Phase control in steering LIDAR output signals

Abstract

To provide an improved mechanism for steering a LIDAR output signal.SOLUTION: A chip has a plurality of steering waveguides arranged on a substrate. Each of the steering waveguides is configured to transmit an output signal. The steering waveguides each terminate at a facet. The facets are arranged so that the output signals are emitted from the chip through the facets and combined to form a LIDAR output signal. The chip further has a phase tuner arranged at least at part of the steering waveguide. An electronic circuit causes the phase tuner to operate to adjust the phase difference between the output signals on the adjacent steering waveguides. The electronic circuit adjusts the phase difference to adjust a direction in which the LIDAR output signal separates from the chip.SELECTED DRAWING: Figure 6

Description

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application, Ser. No. 62 / 680,787, filed Jun. 5, 2018, entitled "Optical Sensor Chip," and U.S. Provisional Patent Application, Ser. No. 62 / 683,958, filed Jun. 12, 2018, entitled "Optical Sensor Chip," which are incorporated herein in their entireties. [Technical field]

[0002] The present invention relates to optical devices, in particular to LIDAR chips. [Background technology]

[0003] There is a growing commercial demand for economically deployable 3D sensing systems for applications such as ADAS (Advanced Driver Assistance Systems) and AR (Augmented Reality). A LIDAR (Light Detection and Ranging) sensor is used to construct a 3D image of the field of view by illuminating different sample areas within the field of view with one or more LIDAR output signals that will be reflected by objects, and measuring the resulting LIDAR input signals that are returned to the LIDAR system.

[0004] LIDAR systems typically steer LIDAR output signals from different sample areas within a field of view. LIDAR data (distance between the LIDAR system and an object and / or radial velocity) is generated for the different sample areas illuminated by the LIDAR output signals. A variety of different mechanisms are used to steer the LIDAR output signal between the different sample areas. Some of these mechanisms rely on the ability to control the phase difference between different optical signals that are then combined to form the LIDAR output signal.

[0005] LIDAR systems can be built on LIDAR chips using platforms such as silicon-on-insulator platforms. However, the waveguides in the LIDAR chips can have undesirably high levels of optical loss and phase noise, and are limited in the amount of optical power they can transmit. These limited parameters cause degradation of the mechanisms that use phase differences to steer the LIDAR output signal. As a result, improved mechanisms for steering the LIDAR output signal are needed. Summary of the Invention

[0006] The LIDAR chip has one or more ridge waveguides having a ridge of optical transmission medium extending away from a slab region of the optical transmission medium. The ridge has a width greater than 1 μm and less than 4 μm and a height greater than 1 μm and less than 4 μm. The slab region has a thickness greater than 0.0 μm and less than 3 μm. In some examples, the chip is a silicon-on-insulator chip.

[0007] Another embodiment of a LIDAR chip includes a utility waveguide that directs the outgoing LIDAR signal to a facet through which the outgoing LIDAR signal exits the chip. The chip also includes a control branch that removes a portion of the outgoing LIDAR signal from the utility waveguide. The control branch includes a control optical sensor that receives an optical signal having light from the removed portion of the outgoing LIDAR signal. The chip also includes a data branch that removes a second portion of the outgoing LIDAR signal from the utility waveguide. The data branch includes an optical combiner that combines a reference optical signal having light from the second portion of the outgoing LIDAR signal into a comparison optical signal having light reflected from an object located away from the chip.

[0008] Another embodiment of the chip includes a utility waveguide terminating in a facet through which an outgoing LIDAR signal exits the chip. The utility waveguide is also configured to receive a LIDAR input optical signal through the facet. The LIDAR input optical signal comprises light from the outgoing LIDAR signal. The chip also includes a data branch having an optical sensor configured to receive an optical signal comprising light from the LIDAR input optical signal.

[0009] Another embodiment of the chip includes a utility waveguide terminating in a facet through which at least a portion of the outgoing LIDAR signal exits the LIDAR chip, the chip also including an optical attenuator configured to attenuate the intensity of the outgoing LIDAR signal on the utility waveguide.

[0010] Another embodiment of the chip includes a waveguide that receives a comparison optical signal that includes light from a LIDAR input optical signal that includes light reflected by an object located away from the chip, and the chip also includes an optical attenuator configured to attenuate the intensity of the comparison optical signal on the waveguide.

[0011] Another embodiment of the chip includes a plurality of steering waveguides disposed on a base, each of the steering waveguides configured to carry an output signal. The steering waveguides each terminate in a facet. The facets are arranged such that the output signals radiate from the chip through the facets and combine to form a LIDAR output signal. The chip also includes a phase tuner disposed on at least a portion of the steering waveguides. The phase tuner is configured to adjust the phase difference between the output signals of adjacent steering waveguides. The steering waveguides have a diameter or height of greater than or equal to 1 μm and less than or equal to 4 μm. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a plan view of the LIDAR chip.

[0013] [Diagram 2] FIG. 2 is a cross-sectional view of the LIDAR chip according to FIG. 1 constructed from a silicon-on-insulator wafer.

[0014] [Diagram 3] FIG. 2 illustrates the LIDAR chip of Figure 1 used with an off-chip scanning mechanism.

[0015] [Figure 4] FIG. 2 illustrates the LIDAR chip of FIG. 1 used with another embodiment of an off-chip scanning mechanism.

[0016] [Diagram 5] FIG. 2 is a cross-sectional view of the LIDAR chip of FIG. 1 with an integrated scanning mechanism.

[0017] [Figure 6] FIG. 13 shows a portion of a chip modified to use the phase difference between output signals to steer the LIDAR output signal.

[0018] [Figure 7] FIG. 7 is a side view of the chip of FIG. 6 looking away from the chip toward the facet.

[0019] [Figure 8] FIG. 2 is a plan view of a chip having multiple steering waveguides, each including a taper terminating in a facet.

[0020] [Figure 9A] FIG. 9 is a cross-sectional side view of a portion of the chip shown in FIG. 8. The cross-section is taken along line A shown in FIG.

[0021] [Figure 9B]FIG. 9 is a perspective view of a portion of the chip shown in FIG. 8.

[0022] [Figure 9C] FIG. 9 is a perspective view of a portion of the chip shown in FIG. 8.

[0023] [Figure 10] 1 shows a portion of a chip having a steering waveguide layout suitable for constructing steering waveguides of increasing length.

[0024] [Figure 11] 1 is a cross-sectional view of a waveguide such as a utility waveguide or steering waveguide.

[0025] [Figure 12] 1 is a graph of the change in effective refractive index of a waveguide as a function of waveguide height.

[0026] [Figure 13] 1 is a graph of transmission loss in a waveguide as a function of waveguide height.

[0027] [Figure 14] 1 is a graph of intensity versus angle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0028] The LIDAR chip has a number of steering waveguides, each of which receives a portion of a common optical signal from a common waveguide. Each of the steering waveguides transmits the received portion of the common optical signal as an output signal. Each of the steering waveguides terminates in a facet. The facets are positioned such that the output signals exit the steering waveguides through the facet and combine to form the LIDAR output signal. A phase tuner is positioned on at least a portion of the steering waveguides. An electronic circuit operates the phase tuner to adjust a phase difference between the output signals of adjacent steering waveguides. The electronic circuit adjusts the phase difference to steer the LIDAR output signal away from the chip.

[0029] The waveguide structures typically used in LIDAR chips built from SOI-based platforms often make these chips difficult or impossible to apply to LIDAR applications. Accurately shaping and steering the LIDAR output signal depends on maintaining a constant phase relationship between the various elements of the steering waveguide array. This phase relationship is difficult to maintain with current waveguide structures because manufacturing limitations cause large variations in the width of the waveguides. These variations in the width of the waveguides cause large variations in the effective refractive index of the different waveguides. These changes in the effective refractive index are the source of phase errors and phase noise. One symptom of these phase errors is the presence of side lobes in the LIDAR output signal generated using steering waveguides with small dimensions. As a result, some form of phase correction must be employed to ensure correct operation. The inventors have found that by increasing the dimensions of the waveguides to 1 μm or more while maintaining a single-mode configuration, these phase errors are reduced.

