Multiplexed optical detection and ranging device

Abstract

A multiplexed LIDAR system generates an image of an object based on the measured distances of various points to the object. Multiplexed LIDAR utilizes at least two sets of light source radiation to the scanner to simultaneously form multiple scanning patterns, effectively improving the scanning speed, scanning area, or image pixel density of the LIDAR system.

Description

[Technical Field]

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

[0002] The present disclosure relates generally to optical detection and ranging systems. More particularly, the present disclosure relates to optical detection and ranging systems that generate multiple laser beams from a single light source, provide a hybrid scanner that scans the multiple laser beams onto a target or multiple targets, and receives retro-reflected laser beams into a multiplexed interferometer circuit for measuring range and velocity. Even more particularly, the present disclosure relates to optical detection and ranging methods, including methods for multiplexing interferometric techniques in measuring range and velocity. [Background technology]

[0003] LIDAR (Light Detection and Ranging) is similar to radar (Radio Detection and Ranging) in that it uses light waves to determine the distance, angle, and velocity of an object. LIDAR uses differences in the return time and wavelength of laser light to create a digital three-dimensional representation of the object, and is used in a wide range of applications, including ground, airborne, and mobile. LIDAR devices consist of one or more laser oscillators, optics, a scanner, a photodetector, and a signal processor. A coherent light beam generated by one or more laser oscillators is transmitted through a series of optics to a scanner, which then transmits it to an object to determine its distance or velocity. For three-dimensional (3D) scans, physical characteristics are sought. The photodetector receives the coherent light reflected from the object and converts it into an electrical signal. This signal is processed to determine the object's distance. The oscillator generates pulses of coherent light. The signal processor records the time the pulsed light is transmitted and also the time the reflected coherent light is received. The distance to the target is calculated by dividing the difference between the transmission time and the reception time by 2 and multiplying it by the speed of light.

[0004] Amplitude-modulated continuous wave (AMCW) LIDAR is a type of phase-differential LIDAR. Unlike direct pulse detection, phase-differential 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. Ranging is achieved by detecting the phase difference between the emitted and reflected signals. The phase shift of the sinusoidally modulated continuous laser waveform can be used to estimate the distance to a target.

[0005] 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 a carrier signal to accurately measure the round-trip time of flight of the laser. By detecting the beat frequency signal between the returning laser and the emitted laser, the time of flight can be calculated with high precision, enabling highly accurate distance measurements.

[0006] Time-of-flight (TOI) LIDAR technology is a novel ranging method that overcomes the limitations of traditional LIDAR technologies, such as time-of-flight (ToF) and frequency-modulated continuous wave (FWCW). Its features include: (1) an interferometer with a balanced detector, which can detect weak interferometric signals from long distances with high sensitivity; (2) the ability to measure the time delay of the interferometric signal even at high signal frequencies, enabling accurate measurement of the distance from the target without the need for a high-speed data acquisition system; and (3) low requirements for phase or wavelength modulation of the light source, simplifying the complexity of the light source driver circuit design. The operating speed of a TOI LIDAR system is primarily limited by the modulation speed of the light source and the efficiency of the optical receiver. The high-sensitivity detection of a TOI LIDAR system reduces the output power requirements of the light source. This allows for greater flexibility in system architecture design, allowing multiple TOI LIDAR systems to be driven simultaneously using a single light source. Summary of the Invention

[0007] An objective of the present disclosure is to provide a multiplexed light detection and ranging (LIDAR) system based on time of interferometry (TOI), time-frequency domain reflectometry, and small wavelength modulation of a coherent light source. A multiplexed LIDAR system records the time delay or time of interferometry (TOI) of two or more interfering signals using a single coherent light source whose output wavelength is determined by its operating current or temperature.

[0008] To this end, the multiplexed LIDAR system includes a coherent light source connected to a modulation scanning controller configured to generate a pulsed wavelength control signal that is transmitted to the coherent light source. The pulsed wavelength control signal may be a current modulation signal or a laser ambient temperature adjustment signal. The pulsed wavelength control signal modulates the coherent light source to generate pulsed wavelength-modulated coherent light emission.

[0009] The pulsed-wavelength-modulated coherent light is coupled to at least two interferometers. Each interferometer is configured to split the pulsed-wavelength-modulated coherent light into a sampling portion and a reference portion. The sampling portion of the pulsed-wavelength-modulated coherent light is positioned to be incident on a measurement object. The reference portion of the pulsed-wavelength-modulated coherent light is positioned to provide a reference basis for determining a 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. The hybrid scanner is configured to physically transfer the sampling portion of the pulsed-wavelength-modulated coherent light from each interferometer to a different location on the object 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 a portion of the pulsed-wavelength-modulated coherent light back-reflected from the 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 combined with the reference portion of the pulsed-wavelength-modulated coherent light to form an optical interference light signal.

[0010] The hybrid scanner is configured to provide a scan pattern for the pulsed wavelength-modulated coherent light from each interferometer. Each scan pattern is configured to cover a different region of the object, thereby increasing the effective scan range of the multiplexed LIDAR system. In various embodiments, each scan pattern is configured to cover the same region of the object, thereby increasing the effective scan pixel density of the multiplexed LIDAR system. The hybrid scanning mirror includes at least one flat mirror that rotates on a first axis and a faceted mirror configured to reflect sampled portions of the multiple pulsed wavelength-modulated coherent light from the multiple interferometers onto the object. The facet mirror rotates on a second axis to establish a scan pattern of sampled portions for the multiple pulsed wavelength-modulated coherent light.

[0011] The multiplexed LIDAR system includes a photodetector array configured to convert the optical interference signal from each interferometer into an electrical interference signal. In various embodiments, the photodetectors are configured as polarization diversity balanced amplification detectors. The photodetectors include at least one power monitor that measures the input power level to the photodetector. The output of the power monitor provides a power level modulated with a time delay related to the target distance.

[0012] The multiplexed LIDAR system includes a signal processor that receives the electrical interference signal and converts the electrical interference signal into digital data representing the amplitude of the electrical interference signal. The signal processor 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 of the interferometers.

[0013] The modulation and scanning controller is configured to generate a low duty cycle wavelength modulation control signal that modulates the coherent light source by controlling a drive current of the narrowband coherent light source, a temperature of the narrowband light source, or adjusting the phase of the light emitted from the light source. In another embodiment, the modulation and scanning controller generates a pulse phase control signal that generates interference when there is a time delay between the light in the sample arm and the reference arm of the interferometer.

[0014] In various embodiments, the interferometer includes a polarization control device that adjusts the polarization state of the coherent light emitted from the light source to maximize the amplitude of the optical or electrical interference signal. The interferometer includes a first coupler that receives the pulsed wavelength-modulated coherent light from the polarization control device. The coupler splits the pulsed wavelength-modulated coherent light. A first portion of the pulsed wavelength-modulated coherent light is provided to at least one sample arm. A second portion of the pulsed wavelength-modulated coherent light is provided to a reference arm. The interferometer includes a circulator connected to receive the first portion of the pulsed wavelength-modulated coherent light from the at least one sample arm. The circulator is configured so that the pulsed wavelength-modulated coherent light from the sample arm enters the circulator and exits through a second port. Typically, the second port directs the pulsed wavelength-modulated coherent light in a clockwise direction toward the scanner. The scanner is configured to physically transfer the sample pulsed wavelength-modulated coherent light to scan the object. The sampled pulsed wavelength-modulated coherent light is reflected back from the target object to the scanner and then transferred to a circulator in the interferometer, from which it is sent to a second coupler.

