Laser cavity structure for wavelength reduction

Abstract

The light source includes a resonant laser cavity having an optical grating and a waveguide having a longitudinal axis, a portion of which extends through the optical grating and serves as a grating axis. The laser cavity is configured to generate a laser signal that exits the laser cavity through the optical grating. The optical grating includes a plurality of perturbation structures that perturb the effective refractive index of the waveguide. The perturbation structures are staggered on the waveguide such that adjacent perturbation structures in the longitudinal direction are spaced apart in the transverse direction. The longitudinal direction is parallel to the grating axis, and the transverse direction is transverse to the longitudinal direction.

Description

Cross - Reference to Related Applications

[0001] This application is a continuation of U.S. Patent Application No. 16 / 805,675, entitled "Laser Cavity Structures for Wavelength Reduction", filed on February 28, 2020, the entire disclosure of which is incorporated herein by reference.

Technical Field

[0002] The present invention relates to optical devices, specifically laser systems.

Background Art

[0003] There is an increasing commercial demand for 3D sensing systems that can be economically deployed in applications such as ADAS (Advanced Driver Assistance Systems) and AR (Augmented Reality). LIDAR (Light Detection and Ranging) sensors are used to construct 3D images of a target scene by illuminating the scene with laser light and measuring the returned signals.

[0004] Lasers used in communication applications often have wavelengths on the order of 1550 nm. Semiconductor lasers having wavelengths on this order often include optical gratings that can be fabricated using a stepper in combination with photolithography. However, shorter wavelengths can enhance system performance in other applications such as LIDAR. As the wavelength decreases, many semiconductor laser structures become smaller. For example, the pitch of the optical grating generally decreases as the wavelength decreases. This reduction in the dimensions of the laser structure often requires a higher degree of resolution in photolithography than can be achieved using a stepper. As a result, it is often necessary to manufacture lasers with shorter wavelengths desired for use in applications such as LIDAR using more expensive technologies. The manufacturing cost of shorter - wavelength semiconductor lasers hinders the commercial adoption of these technologies. Therefore, there is a need for short - wavelength semiconductor lasers with low manufacturing costs. Summary

[0005] The light source has a resonant laser cavity with an optical grating and a waveguide having a longitudinal axis. A part of the longitudinal axis extends through the optical grating and functions as a grating axis. The laser cavity is configured to generate a laser signal that exits the laser cavity through the optical grating. The optical grating includes a plurality of perturbation structures that perturb the effective refractive index of the waveguide. The perturbation structures are alternately arranged on the waveguide such that adjacent perturbation structures in the longitudinal direction are laterally spaced apart. The longitudinal direction is a direction parallel to the grating axis, and the lateral direction is a direction transverse to the longitudinal direction. In some examples, the light source is included in a LIDAR system.

[0006] The light source has a resonant laser cavity including a waveguide and an optical grating. The laser cavity is configured to generate a laser signal that exits the laser cavity through the optical grating. The optical grating includes a plurality of perturbation structures that respectively perturb the effective refractive index of the waveguide. The perturbation structures are arranged in sub-gratings such that each sub-grating includes two or more of the perturbation structures. The perturbation structures within the same sub-group have the same orientation with respect to the longitudinal axis of the waveguide, while the perturbation structures within different sub-groups have different orientations with respect to the longitudinal axis of the waveguide.

Brief Description of the Drawings

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[0015] Figures 9A - 9H illustrate an example of a light source suitable for use with a LIDAR system.

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[0026] The LIDAR system includes a light source having a laser cavity laser including an optical grating. The laser cavity outputs a laser signal that exits the laser cavity through the optical grating. The optical grating includes a perturbation region that causes a perturbation in the effective refractive index of the waveguide. The perturbation regions are arranged alternately on the waveguide such that adjacent perturbation regions on the waveguide are laterally spaced apart. In a conventional reflection grating, the perturbation regions are not laterally spaced apart, but instead overlap each other laterally.

[0027] Separating the perturbation regions horizontally increases the shortest distance between adjacent perturbation regions on the waveguide. When the shortest distance between adjacent perturbation regions increases, the level of resolution required to fabricate the perturbation regions decreases. Reducing the level of resolution required enables the fabrication of an optical grating by conventional manufacturing processes such as photolithography and etching. Conventional manufacturing processes are less costly compared to high-resolution processes. As a result, the manufacturing cost of the optical grating is reduced because the optical grating can be manufactured by conventional manufacturing techniques.

[0028] FIG. 1 is a top view of an example of a LIDAR chip. The LIDAR chip can include an optical integrated circuit (PIC) and can be an optical integrated circuit (PIC) chip. The LIDAR chip includes a light source (10). The output of the light source (10) is received by a utility waveguide (16) and functions as an outgoing LIDAR signal on the utility waveguide (16). The utility waveguide (16) terminates at a facet (18) and carries the outgoing LIDAR signal to the facet (18). The facet (18) can be arranged such that the outgoing LIDAR signal traveling through the facet (18) exits the chip and functions as a LIDAR output signal. For example, since the facet (18) can be arranged at the edge of the chip, the outgoing LIDAR signal traveling through the facet (18) exits the chip and functions as a LIDAR output signal.

[0029] The LIDAR output signal travels away from the chip and can be reflected by an object in the path of the LIDAR output signal. When the LIDAR output signal is reflected, at least a portion of the light from the reflected signal is returned as a first LIDAR input signal to an input waveguide (19) on the LIDAR chip. The input waveguide (19) includes a facet (20) through which the first LIDAR input signal can enter the input waveguide (19). The portion of the first LIDAR input signal incident on the input waveguide (19) can be regarded as an incident LIDAR signal and functions as a comparison signal carried by the input waveguide (19). The input waveguide (19) carries the comparison signal to an optical coupler (28).

[0030] The chip includes a data branch (24) where an optical signal to be processed for LIDAR data is generated. The data branch includes a splitter (26) that moves a portion of the outgoing LIDAR signal from the utility waveguide (16) to the data branch. For example, the splitter (26) moves a portion of the outgoing LIDAR signal from the utility waveguide (16) to the reference waveguide (27) as a reference signal. The reference waveguide (27) carries the reference signal to an optical coupler (28). The illustrated splitter (26) is an optical coupler that operates by bringing the utility waveguide (16) sufficiently close to the reference waveguide (27) so that light from the utility waveguide (16) is coupled into the reference waveguide (27). However, other signal tap elements can be used to move a portion of the optical signal from the utility waveguide (16) onto the reference waveguide (27). Examples of suitable splitters (26) include, but are not limited to, y-junctions, optical couplers, and multimode interference couplers (MMI).

[0031] The optical coupler (28) combines the comparison signal and the reference signal into a composite signal. The reference signal includes light from the outgoing LIDAR signal. For example, the reference signal can function as a sample of the outgoing LIDAR signal. The reference signal can exclude light from the LIDAR output signal and the first LIDAR input signal. On the other hand, the comparison signal includes light from the first LIDAR input signal. For example, the comparison signal can function as a sample of the first LIDAR input signal. Thus, the comparison signal includes or consists of light reflected by an object away from the chip in a sample region within the field of view, while the reference signal does not include the light reflected by the object. When the chip and the reflecting object are moving relative to each other, the comparison signal and the reference signal can have at least partially different frequencies due to the Doppler effect. As a result, a beat is generated between the comparison signal and the reference signal.

[0032] The optical coupler (28) also splits the obtained composite sample signal into a first detector waveguide (36) and a second detector waveguide (38). The first detector waveguide (36) conveys a first portion of the composite sample signal to a first optical sensor (40) that converts the first portion of the composite sample signal into a first electrical signal. The second detector waveguide (38) conveys a second portion of the composite sample signal to a second optical sensor (42) that converts the second portion of the composite sample signal into a second electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0033] The optical coupler (28), the first optical sensor (40), and the second optical sensor (42) can be connected as a balanced optical detector that outputs an electrical data signal. For example, the optical coupler (28), the first optical sensor (40), and the second optical sensor (42) can be connected such that the DC components of the signal photocurrents cancel each other out. This improves the detection sensitivity. A method suitable for connecting the first optical sensor (40) and the second optical sensor (42) as a balanced optical detector includes connecting the first optical sensor (40) and the second optical sensor (42) in series. In one example, the first optical sensor (40) and the second optical sensor (42) are both avalanche photodiodes connected in series. A balanced optical detector is desirable for detecting small signal fluctuations.

[0034] An example of a suitable optical coupler (28) is a multimode interference (MMI) device such as a 2x2 MMI device. Other suitable optical couplers (28) include, but are not limited to, adiabatic splitters and directional couplers. The function of the illustrated optical coupler (28) can be performed by a plurality of optical components.

[0035] The single optical sensor can be replaced by a first optical sensor (40) and a second optical sensor (42), and can output a data signal. When replacing the single optical sensor with the first optical sensor (40) and the second optical sensor (42), the optical coupling part (28) does not need to have the function of optical splitting. As a result, the illustrated optical coupling part (28) can be a 2x1 optical coupling part instead of the illustrated 2x1 optical coupling part. For example, the illustrated optical coupling part may be a 2x1 MMI device. In these cases, the chip includes a single detector waveguide that conveys a composite sample signal to the optical sensor.