[0030] The change in effective index per unit width of the steering waveguide is a strong function of the waveguide dimensions for heights less than 1 μm, but this correlation drops off sharply to 0.0 or near 0.0 for diameters greater than 1 μm. Since the change in effective index affects the signal phase, increasing the diameter or width and height up to 1 μm reduces the amount of phase loss due to the change in the effective index of refraction. Furthermore, the transmission loss of the signal through the steering waveguide drops dramatically as the diameter or width and height increases beyond 1 μm. In view of these results, effective phase-based steering can be achieved by configuring the steering waveguide such that the ridge has a diameter or height and width that is greater than 1 μm and less than 4 μm. In some examples, the steering waveguide is configured such that the waveguide has a diameter or height and width that is greater than 1 μm and less than 4 μm, and extends away from a slab region that has a thickness greater than 0.0 μm and less than 3 μm. A steering waveguide having these dimensions exhibits a surprising reduction in the presence of side lobes in the LIDAR output signal, and thus, by using these dimensions, phase noise is reduced to a level that makes the use of steering waveguides possible and practical.

[0031] Furthermore, the common waveguide typically has the same dimensions as the steering waveguides due to manufacturing limitations. For example, at least the height of the steering waveguide is typically the same as the height of the steering waveguides because it is difficult to tape multiple steering waveguides in the vertical direction. The common waveguide carries light at a higher power level than each steering waveguide because the common optical signal has power from the output optical signals combined into a single signal. For example, the common waveguide carries the common optical signal at a power level P, while the steering waveguides typically carry a power level of about P / N, where n is the number of steering waveguides. However, the effects of self-phase modulation, cross-phase modulation, stimulated Raman scattering, and two-photon absorption in the waveguides each begin to affect the performance of the waveguide as the power carried by the waveguide increases above a certain power threshold. As the dimensions of the waveguide increase, the power threshold increases. Once the dimensions of the waveguide increase beyond 1 μm in diameter or width and height, the power threshold of the waveguide increases beyond 1 W. In many LIDAR applications, it is desirable to increase the power of the LIDAR output signal to levels of 1 W or more. For example, in LIDAR applications such as autonomous vehicles, the LIDAR output signal may have a power level of 1 W or more. These waveguide dimensions therefore allow the common waveguide to transmit signals having power levels of 1 W or more without substantial effects from self-phase modulation, cross-phase modulation, stimulated Raman scattering, and two-photon absorption.

[0032] FIG. 1 is a top view of a LIDAR chip with a laser cavity. The laser cavity includes a light source 10, which may include or constitute a gain medium for a laser (not shown). The chip also includes a resonator waveguide 12 that receives an optical signal from the light source 10. The light source may be placed in a recess 13, such that a facet of the light source is optically aligned with a facet of the resonator waveguide 12, allowing the light source and the resonator waveguide 12 to exchange optical signals. The resonator waveguide 12 conveys the optical signal to a partial reflector 14. The illustrated partial reflector 14 is an optical grating, such as a Bragg grating. However, other partial reflectors 14 may be used, such as mirrors coupled to Etchere gratings and arrayed waveguide gratings.

[0033] The partial reflector 14 returns the return portion of the optical signal to the resonator waveguide 12 as a return signal. For example, the resonator waveguide 12 returns the return signal to the light source 10 so that the return portion of the optical signal passes through the gain medium. The light source 10 is configured such that at least a portion of the return signal is added to the optical signal received at the resonator waveguide 12. For example, the light source 10 can have a highly, fully, or partially reflector 15 that reflects the return signal received from the gain medium back to the gain medium. As a result, light can resonate between the partial reflector 14 and the reflector 15 to form a distributed Bragg reflector (DBR) laser cavity. A DBR laser cavity has an inherently narrower linewidth and a longer coherence length than a DFB laser, thus improving performance when an object reflecting the LIDAR output signal from the chip is located far away from the chip.

[0034] The partial reflector 14 passes a portion of the optical signal received from the resonator waveguide 12 to a utility waveguide 16 included in the chip. The portion of the optical signal that the utility waveguide 16 receives from the partial reflector 14 serves as the output of the laser resonator. The output of the laser resonator serves as the outgoing LIDAR signal on the utility waveguide 16. The utility waveguide 16 terminates at a facet 18 and conveys the outgoing LIDAR signal to the facet 18. The facet 18 can be positioned such that the outgoing LIDAR signal traveling through the facet 18 exits the chip and serves as the LIDAR output signal. For example, the facet 18 can be positioned at the edge of the chip, such that the outgoing LIDAR signal traveling through the facet 18 exits the chip and serves as the LIDAR output signal.

[0035] The LIDAR output signal travels away from the chip and is reflected by an object in the path of the LIDAR signal. The reflected signal travels away from the object. At least a portion of the reflected signal returns to facet 18 of utility waveguide 16. Thus, a portion of the reflected signal can enter utility waveguide 16 through facet 18 and act as a LIDAR input signal guided by utility waveguide 16.

[0036] The utility waveguide 16 can have a tapered section before the facet 18. For example, the utility waveguide 16 can have a taper 20 that terminates at the facet 18. The taper 20 can relax the alignment tolerances required to efficiently couple the utility waveguide 16 to the LIDAR input light and the outgoing LIDAR signal. Thus, the taper 20 can increase the percentage of the LIDAR input signal that is successfully returned to the chip for processing. In some examples, the taper 20 is configured such that the facet 18 has an area that is 2, 5, or 10 times the cross-sectional area of ​​a straight portion of the utility waveguide 16. Although FIG. 1 illustrates the taper 20 as a horizontal taper, the taper 20 can be a horizontal and / or vertical taper. The horizontal and / or vertical tapers can be straight and / or curved. In some examples, the taper 20 is an adiabatic taper.

[0037] The chip includes a data branch 24 where optical signals are generated that are processed for LIDAR data. The data branch includes an optical coupler 26 that couples a portion of the optical signal from the utility waveguide 16 into the data branch. For example, the optical coupler 26 couples a portion of the outgoing LIDAR signal from the utility waveguide 16 into a reference waveguide 27 as a reference signal. The reference waveguide 27 transmits the reference signal to an optical coupling portion 28.

[0038] The optical coupler 26 also couples a portion of the LIDAR input signal from the utility waveguide 16 to a comparison waveguide 30 as a comparison signal. The comparison signal includes at least a portion of the light from the LIDAR input signal. The comparison signal can exclude light from the reference optical signal. The comparison waveguide 30 transmits the comparison signal to an optical combiner 28.

[0039] The illustrated optical coupler 26 is the result of placing the utility waveguide 16 sufficiently close to the reference waveguide 27 and comparison waveguide 30 to couple light from the utility waveguide 16 into the reference waveguide 27 and comparison waveguide 30. However, other signal branching components can be used to transfer portions of the optical signal from the utility waveguide 16 to the reference waveguide 27 and comparison waveguide 30. Examples of suitable signal branching components include, but are not limited to, y-couplers, multimode interference couplers (MMIs), and integrated optical circulators.

[0040] The optical combiner 28 combines the comparison signal and the reference signal into a combined signal. The reference signal comprises light from the starting LIDAR signal. For example, the reference signal can act as a sample of the starting LIDAR signal. The reference signal can exclude light from the LIDAR output signal and the LIDAR input signal. In contrast, the comparison signal light comprises light from the LIDAR input signal. For example, the comparison signal can act as a sample of the LIDAR input signal. Thus, the comparison signal is reflected by an object far from the tip, while the LIDAR output signal is not reflected. If the tip and the reflecting object are moving relative to each other, the comparison signal and the reference signal have different frequencies due to the Doppler effect. As a result, a beat occurs between the comparison signal and the reference signal.

