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US4989972A
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Low reflectivity surface relief gratings for photodetectors
Assignee: HP Inc
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Filing: 1989-05-01
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Granted: 1991-02-05
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Expires: 2009-05-01
Abstract
Abstract Photodetectors having low reflectivity triangular groove, surface relief gratings on homogenous material or one layer of a heterostructure. Preferably, the photodetector is a PIN photodiode in which the p-type layer is triangularly grooved. The surface relief gratings have an optical repeat distance greater than the wavelength of light which impinges on the photodetector surface. Thus, zero order backward diffracted waves are not coupled into optical reflections which would thereby decrease the optical return loss (ORL). Furthermore, the surface relief gratings have minimum side-wall angles to limit reflection at the heterostructure interfaces from contributing to the ORL. The side-angles of the gratings are chosen to ensure that the angle of the higher order backward diffracted wave is greater than the capture angle of an optical receiver into which the photodetector is incorporated. The free-space depth of the grooves is a half-wavelength of the light impinging on the photodetector. Additionally, a novel ion milling technique is disclosed. This technique involves providing a rectangular groove grating initially etched by conventional chemical etching and photoresistive techniques and then ion milling at particular ion mill angles to obtain triangular groove surface relief gratings provided in accordance with this invention.
Inventors
- 👤 David M. Braun
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 09:31
CPC Classifications
G; G02; G02B; G02B1/00; G02B1/10; G02B1/11; G02B1/118; G01; G01J; G01J1/00; G01J1/02; G01J1/04; G01J1/0407; G02B5/00; G02B5/18; G02B5/1809; H; H10; H10F; H10F30/00; H10F30/20; H10F30/21; H10F30/22; H10F30/223; H10F77/00; H10F77/10; H10F77/14; H10F77/148; H10F77/70; H10F77/703; G01J1/0204; G01J1/0209; Y; Y02; Y02E; Y02E10/00; Y02E10/50
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
92 words
A low reflectivity surface relief grating incorporated into optical receiving means responsive to incident light having a given wavelength useful, by way of example, in an optical measurement system, comprising: a plurality of triangular grooves formed on a surface of a layer of material, the grooves having a uniform repeat optical distance greater than the wavelength of the incident light, a uniform free-space depth substantially equal to an integral multiple of a half-wavelength of incident light and a plurality of side-angles with respect to the surface on which the grooves are formed.
Claim 2
Dependent Claim
92 words
A low reflectivity surface relief grating incorporated into optical receiving means responsive to incident light having a given wavelength useful, by way of example, in an optical measurement system, comprising: a plurality of triangular grooves formed on a surface of a layer of material, the grooves having a uniform repeat optical distance greater than the wavelength of the incident light, a uniform free-space depth substantially equal to an integral multiple of a half-wavelength of incident light and a plurality of side-angles with respect to the surface on which the grooves are formed.
Claim 3
Dependent Claim
17 words
The grating recited in claim 1 wherein the plurality of side-angles are substantially equal to each other.
Claim 4
Dependent Claim
13 words
The grating recited in claim 2 wherein the sideangles are approximately twenty degrees.
Claim 5
Dependent Claim
20 words
The grating recited in claim 3 wherein the material consists of a homogeneous semiconducting material for detecting the incident light.
Claim 6
Dependent Claim
27 words
The grating recited in claim 4 wherein the semiconducting material is selected from the group of semiconducting materials consisting of indium phosphide, gallium arsenide, germanium and silicon.
Claim 7
Dependent Claim
20 words
The grating recited in claim 1 wherein the optical repeat distance is in the range of one to four wavelengths.
Claim 8
Dependent Claim
17 words
The grating recited in claim 1 wherein the freespace depth of the triangular grooves is one-half wavelength.
Claim 9
Dependent Claim
62 words
The grating recited in claim 1 wherein the material consists of a semiconducting material, and further comprising: a second semiconducting layer interfaced with the layer of material on a side opposite to the triangular grooves; and a semiconducting substrate interfaced with the second semiconducting layer on a side opposite to the interface of the layer of material and the second semiconducting layer.
Claim 10
Dependent Claim
14 words
The grating recited in claim 8 wherein the semiconducting substrate consists of indium phosphide.
Claim 11
Dependent Claim
16 words
The grating recited in claim 9 wherein the second semiconducting layer consists of indium gallium arsenide.
Claim 12
Dependent Claim
15 words
The grating recited in claim 10 wherein the layer of material consists of indium phosphide.
Claim 13
Dependent Claim
16 words
The grating recited in claim 1 further comprising an antireflection coating applied to the triangular grooves.
Claim 14
Dependent Claim
21 words
The grating recited in claim 12 wherein the antireflection coating consists of silicon nitride having a refractive index of approximately 1.83.
Claim 15
Dependent Claim
14 words
The grating recited in claim 1 wherein the plurality of side-angles are minimum side-angles.
