Multiplexed light detection and rangefinder

Abstract

A multiplexed line scanning LiDAR system generates a line scan of an object based on measured distances from various points to the object. This multiplexed line scanning LiDAR uses at least one set of light source emission to an optical fiber laser element to form a line scanning pattern and determine the distance and velocity of the object.

Description

[Technical Field]

[0001] This disclosure relates to U.S. Patent No. 11,294,040, issued on April 5, 2022, and U.S. Patent Application No. 17 / 708,728, both of which are incorporated herein by reference in their entirety and assigned to a common assignee.

[0002] This application is a continuation-in-part application of U.S. Patent Application No. 17 / 950,178, filed on 22 September 2022, which is assigned by reference in its entirety to the common assignee.

[0003] This disclosure generally relates to optical detection and ranging systems. More specifically, this disclosure relates to an optical detection and ranging system that generates multiple laser beams from a single light source, scans these multiple laser beams at one or more targets, and provides a hybrid scanner that receives the back-reflected laser beams into a multiplexed interferometer circuit to measure distance and velocity. Further specifically, this disclosure relates to an optical detection and ranging method, including a method for multiplexing interferometry techniques when measuring distance and velocity. Further specifically, this disclosure relates to an optical detection and ranging circuit and system that provides a multiplexed line scanning circuit and system. [Background technology]

[0004] LiDAR (Light Detection and Ranging) is similar to radar (Radio Wave Detection and Ranging) in that it uses light waves to determine the distance, angle, and velocity of an object. LiDAR utilizes differences in the return time and wavelength of laser light to represent objects in three dimensions digitally, and is used in a wide range of applications including ground, air, and mobile. A LiDAR system consists of one or more laser oscillators, an optical system, a scanner, a photodetector, and a signal processing unit. A coherent light beam generated from one or more laser oscillators is transferred to the scanner via a series of optical systems and transmitted to the object to determine its distance or velocity. In the case of three-dimensional (3D) scanning, its physical properties are determined. The photodetector receives the coherent light reflected from the object and converts this coherent light into an electrical signal. This signal is processed to determine the distance to the object. The oscillator generates pulsed coherent light. The signal processing unit records the time the pulsed light was transmitted and also records the time the reflected coherent light was received. The distance to the object is calculated by dividing the difference between the transmission time and reception time by 2 and multiplying by the speed of light.

[0005] Amplitude-modulated continuous wave (AMCW) Lidar is a type of phase-difference Lidar. Unlike direct pulse detection, phase-difference Lidar emits a continuous laser signal. The laser emission amplitude is modulated with a high-speed radio frequency (RF) signal to encode the output optical signal. Distance is measured by detecting the phase difference between the emitted signal and the reflected signal. The distance to an object can be estimated by utilizing the phase shift of the sinusoidal-modulated continuous laser waveform.

[0006] Frequency-modulated continuous wave (FMCW) LiDAR is similar to AMCW LiDAR, but modulates and demodulates optically rather than electrically. FMCW LiDAR uses a tunable or phase-modulated light source and an interferometer to measure the distance to an object with high sensitivity. The frequency of the FMCW laser is linearly modulated by the carrier signal, and the round-trip time of flight of the laser is accurately measured. By detecting the beat frequency signal between the returning and emitted laser beams, the time of flight can be calculated with high accuracy, enabling highly accurate distance measurement.

[0007] Interference Time (TOI) Lidar technology is a novel ranging method that overcomes the limitations of conventional Lidar technologies such as Time of Flight (ToF) and Frequency Modulated Continuous Wave (FWCW), and has the following features: (1) It utilizes an interferometer equipped with a balanced detector that can detect weak interference signals from long distances with high sensitivity; (2) It can accurately measure the distance from an object by measuring the time delay of the interference signal even at high signal frequencies, eliminating the need for a high-speed data acquisition system; and (3) It simplifies the complexity of the light source drive circuit design because it has low requirements for phase modulation or wavelength modulation of the light source. The operating speed of a TOI Lidar system is mainly limited by the modulation speed of the light source and the efficiency of the optical receiver. The high sensitivity detection of TOI Lidar systems reduces the output power requirements of the light source. This increases the flexibility of the system architecture design, allowing multiple TOI Lidar systems to be driven using a single light source for simultaneous speed measurement. [Overview of the project]

[0008] The object of this disclosure is to provide a multiplexed optical detection and ranging (LIDAR) system based on interference time (TOI), time-frequency domain reflectance measurement, and small wavelength modulation of a coherent light source. This multiplexed LIDAR system records the time delay or interference time (TOI) of two or more interfering signals using a single coherent light source whose output wavelength is determined by the operating current or operating temperature.

[0009] To achieve this objective, the multiplexed LiDAR system has a coherent light source connected to a modulation and scanning control device. The modulation and scanning control device is configured to generate a pulse wavelength control signal that is transmitted to the coherent light source. This pulse wavelength control signal may be a current modulation signal or a laser ambient temperature adjustment signal. The pulse wavelength control signal modulates the coherent light source, generating pulse wavelength-modulated coherent emission.

[0010] A pulsed wavelength-modulated coherent emission is coupled to at least two interferometers. Each interferometer is configured to split the pulsed wavelength-modulated coherent emission into a sampling portion and a reference portion. The sampling portion of the pulsed wavelength-modulated coherent emission is positioned to be incident on the object being measured. The reference portion of the pulsed wavelength-modulated coherent emission is positioned to provide a reference basis for determining the distance from the multiplexed LIDAR system to the object. Each interferometer is further configured to transfer the pulsed wavelength-modulated coherent light to a hybrid scanner. This hybrid scanner is configured to physically transfer the sampling portion of the pulsed wavelength-modulated coherent light from each interferometer to different locations on the object, and to simultaneously scan the surface of the object with the pulsed wavelength-modulated coherent light from each interferometer. The hybrid scanner is further configured to receive portions of the pulsed wavelength-modulated coherent light that have been back-reflected from different locations on the object. The back-reflected pulsed wavelength-modulated coherent light is transferred from the hybrid scanner to each interferometer, where it is then coupled with the reference portion of the pulsed wavelength-modulated coherent light to form an optical interference signal.

[0011] The hybrid scanner is configured to provide scanning patterns for pulse-wavelength modulated coherent light from each interferometer. Each scanning pattern is configured to cover a different area on the object, thereby expanding the effective scanning range of the multiplexed LiDAR system. In various embodiments, each scanning pattern is configured to cover the same area on the object, thereby expanding the effective scanning pixel density of the multiplexed LiDAR system. The hybrid scanning mirror comprises at least one planar mirror rotating on a first axis and a faceted mirror configured to reflect sampling portions of multiple pulse-wavelength modulated coherent light from multiple interferometers onto the object. The faceted mirror rotates on a second axis to establish scanning patterns for sampling portions of the multiple pulse-wavelength modulated coherent light.

[0012] In various embodiments, the scanning pattern of the hybrid scanner is configured to provide a one-dimensional scan (also called a line scan) for the sampling portion of multiple pulse wavelength-modulated coherent light, thereby effectively increasing the frame rate.

[0013] A multiplexed Lidar system has a photodetector array configured to convert optical interference signals from each interferometer into electrical interference signals. In various embodiments, the photodetector is configured as a polarization diversity balanced amplified detector. The photodetector has at least one power monitor that measures the input power level to the photodetector. The output of this power monitor provides a power level modulated to have a time delay associated with the distance to the object.

[0014] A multiplexed Lidar system has a signal processing unit that receives electrical interference signals and converts these signals into digital data representing the amplitude of the electrical interference signals. This signal processing unit is configured to generate an imaging range based on the distance from the object to be displayed. The imaging range to be displayed is calculated by a computer system programmed to calculate the time delay determined by the optical interference signals from all interferometers.

[0015] The modulation and scanning control device is configured to generate a low-duty-time wavelength modulation control signal that modulates a coherent light source by controlling the drive current of the narrowband coherent light source, the temperature of the narrowband light source, or adjusting the phase of the light emitted from the light source. In other embodiments, the modulation and scanning control device generates a pulse phase control signal that causes interference when there is a time delay between the light of the sample arm and the reference arm of the interferometer.

[0016] In various embodiments, the interferometer includes a polarization control device used to adjust the polarization state of coherent emission from a light source and maximize the amplitude of an optical or electrical interference signal. The interferometer has a first coupler that receives pulse-wavelength modulated coherent light from the polarization control device. This coupler splits the pulse-wavelength modulated coherent light. A first portion of the pulse-wavelength modulated coherent light is supplied to at least one sample arm. A second portion of the pulse-wavelength modulated coherent light is supplied to a reference arm. The interferometer has a circulator connected to receive the first portion of the pulse-wavelength modulated coherent light from at least one sample arm. The circulator is configured so that the pulse-wavelength modulated coherent light from the sample arm enters the circulator and exits through a next port. Typically, the next port directs the pulse-wavelength modulated coherent light clockwise towards a scanner. The scanner is configured to physically transfer the sample pulse-wavelength modulated coherent light to scan an object. The sample pulse wavelength-modulated coherent light is reflected back from the object being measured to the scanner and transferred to a circulator within the interferometer. The back-reflected pulse wavelength-modulated coherent light is then sent from the circulator to a second coupler.

