Source: http://www.google.com/patents/US5299045?dq=6,123,819
Timestamp: 2015-02-26 23:00:51
Document Index: 335024472

Matched Legal Cases: ['art 143', 'art 142', 'art 146', 'art 143', 'arts 142', 'art 143', 'arts 142']

Patent US5299045 - Light detecting apparatus having a diffraction grating - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA light detector provides wavelength tracking, monitoring or similar function by forming a diffraction grating in a light waveguide. Diffracted light from the waveguide is received by a light detecting device having multiple detecting portions. Changes in the emission angle of the diffracted light caused...http://www.google.com/patents/US5299045?utm_source=gb-gplus-sharePatent US5299045 - Light detecting apparatus having a diffraction gratingAdvanced Patent SearchPublication numberUS5299045 APublication typeGrantApplication numberUS 07/819,387Publication dateMar 29, 1994Filing dateJan 10, 1992Priority dateJan 12, 1991Fee statusPaidAlso published asDE69226885D1, DE69226885T2, EP0495413A1, EP0495413B1Publication number07819387, 819387, US 5299045 A, US 5299045A, US-A-5299045, US5299045 A, US5299045AInventorsYoshinobu SekiguchiOriginal AssigneeCanon Kabushiki KaishaExport CitationBiBTeX, EndNote, RefManPatent Citations (19), Non-Patent Citations (4), Referenced by (24), Classifications (36), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetLight detecting apparatus having a diffraction grating
US 5299045 AAbstract
A light detector provides wavelength tracking, monitoring or similar function by forming a diffraction grating in a light waveguide. Diffracted light from the waveguide is received by a light detecting device having multiple detecting portions. Changes in the emission angle of the diffracted light caused by the wavelength or other fluctuation of the incident light are detected. The detected information can be used for wavelength tracking by injecting current into or applying a voltage to the waveguide to regulate the Bragg wavelength of the light waveguide, for monitoring and/or controlling the oscillation wavelength of a semiconductor laser or for other purposes.
1. A light detecting apparatus comprising:a semiconductor light waveguide through which light propagates: a diffraction grating formed in said light waveguide, for diffracting the light propagating through said light waveguide; an electrode for effecting one of injecting electric current into said light waveguide and applying a voltage to said light waveguide; and a light detecting means including a plurality of detecting portions for detecting light diffracted by said diffraction grating to outside said light waveguide; a comparison circuit for comparing quantities of light incident on said plurality of detecting portions and for producing a control signal in accordance with a result of the comparing; and a control circuit for controlling an angle of diffraction of said diffracted light by changing, in accordance with said control signal outputted from said comparison circuit, one of the current injected through said electrode and the voltage applied by said electrode. 2. A light detecting apparatus according to claim 1, wherein said light detecting means comprises an array of light detecting elements.
An object of the present invention is to provide, in view of the above problem, light detecting apparatus having wavelength fluctuation detection of received light, which can be used for various purposes, such as increasing the signal wavelength multiplicity by setting a narrow wavelength band width for each signal wavelength in a wavelength division multiplexing communication.
FIG. 1 is a perspective view of a first embodiment of a light detecting apparatus of the present invention having a light waveguide with a diffraction grating and a light detecting device;
The first embodiment of the present invention will be described by referring to FIGS. 1 and 2. In FIG. 1 illustrating the entire structure of the first embodiment, there are formed, on an n-GaAs substrate 2, an n-Alx Ga1-x As light confinement layer 3, an Aly Ga1-y As light waveguide layer 4 (0≦y<x<1), the energy gap of the light confinement layer 3 is larger than that of the light waveguide layer 4, and the refractive index of the layer 3 is smaller than that of the layer 4 to perform the light confinement function, a p-Alx Ga1-x As light confinement layer 6 and a p-Alz Ga1-z As contact layer 7 (0<z<1) in this order. A high-resistance Alx Gal-x As burying layer 5 is layered by a re-growth after both lateral sides are etched except for a stripe-shaped portion in order to achieve confinement with respect to a lateral direction.