[0036] The chip includes a control branch (55) for controlling the operation of the laser cavity. The control branch includes a directional coupler (56) that moves a part of the emitted LIDAR signal from the utility waveguide (16) onto the control waveguide (57). The part of the combined emitted LIDAR signal functions as a tapped signal. FIG. 1 shows the directional coupler (56) that moves a part of the emitted LIDAR signal onto the control waveguide (57), but other signal tap elements can be used to move a part of the emitted LIDAR signal from the utility waveguide (16) onto the control waveguide (57). Examples of suitable signal tap elements include, but are not limited to, y-junctions and MMIs.

[0037] The control waveguide (57) conveys the tapped signal to an interferometer (58) that splits the tapped signal and recombines different parts of the tapped signal with a phase difference between the parts of the tapped signal. The illustrated interferometer (58) is a Mach-Zehnder interferometer, but other interferometers can also be used.

[0038] The interferometer (58) outputs a control optical signal onto the interferometer waveguide (60). The interferometer waveguide (60) conveys the control optical signal to a control optical sensor (61) that converts the control optical signal into an electrical signal that functions as an electrical control signal. The interferometer signal has an intensity that is a function of the frequency of the emitted LIDAR signal. For example, a Mach-Zehnder interferometer will output a sinusoidal control optical signal having a striped pattern. A change in the frequency of the emitted LIDAR signal will cause a change in the frequency of the control optical signal. Accordingly, the frequency of the electrical control signal output from the control optical sensor (61) is a function of the frequency of the emitted LIDAR signal. Other detection mechanisms can be used instead of the control optical sensor (61). For example, the control optical sensor (61) can be replaced with a balanced photodetector arranged as an optical coupler (28), a first optical sensor (40), and a second optical sensor (42).

[0039] The electronic device (62) can operate one or more components on the chip. For example, the electronic device (62) can communicate electrically with the light source (10), the first optical sensor (40), the second optical sensor (42), and the control optical sensor (61) and control their operations. The electronic device (62) is shown as being separate from the chip, but all or part of the electronic device can be included on the chip. For example, the chip can include a conductor that serially connects the first optical sensor (40) and the second optical sensor (42).

[0040] During operation of the chip, the electronic device (62) operates the light source (10), whereby the light source (10) outputs an emitted LIDAR signal. Next, the electronic device (62) operates the LIDAR chip through a series of cycles in which LIDAR data (radial distance and / or line-of-sight velocity between the LIDAR system and the reflecting object) is generated for each cycle. In some examples, the LIDAR system includes one or more mechanisms for steering the direction in which the LIDAR output signal travels away from the LIDAR system. The electronic device can operate one or more mechanisms to direct the LIDAR output signal to different sample regions within the field of view. The sample regions can be associated with one of the cycles, and / or each cycle can be associated with one of the sample regions. As a result, the result of each LIDAR data can be associated with one sample region within the field of view. Different sample regions may overlap with each other and / or may be separated from each other.

[0041] Each cycle includes one or more data periods. During each data period, the electronic device tunes the frequency of the emitted LIDAR signal. As will be described in more detail below, the electronic device can use the output from the control branch to control the frequency of the emitted LIDAR signal such that the frequency of the emitted LIDAR signal as a function of time is known to the electronic device. In some examples, the cycle includes a first data period and a second data period. During the first data period, the electronic device (62) can increase the frequency of the LIDAR output signal, and during the second data period, the electronic device (62) can decrease the frequency of the LIDAR output signal. In some examples, the increase and decrease in the frequency of the LIDAR output signal is linear. In one example, the laser cavity is operated to output a LIDAR signal (and accordingly a LIDAR output signal) at a wavelength of 1310 nm. During the first data period, the electronic device (62) can linearly increase the frequency of the emitted LIDAR signal (and accordingly the LIDAR output signal) such that the wavelength decreases from 1300 nm to 1299.98 nm, and in a subsequent second data period, the frequency of the emitted LIDAR signal linearly increases from 1299.98 nm to 1300 nm.

[0042] When the frequency of the emitted LIDAR signal increases during the first data period, the LIDAR output signal travels away from the LIDAR chip, and an object placed in the sample area of the field of view can reflect light from the LIDAR output signal. Next, at least a part of the reflected light is returned to the chip in the first LIDAR input signal. As described above, a part of the first LIDAR input signal becomes a comparison signal. While the LIDAR output signal and the first LIDAR input signal move between the chip and the reflecting object, the frequency of the emitted LIDAR signal continues to increase. Since a part of the emitted LIDAR signal becomes a reference signal, the frequency of the reference signal continues to increase. As a result, the comparison signal is incident on the optical coupler at a frequency lower than the reference signal that is simultaneously incident on the optical coupler. Also, the farther the reflecting object is from the chip, the more the frequency of the reference signal increases before the first LIDAR input signal returns to the chip. Therefore, the greater the difference between the frequency of the comparison signal and the frequency of the reference signal, the farther the reflecting object is from the chip. As a result, the difference between the frequency of the comparison signal and the frequency of the reference signal is a function of the distance between the chip and the reflecting object.

[0043] For similar reasons, when the frequency of the emitted LIDAR signal decreases during the second data period, the comparison signal is incident on the optical coupler at a frequency higher than the reference signal that is simultaneously incident on the optical coupler, and the difference between the frequency of the comparison signal and the frequency of the reference signal in the second data period is also a function of the distance between the LIDAR system and the reflecting object.

[0044] In some examples, the relative movement of the LIDAR system and the reflective object can also affect the frequency of the comparison signal, so the difference between the frequency of the comparison signal and the frequency of the reference signal may be a function of the Doppler effect. For example, when the LIDAR system moves towards or away from the reflective object, and / or when the reflective object moves towards or away from the LIDAR system, the Doppler effect can affect the frequency of the comparison signal. Since the frequency of the comparison signal is a function of the line-of-sight velocity between the reflective object and the LIDAR system, the difference between the frequency of the comparison signal and the frequency of the reference signal is also a function of the line-of-sight velocity between the reflective object and the LIDAR system. Therefore, the difference between the frequency of the comparison signal and the frequency of the reference signal is a function of the distance and / or line-of-sight velocity between the LIDAR system and the reflective object.

[0045] The composite sample signal and the data signal each effectively compare the comparison signal and the reference signal. For example, the photosynthetic component combines the comparison signal and the reference signal, and since these signals have different frequencies, beats occur between the comparison signal and the reference signal. Therefore, the composite sample signal and the data signal have a beat frequency related to the frequency difference between the comparison signal and the reference signal. The beat frequency can be used to determine the difference in the frequencies of the comparison signal and the reference signal. A high beat frequency for the composite sample signal and / or the data signal indicates a higher difference between the frequency of the comparison signal and the reference signal. As a result, the beat frequency of the data signal is a function of the distance and / or line-of-sight velocity between the LIDAR system and the reflective object.

[0046] JPEG0007717074000001.jpg103156

[0047] When the line-of-sight velocity between the LIDAR chip and the reflective object is zero or very small, the contribution of the Doppler effect to the beat frequency is essentially zero. In these cases, the Doppler effect does not substantially contribute to the beat frequency, and the electronic device (62) can measure the distance between the chip and the reflective object using only the first data period.

[0048] During operation, the electronic device (62) can adjust the frequency of the emitted LIDAR signal in response to the electrical control signal output from the control optical sensor (61). As described above, the magnitude of the electrical control signal output from the control optical sensor (61) is a function of the frequency of the emitted LIDAR signal. Therefore, the electronic device (62) can adjust the frequency of the emitted LIDAR signal according to the magnitude of the control. For example, while changing the frequency of the emitted LIDAR signal during the data period, the electronic device (62) can have an appropriate range of values for the magnitude of the electrical control signal as a function of time. At multiple different times during the data period, the electronic device (62) can compare the magnitude of the electrical control signal with the range of values associated with the current time in the sample. If the magnitude of the electrical control signal indicates that it is outside the range of the magnitude of the electrical control signal related to the frequency of the emitted LIDAR signal, the electronic device (62) can change the frequency of the emitted LIDAR signal and operate the light source (10) so that it falls within the related range. If the magnitude of the electrical control signal indicates that the frequency of the emitted LIDAR signal is within the related range of the magnitude of the electrical control signal, the electronic device (62) does not change the frequency of the emitted LIDAR signal.

[0049] The LIDAR chip of FIG. 1 can be modified to receive a plurality of first LIDAR input signals. For example, FIG. 2 shows the LIDAR chip of FIG. 1 modified to receive two first LIDAR input signals. The splitter (70) is configured to move a part of the reference signal carried on the reference waveguide (27) onto the first reference waveguide (72) and another part of the reference signal onto the second reference waveguide (74). Therefore, the first reference waveguide (72) carries the first reference signal, and the second reference waveguide (74) carries the second reference signal. The first reference signal is carried to the optical coupler (28) and is processed by the optical coupler (28) as described in relation to FIG. 1. Examples of suitable splitters (70) include, but are not limited to, y-junctions, optical couplers, and multimode interference couplers (MMI).

[0050] As described above, the LIDAR output signal traveling away from the chip can be reflected by one or more objects in the path of the LIDAR output signal. The reflected signal travels away from the object. When the travel of the LIDAR output signal is reflected, at least a portion of the reflected signal is returned as a second LIDAR input signal to a second input waveguide (76) on the LIDAR chip. The second input waveguide (76) includes a facet (78) through which the first LIDAR input signal can enter the second input waveguide (76). The portion of the second LIDAR input signal incident on the input waveguide (19) functions as a second comparison signal carried by the second input waveguide (76).

