Method and apparatus for light amplification exhibiting a flat gain spectrum

Claim 2

A semiconductor light amplifier according to Claim 1 wherein said means for imparting the loss includes an optical wave guide layer laminated on said activation layer on said substrate and a grating coupler for coupling the light propagated through said activation layer which has the wavelength in said portion of the range.

Claim 3

A semiconductor light amplifier according to Claim 1 wherein said activation layer has a first channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a second channel type wave guide formed in a portion of said activation layer and having no amplification function and a directional optical coupler for coupling the light propagated through said first channel type wave guide which has the wavelength in said portion of range to said second channel type wave guide.

Claim 4

A semiconductor light amplifier according to Claim 1 wherein said activation layer has a channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a slab type wave guide formed externally of said channel type wave guide and having no amplification function and a grating for diffracting the light propagated through said channel type wave guide which has the wavelength in said portion of range to couple the light to said slab type wave guide.

Claim 5

A semiconductor light amplifier according to Claim 1 wherein said means for imparting the loss includes a light absorption region formed on a portion of said activation layer for absorbing the light having the wavelength in said portion of range.

Claim 7

A semiconductor light amplifier comprising: a substrate; a semiconductor activation layer formed on said substrate for propagating a light; said activation layer amplifying a light propagated through said activation layer and having a wavelength within a predetermined range when a current is applied thereto; said activation layer having a non-flat gain spectrum in said predetermined wavelength range; an electrode for supplying a current to at least a portion of said activation layer; and means for imparting a loss to the light propagated through said activation layer which has a wavelength in a portion of said predetermined wavelength range; said portion of wavelength range corresponding to a wavelength range having a relatively high gain in a gain spectrum of said activation layer; said means flattening a gain spectrum of the light outputted from said activation layer for the light inputted to said activation layer, relative to the gain spectrum of said activation layer.

Claim 8

A semiconductor light amplifier according to Claim 7 wherein said means for imparting the loss includes an optical wave guide layer laminated on said activation layer on said substrate and a grating coupler for coupling the light propagated through said activation layer which has the wavelength in said portion of the range.

Claim 9

A semiconductor light amplifier according to Claim 7 wherein said activation layer has a first channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a second channel type wave guide formed in a portion of said activation layer and having no amplification function and a directional optical coupler for coupling the light propagated through said first channel type wave guide which has the wavelength in said portion of range to said second channel type wave guide.

Claim 10

A semiconductor light amplifier according to Claim 7 wherein said activation layer has a channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a slab type wave guide formed externally of said channel type wave guide and having no amplification function and a grating for diffracting the light propagated through said channel type wave guide which has the wavelength in said portion of range to couple the light to said slab type wave guide.

Claim 11

A semiconductor light amplifier according to Claim 7 wherein said means for imparting the loss includes a light absorption region formed on a portion of said activation layer for absorbing the light having the wavelength in said portion of range.

Claim 13

A semiconductor light amplifier comprising: a substrate; a semiconductor activation layer formed on said substrate for propagating a light in a first propagation mode; said activation layer amplifying a light propagated through said activation layer and having a wavelength within a predetermined range; an electrode for supplying a current to at least a portion of said activation layer; a wave guide layer formed on said substrate to be laminated on said activation layer thicknesswise; said wave guide layer propagating the light in a second propagation mode different from said first propagation mode; and a diffraction grating formed in an overlapping area of said first propagation mode and said second propagation mode; said diffraction grating coupling the light propagated through said activation layer which has a wavelength in a portion of said predetermined wavelength range, to said wave guide layer; the light coupled to said wave guide layer being separated from the light amplified by said activation layer.

Claim 14

A semiconductor light amplifier according to Claim 13 further comprising first, second and third clad layers; said first clad layers, said activation layer, said second clad layer, said wave guide layer and said third clad layer being laminated on said substrate in this sequence.

