Patent Grant
12339399
The invention relates to optical devices. In particular, the invention relates to LIDAR chips.
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 a 3D image of a target scene by illuminating the scene with laser light and measuring the returned signal.
Frequency Modulated Continuous Wave (FMCW) is an example of a coherent detection method can be used for LIDAR applications. The FMCW technique is capable of determining both distance and velocity of an object with a single measurement. Additionally, FMCW techniques have reduced sensitivity to ambient light and light from other LIDAR systems.
For many LIDAR applications there is a need to scan the light beam externally to build up an image of the field of view. Methods of scanning the beam include mechanical methods such as rotating the assembly containing the lasers, rotating mechanical mirrors, and MEMS mirrors. ‘Solid-state’ approaches are of interest due to their lack of moving parts and may improve scanning speeds. However, the solid-state approaches that have been tried have limited angular ranges and require a large number of control elements. As a result, there is a need for a practical solid-state scanning mechanism.
An optical system has a LIDAR chip that includes a switch configured to direct an outgoing LIDAR signal to one of multiple different alternate waveguides. The system also includes a redirection component configured to receive the outgoing LIDAR signal from any one of the alternate waveguides. The redirection component is also configured to redirect the received outgoing LIDAR signal such that a direction that the outgoing LIDAR signal travels away from the redirection component is a function of the alternate waveguide from which the redirection component receives the outgoing LIDAR signal.
A LIDAR system has a LIDAR chip that includes a switch configured to direct an outgoing LIDAR signal to any one of multiple different alternate waveguides. A redirection component receives the outgoing LIDAR signal from any one of the alternate waveguides. The redirection component also redirects the received outgoing LIDAR signal such that a direction that the outgoing LIDAR signal travels away from the redirection component changes in response to changes in the alternate waveguide from which the redirection component receives the outgoing LIDAR signal. As a result, the outgoing LIDAR signal can be steered to different sample regions in a field of view by operating the optical switch so as to change the alternate waveguides to which the outgoing LIDAR signal is directed. The optical switch can be a solid-state optical switch that includes or consists of optical components such as cascaded 2×2 Mach-Zehnder (MZ) modulators interferometers. Additionally, an example of a suitable redirection component is one or more lenses and/or one or more mirrors. The one or more lenses and/or one or more mirrors can be stationary relative to the optical switch. As a result, steering of the outgoing LIDAR signal can be achieved with a practical solid-state device. Additionally, the angular range over which the outgoing LIDAR signal can be steered can be increased by increasing the separation between the alternate waveguides. As a result, the LIDAR system can have a solid-state steering mechanism with a wide angular range.
Another example of a suitable redirection component includes a splitter configured to receive the outgoing LIDAR signal from any one of the alternate waveguides and to split the outgoing LIDAR signal into output signals. The redirection component also includes multiple steering waveguides that are each configured to receive a different one of the output signals. The steering waveguides each terminates at a facet and the facets are arranged such that output signals exiting from the steering waveguides through the facets re-form the outgoing LIDAR signal with the re-formed outgoing LIDAR signal traveling away from the redirection component. At least a portion of the steering waveguides each includes a phase tuner configured to tune a phase differential between the output signals such the direction that the reformed outgoing LIDAR signal travels away from the redirection component changes. As a result, steering of the LIDAR output signal can be achieved with both the phase tuners and selection of the alternate waveguide. This combination of steering mechanisms allows the outgoing LIDAR signal to be steered continuously within a field of view. Additionally, the splitter, steering waveguides and phase tuners can all exclude moving parts. As a result, the steering of the outgoing LIDAR signal can be achieved with a practical solid-state device. Further, the angular range over which the outgoing LIDAR signal can be steered can be increased by increasing the separation between the alternate waveguides. As a result, the LIDAR system can have a solid-state steering mechanism with a wide angular range.
The partial return device 14 returns a return portion of the light signal to the cavity waveguide 12 as a return signal. For instance, the cavity waveguide 12 returns the return signal to the light source 10 such that the return portion of the light signal travels through the gain medium. The light source 10 is configured such that at least a portion of the return signal is added to the light signal that is received at the cavity waveguide 12. For instance, the light source 10 can include a highly, fully, or partially reflective device 15 that reflects the return signal received from the gain medium back into the gain medium. As a result, light can resonate between the partial return device 14 and the reflective device 15 so as to form a Distributed Bragg Reflector (DBR) laser cavity. A DBR laser cavity has an inherently narrow-linewidth and a longer coherence length than DFB lasers and accordingly improves performance when an object reflecting the LIDAR output signal from the chip is located further away from the chip.
The partial return device 14 passes a portion of the light signal received from the cavity waveguide 12 to a utility waveguide 16 included on the chip. The portion of the light signal that the utility waveguide 16 receives from the partial return device 14 serves as the output of the laser cavity. The output of the laser cavity serves 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 positioned such that the outgoing LIDAR signal traveling through the facet 18 exits the chip and serves as a LIDAR output signal. For instance, the facet 18 can be positioned at an edge of the chip so the outgoing LIDAR signal traveling through the facet 18 exits the chip and serves as a LIDAR output signal.