[0051] The second input waveguide (76) conveys the second comparison signal to a second optical coupler (80). Also, the second reference waveguide (74) conveys a second reference signal to the second optical coupler (80). The second optical coupler (80) combines the second comparison signal and the second reference signal into a second composite signal. The second reference signal includes light from the emitted LIDAR signal. For example, the second reference signal can function as a sample of the emitted LIDAR signal. The second reference signal can exclude light from the LIDAR output signal and the second LIDAR input signal. In contrast, the second comparison signal includes light from the second LIDAR input signal. For example, the second comparison signal can function as a sample of the second LIDAR input signal. Thus, the second comparison signal is reflected by an object located outside the LIDAR system, while the second reference signal is not reflected. When the chip and the reflecting object move relative to each other, the second comparison signal and the second reference signal can have at least partially different frequencies due to the Doppler effect. As a result, a beat is generated between the second comparison signal and the second reference signal.

[0052] The second optical coupling unit (80) also splits the obtained second composite signal into a first detector waveguide (82) and a second detector waveguide (84). The first detector waveguide (82) conveys a first portion of the second composite signal to the first optical sensor (40), and the first optical sensor (40) converts the first portion of the second composite signal into a first electrical signal. The second detector waveguide (84) conveys a second portion of the second composite sample signal to the second optical sensor (42), and the second optical sensor (42) converts the second portion of the composite sample signal into a second electrical signal. Examples of suitable optical sensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0053] The second optical coupling unit (80), the associated first optical sensor (40) and the associated second optical sensor (42) can be connected as a balanced optical detector that outputs a second electrical data signal. For example, the second optical coupling unit (80), the associated first optical sensor (40) and the associated second optical sensor (42) can be connected such that the DC component of the signal photocurrent cancels out and the detection sensitivity is improved. A method suitable for connecting the first optical sensor (40) and the second optical sensor (42) as a balanced optical detector includes connecting the first optical sensor (40) and the second optical sensor (42) in series. In one example, the first optical sensor (40) and the second optical sensor (42) are both avalanche photodiodes connected in series. Balanced optical detection is desirable for detecting small signal fluctuations.

[0054] An example of a suitable second optical coupling unit (80) is a multimode interference (MMI) device such as a 2x2 MMI device. Other suitable second optical coupling units (80) include, but are not limited to, adiabatic splitters and directional couplers. The function of the illustrated second optical coupling unit (80) can be performed by a plurality of optical components.

[0055] The electronic device (62) can operate a plurality of components on the chip and generate a LIDAR output signal over a plurality of different cycles as described above. Also, the electronic device (62) can process the second electrical signal as described above in connection with FIG. 1. Accordingly, the electronic device can generate the result of the second LIDAR data from the result of the second composite signal and / or the LIDAR data from the composite signal. As a result, the result of the second LIDAR data and / or the result of the LIDAR data can be generated from the same LIDAR output signal.

[0056] The LIDAR chip can be modified to include other components. For example, FIG. 3 shows the LIDAR chip of FIG. 2 modified to include an amplifier (85) disposed at the end of the LIDAR chip such that the utility waveguide (16) terminates at a facet of the amplifier (85). The amplifier (85) is operable by the electronic device (62). As a result, the electronic device (62) can control the power of the LIDAR output signal. Suitable amplifiers include, but are not limited to, erbium-doped fiber amplifiers (EDFAs), erbium-doped waveguide amplifiers (EDWAs), and semiconductor optical amplifiers (SOAs).

[0057] Suitable platforms for the LIDAR chip include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers. FIG. 4 is a cross-sectional view of a portion of a chip constructed from a silicon-on-insulator wafer. The silicon-on-insulator (SOI) wafer includes a buried layer (90) between a substrate (92) and a light-transmissive medium (94). In a silicon-on-insulator wafer, the buried layer is silica and the substrate and the light-transmissive medium are silicon. The substrate of an optical platform such as an SOI wafer can function as a base for the entire chip. For example, the optical components shown in FIGS. 1-3 can be disposed on, above, and / or on the sides of the substrate.

[0058] The portion of the chip illustrated in FIG. 4 includes a waveguide structure suitable for use with a chip constructed from a silicon-on-insulator wafer. The ridge (96) of the light-transmissive medium extends away from the slab region (98) of the light-transmissive medium. The optical signal is confined between the top of the ridge and the embedded oxide layer.

[0059] The dimensions of the ridge waveguide are shown in FIG. 4. For example, the ridge has a width labeled w and a height labeled h. The thickness of the slab region is labeled T. For LIDAR applications, these dimensions are more important than other dimensions because a higher level of optical power needs to be used than in other applications. The ridge width (labeled w) is greater than 1 μm and less than 4 μm, the ridge height (labeled h) is greater than 1 μm and less than 4 μm, and the thickness of the slab region is greater than 0.5 μm and less than 3 μm. These dimensions can be applied to the linear or substantially linear portions of the waveguide, the curved portions of the waveguide, and the tapered portions of the waveguide. Thus, these portions of the waveguide are single-mode. However, in some examples, these dimensions are applied to the linear or substantially linear portions of the waveguide. Additionally or alternatively, to reduce optical loss in the curved portions of the waveguide, the slab thickness of the curved portion of the waveguide can be made thinner. For example, the curved portion of the waveguide can have a ridge extending away from a slab region having a thickness greater than or equal to 0.0 μm and less than 0.5 μm. The above dimensions generally provide a linear or substantially linear portion of the waveguide having a single-mode structure, but can result in tapered and / or curved portions that are multimode. The coupling between the multimode geometry and the single-mode geometry can be done using a taper that does not substantially excite higher-order modes. Thus, the waveguide can be constructed such that even if the signal is carried into a portion of the waveguide having multimode dimensions, the signal carried in the waveguide is carried in single mode. The waveguide construct of FIG. 4 is suitable for all or part of the waveguide on a LIDAR chip constructed according to FIGS. 1-3.

[0060] The optical sensor interfacing with the waveguide on the chip may be a component that is attached to the chip after being separated from the chip. For example, the optical sensor may be a photodiode or an avalanche photodiode. Examples of suitable optical sensor components include, but are not limited to, InGaAs PIN photodiodes manufactured by Hamamatsu Corporation in Hamamatsu, Japan, or InGaAs APDs (avalanche photodiodes) manufactured by Hamamatsu Corporation in Hamamatsu, Japan. These optical sensors can be intensively arranged on the chip as shown in FIG. 1. Alternatively, all or part of the waveguide terminated by the optical sensor can be terminated by a facet (18) located at the end of the chip, and the optical sensor can be attached to the end of the chip on the facet (18) so that the optical sensor receives the light passing through the facet (18). The use of an optical sensor that is a separate component is suitable for all or part of the optical sensors selected from the group consisting of the first optical sensor (40), the second optical sensor (42), and the control optical sensor (61).

[0061] As an alternative to an optical sensor that is a separate component, all or part of the optical sensor can be integrated with the chip. For example, examples of optical sensors interfacing with ridge waveguides on chips constructed from silicon-on-insulator wafers can be found in Optics Express Vol. 15, No. 21, 13965-13971 (2007), U.S. Patent No. 8,093,080, which became effective on January 10, 2012, U.S. Patent No. 8,242,432, which became effective on August 14, 2012, and U.S. Patent No. 6,108,8472, which became effective on August 22, 2000, and the entire contents of each of them are incorporated herein by reference. The use of an optical sensor integrated with the chip is suitable for all or part of the optical sensors selected from the group consisting of the first optical sensor (40), the second optical sensor (42), the sampling optical sensor (54), and the control optical sensor (61).

[0062] The amplifier interfaced with the waveguide on the chip can be a component that is attached to the chip after being separated from the chip. For example, the amplifier may be a semiconductor optical amplifier (SOA) or a booster optical amplifier (BOA) as a separate component. Examples of amplifiers as separate components include, but are not limited to, the BOA1007C manufactured by Thorlabs in Newton, New Jersey, USA. These amplifiers can be intensively arranged on the LIDAR chip. Alternatively, all or part of the waveguide terminates with an amplifier (18) arranged at the end of the LIDAR chip such that the amplifier receives the light passing through the amplifier. As an alternative to the amplifier as a component, all or part of the amplifier can be integrated with the LIDAR chip. For example, examples of amplifiers interfaced with ridge waveguides on chips constructed from silicon-on-insulator wafers can be found in U.S. Patent Application Serial No. 62 / 814,844, U.S. Patent No. 9,025,241, and U.S. Patent No. 7,542,641, the entire contents of each of which are incorporated herein by reference.

[0063] Constructs of optical gratings integrated with platforms of various optical devices are available. For example, a Bragg grating can be formed in a ridge waveguide by forming grooves on the top and / or the rear side of the ridge.

[0064] Suitable electronic devices include, but are not limited to, controllers that include or consist of analog electrical circuits, digital electrical circuits, processors, microprocessors, digital signal processors (DSPs), computers, microcomputers, or suitable combinations for performing the above-described operations, monitoring, and control functions. In some examples, the controller accesses a memory that includes instructions executed by the controller during execution of the operations, control, and monitoring functions. Although the electronic device is illustrated as a single component in a single location, the electronic device can include a plurality of different components that are independent of each other and / or located in different locations. Also, as described above, all or part of the disclosed electronic device can be included on a chip that includes an electronic device integrated with the chip.