[0015] The interferometer's reference arm is longer than the sampling arm by more than twice the system's maximum ranging depth. A second portion of the pulsed-wavelength-modulated coherent light in the reference arm is applied to a second coupler. The second portion of the pulsed-wavelength-modulated coherent light traveling in the reference arm is combined with the recovered back-reflected pulsed-wavelength-modulated light to form an optical interference optical signal. This optical interference optical signal exits the second coupler and enters a photodetector array.

[0016] 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 minimum frequency of the optical interference signal corresponds to the maximum ranging depth of the multiplexed LIDAR system. The time delay of the detected optical interference is measured at the falling edge of the envelope of the optical interference signal.

[0017] In various embodiments, the multiplexed LIDAR system can be configured to simultaneously measure distances from multiple objects and display imaging ranges by directing the sampled pulsed wavelength-modulated coherent light beam of each interferometer to a separate scanner aimed in a different direction.

[0018] In various embodiments, a multiplexed LIDAR system can utilize two or more time-of-flight (ToF) or FMCW ranging methods using a single hybrid scanner configured to provide a scan pattern for each ToF or FMCW subsystem, with each scan pattern configured to cover a different region of the object to increase the effective scan range of the multiplexed LIDAR system, or to cover the same region of the object to increase the effective scan pixel density of the multiplexed LIDAR system. [Brief explanation of the drawings]

[0019] [Figure 1A] FIG. 1 is a schematic diagram of a related art TOI LIDAR system 100.

[0020] [Figure 1B]FIG. 1 is a schematic diagram of a LIDAR module embodying the principles of the present disclosure.

[0021] [Figure 2] FIG. 1 is a schematic diagram of a multiplexed LIDAR system embodying the principles of the present disclosure.

[0022] [Figure 3A] FIG. 1C is a schematic diagram of a scanner configured to scan two illumination light beams from the two LIDAR modules of FIG. 1B to form a larger scan pattern, embodying the principles of the present disclosure.

[0023] [Figure 3B] FIG. 1C is a schematic diagram of a scanner configured to scan two illumination light beams from the two LIDAR modules of FIG. 1B to form a denser scan pattern, embodying the principles of the present disclosure.

[0024] [Figure 4] FIG. 1C is a schematic diagram of a scanner configured to scan two illumination light beams from the two LIDAR modules of FIG. 1B to form two scan patterns having different scan areas and scan pixel densities, embodying the principles of the present disclosure.

[0025] [Figure 5A] FIG. 1C is a schematic diagram of a scanner using an angled polygon mirror configured to scan two illumination light beams from the two LIDAR modules of FIG. 1B to form a larger scan pattern, embodying the principles of the present disclosure.

[0026] [Figure 5B] FIG. 1C is a schematic diagram of a scanner using an angled polygon mirror configured to scan two illumination light beams from the two LIDAR modules of FIG. 1B to form two scan patterns with different scan areas and scan pixel densities, embodying the principles of the present disclosure.

[0027] [Figure 6A]FIG. 1 is a block diagram of an electrical TOI measurement circuit illustrating the program structure of a signal processor configured to perform multiplexed TOI LIDAR-based distance measurements, embodying the principles of the present disclosure.

[0028] [Figure 6B] FIG. 10 is a plot of the back-reflected pulse fringes and envelope of the sample arm at zero (0) meter position embodying the principles of the present disclosure.

[0029] [Figure 6C] FIG. 10 is a plot of the back-reflected pulse fringes and envelope of the sample arm at 180 meters embodying the principles of the present disclosure.

[0030] [Figure 7] FIG. 1 illustrates a frame-based velocity measurement method for a TOI LIDAR system embodying the principles of the present disclosure.

[0031] [Figure 8A] 1 is a flowchart of a method for determining distance to an object employing multiplexed distance measurements, embodying the principles of the present disclosure.

[0032] [Figure 8B] 1 is a flowchart of a method for determining the velocity of an object employing multiplexed distance measurements, embodying the principles of the present disclosure.

[0033] [Figure 9A] FIG. 1 is a schematic diagram of a multiplexed LIDAR system having multiple front-end scanners embodying the principles of the present disclosure.

[0034] [Figure 9B] FIG. 1 is a schematic diagram of an implementation of a multiplexed LIDAR system having multiple front-end scanners embodying the principles of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0035] A multiplexed LIDAR system is configured to generate an image of an object based on measured distances of various points to the object, and the multiplexed LIDAR system splits light emitted from a pulsed wavelength-modulated light source into at least two sets of optical radiation and sends them to a scanner to simultaneously form multiple scanning patterns, thereby effectively increasing the scanning speed, scanning area, or image pixel density of the LIDAR system.

[0036] FIG. 1A is a schematic diagram of a related art TOI system 100. In FIG. 1A, the TOI LIDAR system 100 includes a pulsed, wavelength-modulated, narrow-bandwidth light source 105. The pulsed, wavelength-modulated light source 105 emits pulsed, coherent light with 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 resonant cavity, typically consisting of two or more mirrors. The cavity has mirrored walls that reflect light, allowing standing wave modes to exist within the cavity with little loss. The longitudinal modes correspond to wavelengths of the reflected waves that are strengthened by constructive interference after multiple reflections off the reflective surfaces of the cavity. All other wavelengths are suppressed by destructive interference. The longitudinal mode pattern has nodes arranged axially along the length of the cavity. The laser in the pulsed, wavelength-modulated light source 105 is known in the art and can be implemented as one of four types of lasers: solid-state lasers, gas lasers, liquid lasers, or semiconductor lasers. In the configurations described in this disclosure, 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 now be described.

[0037] Pulsed wavelength-modulated narrow-band light source 105 emits pulsed wavelength-modulated coherent light to interferometer 110. The light emitted by pulsed wavelength-modulated narrow-band light source 105 is transmitted to interferometer 110 via free space, optical fiber, or optical waveguide.

[0038] In various embodiments, the interferometer 110 is implemented as optical fiber, bulk optics, integrated optical circuits, or some combination thereof. The interferometer 110 includes a polarization controller 115 that receives the pulsed wavelength-modulated coherent light and adjusts the polarization state of the pulsed wavelength-modulated coherent light from the light source 105. The polarization controller 115 maximizes the amplitude of the optical interference signal or electrical interference signal 162 forwarded along optical paths 155a and 155b. The pulsed wavelength-modulated coherent light from the light source 105 or forwarded through the polarization controller 115 is sent to a coupler 120. The coupler 120 splits the coherent light into a sample portion that is fed to at least one sample arm 122 and a reference portion of the pulsed wavelength-modulated coherent light that is fed to a reference arm 140 within the interferometer 110. The sample arm 122 and the reference arm 140 are implemented as free-space paths, optical fibers, or optical waveguides.

