High-speed time-of-interference light detection and ranging apparatus

Abstract

To provide a high-speed time-of-interference (TOI) light detection and ranging (LIDAR) system based on time-frequency domain reflectance measurement and small wavelength transient modulation of a coherent light source.SOLUTION: A TOI LIDAR system generates an image of an object based on the distance of various point measurements to the object. The TOI LIDAR system detects the envelope of an electrical signal created from an interference light signal. The interference light signal is produced from the back-reflected light resulting from a sampling arm light emission to the object combined with a reference light emission. The reference light emission is created by splitting a pulse-modulated coherent light source's emission signal and passing the reference light emission through a reference arm. The optical interference signal is transferred to a balanced photodetector to convert to an electrical signal converted to digital data. The digital data is evaluated to determine the rising edges or falling edges of a digitized electrical interference signal to determine a time delay between the reference light emission and back-reflected light used to calculate the distance.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] This application is a continuation-in-part application of U.S. Patent Application No. 17 / 315,678, filed on 10 May 2021, which is assigned by reference in its entirety to the common assignee.

[0002] This disclosure relates to optical detection and ranging systems, and more particularly to optical detection and ranging systems that utilize optical interferometers and methods for measuring distance and speed. [Background technology]

[0003] 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 a three-dimensional (3D) scan, 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.

[0004] 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.

[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 article “Comb-Calibrated Frequency-Modulated Continuous-wave LiDAR, Y. Xie et al., 2020 IEEE 7th International Workshop on Metrology for AeroSpace (MetroAeroSpace), Pisa, Italy, 2020, pp.372-376, URL:https: / / ieeexplore.ieee.org / stamp / stamp.jsp?tp=&arnumber=9160234&isnumber=9159966” published on 2 / 15 / 2021, describes FMCW LiDAR as being very suitable for measuring absolute distance. The frequency of the FMCW laser is linearly modulated by the carrier signal, and the round-trip flight time of the laser is accurately measured. By detecting the beat frequency signal between the returning and emitted lasers, the flight time can be calculated with high precision, enabling highly accurate distance measurement.

[0006] 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 characteristics: (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 because it can measure 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. [Overview of the Initiative]

[0007] The object of this disclosure is to provide a fast time-of-interference (TOI) optical detection and ranging (LIDAR) system based on time-frequency domain reflectivity measurement and short-wavelength transient modulation of a coherent light source. The fast TOI LIDAR system records the time delay or interference time (TOI) of the interference signal using a time-to-digital converter or data acquisition system. The output wavelength is determined by the operating current or operating temperature of the coherent light source.

[0008] To achieve this objective, the high-speed TOI Lidar system has a coherent light source connected to a modulation control device. The modulation control device is configured to generate a pulse wavelength control signal that is transmitted to the coherent light source. The pulse wavelength control signal may be a current modulation signal or a laser ambient temperature control signal. The pulse wavelength control signal modulates the coherent light source, generating pulse wavelength-modulated coherent emission.

[0009] Pulse wavelength-modulated coherent light emission serves as an input to an interferometer. The interferometer is configured to split the pulse wavelength-modulated coherent light emission into a sampling portion and a reference portion. The sampling portion of the pulse wavelength-modulated coherent light emission is arranged to be incident on the object to be measured. The reference portion of the pulse wavelength-modulated coherent light emission is arranged to serve as a reference basis for determining the distance from the TOI LIDAR system to the object. The interferometer is further configured to transfer the pulse wavelength-modulated coherent light to a scanner. The scanner is configured to physically transfer a first portion of the pulse wavelength-modulated coherent light to the object and scan the surface of the object with the pulse-modulated coherent light. The scanner is further configured to receive a portion of the pulse wavelength-modulated coherent light retroreflected from the object. The retroreflected pulse wavelength-modulated coherent light is transferred from the scanner to the interferometer and then combined with the reference portion of the pulse wavelength-modulated coherent light to form an optical interference light signal.

[0010] The TOI LIDAR system has an optical detector array configured to convert the optical interference signal into an electrical interference signal. In various embodiments, the optical detector is configured as a polarization diversity balanced amplification detector. The optical detector has at least one power monitor for measuring the input power level to the optical detector. From the output of this power monitor, a power level modulated with a time delay related to the distance of the object is obtained.

[0011] The TOI LIDAR system has a signal processing device that receives the electrical interference signal and converts this electrical interference signal into digital data representing the amplitude of the electrical interference signal as digital data. This signal processing device is configured to generate an imaging range displayed based on the distance from the object. The displayed imaging range is calculated by a computer system programmed to calculate the time delay determined by the optical interference signal.

[0012] The modulation 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 the phase of the light emitted from the light source. In other embodiments, the modulation 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.

[0013] 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 sampled 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.

[0014] The interferometer's reference arm is at least twice the length of the sampling arm. A second portion of pulse-wavelength modulated coherent light within the reference arm is applied to a second coupler. This 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.

[0015] The optical path length of the reference arm is longer than twice the maximum ranging depth of the system than that of the sample arm. The maximum frequency of the optical interference signal corresponds to the minimum ranging depth of the system.

[0016] The maximum frequency of the optical interference signal corresponds to the minimum ranging depth of the TOI LIDAR system and is greater than the Nyquist sampling frequency of the digitizer in the data acquisition and signal processing device. The minimum frequency of the optical interference signal corresponds to the maximum ranging depth of the TOI LIDAR system. The time delay of the detected optical interference is measured at the falling edge of the envelope of the optical interference signal.

Brief Description of the Drawings

[0017] [Figure 1A] FIG. 1A is a schematic diagram of a TOI LIDAR system embodying the principle of the present disclosure. [Figure 1B] FIG. 1B is a schematic diagram of a TOI LIDAR system embodying the principle of the present disclosure. [Figure 1C] FIG. 1C is a schematic diagram of a TOI LIDAR system embodying the principle of the present disclosure.

[0018] [Figure 1D] FIG. 1D is a schematic diagram of a scanner that receives a refractive index distribution type lens at the end of the sample arm of FIGS. 1A, 1B, and 1C embodying the principle of the present disclosure.

[0019] [Figure 2A] FIG. 2A is a block diagram of an electrical TOI measurement circuit embodying the principle of the present disclosure.

[0020] [Figure 2B] FIG. 2B is a block diagram showing the program structure of a signal processing device configured to perform electrical TOI measurement embodying the principle of the present disclosure.

[0021] [Figure 2C]Figure 2C is a plot of the back-reflected pulse fringe and envelope of the sample arm at zero (0) meter position, embodying the principle of this disclosure.

[0022] [Figure 2D] Figure 2D is a plot of the back-reflected pulse fringe and envelope of the sample arm at a position of 180 meters, embodying the principle of this disclosure.