[0065] A LIDAR chip can be used with a LIDAR adapter. In some examples, the LIDAR adapter can be physically and optically positioned between the LIDAR chip and one or more reflective objects and / or the field of view. The field of view has an optical path through which a first LIDAR input signal and / or a LIDAR output signal travels from the LIDAR chip to the field of view. Also, the LIDAR adapter can be configured to operate on the first LIDAR input signal and the LIDAR output signal such that the first LIDAR input signal and the LIDAR output signal travel on different optical paths between the LIDAR adapter and the LIDAR chip but on the same optical path between the LIDAR adapter and the reflective object within the field of view.

[0066] An example of a LIDAR adapter suitable for use with the LIDAR chip of FIG. 1 is shown in FIG. 5. The LIDAR adapter includes a plurality of components disposed on a base. For example, the LIDAR adapter includes a circulator (100) located on a base (102). The illustrated optical circulator (100) includes three ports and is configured such that light entering one port exits from the next port. For example, the illustrated optical circulator includes a first port (104), a second port (106), and a third port (108). The LIDAR output signal is incident from the utility waveguide (16) of the LIDAR chip on the first port (104) and exits from the second port (106). The LIDAR adapter can be configured such that the output of the LIDAR output signal from the second port (106) can also function as the output of the LIDAR output signal from the LIDAR adapter. As a result, the LIDAR output signal can be output from the LIDAR adapter such that the LIDAR output signal travels towards a sample region within the field of view.

[0067] The LIDAR output signal output from the LIDAR adapter includes or consists essentially of light from the LIDAR output signal received from the LIDAR chip. Accordingly, the LIDAR output signal output from the LIDAR adapter may be the same or substantially the same as the LIDAR output signal received from the LIDAR chip. However, there may be a difference between the LIDAR output signal output from the LIDAR adapter and the LIDAR output signal received from the LIDAR chip. For example, light may be lost when the LIDAR output signal passes through the LIDAR adapter.

[0068] When an object within the sample region reflects the LIDAR output signal, at least a portion of the reflected light returns to the circulator (100) as a LIDAR return signal. The LIDAR return signal is incident on the circulator (100) via the second port (106). FIG. 5 shows the LIDAR output signal and the LIDAR return signal traveling along the same optical path between the LIDAR adapter and the sample region.

[0069] The LIDAR return signal exits the circulator (100) via the third port (108) and is guided to the input waveguide (19) on the LIDAR chip. Thus, the light from the LIDAR return signal can function as a first LIDAR input signal, which includes or consists of the light from the LIDAR return signal. Therefore, the LIDAR output signal and the first LIDAR input signal travel along different optical paths between the LIDAR adapter and the LIDAR chip.

[0070] As is apparent from FIG. 5, the LIDAR adapter can include optical components in addition to the circulator (100). For example, the LIDAR adapter can include components for guiding and controlling the optical paths of the LIDAR output signal and the LIDAR return signal. As an example, the adapter of FIG. 5 includes any optical amplifier (110) arranged to receive and amplify the LIDAR output signal before the LIDAR output signal is incident on the circulator (100). The amplifier (110) can be operated by an electronic device (62) that enables the power of the LIDAR output signal to be controlled.

[0071] FIG. 5 also shows a LIDAR adapter that includes an optional first lens (112) and an optional second lens (114). The first lens (112) can be configured to couple the LIDAR output signal to a desired location. In some examples, the first lens (112) is configured to focus or collimate the LIDAR output signal to a desired location. In one example, when the LIDAR adapter does not include an amplifier (110), the first lens (112) is configured to couple the LIDAR output signal to the first port (104). As another example, when the LIDAR adapter includes an amplifier (110), the first lens (112) can be configured to couple the LIDAR output signal on the input port to the amplifier (110). The second lens (114) can be configured to couple the LIDAR output signal to a desired location. In some examples, the second lens (114) is configured to focus or collimate the LIDAR output signal to a desired location. For example, the second lens (114) can be configured to couple the LIDAR output signal to the facet (20) of the input waveguide (19).

[0072] The LIDAR adapter can also include one or more beam steering components such as mirrors. FIG. 5 shows a LIDAR adapter that includes a mirror as a beam steering component (116) that redirects the LIDAR return signal from the circulator (100) back into the facet (20) of the input waveguide (19).

[0073] The LIDAR chip includes one or more waveguides that confine the optical paths of one or more optical signals. The LIDAR adapter can include waveguides, but the optical paths through which the LIDAR return signal and the LIDAR output signal travel between components on the LIDAR adapter and / or between the LIDAR chip and components on the LIDAR adapter can be free space. For example, the LIDAR return signal and / or the LIDAR output signal can travel through the space in which the LIDAR chip, the LIDAR adapter, and the base (102) are located when traveling between different components on the LIDAR adapter and / or between a component on the LIDAR adapter and the LIDAR chip. As a result, optical components such as lenses and beam deflectors can be used to control the characteristics of the optical paths through which the LIDAR return signal and the LIDAR output signal travel on, to, or from the LIDAR adapter.

[0074] Suitable bases (102) for the LIDAR adapter include, but are not limited to, substrates, platforms, and plates. Suitable substrates include, but are not limited to, glass, silicon, and ceramics. The components can be discrete components attached to the substrate. Techniques suitable for attaching discrete components to the base (102) include, but are not limited to, epoxy, solder, and mechanical clamps. In one example, one or more components are integrated components and the remaining components are discrete components. In another example, the LIDAR adapter includes one or more integrated amplifiers and the remaining components are discrete components.

[0075] The LIDAR system can be configured to correct polarization. Since the light from the laser source is typically linearly polarized, the LIDAR output signal is also typically linearly polarized. Reflection from an object can change the polarization angle of the returned light. Therefore, the LIDAR return signal can include light in different linear polarization states. For example, the first portion of the LIDAR return signal can include light in a first linear polarization state, and the second portion of the LIDAR return signal can include light in a second linear polarization state. The intensity of the resulting composite signal is proportional to the square of the cosine of the angle between the comparison signal polarization field and the reference signal polarization field. If the angle is 90 degrees, LIDAR data may be lost in the resulting composite signal. However, the LIDAR system can be modified to correct for changes in the polarization state of the LIDAR output signal.

[0076] Figure 6 shows the LIDAR system of FIG. 5 modified to be suitable for use with the LIDAR chip of FIG. 2 or FIG. 3. The LIDAR adapter includes a beam splitter (120) that receives the LIDAR return signal from the circulator (100). The beam splitter (120) splits the LIDAR return signal into a first portion of the LIDAR return signal and a second portion of the LIDAR return signal. Suitable beam splitters include, but are not limited to, Wollaston prisms and MEM-based beam splitters.

[0077] The first portion of the LIDAR return signal is directed to the input waveguide (19) on the LIDAR chip and functions as the first LIDAR input signal described in the context of FIGS. 1-5. The second portion of the LIDAR return signal is directed to the polarization rotator (122). The polarization rotator (122) outputs a second LIDAR input signal directed to the second input waveguide (76) on the LIDAR chip and functions as the second LIDAR input signal described in the context of FIGS. 2-5.

[0078] The beam splitter (120) can be a polarization beam splitter. An example of a polarization beam splitter is constructed such that the first portion of the LIDAR return signal has a first polarization state but does not have or substantially does not have a second polarization state, and the second portion of the LIDAR return signal has a second polarization state but does not have or substantially does not have a first polarization state. The first polarization state and the second polarization state can be linear polarization states, and the second polarization state is different from the first polarization state. For example, the first polarization state can be TE, and the second polarization state can be TM, or the first polarization state can be TM, and the second polarization state can be TE. In some examples, the laser source can be linearly polarized such that the LIDAR output signal has a first polarization state. Suitable beam splitters include, but are not limited to, Wollaston prisms and MEM-based polarization beam splitters.

[0079] A polarization rotator can be configured to change the polarization state of the first portion of the LIDAR return signal and / or the second portion of the LIDAR return signal. For example, the polarization rotator (122) shown in FIG. 6 can be configured to change the polarization state of the second portion of the LIDAR return signal from the second polarization state to the first polarization state. As a result, the second LIDAR input signal has the first polarization state but does not have or substantially does not have the second polarization state. Thus, the first LIDAR input signal and the second LIDAR input signal each have the same polarization state (here, the first polarization state). Despite carrying light of the same polarization state, the first LIDAR input signal and the second LIDAR input signal are associated with different polarization states as a result of using a polarization beam splitter. For example, the first LIDAR input signal carries light reflected in the first polarization state, and the second LIDAR input signal carries light reflected in the second polarization state. As a result, the first LIDAR input signal is associated with the first polarization state, and the second LIDAR input signal is associated with the second polarization state.

[0080] Since the first LIDAR input signal and the second LIDAR input signal carry light in the same polarization state, the comparison signal generated from the first LIDAR input signal has the same polarization angle as the comparison signal generated from the second LIDAR input signal.

[0081] Suitable polarization rotators include, but are not limited to, rotators of polarization-maintaining fibers, Faraday rotators, half-wave plates, MEM-based polarization rotators, and integrated optical polarization rotators using asymmetric y-branches, Mach-Zehnder interferometers, and compound mode interference couplers.

[0082] Since the output LIDAR signal is linearly polarized, the first reference signal can have the same linear polarization angle as the second reference signal. Also, components on the LIDAR adapter can be selected such that the first reference signal, the second reference signal, the comparison signal, and the second comparison signal each have the same polarization state. In the example disclosed in the context of FIG. 6, the first comparison signal, the second comparison signal, the first reference signal, and the second reference signal can each have light in the first polarization state.

