LIDAR System with a Multi-Mode Waveguide Photodetector

Abstract

Provided is a light detection and ranging (LIDAR) device that includes a light source configured to emit a light beam. The LIDAR device further includes free-space optics configured to receive a first portion of the light beam as a target signal and a second portion of the light beam as a local oscillator signal, and to combine the target signal and the local oscillator signal. The LIDAR device includes a multimode (MM) waveguide configured to receive the combined signal.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 375,511, filed Apr. 4, 2019, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure generally relates to light detection and ranging (LIDAR) for providing simultaneous measurement of range and velocity across two dimensions. Background Art

[0004] Fast steering mirrors are the main components used to illuminate scenes in most conventional LIDAR systems. One mirror typically scans rapidly along the X direction (azimuth), while the other mirror scans slowly along the Y direction (elevation). Optical emission and detection of the reflected light from the target are typically done coaxially via a single-mode fiber. The collected light has a measurement delay or altered frequency signature for extracting range and potentially velocity information. When the range information detected point-by-point is combined with the angular position feedback from the scanning mirror, a 3D point cloud can be established.

[0005] To achieve a higher frame rate, the angular velocity of the mirrors is increased, particularly for the scanner in the faster scanning direction (in this case the X scanner). When using mirrors with high angular velocity and single-mode fiber-based detection, the target signal from distant objects degrades severely. The signal degradation is mainly due to the difference in the angular position of the scanner mirror from the time of emission of the optical signal (pulse or swept frequency) until the collection time of the same signal from the distant scattering target. This slight angular change causes walk-off of the target signal at the fiber tip, thereby reducing the coupling efficiency, which manifests itself as a weaker signal detection. This degradation becomes more severe as the fiber diameter decreases, such as for a single-mode fiber with a diameter of ~10 μm, or as the angular velocity of the mirror increases. Summary of the Invention

[0006] The present disclosure includes, but is not limited to, the following example implementations.

[0007] Some example implementations provide a light detection and ranging device, i.e., a LIDAR device, that includes a light source configured to emit a light beam. The LIDAR device includes free-space optics configured to: receive a first portion of the light beam as a target signal and a second portion of the light beam as a local oscillator signal, and combine the target signal and the local oscillator signal. The LIDAR device may further include a multimode (MM) waveguide configured to receive the combined signal.

[0008] Some example implementations provide a method that includes: generating, by a light source of a light detection and ranging system, i.e., a LIDAR system, a light beam toward a target. The method includes receiving, by the LIDAR system, a target signal associated with a reflection of the light beam by the target and a local oscillator signal associated with a reflection of the light beam by a free space optical device. The method further includes combining the target signal and the local oscillator signal into a multimode waveguide, i.e., an MM waveguide.

[0009] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description and the accompanying drawings briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements set forth in the present disclosure, regardless of whether those features or elements are explicitly combined or otherwise recited in a particular example implementation described herein. Unless the context of the present disclosure clearly dictates otherwise, the present disclosure is intended to be read as a whole such that any separable feature or element thereof should be considered combinable in any aspect and example implementation.

[0010] Accordingly, it should be understood that the present invention content is provided only to summarize some example implementations to provide a basic understanding of some aspects of the present disclosure. Accordingly, it should be understood that the above example implementations are merely examples and should not be construed as narrowing the scope or spirit of the present disclosure in any way. Other example implementations, aspects, and advantages will become apparent from the following detailed description in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of some of the described example implementations. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The embodiments and implementations of the present disclosure will be more fully understood from the following detailed description and the accompanying drawings of various aspects and implementations of the present disclosure. However, the present disclosure should not be limited to the specific embodiments or implementations, but is only for explanation and understanding.

[0012] Figure 1 A LIDAR system is shown in accordance with an example implementation of the present disclosure.

[0013] Figure 2 Aspects of an optical circuit of a scanning system are shown in accordance with an embodiment of the present disclosure.

[0014] Figure 3 Aspects of a LIDAR system are shown in accordance with an embodiment of the present disclosure.

[0015] Figure 4 Aspects of a LIDAR system having multiple light sources are shown in accordance with an embodiment of the present disclosure.

[0016] Figure 5A A diagram of an example demultiplexer is shown in accordance with an embodiment of the present disclosure.

[0017] Figure 5B Illustrated is an example demultiplexer in accordance with some embodiments of the present disclosure.

[0018] Figure 6 Aspects of an optical circuit of a scanning system are shown.

[0019] Figure 7A Aspects of a LIDAR system having multiple light sources for generating multiple light beams in accordance with embodiments of the present disclosure are shown.

[0020] Figure 7B Aspects of a LIDAR system having multiple light sources for generating multiple light beams in accordance with other embodiments of the present disclosure are shown.