[0041] The optical combiner 28 also splits the resulting composite sample signal onto a first detector waveguide 36 and a second detector waveguide 38. The first detector waveguide 36 transmits a first portion of the composite sample signal to a first photosensor 40 that converts the first portion of the composite sample signal into a first electrical signal. The second detector waveguide 38 transmits a second portion of the composite sample signal to a second photosensor 42 that converts the second portion of the composite sample signal into a second electrical signal. Examples of suitable photosensors include germanium photodiodes (PDs) and avalanche photodiodes (APDs).

[0042] 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 photocurrent cancel each other, improving detection sensitivity. A suitable method 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 avalanche photodiodes connected in series. Balanced optical detection is desirable for detecting small signal fluctuations.

[0043] One example of a suitable optical combiner 28 is a multimode interference (MMI) device, such as a 2x2 MMI device. Other suitable optical combiners 28 include, but are not limited to, adiabatic splitters and directional couplers. In some embodiments, the functionality of the illustrated optical combiner 28 is performed by two or more optical components or combinations of optical components.

[0044] A single photosensor can replace the first photosensor 40 and the second photosensor 42 and output the data signal. If a single photosensor replaces the first photosensor 40 and the second photosensor 42, the optical combiner 28 need not have an optical splitting function. As a result, the illustrated optical combiner 28 can be a 2×1 optical combiner rather than the 2×1 optical combiner shown. For example, the illustrated optical combiner can be a 2×1 MMI device. In these cases, the chip has a single detector waveguide that transmits a composite sample signal to the photosensor.

[0045] The data branch includes a data optical attenuator 44 disposed along the comparison waveguide 30, and the data optical attenuator 44 can be operated to attenuate the comparison signal on the comparison waveguide 30. The chip also includes an output optical attenuator 46 disposed along the utility waveguide 16, and the output optical attenuator 46 can be operated to attenuate the outgoing LIDAR signal on the utility waveguide 16. Suitable attenuators for the data optical attenuator 44 and / or the output optical attenuator 46 are configured to attenuate the intensity of the optical signal. Examples of suitable attenuators configured to attenuate the intensity of the optical signal include carrier injection based PIN diodes, electroabsorption modulators, and Mach-Zehnder (MZ) modulators.

[0046] The chip also includes a sampling directional coupler 50 that couples a portion of the comparison signal from the comparison waveguide 30 to a sampling waveguide 52. The combined portion of the comparison signal acts as a sampling signal. The sampling waveguide 52 transmits the sampling signal to a sampling optical sensor 54. Although FIG. 1 shows the sampling directional coupler 50 transmitting a portion of the comparison signal to the sampling waveguide 52, other signal branching components can be used to transmit a portion of the comparison signal from the comparison waveguide 30 to the sampling waveguide 52. Examples of suitable signal branching components include, but are not limited to, a y-coupler and an MMI.

[0047] The chip has a control branch 55 for controlling the operation of the laser cavity. The control branch has a directional coupler 56 that routes a portion of the outgoing LIDAR signal from the utility waveguide 16 to a control waveguide 57. The coupled portion of the outgoing LIDAR signal acts as a branch signal. Although FIG. 1 shows a directional coupler 56 that transfers a portion of the outgoing LIDAR signal to the control waveguide 57, other signal branching components can be used to route a portion of the outgoing LIDAR signal from the utility waveguide 16 to the control waveguide 57. Examples of suitable signal branching components include, but are not limited to, y-couplers and MMIs.

[0048] The control waveguide 57 transmits the branched signal to an interferometer 58 which splits the branched signal and then recombines the different portions of the branched signal with the phase difference between the portions of the branched signal. The interferometer 58 shown is a Mach-Zehnder interferometer, although other interferometers could be used.

[0049] The interferometer 58 outputs the control light signal to the interferometer waveguide 60. The interferometer waveguide 60 transmits the control light signal to the control light sensor 61, which converts the control light signal into an electrical signal as an electrical control signal. The interferometer signal has an intensity that is a function of the frequency of the outgoing LIDAR signal. For example, a Mach-Zehnder interferometer outputs a sinusoidal control light signal with a fringe pattern. A change in frequency of the output LIDAR signal causes a change in frequency of the control light signal. Thus, the frequency of the electrical control signal output from the control light sensor 61 is a function of the frequency of the outgoing LIDAR signal. Other detection mechanisms can be used in place of the control light sensor 61. For example, the control light sensor 61 can be replaced by a balanced photodetector arranged as the optical coupling unit 28, the first light sensor 40, and the second light sensor 42.

[0050] The electronic circuitry 62 can operate one or more components on the chip. For example, the electronic circuitry 62 can be in electrical communication with and can control the operation of the light source 10, the data light attenuator 44, the output light attenuator 46, the first light sensor 40, the second light sensor 42, the sampling light sensor 54, and the control light sensor 61. Although the electronic circuitry 62 is shown off-chip, all or a portion of the electronic circuitry can be included on-chip. For example, the chip can have electrical conductors connecting the first light sensor 40 with the second light sensor 42 in series.

[0051] During operation of the chip, the electronic circuitry 62 operates the light source 10 such that the laser resonator outputs an outgoing LIDAR signal. The electronic circuitry 62 then operates the chip through a series of cycles, with each cycle producing at least a range data point. During each cycle, the data signal is sampled multiple times. During each sample, the electronics adjust the frequency of the outgoing LIDAR signal. As described in more detail below, the electronics can use an output from the control branch to control the frequency of the outgoing LIDAR signal such that the frequency of the outgoing LIDAR signal as a function of time is known to the electronic circuitry. In some examples, a cycle has a first sample and a second sample. During the first sample, the electronic circuitry 62 can increase the frequency of the outgoing LIDAR signal, and during the second sample, the electronic circuitry 62 can decrease the frequency of the outgoing LIDAR signal. For example, the laser resonator can be configured to output an outgoing LIDAR signal (and, correspondingly, the LIDAR output signal) having a wavelength of 1550 nm. During the first sample, the electronic circuitry 62 can increase the frequency of the outgoing LIDAR signal (and, correspondingly, the LIDAR output signal) such that the wavelength decreases from 1550 nm to 1459.98 nm, and subsequently decrease the frequency of the outgoing LIDAR signal such that the wavelength increases from 1459.98 nm to 1550 nm.

[0052] During the first sample, when the frequency of the outgoing LIDAR signal is increased, the LIDAR output signal travels away from the chip and returns to the chip as the LIDAR input signal. A portion of the LIDAR input signal becomes the comparison signal. The frequency of the outgoing LIDAR signal continues to increase while the LIDAR output signal and the LIDAR input signal are moving between the chip and the reflecting object. As a portion of the outgoing LIDAR signal becomes the reference signal, the frequency of the reference signal continues to increase. As a result, the comparison signal enters the optical coupling at a lower frequency than the reference signal that is simultaneously entering the optical coupling. Furthermore, the farther the reflecting object is located from the chip, the more the frequency of the reference signal increases before the LIDAR input signal returns to the chip. Thus, the greater the difference between the frequency of the comparison signal and the frequency of the reference signal, the further away 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.

[0053] For the same reason, when decreasing the frequency of the outgoing LIDAR signal during the second sample, the comparison signal is incident on the optical coupler at a higher frequency 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 during the second sample is also a function of the distance between the tip and the reflecting object.

[0054] In some examples, the relative movement of the tip and the reflecting object also affects the frequency of the comparison signal, so the difference between the frequency of the comparison signal and the frequency of the reference signal can be a function of the Doppler effect. For example, when the tip is moving towards or away from the reflecting object and / or the reflecting object is moving towards or away from the tip, the Doppler effect can affect the frequency of the comparison signal. Since the frequency of the comparison signal is a function of the speed at which the reflecting object is moving towards or away from the tip and / or the speed at which the tip is moving towards or away from the reflecting object, the difference between the frequency of the comparison signal and the frequency of the reference signal is also a function of the speed at which the reflecting object is moving towards or away from the tip and / or the speed at which the tip is moving towards or away from the reflecting object. Thus, the difference between the frequency of the comparison signal and the frequency of the reference signal is a function of the distance between the tip and the reflecting object and is also a function of the Doppler effect.