Claim 15

A semiconductor light amplifier according to Claim 14 wherein said diffraction grating is formed on a boundary surface between said second clad layer and said wave guide layer.

Claim 16

A semiconductor light amplifier according to Claim 14 wherein said third clad layer and said wave guide layer have opposite ends along the direction of light propagation etched away.

Claim 17

A semiconductor light amplifier according to Claim 14 wherein a portion of said first clad layer, said activation layer, said second clad layer, said wave guide layer and said third clad layer are mesa-etched except a stripe area extending along the direction of light propagation, and buried layers are formed on the opposite sides of the mesa.

Claim 18

A semiconductor light amplifier according to Claim 14 wherein said activation layer and said wave guide layer have a multi-quantum well structure.

Claim 19

A semiconductor light amplifier according to Claim 14 wherein said substrate and said layers are made of GaAs and AlGaAs, respectively.

Claim 20

A semiconductor light amplifier according to Claim 13 wherein said wave guide layer is curved so that a distance from said activation layer is shorter at a center and longer at the opposite ends.

Claim 21

A semiconductor light amplifier according to Claim 13 wherein β₁( λ ) - β₂( λ ) = 2 π/Λ is met, where λ is a wavelength of said portion of range, β₁( λ ) is a propagation constant in said first propagation mode, β₂( λ ) is a propagation constant in said second propagation mode and Λ is a pitch of said diffraction grating.

Claim 22

A semiconductor light amplifier according to Claim 21 wherein L < π/2K K = E₁A₁(x)E₂dx is met, where E₁ is an electric field distribution in said first propagation mode, E₂ is an electric field distribution in said second propagation mode, A₁(x) is a component of Fourier progression development of said diffraction grating corresponding to a primary diffracted light and L is a length of said diffraction grating.

Claim 24

A semiconductor light amplifier comprising: a substrate made of an n-type semiconductor; a first clad formed on said substrate and made of an n-type semiconductor; an activation layer formed on said first clad layer and made of a non-doped semiconductor for propagating a light in a first propagation mode; said activation layer amplifying a light propagated through said activation layer and having a wavelength within a predetermined range when a current is applied thereto; a second clad layer formed on said activation layer and made of a p-type semiconductor; a wave guide layer formed on said second clad layer and made of a p-type semiconductor; said wave guide layer propagating a light in a second propagation mode different from said first propagation mode; a third clad layer formed on said wave guide layer and made of a p-type semiconductor; a p-type electrode formed on said third clad layer; an n-type electrode formed on a bottom surface of said substrate; and a diffraction grating formed in an overlapping area of said first propagation mode and said second propagation mode; said diffraction grating coupling the light propagated through said activation layer which has a wavelength in a portion of said predetermined wavelength range to said wave guide layer; the light coupled to said wave guide layer being separated from the light amplified by said activation layer.

Claim 25

A semiconductor light amplifier according to Claim 24 wherein said diffraction grating is formed on a boundary surface between said second clad layer and said wave guide layer.

Claim 26

A semiconductor light amplifier according to Claim 24 wherein said third clad layer and said wave guide layer have opposite ends along the direction of light propagation etched away.

Claim 27

A semiconductor light amplifier according to Claim 24 wherein a portion of said first clad layer, said activation layer, said second clad layer, said wave guide layer and said third clad layer are mesa-etched except a stripe area extending along the direction of light propagation, and buried layers are formed on the opposite sides of the mesa.

Claim 28

A semiconductor light amplifier according to Claim 24 wherein said activation layer and said wave guide layer have a multi-quantum well structure.

Claim 29

A semiconductor light amplifier according to Claim 24 wherein said substrate and said layers are made of GaAs and AlGaAs, respectively.

Claim 30

A semiconductor light amplifier according to Claim 24 wherein said wave guide layer is curved so that a distance from said activation layer is shorter at a center and longer at the opposite ends.