[0021] Figure 8 A flowchart depicting a method for combining a target signal and a local oscillator signal into a multimode waveguide in accordance with an implementation of the present disclosure is shown. DETAILED DESCRIPTION

[0022] Example implementations of the present disclosure relate to an improved scanning LIDAR system. Example implementations of the present disclosure are a type of LIDAR that is based on using frequency modulation (FM) and coherent detection to overcome the disadvantages of traditional LIDAR systems and the limitations of existing FM LIDAR systems. Historically, FM LIDAR systems have suffered significant losses in the return path of the light beam; thus, such systems, which are typically quite bulky, require higher average light beam output power to measure distances comparable to time-of-flight (TOF) LIDAR systems. However, the range is limited by the operating distance of the eye-safe output power.

[0023] Example implementations of the present disclosure are configured to simultaneously measure range and velocity using coherent detection and have the additional benefit of immunity to crosstalk from other LIDAR systems. Other implementations may be used with non-coherent systems to improve range, frame rate, or detection. Example implementations minimize optical losses in the return path of the light beam, thereby increasing the measurement range of the system. Additionally, by using non-degenerate light sources, example implementations can utilize the well-established wavelength division multiplexing (WDM) technology commonly used in integrated silicon photonics, which is a desirable platform due to its compactness and relative stability under varying environmental conditions.

[0024] As described above, eccentricity at the fiber tip when the target signal returns is a major source of degradation in coupling efficiency. To mitigate the obstructive effect of the eccentric return light at the fiber tip, a conventional FM LIDAR system can combine the local oscillator (LO) signal and the target signal into a single-mode (SM) waveguide. The combined signal can then be provided to an optical photodetector. Generally, the efficiency of combining the target signal and the LO signal is based on the spatial overlap between the LO signal and the target signal on the photodetector. Since the mode field diameter of the SM waveguide is relatively small, coupling the target signal to the SM waveguide is extremely challenging and difficult to fabricate. Additionally, the SM waveguide does not compensate for time-dependent detrimental effects of coaxial beam scanning, such as insufficient de-scan or signal deviation.

[0025] Example implementations of the present disclosure address the above and other deficiencies by combining the LO signal and the target signal by an FM LIDAR system and providing the combined signal to a multimode (MM) waveguide. The polarization state of the light exiting the system can be transformed with a polarization waveplate of free-space optics. After the polarization waveplate, a portion of the light can be reflected back towards the system as the LO signal, while the remaining light travels into the environment and can be reflected back as the target signal by one or more objects within the field of view (FOV) of the system. The free-space optics can be configured to combine the LO signal and the received target signal to generate a combined signal. In the free-space optics, the target signal interferes with the LO signal to form the combined signal. Since the polarization state of the combined signal is transformed, the combined signal can be reflected by a polarization beam splitter to one or more MM waveguides having a larger mode area relative to the SM waveguide. The combined signal can then be provided to one or more waveguide photodetectors (WGPD).

[0026] Accordingly, by providing the combined signal to the MM waveguide, the performance of the FM LIDAR system is improved. Since the MM waveguide has a larger mode area compared to the SM waveguide, coupling the combined signal to the MM waveguide is more efficient compared to a conventional FM LIDAR system utilizing an SM waveguide, thereby improving the performance and manufacturability of the FM LIDAR system. Additionally, using the MM waveguide to receive the combined signal can help compensate for insufficient de-scan effects and deviations that may be inherent in a coaxial LIDAR system, thereby further improving the performance of the FM LIDAR system.

[0027] Figure 1 FIG. 100 shows a LIDAR system 100 according to an example implementation of the present disclosure. The LIDAR system 100 includes one or more of each of a plurality of components, but may include Figure 1Fewer or additional components than shown. The LIDAR system 100 can be implemented in any sensing market, such as but not limited to transportation, manufacturing, metrology, medical, and security systems, etc. For example, in the automotive industry, the described beam delivery system becomes the front end of a frequency-modulated continuous-wave (FMCW) device, which can assist in the spatial perception of an autonomous driver assistance system or an autonomous vehicle. As shown, the LIDAR system 100 includes an optical circuit 101 implemented on a photonic chip. The optical circuit 101 can include a combination of active optical components and passive optical components. The active optical components can generate, amplify, or detect optical signals, etc. In some examples, the active optical circuit includes optical beams of different wavelengths, one or more optical amplifiers, or one or more optical detectors, etc.

[0028] The free-space optical device 115 can include one or more optical waveguides to carry optical signals and route and manipulate the optical signals to appropriate input / output ports of the active optical circuit. The free-space optical device 115 can also include one or more optical components, such as taps, wavelength division multiplexers, beam splitters / combiners, polarization beam splitters, collimators, etc. In some embodiments, as further discussed below, the free-space optical device 115 can include components for transforming the polarization state and guiding the received polarized light to an optical detector using a PBS.