[0083] As a result of the above configuration, the composite signal and the second composite signal each result from the combination of a reference signal and a comparison signal in the same polarization state, and thus will provide a desired beat between the reference signal and the comparison signal. For example, the composite signal results from the combination of the first reference signal and the first comparison signal in the first polarization state, excluding or substantially excluding light in the second polarization state. Or, the composite signal results from the combination of the first reference signal and the first comparison signal in the second polarization state, excluding or substantially excluding light in the first polarization state. Similarly, the second composite signal includes the second reference signal and the second comparison signal in the same polarization state, and thus will provide a desired beat between the reference signal and the comparison signal. For example, the second composite signal results from the combination of the second reference signal and the second comparison signal in the first polarization state, excluding or substantially excluding light in the second polarization state, or the second composite signal results from the combination of the second reference signal and the second comparison signal in the second polarization state, excluding or substantially excluding light in the first polarization state.

[0084] With the above configuration, LIDAR data for a single sample region within the field of view generated from a plurality of different composite signals (i.e., a first composite signal and a second composite signal) is obtained. In some examples, measuring the LIDAR data for the sample region includes an electronic device that combines LIDAR data from different composite signals (i.e., a composite signal and a second composite signal). In some examples, the LIDAR data is combined by combining the signals that each carry the LIDAR data before the frequency of the beat signal is measured. As a result, the frequency of the beat signal can be measured from the signal containing the combined LIDAR data. In some examples, combining the LIDAR data can include taking the average, median, or mode of the LIDAR data generated from different composite signals. For example, the electronic device can average the distance between the LIDAR system and the reflective object measured from the composite signal with the distance measured from the second composite signal, and / or the electronic device can average the line-of-sight velocity between the LIDAR system and the reflective object measured from the composite signal with the line-of-sight velocity measured from the second composite signal.

[0085] In some examples, measuring LIDAR data of a sample region includes an electronic device that identifies one or more composite signals (i.e., a composite signal and / or a second composite signal) as the most representative source of LIDAR data (representative LIDAR data). The electronic device can then use the LIDAR data from the identified composite signal as representative LIDAR data for other processing. For example, the electronic device can identify a signal (composite signal or second composite signal) having a larger amplitude as having representative LIDAR data and use the LIDAR data from the identified signal for further processing by the LIDAR system. In some examples, the electronic device combines identifying a composite signal with representative LIDAR data with combining LIDAR data from different LIDAR signals. For example, the electronic device can identify each composite signal having an amplitude above an amplitude threshold as having representative LIDAR data, and if more than two composite signals are identified as having representative LIDAR data, the electronic device can combine the LIDAR data from each identified composite signal. When one composite signal is identified as having representative LIDAR data, the electronic device can use the LIDAR data from that composite signal as representative LIDAR data. If none of the composite signals are identified as having representative LIDAR data, the electronic device can discard the LIDAR data of the sample region associated with these composite signals.

[0086] Figure 6 is described in the context of components arranged such that the first comparison signal, the second comparison signal, the first reference signal, and the second reference signal each have a first polarization state. However, other configurations of the components in FIG. 6 can be arranged such that the composite signal is derived from the combination of the reference signal and the comparison signal in the same linear polarization state, and the second composite signal is derived from the combination of the reference signal and the comparison signal in the same linear polarization state. For example, the beam splitter (120) can be constructed such that the second portion of the LIDAR return signal has a first polarization state, the first portion of the LIDAR return signal has a second polarization state, the polarization rotator receives the first portion of the LIDAR return signal, and the output LIDAR signal has a second polarization state. In this example, the first LIDAR input signal and the second LIDAR input signal each have a second polarization state.

[0087] With the above system configuration, the first portion of the LIDAR return signal and the second portion of the LIDAR return signal are directed to different composite signals. As a result, the first portion of the LIDAR return signal and the second portion of the LIDAR return signal are each associated with a different polarization state, but the electronic device can process each composite signal. The LIDAR system corrects for changes in the polarization state of the LIDAR output signal in response to reflections of the LIDAR output signal.

[0088] The LIDAR adapter of FIG. 6 can comprise other optical components including passive optical components. For example, the LIDAR adapter can comprise any third lens (126). The third lens (126) can be configured to couple the second LIDAR output signal to a desired location. In some examples, the third lens (126) focuses or collimates the second LIDAR output signal to a desired location. For example, the third lens (126) can be configured to focus or collimate the second LIDAR output signal onto the facet (78) of the second input waveguide (76). The LIDAR adapter can also include one or more direction conversion components (124) such as mirrors and prisms. FIG. 6 shows a LIDAR adapter including a mirror as a direction conversion component (124) that re-directs a second portion of the LIDAR return signal from the circulator (100) to the facet (78) of the second input waveguide (76) and / or the third lens (126).

[0089] FIG. 7 shows the LIDAR system of FIG. 6 modified to be suitable for use with the LIDAR chip of FIG. 2 or FIG. 3. The LIDAR output signal is not amplified on the LIDAR adapter of FIG. 7. FIG. 7 shows a LIDAR adapter used with the LIDAR chip of FIG. 3. Accordingly, an amplifier (85) operated by an electronic device is disposed on the LIDAR chip rather than on the LIDAR adapter. In this situation, the active components of the LIDAR system that are operated by and / or provide an electrical output to the electronic device are disposed on the LIDAR chip. On the other hand, the passive components are disposed on the LIDAR adapter. Accordingly, an example of a LIDAR system has a LIDAR adapter that includes passive components on a base and excludes integrated components on the base. On the other hand, the LIDAR chip includes a combination of discrete and integrated components or includes only integrated optical components.

[0090] A LIDAR chip, an electronic device, and a LIDAR adapter can be arranged on a common mount. Suitable common mounts include, but are not limited to, glass plates, metal plates, silicon plates, and ceramic plates. As an example, FIG. 8 is a top view of a LIDAR system including the LIDAR chip of FIG. 1, an electronic device (62), and the LIDAR adapter of FIG. 5 on a common support (140). The electronic device (62) is shown arranged on the common support, but all or part of the electronic device can be arranged away from the common support. Suitable methods for attaching the LIDAR chip, the electronic device, and / or the LIDAR adapter to the common support include, but are not limited to, epoxy, solder, and mechanical clamps.

[0091] The LIDAR system is shown operating with one LIDAR chip that outputs a single LIDAR output signal, but the LIDAR chip can be configured to output multiple LIDAR output signals. Multiple LIDAR adapters can be used with one LIDAR chip and / or one LIDAR adapter can be adjusted to receive multiple LIDAR output signals.

[0092] Figures 9A-9H show an example of a suitable light source for use with a LIDAR system. Figure 9A is a top view of the light source. Figure 9A includes dashed lines each showing a part or a portion of a part located under other parts shown by solid lines. The relationships between the parts shown in Figure 9A are also apparent in Figures 9B-9H. Figure 9B is a cross-sectional view of the light source shown in Figure 9A taken along the line labeled B in Figure 9A through a utility waveguide (16). The utility waveguide (16) shown in Figure 9B is a ridge waveguide that can be constructed as disclosed in connection with Figure 4. Figure 9C is a cross-sectional view of the light source taken along the line extending between the parentheses labeled C in Figure 9A. Figure 9C is a cross-sectional view of the light source taken along the line extending between the parentheses labeled C in Figure 9A. Figure 9C is a cross-sectional view of the light source taken along the line extending between the parentheses labeled C in Figure 9A. Figure 9D is a cross-sectional view of the light source taken along the line extending between the parentheses labeled D in Figure 9A. Figure 9E is a cross-sectional view of the light source of Figure 9A taken along the line extending between the parentheses labeled E in Figure 9A. Figure 9F is a top view of a portion of the light source shown in Figure 9A. The top surface of Figure 9F shows a close-up of a portion of the utility waveguide (16) shown in Figure 9A. The portion of the utility waveguide (16) shown in Figure 9F includes an optical grating that operates as a partial return device. Figure 9G is a perspective view of a portion of the utility waveguide and the optical grating shown in Figure 9F. Figure 9H is an example of a cross-section of the utility waveguide (16) and the optical grating taken along the line labeled H in Figure 9G. The light source is illustrated as being on a silicon-on-insulator platform, although other platforms are possible.

[0093] The first recess (271) extends within or through the light-transmissive medium (94). In some examples where the first recess (271) extends through the light-transmissive medium (94), the first recess (271) can extend within or through the embedded layer (90). The second recess (272) extends to the bottom of the first recess (271) such that the substrate (92) includes a pillar (273) that extends upward from the bottom of the second recess (272). The electrical contact (274) is disposed at the bottom of the second recess (272). The first conductor (275) on the light-transmissive medium (94) is in electrical communication with the electrical contact (274). The second conductor (276) on the light-transmissive medium (94) is disposed adjacent to the first recess (271). The first conductor (275) and the second conductor (276) are each in electrical communication with a contact pad (277) on the light-transmissive medium (94). The contact pad (277) can be used to provide electrical communication between the electronic device and the light source (10).

[0094] The gain element (278) is disposed in the first recess (271) and on the pillar (273). The gain element (278) includes a gain medium (279). The gain waveguide (283) is defined within the gain medium (279). The gain element can be attached to the LIDAR chip using flip-chip technology. Examples of suitable interfaces between the gain element constructed from a silicon-on-insulator wafer and the chip can be found in U.S. Patent No. 9,705,278, issued July 11, 2017, and U.S. Patent No. 5,991,484, issued November 23, 1999.

[0095] The second conductive layer (280) is disposed on the gain medium (279). The third conductor (281) provides electrical communication between the second conductive layer (280) and the second conductor (276).