[0023] [Figure 3] Figure 3 shows a frame-based velocity measurement method for a TOI LIDAR system that embodies the principle of this disclosure.

[0024] [Figure 4A] Figure 4A is a block diagram of a transient light source modulator that embodies the principle of this disclosure.

[0025] [Figure 4B] Figure 4B is a schematic diagram of a transient light source modulator and a coherent light source that embody the principle of this disclosure.

[0026] [Figure 5A] Figure 5A is a block diagram showing an SSM-TOI electrical measurement circuit that embodies the principle of this disclosure.

[0027] [Figure 5B] Figure 5B is a block diagram showing the program structure of a signal processing device configured to perform SSM-TOI electrical measurement, which embodies the principle of this disclosure.

[0028] [Figure 6] Figure 6 is a block diagram of a digital signal processing device configured to perform SSM-TOI Doppler velocity measurement, which embodies the principle of this disclosure.

[0029] [Figure 7] Figure 7 is a block diagram of a TOI and time-of-flight integrated circuit that embodies the principles of this disclosure.

[0030] [Figure 8A] Figure 8A is a flowchart illustrating a method for determining the distance to an object using SSM-TOI electrical measurement, which embodies the principle of this disclosure.

[0031] [Figure 8B] Figure 8B is a flowchart illustrating a method for determining the velocity of an object using SSM-TOI electrical measurement, which embodies the principle of this disclosure. [Modes for carrying out the invention]

[0032] The TOI LiDAR system is configured to generate an image of an object based on the measured distances to various points on the object. This TOI LiDAR system detects the envelope of an electrical signal generated from an interference optical signal. This interference optical signal is generated from the back-reflected light from the sample arm emission onto the object and a reference emission. The reference emission is created by splitting the emission signal of a pulse-wavelength modulated coherent light source and passing the reference emission through the reference arm. The optical interference signal is transferred to a photodetector, converted into an electrical signal, and then converted into digital data. This digital data is evaluated to determine the falling edges of the reference emission and back-reflected light, and to determine the time delay between the reference emission and back-reflected light. Then, the distance is calculated from this time delay.

[0033] Figures 1A, 1B, and 1C are schematic diagrams of a TOI LIDAR system embodying the principles of this disclosure. Referring to Figure 1A, the TOI LIDAR system 100 comprises 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 typically consists 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 the wavelengths of reflected waves that have been repeatedly reflected by the reflective surfaces of the cavity and then enhanced 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 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 coherent light source 105 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.

[0034] 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.

[0035] 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 that receives pulsed wavelength-modulated coherent light. The polarization control device 115 adjusts the polarization state of the pulsed wavelength-modulated coherent light from the light source 105 to maximize the amplitude of the optical interference signal or interference electrical signal 162 transmitted in the optical paths 155a, 155b. The pulsed wavelength-modulated coherent light from the light source 105, or the pulsed wavelength-modulated coherent light transmitted via the polarization control device 115, is sent to a coupler 120. The coupler 120 divides the coherent light into a sample portion supplied to at least one sample arm 122 and a reference portion of the pulsed 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 a free-space path, an optical fiber, or an optical waveguide.

[0036] The interferometer 119 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.

[0037] 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 matches the maximum ranging depth of the TOI LIDAR 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 a coupler 150 to generate an optical interference signal.

[0038] Each pulse wavelength-modulated coherent optical signal from at least one sample arm 122 and a reference arm 140 is heterodyne detected to extract the beat frequency from the base signal. The beat signal has a phase difference of 180° at the two outputs from the coupler. The balanced detector 160 subtracts the signals from each input channel to extract the interference signal, which is the beat signal.

[0039] This 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 and transferred to a balanced photodetector 160, where the optical interference signals from optical paths 155a and 155b are converted into an electrical interference signal 162.

[0040] 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, where the interferential electrical signal 162 is converted into digital data. The maximum frequency of the optical interference signal corresponds to the minimum ranging depth of the TOI LIDAR system. The maximum frequency of the optical interference signal is greater than the Nyquist sampling frequency of the digitizer in the data acquisition or signal processing device 165.

[0041] The minimum frequency of the optical interference signal applied to optical paths 155a and 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.

[0042] 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.

[0043] In various embodiments, the computer 170 is connected to the modulation / scanning control unit 175. In other embodiments, the computer 170 is integrated with the modulation / scanning control unit 175. The modulation / scanning control unit 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 unit 175 further has a scanning control circuit that provides a modulation / scanning synchronization signal 179 to the signal processing unit 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.

[0044] 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) deflector, 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 motion necessary to collect measurement information.

[0045] Referring to Figure 1B, the TOI LIDAR system 100 has the same structure as in Figure 1A, except that a second portion of pulsed wavelength-modulated coherent light is applied to the reference arm 200. The optical fiber cable of the reference arm 200, which is implemented as a free-space path, optical fiber, or optical waveguide, has an additional optical path 142 such that the optical path length of the reference arm 200 matches the maximum ranging depth of the TOI LIDAR system 100. The pulsed wavelength-modulated coherent light in the reference arm 200 is applied to the input port of the second circulator 210. The pulsed wavelength-modulated coherent light is transmitted from the input / output port of the second circulator 210 to the additional segment of the reference arm 200. The coherent light is incident on the mirror 215. The mirror 215 delays the coherent light, but in some embodiments, this is replaced by an optical delay line. The mirror 215 reflects the coherent light back directly to the second circulator 210 and leads to the coupler 150. The coherent light reflected by the mirror is combined with the back-reflected pulse wavelength-modulated coherent light to form an optical interference signal. Mirror 215 functions as a reference image plane corresponding to the maximum range of the TOI LIDAR system 100. With mirror 215, if an additional path length 202 is located between the second circulator 210 and mirror 215, the length of the additional path length 202 can be halved by double-passing of light. Mirror 215 enables cost reduction and space saving.

[0046] Replacing mirror 215 with an optical delay line increases the degree of freedom for fine-tuning the entire path length of the reference arm. Since the adjustable range of the delay is typically on the order of centimeters, this is primarily for accommodating small system variations rather than changing the overall imaging range.

[0047] The optical interference signal is applied to optical paths 155a and 155b, which are implemented as free-space paths, optical fibers, or optical waveguides. As described above, the optical interference signal applied to optical paths 155a and 155b is transferred to the balanced photodetector 160, where the optical interference signal from optical paths 155a and 155b is converted into an electrical interference signal 162.

[0048] In some implementations, the reference arms 140 and 200 in Figures 1A and 1B may have longer optical path lengths than the sample arm 103. The timing of interference between the sample arm 122 and the pulse wavelength-modulated coherent optical signals from the reference arms 140 and 200 corresponds to the falling edge of the interference envelope. In various embodiments, the reference arms 140 and 200 may have shorter optical path lengths than the sample arm 122. The timing of interference between the sample arm 122 and the pulse wavelength-modulated coherent optical signals from the reference arms 140 and 200 corresponds to the rising edge of the interference envelope.