[0055] The composite sample signal and the data signal are effectively compared to the comparison signal and the reference signal, respectively. For example, an optical combiner combines the comparison signal and the reference signal, and these signals have different frequencies, so that a beat occurs between the comparison signal and the reference signal. Thus, 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, and the beat frequency can be used to determine the difference in frequency of the comparison signal and the reference signal. A higher beat frequency for the composite sample signal and / or the data signal indicates a higher difference between the frequencies of the comparison signal and the reference signal. As a result, the beat frequency of the data signal is a function of the distance between the tip and the reflecting object, and is also a function of the Doppler effect.

[0056] As mentioned above, the beat frequency is a function of two unknowns, the distance between the tip and the reflecting object, and the relative velocity of the tip and the reflecting object (i.e., the contribution of the Doppler effect). The change in frequency difference (Δf) between the comparison signal and the reference signal is given by Δf=2Δvf / c, where f is the frequency of the LIDAR output signal, and thus the reference signal, Δv is the relative velocity of the tip and the reflecting object, and c is the speed of light in air. By using a large number of different samples, the electronic circuit 62 can resolve the two unknowns. For example, the beat frequency determined for the first sample is related to the unknown distance and the Doppler contribution, and the beat frequency determined for the second sample is also related to the unknown distance and the Doppler contribution. By utilizing the two relationships, the electronic circuit 62 can resolve the two unknowns. Thus, the distance between the tip and the reflecting object can be determined without being affected by the Doppler effect. Additionally, in some examples, electronic circuitry 62 uses this distance in combination with the Doppler effect to determine the velocity of a reflecting object toward or away from the tip.

[0057] When the relative velocities of the target and source are 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 contribute substantially to the beat frequency, and the electronic circuitry 62 can take only the first sample to determine the distance between the tip and the reflecting object.

[0058] In operation, the electronic circuit 62 can adjust the frequency of the outgoing LIDAR signal in response to the electrical control signal output from the control light sensor 61. The magnitude of the electrical control signal output from the control light sensor 61 is a function of the frequency of the outgoing LIDAR signal. Thus, the electronic circuit 62 can adjust the frequency of the outgoing LIDAR signal depending on the magnitude of the control. For example, while varying the frequency of the outgoing LIDAR signal during one sample, the electronic circuit 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 sample, the electronic circuit 62 can compare the magnitude of the electrical control signal to a range of values ​​associated with the current time during the sample. If the magnitude of the electrical control signal indicates that the frequency of the outgoing LIDAR signal is outside the associated range of the magnitude of the electrical control signal, the electronic circuit 62 can operate the light source 10 to change the frequency of the outgoing LIDAR signal so that it is incident within the associated range. If the magnitude of the electrical control signal indicates that the frequency of the outgoing LIDAR signal is within the associated range of the magnitude of the electrical control signal, the electronic circuit 62 does not change the frequency of the outgoing LIDAR signal.

[0059] In operation, the electronic circuitry 62 can adjust the level of attenuation provided by the output optical attenuator 46 in response to the sampled signal from the sampling optical sensor 54. For example, the electronic circuitry 62 can operate the output optical attenuator 46 to increase the amount of attenuation in response to the magnitude of the sampled signal exceeding a first signal threshold, and / or to decrease the amount of output reduction in response to the magnitude of the sampled signal being below a second signal threshold.

[0060] In some examples, the electronic circuit 62 adjusts the level of attenuation provided by the output optical attenuator 46 to prevent or reduce the effect of back reflections on the performance of the laser cavity. For example, the first signal threshold and / or the second signal threshold can be selected arbitrarily to prevent or reduce the effect of back reflections on the performance of the laser cavity. Back reflection occurs when a portion of the LIDAR input signal returns to the laser cavity as a return LIDAR signal. In some examples, as much as 50% of the LIDAR input signal passing through the facet 18 returns to the laser cavity. If the power of the return LIDAR signal entering the partial reflector 14 does not decrease ("power drop") below the power of the outgoing LIDAR signal exiting the partial reflector 14 by more than a minimum power drop threshold, the return LIDAR signal can affect the performance of the laser cavity. In the illustrated chip, the minimum power drop threshold can be about 35 dB (0.03%). Therefore, the returning LIDAR signal can affect the performance of the laser cavity if the power of the returning LIDAR signal entering the partial reflector 14 is less than 35 dB lower than the power of the outgoing LIDAR signal exiting the partial reflector 14.

[0061] The electronic circuitry 62 can operate the output optical attenuator 46 to reduce the effect of low power droop, for example, when the target object is very close and / or highly reflective. As is evident from FIG. 1, operating the output optical attenuator 46 to increase the level of attenuation reduces the power of the return LIDAR signal incident on the partial reflector 14 and reduces the power of the return outgoing LIDAR signal at locations away from the partial reflector 14. Because the output optical attenuator 46 is located away from the partial reflector 14, the power of the outgoing LIDAR signal leaving the partial reflector 14 is not directly affected by the operation of the output optical attenuator 46. Thus, operating the output optical attenuator 46 to increase the level of attenuation increases the level of power droop. As a result, the electronics can use the optical attenuator 46 to adjust the power droop.

[0062] Furthermore, the magnitude of the sampling signal is related to the output drop. For example, the magnitude of the sampling signal is related to the output of the comparison signal, as is evident from FIG. 1. Since the comparison signal is part of the LIDAR input signal, the magnitude of the sampling signal is related to the output of the LIDAR input signal. This result means that since the return LIDAR signal is part of the LIDAR input signal, the magnitude of the sampling signal is also related to the output of the return LIDAR signal. Thus, the magnitude of the sampling signal is related to the output drop.

[0063] Because the magnitude of the sampled signal is related to the power drop, the electronic circuitry 62 can use the magnitude of the sampled signal to operate the output optical attenuator to maintain the magnitude of the comparison signal output within a target range. For example, the electronic circuitry 62 can operate the output optical attenuator 46 to increase the magnitude of the power drop in response to the sampled signal indicating the magnitude of the power drop is less than or equal to a first threshold, and / or the electronic circuitry 62 can operate the output optical attenuator 46 to decrease the magnitude of the power drop in response to the sampled signal indicating the magnitude of the power drop is greater than or equal to a second threshold. In some examples, the first threshold is greater than or equal to a minimum power drop threshold. In one example, the electronic circuitry 62 operates the output optical attenuator 46 to increase the magnitude of the power drop in response to the magnitude of the sampled signal exceeding the first signal threshold, and / or to decrease the magnitude of the power drop in response to the magnitude of the sampled signal less than the second signal threshold. The identity of one, two, three, or four variables selected from the group consisting of the first threshold, the second threshold, the first signal threshold, and the second signal threshold can be determined from a calibration of the optical chip during setup of the LIDAR chip system.

[0064] When the power of the composite optical signal exceeds the power threshold, the optical sensor may become saturated. When the optical sensor becomes saturated, the magnitude of the data signal reaches a maximum value beyond the power threshold where it does not increase with increases in the power of the composite optical signal. Thus, when the power of the composite optical signal exceeds the power threshold, data may be lost. In operation, electronic circuitry 62 adjusts the level of attenuation provided by data optical attenuator 44 so that the power of the composite optical signal is maintained below the power threshold.

[0065] As is evident from FIG. 1, the magnitude of the sampling signal is related to the output of the comparison signal. Thus, the electronic circuit 62 can operate the data light attenuator 44 in response to the output from the sampling signal. For example, the electronic circuit 62 can operate the data light attenuator to increase the attenuation of the comparison signal when the magnitude of the sampling signal indicates the output of the comparison signal, and / or can operate the data light attenuator to decrease the attenuation of the comparison signal when the magnitude of the sampling signal indicates the output of the comparison signal. For example, in some examples, the electronic circuit 62 can increase the attenuation of the comparison signal when the magnitude of the sampling signal is equal to or greater than an upper comparison threshold, and / or can decrease the attenuation of the comparison signal when the magnitude of the sampling signal is equal to or less than an upper comparison signal threshold.