[0096] The gain element (278) includes three ridges that extend into the second recess (272). The central ridge defines part of the gain waveguide (283). The outer ridges are in electrical communication with one of the electrical contacts (274) via a conductive medium (293) such as solder or conductive epoxy. Since the first conductor (275) is in electrical communication with the electrical contact (274), the first conductor (275) is in electrical communication with the outer ridges.

[0097] The gain element (278) includes a reflective structure (285) on the gain medium. In one example, the reflective structure (285) is a highly reflective structure such as a mirror. Suitable reflective structures (285) include, but are not limited to, a metal layer on a layer of the gain medium (279) or one or more dielectric layers configured as a high reflectivity (HR) coating.

[0098] Gain medium (279) includes a sublayer (290) between a lower gain medium (292) and an upper gain medium (294). The lower gain medium (292) and the upper gain medium (294) may be the same or different. Suitable lower gain media (292) include, but are not limited to, InP, doped InP, gallium nitride (GaN), InGaAsP, and GaAs. Suitable upper gain media (294) include, but are not limited to, InP, InGaAsP, and GaAs. Different sublayers (290) can have different compositions. For example, each sublayer (290) can have different dopants and / or dopant concentrations from one or more adjacent sublayers (290), and / or each sublayer (290) can have different dopants and / or dopant concentrations. As an example, each sublayer (290) can include two or more components selected from the group consisting of In, P, Ga, and As, and different sublayers (290) can have elements present in different ratios. In another example, each sublayer (290) includes or consists of In and P, or does not include them, and includes or consists of one or two components selected from the group consisting of Al, Ga, and As, and each of the different sublayers (290) has these components in different ratios. Examples of materials containing multiple elements selected from the above group include different compositions of InP with or without dopants such as In(x)P(l-x) or In-Ga-As-P. Also, there may be other sublayers (290) present to correct for stress due to lattice mismatch between the compositions of different sublayers (290). The position of the laser mode in the laser ridge is defined by different sublayers (290) as a result of the refractive indices of different compositions.

[0099] Electrical communication between the second conductive layer (280) provided by the third conductor (281) and the second conductor (276) can be achieved using traditional techniques such as wire bonding.

[0100] The gain waveguide (283) is aligned with the input facet (287) of the utility waveguide (16) such that the utility waveguide (16) and the gain waveguide (283) can exchange optical signals. Although not shown, the input facet (287) can optionally include one or more anti-reflection coatings such as silicon nitride. The space between the input facet (287) and the facet of the gain waveguide (283) can be filled with a solid or fluid transparent medium. For example, the space between the facet of the gain waveguide (283) and the input facet (287) can be filled with epoxy, air, or gel. As a result, the optical signal can travel directly between the gain element and the input facet (287) through the transparent medium.

[0101] The input facet (287) for the utility waveguide (16) can be arranged at an angle of less than 90 degrees with respect to the propagation direction in the utility waveguide (16). By arranging the input facet (287) at an angle of less than 90 degrees, the optical signal reflected by the input facet (287) can be reflected from the waveguide, thereby reducing the problems associated with back reflection accordingly. Thus or alternatively, the facet of the gain waveguide (283) can be arranged at an angle of less than 90 degrees with respect to the propagation direction in the gain waveguide (283).

[0102] The utility waveguide (16) includes an optical grating (300) configured to operate as a partial return device. For example, the utility waveguide (16) can carry an optical signal to the optical grating (300). The optical grating (300) can be configured to transmit a first portion of the optical signal and return a second portion of the optical signal along the same optical path by which the optical grating (300) received the optical signal. In some examples, the return of the second portion of the optical signal is the result of reflection. Suitable optical gratings include, but are not limited to, Bragg gratings and sampled gratings.

[0103] During operation of the light source, the electronic device can generate an optical signal in the gain medium (279) by driving a current through the gain medium (279). The current can be generated by applying a potential difference between a first conductor (275) and a second conductor (276). The gain waveguide (283) conveys light from the gain medium (279) to the optical grating (300). The optical grating (300) returns a second portion of the laser signal to its original path. The optical grating (300) also transmits a first portion of the optical signal so that the optical signal continues along its path through the utility waveguide (16).

[0104] The second portion of the optical signal returns to the gain waveguide (283). The gain waveguide (283) guides the second portion of the optical signal through the gain medium (279) to the reflective structure (285). The reflective structure (285) reflects the second portion of the optical signal so that the second portion of the optical signal returns to the gain waveguide (283) and ultimately back to the optical grating (300). Thus, the second portion of the optical signal passes through the gain waveguide (279) twice and returns to the optical grating (300). The gain medium (279) in combination with multiple passes of the optical signal through the gain medium (279) is a source of optical gain. Energy can be applied to the gain medium (279) to provide optical gain. Thus, the optical grating (300) and the reflective structure (285) can form a resonant cavity in which the optical signal resonates. As a result, the first portion of the optical signal transmitted by the optical grating (300) can be a laser signal that functions as an output LIDAR signal. In some examples, the energy supplied to the optical signal to pump and / or provide gain to the optical signal is electrical energy provided by the electronic device, but other forms of energy can be used to pump the optical signal.

[0105] FIG. 9F is a top view of a portion of the utility waveguide (16) shown in FIG. 9A. FIG. 9F magnifies the portion of FIG. 9A that includes the optical grating (300). FIG. 9G is a perspective view of a portion of the utility waveguide (16) and the optical grating (300) shown in FIG. 9F. The utility waveguide (16) can directly carry an optical signal from the input facet (287) to the optical grating (300). For example, the utility waveguide (16) can eliminate active components, passive optical components, and waveguide branches between the input facet (287) and the optical grating (300).

[0106] The optical grating (300) includes a perturbation structure (302) disposed within the utility waveguide (16) such that the perturbation structure (302) interacts with an optical signal guided through the utility waveguide (16). Each perturbation structure (302) perturbs the effective refractive index of the utility waveguide (16). For example, each perturbation structure (302) can have an effective refractive index that is different from the effective refractive index of the utility waveguide (16) in the absence of the perturbation structure (302).

[0107] In FIGS. 9A - 9H, the ridge (96) of the light - transmissive medium extends away from the slab region (98) of the light - transmissive medium. The ridge (96) partially defines the utility waveguide (16). The recess (310) extends to the top of the ridge (96). The recess (310) is filled with a medium having a refractive index lower than that of the light - transmissive medium (98). The medium can be a solid such as silica or a gas such as air. Thus, the recess (310) provides a perturbation to the effective refractive index of the utility waveguide (16) and can each function as a perturbation structure (302). In some examples, the recess (310) is formed by a photolithography method that can be performed using a stepper combined with an etching technique such as wet etching.

[0108] The dimensions and shapes of the perturbation structures (302) may be the same or substantially the same. For example, the recess (310) has one or more surfaces with a first width labeled as W in FIG. 9G, and a second width labeled as W in FIG. 9G T and a second width labeled as W in FIG. 9GL one or more surfaces having a second width labeled as such, and d r can have a depth labeled as such. In some examples, the first width (W T ) represents the width of the perturbation structure (302) in a direction (lateral direction) perpendicular to the longitudinal axis of the utility waveguide (16) and can be regarded as the lateral width. Additionally or alternatively, the second width (W L ) represents the width of the perturbation structure (302) in a direction parallel to the longitudinal axis of the utility waveguide (16) and can be regarded as the longitudinal width. In some examples, all or some of the dimensions and shapes of the recesses (310) may be the same or substantially the same. For example, the recesses (310) can each have the same or approximately the same second width (W L ) and the same depth (d r ). Alternatively, the recesses (310) can have the same second width (W L ), the same first width (W T ) and the same depth (d r ).

[0109] The utility waveguide (16) has a longitudinal axis, and the portion of the utility waveguide (16) extending through the optical lattice functions as the lattice axis. The line labeled as L in FIG. 9F P can represent the projection of the longitudinal axis in a direction perpendicular to the substrate (labeled as 92 in FIGS. 9G and 9H) and / or the base onto the upper surface of the utility waveguide (16). The portion of the longitudinal axis projection between the parentheses labeled as Ga represents the projection of the lattice axis onto the upper surface of the utility waveguide (16). The optical lattice has perturbation structures (302) arranged in a plurality of different sub-lattices. For example, the perturbation structures (302) shown below the lattice axis projection in FIG. 9F are included in the first sub-lattice, and the perturbation structures (302) shown above the lattice axis projection in FIG. 9F are included in the second sub-lattice.

[0110] The perturbation structures (302) within the same sub-lattice have the same orientation with respect to the lattice axes, but the perturbation structures (302) in different sub-lattices have different orientations with respect to the lattice axes. For example, FIG. 9H is a cross-sectional view of the utility waveguide (16) taken through a recess (310) that functions as a perturbation structure (302) included in the second sub-lattice. As an example, the cross-section of FIG. 9H may be a cross-section taken along the line labeled H in FIG. 9F and / or FIG. 9G. The dashed line in FIG. 9G represents a recess (310) that functions as a perturbation structure (302) included in the first sub-lattice and is thereby disposed in the background of the cross-section.