[0049] Referring to Figure 1C, the TOI LIDAR system 100 has the same structure as in Figure 1A, except that the second portion of the pulse wavelength-modulated coherent light from the reference arm 140 exits the first coupler 120 and enters the third coupler 300. The reference arm 140 is implemented as a free-space path, optical fiber, or optical waveguide. The third coupler 300 further splits the second portion of the pulse wavelength-modulated coherent light into two pulse wavelength-modulated coherent light beams. The first portion of the second portion of the pulse wavelength-modulated coherent light beam is applied to the second reference arm 305, which is similarly implemented as a free-space path, optical fiber, or optical waveguide. The second portion of the second portion of the pulse wavelength-modulated coherent light beam from the second reference arm 305 is applied to the sweep linear calibration device 315.

[0050] The sweep linear calibration device 315 is a Mach-Zehnder interferometer or Fabry-Perot filter that generates an electrical signal to calibrate the linearity 105 of the wavelength sweep of the coherent light source. If the wavelength modulation is not linear in the optical frequency domain, the sweep linear calibration device 315 generates an interference signal from a fixed path length difference from either the Mach-Zehnder interferometer or the Fabry-Perot filter. Typically, an electrical signal is generated using a photodetector or a balanced detector. Its zero-crossing timing corresponds to equal intervals in the optical frequency domain and provides an optical clock to the data acquisition system in the signal processing device 165. The sweep linear calibration device 315 calibrates the interference signal 162 detected by the balanced detector 160. The output of the sweep linear calibration device 315 is transferred to the signal processing device 165.

[0051] The second pulse wavelength-modulated coherent light beam from the reference arm 305 is applied to the second coupler 150. As described above, the back-reflected coherent light is guided to the coupler 150. The reference coherent light in the reference arm 305 is coupled with the back-reflected coherent light to form an optical interference signal. The optical interference signal is applied to optical paths 155a and 155b, which are implemented as free-space paths, optical fibers, or optical waveguides. As described above, the optical interference signal is transferred through optical paths 155a and 155b to the equilibrium photodetector 160, where the optical interference signals from optical paths 155a and 155b are converted into an interference electrical signal 162.

[0052] Figure 1D is a schematic diagram of a scanner 130 configured to receive a sample arm 122 having the optical fiber cable shown in Figures 1A, 1B, and 1C, embodying the principle of this disclosure. The sample arm 122 is inserted into and fixed in the scanner 130. The distal end of the sample arm 122 is connected to or in contact with a distributed refractive index fiber rod 122a. The distributed refractive index fiber rod 122a has an engineered distributed refractive index lens 122b formed on the distal surface of the distributed refractive index fiber rod 121a to increase overall efficiency for high-speed operation. In another embodiment, this engineered distributed refractive index lens 122b is formed as a separate lens in contact with the distributed refractive index fiber rod 121a. A low numerical aperture is required for the distributed refractive index fiber rod 121a with the engineered distributed refractive index lens 122b for far-field illumination, but a high numerical aperture is required to receive back-reflected pulse wavelength-modulated coherent light from an object. In a distributed refractive index fiber rod 122a having a processed distributed refractive index lens 122b, the on-axis sample pulse wavelength-modulated coherent light 135 emerging from the central portion of the processed tip is parallel light. The off-axis back-reflected pulse wavelength-modulated coherent light 136 from an object passing through the annular portion 122c of the processed distributed refractive index lens 122b is coupled to return to the sample arm 122. A distributed refractive index fiber rod 122a having a processed distributed refractive index (GRIN) lens 122b can be implemented as a distributed refractive index (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, or a free-space collimator. When implementing a distributed refractive index fiber rod 122a having a processed distributed refractive index lens 122b, any combination of these enumerated items may be used. The processed distributed refractive index lens 122b is formed from a tapered tip, a Fresnel surface, a meta-surface, or a combination thereof.

[0053] The sample arm 122 is inserted into and fixed in the scanner 130. The sample arm 122 emits pulsed wavelength-modulated coherent light 135 to the first mirror 132. The first mirror 132 rotates horizontally 134a to reflect the pulsed wavelength-modulated coherent light 135 in a horizontal scanning pattern. The horizontal scanning pattern covers the desired field of view. The reflected pulsed wavelength-modulated coherent light 135 is incident on the second mirror 133. The second mirror 133 rotates vertically 134b to generate a vertical scanning pattern. The vertical scanning pattern covers the vertical field of view.

[0054] The off-axis back-reflected pulse wavelength-modulated coherent light 136 is reflected by the desired object to be measured, and is reflected back to the scanner 130, then to the second mirror 133, and further to the first mirror 132. The off-axis back-reflected pulse wavelength-modulated coherent light 136 is reflected and transmitted to the distributed refractive index fiber rod 122a of the sample arm 122, which has a processed distributed refractive index lens 122b. The off-axis back-reflected pulse wavelength-modulated coherent light 136 is transmitted off-axis to the sample 122, which has a distributed refractive index fiber rod 122a equipped with a processed distributed refractive index lens 122b. The light is transmitted through the distributed refractive index fiber rod 122a and carried to the sample arm 122 for further processing.

[0055] Figure 2A is a block diagram of an electrical TOI measurement circuit embodying the principle of this disclosure. The interfering electrical signals 162 generated by the balanced detector 160 in Figures 1A, 1B, and 1C are received by the envelope detector 400 and converted into an envelope 405 of the interfering electrical signals 162. The envelope detector 400 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, the root mean square (RMS) detector, or the frequency demodulator identifies the envelope of the interfering electrical signals 162 by removing the high-frequency components in the interfering electrical signals 162.

[0056] The envelope signal 405 is transferred to the edge detector 410. The edge detector 410 determines a pulse event and places that pulse event at the output 410 of the edge detector. A pulse event is an indication of the rising or falling edge of the envelope signal 405. The edge detector 410 can be implemented as an edge-glitch converter, an XOR gate and delay circuit, a differentiator circuit, etc. Edge-glitch converters, XOR gates and delay circuits, and differentiators are also known in the art and are commercially available.

[0057] The output 415 of the edge detector is connected to the input of the time-to-digital converter 420. The time-to-digital converter 420 generates a time difference signal and transfers it to its output 430. This time difference signal indicates the time of the rising or falling edge between pulse events 405 and 425. Pulse event 425 corresponds to the rising or falling edge of the light source modulation signal transferred from the modulation / scanning control device 175. Pulse event 425 triggers the time-to-digital converter 420 to start when counting time intervals. The pulse output 415 of the edge detector 410 provides a pulse event to terminate the time interval count by the time-to-digital converter 420. The series of time difference signals at the output 430 of the time-to-digital converter 420 are converted into depth measurements to form the image displayed by the computer 170.