FIG. 3 shows the second embodiment. As explained above, the far field pattern (FFP) of the diffraction light emitted from the light waveguide is very narrow in the direction of the waveguide extension and its span angle θP is about less than 0.2 degrees. The FFP is wide in a direction transverse to the waveguide extension and its span angle θt is about 15 degrees. Thus, since the span angle in the direction transverse to the waveguide extention is large, the amount of the incident light on the array 11 of the light detecting elements becomes a few percent of a total amount of the emitted light.
The third embodiment of the present invention will be described by referring to FIG. 4. FIG. 4 shows a left half of the third embodiment of the light detecting apparatus as viewed from the light incident side. In FIG. 4, there are formed, on an n-GaAs substrate 22, an n-Alx Ga1-x As cladding layer 23, a superlattice waveguide layer 24 in which ten GaAs well layers 31 (thickness thereof is 10 nm) and eleven Aly Ga1-y As barrier layers 32 (thickness thereof is 10 nm; 0≦y<x<1) are alternately layered, a second order diffraction grating 33 having a pitch of about 260 nm, a p-Alx Ga1-x As cladding layer 26 and a p-Alz Ga1-z As contact layer 27 in this order. A high-resistance Alx Ga1-x As burying layer 25 is re-grown after the etching of both sides except for a stripe-shaped portion in order to achieve confinement in a lateral direction. On the contact layer 27, there is formed an upper p-type electrode 28 in which a window 29 for emitting a diffraction light is formed, and on the bottom of the n-GaAs substrate 22, an n-type electrode 21 is formed.
First, the operation principle of the fourth embodiment will be explained. In a superlattice structure, when a barrier layer is thin and quantum wells are in a bonding state, the refractive index (n1) of the superlattice structure is about equal to that (nA) of a mixed crystal (mixed crystal that contains constituent components of the superlattice structure at an equal ratio to that of the superlattice structure) of the barrier layer and the quantum well layers (i.e., n1 ≈nA). However, when the barrier layer is relatively thick and the quantum well layers are not in the bonding state, the refractive index (n2) of the superlattice structure is larger than that (nA) of the mixed crystal by about 0.1 over a wide range of wavelength (i.e., nA +0.1≦n2). The fact is described in Journal of Electronic Materials, vol. 12, p. 397 (1983)).
In the above-discussed embodiments, the current injection into or voltage application to the light waveguide with the diffraction grating is performed in order to make the Bragg wavelength of the diffraction grating close to the wavelength of the incident light. In these embodiments, however, it takes some time to tune the Bragg wavelength to the wavelength of the incident light if the the former differs greatly from the latter when the light detecting apparatus operation is started.
FIG. 10 shows a structure of an array of photodetectors for demultiplexing and detecting light signals of two given wavelengths selected out of wavelength-multiplexed incident lights. The remaining structure thereof is identical with the fifth embodiment. The array of photodetectors comprises a first photodetector 81 having a light receiving surface whose length in the waveguide extension direction is relatively large and second photodetectors including a plurality of light detecting elements 82, 83 and 84 each having a light receiving surface whose length in the waveguide extension direction is relatively short. The second photodetectors 82�84 are disposed separately a little distant from the first photodetector 81. Here, the incident lights involve a plurality of signals of wavelengths λ1 and λ2i (i=1.2, . . . , n), and the signal of wavelength λ1 is a control signal for the wavelength division multiplexing communication and hence should be always received at the receiver side. The band width of the control signal of wavelength λ1 is wide, so the wavelength tracking is not needed for this signal. The wavelengths λ2i are sufficiently distant from the wavelength λ1 and their band widths are narrow to increase the wavelength multiplicity. Therefore, the wavelength tracking is needed for the signals of wavelengths λ2i.
In the above-discussed embodiments, a plurality of photodetectors or light detecting elements are arranged in an array. In a case where the photodetectors are arranged in an array, however, light receiving surfaces thereof can not be continuously disposed since they are inevitably separated from one another by their surface electrodes and gaps therebetween. Therefore, there are limits to making the entire light detecting apparatus compact in size by decreasing the distance between the photodetector and the light waveguide and improving the wavelength resolution by reducing the length of the photodetector in the waveguide extension direction. In the seventh embodiment, a photodetectors are arranged in plural arrays and in such a manner that their light receiving surfaces are continuously disposed as a whole in the waveguide extension direction. As a result, the light detecting apparatus can be made compact in size and the wavelength resolution of the light detecting apparatus can be improved by decreasing the length of the light receiving surface in the waveguide extension direction.