The LIDAR output signal travels away from the chip and is reflected by objects in the path of the LIDAR signal. The reflected signal travels away from the objects. At least a portion of the reflected signal returns to the facet 18 of the utility waveguide 16. Accordingly, a portion of the reflected signal can enter the utility waveguide 16 through the facet 18 and serve as a LIDAR input signal guided by the utility waveguide 16.
The utility waveguide 16 can include a tapered portion before the facet 18. For instance, the utility waveguide 16 can include a taper 20 that terminate at the facet 18. The taper 20 can relax the alignment tolerances required for efficient coupling of the utility waveguide 16 to the LIDAR input light and the outgoing LIDAR signal. Accordingly, the taper 20 can increase the percentage of the LIDAR input signal that is successfully returned to the chip for processing. In some instances, the taper 20 is constructed such that the facet 18 has an area that is more than two, five, or ten times the area of a cross section of a straight portion of the utility waveguide 16. Although
The chip includes a data branch 24 where the optical signals that are processed for LIDAR data (radial velocity and/or distance between a reflecting object and the source of the LIDAR output signal) are generated. The data branch includes an optical coupler 26 that moves a portion of the light signals from the utility waveguide 16 into the data branch. For instance, an optical coupler 26 couples a portion of the outgoing LIDAR signal from the utility waveguide 16 onto a reference waveguide 27 as a reference signal. The reference waveguide 27 carries the reference signal to a light-combining component 28.
The optical coupler 26 also couples a portion of the LIDAR input signal from the utility waveguide 16 onto a comparative waveguide 30 as a comparative signal. The comparative signal includes at least a portion of the light from the LIDAR input signal. The comparative signal can exclude light from the reference light signal. The comparative waveguide 30 carries the comparative signal to the light-combining component 28.
The illustrated optical coupler 26 is a result of positioning the utility waveguide 16 sufficiently close to the reference waveguide 27 and the comparative waveguide 30 that light from the utility waveguide 16 is coupled into the reference waveguide 27 and the comparative waveguide 30; however, other signal tapping components can be used to move a portion of the of the light signals from the utility waveguide 16 onto the reference waveguide 27 and the comparative waveguide 30. Examples of suitable signal tapping components include, but are not limited to, y-junctions, multi-mode interference couplers (MMIs), and integrated optical circulators.
The light-combining component 28 combines the comparative signal and the reference signal into a composite signal. The reference signal includes light from the outgoing LIDAR signal. For instance, the reference signal can serve as a sample of the outgoing LIDAR signal. The reference signal can exclude light from the LIDAR output signal and the LIDAR input signal. In contrast, the comparative signal light includes light from the LIDAR input signal. For instance, the comparative signal can serve as a sample of the LIDAR input signal. Accordingly, the comparative signal has been reflected by an object located off of the chip while the LIDAR output signal has not been reflected. When the chip and the reflecting object are moving relative to one another, the comparative signal and the reference signal have different frequencies due to the Doppler effect. As a result, beating occurs between the comparative signal and the reference signal.
The light-combining component 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 carries a first portion of the composite sample signal to a first light sensor 40 that converts the first portion of the composite sample signal to a first electrical signal. The second detector waveguide 38 carries a second portion of the composite sample signal to a second light sensor 42 that converts the second portion of the composite sample signal to a second electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).
The light combining component 28, the first light sensor 40 and the second light sensor 42 can be connected as a balanced photodetector that outputs an electrical data signal. For instance, the light combining component 28, the first light sensor 40 and the second light sensor 42 can be connected such that the DC components of the signal photocurrents cancel, improving detection sensitivity. Suitable methods for connecting the first light sensor 40 and the second light sensor 42 as balanced photodetectors includes connecting the first light sensor 40 and the second light sensor 42 in series. In one example, the first light sensor 40 and the second light sensor 42 are both avalanche photodiodes connected in series. Balanced photodetection is desirable for detection of small signal fluctuations.
An example of a suitable light-combining component 28 is a Multi-Mode Interference (MMI) device such as a 2×2 MMI device. Other suitable light-combining components 28 include, but are not limited to, adiabatic splitters, and directional coupler. In some instances, the functions of the illustrated light-combining component 28 are performed by more than one optical component or a combination of optical components.
A single light sensor can replace the first light sensor 40 and the second light sensor 42 and can output the data signal. When a single light sensor replaces the first light sensor 40 and the second light sensor 42, the light-combining component 28 need not include light-splitting functionality. As a result, the illustrated light light-combining component 28 can be a 2×1 light-combining component rather than the illustrated 2×1 light-combining component. For instance, the illustrated light light-combining component can be a 2×1 MMI device. In these instances, the chip includes a single detector waveguide that carries the composite sample signal to the light sensor.
