Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/4802—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/491—Details of non-pulse systems
  • G01S7/4912—Receivers
  • G01S7/4915—Time delay measurement, e.g. operational details for pixel components; Phase measurement
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/08—Systems determining position data of a target for measuring distance only
  • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
  • G01S17/26—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/08—Systems determining position data of a target for measuring distance only
  • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
  • G01S17/34—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/08—Systems determining position data of a target for measuring distance only
  • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
  • G01S17/36—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/66—Tracking systems using electromagnetic waves other than radio waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/88—Lidar systems specially adapted for specific applications
  • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes
  • G01S17/931—Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4814—Constructional features, e.g. arrangements of optical elements of transmitters alone
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4816—Constructional features, e.g. arrangements of optical elements of receivers alone
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/4861—Circuits for detection, sampling, integration or read-out
  • G01S7/4863—Detector arrays, e.g. charge-transfer gates
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
  • G01S7/4876—Extracting wanted echo signals, e.g. pulse detection by removing unwanted signals
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/491—Details of non-pulse systems
  • G01S7/4912—Receivers
  • G01S7/4913—Circuits for detection, sampling, integration or read-out
  • G01S7/4914—Circuits for detection, sampling, integration or read-out of detector arrays, e.g. charge-transfer gates
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/491—Details of non-pulse systems
  • G01S7/4912—Receivers
  • G01S7/4917—Receivers superposing optical signals in a photodetector, e.g. optical heterodyne detection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/495—Counter-measures or counter-counter-measures using electronic or electro-optical means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/481—Constructional features, e.g. arrangements of optical elements
  • G01S7/4811—Constructional features, e.g. arrangements of optical elements common to transmitter and receiver
  • G01S7/4812—Constructional features, e.g. arrangements of optical elements common to transmitter and receiver transmitted and received beams following a coaxial path

Definitions

• LIDAR mnemonic ranging
• RADAR radio-wave detection and ranging
• direct ranging based on round trip travel time of an optical pulse to an object
• chirped detection based on a frequency difference between a transmitted chirped optical signal and a returned signal scattered from an object
• phase-encoded detection based on a sequence of single frequency phase changes that are distinguishable from natural signals.
• aspects of the present disclosure relate generally to light detection and ranging (LIDAR) in the field of optics, and more particularly to systems and methods for Doppler compensation and internal reflection subtraction in the operation of an autonomous vehicle.
• LIDAR light detection and ranging
• the system includes a laser source that provides an optical signal.
• the system includes a modulator that modulates the optical signal from the laser to generate a modulated optical signal.
• the system includes an optical coupler that generates a reference optical signal associated with the optical signal from the laser, transmits the modulated optical signal toward an object, and receives a returned optical signal responsive to transmitting the modulated optical signal toward the object.
• the system includes an optical mixer that mixes the returned optical signal with the reference optical signal to generate a mixed optical signal, wherein the reference optical signal is associated with the optical signal from the laser.
• the system includes an optical detector that detects the mixed optical signal to generate an electrical signal.
• the system includes a processor that determines a parameter of an internal reflection of the returned optical signal from one or more optical components based on the electrical signal and the modulated optical signal, and operates a vehicle based on the parameter of the internal reflection.
• the present disclosure is directed to a method for internal reflection subtraction.
• the method includes modulating an optical signal from a laser to generate a modulated optical signal.
• the method includes transmitting the modulated optical signal toward an object.
• the method includes receiving, responsive to transmitting the modulated optical signal, a returned optical signal.
• the method includes mixing the returned optical signal with a reference optical signal associated with the optical signal from the laser to generate a mixed optical signal. In some embodiments, the method includes detecting the mixed optical signal to generate an electrical signal. In some embodiments, the method includes determining, based on the electrical signal and the modulated optical signal, a parameter of an internal reflection of the returned optical signal from one or more optical components. In some embodiments, the method includes operating, based on the parameter of the internal reflection, a vehicle.
• the present disclosure is directed to a system for Doppler compensation.
• the system includes a laser source that provides an optical signal at a carrier frequency.
• the system includes a phase modulator.
• the system includes an optical mixer.
• the system includes a first optical detector.
• the system includes a processor that controls the phase modulator to produce an optical output signal that comprises an optical broadband phase-encoded optical signal.
• the processor receives a real part of a mixed optical signal from the first optical detector as a result of receiving a returned optical signal and mixing the returned optical signal with a reference optical signal.