[0017] The interferometer's reference arm is more than twice the system's maximum ranging depth than the length of the sampling arm. The second portion of pulse-wavelength modulated coherent light within the reference arm is applied to the second coupler. The second portion of pulse-wavelength modulated coherent light moving along the reference arm is coupled with the recovered back-reflected pulse-wavelength modulated light to form an optical interference signal. This optical interference signal exits the second coupler and enters the photodetector array.

[0018] The maximum frequency of the optical interference signal corresponds to the minimum ranging depth of the multiplexed LiDAR system. It is greater than the Nyquist sampling frequency of the digitizer in the data acquisition and signal processing unit. The time delay of the detected optical interference is measured at the falling edge of the envelope of the optical interference signal.

[0019] In various embodiments, the sample pulse wavelength modulated coherent light beams of each interferometer are transferred to one individual scanner or one individual optical fiber element that includes processing lenses and / or collimators that aim in different directions, whereby the multiplexed LIDAR system can be configured to simultaneously measure distances from a plurality of objects in different directions and display an image range.

[0020] In various embodiments, this multiplexed LIDAR system can utilize two or more time-of-flight (ToF) or FMCW ranging methods using a single hybrid scanner, which is configured to provide a scanning pattern to each ToF or FMCW subsystem. Each scanning pattern is configured to cover different regions of an object to expand the effective scanning range of the multiplexed LIDAR system, or is configured to cover the same region of an object to expand the effective scanning pixel density of the multiplexed LIDAR system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] [Figure 1A] Schematic diagram of a related art TOI LIDAR system.

[0022] [Figure 1B] Schematic diagram of a LIDAR module embodying the principles of the present disclosure.

[0023] [Figure 2] Schematic diagram of a multiplexed LIDAR system embodying the principles of the present disclosure.

[0024] [Figure 3A] Schematic diagram of a scanner configured to scan two illumination light beams from two LIDAR modules of FIG. 1B to form a larger scanning pattern embodying the principles of the present disclosure.

[0025] [Figure 3B]Figure 1B is a schematic diagram of a scanner that embodies the principle of this disclosure, configured to scan two illumination beams from two LIDAR modules to form a higher-density scanning pattern.

[0026] [Figure 4] Figure 1B is a schematic diagram of a scanner that embodies the principle of this disclosure, configured to scan two illumination light beams from two LIDAR modules to form two scanning patterns having different scanning regions and scanning pixel densities.

[0027] [Figure 5A] Figure 1B is a schematic diagram of a scanner that embodies the principle of this disclosure, using an angled polyhedron configured to scan two illumination beams from two LIDAR modules to form a larger scanning pattern.

[0028] [Figure 5B] Figure 1B is a schematic diagram of a scanner using an angled polyhedron, which embodies the principle of this disclosure, and is configured to scan two illumination light beams from two LIDAR modules to form two scanning patterns having different scanning regions and scanning pixel densities.

[0029] [Figure 6A] This is a block diagram of an electrical TOI measurement circuit showing the program structure of a signal processing device configured to perform distance measurement based on multiplexed TOI LIDAR, which embodies the principles of this disclosure.

[0030] [Figure 6B] This figure plots the back-reflected pulse fringe and envelope of the sample arm at a zero (0) meter position, embodying the principle of this disclosure.

[0031] [Figure 6C] This figure plots the back-reflected pulse fringe and envelope of the sample arm at a position of 180 meters, embodying the principle of this disclosure.

[0032] [Figure 7] This figure shows a frame-based velocity measurement method for a TOI LIDAR system that embodies the principles of this disclosure.

[0033] [Figure 8A] This is a flowchart illustrating a method for determining the distance of an object using multiplexed distance measurement, which embodies the principles of this disclosure.

[0034] [Figure 8B] This is a flowchart illustrating a method for determining the velocity of an object using multiplexed distance measurement, which embodies the principles of this disclosure.

[0035] [Figure 9A] This is a schematic diagram of a multiplexed LiDAR system having multiple front-end scanners that embodies the principles of this disclosure.

[0036] [Figure 9B] This is a schematic diagram illustrating the implementation of a multiplexed LiDAR system having multiple front-end scanners, which embodies the principles of this disclosure.

[0037] [Figure 10A] This figure shows a lens housing for a multiplexed LiDAR system, which has a single front-end lens or collimator, for determining the distance and / or velocity from the multiplexed LiDAR system to an object, embodying the principles of the present disclosure.

[0038] [Figure 10B] This is a schematic diagram of a mechanism for controlling a single front-end lens or collimator within the lens housing of a multiplexed LiDAR system that embodies the principles of this disclosure.

[0039] [Figure 10C]A schematic diagram of a multiplexed LiDAR system comprising multiple lens housings, each lens housing having a mechanism for controlling a single optical element having a front-end lens or collimator element that embodies the principle of the present disclosure.

[0040] [Figure 11A] This figure shows a line scanning speed measurement method for a TOI LIDAR system that embodies the principles of this disclosure.

[0041] [Figure 11B] This figure shows a sample-based velocity measurement method for a TOI LIDAR system that embodies the principles of this disclosure.

[0042] [Figure 12] This is a flowchart of a line scanning distance measurement method that embodies the principles of this disclosure, for determining the velocity of an object using multiplexed distance measurement and determining the velocity of an object using line scanning distance measurement. [Modes for carrying out the invention]

[0043] A multiplexed LiDAR system is configured to generate an image of an object based on the measured distances to various points on the object. This multiplexed LiDAR system effectively increases the scanning speed, scanning area, or image pixel density of the LiDAR system by splitting the light emitted from a pulse wavelength modulated light source into at least two sets of light emission and sending them to the scanner, thereby simultaneously forming multiple scanning patterns.

[0044] Figure 1A is a schematic diagram of the TOI system 100 of the related technology. In Figure 1A, the TOI LIDAR system 100 includes a pulse wavelength modulated narrowband light source 105. This pulse wavelength modulated light source 105 emits pulse-modulated coherent light having an output spectrum consisting of one or more longitudinal modes. The longitudinal modes of a resonant cavity are specific standing wave patterns formed by waves confined within the cavity. In lasers, light is amplified in a cavity resonator, which is usually composed of two or more mirrors. This cavity has mirrored walls that reflect light, allowing standing wave modes to exist within the cavity with almost no loss. The longitudinal modes correspond to the wavelengths of reflected waves that have been reflected multiple times by the cavity on the reflective surface of the object and then amplified by constructive interference. All other wavelengths are suppressed by canceling interference. In the longitudinal mode pattern, nodes are arranged axially along the length of the cavity. The laser of the pulsed wavelength modulated light source 105 is implemented as one of four types of lasers known in the art, classified as solid-state lasers, gas lasers, liquid lasers, or semiconductor lasers. In the configuration described herein, the pulsed wavelength modulated light source 105 is shown as a semiconductor laser whose wavelength or frequency is controlled by either current or temperature. The modulation of the pulsed wavelength modulated light source 105 will be described below.

[0045] The pulse wavelength modulated narrowband light source 105 emits pulse wavelength modulated coherent light to the interferometer 110. The light emitted from the pulse wavelength modulated narrowband light source 105 is sent to the interferometer 110 via free space, an optical fiber, or an optical waveguide.

[0046] In various embodiments, the interferometer 110 is implemented as an optical fiber, a bulk optical system, an integrated optical circuit, or a combination thereof. The interferometer 110 has a polarization control device 115, which receives pulse wavelength-modulated coherent light and adjusts the polarization state of the pulse wavelength-modulated coherent light from the light source 105. It maximizes the amplitude of the optical interference signal or interference electrical signal 162 transmitted in the optical paths 155a, 155b. The pulse wavelength-modulated coherent light from the light source 105, or the pulse wavelength-modulated coherent light transmitted via the polarization control device 115, is sent to a coupler 120. The coupler 120 splits the coherent light into a sample portion supplied to at least one sample arm 122 and a reference portion of the pulse wavelength-modulated coherent light supplied to a reference arm 140 in the interferometer 110. The sample arm 122 and the reference arm 140 are implemented as free-space paths, optical fibers, or optical waveguides.

[0047] The interferometer has a circulator 125 that receives the sample portion of pulsed wavelength-modulated coherent light from the sample arm 122. The circulator 125 is configured so that the sample portion of pulsed wavelength-modulated coherent light enters the circulator 125 and exits through the next port to a section of the sample arm 122. The next port directs the coherent light through the sample arm 122 to the scanner 130 in a clockwise direction, normally (but not required). The scanner 130 is configured to physically transfer the sampled pulsed wavelength-modulated coherent light 135 to scan an object. The sampled pulsed wavelength-modulated coherent light 135 is back-reflected from the object for distance measurement. The back-reflected pulsed wavelength-modulated coherent light is received by the scanner 130 and transferred to the circulator 125. The back-reflected pulsed wavelength-modulated coherent light is then transferred through the optical path 145 to the second coupler 150. This optical path can be implemented as a free-space path, optical fiber, or optical waveguide.