[0029] The optical scanner 102 includes one or more scanning mirrors that can rotate along corresponding orthogonal axes to manipulate the optical signal to scan the environment according to a scanning pattern. For example, the scanning mirror can be rotated by one or more galvanometers. The optical scanner 102 also collects the light incident on any object in the environment into a return beam, which is returned to the passive optical circuit components of the optical circuit 101. For example, the return beam can be guided to an optical detector by a polarization beam splitter. In addition to the mirror and galvanometer, the optical scanning system can include components such as quarter-wave plates, lenses, or anti-reflection coated windows.

[0030] To control and support the optical circuit 101 and the optical scanner 102, the LIDAR system 100 includes a LIDAR control system 110. The LIDAR control system 110 may include processing means for the LIDAR system 100. In an embodiment, the processing means may be one or more general-purpose processing means, such as a microprocessor or a central processing unit. More particularly, the processing means may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computer (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or a processor for implementing other instruction sets, or a processor for implementing a combination of instruction sets. The processing means may also be one or more dedicated processing means, such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), or a network processor.

[0031] In some embodiments, the LIDAR control system 110 may include a signal processing unit 112, such as a digital signal processor. The LIDAR control system 110 is configured to output digital control signals to control the optical driver 103. In some embodiments, the digital control signals may be converted into analog signals by a signal conversion unit 106. For example, the signal conversion unit 106 may include a digital-to-analog converter. The optical driver 103 may then provide drive signals to the active components of the optical circuit 101 to drive light sources such as lasers and amplifiers. In some embodiments, a plurality of optical drivers 103 and signal conversion units 106 may be provided to drive multiple light sources.

[0032] The LIDAR control system 110 is also configured to output digital control signals for the optical scanner 102. The motion control system 105 may control the galvanometer of the optical scanner 102 based on the control signals received from the LIDAR control system 110. For example, a digital-to-analog converter may convert the coordinate routing information from the LIDAR control system 110 into signals interpretable by the galvanometer in the optical scanner 102. In some embodiments, the motion control system 105 may also return information related to the position or operation of the components of the optical scanner 102 to the LIDAR control system 110. For example, an analog-to-digital converter may further convert the information related to the position of the galvanometer into signals interpretable by the LIDAR control system 110.

[0033] The LIDAR control system 110 is also configured to analyze the input digital signal. In this regard, the LIDAR system 100 includes an optical receiver 104 to measure one or more light beams received by the optical circuit 101. For example, a reference beam receiver can measure the amplitude of the reference beam from the active optical circuit, and an analog-to-digital converter converts the signal from the reference receiver into a signal interpretable by the LIDAR control system 110. The target receiver measures an optical signal carrying information related to the range and velocity of the target in the form of a beat frequency modulated optical signal. The reflected beam can be mixed with a second signal from a local oscillator. The optical receiver 104 can include a high-speed analog-to-digital converter to convert the signal from the target receiver into a signal interpretable by the LIDAR control system 110.

[0034] In some applications, the LIDAR system 100 can additionally include one or more imaging devices 108 configured to capture an image of the environment, a global positioning system 109 configured to provide the geographical location of the system, or other sensor inputs. The LIDAR system 100 can also include an image processing system 114. The image processing system 114 can be configured to receive the images and geographical locations and send these images and locations or information related thereto to the LIDAR control system 110 or other systems connected to the LIDAR system 100.

[0035] In operation according to some examples, the LIDAR system 100 is configured to simultaneously measure range and velocity in two dimensions using a non-degrading light source. This capability enables real-time, remote measurements of the range, velocity, azimuth, and elevation of the surrounding environment. In some example implementations, the system directs multiple modulated light beams at the same target.

[0036] In some examples, the scanning process starts from the optical driver 103 and the LIDAR control system 110. The LIDAR control system 110 instructs the optical driver 103 to independently modulate one or more light beams, and these modulated signals propagate through the passive optical circuit to the collimator. The collimator directs the light at the optical scanning system, which scans the environment according to a pre-programmed pattern defined by the motion control subsystem. The optical circuit can also include a polarization wave plate for transforming the polarization of the light when it exits the optical circuit 101. In an embodiment, the polarization wave plate can be a quarter-wave plate or a half-wave plate. A portion of the polarized light can also be reflected back into the optical circuit 101. For example, a lens or collimation system can have a natural reflection property or a reflective coating for reflecting a portion of the light back into the optical circuit 101.

[0037] The optical signal reflected from the environment passes through the optical circuit 101 and reaches the receiver. Since the polarization of the light has been transformed, it can be reflected by the polarization beam splitter together with the part of the polarized light that is reflected back to the optical circuit 101. Therefore, the reflected light is reflected to a separate optical receiver instead of returning to the same optical fiber or waveguide as the light source. These signals interfere with each other and generate a combined signal. Each beam signal returning from the target generates a time-shifted waveform. The time phase difference between the two waveforms generates a beat frequency measured on the optical receiver (photo-detector). Then, the combined signal can be reflected to the optical receiver 104. The configuration of the optical circuit 101 for polarizing the light beam and guiding it to the optical receiver 104 is further described below.