The data branch includes a data optical attenuator 44 positioned along the comparative waveguide 30 such that the data optical attenuator 44 can be operated so as to attenuate the comparative signal on the comparative waveguide 30. The chip also includes an output optical attenuator 46 positioned along the utility waveguide 16 such that the output optical attenuator 46 can be operated so as 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 intensity of a light signal. Examples of a suitable attenuator configured to attenuate intensity of a light signal include carrier injection based PIN diodes, electro-absorption modulators, and Mach-Zehnder (MZ) modulators.
The chip also includes a sampling directional coupler 50 that couples a portion of the comparative signal from the comparative waveguide 30 onto a sampling waveguide 52. The coupled portion of the comparative signal serves as a sampling signal. The sampling waveguide 52 carries the sampling signal to a sampling light sensor 54. Although
The chip includes a control branch 55 for controlling operation of the laser cavity. The control branch includes a directional coupler 56 that moves a portion of the outgoing LIDAR signal from the utility waveguide 16 onto a control waveguide 57. The coupled portion of the outgoing LIDAR signal serves as a tapped signal. Although
The control waveguide 57 carries the tapped signal to an interferometer 58 that splits the tapped signal and then re-combines the different portions of the tapped signal with a phase differential between the portions of the tapped signal. The illustrated interferometer 58 is a Mach-Zehnder interferometer; however, other interferometers can be used.
The interferometer 58 outputs a control light signal on an interferometer waveguide 60. The interferometer waveguide 60 carries the control light signal to a control light sensor 61 that converts the control light signal to an electrical signal that serves as an electrical control signal. The interferometer signal has an intensity that is a function of the frequency of the outgoing LIDAR signal. For instance, a Mach-Zehnder interferometer will output a sinusoidal control light signal with a fringe pattern. Changes to the frequency of the outgoing LIDAR signal will cause changes to the frequency of the control light signal. Accordingly, 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 instance, the control light sensor 61 can be replaced with a balanced photodetector arranged as the light combining component 28, the first light sensor 40 and the second light sensor 42.
Electronics 62 can operate one or more components on the chip. For instance, the electronics 62 can be in electrical communication with and control operation of the light source 10, the data optical attenuator 44, output optical 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 electronics 62 are shown off the chip, all or a portion of the electronics can be included on the chip. For instance, the chip can include electrical conductors that connect the first light sensor 40 in series with the second light sensor 42.
During operation of the chip, the electronics 62 operate the light source 10 such that the laser cavity outputs the outgoing LIDAR signal. The electronics 62 then operate the chip through a series of cycles where each cycle generates LIDAR data (radial velocity and/or distance between a reflecting object and the source of the LIDAR output signal) associated with one of the sample regions in the field of view. Each cycle can include multiple sample periods. During each sample period, the electronics can tune the frequency of the outgoing LIDAR signal. As will be described in more detail below, the electronics can employ output from the control branch in order 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 electronics. In some instance, a cycle includes a first sample period and a second sample period. During the first sample period, the electronics 62 can increase the frequency of the outgoing LIDAR signal and during the second sample period the electronics 62 can decrease the frequency of the outgoing LIDAR signal. For instance, the laser cavity can be configured to output an outgoing LIDAR signal (and accordingly a LIDAR output signal) with a wavelength of 1550 nm. During the first sample period, the electronics 62 can increase the frequency of the outgoing LIDAR signal (and accordingly a LIDAR output signal) such that the wavelength decreases from 1550 nm to 1459.98 nm followed by decreasing the frequency of the outgoing LIDAR signal such that the wavelength increases from 1459.98 nm to 1550 nm.
When the outgoing LIDAR signal frequency is increased during the first sample period, the LIDAR output signal travels away from the chip and then returns to the chip as a LIDAR input signal. A portion of the LIDAR input signal becomes the comparative signal. During the time that the LIDAR output signal and the LIDAR input signal are traveling between the chip and a reflecting object, the frequency of the outgoing LIDAR signal continues to increase. Since a portion of the outgoing LIDAR signal becomes the reference signal, the frequency of the reference signal continues to increase. As a result, the comparative signal enters the light-combining component with a lower frequency than the reference signal concurrently entering the light-combining component. Additionally, the further 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. Accordingly, the larger the difference between the frequency of the comparative signal and the frequency of the reference signal, the further the reflecting object is from the chip. As a result, the difference between the frequency of the comparative signal and the frequency of the reference signal is a function of the distance between the chip and the reflecting object.
For the same reasons, when the outgoing LIDAR signal frequency is decreased during the second sample period, the comparative signal enters the light-combining component with a higher frequency than the reference signal concurrently entering the light-combining component and the difference between the frequency of the comparative signal and the frequency of the reference signal during the second sample is also function of the distance between the chip and the reflecting object.