[0048] The reference arm 140, implemented as a free-space path, optical fiber, or optical waveguide, has an additional optical path 142 that provides an additional path length so that the path length of the reference arm 140 of the object matches the maximum ranging depth of the TOI system 100. The optical pulse wavelength modulated coherent optical signals from at least one sample arm 122 and the reference arm 140 are coupled together in the coupler 150 to generate an optical interference signal.

[0049] Each pulse wavelength modulated coherent optical signal from at least one sample arm 122 and reference arm 140 is heterodyne detected to extract the beat frequency from the base signal. The beat signal has a phase difference of 180° between the outputs of the coupler. The balanced detector 160 subtracts the signals from each input channel to extract the interference signal, which is the beat signal.

[0050] The optical interference signal is applied to optical paths 155a and 155b, which are implemented as free-space paths, optical fibers, or optical waveguides. The optical interference signal is applied to optical paths 155a and 155b. The optical interference signal is transferred to a balanced photodetector 160, where the optical interference signals from optical paths 155a and 155 are converted into an electrical interference signal 162.

[0051] The interferential electrical signal 162 is generated by the balanced photodetector 160 and transferred to the data acquisition circuit in the signal processing device 165. The data acquisition circuit in the signal processing device 165 converts the interferential electrical signal 162 into digital data. The maximum frequency of the optical interference signal corresponds to the minimum ranging depth of the TOI LIDAR system 100. The optical interference signal is the maximum frequency of the object that is greater than the Nyquist sampling frequency of the digitizer in the data acquisition or signal processing device 165.

[0052] The minimum frequency of the optical interference signal applied to optical paths 155a and 155b corresponds to the maximum measuring depth of the TOI LIDAR system 100. The time delay of the detected optical interference is measured at the falling edge of the optical interference signal of the envelope of the object.

[0053] The digital data is then transferred to the computer 170 for further processing and display. In some embodiments, the signal processing device 165 may be integrated with the computer 170 as a single unit.

[0054] In various embodiments, the computer 170 is connected to the modulation-scanning control device 175. In other embodiments, the computer 170 is integrated with the modulation-scanning control device 175. The modulation-scanning control device 175 has a modulation subcircuit that determines the modulation degree, frequency, and shape of the modulation control signal 177 applied to the coherent light source 105. The modulation-scanning control device 175 further has a scanning control circuit that provides a modulation-scanning synchronization signal 179 to the signal processing device 165 and the scanner 130. This scanning control circuit creates a desired scanning pattern used to generate the appropriate modulation-scanning synchronization signal 179 to be applied to the scanner 130.

[0055] The scanner 130 may be implemented as a one-dimensional or two-dimensional scanner that disperses sample pulse wavelength-modulated coherent light 135 to form an image based on TOI measurements. The one-dimensional scanning pattern may be temporally linear or nonlinear, and may be unidirectional or bidirectional. In some implementations of the TOI LIDAR system 100, the two-dimensional scanning pattern may be temporally linear or nonlinear. It may be a pattern for collecting measurement information, such as a raster scan or spiral scan. The scanner 130 may be implemented mechanically as a galvanometer mirror, a micro-electromechanical system (MEMS), a piezoelectric actuator, or optically with an acousto-optic (AO) polarizer, or as a solid-state scanner. There may be other methods in line with the principle of this disclosure, which is to provide the scanning operation necessary to collect measurement information.

[0056] Figure 1B is a schematic diagram of a LIDAR module 200 embodying the principle of this disclosure. The LIDAR module 200 comprises an interferometer 110 and a balanced detector 160. The interferometer 110 and the balanced detector 160 are identical in structure and operation to the interferometer 110 and balanced detector 160 of the related technology shown in Figure 1A.

[0057] Figure 2 is a schematic diagram of a multiplexed LiDAR system 300 based on a TOI LiDAR system that embodies the principles of this disclosure. The multiplexed LiDAR system 300 has a pulse wavelength modulated narrowband light source 305. This pulse wavelength modulated light source 305 emits pulse-modulated coherent light having an output spectrum consisting of one or more longitudinal modes. The longitudinal modes of a resonant cavity are specific standing wave patterns formed by waves confined within the cavity. In lasers, light is amplified in a cavity resonator, which is usually composed of two or more mirrors. The cavity has mirrored walls that reflect light, allowing standing wave modes to exist within the cavity with almost no loss. The longitudinal modes correspond to the wavelengths of reflected waves that have been reflected multiple times by the cavity on the reflective surface of the object and then amplified by constructive interference. All other wavelengths are suppressed by canceling interference. In the longitudinal mode pattern, nodes are arranged axially along the length of the cavity. The pulsed wavelength modulated light source 305 is implemented as one of four types of lasers known in the art, classified as solid-state lasers, gas lasers, liquid lasers, or semiconductor lasers. In the configuration described herein, the pulsed wavelength modulated light source 305 is shown as a coherent light source 305 whose wavelength or frequency is controlled by either current or temperature. The modulation of the pulsed wavelength modulated light source 305 will be described below.

[0058] The pulse wavelength modulated narrowband light source 305 emits pulse wavelength modulated coherent light, which is split by the optical splitter 307 into two LiDAR modules 200c and 200d. The light emitted from the pulse wavelength modulated narrowband light source 305 travels to the optical splitter 307 via free space, optical fiber, or optical waveguide. A first leg from the optical splitter 307 is connected to the first LiDAR module 200a, and a second leg from the optical splitter 307 is connected to the second LiDAR module 200b. In various embodiments, where high detection sensitivity is required and slower detection speeds are acceptable, an optical switch can be used instead of the optical splitter 307.

[0059] In various embodiments, LIDAR modules 200c and 200d have the structure described above in Figure 1B and are implemented as optical fibers, bulk optics, integrated optical circuits, or some combination thereof. Optical pulse wavelength-modulated coherent optical signals are transferred from LIDAR modules 200a and 200b to the hybrid scanner 330. The hybrid scanner 300 is implemented as a one-dimensional or two-dimensional scanner that disperses sample pulse wavelength-modulated coherent light beams 135a and 135B to form an image based on TOI measurements. The one-dimensional scanning pattern may be temporally linear or nonlinear, and may be unidirectional or bidirectional. Next, the sample pulse wavelength-modulated coherent light beams 135a and 135b are back-reflected by the hybrid scanner 330 and transferred to LIDAR modules 200a and 200b. The back-reflected sample pulse wavelength-modulated coherent light 135a and 135b is sent to the circulator 125 in Figure 1B, and from the circulator 125 proceeds to the optical paths 145 and optical coupler 150 of the LIDAR modules 200a and 200b. The reference signal from the reference path 140 is coupled with the back-reflected light signal from the circulator 145 in both the LIDAR modules 200a and 200b within the optical coupler 150 to generate the optical interference signals 155a and 155b in Figure 1B. Furthermore, as shown in Figure 1B, the back-reflected pulse wavelength-modulated coherent light signals from the sample arms 122a and 122b and the reference arm 140 are heterodyne detected to extract the beat frequency from the base signal. The beat signal has a phase difference of 180° at the two outputs 155a and 155b from the coupler 150. The equilibrium detector 160 subtracts the signals from each input channel to extract an interference signal, which is a beat signal.

[0060] The optical interference signals are applied to optical paths 155a and 155b, which are implemented as free-space paths, optical fibers, or optical waveguides. The optical interference signals are applied to optical paths 155a and 155b and transferred to a balanced photodetector 160, where the optical interference signals from optical paths 155a and 155b of the two interferometers 110 in the two LIDAR modules 200a and 200b are converted into the first interferometric electrical signal 362a and the second interferometric electrical signal 362b in Figure 2.

[0061] The first interference electrical signal 362a and the second interference electrical signal 362b are transferred to a data acquisition circuit in the signal processing device 365, where the first interference electrical signal 362a and the second interference electrical signal 362b are converted into digital data. In some embodiments, the time delay of the detected electrical interference signals 362a and 362b can be measured in the signal processing device 365, which is equipped with an analog signal processing circuit, at the rising or falling edge of the electrical interference signal of the envelope of the object, without being converted into digital data.

[0062] The digital data is then transferred to the computer 370 for further processing and display. In some embodiments, the signal processing device 365 may be integrated with the computer 370 as a single unit.

[0063] In various embodiments, the computer 370 is connected to the modulation-scanning control device 375. In other embodiments, the computer 370 is integrated with the modulation-scanning control device 375. The modulation-scanning control device 375 has a modulation subcircuit that determines the modulation degree, frequency, and shape of the modulation control signal 377 applied to the coherent light source 305. The modulation-scanning control device 375 further has a scanning control circuit that provides a modulation-scanning synchronization signal 379 to the signal processing device 365 and the scanner 330. The modulation-scanning control device 375 creates a desired scanning pattern used to generate the appropriate modulation-scanning synchronization signal 379 to be applied to the scanner 330.