[0038] The analog signal from the optical receiver 104 is converted to a digital signal using an ADC. Then the digital signal is sent to the LIDAR control system 110. Then, the signal processing unit 112 can receive these digital signals and interpret them. In some embodiments, the signal processing unit 112 also receives position data from the motion control system 105 and the galvanometer (not shown) and image data from the image processing system 114. Then, the signal processing unit 112 can generate a 3D point cloud with information related to the range and velocity of points in the environment as the optical scanner 102 scans additional points. The signal processing unit 112 can also overlay the 3D point cloud data with the image data to determine the velocity and distance of objects in the surrounding area. The system also processes satellite-based navigation position data to provide an accurate global position.

[0039] Figure 2 Aspects of the optical circuit 200 of the scanning system are shown. For example, according to some example implementations, Figure 2 the optical circuit 200 can be a part of the optical circuit 101 of the LIDAR system 100 as shown with respect to Figure 1 As shown, the light source 202 is configured to provide a light beam such as a laser beam to the passive optical components of the LIDAR system. For example, the light source 202 can be a laser source. The light beam can pass through a polarization beam splitter (PBS) 214 as unpolarized light. After passing through the PBS 214, the light beam can enter the free space optics 212. In an embodiment, the free space optics 212 can include a lens 210 and a polarization wave plate 208. The lens 210 can be used to converge / collimate the light. The polarization of the light beam can be transformed by using the polarization wave plate 208. Then, the polarization of the light beam will be transformed into circular polarization. In an embodiment, the polarization wave plate 208 can reflect a part of the polarized light back to the light source 202. In some embodiments, a separate mirror, microlens array, filter, or reflective coating on the lens 210 or the polarization wave plate 208 can be used. The reflected part of the light becomes a local oscillator for interfering with the return light from the target.

[0040] Although the present figure shows a particular arrangement of the lens 210 and the polarization wave plate 208 of the free space optical device 212, in other embodiments, the lens 210, the polarization wave plate 208, and any other components of the free space optical device 212 can be arranged in various configurations. For example, the free space optical device 212 can be configured such that the light beam passes through the polarization wave plate 208 and reaches the lens 210. In some embodiments, the lens 210 can also reflect a portion of the polarized light back to the light source 202. In some embodiments, the polarization wave plate 208 can be located before the PBS 214. Then, the tilt angle of the PBS 214 can be adjusted such that a portion of the light beam is redirected towards the WGPD 204 as a local oscillator signal.

[0041] After passing through the polarization wave plate 208, the light beam is transmitted to the environment, and a portion of the pulse can be reflected back from one or more objects. For example, the light can be transmitted to the environment in a raster pattern through one or more fast steering mirrors as discussed with respect to Figure 1 A portion of the reflected light can return in the direction of the light source 202 as a target signal. The free space optical device 212 can be configured to combine the received target signal with the local oscillator signal to generate a combined signal that is spatially aligned and co-propagating. Since the combined signal including the target signal and the local oscillator signal is polarized, when the combined signal returns to the polarization beam splitter 214 instead of being transmitted back to the light source 202, the combined signal is reflected to the waveguide photodetector 204. The local oscillator signal and the signal from the target have interfered to generate the combined signal. Therefore, it is not necessary to interfere these two signals with each other. Then, the combined signal can be used to interpret the distance, velocity, or other factors related to the environment at the target point.

[0042] Figure 3 Aspects of a LIDAR system 300 according to an embodiment of the present disclosure are shown. The LIDAR system 300 can include a photon chip 302, and the photon chip 302 includes one or more components in the LIDAR system 300. In an embodiment, as previously described in Figure 1 The optical circuit 101 is implemented on the photon chip 302. The optical circuit 101 can generate a light beam that passes through a single-mode waveguide 306 configured for single-mode propagation of the light beam. In some embodiments, the light beam can be provided from the SM waveguide 306 to an optional beam expander 308a configured to expand the mode area of the light beam.

[0043] When leaving the photon chip 302, as described above, the light beam can pass through a polarization beam splitter (PBS) 214. In an embodiment, a lens (not shown) can be located between the photon chip 302 and the PBS 214 to collimate the light beam before it enters the PBS 214. As previously inFigure 2 As described above, the LIDAR system 300 may also include free-space optics 212 to transform the polarization of light, reflect a portion of the light as a local oscillator signal 314, combine the target signal and the local oscillator signal, and so on.