[0111] Each perturbation structure (302) is associated with a direction line that depicts the shortest distance between the lattice axis and the perturbation structure (302). For example, in FIG. 9H, the line labeled V represents a direction line that extends the shortest distance between the lattice axis labeled L and the recess (310) that functions as a perturbation structure (302) included in the second sub-lattice. The direction and / or length of the direction line labeled V can be the same or substantially the same for each recess (310) that functions as a perturbation structure (302) included in the second sub-lattice. The line labeled V' extends the shortest distance between the lattice axis and the recess (310) that functions as a perturbation structure (302) included in the first sub-lattice. The direction and / or length of the direction line labeled V' can be the same or substantially the same for each recess (310) that functions as a perturbation structure (302) included in the first sub-lattice. However, the direction of the direction line labeled V' is different from the direction of the direction line labeled V. As a result, the perturbation structures (302) included in the second sub-lattice have a different orientation with respect to the lattice axis than the perturbation structures (302) included in the first sub-lattice.

[0112] In some examples, each perturbation structure (302) has one or more associated facilities that are common to each perturbation structure. In these cases, the perturbation structures (302) are each associated with a different common axis parallel to the lattice axis. For example, the perturbation structures (302) in each sub-lattice can be arranged such that the associated common axis extends through the same associated facility of each perturbation structure (302) included in the same sub-lattice. However, even when the common axis extends through the same associated facility within perturbation structures (302) from different sub-lattices, the common axes associated with different sub-lattices are spaced apart from each other.

[0113] As an example of a common axis, FIG. 9F shows two common axes each extending through the same associated facility of perturbation structures (302) in different sub-lattices. For example, each common axis extends through a corresponding surface of the perturbation structures (302) in different sub-lattices. This corresponding surface is the surface of the perturbation structure (302) closest to the upper side surface of the ridge (96) that defines the utility waveguide (16). For example, FIG. 9F shows a first common axis labeled CA1 that extends through the corresponding surface of each perturbation structure (302) included in the first sub-lattice. Also, a second common axis labeled CA2 extends through the same corresponding surface within each perturbation structure (302) included in the second sub-lattice. Although the first common axis and the second common axis intersect the perturbation structures (302) of the same associated facility included in different sub-lattices, the first common axis is spaced apart from the second common axis. For example, the first common axis and the second common axis each extend through the perturbation structure surface closest to the side of the ridge (96) labeled CR. Suitable associated facilities include, but are not limited to, the center of gravity of each perturbation structure (302), corresponding points on each perturbation structure (302), and corresponding surfaces on each perturbation structure (302). In some examples, neither common axis extends through a perturbation structure (302) that is a member of a sub-lattice other than the sub-lattice with which the common axis is associated, as is apparent in FIG. 9F.

[0114] The arrangement of the perturbation structure (302) can be described in relation to the Cartesian coordinate system shown in FIG. 9F. The coordinate system has a longitudinal direction having an axis parallel to the longitudinal axis (labeled LA) and a transverse direction having a transverse axis (labeled TA). The transverse direction crosses the longitudinal direction. In some examples, the transverse axis is parallel to a substrate and / or the surface of a substrate such as the substrate (92) shown in FIGS. 9E and 9G. The perturbation structures (302) in the same sub-lattice overlap each other in the transverse direction, but the perturbation structures (302) in different sub-lattices do not overlap each other in the transverse direction. Instead, they are spaced apart in the transverse direction.

[0115] In some examples, the perturbation structures (302) that are members of the same sub-lattice have the same dimensions and shape. For example, the recesses (310) in each sub-lattice can have the same or substantially the same longitudinal width (W L ) and the same depth (d r ). Alternatively, the recesses (310) in each sub-lattice can have the same or substantially the same longitudinal width (W L ), the same transverse width (W T ) and the same depth (d r ).

[0116] In some examples, the perturbation structures (302) that are members of the same sub-lattice have the same dimensions and shape, and the perturbation structures (302) that are different sub-lattices have the same dimensions and / or shape. For example, the perturbation structure (302) that is a member of the same sub-lattice and the perturbation structure (302) that is a member of a different sub-lattice have the same longitudinal width (W L ), the same transverse width (W T ) and the same depth (d r ). In some examples, the perturbation structures (302) that are members of the same sub-lattice have the same dimensions and shape, but the perturbation structures (302) that are different sub-lattices have different dimensions and / or shape. For example, the perturbation structure (302) that is a member of the same sub-lattice has the same longitudinal width (W L ), the same transverse width (W T ) and the same depth (d rcan have, but the perturbation structures (302), which are different sub-lattices, have the same vertical width (W L ) and the same depth (d r ) can have, but can have different horizontal widths (W T ).

[0117] The perturbation structures (302) within each sub-lattice can be periodically spaced in the vertical direction. The sub-lattice period is labeled as P in FIG. 9F i , where i is an integer and each value of i is associated with a different one of the sub-lattices. In some examples, all or some of the values of the sub-lattice period (P i ) are the same for each sub-lattice.

[0118] The perturbation structures (302) from different sub-lattices are vertically spaced. For example, in the vertical direction, the perturbation structures (302) from one sub-lattice can be interleaved with the perturbation structures (302) from other sub-lattices. As an example, in the vertical direction, each of one or more perturbation structures (302) adjacent to each perturbation structure (302) can be arranged such that it is a member of a sub-lattice other than the sub-lattice to which the perturbation structure (302) belongs. When the perturbation structures (302) from different sub-lattices are considered in combination, the perturbation structures (302) are periodically spaced in the vertical direction. For example, the periodic spacing between the perturbation structures (302) from different sub-lattices in the vertical direction (the complex lattice period) is labeled as P in FIG. 9F c . The pattern of the perturbation structures (302) within the complex lattice period (P c ) is repeated multiple times within the lattice length (Lth). Conventional optical lattices, such as conventional Bragg lattices that exclude multiple sub-lattices with a period (or pitch) having the same value as the complex lattice period (P c ), produce laser signals of the same or approximately the same wavelength as the disclosed optical lattice.

[0119] In some examples, the perturbation structures (302) have the sub-lattice period (P i ) the same for each sub-lattice and the complex lattice period (P c) is arranged to be equal to the sub-lattice period (P i ) / N, where N is an integer greater than or equal to 2. In some examples, N represents the number of sub-lattices within the optical lattice.

[0120] The perturbation structures (302) from different sub-lattices are also laterally spaced apart. For example, in the lateral direction, a perturbation structure (302) from one sub-lattice can be separated from a perturbation structure (302) from another sub-lattice by a gap labeled G in FIG. 9F. As a result, the perturbation structures (302) from different sub-lattices are laterally spaced such that there is no axis parallel to the lattice axis passing through the perturbation structures (302) from the different sub-lattices. As will be described in more detail below, as the value of G increases, the shortest distance between the perturbation structures (302) increases, and thus the level of resolution required to successfully etch the perturbation structures (302) is reduced.

[0121] Since the perturbation structures (302) from different sub-lattices are spaced apart in both the lateral and longitudinal directions, the shortest distance between a perturbation structure (302) and an adjacent perturbation structure (302) is indicated by a line that is diagonal with respect to the lattice axis. An example of a diagonal associated with a single perturbation structure (302) is labeled D1 and D2 in FIG. 9F. The diagonal is oblique with respect to both the longitudinal and lateral directions in that the diagonal is neither parallel nor perpendicular to the lattice axis.

[0122] In some examples, the perturbation structures (302) are arranged such that the diagonals extending between the perturbation structures (302) in different sub-lattices have the same length or approximately the same length. Each of the diagonals has a length that is longer than the length of the spacing (labeled S in FIG. 9F) between the perturbation structures (302) in the longitudinal direction. The length of the spacing is equal to the complex lattice period minus the width of the perturbation structure (302) in the longitudinal direction (P C -W L ). As a result, the diagonal mediators have a length that is longer than the length of the complex lattice period minus the width of the perturbation structure (302) in the longitudinal direction (P C -W L ).

[0123] As described above, in some examples, the perturbation structure (302) is formed by photolithography and etching. Etched devices such as the perturbation structure (302) can merge with each other as the distance between the etched devices becomes less than the resolution limit of the photolithography process. In the prior art optical grating, the shortest distance between the perturbation structures (302) is the grating period or pitch (P) minus the vertical width of the perturbation structure (302) (P - W L ). The composite grating period P c of the grating of the present disclosure and the width (W L ) of the perturbation structure (302) in the vertical direction are the same as the grating period or pitch (P) of the prior art grating and the width (W L ) of the perturbation structure (302) in the vertical direction. When they are the same, the optical grating of the present disclosure and the prior art optical grating output the same wavelength or approximately the same wavelength. However, since each diagonal has a length longer than the length of the interval between the perturbation structures (302) in the prior art optical grating, the shortest distance between the etching devices in the grating of the present disclosure is greater than the shortest distance between the etching devices in the prior art grating. By increasing the interval between the etched devices (perturbation structures (302)), a grating can be obtained within the resolution of the conventional photolithography process, thus enabling the use of affordable photolithography technology in the manufacture of optical gratings.

[0124] As is apparent from FIG. 9F, the separation distances (D1, D2) between the perturbation structures (302) can be increased by increasing the separation of the lateral perturbation structures (302) indicated by the gap labeled G in FIG. 9F and / or the spacing between the perturbation structures (302) in the longitudinal direction labeled S in FIG. 9F. However, the wavelength of the laser signal output from the optical lattice can be a function of the longitudinal spacing between the perturbation structures 302(S). As a result, the change (S) in the longitudinal spacing between the perturbation structures 302 can be limited by the desire to output a laser signal having a specific wavelength. Therefore, the separation of the perturbation structures (302) in the lateral direction (G) can be selected in order to be able to separate between the perturbation structures (302) at a desired level. In some examples, the perturbation structures (302) are arranged such that the shortest diagonal is 60, 70, or 80 nm or more and / or 90, 100, or 110 nm or less.