• either the output optical signal or the reference optical signal includes a pilot tone having a pilot frequency that is offset a known signed non-zero frequency from the carrier frequency.
• the processor determines a peak frequency of the returned optical signal based, at least in part, on a Fourier transform of a digital signal comprising the real part of the mixed optical signal.
• the processor determines a signed Doppler frequency shift of the returned optical signal based on the peak frequency and the pilot frequency.
• the processor operates a device based on the signed Doppler frequency shift.
• the present disclosure is directed to a method for Doppler compensation.
• the method includes producing an optical output signal by phase modulation of an optical signal at a carrier frequency from a laser with a broadband RF phase-encoded signal.
• the output optical signal includes an optical broadband phase-encoded optical signal.
• the method includes transmitting the output optical signal.
• the method includes receiving a returned optical signal in response to transmitting the output optical signal.
• the method includes producing a mixed optical signal by mixing the returned optical signal with a reference optical signal, wherein either the output optical signal or the reference optical signal includes a pilot tone having a pilot frequency that is offset a known signed non-zero frequency from the carrier frequency.
• the method includes detecting a real part of the mixed optical signal at a first optical detector. In some embodiments, the method includes determining on a processor a peak frequency of the returned optical signal based, at least in part, on a Fourier transform of a digital signal comprising the real part of the mixed optical signal. In some embodiments, the method includes determining on a processor a signed Doppler frequency shift of the returned optical signal based on the peak frequency and the pilot frequency. In some embodiments, the method includes operating a device based on the signed Doppler frequency shift.
• FIG. 1 A is a schematic graph that illustrates an example transmitted optical phase- encoded signal for measurement of range, according to an embodiment
• FIG. IB is a schematic graph that illustrates the example transmitted signal of FIG.
• FIG. 1C is a schematic graph that illustrates example cross-correlations of a reference signal with two returned signals, according to an embodiment
• FIG. 2 is a block diagram that illustrates example components of a high resolution LIDAR system, according to an embodiment
• FIG. 3 is a block diagram that illustrates example components of a Doppler compensated phase-encoded LIDAR system using in-phase/quadrature (EQ) processing, according to an embodiment
• FIG. 4A is a schematic graph that illustrates an example spectrum of the output optical signal, according to an embodiment
• FIG. 8 is a graph that illustrates an example transmitted optical signal with a non carrier pilot tone, according to an embodiment
• FIG. 9A is a flow chart that illustrates an example method for operating a phase- encoded LIDAR system to determine and compensate for internal reflections, according to an embodiment
• FIG. 9B is a flow chart that illustrates an example method for operating a phase- encoded LIDAR system to determine and compensate for internal reflections, according to an embodiment
• FIG. 11 is a flow chart that illustrates an example method for phase tracking internal reflections before subtraction, according to an embodiment
• FIG. 13 is a graph that illustrates example internal reflection subtraction, according to an embodiment
• FIG. 14 is a block diagram that illustrates a computer system upon which an embodiment of the invention may be implemented.
• LIDAR detection with phase-encoded microwave signals modulated onto an optical carrier have been used as well.
• This technique relies on correlating a sequence of phases (or phase changes) of a particular frequency in a return signal with that in the transmitted signal.
• a time delay associated with a peak in correlation is related to range by the speed of light in the medium.
• Range resolution is proportional to the pulse width t. Advantages of this technique include the need for fewer components, and the use of mass produced hardware components developed for phase-encoded microwave and optical communications.
• Crouch 7 entitled“Method and System for Doppler Detection and Doppler Correction of Optical Phase-Encoded Range Detection” (hereinafter Crouch 7) and PCT International application No. PCT/US2018/041388 by Crouch et al. entitled“Method and System for Time Separated Quadrature Detection of Doppler Effects in Optical Range Measurements” (hereinafter Crouch 77), the entire contents of each of which are hereby incorporated by reference as if fully set forth herein.
• the reflections also referred to herein as,“internal reflections” or “internal optical reflections”
• internal optical components associated with the phase-encoded LIDAR system (or any LIDAR system)
• strong back-reflections from circulator optics can limit measurement dynamic range and obscure small target returns by increasing the noise floor (through unwanted sidelobe structure) above the shot noise.
• phase-encoded LIDAR systems use a technique called circulator subtraction to estimate the stationary signal (internal back-reflection) and digitally remove it, which has proven to be very effective way to observe weak non-stationary target signals.