[0058] Figure 2B is a block diagram showing the program structure of a signal processing device embodying the principles of this disclosure. The interferential electrical signals 162 generated by the balanced detector 160 in Figures 1A, 1B, and 1C are digitized by the data acquisition module 440. The data acquisition module 440 is triggered by a modulation / scan synchronization signal 179 from the modulation / scan control device 175. The interferential electrical signals are converted into digital signals 442 and placed at the output of the data acquisition module 440. The maximum frequency of the interferential electrical signals 162 corresponds to the minimum ranging depth of the TOI LIDAR system 100. The maximum frequency of the interferential electrical signals 162 is greater than the Nyquist sampling frequency of the digitizer in the data acquisition module 440. The minimum frequency of the interferential electrical signals corresponds to the maximum ranging depth of the TOI LIDAR system 100. The time delay of the detected interferential electrical signals 162 is measured at the falling edge of the envelope of the interferential electrical signals 162.

[0059] The digital signal 442 is processed by an envelope detection process 445 performed by a signal processing device 165 to obtain the envelope signal 447 of the digital interference electrical signal 442. The envelope detection process 445 is performed by taking the absolute value of the Hilbert transform of the digital signal 442. Next, the envelope signal 447 is processed by an edge detection process 450 to identify the timing of the interference electrical signal's occurrence. The time difference 457 between the envelope signal 447 and the rising or falling edge of the modulation / scan synchronization signal 179 can be calculated.

[0060] Figure 2C is a plot of the pulse input fringe 460 and envelope 465 of a reference arm embodying the principle of this disclosure. Figure 2C is an example of the interference electrical signal of a prototype TOI system 100 that detects an object at zero (0) meters. Figure 2D is a plot of the back-reflected pulse fringe 470 and envelope 475 of a sample arm embodying the principle of this disclosure. Figure 2D is an example of the interference electrical signal of a prototype TOI system 100 that detects an object at 180 meters. The edge detector 410 in Figure 2A or the edge detector process 450 in Figure 2B determines the time of the falling edge t0 of the envelope of the reference arm 460 and the time of the falling edge t1 of the envelope of the sample arm 475. The counter 420 or counter process 455 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 to the object to be measured is determined by the following formula: Distance=c*(t0-t1) however c represents the speed of light, t0 is the falling edge time of the reference arm. t1 represents the falling edge time of the sample arm. The series of time differences 457 can be converted into depth information and form an image that can be displayed by the computer 170.

[0061] Figure 3 shows a frame-based velocity measurement method for a TOI LIDAR system embodying the principle of this disclosure. Each frame 490a, 490a, 490b, ..., 490m, 490m+1, ..., 490y, 490z is captured by the equilibrium photodetector 160 in Figures 1A, 1B, and 1C, and represents data 495n and 495m+1. Data 495n and 495m+1 are transferred to the signal processing unit 165 and processed as described in Figures 2A and 2B to determine the rising or falling edge of the data. Thus, by determining the rising or falling edge of the data, the time difference between data 495n and 495n+1 is obtained. Next, the distance between data 495n and 495n+1 is calculated as the time difference between data 495n and 495n+1 (tm+1-t).m The time difference between data 495n and 495m+1 is calculated as (t). m+1 -t m The velocity of the object being measured is determined by multiplying this by the sampling frame rate of the optical interference signals applied to optical paths 155a and 155b.

[0062] Figure 4A is a block diagram of a small-signal transient modulator incorporated into the modulation drivers of Figures 1A, 1B, and 1C, which embody the principle of this disclosure. The transient light source modulator is connected to a DC voltage source V DC and modulated voltage V MOD It has an adder circuit 500 connected to receive a DC voltage source V. DC and modulated voltage V MOD These are added together to form the modulated signal 505. The modulated signal 505 is the voltage source V DC The amplitude is smaller than the voltage. The modulated signal 505 is selected from a group of waveforms including a square wave, triangular wave, sine wave, sawtooth wave, or any waveform, or a combination of these waveforms. The transient generator 507 generates a spiked transient modulated signal 508 by introducing voltage spikes into the modulated signal 505. The spiked transient modulated signal 508 is applied to the laser driver 510. The voltage of the spiked transient modulated signal 508 is converted into a current to drive the coherent light source 105. The function of the transient generator 507 is to change the effective inductance value of the transient light source modulator to generate a very large spiked transient current in order to shorten the response time of the laser driver 510, thereby overcoming the speed limitations of conventional laser driving methods. A schematic of the transient generator 507 is described later in Figure 4B. Alternatively, the current obtained by converting the modulated signal 505 is applied to a thermoelectric cooling device used to stabilize the temperature of the laser diode of the coherent light source 105. By applying the modulated current via the thermoelectric cooling device, the temperature of the laser diode of the coherent light source 105 changes. The laser diode of the coherent light source 105 has a built-in thermistor for monitoring the diode temperature, thereby forming a control loop between the thermoelectric cooling device and the thermistor that provides temperature monitoring and accurate temperature modulation.

[0063] The coherent light source 105 emits a coherent optical signal 520 to the interferometer. When there is a difference in the optical path lengths between the reference arms 140, 200, 305 and the sample arm 122 in FIGS. 1A, 1B, and 1C, wavelength / optical frequency waveform modulation is selected to introduce optical interference.

[0064] FIG. 4B is a schematic diagram of a transient light source modulator and a coherent light source embodying the principles of the present disclosure. The adder circuit 500 has a 2×1 multiplexer MUX1 used to combine a DC voltage source V DC and an analog modulation signal V DMOD controlled by a digital modulation signal V AMOD The first input of the 2×1 multiplexer MUX1 is the DC voltage V DC which provides a lower base voltage. The second input to the 2×1 multiplexer MUX1 is the modulation voltage V MOD which is a higher voltage for forming the output voltage. The output V O of the 2×1 multiplexer MUX1 provides a transient modulation signal 505 that is an input to the transient generator 507. The output of the transient generator 507 is a transient modulation signal 508 applied to the input of the laser driver 510. The laser driver 510 converts the transient modulation signal 508 into a current and drives the coherent light source 105.

[0065] The multiplexer MX1 is formed by two transfer gates TG1, TG2. These two transfer gates TG1, TG2 are connected in parallel. Each transfer gate of the two transfer gates TG1 and TG2 has connected complementary NMOS and PMOS transistors as known in the art. The sources and drains of the respective complementary NMOS and PMOS transistors are connected. The DC voltage source V DC and the modulation voltage V MOD are respectively connected to the sources of the transfer gates TG1, TG2. The digital modulation signal V DMODIt is connected to the input of the first inverter INV1. The output of the first inverter INV1 is connected to the input of the second inverter INV2. The output of the first inverter INV1 is connected to the out-of-phase gate of transfer gate TG1 and the in-phase gate of transfer gate TG2. The output of the second inverter INV2 is connected to the out-of-phase gate of transfer gate TG2 and the in-phase gate of transfer gate TG1.

