EP0044074A1
Expired / Lapsed
EP
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Focus detector
Assignee: Cessione cray Valley Sa
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Filing: 1981-07-13
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Granted: —
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Expires: 2001-07-13
Abstract
Abstract Electro-optical focus detection apparatus for providing a signal indicative of the magnitude and polarity of focus error in a light beam impinging on a surface, such as a recording surface in a recording or playback system. The detector includes a beam splitter for dividing the beam reflected from the recording surface into two reflected beams of equal power, and includes an aperture placed in the path of the two reflected beams. The first reflected beam converges at a focal point before encountering the aperture and the second reflected beam converges at a focal point after encountering the aperture, both beams thereafter impinging upon separate photodetector elements. The aperture reduces the light incident on the photodetectors from both reflected beams, and the apparatus is so configured that the powers of the reflected beams incident on the photodetector elements are identical when the original beam is in focus on the recording surface. When the original beam moves out of focus with the recording surface, both focal points of the reflected beams move in the same direction, to provide an increase in the light falling on one of the photodetector elements and a decrease in light falling on the other, such that the differential output derived from the photodetector elements provides a signal indicative of the magnitude and polarity of the focus error.
Inventors
- 👤 John S. Winslow
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 12:26
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/08; G11B7/085; G11B7/09; G11B7/0908; G11B7/0912; G02; G02B; G02B27/00; G02B27/40
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
223 words
Apparatus for detecting the focus error of a radiant energy beam with respect to a surface to which it is directed through an objective lens, said apparatus comprising: beam splitting means disposed in the path of a beam reflected from the surface back through the objective lens, said beam splitting means producing first and second reflected beams of approximately equal power; aperture means disposed in the path of said first and second reflected beams such that, when the original beam is focused on the surface, the first reflected beam converges to a first focal point prior to encountering said aperture means and the second reflected beam converges to a second focal point after encountering said aperture means, and such that the total power of the first beam after passing through said aperture means is substantially the same as the total power of the second beam after passing through said aperture means; detection means disposed in the paths of said first and second reflected beams after passing through said aperture means, for producing electrical signals proportional to the power of each of the first and second reflected beams; and subtraction means for producing a signal proportional to the difference between the powers of the first and second reflected beams, and therefore indicative of'the magnitude and polarity of the focus error of the original beam.
Claim 2
Dependent Claim
223 words
Apparatus for detecting the focus error of a radiant energy beam with respect to a surface to which it is directed through an objective lens, said apparatus comprising: beam splitting means disposed in the path of a beam reflected from the surface back through the objective lens, said beam splitting means producing first and second reflected beams of approximately equal power; aperture means disposed in the path of said first and second reflected beams such that, when the original beam is focused on the surface, the first reflected beam converges to a first focal point prior to encountering said aperture means and the second reflected beam converges to a second focal point after encountering said aperture means, and such that the total power of the first beam after passing through said aperture means is substantially the same as the total power of the second beam after passing through said aperture means; detection means disposed in the paths of said first and second reflected beams after passing through said aperture means, for producing electrical signals proportional to the power of each of the first and second reflected beams; and subtraction means for producing a signal proportional to the difference between the powers of the first and second reflected beams, and therefore indicative of'the magnitude and polarity of the focus error of the original beam.
Claim 3
Dependent Claim
80 words
Apparatus as set forth in claim 1, wherein: said aperture means is a single aperture; said beam splitting means includes a beam splitter to provide said first and second reflected beams, and a mirror disposed in the path of the first beam to increase its path length and to produce convergence of the beam prior to encountering said aperture; and said detection means includes a split photodiode having two transducer elements positioned to receive the first and second beams, respectively.
Claim 4
Dependent Claim
70 words
Apparatus as set forth in claim 1, wherein: said beam splitting means includes a beam splitter for producing the first and second reflected beams; said aperture means includes first and second apertures disposed in the respective paths of the first and second reflected beams; and said detection means includes first and second transducers disposed to receive the first and second beams, respectively, after passing through said first and second apertures.
Claim 5
Dependent Claim
43 words
Apparatus as set forth in claim 1, and further including: summing means for producing a signal proportional to the sum of the powers of the first and second reflected beams, and therefore proportional to the intensity of radiant energy reflected from the surface.
Claim 6
Dependent Claim
154 words
Apparatus for detecting the focus error of a radiant energy beam directed at a surface through an objective lens and reflected therefrom through the same lens, said apparatus comprising: beam splitting means for producing first and second reflected beams from the beam reflected from the surface; aperture means disposed in the paths of the first and second means such that, when the original beam is perfectly focused on the surface, the difference between the power of the first beam passed by said aperture means and the power of the second beam passed by said aperture means is. equal to a predetermined value; detection means disposed in the path of the first and second reflected beams after passing through said aperture means, and providing a signal indicative of the difference between the powers of the first and second beams, and therefore indicative of the focus error of the original beam with respect to the surface.
Claim 7
Dependent Claim
154 words
Apparatus for detecting the focus error of a radiant energy beam directed at a surface through an objective lens and reflected therefrom through the same lens, said apparatus comprising: beam splitting means for producing first and second reflected beams from the beam reflected from the surface; aperture means disposed in the paths of the first and second means such that, when the original beam is perfectly focused on the surface, the difference between the power of the first beam passed by said aperture means and the power of the second beam passed by said aperture means is. equal to a predetermined value; detection means disposed in the path of the first and second reflected beams after passing through said aperture means, and providing a signal indicative of the difference between the powers of the first and second beams, and therefore indicative of the focus error of the original beam with respect to the surface.
Claim 8
Dependent Claim
44 words
Apparatus as set forth in claim 5, wherein said detection means further includes: summing means to provide a signal proportional to the sum of the powers of the first and second beams, to be used in the reproduction of information recorded on the surface.
Claim 9
Dependent Claim
34 words
Apparatus as set forth in claim 5, wherein the predetermined difference value is zero, and the signal obtained from the detection means is substantially proportional to the magnitude and polarity of the focus error.
Claim 10
Dependent Claim
113 words
Apparatus as set forth in claim 7, wherein: said aperture means is a-single aperture; and said beam splitting means includes a beam splitter to provide the first and second beams, the second beam converging at a focal point located beyond said aperture, and further includes a mirror disposed in the path of the first beam to increse its path length and to provide convergence of the first beam to a focal point prior to passing through said aperture; whereby a focus error causes movement of both focal points in the same direction and simultaneously increases the power of one beam and decreases the power of the other, as measured by said detection means.
Claim 11
Dependent Claim
19 words
Apparatus as set forth in claim 8, wherein said detection means includes a split photodiode and a differential amplifier.
Claim 12
Dependent Claim
90 words
Apparatus as set forth in claim 7, wherein: said aperture means includes a first aperture positioned in the path of the first beam after its convergence to a first focal point, and a second aperture positioned in the path of the second before its convergence to a second focal point, whereby a focus error causes movement of the first and second focal points in the same direction, reducing the power of one beam passed by one of said apertures and increasing the power passed by the other of said apertures.
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