• the present disclosure is directed to systems and methods for compensating for the Doppler shift and the negative effects of any internal optical reflections of a returned signal from one or more internal optical components. That is, the present disclosure describes systems (e.g., a phase-encoded LIDAR system) and methods that add a non-carrier pilot tone to either an output optical signal or a reference optical signal such that the Doppler shift can be used to correct the cross-correlation calculation, which in turn, improves the system’s capability to determine range. The system may further improve its capability to determine range by subtracting out (or removing) the internal reflections of the returned signal from the optical components.
• systems e.g., a phase-encoded LIDAR system
• methods that add a non-carrier pilot tone to either an output optical signal or a reference optical signal such that the Doppler shift can be used to correct the cross-correlation calculation, which in turn, improves the system’s capability to determine range.
• the system may further improve its capability to determine range by subtracting out
• FIG. 1 A is a schematic graph 110 that illustrates an example transmitted optical phase-encoded signal for measurement of range, according to an embodiment.
• the horizontal axis 112 indicates time in arbitrary units from a start time at zero.
• the left vertical axis 114a indicates power in arbitrary units during a transmitted signal; and, the right vertical axis 114b indicates phase of the transmitted signal in arbitrary units.
• Trace 115 indicates the power relative to the left axis 114a and is constant during the transmitted signal and falls to zero outside the transmitted signal.
• Dotted trace 116 indicates phase of the signal relative to a continuous wave signal.
• the shortest interval of constant phase is a parameter of the encoding called pulse duration r and is typically the duration of several periods of the lowest frequency in the band.
• the reciprocal, 1/ r, is baud rate, where each baud indicates a symbol.
• the number N of such constant phase pulses during the time of the transmitted signal is the number N of symbols and represents the length of the encoding.
• phase values In binary encoding, there are two phase values and the phase of the shortest interval can be considered a 0 for one value and a 1 for the other, thus the symbol is one bit, and the baud rate is also called the bit rate.
• each symbol indicates the same amount of information as two bits and the bit rate is twice the baud rate.
• Phase-shift keying refers to a digital modulation scheme that conveys data by changing (modulating) the phase of a reference signal (the carrier wave) as illustrated in FIG. 1 A.
• the modulation is impressed by varying the sine and cosine inputs at a precise time.
• RF radio frequencies
• PSK is widely used for wireless local area networks (LANs), RF identification (RFID) and Bluetooth communication.
• LANs wireless local area networks
• RFID RF identification
• Bluetooth communication Alternatively, instead of operating with respect to a constant reference wave, the transmission can operate with respect to itself. Changes in phase of a single transmitted waveform can be considered the symbol.
• the demodulator determines the changes in the phase of the received signal rather than the phase (relative to a reference wave) itself.
• DPSK differential phase-shift keying
• the carrier frequency is an optical frequency /c and a RF /o is modulated onto the optical carrier.
• the number N and duration rof symbols are selected to achieve the desired range accuracy and resolution.
• the pattern of symbols is selected to be distinguishable from other sources of coded signals and noise.
• a strong correlation between the transmitted and returned signal is a strong indication of a reflected or backscattered signal.
• the transmitted signal is made up of one or more blocks of symbols, where each block is sufficiently long to provide strong correlation with a reflected or backscattered return even in the presence of noise.
• the transmitted signal is made up of M blocks of N symbols per block, where M and N are non-negative integers.
• FIG. IB is a schematic graph 120 that illustrates the example transmitted signal of FIG. 1A as a series of binary digits along with returned optical signals for measurement of range, according to an embodiment.
• the horizontal axis 122 indicates time in arbitrary units after a start time at zero.
• the vertical axis 124a indicates amplitude of an optical transmitted signal at frequency /c+/o in arbitrary units relative to zero.
• the vertical axis 124b indicates amplitude of an optical returned signal at frequency /c+/o in arbitrary units relative to zero, and is offset from axis 124a to separate traces.
• Trace 125 represents a transmitted signal of M*N binary symbols, with phase changes as shown in FIG.
• Trace 126 represents an idealized (noiseless) return signal that is scattered from an object that is not moving (and thus the return is not Doppler shifted). The amplitude is reduced, but the code 00011010 is recognizable.
• Trace 127 represents an idealized (noiseless) return signal that is scattered from an object that is moving and is therefore Doppler shifted. The return is not at the proper optical frequency /c+/o and is not well detected in the expected frequency band, so the amplitude is highly diminished.