In some instances, the difference between the frequency of the comparative signal and the frequency of the reference signal can also be a function of the Doppler effect because relative movement of the chip and reflecting object can also affect the frequency of the comparative signal. For instance, when the chip is moving toward or away from the reflecting object and/or the reflecting object is moving toward or away from the chip, the Doppler effect can affect the frequency of the comparative signal. Since the frequency of the comparative signal is a function of the speed the reflecting object is moving toward or away from the chip and/or the speed the chip is moving toward or away from the reflecting object, the difference between the frequency of the comparative signal and the frequency of the reference signal is also a function of the speed the reflecting object is moving toward or away from the chip and/or the speed the chip is moving toward or away from the reflecting object. Accordingly, the difference between the frequency of the comparative signal and the frequency of the reference signal is a function of the distance between the chip and the reflecting object and is also a function of the Doppler effect.
The composite sample signal and the data signal each effectively compares the comparative signal and the reference signal. For instance, since the light-combining component combines the comparative signal and the reference signal and these signals have different frequencies, there is beating between the comparative signal and reference signal. Accordingly, the composite sample signal and the data signal have a beat frequency related to the frequency difference between the comparative signal and the reference signal and the beat frequency can be used to determine the difference in the frequency of the comparative signal and the reference signal. A higher beat frequency for the composite sample signal and/or the data signal indicates a higher differential between the frequencies of the comparative signal and the reference signal. As a result, the beat frequency of the data signal is a function of the distance between the chip and the reflecting object and is also a function of the Doppler effect.
As noted above, the beat frequency is a function of two unknowns; the distance between the chip and the reflecting object and the relative velocity of the chip and the reflecting object (i.e., the contribution of the Doppler effect). The change in the frequency difference between the comparative signal and the reference signal (Δf) is given by Δf=2Δvf/c where f is the frequency of the LIDAR output signal and accordingly the reference signal, Δv is the relative velocity of the chip and the reflecting object and c is the speed of light in air. The use of multiple different sample periods permits the electronics 62 to resolve the two unknowns. For instance, the beat frequency determined from the first sample period is related to the unknown distance and Doppler contribution and the beat frequency determined from the second sample period is also related to the unknown distance and Doppler contribution. The availability of the two relationships allows the electronics 62 to resolve the two unknowns. Accordingly, the distance between the chip and the reflecting object can be determined without influence from the Doppler effect. Further, in some instances, the electronics 62 use this distance in combination with the Doppler effect to determine the radial velocity of the reflecting object toward or away from the LIDAR chip.
In instances where the radial velocity of target and source is zero or very small, the contribution of the Doppler effect to the beat frequency is essentially zero. In these instances, the Doppler effect does not make a substantial contribution to the beat frequency and the electronics 62 can use only the beat frequency from the first sample period to determine the distance between the chip and the reflecting object.
During operation, the electronics 62 can adjust the frequency of the outgoing LIDAR signal in response to the electrical control signal output from the control light sensor 61. As noted above, 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. Accordingly, the electronics 62 can adjust the frequency of the outgoing LIDAR signal in response to the magnitude of the control. For instance, while changing the frequency of the outgoing LIDAR signal during one of the sample periods, the electronics 62 can have a range of suitable values for the electrical control signal magnitude as a function of time. At multiple different times during a sample period, the electronics 62 can compare the electrical control signal magnitude to the range of values associated with the current time in the sample period. If the electrical control signal magnitude indicates that the frequency of the outgoing LIDAR signal is outside the associated range of electrical control signal magnitudes, the electronics 62 can operate the light source 10 so as to change the frequency of the outgoing LIDAR signal so it falls within the associated range. If the electrical control signal magnitude indicates that the frequency of the outgoing LIDAR signal is within the associated range of electrical control signal magnitudes, the electronics 62 do not change the frequency of the outgoing LIDAR signal.
During operation, the electronics 62 can adjust the level of attenuation provided by the output optical attenuator 46 in response to the sampling signal from the sampling light sensor 54. For instance, the electronics 62 operate the output optical attenuator 46 so as to increase the level of attenuation in response to the magnitude of the sampling signal being above a first signal threshold and/or decrease the magnitude of the power drop in response to the magnitude of the sampling signal being below a second signal threshold.
In some instance, the electronics 62 adjust the level of attenuation provided by the output optical attenuator 46 to prevent or reduce the effects of back-reflection on the performance of the laser cavity. For instance, the first signal threshold and/or the second signal threshold can optionally be selected to prevent or reduce the effects of back-reflection 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 returned LIDAR signal. In some instances, on the order of 50% of the LIDAR input signal that passes through the facet 18 returns to the laser cavity. The returned LIDAR signal can affect performance of the laser cavity when the power of the returned LIDAR signal entering the partial return device 14 does not decrease below the power of the outgoing LIDAR signal exiting from the partial return device 14 (“power drop”) by more than a minimum power drop threshold. In the illustrated chip, the minimum power drop threshold can be around 35 dB (0.03%). Accordingly, the returned LIDAR signal can affect the performance of the laser cavity when the power of the returned LIDAR signal entering the partial return device 14 is not more than 35 dB below the power of the outgoing LIDAR signal exiting from the partial return device 14.