In the light detecting apparatus having the wavelength tracking function of the first embodiment, etc., there are provided the semiconductor light waveguide having the diffraction grating, the electrode for the current injection or voltage application, a plurality of photodetectors disposed for receiving the diffraction light emitted outside of the waveguide, and the control device for changing the Bragg wavelength of the waveguide by injected current or applied voltage so that the diffraction light is always incident on a determined photodetector, based on the information of the change in the emission angle of the diffraction light due to the wavelength fluctuation of the incident light on the waveguide which is detected by the plural photodetectors.
FIG. 13 shows the structure of the ninth embodiment of the present invention. FIG. 13 is a partly broken perspective view. In FIG. 13, there are provided a light waveguide part 143 with a diffraction grating, a first optical amplifier part 142, a second optical amplifier part 146 and an array 141 of light detecting elements. In the light waveguide part 143 with the diffraction grating and the first and second optical amplifier parts 142 and 146, there are formed, on an n-GaAs substrate 132, an n-Alx Ga1-x As light confinement layer 133, an Aly Ga1-y As light waveguide layer 134 (0≦y<x<1) a high-resistance Alx Ga1-x As burying layer 135, a p-Alx Ga1-x As light confinement layer 136 and a p-Alz Ga1-z As contact layer 137 (0<z<1). The extension direction of the waveguide is set to form a non-zero predetermined angle relative to a nomal to the end surface of the substrate 132. On the bottom of the n-type substrate 132, there is formed an n-type electrode 131. Further, on the light waveguide part 143, an upper p-type electrode 139 having a window 140 for emitting a diffraction light is formed, and on the first and second optical amplifier parts 142 and 146, upper p-type electrodes 138 and 147 are respectively formed.
FIG. 14 shows the structure of the tenth embodiment of the present invention in which a three-electrode distributed Bragg reflection (DBR) type tunable semiconductor laser part and a waveguide portion of a monitoring part for detecting wavelength and output power are monolithically formed. In FIG. 14 showing a left half structure of the tenth embodiment, there are formed on an n-GaAs substrate 152, an n-Alx Ga1-x As light confinement layer 153, an Aly Ga1-y As light waveguide layer 154 (0≦y<x<1; the energy gap of the light confinement layer 153 is larger than that of the light waveguide layer 154, and the refractive index of the layer 153 is smaller than that of the layer 154 to perform the light confinement function), a p-Alx Ga1-x As light confinement layer 155 and a p-Alz Ga1-z As contact layer 157 (0<z<1) in that order. The mole fraction z of Al of the contact layer 157 is selected so that the light absorption is small for the oscillation wavelength. A high-resistance Alx Ga1-x As burying layer 156 is re-grown after etching both sides except for a stripe-shaped portion in order to achieve confinement in a lateral direction.
FIG. 16 shows a structure of the eleventh embodiment of the present invention in which a Fabry-Perot type semiconductor laser (FP-LD) part and a waveguide portion of a monitoring part for detecting wavelength and output power are monolithically formed. Portions having the same functions as those in FIG. 14 are designated by the same reference numerals. The resonator of the FP-LD part is formed by a cleaved surface at the light output side and a mirror surface produced by etching at the monitoring part side. Part of the transmitted light through the mirror surface formed by the etching enters the waveguide in the monitoring part.
FIG. 18 shows the twelfth embodiment of the present invention of an optical communication system including the light detecting apparatus of the present invention. In FIG. 18, reference numerals 200 designate transmitter end office terminals, reference numerals 250 and 300 designate branching-combining devices, reference numerals 400 designate receiver end offices or terminals and reference numeral 500 designates a light transmission line such as an optical fiber and the like. The transmitter end offices 200 respectively comprise a signal processing part, and a light transmitter part including an electro-optical conversion portion which is a light detecting apparatus provided with a semiconductor laser of, for example, the tenth embodiment and so forth. The receiver end offices are respectively composed of a light detecting apparatus 410 such as that of the first embodiment, a signal processing part or processor 420 and so forth.
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OF JAPAN, JAPANFree format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:SEKIGUCHI, YOSHINOBU;REEL/FRAME:006058/0978Effective date: 19920310RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services