[0064] The scanner 330 may be implemented as a one-dimensional or two-dimensional scanner that disperses sample pulse wavelength-modulated coherent light 335a and 335B to form an image based on TOI measurements. The one-dimensional scanning pattern may be temporally linear or nonlinear, and may be unidirectional or bidirectional. In some implementations of the TOI LIDAR system 300, the two-dimensional scanning pattern may be temporally linear or nonlinear. It may be a pattern for collecting measurement information, such as a raster scan or spiral scan. The scanner 330 may be implemented mechanically as a galvanometer mirror, polyhedron, micro-electromechanical system (MEMS), piezoelectric actuator, or optically with an acousto-optic (AO) polarizer, or as a solid-state scanner. There may be other methods in line with the principles of this disclosure that provide the scanning motion necessary to collect measurement information.

[0065] Figures 3A and 3B are schematic diagrams of a scanner 330 configured to receive the sampling arms 322a and 322b of LIDAR modules 200c and 200d, as shown in Figure 1B. The sampling arm 322a of the first LIDAR module 200c and the sampling arm 200d of the second LIDAR module 200d are inserted into and fixed in the scanner 330. The distal ends of the first sampling arms 322a and 322b are connected to collimators 325a and 325b to parallelize the sample pulse wavelength modulated coherent light beams 322a and 322b. To increase the overall efficiency of LIDAR operation, the collimators 325a and 325b require a lower numerical aperture for long-distance illumination but a higher numerical aperture to receive pulse wavelength modulated coherent light reflected back from the object. Therefore, the collimators 325a and 325b may be single optical fiber lenses with machined tips. Therefore, the on-axis sample pulse wavelength-modulated coherent light beams 335a and 335b emerging from the central portion of the processed tip are parallel light. On the other hand, the off-axis back-reflected wavelength-modulated pulse coherent light from the object can pass through the annular portion of the processed tip and be re-coupled to the sample arm fibers 322a and 322b. The collimator's optical fiber lens can be implemented as a refractive index-dispersive (GRIN) optical fiber lens with a single-mode fiber, a GRIN optical fiber lens with a few-mode fiber, an optical fiber ball lens, a GRIN lens assembly, a free-space collimator, or a combination thereof. The processed tip can be a tapered tip, a Fresnel surface, a meta-surface, or a combination thereof.

[0066] In Figure 3A, pulse-wavelength modulated coherent light beams 335a and 335b are directed towards slow-axis scanning mirrors 340a and 340b. The slow-axis scanning mirrors 340a and 340b are on the first axis. In this example, the slow-axis scanning mirrors 340a and 340b rotate vertically to reflect the pulse-wavelength modulated coherent light beams 335a and 335b in a vertical scanning pattern. The vertical scanning pattern covers the desired field of view. The first and second slow-axis scanning mirrors 340a and 340b are configured to be offset so that the reflected pulse-wavelength modulated coherent light beams 345a and 345b are incident on different facets of the fast-axis scanning mirror 350. The high-speed axis scanning mirror 350 is a polygonal cylindrical portion, and each facet 351a, 351b, and 351c of the high-speed axis scanning mirror 350 has a rectangular mirror surface shape 351a, 351b, and 351c of equal size formed on the outer surface of the polygonal cylindrical portion of the high-speed axis scanning mirror 350.

[0067] The high-speed axis scanning mirror 350 rotates horizontally on the shaft 353 by the motor 352, forming a horizontal scanning pattern. This horizontal scanning pattern covers the horizontal field of view. The combination of the vertical and horizontal scanning patterns generates a first two-dimensional scanning pattern 355a and a second two-dimensional scanning pattern 355b from the reflected pulse wavelength modulated coherent light beams 135a and 135b, respectively. The positional offset of the first and second low-speed axis scanning mirrors 340a and 340b determines the separation of the first and second two-dimensional scanning patterns 355a and 355b. These two two-dimensional scanning patterns 355a and 355b form a composite scanning pattern with a scanning area twice as large as that of each individual two-dimensional scanning pattern 355a and 355b, thereby expanding the effective scanning area.

[0068] In Figure 3B, collimators 325a and 325b are configured to have a sufficiently small positional offset so that the pulse wavelength-modulated coherent light beams 345a and 345b are directed towards different portions of a single low-speed axis scanning mirror 340. The low-speed axis scanning mirror 340 rotates vertically and reflects the pulse wavelength-modulated coherent light beams 345a and 345b in a vertical scanning pattern. The reflected pulse wavelength-modulated coherent light beams 345a and 345b are incident on different portions of a high-speed axis scanning mirror 350. The high-speed axis scanning mirror 350 is the same as the high-speed axis scanning mirror 350 in Figure 3A.

[0069] The high-speed axial scanning mirror 350 is rotated horizontally on the shaft 353 by the motor 352 to form a horizontal scanning pattern. The combination of the vertical and horizontal scanning patterns generates a first two-dimensional scanning pattern 355a and a second two-dimensional scanning pattern 355b from the reflected pulse wavelength modulated coherent light beams 135a and 135b, respectively. These two two-dimensional scanning patterns 355a and 355b completely overlap to form a composite scanning pattern with twice the scanning pixel density compared to each individual two-dimensional scanning pattern, thereby improving the effective scanning pixel density or effective scanning speed. In some embodiments, the two-dimensional scanning patterns 355a and 355b partially overlap, resulting in increased pixel density and scanning pixel area in some parts of the composite scanning patterns 355a and 355b.

[0070] Figure 4 is a schematic diagram of scanner 330 configured to accept sampling arms 122a and 122b of LIDAR modules 200c and 200d in Figure 3A. As shown in Figure 3A, scanner 330 is configured to accept sampling arms 322a and 322b of LIDAR modules 200c and 200d. Pulse wavelength modulated coherent light from sampling arms 322a and 322b of LIDAR modules 200c and 200d is applied to collimators 325a and 325b. Pulse wavelength modulated coherent light beams 345a and 345b from collimators 325a and 325b are directed toward slow-axis scanning mirrors 340a and 340b, respectively. The slow-axis scanning mirrors 340a and 340b rotate vertically and reflect the pulse wavelength modulated coherent light beams 345a and 345b in a vertical scanning pattern. The vertical scanning pattern covers the desired field of view. The first and second low-speed axis scanning mirrors 340a and 340b are configured to be offset in position so that the reflected pulse wavelength modulated coherent light beams 345a and 345b are incident on different locations on the high-speed axis scanning mirror 405. The high-speed axis scanning mirror 405 is a rotating polygonal mirror consisting of two sets of different facet configurations, including a low-facet section (small number of facets) 405a and a high-facet section (large number of facets) 405b. The low-facet section 405a has facets 406a, 406b, and 406c, while the high-facet section 405b has facets 409a, 409b, 409c, 409d, 409e, and 409f, which are formed by equally sized rectangular mirror shapes 409a, 409b, 409c, 409d, 409e, and 409f formed on the outer surface of the polygonal cylindrical portion of the high-speed axis scanning mirror 405.

[0071] The first reflected pulse wavelength modulated coherent light is incident on the low-facet portion 405a of the polyhedron 405, and the second reflected pulse wavelength modulated coherent light 405b is incident on the high-facet portion 405b of the polyhedron 405. Alternatively, although not shown in the figures, it may be possible to invert the polyhedron 405 so that the second reflected pulse wavelength modulated coherent light beam 345b is incident on the low-facet portion 405b and the first reflected pulse wavelength modulated coherent light beam 345a is incident on the high-facet portion 405b. According to the first example, the pulse wavelength modulated coherent light beam 135a forms a first two-dimensional scanning pattern 415a with a large scanning area and low scanning pixel density, while the pulse wavelength modulated coherent light beam 135b, which forms a second two-dimensional scanning pattern 415b, has a small scanning area and high scanning pixel density. This implementation allows the multiplexed LiDAR system to simultaneously accommodate different scanning requirements and parameters, including, but not limited to, field of view (FOV) and pixel density for near-field and far-field image formation.

[0072] As mentioned above, the motor 408 rotates the shaft 407, which in turn rotates the high-speed axis scanning mirror 405.

[0073] Figures 5A and 5B are schematic diagrams of scanner 130 configured to receive sampling arms. As shown in Figure 5A, scanner 330 is configured to receive sampling arms 322a and 322b of interferometers 110a and 110b of LIDAR modules 200c and 220d. Collimators 325a and 325b are configured to have sufficiently small positional and angular offsets so that pulse wavelength modulated coherent light beams 325a and 325b are directed to different locations on a single slow-axis scanning mirror 340. The slow-axis scanning mirror 340 rotates vertically and reflects the pulse wavelength modulated coherent light beams 325a and 325b in a vertical scanning pattern. The reflected pulse wavelength modulated coherent light beams 345a and 345b are incident on different portions of the fast-axis scanning mirror 410.

[0074] The high-speed axial scanning mirror 410 has two polygonal cylindrical sections 410a and 410b. The first polygonal cylindrical section 410a has a plurality of isosceles trapezoidal faceted mirrors 411a, 4116b, and 411c. The isosceles trapezoidal faceted mirrors 411a, 4116b, and 411c are formed on each facet surface of the first polygonal cylindrical section 410a, with their upper edges being longer than their lower edges.