Claim 31

A semiconductor light amplifier according to Claim 24 wherein β₁( λ ) - β₂( λ ) = 2 π/Λ is met, where λ is a wavelength of said portion of range, β₁( λ ) is a propagation constant in said first propagation mode, β₂( λ ) is a propagation constant in said second propagation mode and Λ is a pitch of said diffraction grating.

Claim 32

A semiconductor light amplifier according to Claim 24 wherein L < π/2K K = E₁A₁(x)E₂dx is met, where E₁ is an electric field distribution in said first propagation mode, E₂ is an electric field distribution in said second propagation mode, A₁(x) is a component of Fourier progression development of said diffraction grating corresponding to a primary diffracted light and L is a length of said diffraction grating.

Claim 33

A semiconductor light amplifier comprising: a substrate; a semiconductor activation layer formed on said substrate for propagating a light; said activation layer amplifying a light propagated through said activation layer and having a wavelength in a predetermined range when a current is applied thereto; an electrode for supplying the current to at least a portion of said activation layer; means for imparting a loss to the light propagated through said activation layer which has a wavelength in a portion of said predetermined wavelength range; and a power supply connected to said electrode.

Claim 34

A semiconductor light amplifier according to Claim 33 wherein said means for imparting the loss includes an optical wave guide layer laminated on said activation layer on said substrate and a grating coupler for coupling the light propagated through said activation layer which has the wavelength in said portion of the range.

Claim 35

A semiconductor light amplifier according to Claim 33 wherein said activation layer has a first channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a second channel type wave guide formed in a portion of said activation layer and having no amplification function and a directional optical coupler for coupling the light propagated through said first channel type wave guide which has the wavelength in said portion of range to said second channel type wave guide.

Claim 36

A semiconductor light amplifier according to Claim 33 wherein said activation layer has a channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a slab type wave guide formed externally of said channel type wave guide and having no amplification function and a grating for diffracting the light propagated through said channel type wave guide which has the wavelength in said portion of range to couple the light to said slab type wave guide.

Claim 37

A semiconductor light amplifier according to Claim 33 wherein said means for imparting the loss includes a light absorption region formed on a portion of said activation layer for absorbing the light having the wavelength in said portion of range.

Claim 39

A light communication system comprising: (a) a plurality of terminals each including at least one of a light transmitter and a light receiver; (b) a light transmission line for interconnecting said terminals; and (c) a light amplifier arranged in a path of said light transmission line for amplifying a light signal transmitted through said line, said light amplifier including; a substrate; a semiconductor activation layer formed on said substrate for propagating a light; said activation layer amplifying a light propagated through said activation layer and having a wavelength in a predetermined range when a current is applied thereto; an electrode for supplying the current to at least a portion of said activation layer; and means for imparting a loss to the light propagated through said activation layer which has a wavelength in a portion of said predetermined wavelength range.

Claim 40

A semiconductor light amplifier according to Claim 39 wherein said means for imparting the loss includes an optical wave guide layer laminated on said activation layer on said substrate and a grating coupler for coupling the light propagated through said activation layer which has the wavelength in said portion of the range.

Claim 41

A semiconductor light amplifier according to Claim 39 wherein said activation layer has a first channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a second channel type wave guide formed in a portion of said activation layer and having no amplification function and a directional optical coupler for coupling the light propagated through said first channel type wave guide which has the wavelength in said portion of range to said second channel type wave guide.

Claim 42

A semiconductor light amplifier according to Claim 39 wherein said activation layer has a channel type wave guide through which the light to be amplified is propagated, and said means for imparting the loss includes a slab type wave guide formed externally of said channel type wave guide and having no amplification function and a grating for diffracting the light propagated through said channel type wave guide which has the wavelength in said portion of range to couple the light to said slab type wave guide.

Claim 43

A semiconductor light amplifier according to Claim 39 wherein said means for imparting the loss includes a light absorption region formed on a portion of said activation layer for absorbing the light having the wavelength in said portion of range.