[0039] The interferometer includes a circulator 125 that receives a sample portion of the pulsed wavelength-modulated coherent light from the sample arm 122. The circulator 125 is configured so that the sample portion of the pulsed wavelength-modulated coherent light enters the circulator 125 and exits a section of the sample arm 122 through a next port. The next port directs the coherent light, typically (but not necessarily) in a clockwise direction, through the sample arm 122 to a scanner 130. The scanner 130 is configured to physically transfer the sampled pulsed wavelength-modulated coherent light 135 to scan the object. The sampled pulsed wavelength-modulated coherent light 135 is back-reflected from the object to perform ranging measurements. The back-reflected pulsed wavelength-modulated coherent light is received by the scanner 130 and forwarded to the circulator 125. The back-reflected pulsed wavelength-modulated coherent light is then forwarded via optical path 145 to a second coupler 150. The optical path may be implemented as a free space path, an optical fiber, or an optical waveguide.

[0040] The reference arm 140, implemented as a free space path, optical fiber, or optical waveguide, has an additional optical path 142 that provides additional path length so that the path length of the reference arm 140 matches the maximum ranging depth of the TOI system 100. The optical pulse wavelength modulated coherent optical signals from at least one of the sample arm 122 and the reference arm 140 are combined in a coupler 150 to generate an optical interference signal.

[0041] Each pulse wavelength modulated coherent optical signal from at least one of the sample arm 122 and the reference arm 140 is heterodyne detected to extract the beat frequency from the base signal. The beat signal has a 180° phase difference between each output of the coupler. A balanced detector 160 subtracts the signals from each input channel to extract the interference signal, which is the beat signal.

[0042] The optical interference signal is applied to optical paths 155a and 155b, which may be implemented as free space paths, optical fibers, or optical waveguides, and forwarded to a balanced photodetector 160, which converts the optical interference signal from optical paths 155a and 155b into an interferometric electrical signal 162.

[0043] An interferometric electrical signal 162 is generated by the balanced photodetector 160 and transferred to data acquisition circuitry within the signal processor 165. The data acquisition circuitry within the signal processor 165 converts the interferometric electrical signal 162 into digital data. The maximum frequency of the optical interferometric signal corresponds to the minimum ranging depth of the TOI LIDAR system 100. The maximum frequency of the optical interferometric signal is greater than the Nyquist sampling frequency of the digitizer within the data acquisition or signal processor 165.

[0044] The minimum frequency of the optical interference signal applied to optical paths 155a, 155b corresponds to the maximum ranging depth of the TOI LIDAR system 100. The time delay of the detected optical interference is measured at the falling edge of the envelope of the optical interference signal.

[0045] The digital data is then transferred to computer 170 for further processing and display. In some embodiments, signal processor 165 may be integrated with computer 170 as a single unit.

[0046] In various embodiments, computer 170 is connected to modulation and scanning controller 175. In other embodiments, computer 170 is integrated with modulation and scanning controller 175. Modulation and scanning controller 175 includes a modulation subcircuit that determines the modulation depth, frequency, and shape of modulation control signal 177 applied to coherent light source 105. Modulation and scanning controller 175 also includes a scan control circuit that provides modulation and scanning synchronization signals 179 to signal processor 165 and scanner 130. This scan control circuit creates the desired scan pattern, which is used to generate the appropriate modulation and scanning synchronization signals 179 applied to scanner 130.

[0047] The scanner 130 may be implemented as a one-dimensional or two-dimensional scanner that disperses the sample pulsed wavelength-modulated coherent light 135 to form an image based on the TOI measurement. The one-dimensional scanning pattern may be linear or nonlinear in time, and may be unidirectional or bidirectional. In some implementations of the TOI lidar system 100, the two-dimensional scanning pattern may be linear or nonlinear in time. It may be a raster scan, a spiral scan, or other pattern for collecting measurement information. The scanner 130 may be implemented mechanically as a galvanometer mirror, a microelectromechanical system (MEMS), a piezoelectric actuator, or optically with an acousto-optic (AO) deflector, or as a solid-state scanner. Other methods consistent with the principles of the present disclosure for providing the necessary scanning motion to collect measurement information may exist.

[0048] 1B is a schematic diagram of a LIDAR module 200 embodying the principles of the present disclosure. The LIDAR module 200 includes an interferometer 110 and a balanced detector 160. The interferometer 110 and the balanced detector 160 are identical in structure and operation to the related art interferometer 110 and balanced detector 160 shown in FIG. 1A.

[0049] Figure 2 is a schematic diagram of a multiplexed LIDAR system 300 based on a TOI LIDAR system embodying the principles of the present disclosure. The multiplexed LIDAR system 300 includes a pulsed, wavelength-modulated, narrow-bandwidth light source 305. The pulsed, wavelength-modulated light source 305 emits pulsed, coherent light with 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 resonant cavity, typically consisting of two or more mirrors. The cavity has mirrored walls that reflect light, allowing the standing wave modes to exist within the cavity with little loss. The longitudinal modes correspond to wavelengths of the reflected waves that are enhanced by constructive interference after multiple reflections off the reflective surfaces of the cavity. All other wavelengths are suppressed by destructive interference. The longitudinal mode pattern has nodes arranged axially along the length of the cavity. The pulsed wavelength-modulated light source 305 is known in the art and may be implemented as one of four types of lasers: solid-state laser, gas laser, liquid laser, or semiconductor laser. In the configurations described in this disclosure, the pulsed wavelength-modulated light source 305 is depicted as a coherent light source 305 whose wavelength or frequency is controlled by either current or temperature. Modulation of the pulsed wavelength-modulated light source 305 is described below.

[0050] A pulsed wavelength-modulated narrow-band light source 305 emits pulsed wavelength-modulated coherent light, which is split by an optical splitter 307 to the two LIDAR modules 200c and 200d. The light emitted by the pulsed wavelength-modulated narrow-band light source 305 travels to the optical splitter 307 via free space, optical fiber, or an 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, an optical switch can be used instead of the optical splitter 307 for applications requiring high detection sensitivity and where slower detection speeds are acceptable.

[0051] In various embodiments, the LIDAR modules 200c and 200d are configured as described above in FIG. 1B and are implemented as optical fibers, bulk optics, integrated optical circuits, or some combination thereof. The optical pulse wavelength-modulated coherent optical signal is forwarded from the 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 the sample pulse wavelength-modulated coherent light 135a and 135b to form an image based on the TOI measurement. The one-dimensional scanning pattern may be linear or nonlinear in time and may be unidirectional or bidirectional. The sample pulse wavelength-modulated coherent light beams 135a and 135b are then reflected back to the hybrid scanner 330 and forwarded to the LIDAR modules 200a and 200b. The back-reflected sample pulse wavelength-modulated coherent light 135a and 135b is sent to the circulator 125 of FIG. 1B, from which it travels to the optical paths 145 of the LIDAR modules 200a and 200b and the optical coupler 150. The reference signal from the reference path 140 is combined with the back-reflected optical signals from the circulator 145 in both the LIDAR modules 200a and 200b in the optical coupler 150 to generate the optical interference signals 155a and 155b of FIG. 1B. As further shown in FIG. 1B, the back-reflected pulse wavelength-modulated coherent optical signals from the sample arms 122a, 122b and the reference arm 140 are heterodyne detected to extract the beat frequency from the base signal. The beat signals have a 180° phase difference at the two outputs 155a and 155b from the coupler 150. The balanced detector 160 subtracts the signals from each input channel to extract the interfering signal, which is the beat signal.