[0075] The second polygonal cylindrical portion 410b has a plurality of isosceles trapezoidal faceted mirrors 411d, 4116e, and 411f. The isosceles trapezoidal faceted mirrors 411d, 4116e, and 411f are formed on each facet surface of the first polygonal cylindrical portion 410b, with the lower side being longer than the upper side.

[0076] A high-speed axial scanning mirror 410, equipped with isosceles trapezoidal faceted mirrors 411a, 4116b, 411c, 411d, 4116e, and 411f, corrects the angular offset of the reflected pulse wavelength modulated coherent light beams 345a and 345b. The high-speed axial scanning mirror 410 is rotated horizontally via a shaft 413 by a motor 412 to form a horizontal scanning pattern. The combination of the vertical and horizontal scanning patterns generates a first two-dimensional scanning pattern 415a and a second two-dimensional scanning pattern 415b, with the two two-dimensional scanning patterns 415a and 415b from the reflected pulse wavelength modulated coherent light beams 135a and 135b, respectively, completely overlapping. These two two-dimensional scanning patterns 415a and 415b form a composite scanning pattern with twice the scanning pixel density compared to each individual two-dimensional scanning pattern, thereby improving the effective scanning pixel density or effective scanning speed. In some embodiments, the two-dimensional scanning patterns 415a and 415b partially overlap, resulting in an increase in the pixel density of some parts of the combined scanning patterns 415a and 415b, as well as an increase in the scanned pixel area.

[0077] In Figure 5B, the basic structure of the hybrid scanner 330 is the same as the basic structure of the hybrid scanner 330 in Figure 5A. The high-speed axial scanning mirror 420 is a rotating polyhedron mirror. The rotating polyhedron mirror 420 consists of two different polygonal cylindrical parts 420a and 420b, which include a low-facet part 420a with the fewest facets and a second part 420b with the most facets. The first reflected pulse wavelength-modulated coherent light beam 135a is incident on the second part 420a of the polyhedron mirror 420. The second reflected pulse wavelength-modulated coherent light beam 135b is incident on the first part 420b of the rotating polyhedron mirror 420, resulting in a first two-dimensional scanning pattern 415a with a wide scanning area and low scanning pixel density, and a second two-dimensional scanning pattern 415b with a narrow scanning area and high scanning pixel density. This implementation allows the multiplexed LiDAR system 300 shown in Figure 2 to simultaneously accommodate different scanning requirements and parameters, including, but not limited to, field of view (FOV) and pixel density for near-field and far-field image formation.

[0078] Figure 6A is a block diagram of the electrical TOI measurement circuit contained within the signal processing unit. The interfering electrical signals 362a and 362b in Figure 2, generated from the LIDAR modules 200a and 200b, are received by a multi-channel envelope detector 500 and converted into envelopes 505a and 505b of the interfering electrical signals 362a and 362b. The multi-channel envelope detector 500 is implemented as a radio frequency (RF) power detector, root mean square (RMS) detector, or frequency demodulator. Radio frequency (RF) power detectors, RMS detectors, or frequency demodulators are known in the art and are commercially available devices. The radio frequency power detector, RMS detector, or frequency demodulator extracts the envelopes of the interfering electrical signals 362a and 362b by removing the high-frequency components in the electrical interfering signals 362a and 362b.

[0079] The envelope signals 505a and 505b are transferred to a multi-channel edge detector 510. This multi-channel edge detector 510 determines pulse events and places those pulse events at the output 510 of the edge detector target. A pulse event represents the rising or falling edge of the envelope signals 505a and 505b. The multi-channel edge detector 510 can be implemented as an edge-glitch converter, an XOR gate and delay circuit, a differentiating circuit, etc. Edge-glitch converters, XOR gates and delay circuits, and differentiating circuits are also known in the art and are commercially available.

[0080] The edge detectors of outputs 515a and 515b of the object 510 are connected to the inputs of a multiplex channel time-to-digital converter 520. This multiplex channel time-to-digital converter 520 generates a time difference signal and transfers it to outputs 530a and 530b. This time difference signal at outputs 530a and 530b of the multiplex channel time-to-digital converter 520 indicates the time of the rising or falling edge between pulse events 505a and 505b and pulse event 525. Pulse event 525 corresponds to the rising or falling edge of the light source modulation signal 377 transferred from the modulation / scanning control device 375. Pulse event 525 triggers the multiplex channel time-to-digital converter 520 to start when counting time intervals. The pulse outputs 515a and 515b of the multiplex channel edge detector 510 provide pulse events to terminate the time interval counting by the multiplex channel time-to-digital converter 520. The series of time-difference signals at outputs 530a and 530b of the multi-channel time-to-digital converter 520 are converted into depth measurements to form an image displayed by the computer 170.

[0081] Figure 6B is a plot of the pulse input fringe 560 and envelope 565 of an object, embodying the principle of this disclosure. Figure 6B is an example of plotting the interference electrical signals of the prototype TOI system 300 of Figure 2, which detects an object at zero (0) meters. Figure 6C is a plot of the back-reflected pulse fringe 570 and envelope 575 of another object, embodying the principle of this disclosure. Figure 6C is an example of the interference electrical signals of the prototype TOI system 300, which detects an object at 180 meters. The multi-channel edge detector 510 of Figure 6A determines the time of the falling edge t0 of the envelope of the fringe signal 565 and the time of the falling edge t1 of the envelope of the fringe signal 575. The multi-channel time-to-digital converter 520 counts the time interval between the falling edge times t0 and t1. The distance of the object to be measured is determined by the following formula: Distance=c*(t0-t1) However, c represents the speed of light, t0 represents the falling edge time when the object is at 0m, and t1 represents the falling edge time when the object is at 180m. The series of time-difference signals at outputs 530a and 530b of the multi-channel time-to-digital converter 520 can be converted into depth information to form an image displayed by the computer 370.

[0082] Figure 7 shows a frame-based velocity measurement method using a multiplexed LiDAR system embodying the principles of this disclosure. The multiplexed LiDAR system can be configured such that a small time delay is encoded within the second TOI module, so that frames 590a(1), 590a(2), ..., 590a(m) and 590b(1), 590b(2), ..., 590b(m) are interleaved by TOI modules 200a and 200b in Figure 2, respectively, and represent the first and second interfering electrical signals 362a and 362b in Figure 2.

[0083] Data 595a and 595b are transferred to the signal processing device 365 and processed as shown in Figure 6A to determine the rising or falling edge of the data and the object. Therefore, by determining the rising or falling edge of the data, the time difference between data 595a and 595b is obtained. Next, the distance between the data is calculated by the time difference (t) between data 595a and 595b. b -t a ) is calculated as the time difference (t) between data 595a and 595b. b -t a The velocity of the object to be measured is determined by multiplying the optical interference signal applied to the optical paths of LIDAR modules 200a and 200b by the frame rate of sampling the object.

[0084] Figure 8A is a flowchart illustrating a method for determining the distance to an object using a TOI-based multiplexed LiDAR system that embodies the principles of this disclosure. A laser beam is generated (Box 700). The laser beam is modulated with a wavelength-modulated signal or a frequency-modulated signal (Box 705) to adjust the wavelength or frequency of the laser beam to that of the object. Next, the laser beam is polarized (Box 710) to adjust the polarization state of the laser beam and the object, maximizing the amplitude of the optical interference signal or electrical interference signal.

[0085] The laser beam is optically split into multiple beams (Box 715), and each of the split laser beams is combined into a single LIDAR module (Box 720) to create a sampling arm and a reference arm. Each sampling arm is connected to a single hybrid scanner (Box 725) to establish a scanning pattern for each sampling laser beam. The object to be measured is scanned with each sampling laser beam (730). A portion of each laser coherent beam is back-reflected from the object to be measured and received by each hybrid scanner associated with the back-reflected pulse-wavelength modulated coherent laser beam (Box 735). The back-reflected pulse-wavelength modulated coherent laser beam is coupled to the optical circulator of the interferometer (Box 740), connected to an optical coupler, and coupled with the reference pulse-wavelength modulated coherent laser beam to form an optical interference signal. The optical interference signal is converted into an oscillating electrical interference signal (Box 745).

[0086] The envelope detection process identifies the envelope of this electrical interference signal (Box 750). The time of the rising or falling edge of the envelope of the digital electrical interference signal is determined (Box 755). The time difference between the rising or falling edge of the envelope of the electrical interference signal and the modulation / scanning synchronization signal is determined (Box 760), and the distance to the object being measured is calculated (Box 765). As multiple laser beams scan the object, a two-dimensional distance measurement image is formed based on all the measured distances and the angular position of the scanner (Box 760).

[0087] Figure 8B is a flowchart illustrating a method for determining the velocity of an object using a time-of-interference (TOI) based multiplexed LiDAR system, which embodies the principle of this disclosure. The method for determining the velocity of an object using a TOI-based multiplexed LiDAR system begins by performing the method steps in Figure 8A multiple times (Box 775). The velocity of the object is determined as the difference in distance measured by each multiplexed TOI module over time (Box 780).