[0044] When transforming the polarization of light, a portion of the light beam may be transmitted toward a target 316 via a scanner 312 (e.g., Figure 1 the optical scanner 102). When the light beam hits the target 316, a portion of the light beam returns to the LIDAR system 300 as a target signal 318. The target signal 318 is received by the free-space optics 212, where, as described above, the target signal 318 is combined with the local oscillator signal 314. The combined signal is then received by the PBS 214 and redirected toward a multimode (MM) waveguide 326. In an embodiment, the combined signal may be redirected from the PBS 214 to the MM waveguide 326 via one or more flip mirrors 322. In some embodiments, before entering the MM waveguide 326, the combined signal may pass through an optional beam expander 308b to expand the mode area of the combined signal. The combined signal may then pass through the MM waveguide 326, where the combined signal is received by a waveguide photodetector (WGPD) 320. The combined signal may then be used to interpret distance, velocity, or other factors related to the environment at the target point.

[0045] Figure 4 Aspects of a LIDAR system 400 having multiple light sources in accordance with embodiments of the present disclosure are shown. The LIDAR system 400 may include a photonic chip 402 that includes one or more components in the LIDAR system 400. In an embodiment, the photonic chip 402 may include an optical circuit 101 as previously described in Figure 1 . The optical circuit 101 may include multiple light sources for generating light beams. In an embodiment, a first light beam may have a first wavelength (e.g., λ1), and a second light beam may have a second wavelength (e.g., λ2). When generating the light beams, the light beams may be multiplexed together by a multiplexer (MUX) 404 into a single output light beam. The multiplexed light beam may pass through a single-mode waveguide 406 configured for single-mode propagation of the light beam. In some embodiments, the light beam may be provided to a beam expander 408a configured to expand the mode area of the light beam.

[0046] When leaving the photonic chip 402, as described above, the light beam may pass through a polarization beam splitter (PBS) 414. In an embodiment, a lens (not shown) may be located between the photonic chip 402 and the PBS 414 to collimate the light beam before it enters the PBS 414. As previously described in Figure 2As described above, the LIDAR system 400 may also include free-space optics 412 to transform the polarization of the light beam, reflect a portion of the light as a local oscillator signal 422, combine the target signal 418 and the local oscillator signal 422, and so on.

[0047] When transforming the polarization of the light, a portion of the light beam may be transmitted towards the target 416 via a scanner 424 (e.g., Figure 1 the optical scanner 102). When the light beam hits the target 416, a portion of the light beam returns to the LIDAR system 400 as the target signal 418. The target signal 418 is received by the free-space optics 412, where the target signal 418 is combined with the local oscillator signal 422. Then, the combined signal is received by the PBS 414 and redirected towards a demultiplexer (DEMUX) 430. The DEMUX 430 may be configured to receive the light beam and redirect a first portion of the light beam to a first location and a second portion of the light beam to a second location based on wavelength. For example, the DEMUX 430 may redirect a first portion of the light beam having a wavelength λ1 to a first location and a second portion of the light beam having a wavelength λ2 to a second location. Further details related to the DEMUX 430 are described below in Figure 5A and 5B The first combined signal including the first LO signal having wavelength λ1 and the first target signal may be redirected by the DEMUX 430 towards the first MM waveguide 426a. In some embodiments, before entering the first MM waveguide 426a, the first combined signal may pass through a beam expander 408b configured to expand the mode area of the first combined signal. Then, the first combined signal may pass through the first MM waveguide 426a, where the combined signal is received by the first waveguide photodetector (WGPD) 420a.

[0048] The second combined signal including the second LO signal having wavelength λ2 and the second target signal may be redirected by the DEMUX 430 towards the second MM waveguide 426b. In some embodiments, before entering the second MM waveguide 426a, the second combined signal may pass through a beam expander 408c configured to expand the mode area of the second combined signal. Then, the second combined signal may pass through the second MM waveguide 426b, where the combined signal is received by the second waveguide photodetector (WGPD) 420b.

[0049]

[0050] Figure 5A Figure 4 FIG. is an illustration of an example demultiplexer 500 according to an embodiment of the present disclosure. In an embodiment, the demultiplexer (DEMUX) 500 may correspond to Figure 4The DEMUX 430. The DEMUX 500 may include a dichroic mirror 502 and a flip mirror 504.

[0051] The dichroic mirror 502 may be configured to reflect / redirect a light beam of a specific wavelength while allowing light beams of different wavelengths to pass through the dichroic mirror 502. For example, the dichroic mirror 502 may be configured to redirect a light beam having a wavelength λ1 while allowing a light beam having a wavelength λ2 to pass through the dichroic mirror 502. Refer to Figure 5A , the dichroic mirror 502 is configured to redirect a light beam having a wavelength λ1 while allowing a light beam having a wavelength λ2 to pass through the dichroic mirror 502. Thus, as previously described in Figure 4 , the first portion of the combined signal including the first LO signal having a wavelength λ1 and the first target signal is redirected into the MM waveguide 426a.

[0052] As previously described in Figure 4 , the second portion of the combined signal including the second LO signal having a wavelength λ2 and the second target signal passes through the dichroic mirror 502, and the second portion of the combined signal is redirected by the flip mirror 504 into the MM waveguide 426b.