[0052] The optical interference signals are applied to optical paths 155a and 155b, which may be implemented as free space paths, optical fibers, or optical waveguides, and forwarded to a balanced photodetector 160, which converts the optical interference signals from the optical paths 155a and 155b of the two interferometers 110 in the two LIDAR modules 200a and 200b into first and second interferometric electrical signals 362a and 362b of FIG.

[0053] The first interfering electrical signal 362a and the second interfering electrical signal 362b are forwarded to data acquisition circuitry within the signal processor 365, which converts the first interfering electrical signal 362a and the second interfering electrical signal 362b into digital data. In some embodiments, the time delay of the detected electrical interfering signals 362a and 362b can be measured at the rising or falling edge of the envelope of the electrical interfering signals within the signal processor 365 with analog signal processing circuitry, without being converted to digital data.

[0054] The digital data is then transferred to computer 370 for further processing and display. In some embodiments, signal processor 365 may be integrated with computer 370 as a single unit.

[0055] In various embodiments, computer 370 is connected to modulation and scanning controller 375. In other embodiments, computer 370 is integrated with modulation and scanning controller 375. Modulation and scanning controller 375 includes a modulation subcircuit that determines the modulation depth, frequency, and shape of a modulation control signal 377 applied to coherent light source 305. Modulation and scanning controller 375 also includes a scanning control circuit that provides modulation and scanning synchronization signals 379 to signal processor 365 and scanner 330. Modulation and scanning controller 375 creates the desired scan pattern, which is used to generate the appropriate modulation and scanning synchronization signals 379 applied to scanner 330.

[0056] The scanner 330 may be implemented as a one-dimensional or two-dimensional scanner that disperses the sample pulsed wavelength-modulated coherent light 335a and 335B to form an image based on the TOI measurement. The one-dimensional scanning pattern may be linear or nonlinear in time, and may be unidirectional or bidirectional. In some implementations of the TOI LIDAR system 300, the two-dimensional scanning pattern may be linear or nonlinear in time. It may be a raster scan, a spiral scan, or other pattern for collecting measurement information. The scanner 330 may be realized mechanically as a galvanometer mirror, a polygonal mirror, a microelectromechanical system (MEMS), a piezoelectric actuator, or optically with an acousto-optic (AO) deflector or a solid-state scanner. There may be other methods consistent with the principles of the present disclosure that provide the scanning motion required to collect measurement information.

[0057] 3A and 3B are schematic diagrams of a scanner 330 configured to receive the sampling arms 322a and 322b of the LIDAR modules 200c and 200d, as shown in FIG. 1B. The sampling arm 322a from the first LIDAR module 200c and the sampling arm 200d of the second LIDAR module 200d are inserted and secured into the scanner 330. The distal ends of the first sampling arms 322a and 322b are connected to collimators 325a and 325b for collimating the sample pulsed wavelength-modulated coherent light beams 322a and 322b. To improve the overall efficiency of the LIDAR operation, the collimators 325a and 325b require a low numerical aperture for long-distance illumination, but a higher numerical aperture for receiving the pulsed wavelength-modulated coherent light reflected back from the target. Thus, collimators 325a and 325b may be single fiber optic lenses with engineered tips, such that on-axis sample pulsed wavelength-modulated coherent light beams 335a and 335b emerging through the central portion of the engineered tip are collimated, while off-axis back-reflected pulsed wavelength-modulated coherent light from the target through the annular portion of the engineered tip can be coupled back into sample arm fibers 322a and 322b. The collimator fiber optic lenses are implemented as a gradient index (GRIN) fiber optic lens with single-mode fiber, a GRIN fiber optic lens with few-mode fiber, a fiber optic ball lens, a GRIN lens assembly, a free-space collimator, or a combination thereof. The engineered tip can be a tapered tip, a Fresnel surface, a metasurface, or a combination thereof.

[0058] In FIG. 3A, pulsed wavelength-modulated coherent light beams 335a and 335b are directed toward slow-axis scanning mirrors 340a and 340b. The slow-axis scanning mirrors 340a and 340b are on a first axis. In this example, the slow-axis scanning mirrors 340a and 340b rotate vertically and reflect the pulsed wavelength-modulated coherent light beams 335a and 335b in a vertical scanning pattern that covers the desired field of view. The first and second slow-axis scanning mirrors 340a and 340b are configured to be offset in position so that the reflected pulsed wavelength-modulated coherent light beams 345a and 345b are incident on different facets of the fast-axis scanning mirror 350. The fast axis scanning mirror 350 is a polygonal cylindrical portion, and each facet 351 a, 351 b, 351 c of the fast axis scanning mirror 350 has an equally sized rectangular mirror surface 351 a, 351 b, 351 c formed on the outer surface of the polygonal cylindrical portion of the fast axis scanning mirror 350.

[0059] The fast axis scan mirror 350 is rotated horizontally on a shaft 353 by a motor 352 to form a horizontal scan pattern. The horizontal scan pattern covers a horizontal field of view. The vertical scan pattern and the horizontal scan pattern combine to generate a first two-dimensional scan pattern 355a and a second two-dimensional scan pattern 355b from the reflected pulsed wavelength-modulated coherent light beams 135a and 135b, respectively. The position offset of the first and second slow axis scan mirrors 340a and 340b determines the separation of the first and second two-dimensional scan patterns 355a and 355b. The two two-dimensional scan patterns 355a and 355b form a composite scan pattern with a scan area twice as large as each of the two-dimensional scan patterns 355a and 355b, thereby increasing the effective scan area.

[0060] In Figure 3B, collimators 325a and 325b are configured to have a small enough positional offset that pulsed wavelength-modulated coherent light beams 345a and 345b are directed to different portions of a single slow axis scan mirror 340. Slow axis scan mirror 340 rotates vertically, reflecting pulsed wavelength-modulated coherent light beams 345a and 345b in a vertical scan pattern. After reflection, pulsed wavelength-modulated coherent light beams 345a and 345b are incident on different portions of fast axis scan mirror 350, which is identical to fast axis scan mirror 350 in Figure 3A.

[0061] Fast axis scan mirror 350 is rotated horizontally on shaft 353 by motor 352 to form a horizontal scan pattern. The vertical and horizontal scan patterns combine to produce first and second two-dimensional scan patterns 355a and 355b, respectively, from reflected pulsed wavelength-modulated coherent light beams 135a and 135b. The two two-dimensional scan patterns 355a and 355b completely overlap to form a composite scan pattern with twice the scan pixel density of each individual two-dimensional scan pattern, thereby increasing the effective scan pixel density or effective scan speed. In some embodiments, two-dimensional scan patterns 355a and 355b partially overlap, resulting in an increased pixel density and scan pixel area for portions of composite scan patterns 355a and 355b.