[0088] In various embodiments, each LiDAR module of a multiplexed LiDAR system is equipped with multiple scanners so that the distances to multiple objects at different locations can be measured simultaneously by a single LiDAR system. Figure 9A is a schematic diagram of a multiplexed LiDAR system 500 based on a TOI LiDAR system that embodies the principles of the present disclosure. Instead of using a single scanner as in the system shown in Figure 2, the sample arms of the first and second TOI modules 200a and 200b are separately connected to the first scanner 805a and the second scanner 805b, respectively, and physically transfer the first sample pulse wavelength-modulated coherent light 135a and the second sample pulse wavelength-modulated coherent light 135b to scan different objects.

[0089] Figure 9B is a schematic diagram of a multiplexed LiDAR system 900 for multiplexed distance measurement embodying the principles of this disclosure. A single backend system 910 comprises a single pulsed wavelength modulated light source 905 that transfers a pulsed wavelength modulated light beam 906 to a multibeam splitter 907. An exemplary multibeam splitter 907 is a diffraction beam splitter 908 that provides the required number of individual beams for the LiDAR system 900. The multiple wavelength modulated light beams are directed towards a focusing lens 909 to make each light beam parallel again. Each light beam is transferred to TOI LiDAR modules 920a, 920b, 920c, 920d, 920e, ..., 920n. In various embodiments, a multichannel optical switch can be used instead of the multibeam splitter 907 in applications requiring high detection sensitivity and a narrow field of view, or in applications where a slow detection speed is acceptable.

[0090] Each LIDAR module 920a, 920b, 920c, 920d, 920e, ..., 920n is connected to scanners 925a, 925b, 925c, 925d, 925e, ..., 925n in the front end of the multiplexed LIDAR system 800. Each scanner 925a, 925b, 925c, 925d, 925e, ..., 925n is configured as either a one-dimensional or two-dimensional scanner, as described in Figures 3A, 4, 5A, and 5B. Scanners 925a, 925b, 925c, 925d, 925e, ..., 925n transfer sample pulse wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n to scan one or more objects in different directions within a circle of the surrounding environment.

[0091] Wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n, which are back-reflected from the scanned object(s) (multiple objects), are received by scanners 925a, 925b, 925c, 925d, 925e, ..., 925n and transferred to LIDAR modules 920a, 920b, 920c, 920d, 920e, ..., 920n, where an image is formed based on TOI measurements. The one-dimensional scanning pattern may be temporally linear or nonlinear, and may be unidirectional or bidirectional. In some implementations of the multiplexed LIDAR system 900, the two-dimensional scanning pattern may be temporally linear or nonlinear. It may also be a pattern for collecting measurement information, such as a raster scan or spiral scan.

[0092] In the various embodiments shown in Figure 9B, each of the scanners 925a, 925b, 925c, 925d, 925e, ..., 925n operates with different scanning patterns and scanning speeds for different types of objects or purposes. The scanning patterns may be one-dimensional scanning with a narrow scanning range (less than 5 degrees) and a fast scanning speed (higher than 50 Hz), one-dimensional scanning with a wide scanning range (greater than 5 degrees) and a slow scanning speed (less than 50 Hz), two-dimensional scanning with a narrow scanning range (less than 5 degrees in each dimension) and a fast scanning speed (greater than 20 Hz), two-dimensional scanning with a wide scanning range (greater than 5 degrees in each dimension) and a slow scanning speed (less than 20 Hz), or a combination thereof.

[0093] The back-reflected wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n are received by TOI LIDAR modules 920a, 920b, 920c, 920d, 920e, ..., 920n and processed by TOI LIDAR modules 920a, 920b, 920c, 920d, 920e, ..., 920n. The processed back-reflected wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n are transferred to the signal processing unit 965 as back-reflected wavelength-modulated coherent light beams 962a, 962b, 962c, 935d, 962e, ..., 962n. The signal processing unit 965 has a plurality of balanced detectors 160 as shown in Figure 1B, which receive back-reflection wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n. The balanced detectors 160 in Figure 1B convert the light beams 935a, 935b, 935c, 935d, 935e, ..., 935n into electrical signals, which are processed by the computer 970 to generate an image based on TOI measurements.

[0094] Scanners 925a, 925b, 925c, 925d, 925e, ..., 925n may be implemented mechanically as a galvanometer mirror, polyhedron, micro-electromechanical system (MEMS), piezoelectric actuator, optically with an acousto-optic (AO) polarizer, or as a solid-state scanner. Other methods may be in line with the principles of this disclosure, which provide the scanning motion necessary to collect measurement information.

[0095] Figure 10A shows a lens housing 1000 for a multiplexed LiDAR system 1900, which embodies the principle of the present disclosure, and includes a single optical fiber laser element 1005 for determining the distance and / or velocity from the multiplexed LiDAR system to an object. The optical fiber laser element 1005 has a lens or collimator 1007 at its front end. The lens housing 1000 has an opening 1010 configured to allow the optical fiber laser element 1005 to move horizontally and vertically. Figure 10B is a schematic diagram of a mechanism for controlling the single optical fiber laser element 1005, which embodies the principle of the present disclosure. The optical fiber laser element 1005, with its lens or collimator 1007, is fixed to a pitch-yaw control mechanism 1015 within the lens housing 1000 for the multiplexed LiDAR system. The pitch-yaw control mechanism 1015 includes a horizontal yaw control device 1020 and a vertical pitch control aiming device 1030. The optical fiber laser element 1005 is fixed to the vertical pitch control aiming device 1030, which rotates the optical fiber laser element 1005 over its vertical operating range. The vertical pitch control aiming device 1030 is attached to the motor 1035. The motor 1035 controls the vertical movement of the optical fiber laser element 1005. The vertical pitch control aiming device 1030 is attached to the horizontal yaw control device 1020. The horizontal yaw control device 1020 rotates within a horizontal plane over a desired operating range.

[0096] As shown in Figure 9A, the LIDAR module 200e is connected to the coherent light source 905. The LIDAR module 200e is connected to the optical fiber cable 345c, which transfers the modulated light beam to the optical element 1005. The scanning control device 1040 provides rotational control to motors 1025 and 1035 to fix the horizontal (yaw) and vertical (pitch) motion of the light beam 1045, defining the one-dimensional scanning field of each line scan 1050.

[0097] Figure 10C is a schematic diagram of a multiplexed LiDAR system 1900 having multiple lens housings 1100a, 1100b, 1100c, 100d, 1100e, ... 1100n, and having a mechanism for controlling the two-dimensional movement of a single optical element 1035a, 1035b, 1035c, 1035d, 1035e, ... 1035n having a front-end lens or collimator element 1037a, 1037b, 1037c, 1037d, 10377e, ... 1037n that embodies the principle of this disclosure.

[0098] A single backend system 1110 comprises a single pulse wavelength modulated light source 1105 that transfers a pulse wavelength modulated light beam 1106 to a multibeam splitter 1107. An exemplary multibeam splitter 1107 is a diffraction beam splitter 1108 that provides the required number of individual beams to the LIDAR system 1100. The multiple wavelength modulated light beams are directed towards a focusing lens 1109 to re-parallelize each of the light beams 1122a, 1122b, 1122c, 1122d, 1122e…1122n. Each of the light beams 1122a, 1122b, 1122c, 1122d, 1122e…1122n is transferred to the TOI LIDAR modules 1120a, 1120b, 1120c, 1120d, 1120e,…, 1120n. In various embodiments, a multi-channel optical switch can be used instead of the multi-beam splitter 1107 in applications requiring high detection sensitivity and a narrow field of view, or in applications where a slow detection speed is acceptable.

[0099] Each LIDAR module 1120a, 1120b, 1120c, 1120d, 1120e, ..., 1120n is connected to lens housings 1100a, 1100b, 1100c, 100d, 1100e, ..., 1100n, each containing a single optical fiber laser element 1035a, 1035b, 1035c, 1035d, 103e, ..., 1035n within the front end of the multiplexed LIDAR system 1110. Each lens housing 1100a, 1100b, 1100c, 100d, 1100e, ..., 1100n is configured for one-dimensional scanning, as described in Figure 10B. The lens housings 1100a, 1100b, 1100c, 100d, 1100e, ..., 1100n have optical fiber laser elements 1035a, 1035b, 1035c, 1035d, 103e, ..., 1035n that transfer a sample pulse wavelength-modulated coherent optical beam 1122a, 1122b, 1122c, 1122d, 1122e, ..., 1122n to scan one or more objects in different directions within the circumference of the surrounding environment.

[0100] Back-reflection wavelength-modulated coherent light beams 1122a, 1122b, 1122c, 1122d, 1122e, ..., 1122n, reflected from scanned objects (multiple objects), are received by optical fiber laser elements 1035a, 1035b, 1035c, 1035d, 103e, ..., 1035n and transmitted to LIDAR modules 1120a, 1120b, 1120c, 1120d, 1120e, ..., 1120n to form an image based on TOI measurements. The one-dimensional scanning pattern may be temporally linear or nonlinear, and may be unidirectional or bidirectional. In some implementations of the multiplexed LIDAR system 1110, the one-dimensional scanning pattern may be temporally linear or nonlinear. It may also be a pattern for collecting measurement information, such as a raster scan or spiral scan.