Claim 16
Dependent Claim
13 words
The grating recited in claim 14 wherein the minimum side-angles are approximately 19.8°.
Claim 17
Dependent Claim
22 words
The grating recited in claim 12 wherein the reflected optical power in the zero order backward diffracted wave is less than 0.035%.
Claim 18
Dependent Claim
72 words
An optical receiver adapted to detect incident light having a given wavelength useful, by way of example, in an optoelectronic measurement system comprising: photodetector means comprising a surface having a plurality of triangular grooves formed thereon, the grooves having a uniform free-space depth substantially equal to about half the wavelength of the incident light, a uniform repeat optical distance greater than the wavelength of the incident light and a plurality of side-angles.
Claim 19
Dependent Claim
72 words
An optical receiver adapted to detect incident light having a given wavelength useful, by way of example, in an optoelectronic measurement system comprising: photodetector means comprising a surface having a plurality of triangular grooves formed thereon, the grooves having a uniform free-space depth substantially equal to about half the wavelength of the incident light, a uniform repeat optical distance greater than the wavelength of the incident light and a plurality of side-angles.
Claim 20
Dependent Claim
13 words
The receiver recited in claim 17 wherein the sideangles are minimum side angles.
Claim 21
Dependent Claim
12 words
The receiver recited in claim 18 wherein the minimum side-angles are equal.
Claim 22
Dependent Claim
39 words
The optical receiver recited in claim 17, further comprising: an objective lens having a numerical aperture for transmitting incident light; the photodetector means being in optical communication with the objective lens for detecting light transmitted by the objective lens.
Claim 23
Dependent Claim
32 words
The receiver recited in claim 20 wherein a given capture angle of the numerical aperture is less than a given reflection angle of first order backward diffracted waves from the triangular grooves.
Claim 24
Dependent Claim
26 words
The receiver recited in claim 21 wherein the numerical aperture of the objective lens is less than 0.18 and the side-angles are greater than approximately 19.8°.
Claim 25
Dependent Claim
26 words
The receiver recited in claim 17 wherein the photodetector means further comprises an antireflection coating applied to the grooves for minimizing reflection of the incident light.
Claim 26
Dependent Claim
21 words
The receiver recited in claim 23 wherein the antireflection coating consists of silicon nitride having a refractive index of approximately 1.83.
Claim 27
Dependent Claim
81 words
The receiver recited in claim 17 wherein the photodetector means further comprises: a semiconducting substrate; an absorbing layer interfaced with the substrate, the substrate being interfaced with a first side of the absorbing layer; and a semiconducting layer interfaced with a second side of the absorbing layer opposite to the first side of the absorbing layer interfaced with the substrate, the semiconducting layer having the triangular grooves integrally formed on a side opposite to the side interfaced with the absorbing layer.
Claim 28
Dependent Claim
14 words
The receiver recited in claim 25 wherein the semiconducting substrate consists of indium phosphide.
Claim 29
Dependent Claim
15 words
The receiver recited in claim 26 wherein the absorbing layer consists of indium gallium arsenide.
Claim 30
Dependent Claim
14 words
The receiver recited in claim 27 wherein the semiconducting layer consists of indium phosphide.
Claim 31
Independent Claim
100 words
A method of determining optical parameters of a unit under test with an optoelectronic measurement system comprising the steps of: focusing light received from the unit under test onto photodetector means comprising a low reflectivity surface relief grating, the grating having a plurality of triangular grooves formed thereon, the grooves having a uniform free-space depth substantially equal to approximately half the wavelength of the light, a uniform optical repeat distance greater than the wavelength of the light and at least two side-angles; and analyzing the light focused on the photodetector to determine the optical parameters of the unit under test.
Claim 32
Independent Claim
100 words
A method of determining optical parameters of a unit under test with an optoelectronic measurement system comprising the steps of: focusing light received from the unit under test onto photodetector means comprising a low reflectivity surface relief grating, the grating having a plurality of triangular grooves formed thereon, the grooves having a uniform free-space depth substantially equal to approximately half the wavelength of the light, a uniform optical repeat distance greater than the wavelength of the light and at least two side-angles; and analyzing the light focused on the photodetector to determine the optical parameters of the unit under test.
Claim 33
Dependent Claim
18 words
The method recited in claim 29 wherein the triangular grooves have minimum side-angles for reducing reflected optical power.
Claim 34
Dependent Claim
23 words
The method recited in claim 30 wherein the focused light is reflected from the triangular grooves having minimum side-angles that are substantially equal.
Claim 35
Dependent Claim
19 words
The method recited in claim 31 wherein the triangular grooves have minimum side-angles that are greater than approximately 19.8°.
References Cited (Backward Citations)
JPS6088482A
Cited
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1994-02-04 | 1994-08-06 | 1995-02-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-02-04 | 1998-08-06 | 1999-02-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-02-04 | 2002-08-06 | 2003-02-05 | $7700.00 | Window Closed / Lapsed |