[0062] FIG. 4 is a schematic diagram of a scanner 330 configured to accept the sampling arms 122a and 122b of the LIDAR modules 200c and 200d of FIG. 3A. As shown in FIG. 3A, the scanner 330 is configured to accept the sampling arms 322a and 322b of the LIDAR modules 200c and 200d. The pulsed wavelength-modulated coherent light from the sampling arms 322a and 322b of the LIDAR modules 200c and 200d is applied to collimators 325a and 325b. The pulsed wavelength-modulated coherent light beams 345a and 345b from the collimators 325a and 325b are directed to slow axis scanning mirrors 340a and 340b, respectively. The slow axis scanning mirrors 340a and 340b rotate vertically, reflecting the pulsed wavelength-modulated coherent light beams 345a and 345b in a vertical scanning pattern. The vertical scanning pattern covers a desired field of view. The first and second slow axis scanning mirrors 340a and 340b are configured with an offset position such that the reflected pulsed wavelength-modulated coherent light beams 345a and 345b are incident on different locations on the fast axis scanning mirror 405. The fast axis scanning mirror 405 is a rotating polygon mirror that has two sets of different facet configurations, including a low facet section (fewer facets) 405a and a high facet section (more facets) 405b. The low facet portion 405a has facets 406a, 406b, and 406c, and the high facet portion 405b has facets 409a, 409b, 409c, 409d, 409e, and 409f formed by equally sized rectangular mirror surface shapes 409a, 409b, 409c, 409d, 409e, and 409f formed on the outer surface of the polygonal cylindrical portion of the fast axis scanning mirror 405.

[0063] The first reflected pulse-wavelength-modulated coherent light beam 345b is incident on the low facet portion 405a of the polygon mirror 405, and the second reflected pulse-wavelength-modulated coherent light beam 405b is incident on the high facet portion 405b of the polygon mirror 405. Alternatively, although not shown, the polygon mirror 405 could be inverted 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 a first example, the pulse-wavelength-modulated coherent light beam 135a forms a first two-dimensional scan pattern 415a with a wide scan area and a low scan pixel density, and the pulse-wavelength-modulated coherent light beam 135b forming the second two-dimensional scan pattern 415b has a narrow scan area and a high scan 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 imaging.

[0064] As previously described, motor 408 rotates shaft 407 to rotate fast axis scan mirror 405 .

[0065] 5A and 5B are schematic diagrams of scanner 130 configured to accept sampling arms. As shown in FIG. 5A, scanner 330 is configured to accept sampling arms 322a and 322b of interferometers 110a and 110b of LIDAR modules 200c and 200d. Collimators 325a and 325b are configured to have small enough positional and angular offsets that pulsed wavelength-modulated coherent light beams 325a and 325b are directed to different locations on a single slow axis scanning mirror 340. Slow axis scanning mirror 340 rotates vertically, reflecting pulsed wavelength-modulated coherent light beams 325a and 325b in a vertical scan pattern. After reflection, pulsed wavelength-modulated coherent light beams 345a and 345b are incident on different portions of fast axis scanning mirror 410.

[0066] The fast axis scanning mirror 410 has two polygonal cylindrical sections 410a and 410b. The first polygonal cylindrical section 410a has multiple isosceles trapezoidal facet mirrors 411a, 411b, and 411c. The isosceles trapezoidal facet mirrors 411a, 411b, and 411c are formed on each facet surface of the first polygonal cylindrical section 410a, with the upper side longer than the lower side.

[0067] The second polygonal cylindrical portion 410b has a plurality of isosceles trapezoidal facet mirrors 411d, 4116e, 411f. The isosceles trapezoidal facet mirrors 411d, 4116e, 411f are formed on each facet surface of the first polygonal cylindrical portion 410b, and the bottom side is longer than the top side.

[0068] A fast-axis scan mirror 410, comprising isosceles trapezoidal facet mirrors 411a, 411b, 411c, 411d, 4116e, and 411f, corrects the angular offset of the reflected pulsed-wavelength-modulated coherent light beams 345a and 345b. The fast-axis scan mirror 410 is rotated horizontally by a motor 412 via a shaft 413 to form a horizontal scan pattern. The vertical and horizontal scan patterns combine to produce a first two-dimensional scan pattern 415a and a second two-dimensional scan pattern 415b, which fully overlap to form the reflected pulsed-wavelength-modulated coherent light beams 135a and 135b, respectively. The two two-dimensional scan patterns 415a and 415b form a composite scan pattern with a scan pixel density twice as large as each individual two-dimensional scan pattern, thereby increasing the effective scan pixel density or effective scan speed. In some embodiments, the two-dimensional scan patterns 415a and 415b partially overlap, resulting in an increased pixel density and increased scan pixel area in portions of the composite scan patterns 415a and 415b.

[0069] In Figure 5B, the basic structure of the hybrid scanner 330 is the same as that of the hybrid scanner 330 in Figure 5A. The fast axis scanning mirror 420 is a rotating polygon mirror. The rotating polygon mirror 420 consists of two distinct polygonal cylinders 420a and 420b, including a low-faceted portion 420a with the fewest facets and a second portion 420b with the most facets. The first reflected pulse-wavelength-modulated coherent light beam 135a is incident on the second portion 420a of the polygon mirror 420. The second reflected pulse-wavelength-modulated coherent light beam 135b is incident on the first portion 420b of the rotating polygon mirror 420, resulting in a first two-dimensional scanning pattern 415a with a wide scanning area and a low scanning pixel density and a second two-dimensional scanning pattern 415b with a narrow scanning area and a high scanning pixel density. This implementation allows the multiplexed LIDAR system 300 of FIG. 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 imaging.

[0070] 6A is a block diagram of an electrical TOI measurement circuit included in the signal processing device. The interfering electrical signals 362a and 362b of FIG. 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, a root mean square (RMS) detector, or a frequency demodulator. Radio frequency (RF) power detectors, root mean square (RMS) detectors, or frequency demodulators are known in the art and are commercially available devices. The radio frequency (RF) power detector, root mean square (RMS) detector, or frequency demodulator extracts the envelope of the interfering electrical signal 162 by removing high-frequency components in the interfering electrical signals 362a and 362b.

[0071] The envelope signals 505a and 505b are forwarded to a multi-channel edge detector 510, which determines pulse events and places the pulse events at the edge detector output 510. A pulse event is indicative of a rising or falling edge of the envelope signals 505a and 505b. The multi-channel edge detector 510 may be implemented as an edge-to-glitch converter, an XOR gate and delay circuit, a differentiator, etc. Edge-to-glitch converters, XOR gate and delay circuits, and differentiators are also known in the art and commercially available.

[0072] The outputs 515a and 515b of the edge detector 510 are connected to the inputs of the multi-channel time-to-digital converter 520. The multi-channel time-to-digital converter 520 generates a time difference signal and forwards it to the outputs 530a and 530b of the multi-channel time-to-digital converter 520. The time difference signal at the outputs 530a and 530b of the multi-channel time-to-digital converter 520 indicates the time of the rising or falling edge between the pulse events 505a and 505b and the pulse event 525. The pulse event 525 corresponds to the rising or falling edge of the light source modulation signal 377 forwarded from the modulation and scanning controller 375. The pulse event 525 triggers the multi-channel time-to-digital converter 520 to start counting time intervals. The pulse outputs 515a and 515b of the multi-channel edge detector 510 provide the pulse event that terminates the counting of time intervals by the multi-channel time-to-digital converter 520. The series of time difference signals at outputs 530a and 530b of multi-channel time-to-digital converter 520 are converted into depth measurements to form an image that is displayed by computer 170.