[0053] Figure 5B FIG. is a diagram of an example demultiplexer 550 according to some embodiments of the present disclosure. In an embodiment, the demultiplexer (DEMUX) 550 may correspond to Figure 4 the DEMUX 430. The DEMUX 550 may include a dispersion element 552 and flip mirrors 554 and 556.

[0054] The dispersion element 552 may be formed of one or more materials configured to disperse a portion of a light beam at different angles based on the wavelength of the light beam. For example, the dispersion element 552 may be configured to direct a first portion of the light beam having a wavelength λ1 at a first angle and a second portion of the light beam having a wavelength λ2 at a second angle. Refer to Figure 5B , the dispersion element 552 is configured to direct a first portion of the light beam having a wavelength λ1 at a first angle toward the flip mirror 554 and a second portion of the light beam having a wavelength λ2 at a second angle toward the flip mirror 556. The flip mirror 554 may be configured to redirect the first portion of the light beam into the first MM waveguide 426a, and the flip mirror 556 may be configured to redirect the second portion of the light beam into the second MM waveguide 426b.

[0055] Thus, the first portion of the combined signal including the first LO signal having a wavelength λ1 and the first target signal is redirected by the dispersion element 552 to the flip mirror 554 and into the MM waveguide 426a. As previously described in Figure 4As described in , the second part of the combined signal including the second LO signal having wavelength λ2 and the second target signal is redirected by the dispersion element 552 to the flip mirror 556 and enters the MM waveguide 426b.

[0056] Figure 6 Aspects of the optical circuit 600 of the scanning system are shown. For example, according to some example implementations, Figure 6 the optical circuit 600 can be part of the optical circuit 101 of the LIDAR system 100 as shown with respect to Figure 1 As shown, the optical circuit 600 includes a plurality of light sources 602a, 602b and a plurality of WGPDs 604a, 604b. The plurality of light sources 602a, 602b and WGPDs 604a, 604b can provide a plurality of data points during a single time interval. Thus, fewer rotations of the fast steering mirror can provide additional data. The remainder of the optical circuit 600 can be the same or similar to those described above with reference to Figure 2 For example, the optical circuit 600 can include free space optics 412 which has a polarization wave plate 608 for transforming the polarization of light and a lens 610 for collimating light, etc. In some embodiments, the alignment of the PBS 414 can be set such that the light sources 602a, 602b and WGPDs 604a, 604b are aligned when the return light is reflected. In some embodiments, there can be a plurality of light sources 602a, 602b, a plurality of WGPDs 604a, 604b, and there can also be a plurality of PBSs 414. The signals received at the WGPDs 604a, 604b respectively can be analyzed separately to generate distance or velocity data at a certain point. In some embodiments, the light sources 602a, 602b can provide light beams of different wavelengths.

[0057] Figure 7A Aspects of a LIDAR system 700 having a plurality of light sources for generating a plurality of light beams according to an embodiment of the present disclosure are shown. The components of the LIDAR system 700 can be similar to the components of the LIDAR system 400. However, instead of having two light sources each generating one light beam, two light sources each generate two light beams. For example, the first light source can generate a first light beam having a first wavelength and a second light beam having a second wavelength. Similarly, the second light source can generate a third light beam having a third wavelength and a fourth light beam having a fourth wavelength.

[0058] The light beams generated by the first light source can be multiplexed together by MUX 404a, and the light beams generated by the second light source can be multiplexed together by MUX 404b. Then, as described above, the multiplexed light beam from the first light source (e.g., source 1) and the multiplexed light beam from the second light source (e.g., source 2) are directed towards the target 416. The target signal 418 is received and combined with the LO signal 422. The combined signal is redirected by PBS 414 towards DEMUX 430. DEMUX 430 is configured to separate the combined signal based on wavelength and light source. For example, DEMUX 430 can separate the first portion of the combined signal corresponding to the first wavelength (e.g., λ1) from the first light source (e.g., source 1) and direct the first portion of the combined signal towards MM waveguide 426a. DEMUX 430 can separate the second portion of the combined signal corresponding to the first wavelength from the second light source and direct the second portion of the combined signal towards MM waveguide 426b. DEMUX 430 can also separate the third portion of the combined signal corresponding to the second wavelength (e.g., λ2) from the first light source and direct the third portion of the combined signal towards MM waveguide 426c. DEMUX 430 can also separate the fourth portion of the combined signal corresponding to the second wavelength from the second light source and direct the fourth portion of the combined signal towards MM waveguide 426d.

[0059] Although described as having two light sources for generating multiple light beams, embodiments of the present disclosure can utilize any number of laser sources for generating multiple light beams of different wavelengths. For example, aspects of the present disclosure can be utilized by a LIDAR system having a single light source for generating two or more light beams of different wavelengths.