[0066] As discussed above, the electronic circuitry 62 can adjust the level of attenuation provided by the output optical attenuator 46 in response to the sampling signal. Additionally, or instead of adjusting the level of attenuation provided by the output optical attenuator 46 in response to the sampling signal, the electronic circuitry 62 can adjust the level of attenuation provided by the data optical attenuator 44 in response to the sampling signal.

[0067] Suitable platforms for the chip include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers. FIG. 2 is a cross-sectional view of a portion of a chip constructed from a silicon-on-insulator wafer. A silicon-on-insulator (SOI) wafer has a buried layer 80 between a substrate 82 and an optical transmission medium 84. In a silicon-on-insulator wafer, the buried layer is silica, while the substrate and the optical transmission medium are silicon. The substrate of the optical platform, such as a SOI wafer, can serve as the foundation for the entire chip. For example, the optical components shown in FIG. 1 can be located on or on the top and / or sides of the substrate.

[0068] The portion of the chip shown in Figure 2 has a waveguide structure suitable for use with chips constructed from silicon-on-insulator wafers. A ridge 86 of optical transmission medium extends away from a slab region 88 of optical transmission medium. The optical signal is confined between the apex of the ridge and the buried oxide layer.

[0069] The dimensions of the ridge waveguide are labeled in FIG. 2. 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 applications because of the need to use higher levels of optical power 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 apply to straight or substantially straight portions of the waveguide, curved portions of the waveguide, and tapered portions of the waveguide. These portions of the waveguide are therefore single mode. However, in some cases, these dimensions apply to straight or substantially straight portions of the waveguide, while the curved and / or tapered portions of the waveguide have dimensions outside these ranges. For example, the tapered portion of the utility waveguide 16 shown in FIG. 1 may have a width and / or height greater than 4 μm and between 4 μm and 12 μm. Additionally or alternatively, the curved portion of the waveguide may have a thinned slab thickness to reduce optical loss in the curved portion of the waveguide. For example, the curved portion of the waveguide may have a ridge extending away from the slab region with a thickness of 0.0 μm or more and less than 0.5 μm. While the above dimensions generally provide straight or substantially straight portions of the waveguide with a single mode structure, they may result in tapered and / or curved portions that are multimode. Coupling between multimode and single mode geometries may be achieved using tapers that do not substantially excite higher order modes. Thus, the waveguide may be configured such that signals transmitted in the waveguide are transmitted in a single mode even when transmitted in a waveguide section having multimode dimensions.The waveguide structure of FIG. 2 is suitable for all or a portion of the waveguides selected from the group consisting of the resonator waveguide 12, the utility waveguide 16, the reference waveguide 27, the comparison waveguide 30, the first detector waveguide 36, the second detector waveguide 38, the sampling waveguide 52, the control waveguide 57, and the interferometer waveguide 60.

[0070] The light source 10, interfaced with the utility waveguide 16, can be a gain element that is separate from the chip and then attached to the chip, for example, the light source 10 can be a gain element that is attached to the chip using a flip-chip arrangement.

[0071] The use of a flip-chip arrangement is suitable where the light source 10 would be interfaced with a ridge waveguide on a chip constructed from a silicon-on-insulator wafer. Examples of suitable interfaces between flip-chip gain elements and ridge waveguides on a chip constructed from a silicon-on-insulator wafer 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, each of which is incorporated herein in its entirety. This configuration is suitable for use as the light source 10. If the light source 10 is a gain element, the electronic circuitry 62 can change the frequency of the outgoing LIDAR signal by varying the level of current applied through the gain element.

[0072] The attenuator may be a component separate from the chip and then attached to the chip. For example, the attenuator may be included in an attenuator chip that is attached to the chip in a flip-chip arrangement. The use of an attenuator chip is suitable for all or part of an attenuator selected from the group consisting of a data attenuator and a control attenuator.

[0073] Instead of including the attenuator on a separate component, all or a portion of the attenuator can be integrated on the chip. For example, an example of an attenuator interfaced with a ridge waveguide on a chip constructed from a silicon-on-insulator wafer can be found in U.S. Patent No. 5,908,305, issued June 1, 1999, each of which is incorporated herein in its entirety. The use of an attenuator integrated on the chip is suitable for all or a portion of the optical sensor selected from the group consisting of a data attenuator and a control attenuator.

[0074] The light sensor that interfaces with the waveguide on the chip can be a component separate from the chip and then attached to the chip. For example, the light sensor can be a photodiode or avalanche photodiode. Examples of suitable light sensor elements include, but are not limited to, InGaAs PIN photodiodes manufactured by Hamamatsu, Hamamatsu, Japan, or InGaAs APDs (Avalanche Photodiodes) manufactured by Hamamatsu, Hamamatsu, Japan. These light sensors can be centrally located on the chip as shown in FIG. 1. Alternatively, all or a portion of the waveguide that terminates in the light sensor can terminate on a facet 18 located at the end of the chip, and the light sensor can be attached to the end of the chip on the facet 18, such that the light sensor receives light passing through the facet 18. The use of a light sensor that is a component separate from the chip is suitable for all or a portion of the light sensors selected from the group consisting of the first light sensor 40, the second light sensor 42, the sampling light sensor 54, and the control light sensor 61.

[0075] Instead of the optical sensor being a separate component, all or part of the optical sensor can be integrated on the chip. For example, examples of optical sensors interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in Optics Express Vol. 15, No. 21, pp. 13965-13971 (2007), U.S. Patent No. 8,093,080 issued Jan. 10, 20012, U.S. Patent No. 8,242,432 issued Aug. 14, 2012, and U.S. Patent No. 6,108,8472 issued Aug. 22, 2000, which are incorporated herein in their entirety. The use of an optical sensor integrated on 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.

[0076] Optical grating structures integrated with a variety of optical device platforms are available. For example, Bragg gratings can be formed in a ridge waveguide by forming grooves at the apex and / or behind the ridge.

[0077] In some embodiments, it may be desirable to scan the LIDAR output signal. The above chip structures are suitable for use with various scanning mechanisms used in LIDAR applications. For example, the outgoing LIDAR signal may be received by one or more reflectors and / or one more collimated device. The one or more reflectors may be configured to redirect and / or steer the LIDAR output signal to provide scanning of the LIDAR output signal. Suitable reflectors include, but are not limited to, mirrors, including mechanically driven mirrors and microelectromechanical system (MEMS) mirrors. One or more collimating devices may provide collimation of the LIDA output signal and thus increase the portion of the LIDA input signal that is received at the utility waveguide 16. Suitable collimating devices include, but are not limited to, simple lenses and compound lenses.

[0078] FIG. 3 shows the above chip used with a reflecting device 90 and a collimating device 92. For example, a lens serves as a collimating device to receive the LIDA output signal and provide collimation of the LIDA output signal. A mirror serves as a reflecting device 90 to receive the collimated LIDA output signal and reflect the collimated LIDA output signal in a desired direction. As shown by the arrow labeled A, electronic circuitry can move the mirror to steer the collimated LIDA output signal and / or scan the collimated LIDA output signal. The movement of the mirror can be in two or three dimensions. Suitable mirrors include, but are not limited to, mechanically actuated mirrors and microelectromechanical system (MEMS) mirrors.

[0079] FIG. 4 shows the above chip used with a reflecting device 90 and a collimating device 92. For example, a mirror serves as a reflecting device 90 that receives the LIDA output signal and reflects the LIDA output signal in a desired direction. As shown by the arrow labeled A, electronic circuitry can move the mirror to steer and / or scan the LIDA output signal. A lens serves as a collimating device 92 that receives the LIDA output signal from the mirror and provides collimation of the LIDA output signal. The lens can be configured to move with the movement of the mirror such that the lens continues to receive the LIDA output signal at different positions of the mirror. Alternatively, the movement of the mirror can be sufficiently limited such that the lens continues to receive the LIDA output signal at different positions of the mirror. The movement of the mirror can be in two or three dimensions. Suitable mirrors include, but are not limited to, mechanically driven mirrors and microelectromechanical system (MEMS) mirrors.

