment apparatus according to claim 110 in which the height H of the relief in the grating pattern is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram lens for the second reference light is gradually lowered toward the outer direction of the pattern region.

Claim 115

An alignment apparatus according to claim 110 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of one of the bottom portions and one of the top portions, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an outer direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the outer direction of the pattern region, and a diffraction efficiency of the hologram lens for the second reference light is gradually lowered toward the outer direction of the pattern region.

Claim 116

An alignment apparatus according to claim 110 in which the height H of the relief in the grating pattern is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn, and a diffraction efficiency of the hologram means for the second reference light is gradually lowered toward the inner direction of the pattern region.

Claim 117

An alignment apparatus according to claim 110 in which the grating pattern of the hologram lens is partitioned into a plurality of pattern blocks which each are composed of a bottom portion and a top portion, each block of the grating pattern is formed in a step-wise shape and is composed of a flight of stairs, an inclined angle of the stairs is gradually lowered toward an inner direction of a pattern region in which the grating pattern is drawn to gradually lower the height H of the relief in the grating pattern toward the inner direction of the pattern region, and a diffraction efficiency of the hologram lens for the second reference light is gradually lowered toward the inner direction of the pattern region.

Claim 118

A focusing method for focusing light on a first information medium having a first thickness or a second information medium having a second thickness to record or reproduce a piece of information on or from the first information medium or the second information medium, comprising the steps of: moving an optical head apparatus in a direction to decrease or increase the distance between the optical head apparatus and the first or second information medium, the optical head apparatus comprising a light source for radiating a beam of incident light, hologram means for transmitting a part of the incident light radiated from the light source without any diffraction on an outgoing path to form a beam of transmitted light and diffracting a remaining part of the incident light radiated from the light source on the outgoing path to form a beam of diffracted light, the hologram means functioning as a lens for the diffracted light to diverge the diffracted light from the hologram means or converge the diffracted light, lens means for converging the transmitted light formed in the hologram means at a first focal length on the outgoing path to form a first converging spot at a front surface of the first information medium or converging the diffracted light formed in the hologram means at a second focal length on the outgoing path to form a second converging spot at a front surface of the second information medium, the transmitted light being incident on a rear surface of the first information medium and being converged at the front surface of the first information medium, the transmitted light being reflected at the rear surface of the first information medium and again passing through the lens means and the hologram means on an incoming path, the diffracted light being incident on a rear surface of the second information medium and being converged at the front surface of the second information medium, and the diffracted light being reflected at the rear surface of the first information medium and again passing through the lens means and the hologram means on the incoming path, wavefront changing means for changing a wavefront of the transmitted light or the diffracted light passing through the lens means and the hologram means on the incoming path to form one or more beams of information light, and detecting means for detecting intensities of the information light formed by the wavefront changing means and generating an information signal and a focus error signal according to the intensities of the information light, the information signal expressing a piece of information recorded on the first information medium or the second information medium; judging whether or not an intensity of the focus error signal generated in the detecting means is larger than a threshold value; and adjusting the position of the optical head apparatus to decrease the intensity of the focus error signal to zero when the intensity of the focus error signal becomes larger than the threshold value.

Claim 119

An information reproducing method for reproducing a piece of recording information from an optical disk in which the recording information are recorded at a high density on a first substrate having a first thickness and a piece of distinguishing information informing that the recording information are recorded on the first substrate is recorded at an ordinary density on a second substrate having a second thickness larger than the first thickness, comprising the step of: moving an optical disk apparatus under the second substrate of the optical disk, the optical disk comprising rotating means for rotating the optical disk at a regular speed, a light source for radiating a beam of incident light; hologram means for transmitting a part of the incident light radiated from the light source without any diffraction on an outgoing path to form a beam of transmitted light and diffracting a remaining part of the incident light radiated from the light source on the outgoing path to form a beam of diffracted light, the hologram means functioning as a lens for the diffracted light to diverge the diffracted light from the hologram means, lens means for converging the transmitted light formed in the hologram means on the first substrate of the optical disk rotated by the rotating means to record or reproduce a piece of recording information on or from the optical disk and converging the diffracted light formed in the hologram means on the second substrate of the optical disk rotated by the rotating means to reproduce the distinguishing information from the optical disk, the transmitted light being reflected by the first substrate of the optical disk and again passing through the lens means and the hologram means on an incoming path, and the diffracted light being reflected by the second substrate of the optical disk and again passing through the lens means and the hologram means on the incoming path, wavefront changing means for changing a wavefront of the transmitted light passing through the lens means and the hologram means on the incoming path to form one or more beams of recording information light and changing a wavefront of the diffracted light passing through the lens means and the hologram means on the incoming path to form one or more beams of distinguishing information light, and detecting means for detecting intensities of the recording information light formed by the wavefront changing means to generate a recording information signal according to the intensities of the recording information light and detecting intensities of the distinguishing information light formed by the wavefront changing means to generate a distinguishing information signal according to the intensities of the distinguishing information light, the distinguishing information signal expressing the distinguishing information recorded on the second substrate of the optical disk, and the recording information signal expressing the recording information recorded on the first substrate of the optical disk; and converging the diffracted light on the second substrate of the optical disk to reproduce the distinguishing information; moving the optical disk apparatus to a position under the first substrate of the optical disk to converge the transmitted light on the first substrate of the optical disk when the distinguishing information is detected in the detecting means; and reproducing the recording information by generating the recording information signal in the detecting means.