The electronics 62 can operate the output optical attenuator 46 so as to reduce the effect of low power drops, e.g. when the target object is very close or highly reflective or both. As is evident from
Additionally, the magnitude of the sampling signal is related to the power drop. For instance, the magnitude of the sampling signal is related to the power of the comparative signal as is evident from
Since the magnitude of the sampling signal is related to the power drop, the electronics 62 can use the magnitude of the sampling signal to operate the output optical attenuator so as to keep the magnitude of the comparative signal power within a target range. For instance, the electronics 62 can operate the output optical attenuator 46 so as to increase the magnitude of the power drop in response to the sampling signal indicating that the magnitude of power drop is at or below a first threshold and/or the electronics 62 can operate the output optical attenuator 46 so as to decrease the magnitude of the power drop in response to the sampling signal indicating that the magnitude of power drop is at or above a second threshold. In some instances, the first threshold is greater than or equal to the minimum power drop threshold. In one example, the electronics 62 operate the output optical attenuator 46 so as to increase the magnitude of the power drop in response to the magnitude of the sampling signal being above a first signal threshold and/or decrease the magnitude of the power drop in response to the magnitude of the sampling signal being below a second signal threshold. The identification of the value(s) for 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 calibration of the optical chip during set-up of the LIDAR chip system.
Light sensors can become saturated when the power of the composite light signal exceeds a power threshold. When a light sensor becomes saturated, the magnitude of the data signal hits a maximum value that does not increase despite additional increases in the power of the composite light signal above the power threshold. Accordingly, data can be lost when the power of the composite light signal exceeds a power threshold. During operation, the electronics 62 can adjust the level of attenuation provided by the data optical attenuator 44 so the power of the composite light signal is maintained below a power threshold.
As is evident from
As noted above, the electronics 62 can adjust the level of attenuation provided by the output optical attenuator 46 in response to the sampling signal. The electronics 62 can adjust the level of attenuation provided by the data optical attenuator 44 in response to the sampling signal in addition or as an alternative to adjusting the level of attenuation provided by the output optical attenuator 46 in response to the sampling signal
Suitable platforms for the chip include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers.
The portion of the chip illustrated in
The dimensions of the ridge waveguide are labeled in
The light source 10 that is interfaced with the utility waveguide 16 can be a gain element that is a component separate from the chip and then attached to the chip. For instance, the light source 10 can be a gain element that is attached to the chip using a flip-chip arrangement.
Use of flip-chip arrangements is suitable when the light source 10 is to be interfaced with a ridge waveguide on a chip constructed from silicon-on-insulator wafer. Examples of suitable interfaces between flip-chip gain elements and ridge waveguides on chips constructed from silicon-on-insulator wafer can be found in U.S. Pat. No. 9,705,278, issued on Jul. 11, 2017 and in U.S. Pat. No. 5,991,484 issued on Nov. 23 1999; each of which is incorporated herein in its entirety. The constructions are suitable for use as the light source 10. When the light source 10 is a gain element, the electronics 62 can change the frequency of the outgoing LIDAR signal by changing the level of electrical current applied to through the gain element.
The attenuators can be a component that is separate from the chip and then attached to the chip. For instance, the attenuator can be included on an attenuator chip that is attached to the chip in a flip-chip arrangement. The use of attenuator chips is suitable for all or a portion of the attenuators selected from the group consisting of the data attenuator and the control attenuator.
As an alternative to including an attenuator on a separate component, all or a portion of the attenuators can be integrated with the chip. For instance, examples of attenuators that are interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in U.S. Pat. No. 5,908,305, issued on Jun. 1 1999; each of which is incorporated herein in its entirety. The use of attenuators that are integrated with the chip are suitable for all or a portion of the light sensors selected from the group consisting of the data attenuator and the control attenuator.
Light sensors that are interfaced with waveguides on a chip can be a component that is separate from the chip and then attached to the chip. For instance, the light sensor can be a photodiode, or an avalanche photodiode. Examples of suitable light sensor components include, but are not limited to, InGaAs PIN photodiodes manufactured by Hamamatsu located in Hamamatsu City, Japan, or an InGaAs APD (Avalanche Photo Diode) manufactured by Hamamatsu located in Hamamatsu City, Japan. These light sensors can be centrally located on the chip as illustrated in
As an alternative to a light sensor that is a separate component, all or a portion of the light sensors can be integrated with the chip. For instance, examples of light sensors that are interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in Optics Express Vol. 15, No. 21, 13965-13971 (2007); U.S. Pat. No. 8,093,080, issued on Jan. 10 2012; U.S. Pat. No. 8,242,432, issued Aug. 14 2012; and U.S. Pat. No. 6,108,872, issued on Aug. 22, 2000 each of which is incorporated herein in its entirety. The use of light sensors that are integrated with the chip are 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.
Construction of optical gratings that are integrated with a variety of optical device platforms are available. For instance, a Bragg grating can be formed in a ridge waveguides by forming grooves in the top of the ridge and/or in the later sides of the ridge.