• FIG. 1C is a schematic graph 130 that illustrates example cross-correlations of the transmitted signal with two returned signals, according to an embodiment.
• phase coded ranging the arrival of the phase coded reflection is detected in the return by cross correlating the transmitted signal or other reference signal with the returned signal, implemented practically by cross correlating the code for an RF signal with an electrical signal from an optical detector using heterodyne detection and thus down-mixing back to the RF band.
• the horizontal axis 132 indicates a lag time in arbitrary units applied to the coded signal before performing the cross-correlation calculation with the returned signal.
• the vertical axis 134 indicates amplitude of the cross-correlation computation.
• Cross-correlation for any one lag is computed by convolving the two traces, i.e., multiplying corresponding values in the two traces and summing over all points in the trace, and then repeating for each time lag.
• the cross-correlation can be accomplished by a multiplication of the Fourier transforms of each of the two traces followed by an inverse Fourier transform.
• Efficient hardware and software implementations for a Fast Fourier transform (FFT) are widely available for both forward and inverse Fourier transforms.
• the cross-correlation computation is typically done with analog or digital electrical signals after the amplitude and phase of the return is detected at an optical detector.
• the optical return signal is optically mixed with the reference signal before impinging on the detector.
• a copy of the phase-encoded transmitted optical signal can be used as the reference signal, but it is also possible, and often preferable, to use the continuous wave carrier frequency optical signal output by the laser as the reference signal and capture both the amplitude and phase of the electrical signal output by the detector.
• Trace 136 represents cross correlation with an idealized (noiseless) return signal that is reflected from an object that is not moving (and thus the return is not Doppler shifted). A peak occurs at a time At after the start of the transmitted signal. This indicates that the returned signal includes a version of the transmitted phase code beginning at the time At.
• the range R to the reflecting (or backscattering) object is computed from the two-way travel time delay based on the speed of light c in the medium, as given by Equation 3.
• Dotted trace 137 represents cross correlation with an idealized (noiseless) return signal that is scattered from an object that is moving (and thus the return is Doppler shifted).
• the return signal does not include the phase encoding in the proper frequency bin, the correlation stays low for all time lags, and a peak is not as readily detected, and is often undetectable in the presence of noise.
• range R is not as readily produced.
• FIG. 2 is a block diagram that illustrates example components of a Doppler compensated LIDAR system, according to an embodiment.
• the LIDAR system 200 includes a laser source 212, a splitter 216, a modulator 282a, a reference path 220, scanning optics 218, a processing system 250, an acquisition system 240, and a detector array 230.
• the laser source 212 emits a carrier wave 201 that is phase or frequency modulated in modulator 282a, before or after splitter 216, to produce a phase coded or chirped optical signal 203 that has a duration D.
• a splitter 216 splits the modulated (or, as shown, the unmodulated) optical signal.
• a target beam 205 also called transmitted signal or output optical signal herein, with most of the energy of the beam 201 is produced.
• a modulated or unmodulated reference beam 207a with a much smaller amount of energy that is nonetheless enough to produce good mixing with the returned beam 291 scattered from an object (not shown) is also produced.
• the reference beam 207a is separately modulated in modulator 282b; but, in some embodiments, modulator 282b is omitted.
• the reference beam 207a passes through reference path 220 and is directed to one or more detectors as reference beam 207b.
• the reference path 220 introduces a known delay sufficient for reference beam 207b to arrive at the detector array 230 with the scattered light from an object outside the LIDAR.
• the reference beam 207b is called the local oscillator (LO) signal referring to older approaches that produced the reference beam 207b locally from a separate oscillator.
• LO local oscillator
• the reference is caused to arrive with the scattered or reflected field by: 1) putting a mirror in the scene to reflect a portion of the transmit beam back at the detector array so that path lengths are well matched; 2) using a fiber delay to closely match the path length and broadcast the reference beam with optics near the detector array, as suggested in FIG. 2, with or without a path length adjustment to compensate for the phase or frequency difference observed or expected for a particular range; or, 3) using a frequency shifting device (acousto-optic modulator) or time delay of a local oscillator waveform modulation (e.g., in modulator 282b) to produce a separate modulation to compensate for path length mismatch; or some combination.
• the object is close enough and the transmitted duration long enough that the returns sufficiently overlap the reference signal without a delay.
• the number is often a practical consideration chosen based on number of symbols per signal, signal repetition rate and available camera frame rate.
• the frame rate is the sampling bandwidth, often called “digitizer frequency.”