[0073] FIG. 6B is a plot of pulse input fringes 560 and envelope 565 of a reference arm embodying the principles of the present disclosure. FIG. 6B is an example of an interference electrical signal from the prototype TOI system 300 of FIG. 2 detecting an object at zero (0) meters. FIG. 6C is a plot of back-reflected pulse fringes 570 and envelope 575 of another sample arm embodying the principles of the present disclosure. FIG. 6C is an example of an interference electrical signal from the prototype TOI system 300 detecting an object at 180 meters. The multi-channel edge detector 510 of FIG. 6A determines the time of the falling edge t0 of the envelope of the reference arm 565 and the time of the falling edge t1 of the envelope of the sample arm 575. The multi-channel time-to-digital converter 520 counts the time interval between the falling edge time t0 of the reference arm and the falling edge time t1 of the sample arm. The distance of the object being measured is determined by the following equation: Distance=c×(t0-t1) where: c is the speed of light, t0 is the falling edge time of the reference arm, t1 is the falling edge time of the sample arm. The series of time difference signals at the outputs 530 a and 530 b of the multi-channel time-to-digital converter 520 can be converted into depth information to form an image that is displayed by the computer 370 .

[0074] 7 illustrates a frame-based velocity measurement method using a multiplexed LIDAR system embodying the principles of the present disclosure. The multiplexed LIDAR system can be configured such that a small time delay is encoded within the second TOI module, such that frames 590a(1), 590a(2), ..., 590a(m) and 590b(1), 590b(2), ..., 590b(m) are captured in an interleaved manner by TOI modules 200a and 200b of FIG. 2, respectively, to represent first and second interfering electrical signals 362a and 362b of FIG. 2.

[0075] The data 595a and 595b are transferred to the signal processor 365 and processed as described in FIG. 6 to determine the rising or falling edge of the data. Thus, determining the rising or falling edge of the data provides the time difference between the data 595a and 595b. The distance between the data 615a and 615b is then calculated as the time difference (t b -t a ) is calculated as the time difference between data 595a and 595b (t b -t a ) is multiplied by the frame rate of sampling of the optical interference signals applied to the optical paths of the LIDAR modules 200a and 200b to obtain the velocity of the object to be measured.

[0076] 8A is a flowchart of a method for determining distance to an object employing a TOI-based multiplexed LIDAR system embodying the principles of the present disclosure. A laser light beam is generated (Box 700). The laser light beam is modulated (Box 705) with a wavelength- or frequency-modulated signal to adjust the wavelength or frequency of the laser light beam. The laser light beam is then polarized (Box 710) to adjust the polarization state of the laser light and maximize the amplitude of the optical or electrical interference signal.

[0077] The laser light beam is optically split into multiple light beams (Box 715), and each split laser light beam is coupled to a LIDAR module (Box 720) to create a sampling arm and a reference arm. Each sampling arm is connected to a hybrid scanner (Box 725) to establish a scanning pattern for each sampling laser light beam. Each sampling laser beam is scanned over the measurement object (Box 730). A portion of each laser coherent light beam is reflected back from the measurement object and received by each hybrid scanner associated with the back-reflected pulsed wavelength-modulated coherent laser beam (Box 735). The back-reflected pulsed wavelength-modulated coherent laser beam is coupled to an optical circulator of the interferometer (Box 740), connected to an optical coupler, and combined with the reference pulsed 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).

[0078] The envelope of this electrical interference signal is identified through an envelope detection process (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 and scanning synchronization signal is determined (Box 760), and the distance to the measurement target is calculated (Box 765). As the multiple laser light beams scan the target, a two-dimensional ranging image is formed based on all the measured distances and the angular position of the scanner (Box 760).

[0079] 8B is a flowchart of a method for determining the velocity of an object employing a multiplexed LIDAR system based on time of interferometry (TOI), embodying the principles of the present disclosure. The method for determining the velocity of an object using a multiplexed LIDAR system based on TOI begins by performing the method steps of FIG. 8A multiple times (box 775). The velocity of the object is determined as the difference in distance measured by the multiplexed TOI modules over time (box 780).

[0080] In various embodiments, each LIDAR module in a multiplexed LIDAR system includes multiple scanners so that 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 TOI LIDAR that embodies the principles of the present disclosure. Instead of using a single scanner as in the system shown in Figure 2, each sample arm of the first and second TOI modules 200a and 200b is separately connected to a first scanner 805a and a second scanner 805b, which 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.

[0081] FIG. 9B is a schematic diagram of a multiplexed LIDAR system 900 for multiplexed distance measurement embodying the principles of the present disclosure. A single back-end system 910 includes a pulsed-wavelength-modulated light source 905 that forwards a pulsed-wavelength-modulated light beam 906 to a multi-beam splitter 907. An exemplary multi-beam splitter 907 is a diffractive beam splitter 908 that provides the required number of individual beams for the LIDAR system 900. The multiple wavelength-modulated light beams are directed to focusing lenses 909 that re-collimate each light beam. Each light beam is forwarded to a TOI LIDAR module 920a, 920b, 920c, 920d, 920e, ..., 920n. In various embodiments, a multi-channel optical switch can be used in place of the multi-beam splitter 907 for applications requiring high detection sensitivity and a narrow field of view, or where slow detection speed is acceptable.

[0082] Each LIDAR module 920a, 920b, 920c, 920d, 920e, ..., 920n is connected to a scanner 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 a one-dimensional scanner or a two-dimensional scanner as described in Figures 3A, 3A, 4, 5A, and 5B. The scanners 925a, 925b, 925c, 925d, 925e, ..., 925n transmit sample pulsed wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n to scan one or more objects in different directions within a circumference of the surrounding environment.

[0083] The back-reflected wavelength-modulated coherent light beams 935a, 935b, 935c, 935d, 935e, ..., 935n from the scanned object(s) are received by the scanners 925a, 925b, 925c, 925d, 925e, ..., 925n and forwarded to the LIDAR modules 920a, 920b, 920c, 920d, 920e, ..., 920n, where an image is formed based on the TOI measurement. The one-dimensional scanning pattern may be linear or nonlinear in time and may be unidirectional or bidirectional. In some implementations of the multiplexed LIDAR system 900, the two-dimensional scanning pattern may be linear or nonlinear in time. It may be a pattern for collecting measurement information, such as a raster scan or a spiral scan.

[0084] The back-reflected wavelength-modulated coherent optical beams 935a, 935b, 935c, 935d, 935e, ..., 935n received by the TOI LIDAR modules 920a, 920b, 920c, 920d, 920e, ..., 920n are then forwarded to a signal processor 965. The signal processor 965 includes a plurality of balanced detectors 160 of FIG. 1B that receive the back-reflected wavelength-modulated coherent optical beams 935a, 935b, 935c, 935d, 935e, ..., 935n. The balanced detectors 160 of FIG. 1B convert the optical beams 935a, 935b, 935c, 935d, 935e, ..., 935n into electrical signals that are processed by a computer 970 to generate an image based on the TOI measurements.

[0085] Scanners 925a, 925b, 925c, 925d, 925e, ..., 925n may be implemented mechanically as galvanometer mirrors, polygonal mirrors, microelectromechanical systems (MEMS), piezoelectric actuators, or optically with acousto-optic (AO) deflectors, or as solid-state scanners. There may be other methods consistent with the principles of the present disclosure that provide the scanning motion necessary to collect measurement information.