In some instances, it is desirable to scan the LIDAR output signal. The above chip construction is suitable for use with various scanning mechanisms used in LIDAR applications. For instance, the output LIDAR signal can be received by one or more reflecting devices and/or one more collimating devices. The one or more reflecting devices can be configured to re-direct and/or steer the LIDAR output signal so as to provide scanning of the LIDAR output signal. Suitable reflecting devices include, but are not limited to, mirrors such mechanically driven mirrors and Micro Electro Mechanical System (MEMS) mirrors. The one or more collimating devices provide collimation of the LIDAR output signal and can accordingly increase the portion of the LIDAR input signal that is received in the utility waveguide 16. Suitable collimating devices include, but are not limited to, individual lenses and compound lenses.
Technologies such as SOI MEMS (Silicon-On-Insulator Micro Electro Mechanical System) technology can be used to incorporate a reflecting device such as a MEMS mirror into the chip. For instance,
The above chips can include alternative methods of scanning and/or steering the LIDAR output signal in addition to a reflecting device or as an alternative device. For instance, the chip can include a component for splitting the outgoing LIDAR signal into multiple output signals. The chip can then tune the phase difference between different output signals so as to control the direction that the LIDAR output signal travels away from the chip. The LIDAR output signal can be steered or scanned by changing the level of the phase difference between the output signals. Suitable systems that employ phase differential between output signals to steer a LIDAR output signal are described in U.S. Patent Application Ser. No. 62/683,958, filed on Jun. 12, 2018, and incorporated herein in its entirety and in U.S. Patent Application Ser. No. 62/680,787, filed on Jun. 5, 2018, and incorporated herein in its entirety.
Another alternative for scanning and/or steering the LIDAR output signal can include optical switching.
The utility waveguide 16 carries the outgoing LIDAR signal to an optical switch 100 that directs the outgoing LIDAR signal to one of multiple alternate waveguide 102 that are each associated with a waveguide index n=1 through N. Each of the alternate waveguides 102 terminates at a facet 18. The alternate waveguide 102 that receives the outgoing LIDAR signal guides the outgoing LIDAR signal to a facet 18 through which the outgoing LIDAR signal exits from the alternate waveguide 102 and serves as the LIDAR output signal. Accordingly, the optical switch 100 can direct the outgoing LIDAR signal to any one of the facets 18 through which the outgoing LIDAR signal passes and serves as a LIDAR output signal.
The LIDAR output signal can be reflected off an object located off of the chip. At least a portion of the reflected signal travels back to the facet 18 through which it exited the alternate waveguide and enters the associated alternate waveguide 102 as a LIDAR input signal. The alternate waveguide 102 guides the LIDAR input signal to the optical switch 100 which directs the LIDAR input signal back to the utility waveguide 16. The chip and electronics can then process the LIDAR input signal.
The electronics can operate the optical switch 100 so as to change the alternate waveguide 102 that receives the outgoing LIDAR signal. Accordingly, the electronics can cause the outgoing LIDAR signal to be directed to a particular one of the alternate waveguides 102 and accordingly to a particular one of the facets 18.
The LIDAR system also includes a redirection component configured to receive the outgoing LIDAR signal from any one of the alternate waveguides and to redirect the received outgoing LIDAR signal such that a direction that the outgoing LIDAR signal travels away from the redirection component is a function of the alternate waveguide from which the redirection component receives the outgoing LIDAR signal. The direction of the outgoing LIDAR signal can be a function of the alternate waveguide in that the direction that the outgoing LIDAR signal travels away from the redirection component changes in responses to changes in the alternate waveguide from which the redirection component receives the outgoing LIDAR signal. In some instances, the redirection component is configured such that none of the different directions is parallel to one another. For instance, the redirection component can be configured such that the outgoing LIDAR signal travels away from the redirection component at a different transmission angle when the redirection component receives the outgoing LIDAR signal from different alternate waveguides where the transmission angle being measured relative to the redirection component.
In
During operation of the system, the electronics can delay switching the alternate waveguide 102 that receives the outgoing LIDAR signal until the chip has received the LIDAR input signal that is needed for the desired processing. As a result, the LIDAR output signal and the associated LIDAR input signal are guided by the same alternate waveguide 102.
In
The center-to-center distance of the facets 18 is labeled d in
The maximum value for N can be the nearest integer value to (1+2(R′−R)/d) where R is the diameter of the LIDAR output signals at the input side of the lens 104 and R′ is the lens radius. Accordingly, the chip can include a number of alternate waveguides 102 less than or equal to the nearest integer value of (1+2(R′−R)/d). In some instances, N is greater than or equal to 5, 10, or 50 and/or less than 100, 500, or 1000. The angular range that can be scanned (2θN) by sequentially directing the LIDAR output signal to each of the alternate waveguides 102 can be increased by increasing N. Accordingly, an improved resolution can be obtained by decreasing d and an improved scan range obtained by increasing N within the limits of the optical system.