[0066] DC voltage source V DC This is connected to the input source / drain of the transfer gate TG1, and the modulated voltage V MOD The input source / drain of transfer gate TG2 is connected. The output source / drain of transfer gate TG1 and transfer gate TG2 are connected to the inverse phase input of comparator COMP1. The common-mode input of comparator COMP1 is connected to the limiting voltage source V L It is connected to the output voltage V of the transfer gates TG1 and TG2. Comparator COMP1 controls the output voltage V of the transfer gates TG1 and TG2. O and limiting voltage source V L Compare with the voltage level of the limiting voltage source V. L The voltage level of the output voltage V of the transfer gates TG1 and TG2 O If the value is greater than this, the coherent light source 105 is shut down for safety reasons, as will be described later.

[0067] The 2x1 multiplexer MX1 ​​has an output voltage Vo which is applied to the input of the transient generator 507 as the output of the summing circuit 500. The transient generator 507 has an inductor L, the first terminal of which is connected to the output Vo of the 2x1 multiplexer MX1. The second terminal of the inductor L is connected in common to the first terminal of the capacitor C and the resistor R1. The second terminal of the capacitor C is connected to the earth reference power supply, and this second terminal is connected to the laser driver 510.

[0068] The laser driver 510 has a first NMOS transistor TX1 whose gate is connected to the output of the transient generator 507. The drain of the MOS transistor TX1 is connected to the anode of the coherent light source LD1 105. The source of the first MOS transistor TX1 is connected to the drain of the second MOS transistor TX2. The source of the second MOS transistor TX2 is connected to the first terminal of resistor R2. The gate of the second MOS transistor TX2 is connected to the output of comparator COMP1, which receives a shutdown command for the coherent light source LD1 105. The second terminal of resistor R2 is connected to an earth reference power supply. Resistor R2 sets the shutdown voltage of the coherent light source LD1 105. The gate of the NMOS transistor TX1 is configured as a current source that generates the laser current.

[0069] In the parent embodiment of this disclosure, there is no transient generator 507, and the gate capacitance of the first MOS transistor TX1, as well as the resistance and inductance on the wiring connected to the first MOS transistor TX1, are at a level where overshoot and spikes on the rising edge of the modulated signal 505 are negligible. Output V of the 2×1 multiplexer MX1 O The switching transition time, the inductance L, the large gate size of the first NMOS transistor TX1, and the capacitor C on the wiring push up overshoot, generating current spikes and transient signals. The degree of transient current spikes depends heavily on the rise time of the modulated signal 505, the parameters of inductance L, and the gate size of the first NMOS transistor TX1. Positive spikes occur at the rising edges of the first NMOS transistor TX1 and the DC voltage source V DC When the base voltage level switches back, a negative spike occurs at the falling edge of the first NMOS transistor TX1. Therefore, there are two spike events for each switching of the modulation signal 505.

[0070] The switching pulse width of the modulated signal 505 plays a crucial role in driving the current source transistor TX1. At the rising edge, a current spike immediately occurs, followed by ringing. Subsequently, the current spike gradually decreases to the charging voltage of capacitor C, equal to the amplitude of the modulated signal 505. At the falling edge of the modulated signal 505, the 2x1 multiplexer MX1 ​​is switched, and the DC voltage source V DC When the voltage level returns to the base voltage level, a negative spike occurs.

[0071] The key point is to control the switching pulse width of the modulated signal 505 to fuse the positive and negative transient voltage spikes of the transient modulated signal 508. This fusion of positive and negative transient voltage spikes ensures sufficient time for voltage ringing and settling between the two spikes due to the on / off switching of the multiplexer MX1. A shorter time between the positive and negative transient voltage spikes is more suitable for TOI LIDAR applications. The time difference between the positive and negative transient voltage spikes contributes to the TOI LIDAR detection distance (edge ​​detection), especially when the target is very close to the LIDAR device.

[0072] The coherent light source 105 is a coherent light source 105. The coherent light source 105 is a type of laser diode, quantum cascade laser, or optical fiber laser in which the active region of the device includes a periodic structure element or diffraction grating. Power supply voltage source V CC This is applied to the coherent light source LD1 105.

[0073] Digital modulated signal V DMOD If the digital modulation signal V is high and low, the coherent light source 105 can be turned on and off, respectively. DMOD When it is high, the analog modulated signal V AMOD This can provide small-signal modulation to the light source 105. Multiplexer output V O The predetermined limiting voltage V LIf the voltage is higher than the threshold and the transition time by the second transistor TX2 is short, the light source LD1 105 is deactivated. The protection current limit setting is based on the current limiting characteristics of the NMOS gate TX2 and the coherent light source LD1 105. In this embodiment, the breakdown voltage of the NMOS gate TX2 is 20V, which is sufficient for protection. Although the transient current of the coherent light source LD1 105 is high, the duration of the transient current is approximately 1 nanosecond, so it should not be a problem for the coherent light source LD1(105).

[0074] Digital modulated signal V DMOD While the signal transitions from low to high, the transient generator 507 generates a voltage spike that switches on the first transistor TX1, which immediately discharges the current in the light source LD1, thus generating a short transition time suitable for TOI applications.

[0075] Figure 5A is a block diagram illustrating an SSM-TOI electrical measurement circuit embodying the principle of this disclosure. An interference electrical signal 162 generated from the balanced detector 160 is received by a frequency-to-voltage converter 525. The frequency of the interference electrical signal 162 is converted into a voltage at the output 530 of the frequency-to-voltage converter 525. This voltage is proportional to the frequency of the interference electrical signal 162. The frequency-to-voltage converter 525 comprises an FM demodulator, a frequency detector, or any frequency-to-voltage converter circuit known in the art. The voltage level of the output 530 becomes the input to the edge detector 535, which generates a pulse at the output 540 of the edge detector 535. This pulse corresponds to a rising edge, i.e., the rising or falling edge of the voltage level at the output 530 of the frequency-to-voltage converter 525. The edge detector 535 is formed by an edge-to-glitch converter, an XOR gate and delay circuit, a differentiating circuit, or any edge detection circuit known in the art. The time-to-digital converter 550 receives the time difference signal Δ at the output 555 of the time-to-digital converter 550. TD This generates the time difference signal Δ TDThis is the difference between the rising or falling edge pulse at the output 540 of the edge detector 535 and the modulation / scanning synchronization signal 179 from the modulation / scanning control device 175. The series of time differences 507 are converted into depth and form the image displayed by the computer 170.