[0125] All or part of the above-described lattice equipment can be modified to provide a lattice that outputs a laser signal of a desired wavelength while maintaining a separation between the perturbation structures (302) sufficient to allow the use of the desired technology to form the perturbation structures (302). For example, the optical lattice can be constructed as a primary lattice that outputs a laser signal having a wavelength greater than 850 nm and less than or equal to 1270, 1310, or 1350 nm. The composite lattice period (P c ) for the primary lattice can be configured to have a composite lattice period (P c ) equal to or substantially equal to one-half of the desired wavelength. In some examples, the perturbation structures (302) are arranged to provide a composite lattice period (P c ) of 180, 182 nm or more and / or 192, or 194 nm or less.

[0126] In some examples, the optical lattice has a wavelength of 1000, 1300, or 1340 nm or more and 1350, 1400, or 1450 nm or less, and is constructed to output a laser signal having all, some, three, four, or five of the following equipment selected from the group: a sub-lattice period (P i ) of 360, 372, or 384 nm or more and 386, 400, or 414 nm or less; one or more sub-lattices having a composite lattice period (P c ) of 180, 186, or 192 nm or more and 193, 200, or 207 nm or less; a perturbation structure (302) separation in the lateral direction by a gap (G) of 50, 60, or 70 nm or more and 80, 90, or 100 nm or less; perturbation structures (302) arranged such that the diagonal distance between each pair of perturbation structures (302) including perturbation structures (302) from different sub-lattices adjacent to each other in the vertical direction is 110, 115, or 120 nm or more and 130, 135, or 140 nm or less; perturbation structures (302) having a vertical width (W L ) of 80, 90, or 100 or more and 110, 120, or 130 nm or less; a lattice length (Lth) of 100, 200, or 300 μm or more and 1000, 5000, or 10,000 μm or less, the pattern of perturbation structures (302) within the composite lattice period (P c ) is repeated 500, 1000, or 1500 or more and 5000, 25000, or 50000 or less times within the lattice length (Lth); a vertical interval between perturbation structures (302) of 80, 90, or 100 nm or more and 110, 120, or 130 nm or less.

[0127] In FIG. 9F, the perturbation structure (302) is shown spaced from the sides of the ridge (96) by lateral gaps labeled TS1 or TS2. The lateral gap labeled TS1 may be the same as or different from the lateral gap labeled TS2. In some examples, one or both of the lateral gaps (TS1 and TS2) are 100, 110, or 120 nm or more, and / or 200, 210, or 220 nm or less. The lateral gaps are optional, and the perturbation structure (302) can extend laterally to the ridge as shown in FIG. 10. In addition to or alternatively to the recess (310) extending to the top of the ridge, the recess (310) can extend laterally to the ridge and / or into the slab region (98) adjacent to the ridge (96).

[0128] FIGS. 9A-9H show an optical lattice having two sub-lattices, but the optical lattice can include more than two sub-lattices. For example, FIG. 11 is a top view of an optical lattice including three sub-lattices. The two sub-lattices are arranged at the same vertical position but include a perturbation structure (302) spaced laterally.

[0129] When the optical lattice includes more than two sub-lattices, the perturbation structures (302) from different sub-lattices do not have to be arranged at the same vertical position. For example, FIG. 12 is a top view of an optical lattice including three sub-lattices. None of the perturbation structures (302) are arranged at the same vertical position.

[0130] The lateral width (W T ) of the perturbation structure (302) is shown to be the same, but the lateral widths (W T ) of the perturbation structures (302) in different sub-lattices can be different. For example, the perturbation structures (302) in the outermost sub-lattices of FIGS. 11 and 12 can have a lateral width (W T ) that is narrower than the lateral width (W T ) of the perturbation structures (302) in the central sub-lattice.

Example 1

[0131] A prior art first-order Bragg grating without a sub-lattice can be constructed in a recess in a ridge waveguide that functions as a perturbation structure. The perturbation structure has a pitch of 185 nm, a longitudinal perturbation structure width (W L ), and a transverse perturbation structure width (W T ) that can be 110 nm and 2200 nm, respectively. The Bragg grating outputs a laser signal having a wavelength of about 1295 nm. The shortest distance between the perturbation structures was 75 nm.

[0132] The optical grating can be constructed according to FIGS. 9F-9H. The first and second sub-lattices can each have a sub-lattice period (P c ) of 370 nm arranged to provide a composite grating period (P i ) of 185 nm. The perturbation structure can have a longitudinal perturbation structure width (W L ) of 110 nm and a transverse perturbation structure width (W T ) of 1055 nm. The perturbation structure in the first sub-lattice can be separated from the perturbation structure in the second sub-lattice by a 90 nm gap in the transverse direction (G). Similar to the prior art Bragg grating, the optical grating outputs a laser signal having a wavelength of about 1295 nm, but the shortest distance between the perturbation structures was along a diagonal line having a length of about 117 nm.

[0133] The light source is disclosed as having recesses used as perturbation structures, but other perturbation structures are possible. Examples of other suitable perturbation structures include, but are not limited to, an over-layer that increases the thickness of the waveguide and an over-layer that changes the effective refractive index of the waveguide in ion species introduced via stress or by diffusion or implantation.

[0134] The light source is disclosed in the context of a LIDAR system, but the light source can be used for other applications such as sensing, imaging, and telecommunications. The light source is disclosed as an external cavity laser, but the optical grating can be included in other laser cavity configurations such as distributed feedback lasers, distributed Bragg reflector lasers, and discrete mode lasers.

[0135] Those skilled in the art will readily make other embodiments, combinations, and modifications of the present invention in view of the present teachings. Accordingly, the present invention should be limited only by the following claims, which encompass all such embodiments and modifications when viewed in connection with the above specification and the accompanying drawings.

Claims

1. A LIDAR system, comprising a resonant laser cavity including an optical grating and a ridge waveguide having a longitudinal axis, a part of the longitudinal axis extending through the optical grating functioning as a grating axis, the laser cavity being configured to produce a laser signal that exits the laser cavity through the optical grating, the optical grating including a plurality of perturbation structures that respectively perturb the effective refractive index of the waveguide, the perturbation structures each including a recess in a ridge of the ridge waveguide, furthermore, the perturbation structures being arranged alternately on the waveguide such that perturbation structures adjacent to each other in the longitudinal direction are laterally spaced apart, the longitudinal direction being parallel to the grating axis and the lateral direction being transverse to the longitudinal direction, the perturbation structures being arranged within sub-gratings, perturbation structures of different sub-gratings being arranged at intervals in the lateral and longitudinal directions, and each of the different sub-gratings having the same pitch, A LIDAR system.

2. The LIDAR system according to claim 1, wherein the perturbation structures are arranged in sub-gratings such that perturbation structures adjacent to each other in the longitudinal direction are members of different sub-gratings.

3. The LIDAR system according to claim 2, wherein perturbation structures from different sub-gratings are laterally spaced apart by a gap greater than 90 nm.

4. The LIDAR system according to claim 3, wherein the optical grating outputs a laser signal having a wavelength of less than 1450 nm.

5. The LIDAR system according to claim 4, wherein the optical grating is a primary grating.

6. In the LIDAR system according to claim 5, the perturbation structures within each sub-grating are periodically spaced apart in the longitudinal direction.

7. The perturbation structures from the different sub-lattices are combined to be periodically spaced in the longitudinal direction with a composite period (P c ) as claimed in claim 6, of the LIDAR system.

8. The periodic arrangement of the perturbation structures in each sub-grating is spaced apart by a sub-grating period, the perturbation structures being arranged such that the composite period is 1 / N times the sub-grating period, where N is the number of sub-gratings included in the optical grating, The LIDAR system according to claim 7.

9. The LIDAR system according to claim 2, wherein any of the perturbation structures has a lateral width measured in the lateral direction, and the lateral widths of the perturbation structures in the same sub-grating are the same.

10. The LIDAR system according to claim 1, wherein the perturbation structures are arranged in sub-gratings such that a line parallel to the grating axis does not extend through the perturbation structures in two or more sub-gratings.

11. The LIDAR system according to claim 10, wherein the perturbation structure is arranged such that a line parallel to the grating axis can extend through each perturbation structure within the same sub-grating.

12. The LIDAR system according to claim 1, wherein the perturbation structure is arranged such that a shortest straight line that can be drawn between perturbation structures adjacent to each other in the longitudinal direction is a diagonal line with respect to the grating axis.

13. The LIDAR system according to claim 12, wherein the length of the shortest straight line is less than 110 nm.

14. The LIDAR system according to claim 13, wherein the optical grating outputs a laser signal having a wavelength of less than 1450 nm.

15. The LIDAR system according to claim 1, wherein a light source included in the LIDAR system is included in an optical integrated circuit (PIC) on a LIDAR chip.

16. The LIDAR system according to claim 1, wherein a LIDAR chip included in the LIDAR system is constructed on a silicon-on-insulator platform.

17. The LIDAR system according to claim 1, wherein the perturbation structure is arranged such that a shortest distance between one of the perturbation structures and the perturbation structure laterally spaced apart from the one perturbation structure is less than 110 nm.

18. The LIDAR system according to claim 1, wherein the perturbation structure is arranged such that a shortest distance between each of the perturbation structures and the perturbation structure laterally spaced apart from the one perturbation structure is less than 110 nm.

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