[0080] Technologies such as SOI MEMS (silicon-on-insulator Micro Electro Mechanical System) technology can be used to incorporate reflective devices such as MEMS mirrors into the chip. For example, FIG. 5 is a cross-sectional view of a portion of the chip taken through the longitudinal axis of the utility waveguide 16. The illustrated chip is formed on a silicon-on-insulator waveguide. A mirror recess extends through the optical transmission medium to the substrate. The mirror is disposed within the mirror recess to receive the LIDAR output signal from the utility waveguide. A lens receives the LIDAR output signal from the mirror and serves as a collimating device 92 to provide collimation of the LIDAR output signal. The lens can be configured to move with the movement of the mirror such that the lens continues to receive the LIDAR output signal at different positions of the mirror. Alternatively, the movement of the mirror can be sufficiently limited such that the lens continues to receive the LIDAR output signal at different positions of the mirror. Electronic circuitry can control the movement of the mirror in one or two dimensions.

[0081] The chip may have alternative ways of scanning and / or steering the LIDAR output signal in addition to or as an alternative to a reflector. For example, the chip may have components to spit out an incoming LIDAR signal into multiple output signals. The chip may then adjust the phase difference between the different output signals to control the direction in which the LIDAR output signal travels away from the chip. By varying the level of the phase difference between the output signals, the LIDAR output signal can be steered or scanned.

[0082] FIG. 6 illustrates a portion of the chip configured to use a phase difference between output signals to steer the LIDAR output signal. Portions of the chip not illustrated in FIG. 6 can be configured as described above. For example, the utility waveguide 16 illustrated in FIG. 6 can be the utility waveguide 16 of a chip configured as illustrated in FIG. 1. As is evident from FIG. 6, the utility waveguide 16 can function as the common waveguide described above. Thus, the outgoing LIDAR signal can act as the common optical signal described above.

[0083] The utility waveguide 16 carries the outgoing LIDAR signal to a splitter 100 that splits the outgoing LIDAR signal into multiple output signals that are each carried on a steering waveguide 102. Each steering waveguide 102 terminates in a facet 18. The facets 18 are positioned such that the output signals exiting the chip through the facets 18 combine to form a LIDAR output signal.

[0084] The splitter 100 and steering waveguides 102 can be configured such that there is no phase difference between the output signals at the facets 18 of adjacent steering waveguides 102. For example, the splitter 100 can be configured such that each output signal is in phase upon exiting the splitter 100, and each steering waveguide 102 can have the same length. Alternatively, the splitter 100 and steering waveguides 102 can be configured such that there is a small, linearly increasing phase difference between the output signals at the facets 18 of adjacent steering waveguides 102. For example, the steering waveguides 102 can be configured such that the phase of steering waveguide numbered j is f0+(j-1)f, where j is an integer from 1 to N and represents the number associated with the steering waveguide when the steering waveguides are numbered consecutively as shown in FIG. 6. f is the phase difference between adjacent steering waveguides when a phase tuner (described below) does not affect the phase difference, and f0 is the phase of the output signal at facet 18 of steering waveguide j=1. In some examples, this phase difference is achieved by configuring the steering waveguides such that they have a linearly increasing length difference. For example, the length of steering waveguide j can be expressed as l0+(j-1)Δl, where j is an integer from 1 to N and represents the number associated with the steering waveguide when the steering waveguides are numbered consecutively as shown in FIG. 6. Δl is the length difference between adjacent steering waveguides, and l0 is the length of steering waveguide j=1. When the steering waveguides are the same length, the value of Δl is zero and the value of f is zero. Suitable Δl include, but are not limited to, Δl greater than 0 μm or 5 μm and / or less than 10 μm or 15 μm. Suitable f include, but are not limited to, f greater than oπ or 7π and / or less than 15π or 20π. Suitable N include, but are not limited to, N greater than 10, 100, or 1000 and / or less than 10,000 or 50,000.Suitable splitters include, but are not limited to, a star coupler cascaded into a Y junction and a 1x2 MMI coupler cascaded into a 1x2 MMI coupler.

[0085] Phase tuners 104 can be disposed along at least a portion of steering waveguide 102. Although phase tuners 104 are shown disposed along the first and last steering waveguides, these phase tuners are optional. For example, a chip need not have a phase tuner for steering waveguide j=1.

[0086] The electronic circuitry can be configured to operate the phase tuner to generate a phase difference between output signals at facets 18 of adjacent steering waveguides 102. The electronic circuitry can operate the phase tuner such that the phase difference is constant in that it increases linearly across the steering waveguide. For example, the electronics can operate the phase tuner such that the tuner induced phase of steering waveguide number j is (j-1)α, where j is an integer from 1 to N and represents the number associated with the steering waveguide when the steering waveguides are numbered consecutively as shown in FIG. 6, and α is the tuner induced phase difference between adjacent steering waveguides. Thus, the phase of steering waveguide number j is f0+(j-1)f+(j-1)α. Although FIG. 6 shows a chip with only four steering waveguides for ease of illustration, the chip may have many more steering waveguides. For example, a chip may have more than 4 steering waveguides, more than 100 steering waveguides, or more than 1000 steering waveguides, and / or less than 5000 steering waveguides.

[0087] An electronic circuit can be configured to operate the phase tuner to adjust the value of the phase difference α. Adjusting the value of the phase difference α changes the direction (θ) in which the LIDAR output signal travels away from the chip. This allows the electronic circuit to scan the LIDAR output signal by varying the phase difference α. The range of angles over which the LIDAR output signal can be scanned is Φ R and in some examples, Φ = 0°, measured in the direction of the LIDAR output signal when α = 0, v From -Φ v When the value of Δl is non-zero, the length difference causes diffraction such that light of different wavelengths travels away from the chip in different directions (θ). Thus, there will be some spreading in the outgoing LIDAR signal as it travels away from the chip. Furthermore, by varying the level of diffraction, the angle at which the outgoing LIDAR signal travels away from the chip when α=0° changes. However, by providing the steering waveguide with a length difference (Δl≠0), the layout of the steering waveguide on the chip can be simplified.

[0088] FIG. 7 is a side view of the chip looking towards the facet of the steering waveguide from a position away from the chip. Construct the steering waveguide 102 according to FIG. 2. For example, as shown in FIG. 2, the steering waveguide 102 has a width, labeled w, and a height, labeled h. The thickness of the slab region is labeled t. These dimensions are more important in LIDAR applications because of the need to use higher levels of optical power than in other applications and the need to maintain relative phase in applications such as steering waveguides. 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 0.0 μm or 0.05 μm or greater and less than 3 μm. These dimensions are applicable to straight or substantially straight sections of the waveguide, curved sections of the waveguide, and tapered sections of the waveguide. Thus, these portions of the waveguide are single mode. However, in some examples, these dimensions apply to straight or substantially straight portions of the waveguide, while curved and / or tapered portions of the waveguide have dimensions outside of these ranges. For example, the tapered portions of the waveguide may have widths and / or heights that are >4 μm and may range from 4 μm to 12 μm. Additionally, the tapers or curved portions of the waveguide may have reduced slab thicknesses to reduce optical losses in the curved portions of the waveguide. For example, the curved portions of the waveguide may have ridges that extend away from the slab regions that are greater than 0.0 μm and less than 0.5 μm thick. While the above dimensions generally provide straight or substantially straight portions of the waveguide with a single mode structure, they may result in tapered and / or curved portions that are multimode. Coupling between multimode and single mode geometries can be achieved using tapers that do not substantially excite higher order modes.Thus, a waveguide can be configured such that signals transmitted in the waveguide are transmitted in a single mode even when transmitted in a waveguide section having multimode dimensions.