[0101] In the various embodiments shown in Figure 10C, each optical fiber laser element 1035a, 1035b, 1035c, 1035d, 1035e, ..., 1035n operates with different line scanning patterns and line scanning speeds for different types of objects or purposes. The line scanning patterns may be one-dimensional scanning with a narrow scanning range (less than 5 degrees) and a fast scanning speed (higher than 50 Hz), one-dimensional scanning with a wide scanning range (greater than 5 degrees) and a slow scanning speed (less than 50 Hz), two-dimensional scanning with a narrow scanning range (less than 5 degrees in each dimension) and a fast scanning speed (greater than 20 Hz), two-dimensional scanning with a wide scanning range (greater than 5 degrees in each dimension) and a slow scanning speed (less than 20 Hz), or a combination thereof.

[0102] The back-reflection wavelength-modulated coherent light beams 1122a, 1122b, 1122c, 1122d, 1122e, ..., 1122n are received by the interferometers of the LIDAR modules 1120a, 1120b, 1120c, 1120d, 1120e, ..., 1120. The coherent light beams 1022a, 1022b, 1022c, 1022d, 1022e, ..., 1022n are then processed by the equilibrium detectors 160 of the LIDAR modules 1120a, 1120b, 1120c, 1120d, 1120e, ..., 1120. The back-reflected coherent light beams 1022a, 1022b, 1022c, 1022d, 1022e, ..., 1022n are converted into electrical signals which are then transferred to the signal processing unit 1065. Each LIDAR module 1120a, 1120b, 1120c, 1120d, 1120e, ..., 1120n has a balanced detector 160 as shown in Figure 1B. The balanced detector 160 as shown in Figure 1B converts the light beams 1062a, 1082b, 1062c, 1062d, 1062e, ..., 1062n into electrical signals which the computer 970 processes to generate an image based on TOI measurements.

[0103] Lens housings 1100a, 1100b, 1100c, 100d, 1100e, ..., 1100n, each equipped with a single optical fiber laser element 1035a, 1035b, 1035c, 1035d, 1035e, ..., 1035n, are mechanically realized to provide individual horizontal and vertical scanning operations of the single optical fiber laser element 1035a, 1035b, 1035c, 1035d, 1035e, ..., 1035n, as shown in Figure 10B, in accordance with the principle of this disclosure that individual horizontal and vertical scanning operations are necessary to collect measurement information. In various embodiments of Figure 10C, lens housings 1100a, 1100b, 1100c, 100d, 1100e, ..., 1100n, each containing a single optical fiber laser element 1035a, 1035b, 1035c, 1035d, 1035e, ..., 1035n, do not provide scanning motion. Therefore, the single optical fiber laser elements 1035a, 1035b, 1035c, 1035d, 1035e, ..., 1035n remain stationary but are oriented in different directions to collect measurement information.

[0104] Figure 11A shows a line-scan-based velocity measurement method for a TOI LIDAR system embodying the principles of this disclosure. The multiplexed LIDAR system can be configured such that small time delays are encoded within the second TOI module, so that lines 1200, 1205, ... 1210, and 1215, 1220, ... 1225 are interleaved by TOI modules 200a and 200b in Figure 2, respectively, representing the first and second interfering electrical signals 362a and 362b in Figure 2.

[0105] Data 1230 and 1235 are transferred to the signal processing device 365 and processed as shown in Figure 6A to determine the rising or falling edge of the data. Therefore, the time difference between data 1230 and 1235 is obtained by determining the rising or falling edge of the data object. Next, the distance between data 1230 and 1235 is calculated by the time difference (t) between data 1230 and 1235. b -t a) is obtained. The time difference (t b -t a ) between data 2030 and 2035 is multiplied by the line scan rate of the optical interference signal applied to the optical paths of the LIDAR modules 200a and 200b in FIG. 2 and the sampling of the object to obtain the speed of the measurement object.

[0106] FIG. 11B is a diagram showing a sample-based speed measurement method using a multiplexed LIDAR system embodying the principle of the present disclosure. This multiplexed LIDAR system can be configured such that a small time delay is encoded in the second TOI module, so samples 1240(1), 1240(2),... 1240(m), and 1245(1), 1245(2),... 1245(m) are respectively captured in an interleaved manner by the TOI modules 200a and 200b in FIG. 2 and represent the first and second interference electrical signals 362a and 362b in FIG. 2.

[0107] Data 1260 and 1265 are transferred to the signal processing device 365 and processed as described in FIG. 6A to obtain the rising edge or falling edge of the data. Therefore, the time difference between data 1260 and 1265 is obtained by determining the rising edge or falling edge of the object of the data. Next, the distance between data 1260 and 1265 is obtained as the time difference (t b -t a ) between data 1260 and 1265. The time difference (t b -t a ) between data 1230 and 1235 is multiplied by the optical interference signal applied to the optical paths of the LIDAR modules 200a and 200b and the sampling rate of the object to obtain the speed of the measurement object.

[0108] Figure 12 is a flowchart illustrating a method for determining the distance to an object using a TOI-based multiplexed LiDAR system that embodies the principle of this disclosure. A laser beam is generated (Box 1300). The laser beam is modulated with a wavelength-modulated signal or a frequency-modulated signal (Box 1305) to adjust the wavelength or frequency of the laser beam. Next, the laser beam is polarized (Box 1310) to adjust the polarization state of the laser light and maximize the amplitude of the optical interference signal or electrical interference signal.

[0109] The laser beam is optically split into multiple beams (Box 1315), and each of the split laser beams is combined into a single TOI LIDAR module (Box 1320) to create a sampling arm and a reference arm. Each laser beam is transferred to an optical fiber cable connected to a lens housing, where the optical fiber cable is connected to an optical fiber lens element (Box 1325). The optical fiber lens element is swept along the horizontal and / or vertical axes toward the object whose distance is to be measured (Box 1330). A scan line is formed each time the optical fiber lens element is swept (Box 1335).

[0110] The pulse wavelength-modulated coherent laser beam is reflected back from the object being measured (Box 1340), sent to the optical circulator of the interferometer, then to the optical coupler, where it is coupled with a reference pulse wavelength-modulated coherent laser beam to form an optical interference signal. This optical interference signal is then converted into an oscillating electrical interference signal (Box 1345).

[0111] The envelope detection process identifies the envelope of this electrical interference signal (Box 1350). The time of the rising or falling edge of the envelope of the digital electrical interference signal is determined (Box 1355). The time difference between the rising or falling edge of the envelope of the electrical interference signal and the modulation / scan synchronization signal is determined (Box 1360), and the distance to the object being measured is calculated (Box 1365).

[0112] A one-dimensional distance measurement image is formed based on a distance measurement line scan created by one or more light beams crossing the object to be measured (Box 1370).

[0113] In Figure 12, the method for determining the velocity of an object using a TOI-based multiplexed LiDAR system begins by performing the method steps in Figure 8A multiple times (Box 1375). Over time, the velocity of the object is determined as the difference in distance measured by the multiplexed TOI module (Box 1380).

[0114] While this disclosure is shown and described in particular with reference to its preferred embodiments, it will be understood by those skilled in the art that various modifications can be made in form and detail without departing from the spirit and scope of this disclosure. In particular, the multiplexing system 100 in Figure 2 and the system 800 in Figure 9A may be implemented using time-of-flight (ToF), amplitude-modulated continuous wave (AMCW), frequency-modulated continuous wave (FMCW), or any combination of LiDAR devices known in the art.

Claims

1. A multiplexed line scanning device in a multiplexed optical detection and ranging (LIDAR) system for performing line scanning patterns for each of multiple sample pulse wavelength modulated coherent optical beams, A pulse wavelength modulated narrowband light source that emits pulse wavelength modulated coherent light transmitted via a free-space path, optical fiber, or optical waveguide, A LIDAR module comprising at least one interferometer and a balanced detector, connected to receive pulse wavelength modulated coherent light from the pulse wavelength modulated narrowband light via the free space path, optical fiber, or optical waveguide, A lens housing connected to the LIDAR module for receiving and transmitting pulse wavelength modulated narrowband light, The LIDAR module includes at least one optical fiber lens element configured to receive the pulse wavelength modulated narrowband light from the LIDAR module and transfer the pulse wavelength modulated narrowband light to the object to be measured, wherein the optical fiber lens element is A lens or collimator, A lens housing comprising: a cylindrical casing that provides structural support for the optical fiber lens element, the cylindrical casing housing the free-space path, optical fiber, or optical waveguide inside the casing, and fixing the lens or collimator to the casing; A two-axis pitch-yaw aiming device that is attached to the lens housing and attached to the optical fiber lens element, thereby fixing the optical fiber lens element to the lens housing, A pitch motion control device connected to the lens housing and providing pitch control for orienting the optical fiber lens element toward the first axis, A two-axis pitch-yaw aiming device comprising: a pitch motion control device connected to the lens housing, which provides yaw control for orienting the optical fiber lens toward the second axis and directing the lens or collimator along a linear scanning path to determine the distance or velocity of an object; A multiplexed line scanning device comprising a scanning control device that provides programming instructions for controlling the pitch motion control device and the yaw motion control device.