The lens 104 can be configured such that the lens 104 collimates the LIDAR output signals from different facets. Additionally or alternately, the lens 104 can be positioned such that one or more of the facets is located at a focal point of the lens 104. However, the focal points are typically positioned along an arced line. For instance,
As an alternative to the positioning the facets 18 along an arced focal point line or in addition to positioning the facets along an arced focal point line, the alternate waveguides 102 can be curved such that direction of propagation of the outgoing LIDAR signals at the facets of different alternate waveguides 102 is different for different alternate waveguides 102. For instance,
Another alternative is to angle the chip and/or the facets such that the positions of at least a portion of the facets 18 are positioned along a line that approximates the arced focal point line. In particular, the facets 18 on one side of the optical axis of the lens can be positioned along a line that approximates the arced focal point line. For instance,
Positioning the chip such that the facets 18 are positioned along a line that approximates the arced focal point line can include positioning the chip such that a portion of the facets 18 are positioned on one side of the arced focal point line and another portion of the facets are positioned on another side of the arced focal point line. In some instances, the chip includes the facets arranged such that a line can pass through each of the facets and the chip is positioned such that a portion of the facets 18 are positioned on one side of the arced focal point line and another portion of the facets 18 are positioned on another side of the arced focal point line and the arced focal point line passes through the line through the facets 18 at least two times.
Although the lens is illustrated as being spaced apart from the chip, the lens can be integrated with the chip. For instance,
Suitable optical switches for use with the chip include, but are not limited to, cascaded 2×2 Mach-Zehnder (MZ) modulators interferometers using thermal or free-carrier injection phase shifters, and micro-ring resonator switches.
Although the above discussion uses a lens as a redirection component, other redirection components can be employed. For instance, a mirror can be used in place of the lens. Suitable mirrors include, but are not limited to curved mirrors such as parabolic curved mirrors. In some instances, the mirror is angled to reflect the LIDAR output beams above or below the surface of the LIDAR chip and or facets polished at an angle may be used to direct the LIDAR output signals initially above the plane of the chip.
The utility waveguide 16 carries the outgoing LIDAR signal to an optical switch 100 that directs the outgoing LIDAR signal to one of multiple alternate waveguide 102. The alternate waveguide 102 that receives the outgoing LIDAR signal guides the outgoing LIDAR signal to the redirection component 103. Although the redirection component of
The electronics can operate the optical switch 100 so as to change the alternate waveguide 102 that receives the outgoing LIDAR signal. Accordingly, the electronics can cause the outgoing LIDAR signal to be directed to a particular one of the alternate waveguides 102.
The redirection component is configured to receive the outgoing LIDAR signal from any one of the alternate waveguides and then direct the received outgoing LIDAR signal such that outgoing LIDAR signals received from different alternate waveguides travel away from the redirection component 103 in different directions. In some instances, the redirection component is configured such that none of the different directions is parallel to one another.
The redirection component 103 includes a splitter 110 that divides the outgoing LIDAR signal into multiple output signals that are each carried on a steering waveguide 112. Each of the steering waveguides 112 ends at a facet 18. The facets 18 are arranged such that the output signals exiting the chip through the facets 18 combine to form the LIDAR output signal and/or to effectively re-form the outgoing LIDAR signal.
The splitter 110 and steering waveguides 112 can be constructed such that there is not a phase differential between output signals at the facet 18 of adjacent steering waveguides 112. For instance, the splitter 110 can be constructed such that each of the output signals is in-phase upon exiting from the splitter 110 and the steering waveguides 112 can each have the same length. Alternately, the splitter 110 and steering waveguides 112 can be constructed such that there is a linearly increasing phase differential between output signals at the facet 18 of adjacent steering waveguides 112. For instance, the steering waveguides 112 can be constructed such that the phase of steering waveguide number j is fo+(j−1)f where j is an integer from 1 to M and represents the number associated with a steering waveguide when the steering waveguides are sequentially numbered as shown in
A phase tuner 104 can be positioned along at least a portion of the steering waveguides 102. Although a phase tuner 104 is shown positioned along the first and last steering waveguide, these phase tuners are optional. For instance, the chip need not include a phase tuner on steering waveguide j=1.
The electronics can be configured to operate the phase tuners so as to create a phase differential between the output signals at the facet 18 of adjacent steering waveguides 102. The electronics can operate the phase tuners such that the phase differential is constant in that it increases linearly across the steering waveguides. For instance, electronics can operate the phase tuners such that the tuner-induced phase of steering waveguide number j is (j−1)α where j is an integer from 1 to M and represents the number associated with a steering waveguide 112 when the steering waveguides 112 are sequentially numbered as shown in
The electronics can be configured to operate the phase tuners so as to tune the value of the phase differential α. Tuning the value of the phase differential α changes the direction that the LIDAR output signal travels away from the chip (θ). Accordingly, the electronics can scan the LIDAR output signal by changing the phase differential α. The range of angles over which the LIDAR output signal can be scanned is ϕR and, in some instances, extends from ϕv to −ϕv with ϕ=0° being measured in the direction of the LIDAR output signal when α=0. When the value of Δl is not zero, the length differential causes diffraction such that light of different wavelengths travels away from chip in different directions (θ). Accordingly, there may be some spreading of the outgoing LIDAR signal as it travels away from the chip. Further, changing the level of diffraction changes the angle at which the outgoing LIDAR signal travels away from the chip when α=0°. However, providing the steering waveguides with a length differential (Δl≠0) can simplify the layout of the steering waveguides on the chip.