[0089] Pitch is the distance between the facets of the steering waveguide and is labeled P in FIG. 7. Pitch can be measured center-center or from the side of one facet 18 to the corresponding side of an adjacent facet 18. Reducing the pitch increases the range of angles over which the LIDAR output signal can be effectively scanned. However, as the facets get closer together, evanescent coupling can occur. When the separation between adjacent sides of the facets 18 (labeled S in FIG. 7) is greater than 1 μm, evanescent coupling is prevented or reduced. This level of separation can also be applied to the portion of the steering waveguide located between the facet and the phase tuner to prevent or reduce coupling between adjacent steering waveguides.

[0090] One or more of the steering waveguides may have a taper. For example, FIG. 8 is a top view of a chip in which at least a portion of the steering waveguides each have a taper 106 that terminates at one of the facets 18. Although the tapers are shown terminating at the facets 18, the tapers may terminate before the facets 18. Thus, there may be a non-tapered portion of the steering waveguide between the taper and the facets 18. Although the tapers 106 in FIG. 8 are shown to increase the width of the steering waveguide as they approach the facet, the tapers 106 may be configured to decrease the width of the steering waveguide as they approach the facet. Reducing the width of the steering waveguide at the facet can help bring the facets of different steering waveguides closer together. The resulting taper of decreasing width allows a low pitch level to be maintained while allowing a level of separation that prevents or reduces coupling between adjacent steering waveguides.

[0091] The taper shown in FIG. 8 is a horizontal taper, but the taper may also be a vertical taper. The width of the facet is w t and the facet height is denoted by h in FIG. t The facet width (w t The taper can be configured such that the pitch is greater than 1.5, 3, or 6 μm and / or less than 10, 20, or 10 μm. Thus, the non-tapered portion of the steering waveguide located between the taper and the splitter 100 can have a width greater than 1 μm and less than 4 μm and a height greater than 1 μm and less than 4 μm, and the non-tapered portion of the steering waveguide located between the taper and the facet and / or the facet itself can have a width greater than 1 μm and less than 4 μm and a height greater than 1 μm and less than 4 μm. Additionally or alternatively, the taper can be configured such that the separation between adjacent facets is greater than 0.2, 0.3, or 0.4 μm and / or less than 0.6, 0.8, or 1 μm, while the pitch is greater than 1.5, 3, or 6 μm and / or less than 10, 20, or 30 μm. With these dimensions, and at a wavelength of 1550 nm, a scan angle range (Φ 1.0) of less than 60°, 30°, or 20° and / or greater than 5°, 3°, or 1° can be achieved. R ) can be achieved.

[0092] By reducing the thickness of the slab region in the region of the facet 18, the optical coupling between the steering waveguides in the region of the facet 18 can be reduced. FIG. 9A is a side view of a cross section of a portion of the chip shown in FIG. 8. The cross section is taken along the line labeled A in FIG. 8. Because FIG. 9A is a side view, features of the chip in the background of the cross section are also shown. For example, the cross section is taken through the slab region 88. However, steering waveguide 102 can be seen in the background of slab region 88. FIG. 9B is a perspective view of a portion of the chip shown in FIG. 8. The image shown in FIG. 9B does not have the taper 106 shown in FIG. 8, although the slab region configuration shown in FIG. 9B can be used for coupling with a taper.

[0093] Each steering waveguide 102 extends from a slab region 88. As the slab region 88 approaches the facets and / or sides of the chip, the thickness of the slab region 88 decreases. For example, the slab region may have a recess 108 that extends at least part way through the slab region 88. As shown in FIG. 9, when the recess 108 extends part way through the slab region 88, the optical transmission medium 84 at the bottom of the recess 108 may be continuous with the optical transmission medium 84 of the slab region, thus acting as a reduced portion of the slab region 88. In FIG. 9, the thickness of the slab region is labeled with T, and the thickness of the reduced slab region is labeled with t. Suitable thicknesses of the reduced slab region at one or more locations selected between the facets include, but are not limited to, a thickness of 0.0 μm or more, 0.2 μm, or less than 0.5 μm. The chip can be configured such that the ratio of slab region thickness (T):reduced slab region thickness (t) is greater than 1.2:1, 2:1, or 4:1, and / or less than 10:1 or 5:1.

[0094] The slab region can be tapered vertically and / or horizontally near the facet. For example, FIG. 9C is a perspective view of a portion of the chip shown in FIG. 8. The portion of the slab region adjacent to the facet is tapered vertically such that the thickness of the slab region increases as the slab region approaches the facet. To simplify the drawing, the taper 106 is not shown in FIG. 9C. However, a vertical and / or horizontal taper of the slab region can be used to interface with the taper 106 of the steering waveguide 102 as shown in FIG. 8, or a taper 106 that narrows as it approaches the facet. Thus, the vertical taper of the slab region shown in FIG. 9C can be located between the taper 106 regions of the steering waveguide. Such a configuration can reduce optical loss.

[0095] In some examples, the steering waveguides 102 are designed such that the length of the steering waveguide 102 increases linearly. For example, the length of steering waveguide j can be expressed as l0+(j-1)ΔL, where j is an integer from 1 to N and represents the number associated with the steering waveguide when the steering waveguides are numbered sequentially as shown in Figure 6, ΔL is the length difference between adjacent steering waveguides, and L0 is the length of steering waveguide j=1. As mentioned above, the length difference results in the phase of steering waveguide number j, represented by f0+(j-1)f+(j-1)α.

[0096] The length difference causes diffraction such that light of different wavelengths travels away from the chip in different directions (θ). The combination of the angles that can be achieved by this wavelength-dependent diffraction and the angles that can be achieved by adjusting the phase tuner 104 determines the range of angles, Φ, over which the LIDAR output signal can be scanned. R For example, steering waveguide configurations such as those described above can be used with output waveguide pitches of up to 30 μm to achieve scan angle ranges (Φ R ) can be achieved. Suitable ΔL includes, but is not limited to, ΔL greater than 0 or 100 μm and / or less than 200 or 300 μm. Suitable N includes, but is not limited to, N greater than 100 or 1000 and / or less than 10,000 or 50,000.

[0097] To increase the range of wavelengths that can be included in the LIDAR output signal, the chip can have multiple different laser resonators and a multiplexer instead of the laser resonators of the chip of FIG. 1. The multiplexer can receive the output from each laser resonator and combine the outputs to form an output LIDAR signal that is received by the utility waveguide 1 of FIG. 1. The electronic circuitry can operate the laser resonators sequentially such that LIDAR output signals of different wavelengths are output from the chip sequentially. The electronic circuitry can operate a phase tuner to sequentially scan the LIDAR output signals of different wavelengths. Alternatively, the electronic circuitry can operate two or more laser resonators simultaneously such that the LIDAR output signal has light from multiple different laser resonators. The electronic circuitry can operate a phase tuner to scan the LIDAR output signal with light from multiple different laser resonators. The values ​​ΔL are different percentages of the different wavelengths so that the LIDAR output signals with different wavelengths travel away from the chip in different directions.

[0098] The steering waveguide layout shown in Figure 6 is suitable for constructing steering waveguides having the same or substantially the same length. However, other steering waveguide layouts are possible. For example, Figure 10 shows a portion of a chip having a steering waveguide layout that is more suitable for constructing steering waveguides having increasing lengths.

[0099] The steering waveguide can be configured such that the direction of propagation of the output signal in the steering waveguide at the facet is substantially parallel to the plane of the device, the top surface of the substrate, and / or the bottom surface of the substrate. In some examples, the facet 18 is perpendicular or substantially perpendicular to the base and / or the top surface of the substrate and / or the bottom surface of the substrate. Additionally or alternatively, the facet 18 can be configured such that the minimum angle between the plane of the facet and the direction of propagation of the output signal at the facet is between 80° and 90°. For example, FIG. 11 is a cross-section of a waveguide such as the utility waveguide 16 or steering waveguide 102, where the angle θ represents the minimum angle between the facet and the direction of propagation of the output signal. Suitable values ​​of the angle include, but are not limited to, greater than 10°, 9°, or 8° and / or less than 7°, 6°, or 5°.