• the only fundamental limitations of range extent are the coherence length of the laser and the length of the chirp or unique phase code before it repeats (for unambiguous ranging). This is enabled as any digital record of the returned heterodyne signal or bits could be compared or cross correlated with any portion of transmitted bits from the prior transmission history.
• the acquired data is made available to a processing system 250, such as a computer system described below with reference to FIG. 14, or a chip set described below with reference to FIG. 10.
• the processing system 250 includes a Doppler compensation module 270a and a phase tracking internal reflection subtraction module 270b (shown in FIG. 2 as an internal reflection subtraction module 270b).
• the Doppler compensation module 270a determines the sign and size of the Doppler shift and the corrected range based thereon along with any other corrections described herein.
• the internal reflection subtraction module 270b determines the phase tracked internal reflection correction used by the processing system 250 along with any other corrections known to provide a corrected range measurement (e.g., signals produced from Doppler compensation module 270a).
• the data processing also provides estimates of Doppler shift in which the frequency of a return signal is shifted due to motion of the object.
• the processing system 250 also provides scanning signals to drive the scanning optics 218, and includes a modulation signal module 272 to send one or more electrical signals that drive modulators 282a, 282b, as illustrated in FIG. 2.
• any known apparatus or system may be used to implement the laser source 212, modulators 282a, 282b, beam splitter 216, reference path 220, optical mixers 284, detector array 230, scanning optics 218, or acquisition system 240.
• Optical coupling to flood or focus on a target or focus past the pupil plane are not depicted.
• an optical coupler is any component that affects the propagation of light within spatial coordinates to direct light from one component to another component, such as a vacuum, air, glass, crystal, mirror, lens, optical circulator, beam splitter, phase plate, polarizer, optical fiber, optical mixer, among others, alone or in some combination.
• electro-optic modulators provide the modulation.
• M*N the total number of pulses M*N is in a range from about 500 to about 4000.
• M*N the total number of pulses M*N is in a range from about 500 to about 4000.
• M is 1 when no averaging is done. If there are random noise contributions, then it is advantages for M to be about 10.
• splitter 216 and reference path 220 include zero or more optical couplers.
• FIG. 3 is a block diagram that illustrates example components of a phase-encoded LIDAR system using previous approaches.
• the system includes laser 310 and phase modulator 320, beam splitter 312, an optical mixer 360, such as a circulator and combiner, scanning optics 322 including transmission/receiver optics such as circulator 323, and a photodetector 330 (also referred to herein as,“optical detector 330”).
• the output of the beam splitter 312 is used as the local oscillator (LO) reference signal 314 (also referred to herein as,“LO 314”) and input to optical mixer 360.
• LO local oscillator
• a sinusoid with phase modulation (corresponding to an angle modulation between the real and imaginary parts of the mathematical function exp (icot)) can be decomposed into, or synthesized from, two amplitude-modulated sinusoids that are offset in phase by one-quarter cycle (p/2 radians). All three functions have the same frequency.
• the amplitude modulated sinusoids are known as in-phase component (I) at 0 phase and quadrature component (Q) at a phase of p/2.
• a laser produces an optical signal at a carrier frequency /c.
• the modulated laser optical signal, L is represented mathematically by Equation 4.
• the modulation signal module in the processing system sends an electrical signal that indicates a digital code of symbols to be imposed as phase changes on the optical carrier, represented as B(/) where B(t) switches between 0 and p/2 as a function of t.
• the phase modulator 320 acting as modulator 282a imposes the phase changes on the optical carrier by taking digital lines out of a field programmable gate array (FPGA), amplifying them, and driving the EO phase modulator.
• the transmitted optical signal, T is then given by Equation 6a.
• T C ⁇ R exp(/[c#]) + S exp (i ⁇ cot + B(/)]) ⁇ (6a)
• C is a constant that accounts for the reduction in Io by splitting of the fraction A and any amplification or further reduction imposed by the phase modulator 320 or other components of the transmitted path
• R is the amplitude of the residual carrier after phase modulation
• S is the amplitude for the phase coded signal.
• the returned signal is directed to an optical mixer, where the return optical signal is mixed with the reference optical signal (LO) given by Equation 5a through Equation 5c.
• FIG. 4A is a schematic graph 140a that illustrates an example spectrum of the transmitted signal
• FIG. 4B is a schematic graph 440a that illustrates an example spectrum of a Doppler shifted complex return signal.
• the horizontal axis 442 indicates RF frequency offset from an optical carrier /c in arbitrary units.