The alternate waveguides 102 are constructed such that different alternate waveguides 102 guide the outgoing LIDAR signal to different locations on an input side of the splitter 110. The splitter is constructed such that the output signals enter the steering waveguides 112 with a phase differential that changes in response to the location where the outgoing LIDAR signal enters the splitter 110. As a result, the phase differential between the output signals changes based on which alternate waveguide the outgoing LIDAR signal uses to enter the splitter 110. The splitter 100 can be wavelength independent in contrast to a demultiplexer. Examples of wavelength independent splitters where the phase differential between the output signals changes in response to the location where the outgoing LIDAR signal enters the splitter 110 include, but are not limited to, star couplers.
Since the phase differential between the output signals changes based on the alternate waveguide the outgoing LIDAR signal uses to enter the splitter 110, the direction that resulting LIDAR output signal travels away from the redirection component is a function of the alternate waveguide 102 that the outgoing LIDAR signal uses to enter the splitter 110. As a result, the LIDAR output signal can be associated with different alternate waveguides 102. For instance,
Because the optical switch 100 can also be used to affect the phase differential between adjacent output signals at the facet 18 of adjacent steering waveguides, the phase differential between adjacent output signals at the facet 18 of adjacent steering waveguides can be a function of one or more factors selected from the group consisting of construction of the splitter 110, construction of the steering waveguides 112, the operation of any phase tuners 104, and the alternate waveguide 102 to which the outgoing LIDAR signals is directed. As a result, the direction that the LIDAR output signal travels away from the redirection component 103 is a function of one or more factors selected from the group consisting of construction of the splitter 110, construction of the steering waveguides 112, the operation of any phase tuners 104, and the alternate waveguide 102 to which the outgoing LIDAR signals is directed.
More than one of these factors can be used to tune the direction of the outgoing LIDAR signal. For instance, the optical switch 100 and the phase tuners 104 can be used together to tune the direction of the LIDAR output signal. Each of the LIDAR output signals labeled LOSn in
A variety of approaches can be used to increase the angular ranges for the LIDAR output signal modes (LOSn). For instance, increasing the separation between the waveguides 102 can increase the angular ranges for the LIDAR output signal modes (LOSn).
When the selection of the alternate waveguide 102, the construction of the splitter 110 and steering waveguides 112 and the operation of any phase tuners 104 is such that the phase differential between adjacent output signals at the facet 18 of adjacent steering waveguides 112 changes linearly, the resulting LIDAR output signals are collimated. When the selection of the alternate waveguide 102, the construction of the splitter 110 and steering waveguides 112 and the operation of any phase tuners 104 is such that the phase differential between adjacent output signals at the facet 18 of adjacent steering waveguides 112 changes non-linearly, the resulting LIDAR output signals can be focused. Accordingly, the level of divergence, collimation, or focus can be selected by construction of one or more factors selected from the group consisting of the selection of the alternate waveguide 102, the construction of the splitter 110, construction of the steering waveguides 112 and the operation of any phase tuners 104.
The LIDAR output signal can be reflected off an object located off of the chip. At least a portion of the reflected signal travels from the back into the steering waveguides 112 and enters the alternate waveguide 102 from which the outgoing LIDAR signal originated as a LIDAR input signal or incoming LIDAR signal. The alternate waveguide 102 guides the LIDAR input signal to the optical switch 100 which directs the LIDAR input signal back to the utility waveguide 16. The chip and electronics can then process the LIDAR input signal as described elsewhere in this application.
During operation of the system, the electronics can delay switching the alternate waveguide 102 that receives the outgoing LIDAR signal until the chip has received the reflected LIDAR input signal that is needed for the desired processing. As a result, the LIDAR output signal and the associated LIDAR input signal are guided by the same alternate waveguide 102.
The optical switch 100 may be monolithically integrated on the same LIDAR chip, or may be separate from the LIDAR chip and connected by an optical fiber.
Other embodiments, combinations and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.
This Patent Application is a Divisional of U.S. patent application Ser. No. 16/277,790, filed on Feb. 15, 2019, entitled “Optical Switching for Tuning Direction of LIDAR Output Signals” and incorporated herein in its entirety; and U.S. patent application Ser. No. 16/277,790 claims the benefit of U.S. Provisional Patent Application Ser. No. 62/689,716, filed on Jun. 25, 2018, entitled “Optical Sensor System” and incorporated herein in its entirety.
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| Number | Date | Country | |
|---|---|---|---|
| 20220342048 A1 | Oct 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62689716 | Jun 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16277790 | Feb 2019 | US |
| Child | 17858977 | US |