[0076] Figure 5B is a block diagram showing the program structure of a signal processing device 175 configured to perform SSM-TOI electrical measurement, embodying the principles of this disclosure. The interference electrical signal 162 generated by the balanced detector 160 is digitized by a data acquisition module 605 triggered by a modulation / scan synchronization signal 179 from the modulation / scan control device 175. The interference electrical signal 162 is converted into a digital interference signal at output 565. The maximum frequency of the interference electrical signal 162 corresponds to the minimum ranging depth of the TOI LIDAR system 100. The interference electrical signal 162 is greater than the Nyquist sampling frequency of the digitizer in the data acquisition module 605.

[0077] The minimum frequency of the optical interference signal applied to the optical paths 155a and 155b corresponds to the maximum ranging depth of the TOI LIDAR system 100. The time delay of the detected electrical interference 162 is measured at the falling edge of the envelope of the interfering electrical signal 162. The interfering digital signal is processed by a frequency detector process 570 to identify its instantaneous frequency value at the output 575 of the frequency detector process 570. The frequency detector process 570 performs methods such as a short-time Fourier transform, a wavelet transform, or another frequency detector process known in the art. The instantaneous frequency value at the output 575 of the frequency detector process 570 is then processed by an edge detector process 585 to identify the timing of the rising or falling edge of the interfering electrical signal 162 and the time difference Δ at the output 590 of the edge detector process. TD Identify the time difference Δ TD This is determined as the time between the rising or falling edge of the instantaneous frequency value of output 575 and the modulation / scanning synchronization signal 179. A series of time differences Δ TD This is converted into depth and forms the image that the computer 170 displays.

[0078] Figure 6 is a block diagram of a digital signal processing device configured to perform SSM-TOI Doppler velocity measurement, embodying the principles of this disclosure. Figure 6 shows the sweep linearization correction performed by the sweep linear calibration device 315 of Figure 1C, which is used by the data acquisition and signal processing device 165. When the TOI LIDAR system 100 operates in SSM-TOI mode, velocity information of the object being measured is encoded into an interferential electrical signal 162. The interferential electrical signal 162 generated by the balanced photodetector 160 is digitized by the data acquisition module 605, which is triggered by the modulation / scan synchronization signal 179 from the modulation driver 175 and the optical frequency calibration clock 600, and the interferential electrical signal 162 is converted into a digital signal at the output 607 of the data acquisition module 605. This digital signal is linear in the optical frequency space. The maximum frequency of the interferential electrical signal 162 corresponds to the minimum ranging depth of the TOI LIDAR system 100. The interfering electrical signal 162 is greater than the Nyquist sampling frequency of the data acquisition module 605.

[0079] The minimum frequency of the interferential electrical signal 162 corresponds to the maximum ranging depth of the TOI LIDAR system 100. The time delay of the detected interferential electrical signal 162 is measured at the falling edge of the envelope of the interferential electrical signal 162. The optical frequency calibration clock 600 is generated from a Mach-Zehnder interferometer, a Fabry-Perot resonator, an etalon resonator, or any other interferometer or resonator suitable for generating the optical frequency calibration clock 600. The digital signal 607 becomes the input to the frequency detector process 610 for determining the instantaneous frequency value. The instantaneous frequency value is the solution, which is placed at the output 611 of the frequency detector process 610. In various embodiments, if the digital signal at the output 607 of the data acquisition module 605 is linear in the optical frequency space, the optical frequency calibration clock 600 is not necessary. The frequency detector can be implemented as a short-time Fourier transform, wavelet transform, or any other suitable frequency detector process. Next, the instantaneous frequency value at output 611 of the frequency detector process 610 is processed by the edge detector process 615 to identify the timing of interference occurrence. The edge detector process 615 then detects the time difference Δ between the rising or falling edge of the instantaneous frequency value and the modulation / scan synchronization signal 179. TD The time difference Δ is calculated and then used as the output 620 of the frequency detector process 610. TD Place it.

[0080] In other embodiments of SSM-TOI Doppler velocity measurement, the digital interference electrical signal at output 607 of the data acquisition module 605 becomes the input to the Doppler velocity calculation process 625 for calculating the velocity of the object. The velocity of the object is the output 630 of the Doppler velocity calculation process 625. In one embodiment of the Doppler velocity calculation process 625, the Doppler velocity calculation process 625 calculates the time difference Δ of the frequency of the interference electrical signal 162 between consecutive forward and backward sweeps, which is proportional to the velocity of the object being measured. TD This is achieved by measuring the following. The symmetry of the modulation / scanning synchronization signal 179 minimizes measurement errors. A series of time differences Δ at the output of the edge detector 620.TD The movement speed of the object being measured can be converted into depth and velocity, respectively, to form an image that can be displayed by the computer 170. In some implementations of SSM-TOI Doppler velocity measurement, the velocity introduced by the Doppler frequency shift in the interference electrical signal 162 may be directly extracted using at least one low-pass filter. The frequency shift can be detected and converted into a velocity electrical signal without requiring digital signal processing.

[0081] Figure 7 is a block diagram of an interference time and time-of-flight integrated circuit embodying the principles of the present disclosure. The interference electrical signal 162 generated from the equilibrium photodetector 160 is transferred to the envelope detector 650. The envelope detector 650 obtains the envelope signal of the interference electrical signal 162 applied to the output 652 of the envelope detector 650. The envelope detector 650 is implemented as a radio frequency (RF) power detector, a root mean square (RMS) detector, or a frequency demodulator. Next, the envelope signal of the interference electrical signal 162 passes through the first edge detector 655. The first edge detector 655 generates a first pulse signal at the output 657 of the first edge detector 655 that corresponds to the rising or falling edge of the envelope signal of the interference electrical signal 162 at the output 657 of the envelope detector 650. The edge detector 655 is formed by an edge-glitch converter, an XOR gate and delay circuit, a differentiating circuit, or any edge detection circuit known in the art.

[0082] The electrical signal from the back-reflected coherent light 145 is extracted from the monitor channel of the balanced detector 160, forming the back-reflected electrical signal 145. The back-reflected electrical signal 145 from the monitor channel is the power spectrum of the back-reflected electrical signal 145 and can be considered as the envelope signal. The back-reflected electrical signal 145 is the input to the second edge detector 660. The second edge detector 660 generates a second pulse signal at the output 662 of the second edge detector 660.

[0083] The first pulse signal from the output 657 of the first edge detector 655, the second pulse signal from the output 662 of the second edge detector 660, and the modulation / scan synchronization signal 179 are applied to the multichannel time-to-digital converter 665. The multichannel time-to-digital converter 665 generates a first time difference signal at the output 670 of the time-to-digital converter 665. The first time difference signal Δ TD1 This is a digitized representation of the time between the rising or falling edge of the first pulse signal and the modulation / scan synchronization signal 179 corresponding to the rising or falling edge of the light source modulation / scan synchronization signal 179.