• the vertical axis 444 indicates amplitude of a particular narrow frequency bin, also called spectral density, in arbitrary units relative to zero.
• a typical phase modulator adds the RF phase modulation signal to both sides of the carrier frequency,/:. This is called dual sideband modulation.
• trace 446 represents an idealized (noiseless) complex return signal that is backscattered from an object that is moving toward the LIDAR system and is therefore Doppler shifted to a higher frequency (called blue shifted).
• the time domain signal is sampled with an IQ technique, then the sign of the Doppler shift (positive or negative relative to DC) is evident in the resulting power spectrum.
• optical mixer and processing are configured to determine the in-phase (I) and quadrature (Q) components.
• IQ detection by one or more components can be utilized to resolve the sign of the Doppler shift.
• a 90 degree optical hybrid optical mixer allows for I/Q detection of the optically down-mixed signals on two channels which are then digitized. This system allows for an extremely flexible“software defined” measurement architecture to occur.
• Other hardware embodiments described in Crouch I include the use of 3x3 s multimode interference (MMI) structures. These devices are more compact than free-space 90-degree hybrids. They produce a 120 degree phase shift at each output port. Each port is then independently detected and digitized prior to software based reconstruction of the complex signal.
• MMI multimode interference
• the approach requires at least two detectors and two analog to digital converters (ADCs) to support a measurement. This presents a challenge to scaling where optical hybrids, detectors, electrical routing, and digitizers all take space in heavily integrated designs.
• an advantage is obtained if the in- phase (I) and quadrature (Q) components are detected at separate times.
• the reference signal can be made to be in-phase with the transmitted signal during one time interval to measure at an optical detector 330 an electrical signal related to the real part of the returned optical signal, and the reference signal can be made to be in quadrature with the transmitted signal during a different, non-overlapping time interval to measure at the optical detector 330 an electrical signal related to the complex part of the returned optical signal.
• a complex signal can then be generated digitally in Doppler compensation module 370a from the two measured electrical signals; and, the digitally constructed complex signal can be used to determine the properly signed Doppler shift.
• the I/Q separation was used to first estimate signed COD and then the signed COD was used to correct the cross-correlation computation to derive At.
• the estimate should be within the frequency resolution of the system set by the duration of processing interval.
• the Doppler shifted, time delayed code term (after down-mixing) for electric field due to kth return is given by Equation 7e,
• Equation 7f one can see residual phase terms remains but the oscillating Doppler component of the argument is removed (compensated out).
• the signed value of COD is also used to present the speed and direction of the object, at least on the vector connecting the object to the LIDAR system 300.
• the value of At is then used to determine and present the range to the object using Equation 3 described above.
• the separation of the I and Q signals by the optical mixers enables clearly determining the sign of the Doppler shift.
• I and Q components determined separately, rather than finding A/b by taking the spectrum of both transmitted and returned signals and searching for peaks in each, then subtracting the frequencies of corresponding peaks, it is more efficient to take the cross spectrum of the in- phase and quadrature component of the down-mixed returned signal in the RF band.
• FIG. 4C is a schematic plot that illustrates an example return signal spectrum when IQ processing is not done, according to an embodiment.
• the carrier pilot is seen on both sides of the spectrum.
• the methods utilize electro optic phase modulators to drive dual sideband waveforms.
• modulation depth is chosen to maintain some energy in the carrier frequency.
• the residual carrier acts as a“pilot” tone in the transmitted waveform.
• this CW“pilot” is Doppler shifted, the result is a beat note that can be used to estimate the Doppler shift from a target.
• the estimation of Doppler on the basis of this pilot tone allows for an efficient Doppler correction of the code signal prior to cross-correlation with a reference code - a two stage, Doppler then range, estimation process.
• Electro-optic modulation architectures beyond basic phase modulators are common in optical fiber communications.
• a common architecture allows the realization of single-sideband suppressed carrier (SSBSC) phase modulation.
• SSBSC single-sideband suppressed carrier
• the NC pilot tone is moved away from the carrier frequency (RF fo 1 0) and does not map to fc.
• these SSBSC phase modulators can be used to generate pilot tones at frequencies other than the carrier frequency, which allows for non-base band centered operation of the Doppler shift estimate discussed above.
• the non-carrier pilot tones are called engineered pilot tones, or, simply, NC pilot tones, hereinafter.