[0086] While the present disclosure has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure. In particular, the multiplexing system 100 of Figure 2 and the system 800 of 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. 1. A hybrid scanner in a multiplexed light detection and ranging (LIDAR) system for performing a scanning pattern of a plurality of sample pulsed wavelength-modulated coherent light beams, comprising: a plurality of optical collimators configured to transfer one sampled pulsed wavelength-modulated coherent light beam to each optical collimator of the plurality of optical collimators; at least one slow-axis rotating plane mirror configured to receive and reflect at least one collimated sample pulsed wavelength-modulated coherent light beam and to rotate along a first axis to form a first dimensional scan pattern of the sample pulsed wavelength-modulated coherent light beam; a fast axis rotary polygon mirror configured to reflect the plurality of pulsed wavelength-modulated coherent light beams, the fast axis rotary polygon mirror configured to rotate on a second axis to form a second dimensional scan pattern of the plurality of pulsed wavelength-modulated coherent light beams; A hybrid scanner wherein the plurality of pulsed wavelength modulated coherent light beams are transmitted to an object and a combination of the first dimensional scanning pattern and the second dimensional scanning pattern is used to determine the geometric dimensions of the object.

2. 2. The hybrid scanner of claim 1, wherein the plurality of pulsed wavelength-modulated coherent light beams are reflected back to the hybrid scanner, reflected by the fast axis rotating polygon scanning mirror to the at least one slow axis rotating plane mirror, through the at least one collimator, and to an interferometer in a LIDAR module for determining dimensions of the scanned object.

3. 2. The hybrid scanner of claim 1, wherein the at least one slow-axis rotating plane mirror is two slow-axis rotating plane mirrors, and a first pulse-wavelength-modulated coherent light beam is incident on the first slow-axis rotating plane mirror and a second pulse-wavelength-modulated coherent light beam is incident on the second slow-axis rotating plane mirror.

4. 4. The hybrid scanner of claim 3, wherein the first pulse wavelength modulated coherent light beam reflected from the first slow axis rotating plane mirror and the second pulse wavelength modulated coherent light beam reflected from the second slow axis rotating plane mirror are incident on the fast axis rotating polygon scanning mirror.

5. 5. The hybrid scanner of claim 4, wherein the first and second rotating slow-axis scanning mirrors are configured to have a positional offset therebetween, such that the reflected pulsed wavelength-modulated coherent light beam is incident on each selected facet of the fast-axis rotating multi-faceted scanning mirror.

6. 6. The hybrid scanner of claim 5, wherein each of the pulsed wavelength-modulated coherent light beams reflected from the selected facet of the fast axis rotating polygon scanning mirror is directed to an object, and a combination of the first dimensional scanning pattern and the second dimensional scanning pattern is used to determine a geometric dimension of the object.

7. The fast axis rotating polygonal scanning mirror is a multi-sided polygonal cylindrical portion having a central shaft; a motor connected to the central shaft for rotating the polygonal cylindrical portion; 7. The hybrid scanner of claim 6, comprising a plurality of mirrors, one mirror formed on each face of a polygonal mirror.

8. The hybrid scanner of claim 7 , wherein the plurality of mirrors are rectangular mirrors formed on each facet of the polygonal cylindrical portion.

9. 8. The hybrid scanner of claim 7, wherein the multi-sided polygonal cylinder comprises at least two sections, each having a different sized facet to accommodate one of the plurality of mirrors of a different size.

10. 8. The hybrid scanner of claim 7, wherein each facet of the multi-sided polygonal cylindrical portion is an isosceles trapezoid, and the plurality of mirrors are isosceles trapezoid shapes formed on each facet of the polygonal cylindrical portion.

11. 7. The hybrid scanner of claim 6, wherein a portion of each of the pulsed wavelength-modulated coherent light beams impinging on the object is back-reflected by the selected facet of the fast-axis rotating multi-facet scanning mirror, and the back-reflected pulsed wavelength-modulated coherent light beams are forwarded to the first and second slow-axis rotating scanning mirrors and further forwarded to an interferometer to generate an optical interference signal.

12. 1. A multiplexed light detection and ranging (LIDAR) system for measuring distances to features on an object, comprising: a coherent light source; a modulation controller in communication with the coherent light source, the modulation controller configured to generate and control control signals to modulate the coherent light source to generate a pulsed wavelength-modulated coherent light beam and to transmit to the coherent light source to generate a scan pattern for measuring the surface of the object; at least two LIDAR modules coupled to the coherent light source to receive the pulsed wavelength-modulated coherent light beam, the at least two LIDAR modules comprising: an interferometer comprising an optical splitter that splits the pulsed wavelength-modulated coherent light beam into at least two pulsed wavelength-modulated coherent light beams; a hybrid scanner in communication with the at least two LIDAR modules to receive the pulsed wavelength-modulated coherent light beam and configured to scan a surface of the object with the pulsed wavelength-modulated coherent light beam to trace a scan pattern on the surface of the object to measure a distance from the multiplexed (LIDAR) system to a feature of the object, wherein a portion of each pulsed wavelength-modulated coherent light beam is back-reflected by the hybrid scanner and by each interferometer of the at least two LIDAR modules, and each of the at least two LIDAR modules further comprises a balanced detector that electrically converts the back-reflected pulsed wavelength-modulated coherent light beam; a signal processor in communication with the photodetector array in the balanced detector of the LIDAR module to receive and convert electrical signals into digitized electrical signals; and a computer system programmed to calculate a time delay determined by the digitized electrical signal from the signal processor and generate a displayed image field based on a distance from a target.

13. 13. The multiplexed LIDAR system of claim 12, wherein the at least two LIDAR modules are connected to the coherent light source via an optical splitter or optical switch for receiving the pulsed wavelength-modulated coherent light beam.

14. The hybrid scanner comprises: a plurality of optical collimators configured to transfer one sampled pulsed wavelength-modulated coherent light beam to each optical collimator of the plurality of optical collimators; at least one slow-axis rotating plane mirror configured to receive and reflect at least one collimated sample pulsed wavelength-modulated coherent light beam and to rotate along a first axis to form a first dimensional scan pattern of the sample pulsed wavelength-modulated coherent light beam; a fast axis rotary polygon mirror configured to reflect the plurality of pulsed wavelength-modulated coherent light beams, the fast axis rotary polygon mirror configured to rotate on a second axis to form a second dimensional scan pattern of the plurality of pulsed wavelength-modulated coherent light beams; 13. The multiplexed LIDAR system of claim 12, wherein the plurality of pulsed wavelength-modulated coherent light beams are transmitted to an object, and a combination of the first dimensional scan pattern and the second dimensional scan pattern is used to determine geometric dimensions of the object.

15. 15. The multiplexed LIDAR system of claim 14, wherein the multiple pulsed wavelength-modulated coherent light beams are reflected back to the hybrid scanner, reflected by the fast axis rotating polygon scanning mirror to the at least one slow axis rotating plane mirror, through the at least one collimator, and to an interferometer in a LIDAR module for determining dimensions of the scanned object.

16. 15. The multiplexed LIDAR system of claim 14, wherein the at least one slow-axis rotating plane mirror is two slow-axis rotating plane mirrors, a first pulsed-wavelength-modulated coherent beam of light incident on the first slow-axis rotating plane mirror and a second pulsed-wavelength-modulated coherent beam of light incident on the second slow-axis rotating plane mirror.