[0084] The multi-channel time-digital converter 665 calculates the second time difference signal Δ between the rising or falling edge of the second pulse signal at the output 662 of the second edge detector 660 and the modulation / scanning synchronization signal 179 corresponding to the rising or falling edge of the light source modulation. TD2 Generates the first time difference signal Δ TD1 and the second time difference signal Δ TD2 The two signals are averaged or weighted. The first time difference signal Δ is averaged or weighted. TD1 and the second time difference signal Δ TD2 This is converted into depth and forms the image that the computer 170 displays.

[0085] Figure 8A is a flowchart illustrating a method for determining the distance to an object using SSM-TOI electrical measurement, which embodies the principle of this disclosure. A laser beam is generated (Box 800). The laser beam is modulated with a wavelength-modulated signal or a frequency-modulated signal (Box 805) to adjust the wavelength or frequency of the laser beam. Next, the laser beam is polarized (Box 810) to adjust the polarization state of the laser light and maximize the amplitude of the optical interference signal or electrical interference signal.

[0086] The first portion of the laser beam is coupled to the sampling optical fiber cable (Box 815). The second portion of the laser beam is coupled to the reference optical path (Box 820). The first portion of the laser beam is scanned at the location of the object whose distance from the modulated laser light source is to be determined (Box 825).

[0087] A portion of the first part of the laser coherent light beam is reflected back from the object being measured and received (Box 830). The back-reflected portion of the first part of the laser light beam is combined with the second part of the laser light beam (Box 835) to form an optical interference coherent light signal. The optical interference coherent light signal is transmitted to a balanced photodetector (Box 840), and the optical interference coherent light signal is converted into an oscillating electrical interference signal (Box 845). The oscillating electrical interference signal is digitized (Box 850). The maximum frequency of the interference electrical signal corresponds to the minimum measuring depth of the TOI LIDAR system and is greater than the Nyquist sampling frequency for digitization. The minimum frequency of the interference electrical signal 162 corresponds to the maximum measuring depth of the TOI LIDAR system 100.

[0088] The envelope of the digital electrical interference signal undergoes an envelope detection process to identify the envelope of the digital electrical interference signal (Box 855). The time of the rising or falling edge of the envelope of the digital electrical interference signal is determined (Box 860). The time difference between the rising or falling edge of the envelope of the digital electrical interference signal and the modulation / scan synchronization signal is determined (Box 865), and the distance to the object being measured is calculated (Box 870).

[0089] Figure 8B is a flowchart illustrating a method for determining the velocity of an object using SSM-TOI electrical measurement, which embodies the principle of this disclosure. The method for determining the velocity of an object using SSM-TOI electrical measurement begins by repeatedly performing the method steps in Figure 8A (Box 875). The velocity of the object is determined from the change in distance with respect to time (Box 880).

[0090] While this disclosure has been illustrated and described with reference to particularly preferred embodiments, those skilled in the art will understand that various modifications in form and detail can be made without departing from the spirit and scope of this disclosure. In particular, the TOI LIDAR system 100 shown in Figures 1A, 1B, or 1C can be implemented as an optical fiber, a bulk optical system, an integrated optical circuit, or any combination of optical elements known in the art.

Claims

1. 1. A high-speed Time-of-Irferometry (ToI) detection and ranging (LIDAR) system for measuring distance from a ToI LIDAR system to an object based on time-frequency domain reflectometry, comprising: a coherent light source; a modulation controller coupled to the coherent light source, the modulation controller configured to generate and control a pulse width of a pulsed wavelength control signal forwarded to the coherent light source to modulate the coherent light source to generate pulsed wavelength-modulated coherent light, the modulation controller comprising a transient generator to generate a positive transient voltage spike and a negative transient voltage spike, and controlling a transient modulation signal to blend the positive transient voltage spike and the negative transient voltage spike to ensure voltage ringing and settling time between the two spikes; an interferometer connected to the coherent light source to receive the pulsed wavelength-modulated coherent light, the interferometer configured to split the pulsed wavelength-modulated coherent light into a sample portion and a reference portion, the sample portion of the pulsed wavelength-modulated coherent light positioned to be incident on the object to be measured, and the reference portion of the pulsed wavelength-modulated coherent light positioned to provide a basis for determining a distance from the ToI LIDAR system to the object; a scanner connected to the interferometer to receive the sample portion of the pulsed wavelength modulated coherent light, the scanner comprising a gradient index fiber rod having a textured surface with a low numerical aperture for emitting light and a high numerical aperture for receiving light, the scanner configured to physically transfer the sample portion of the pulsed wavelength modulated coherent light to the object and scan a surface of the object with the pulsed wavelength modulated coherent light, and further configured to receive a back-reflected portion of the pulsed wavelength modulated coherent light and transfer the back-reflected portion from the scanner to the interferometer; a scanner that combines the back-reflected portion of the pulsed wavelength-modulated coherent light with a reference portion of the pulsed wavelength-modulated coherent light to form an optical interference signal; a photodetector array configured to receive the optical interference signal and convert the optical interference signal into an electrical interference signal; a signal processor in communication with the photodetector array to receive the electrical interference signal and convert the electrical interference signal into a digital electrical interference signal; and a computer system programmed to calculate the time delay determined by the optical interference signal and generate a displayed imaging field based on a distance from the object.

2. 2. The interferometric time LIDAR system of claim 1, wherein the modulation controller comprising the transient generator is configured to modulate the coherent light source by controlling a drive current of the coherent light source, adjusting a temperature of a narrowband light source, or adjusting a phase of light emitted from the coherent light source, and the transient generator comprises an inductance, a capacitance, and a resistance configured to generate the positive and negative transient voltage spikes.

3. The interferometer comprises: a first coupler configured to receive the 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 allow the first portion of the pulsed wavelength modulated coherent light 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 to 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 receiving the second portion of the pulsed wavelength-modulated coherent light; 10. The interferometric time LIDAR system of claim 1, comprising: 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 and the second portion of the pulsed wavelength-modulated coherent light to form an optical interference signal.

4. the interferometer further comprising:

4. The interferometric time LIDAR system of claim 3, comprising a polarization controller configured to receive the pulsed wavelength-modulated coherent light, forward the pulsed wavelength-modulated coherent light to the first coupler, and adjust a polarization state of coherent emission from the coherent light source to maximize an amplitude of the optical or electrical interference signal.

5. 10. The interferometric time LIDAR system of claim 1, wherein the photodetector array is configured as a polarization diversity balanced amplification 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 a range of the target.

6. 4. The interferometric time LIDAR system of claim 3, wherein a length of the reference arm is greater than a length of the sample arm, and an optical path length of the reference arm is greater than twice a maximum ranging depth of the system.

7. 10. The interferometric time LIDAR system of claim 1, wherein a maximum frequency of the optical interference signal corresponds to a minimum ranging depth of the system.