• NC pilot tone since the NC pilot tone only exists on one side of the carrier (single sideband) the Doppler shift will be present in signal spectra with no sign ambiguity even without IQ separation. Thus the sign of the Doppler shift (approaching vs. receding targets) will be accurately resolved.
• the NC pilot tone is introduced in the reference optical signal instead of the transmitted optical signal. Doppler correction on the basis of the recovered signed Doppler shift is identical to that described in previous methods.
• a variety of different components are used to introduce a non-carrier pilot tone on either: the output optical signal that is transmitted through scanning optics 322 for interaction with object 390; or, on a reference optical signal for mixing with a returned signal 324 in optical mixer 360.
• FIG. 5A is a block diagram that illustrates an example Doppler compensated LIDAR system using non-carrier pilot tone, according to an embodiment. While an object 390 is depicted for purposes of illustration, object 390 is not part of LIDAR system 500a.
• the scanning optics 322, circulator 323, optical mixer 360, photodetector 330, digital code module 372 and object 390 are as described above with respect to FIG. 3.
• the laser 310 and beam splitter 312 are replaced by optical source(s) 510a, with one or more lasers and other optical couplers to produce an optical base signal (OB 511a) for phase modulation, and a reference signal (REF 514a).
• OB 511a optical base signal
• REF 514a reference signal
• Optical source(s) 510a includes a non-carrier pilot tone generator 588a (shown as,“NC pilot tone generator 588a” in FIG. 5A) configured to generate a pilot tone different from the carrier frequency of a laser used to generate optical base signal 511a.
• This configuration can be achieved either with different driving functions for the previous laser 310, or a separate laser with its own driving functions.
• the dual sideband phase modulator 380 is replaced with one or more phase modulator(s) 580a, including zero or more single sideband (SSB) or single sideband suppressed carrier (SSBSC) phase modulators, or some combination.
• SSB single sideband
• SSBSC single sideband suppressed carrier
• the processing system 350 is replaced with processing system 550a that includes a Doppler compensation module 570a containing a single sideband (SSB) phase processing module 574a.
• the processing system 550a also includes a phase tracking internal reflection subtraction module 572a for determining cross correlation and range based on electrical signal 532a.
• the NC pilot tone generator 588a is controlled by the SSB phase processing module 574a, which supplies the driving functions.
• the SSB phase processing module 574a also determines the signed Doppler shift based on the electrical signal 532a.
• the electrical signal 532a is output by detector 330 when struck by mixed optical signal 562a output by the optical mixer 360 when the REF 514a and return signal 524a are coincident on the optical mixer 360.
• the return signal 524a is received in response to transmitting the optical output signal from the phase modulators 580a through the scanning optics 322.
• the optical sources 510a uses a first laser driven to produce just the carrier frequency optical signal.
• the optical sources 510a uses a separate second laser driven by the SSB phase processing module 574a to produce a non-carrier pilot tone as NC pilot tone generator 588a.
• the optical source(s) 510a includes a splitter that splits the carrier frequency optical signal to be directed both to the phase modulator(s) 580a as a component of the optical base (OB 511a) and to the optical mixer 360 as a component of the optical reference signal (REF 514a).
• the NC pilot tone optical signal from the NC pilot tone generator 588a is added to either the optical base signal (OB 511a) or the optical reference signal (REF 514b) using a combiner optical coupler - but not to both.
• the REF 514a includes only the NC pilot tone without the carrier frequency optical signal and the optical base signal (OB 511a) comprises only the carrier frequency optical signal.
• the optical source(s) includes a single laser that produces the carrier frequency optical signal and a splitter that directs most of the energy to the phase modulator(s) 580a as OB 511a.
• the optical source(s) 510a also includes an acousto-optic modulator (AOM) to shift the optical frequency of the low energy beam emitted from the splitter to the NC pilot tone which is then output to optical mixer 360 as REF 514a.
• the AOM is controlled by the SSB phase processing module 574a by driving an acoustic source to produce an acoustic frequency sufficient to shift the optical frequency to the desired pilot frequency in the AOM.
• FIG. 5B is a block diagram that illustrates an example Doppler compensated LIDAR system using non-carrier pilot tone, according to another embodiment.
• the phase modulator(s) are configured to generate an NC pilot tone and thus include a NC pilot tone generator 588b.
• the NC pilot tone generator 588a of laser sources 510a is omitted from optical source(s) 510b. While an object 390 is depicted for purposes of illustration, object 390 is not part of LIDAR system 500b.