[0060] Figure 7B Aspects of a LIDAR system 750 having multiple light sources for generating multiple light beams are shown in accordance with other embodiments of the present invention. The components of LIDAR system 750 can be similar to the components of LIDAR system 700. However, in Figure 7B stead of having a single set of passive optical circuits utilized by multiple light sources, each light source can have a corresponding set of passive optical circuits. For example, the first light source can have a corresponding PBS 414a, free space optics 412a, and scanner 424a, and the second light source can have a corresponding PBS 414b, free space optics 412b, and scanner 424b. Similarly, each light source can have, as previously described in Figure 4The corresponding DEMUX (e.g., DEMUX 430a and 430b) for separating the received combined signal based on wavelength as described with respect to FIGS. 1-5. For clarity, the optional beam expanders are not shown before the MM waveguides 418a-418d. However, in some embodiments, the beam expanders may be located on the photon chip 402 before the MM waveguides 418a-418d.

[0061] Although described as having two light sources for generating multiple light beams, embodiments of the present disclosure may utilize any number of laser sources for generating multiple light beams of different wavelengths. For example, aspects of the present disclosure may be utilized by a LIDAR system having a single light source for generating two or more light beams of different wavelengths.

[0062] Figure 8 A flowchart depicting a method 800 for combining a target signal and a local oscillator signal into a multimode waveguide according to an implementation of the present disclosure. In an embodiment, various parts of the method 800 may be performed separately by Figure 1 , Figure 3 and Figure 4 of the LIDAR systems 100, 300, and / or 400.

[0063] Referring to Figure 8 , method 800 illustrates example functions used by various embodiments. Although specific function boxes ("boxes") are disclosed in method 800, such boxes are examples. That is, embodiments are well-suited to perform various other boxes or variations of the boxes defined in method 800. It should be understood that the boxes in method 800 may be performed in an order different from the presented order, and not all boxes in method 800 may be performed.

[0064] At block 802, a light source of the LIDAR system generates a light beam towards the target. In an embodiment, multiple light sources may generate multiple light beams. In some embodiments, the multiple light beams may have different wavelengths. As previously described, the generated light beams may pass through the PBS and free space optics towards the target. In an embodiment, the polarization of one or more light beams may be transformed by a polarization waveplate.

[0065] At block 804, the LIDAR system receives a target signal associated with the reflection of the light beam by the target. As previously described at Figure 2 and Figure 6 , the LIDAR system may also receive a local oscillator signal associated with the reflection of the light beam by the free space optics. In an embodiment, multiple target signals and multiple local oscillator signals generated by multiple light sources may be received by the LIDAR system.

[0066] At block 806, the LIDAR system combines the target signal and the local oscillator signal into a multimode (MM) waveguide. In an embodiment, the free-space optics of the LIDAR system can be configured to combine the target signal and the local oscillator signal such that the signals are spatially aligned and propagate in the same direction. The combined signal can be redirected towards the MM waveguide via a PBS and / or one or more folding mirrors. In an embodiment, the combined signal can then be provided to a waveguide photodetector via the MM waveguide. In some embodiments, the waveguide photodetector and the MM waveguide can reside on the same photonic chip.

[0067] In embodiments that utilize multiple light sources to generate multiple beams, a DEMUX can be utilized to direct a first combined signal having a first wavelength into a first MM waveguide and a second combined signal having a second wavelength into a second MM waveguide. In some embodiments, as previously described in Figure 5A the DEMUX can include a dichroic mirror and a folding mirror. In an embodiment, as previously described in Figure 5B the DEMUX can include a dispersive element and one or more folding mirrors.

[0068] The foregoing description sets forth numerous specific details, such as examples of specific systems, components, methods, etc., to provide a good understanding of several embodiments of the present disclosure. However, it will be apparent to those skilled in the art that at least some embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known components or methods have not been described in detail or are presented in a simple block diagram format to avoid unnecessarily obscuring the present disclosure. Accordingly, the specific details set forth are merely exemplary. Specific embodiments may vary from these exemplary details and still be considered within the scope of the present disclosure.

[0069] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" throughout this specification are not necessarily all referring to the same embodiment. Additionally, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or".

[0070] Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method can be altered such that certain operations can be performed in a reverse order, or such that certain operations can be at least partially concurrent with other operations. In another embodiment, the instructions or sub-operations of different operations can be in an intermittent or alternating manner.

[0071] The foregoing description of the illustrated implementations of the invention (including what is described in the abstract) is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific implementations and examples of the invention are described herein for illustrative purposes, various equivalent modifications within the scope of the invention will be apparent to those skilled in the relevant art. The words "example" or "exemplary" are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "example" or "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, the use of the words "example" or "exemplary" is intended to present concepts in a concrete fashion. As used in this application, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or". That is, unless otherwise specified or clear from the context, "X includes A or B" is intended to mean any natural inclusive arrangement. That is, if X includes A; X includes B; or X includes both A and B, then "X includes A or B" is satisfied in any of the foregoing instances. In addition, the articles "a" and "an" as used in this application and the appended claims should generally be construed to mean "one or more" unless otherwise specified or clear from the context to refer to the singular form. Further, the use throughout the text of the terms "embodiment" or "an embodiment" or "implementation" or "an implementation" is not intended to refer to the same embodiment or implementation unless so described. Additionally, as used herein, the terms "first", "second", "third", "fourth", etc. are meant as labels to distinguish between different elements and may not necessarily have the ordinal meaning indicated by their numerical designation.