[0100] Example 1

[0101] Waveguides constructed according to Figure 2 on a silicon-on-insulator wafer were simulated to determine the effective refractive index / width change of the waveguide. Figure 12 shows the resulting refractive index change as a function of waveguide height. Figure 12 shows that the level of refractive index change is a strong function of waveguide diameter (height) for heights above 1 μm, but the correlation drops off rapidly to near zero for diameters (heights) beyond 1 μm.

[0102] Example 2

[0103] Waveguides were constructed according to Figure 2 on a silicon-on-insulator wafer and tested for transmission loss. Figure 13 shows the resulting transmission levels as a function of waveguide height. As the waveguide height passes 1 μm, the transmission loss levels become increasingly weaker. The sharp weakening evident in Figure 13 appears to be reduced by the logarithmic scale associated with the dB dimension shown on the y-axis.

[0104] Example 3

[0105] A first waveguide was constructed according to Figure 2 on a silicon-on-insulator wafer. The first waveguide had a height of 3 μm, a width of 3 μm, and a slab thickness of 0.25 μm. The results in terms of intensity versus beam steering angle are shown in Figure 14. The side lobes present when using the same waveguide structure with a height of 0.5 μm are not evident in Figure 14.

[0106] Suitable phase tuning devices include, but are not limited to, PIN diodes for carrier injection, heaters for thermal tuning, or semiconductor optical amplifiers (SOAs). Examples of phase tuners integrated with the ridge waveguide of a chip constructed from a silicon-on-insulator wafer can be found in U.S. Patent Application Serial No. 09 / 083,395, filed May 22, 1998, and U.S. Patent No. 5,908,305, issued June 1, 1998, which are incorporated herein by reference in their entirety. The phase tuner may be a component separate from and attached to the chip. For example, the phase tuner may be included in a phase tuner chip that is attached to the chip in a flip-chip arrangement. Instead of including the phase tuner in a separate component, all or part of the phase tuner may be integrated into the chip.

[0107] Suitable electronic circuitry includes, but is not limited to, analog circuitry, digital circuitry, processors, microprocessors, digital signal processors (DSPs), field programmable gate arrays (FPGAs), computers, microcomputers, or any combination suitable for performing the operational, monitoring, and control functions described above. In some examples, the controller accesses a memory having instructions that are executed by the controller during the performance of the operational, control, and monitoring functions. Although the electronic circuitry is illustrated as one component and in one location, the electronic circuitry may include multiple different components that are separate from one another and / or located in different locations. Additionally, as described above, all or a portion of the disclosed electronic circuitry may be included on a chip with the electronic circuitry integrated with the chip.

[0108] Although the laser cavity is shown as being located on-chip, all or a portion of the laser cavity can be located off-chip, for example, utility waveguide 16 can be terminated with a second facet through which the outgoing LIDAR signal enters utility waveguide 16 from the off-chip laser cavity.

[0109] The chip may have components in addition to those shown. As an example, optical attenuators (not shown) may be disposed along the first detector waveguide 36 and the second detector waveguide 38. Electronic circuitry may operate these attenuators such that the power of a first portion of the composite sample signal reaching the first photosensor 40 is the same or approximately the same as the power of a second portion of the composite sample signal reaching the second photosensor 40. The electronic circuitry may operate the attenuators in response to an output from the first photosensor 40 indicative of the power level of the first portion of the composite sample signal and an output from the photosensor 42 indicative of the power level of the second portion of the composite sample signal.

[0110] Alternate configurations and / or operations of data branch 24 may be employed. For example, U.S. Provisional Patent Application No. 62 / 671,913, filed May 15, 2018, which is incorporated herein in its entirety, discloses alternative configurations of data branch 24 and alternative methods for generating data from data branch 24.

[0111] Other embodiments, combinations, and modifications of the invention will occur readily to those of ordinary skill in the art in view of these teachings. Accordingly, the invention is limited only by the scope of the following claims, including all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.

Claims

1. 1. A LIDAR chip comprising: a plurality of steering waveguides disposed on a substrate and each configured to carry an output signal, each terminating in a facet, the facets being disposed such that the output signals exit the chip through the facets and combine to form a LIDAR output signal; and a phase tuner disposed on at least a portion of the steering waveguides and configured to adjust a phase difference between the output signals on adjacent steering waveguides, each of the steering waveguides including a ridge of optical transmission medium extending away from a slab region of optical transmission medium located between the ridges, the thickness of the slab region decreasing as the slab region approaches a facet.

2. 2. The LIDAR chip of claim 1, wherein the facets are perpendicular to a top and / or bottom surface of the base, and a minimum angle between a plane of the facet and a direction of transmission of an output signal at the facet is between 80° and 90°.

3. 10. The LIDAR chip of claim 1, wherein the steering waveguide has a length that varies linearly.

4. 13. The LIDAR chip of claim 1 included in a system, the system further comprising electronic circuitry for operating the phase tuner to vary a direction of the LIDAR output signal away from the chip.

5. 10. The LIDAR chip of claim 1, wherein a width of at least a portion of the steering waveguide narrows between the phase tuner and the facet.

6. 10. The LIDAR chip of claim 1, wherein at least some of the steering waveguides each exclude the phase tuner.

7. 10. The LIDAR chip of claim 1, wherein the facets are arranged such that a separation between adjacent facets is less than 1 μm.

8. 10. The LIDAR chip of claim 1, wherein the facets are arranged at a pitch greater than 1.5 μm and / or less than 30 μm.

9. 10. The LIDAR chip of claim 1, wherein at least a portion of the steering waveguides each have a taper, the taper configured such that a width of the steering waveguide decreases as the steering waveguide approaches the facet.

10. 10. The LIDAR chip of claim 1, wherein the LIDAR output signal is one of a plurality of LIDAR output signals formed by combining output signals exiting the chip through the facets, each of the LIDAR output signals having a different wavelength.

11. 2. The LIDAR chip of claim 1 , wherein a thickness of the slab region decreases from a portion of the slab region of thickness T to a reduced-thickness portion of the slab region of thickness t, and a ratio of thickness T:thickness of the reduced slab region (t) is greater than 1.2:1 and / or less than 5:

1.

12. 10. The LIDAR chip of claim 1, wherein the portion of the slab region having the thickness T is horizontally tapered.

13. 12. The LIDAR chip of claim 11, wherein the reduction in thickness of the slab region from the thickness T to the thickness t occurs between non-tapered portions of adjacent steering waveguides.

14. 1. A LIDAR chip comprising: a plurality of steering waveguides disposed on a substrate and each configured to carry an output signal, each terminating in a facet, the facets being disposed such that the output signals exit the chip through the facets and combine to form a LIDAR output signal; and a phase tuner disposed on at least a portion of the steering waveguides and configured to adjust a phase difference between the output signals on adjacent steering waveguides, the steering waveguides having a ridge of optical transmission medium extending away from a slab region of optical transmission medium, a portion of the slab region between the steering waveguides being vertically tapered such that a thickness of the slab region increases as the slab region approaches the facet.

15. 15. The LIDAR chip of claim 14, wherein the steering waveguide has a length that varies linearly.

16. 15. The LIDAR chip of claim 14 included in a system, the system further comprising electronic circuitry for operating the phase tuner to vary a direction of the LIDAR output signal away from the chip.

17. 15. The LIDAR chip of claim 14, wherein a width of at least a portion of the steering waveguide narrows between the phase tuner and the facet.

18. 15. The LIDAR chip of claim 14, wherein at least some of the steering waveguides each exclude the phase tuner.

19. 15. The LIDAR chip of claim 14, wherein the facets are arranged such that a separation between adjacent facets is less than 1 μm.

20. 15. The LIDAR chip of claim 14, wherein the facets are arranged at a pitch greater than 1.5 μm and / or less than 30 μm.

21. 15. The LIDAR chip of claim 14, wherein at least a portion of the steering waveguides each have a taper, the taper configured such that a width of the steering waveguide decreases as the steering waveguide approaches the facet.

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