2. The multiplexed line scanning apparatus according to claim 1, wherein the lens housing has an aperture for receiving pulse wavelength modulated coherent light that is reflected back from the object to be measured after the pulse wavelength modulated narrowband light exits the lens housing and collides with the object to be measured.

3. A multiplexed line scanning light detection and ranging (LIDAR) system for performing line scanning patterns for each of multiple sample pulse wavelength-modulated coherent light beams, A pulse wavelength modulated narrowband light source that emits pulse wavelength modulated coherent light transmitted via a free-space path, optical fiber, or optical waveguide, A LIDAR module comprising an interferometer and a balanced detector, connected to receive pulse wavelength modulated coherent light from the pulse wavelength modulated narrowband light through the free space path, optical fiber, or optical waveguide, A lens housing connected to the LIDAR module for receiving and transmitting pulse wavelength modulated narrowband light, The LIDAR module includes a single optical fiber lens element configured to receive the pulse wavelength modulated narrowband light and transfer the pulse wavelength modulated narrowband light to the object to be measured, wherein the optical fiber lens element is A lens or collimator, A lens housing comprising: a cylindrical casing that provides structural support for the optical fiber lens element, the cylindrical casing housing the free-space path, optical fiber, or optical waveguide inside the casing, and fixing the lens or collimator to the casing; A two-axis pitch-yaw aiming device that is attached to the lens housing and attached to the optical fiber lens element, thereby fixing the optical fiber lens element to the lens housing, A pitch motion control device connected to the lens housing and providing pitch control for orienting the optical fiber lens element toward the first axis, A two-axis pitch-yaw aiming device comprising: a pitch motion control device connected to the lens housing, which provides yaw control for orienting the optical fiber lens toward the second axis and directing the lens or collimator along a linear scanning path to determine the distance or velocity of an object; A multiplexed line scanning light detection and ranging (LIDAR) system comprising a scanning control device that provides programming commands for controlling the pitch motion control device and the yaw motion control device.

4. The multiplexed line scanning light detection and ranging (LIDAR) system according to claim 3, wherein the lens housing has an aperture for receiving pulse wavelength-modulated coherent light that is reflected back from the object to be measured after the pulse wavelength-modulated narrowband light exits the lens housing and strikes the object to be measured.

5. A multiplexed line scanning light detection and ranging (LIDAR) system for measuring the distance to a feature on an object, Coherent light source, A modulation control device communicating with the coherent light source, configured to modulate the coherent light source to generate a pulse wavelength modulated coherent light beam, and to generate and control a control signal to be transmitted to the coherent light source to generate a scanning pattern for measuring the surface of the object, A LiDAR module connected to the coherent light source for receiving the pulse wavelength modulated coherent light beam, the LiDAR module comprising an interferometer for generating a sampled pulse wavelength modulated coherent light beam and a reference pulse wavelength modulated coherent light beam, and a balanced detector, One or more multiplexed line scanning devices for receiving the pulse wavelength modulated coherent light beam and transferring the pulse wavelength modulated coherent light beam to an optical fiber lens element, wherein the optical fiber lens element comprises one or more multiplexed line scanning devices driven by a line scanning pattern so that the sample pulse wavelength modulated coherent light beam scans a desired light pattern, A modulation and scanning control device is configured to modulate the coherent light source to generate the pulse wavelength modulated coherent light beam and to implement the scanning pattern of the optical fiber lens element, A signal processing device that receives an electrical signal generated by the pulse wavelength modulated coherent light beam reflected back by the equilibrium detector and converts the electrical signal into a digital electrical signal, A multiplexed line scanning light detection and ranging (LIDAR) system comprising: a computer system programmed to calculate a time delay determined by the digitized electrical signal from the signal processing device and to generate an imaging range displayed based on the distance from the target object.

6. The multiplexed line scanning LiDAR system according to claim 5, wherein the at least two LiDAR modules are connected to the coherent light source via an optical splitter or optical switch for receiving the pulse wavelength modulated coherent light beam.

7. The aforementioned multiplexing line scanning device further, A lens housing connected to the LIDAR module for receiving and transmitting pulse wavelength modulated narrowband light, The LIDAR module includes a single optical fiber lens element configured to receive the pulse wavelength modulated narrowband light and transfer the pulse wavelength modulated narrowband light to the object to be measured, wherein the optical fiber lens element is A lens or collimator, A lens housing comprising: a cylindrical casing that provides structural support for the optical fiber lens element, the cylindrical casing housing a free-space path, an optical fiber, or an optical waveguide inside the casing, and the lens or collimator fixed to the casing; A two-axis pitch-yaw aiming device that is attached to the lens housing and attached to the optical fiber lens element, thereby fixing the optical fiber lens element to the lens housing, A pitch motion control device connected to the lens housing and providing pitch control for orienting the optical fiber lens element toward the first axis, A two-axis pitch-yaw aiming device comprising: a pitch motion control device connected to the lens housing, which provides yaw control for orienting the optical fiber lens element toward the second axis and directing the lens or collimator along a linear scanning path to determine the distance or velocity of an object; The multiplexed line scanning LiDAR system according to claim 6, comprising a scanning control device that provides programming instructions for controlling the pitch motion control device and the yaw motion control device.

8. The multiplexed line scanning LiDAR system according to claim 7, wherein one or more pulse wavelength modulated coherent light beams are back-reflected to the lens housing, the lens or collimator of the optical fiber lens element, the interferometer, and the equilibrium detector in the LiDAR module for determining the dimensions of the object to be scanned.

9. The lens housing is provided with an opening for scanning the optical fiber lens element on the first axis and the second axis, and the line scanning can have a desired direction, as described in claim 7, for the multiplexed line scanning LiDAR system.

10. The multiplexed line scanning LiDAR system according to claim 7, configured to modulate the coherent light source by controlling the drive current of the coherent light source, adjusting the temperature of the narrowband light source, or adjusting the phase of the light emitted from the coherent light source.

11. The multiplexed line scanning LiDAR system according to claim 7, wherein the signal processing device is configured to determine the envelopes of at least two digitized electrical signals.

12. The multiplexed line scanning LiDAR system according to claim 7, wherein the signal processing device is configured to measure the delay of the at least two digitized electrical signals at the falling edge of the envelope of the digitized electrical signals.

13. The multiplexed line scanning LiDAR system according to claim 7, wherein the scanning control device is configured to create a scanning pattern that generates a scanning synchronization signal, and to apply the scanning synchronization signal to the optical fiber lens element to generate a plurality of scanning patterns that enable the collection of measurement information determining the distance and velocity of the object.

14. The multiplexed line scanning LiDAR system according to claim 7, wherein the multiplexed LiDAR system is implemented as any combination of optical fibers, bulk optical systems, integrated optical circuits, or optical elements.

15. A method for determining the distance of an object, The process of generating a coherent light beam, The process involves modulating the coherent light beam with a pulse wavelength modulation signal, A step of polarizing the pulse wavelength modulated light beam by adjusting the polarization state of the pulse wavelength modulated light beam and maximizing the amplitude of the optical interference signal, The steps include optically splitting the pulse wavelength modulated light beam into at least two pulse wavelength modulated coherent light beams, The steps include: coupling each of the at least two pulse wavelength modulated light beams to one of at least two LIDAR modules to generate a sampling pulse wavelength modulated light beam and a reference pulse wavelength modulated light beam; The steps include transferring the one pulse wavelength modulated light beam to a multiplexing line scanning device to establish a line scanning pattern for the pulse wavelength modulated light beam, The steps include scanning the at least one pulse wavelength-modulated light beam over an object to be measured, where the distance of the wavelength-modulated coherent light beam from the light source is to be measured, The steps include receiving the back-reflected portion of the at least one pulse wavelength modulated light beam from the object to be measured, A step of coupling each back-reflected portion of the at least one pulse wavelength modulated light beam to the LIDAR module of the at least one pulse wavelength modulated light beam to form an electrical signal representing each of the at least two pulse wavelength modulated light beams, The process of digitizing the aforementioned electrical signal, The process of detecting the envelope of each of the digitized electrical signals, A step of determining the time of the rising edge or falling edge of the envelope of the digitized electrical signal, The process of determining the time difference between the rising edge or falling edge of the envelope of the digitized electrical interference signal, A method comprising the step of calculating the distance to the object to be measured.

16. A step of determining the velocity of the object by separately calculating the distance from at least one LIDAR module, The method according to claim 15, further comprising the step of calculating the velocity of the object as a change in distance over time.

17. The method according to claim 16, further comprising the step of carrying out the method using any combination of optical fibers, bulk optical systems, integrated optical circuits, or optical elements.

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