17. 17. The multiplexed LIDAR system of claim 16, wherein the first pulse-wavelength-modulated coherent light beam reflected from the first slow-axis rotating plane mirror and the second pulse-wavelength-modulated coherent light beam reflected from the second slow-axis rotating plane mirror are incident on the fast-axis rotating polygon mirror.

18. 20. The multiplexed LIDAR system of claim 17, wherein the first and second rotating slow axis scanning mirrors are configured to have a positional offset therebetween such that the reflected pulsed wavelength-modulated coherent light beam is incident on selected facets of the fast axis rotating polygon scanning mirror.

19. 20. The multiplexed LIDAR system of claim 18, wherein each of the pulsed wavelength-modulated coherent light beams reflected from the selected facet of the fast axis rotating polygon scanning mirror is directed to a target and a geometric dimension thereof is determined using a combination of the first dimensional scan pattern and the second dimensional scan pattern.

20. The fast axis rotating polygonal scanning mirror is a multi-sided polygonal cylindrical portion having a central shaft; a motor connected to the central shaft for rotating the polygonal cylindrical portion; 20. The multiplexed LIDAR system of claim 19, comprising a plurality of mirrors, one mirror formed on each face of a polygonal mirror.

21. 21. The multiplexed LIDAR system of claim 20, wherein the plurality of mirrors are rectangular mirrors formed on each facet of the polygonal cylinder.

22. 21. The multiplexed LIDAR system of claim 20, wherein the multi-faceted polygonal cylinder comprises at least two sections, each having a different sized facet to accommodate one of the plurality of mirrors of a different size.

23. 21. The multiplexed LIDAR system of claim 20, wherein each facet of the multi-sided polygonal cylinder is an isosceles trapezoid, and wherein the plurality of mirrors are isosceles trapezoid shapes formed on each facet of the polygonal cylinder.

24. 21. The multiplexed LIDAR system of claim 20, wherein a portion of each of the pulsed wavelength-modulated coherent light beams that impinges on the target is back-reflected by the selected facet of the fast axis rotating multi-facet scanning mirror, and the back-reflected pulsed wavelength-modulated coherent light beams are forwarded to the first and second slow axis rotating scanning mirrors and further to an interferometer to generate an optical interference signal.

25. 13. The multiplexed LIDAR system of claim 12, wherein the modulation controller is configured to modulate the coherent light source by controlling a drive current of the coherent light source, adjusting a temperature of the narrowband light source, or adjusting a phase of light emitted from the light source.

26. The LIDAR module includes: a first coupler configured to receive pulsed wavelength-modulated coherent light from the coherent light source and to split the pulsed wavelength-modulated coherent light into a first portion of the pulsed wavelength-modulated coherent light and a second portion of the pulsed wavelength-modulated coherent light; a circulator connected to receive the first portion of the pulsed wavelength modulated coherent light, the circulator configured to enter a first port of the circulator and exit a subsequent port, the circulator directing the first portion of the pulsed wavelength modulated coherent light toward the scanner; a sample arm connected to the first coupler to receive the first portion of the pulsed wavelength-modulated coherent light and to forward the first portion of the pulsed wavelength-modulated coherent light to the scanner; a reference arm connected to the first coupler and configured to receive the second portion of the pulsed wavelength-modulated coherent light; a second coupler configured to receive a back-reflected portion of the pulsed wavelength-modulated coherent light, configured to receive the second portion of the pulsed wavelength-modulated coherent light from the reference arm, and configured to combine the back-reflected portion of the pulsed wavelength-modulated coherent light with the second portion of the pulsed wavelength-modulated coherent light to form an optical interference signal; a photodetector array configured to receive the optical interference signals and convert the optical interference signals into electrical interference signals.

27. The LIDAR module further comprises:

26. The multiplexed LIDAR system of claim 25, comprising a polarization controller configured to receive pulsed wavelength-modulated coherent emission light, forward the pulsed wavelength-modulated coherent emission light to the first coupler, and adjust the polarization state of the coherent emission light from the light source to maximize the amplitude of the optical or electrical interference signal.

28. 13. The multiplexed LIDAR system of claim 12, wherein the photodetector array is configured as a polarization diversity balanced amplified detector and includes at least one power monitor that measures an input power level to the photodetector array, the power monitor outputting a power level modulated to have a time delay related to the range of the target.

29. 13. The multiplexed LIDAR system of claim 12, wherein the signal processor is configured to determine an envelope of at least two digitized electrical signals.

30. 30. The multiplexed LIDAR system of claim 28, wherein the signal processor is configured to measure a delay of the at least two digitized electrical signals at a falling edge of an envelope of the digitized electrical signals.

31. 13. The multiplexed LIDAR system of claim 12, further comprising a scan controller configured to create a scan pattern that generates a scan synchronization signal, the scan controller configured to apply the scan synchronization signal to the scanner to generate a plurality of scan patterns that facilitate collection of measurement information representative of the target object.

32. 13. The multiplexed LIDAR system of claim 12, wherein the multiplexed LIDAR system is implemented as optical fibers, bulk optics, integrated optical circuits, or any combination of optical elements.

33. 13. The multiplexed LIDAR system of claim 12, wherein the scanner gradient index fiber rod is formed with a separate lens that interfaces with the gradient index fiber rod to provide the low numerical aperture required for the gradient index fiber rod and engineered gradient index lens for long distance illumination and the higher numerical aperture required to receive the pulsed wavelength modulated coherent light back reflected from the target.

34. 1. A method for determining a distance to an object, comprising: generating a coherent light beam; modulating the coherent light beam with a pulsed wavelength modulated signal; polarizing the pulsed wavelength-modulated light beam by adjusting the polarization state of the pulsed wavelength-modulated light beam to maximize the amplitude of the optical interference signal; optically splitting the pulsed wavelength-modulated light beam into at least two pulsed wavelength-modulated coherent light beams; coupling each of the at least two pulsed wavelength-modulated light beams into one of at least two LIDAR modules to generate a sampling pulsed wavelength-modulated light beam and a reference pulsed wavelength-modulated light beam; transferring the at least two pulsed wavelength-modulated light beams to a hybrid scanner module to establish a scan pattern for each of the pulsed wavelength-modulated light beams; scanning the at least two pulsed wavelength-modulated light beams onto a measurement object whose distance from a source of the pulsed wavelength-modulated coherent light beam is to be measured; receiving back-reflected portions of the at least two pulsed wavelength-modulated light beams from the measurement object; coupling a respective back-reflected portion of each of the at least two pulsed wavelength-modulated light beams to a corresponding LIDAR module of the at least two pulsed wavelength-modulated light beams to form an electrical signal representative of each of the at least two pulsed wavelength-modulated light beams; digitizing the electrical signal; detecting an envelope of each of the digitized electrical signals to determine the envelope of each of the digitized electrical interference signals; determining the time of a rising edge or a falling edge of the envelope of the digitized electrical interference signal; determining a time difference between rising or falling edges of the envelope of the digitized interference signal; calculating a distance to the measurement object; forming a two-dimensional ranging image based on all distance measurements scanned by the at least two pulsed wavelength modulated light beams across the measurement object.

35. determining a velocity of the object by calculating the distance from the at least two LIDAR modules separately; 34. The method of claim 33, further comprising calculating the velocity of the object as a change in distance over time.

36. 35. The method of claim 34, further comprising implementing the method using optical fibers, bulk optics, integrated optical circuits, or any combination of optical elements.

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