Claims

1. A light detection and ranging device, namely a LIDAR device, comprising: A light source configured to emit a light beam; Free space optics configured to: Receive a first portion of the light beam as a target signal and a second portion of the light beam as a local oscillator signal, and Combine the target signal and the local oscillator signal into a combined signal; One or more multimode waveguides, namely one or more MM waveguides; And A demultiplexer comprising a dispersive element, the demultiplexer being configured to: Disperse the combined signal of each respective wavelength at a corresponding angle via the dispersive element, and Reflect the combined signal of each respective wavelength to a corresponding MM waveguide among the one or more MM waveguides.

2. The LIDAR device according to claim 1, further comprising: A polarization beam splitter configured to allow light in a first polarization state to pass through the polarization beam splitter in a first direction and reflect light in a second polarization state, different from the first direction, in a second direction.

3. The LIDAR device according to claim 2, further comprising: A second lensified optics configured to collimate the light beam passing through the polarization beam splitter.

4. The LIDAR device according to claim 1, further comprising: A waveguide photodetector configured to receive the combined signal from the one or more MM waveguides.

5. The LIDAR device according to claim 4, wherein, The light source, the waveguide photodetector, and the one or more MM waveguides are located on a photonic chip.

6. The LIDAR device according to claim 1, wherein, The free space optics includes a polarization wave plate configured to transform the polarization state of the light beam and a lens configured to collimate the light beam.

7. The LIDAR device according to claim 6, wherein, The polarization wave plate includes one of a quarter-wave plate and a half-wave plate.

8. The LIDAR device according to claim 6, wherein, The polarization wave plate further includes a reflector or coating for returning the second portion of the light beam as the local oscillator signal.

9. The LIDAR device according to claim 1, further comprising: A second light source for emitting a second light beam, wherein a first wavelength of the light beam is different from a second wavelength of the second light beam.

10. The LIDAR device according to claim 9, wherein The demultiplexer includes a dichroic mirror configured to reflect the light beam of the first wavelength and allow the second light beam of the second wavelength to pass through the dichroic mirror.

11. The LIDAR device according to claim 9, wherein The dispersive element is configured to direct the light beam of the first wavelength towards a first flip mirror and direct the second light beam of the second wavelength towards a second flip mirror.

12. The LIDAR device according to claim 9, further comprising: A second waveguide photodetector configured to receive a second combined signal associated with the second light beam.

13. A method for a light detection and ranging system, comprising: Generating, by a light source of a light detection and ranging system, namely a LIDAR system, a light beam towards a target; Receiving, by the LIDAR system, a target signal associated with the reflection of the light beam by the target and a local oscillator signal associated with the reflection of the light beam by free space optics; Combine the target signal and the local oscillation signal into a combined signal; Disperse the combined signal of each corresponding wavelength at a corresponding angle via the dispersion element of the demultiplexer; And Reflect the combined signal of each corresponding wavelength to the corresponding MM waveguide in one or more multimode waveguides, i.e., one or more MM waveguides, via the dispersion element of the demultiplexer.

14. The method according to claim 13, further comprising: Receiving the combined signal from the one or more MM waveguides by a waveguide photodetector.

15. The method according to claim 14, wherein, The LIDAR system, the one or more MM waveguides, and the waveguide photodetector are on a photonic chip.

16. The method according to claim 13, wherein, Generating the light beam includes: Transforming the polarization state of the light beam by the free space optical device.

17. The method according to claim 13, further comprising: Generating a second light beam towards the target by a second light source of the LIDAR system, wherein the second light beam has a wavelength different from that of the light beam; Receiving, by the LIDAR system, a second target signal associated with the second light beam reflected by the target and a second local oscillation signal associated with the light beam reflected by the free space optical device; and Combining the second target signal and the second local oscillation signal into a second combined signal.

18. The method according to claim 17, wherein The second target signal and the second local oscillation signal pass through a dichroic mirror configured to reflect light of a first wavelength associated with the light beam to a flip mirror configured to reflect a second light beam of a second wavelength into an MM waveguide.

19. The method according to claim 17, wherein, The second target signal and the second local oscillation signal pass through the dispersion element configured to direct the second target signal and the second local oscillation signal to a flip mirror configured to reflect the second target signal and the second local oscillation signal into an MM waveguide.

20. The method according to claim 17, further comprising: Receiving the second combined signal from the MM waveguide by a second waveguide photodetector.

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