8. 10. The interferometric time LIDAR system of claim 1, wherein the signal processor is configured to determine an envelope of a digitized electrical interference signal.

9. 9. The interferometric time LIDAR system of claim 8, wherein the signal processor is configured to measure a time delay of the digitized electrical interference signal at a falling edge of an envelope of the digitized electrical interference signal.

10. 10. The interferometric time LIDAR system of claim 1, 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.

11. 10. The interferometric time LIDAR system of claim 1, wherein the interferometric time LIDAR system is implemented as optical fibers, bulk optics, integrated optical circuits, or any combination of optical elements.

12. 3. The interferometric time LIDAR system of claim 2, wherein the gradient index fiber rod has a textured surface formed at its distal end to provide a low numerical aperture required for the gradient index fiber rod and a textured gradient index lens for long distance illumination, and a higher numerical aperture required for receiving pulsed wavelength modulated coherent light back reflected from the target.

13. 10. The interferometric time LIDAR system of claim 1, wherein the 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 pulsed wavelength modulated coherent light back reflected from the target.

14. 10. The interferometric time LIDAR system of claim 1, wherein the transient generator modulates an effective inductance value of a transient light source modulator to create spike-like transients to significantly reduce the response time of the laser driver 510, thereby overcoming speed limitations.

15. 1. A method for determining a distance to an object, comprising: generating a coherent light beam; modulating the coherent light beam with a wavelength-modulated signal; coupling a first portion of the coherent light beam into a sample arm; coupling a second portion of the coherent light beam into a reference arm; generating positive and negative transient voltage spikes to control the coherent light beam; scanning the first portion of the wavelength-modulated coherent light beam through a low numerical aperture portion of a graded index fiber rod having a textured surface at a location of an object whose distance from a source of the wavelength-modulated coherent light beam is to be measured; reflecting a portion of the first portion of the wavelength-modulated coherent light beam back from the object through a high numerical aperture gradient index fiber rod having a textured surface; receiving a back-reflected portion of the wavelength-modulated coherent light beam from the object; combining the back-reflected portion of the coherent light beam with the second portion of the coherent light beam to form an optical interference coherent light signal; optically detecting the optically interferometric wavelength-modulated coherent optical signal to form an oscillating electrical interference signal; digitizing the oscillating electrical interference signal; detecting an envelope of the digitized electrical interference signal to determine the envelope of the digitized electrical interference signal; 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 electrical interference signal; and calculating the distance to the object.

16. determining the Doppler velocity of the object by repeatedly executing the steps of claim 11; 16. The method of claim 15, further comprising calculating the Doppler velocity of the object as a change in distance over time.

17. 16. The method of claim 15, further comprising adjusting the polarization state of the coherent light beam to maximize the amplitude of an optical or electrical interference signal.

18. 16. The method of claim 15, wherein a maximum frequency of the electrical interference signal corresponds to a minimum ranging depth for distance measurements to the object, and wherein the maximum frequency of the electrical interference signal is greater than a Nyquist sampling frequency of the step of digitizing the electrical interference signal.

19. 20. The method of claim 18, wherein the minimum frequency of the electrical interference signal corresponds to a maximum ranging depth for measuring the distance to the object.

20. 16. The method of claim 15, further comprising implementing the method using optical fibers, bulk optics, integrated optical circuits, or any combination of optical elements.

21. providing a gradient index fiber rod having a machined gradient index lens; 16. The method of claim 15, further comprising: packaging the gradient index fiber rod with a textured surface to provide a low numerical aperture required for the gradient index fiber rod and a textured gradient index lens for long-distance illumination, and a higher numerical aperture required for receiving pulsed wavelength-modulated coherent light reflected back from the target.

22. mounting the graded index fiber rod; 22. The method of claim 21, further comprising providing a separate lens in contact 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 reflected back from the object.

23. 16. The method of claim 15, further comprising providing a transient generator configured to modify an effective inductance value of the transient light source modulator to generate spike-like transients to significantly reduce the response time of the laser driver, thereby overcoming the speed limitation.

24. 1. A device for determining a distance to an object, comprising: means for generating a coherent light beam; means for modulating the coherent light beam with a transient wavelength modulation signal to adjust the amplitude of the coherent light beam; means for coupling a first portion of said coherent light beam into a sample fiber optic cable; means for coupling a second portion of the coherent light beam into a reference arm; means for generating positive and negative transient voltage spikes to control said coherent light beam; means for scanning the first portion of the modulated coherent light beam through a low numerical aperture portion of a graded index fiber rod having a textured surface at a location of an object whose distance from a source of the modulated coherent light beam is to be measured; means for reflecting a portion of the first portion of the coherent light beam back from the object through a high numerical aperture gradient index fiber rod having a textured surface; means having a high numerical aperture for receiving a back-reflected portion of said coherent light beam from said object; means for combining the back-reflected portion of the coherent light beam with the second portion of the coherent light beam to form an optically interferometric coherent light signal; means for optically detecting the optical interference coherent optical signal to form an oscillating electrical interference signal; means for digitizing the oscillating electrical interference signal; means for detecting an envelope of the digitized electrical interference signal to determine the envelope of the digitized electrical interference signal; means for determining the time of a rising edge or a falling edge of the envelope of the digitized electrical interference signal; means for determining a time difference between rising or falling edges of the envelope of the digitized electrical interference signal; and means for calculating the distance to the object.

25. means for determining the velocity of the object by repeatedly operating the means for determining the distance of the object of claim 18; and means for calculating the velocity of the object as a change in distance over time.

26. 25. The apparatus of claim 24, further comprising means for adjusting the polarization state of the coherent light beam to maximize the amplitude of an optical or electrical interference signal.

27. 25. The apparatus of claim 24, wherein a maximum frequency of the electrical interference signal corresponds to a minimum ranging depth for distance measurements to the object and is greater than a Nyquist sampling frequency of the means for digitizing the electrical interference signal.

28. 25. The apparatus of claim 24, further comprising means for processing the surface of the gradient index fiber rod to provide a low numerical aperture required for the gradient index fiber rod and a processed gradient index lens for long-distance illumination, and a higher numerical aperture required for receiving pulsed wavelength-modulated coherent light reflected back from the target.

29. a means for mounting the graded index fiber rod; 25. The apparatus of claim 24, further comprising: means for providing a separate lens in contact with the gradient index fiber rod to provide the low numerical aperture required for the gradient index fiber rod and the engineered gradient index lens for long-distance illumination, and the higher numerical aperture required to receive the pulsed wavelength-modulated coherent light reflected back from the object.

30. 25. The apparatus of claim 24, further comprising: means for providing a transient generator configured to modify an effective inductance value of the transient light source modulator to generate spike-like transients to significantly reduce the response time of the laser driver, thereby overcoming the speed limitation.

Images