• the scanning optics 322, circulator 323, optical mixer 360, photodetector 330, digital code module 372 and object 390 are as described above with respect to FIG. 3.
• optical source(s) 510a are replaced by optical source(s) 510b, with one or more lasers and other optical couplers to produce an optical base signal (OB 511b) for phase modulation, and a reference signal (REF 514b).
• OB 511b optical base signal
• REF 514b reference signal
• phase modulator(s) 580a are replaced by phase modulator(s) 580b which include a NC pilot tone generator 588b configured to generate a pilot tone different from the carrier frequency.
• the NC pilot tone generator 588b includes one or more single sideband (SSB) or single sideband suppressed carrier (SSB SC) phase modulators, or other optical components, or some combination.
• SSB single sideband
• SSB SC single sideband suppressed carrier
• a single SSB SC phase modulator imposes both the phase code and the pilot tone.
• the phase modulator(s) 580b include a splitter, a combiner, a dual sideband phase modulator to impose the phase code signal, and a SSB phase modulator as the NC pilot tone generator 588b.
• the splitter splits the optical base signal (OB 511a) into two beams of roughly equal strength, sending one beam into the dual sideband phase modulator and the other into the SSB phase modulator as NC pilot tone generator 588b.
• the outputs from the two modulators are combined in the optical combiner to produce the output optical signal that is transmitted through scanning optics 322.
• the phase modulator(s) includes a single DSB or SSB or SSB SC phase modulator to impose the phase code, and an acousto-optic modulator (AOM) as the NC pilot tone generator 588b to shift the optical frequency of the optical base signal with the carrier frequency to the NC pilot tone.
• the AOM is controlled by the SSB phase processing module 574b by driving an acoustic source to produce an acoustic frequency sufficient to shift the optical frequency to the desired pilot frequency in the AOM.
• the processing system 350 is replaced with processing system 550b that includes a Doppler compensation module 570b containing a single sideband phase processing module 574b.
• the processing system 550b also includes a phase tracking internal reflection subtraction module 572b for determining cross correlation and range based on electrical signal 532a.
• the NC pilot tone generator 588b is controlled by the SSB phase processing module 574b, which supplies the phase codes that generate the pilot tone as well as the phase encoded LIDAR signal.
• the SSB phase processing module also determines the signed Doppler shift based on the electrical signal 532b.
• the electrical signal 532b is output by detector 330 when struck by mixed optical signal 562b output by the optical mixer 360 when the REF 514b and return signal 524b are coincident on the mixer.
• the return signal 524b is received in response to transmitting the optical output signal from the phase modulator(s) 580b through the scanning optics 322.
• FIG. 6A is a schematic graph 640a that illustrates an example spectrum 645 of the SSB output optical signal, according to an embodiment.
• This non-carrier pilot tone will not only guide the detection of a Doppler shift; but, also provide an unambiguous determination of Doppler shift sign as described in more detail below.
• FIG. 6B is a schematic graph 640b that illustrates an example spectrum of a Doppler shifted SSB optical return signal when IQ processing is done, according to an embodiment.
• This shows back-reflected and Doppler shifted spectrum from an object as trace 646 in the case of single sideband suppressed carrier.
• the Doppler shift and sign are readily determined as the difference between the measured dominant spectral peak at the shifted non-carrier pilot tone 646a (designated fps) and the pilot frequency fp (see Equation 9, below).
• This new calculation of the signed Doppler shift is used in the SSB phase processing module 574a,
• FIG. 6C is a schematic plot 640c that illustrates an example spectrum of a Doppler shifted SSB return signal spectrum when IQ processing is not done, according to an embodiment.
• the resulting spectrum 647 is the true response 646 and the reflection thereof around the carrier frequency. Note that, when converting to the RF signal, both in driving the modulation and after down-mixing in the optical mixer, the carrier frequency corresponds to the DC component of the RF signal at 0 frequency. Because the non-carrier pilot tone frequency 647a is off the symmetry axis, it is evident in both halves of the return spectrum.
• FIG. 7 is a flow chart that illustrates an example method for using single-sideband phase-encoded LIDAR system to determine and compensate for signed Doppler shift effects on ranges, according to an embodiment.
• operations are depicted in FIG. 7 as integral operations in a particular order for purposes of illustration, in other embodiments, one or more operations, or portions thereof, are performed in a different order, or overlapping in time, in series or in parallel, or are omitted, or one or more additional operations are added, or the method is changed in some combination of ways.
• some or all operations of method 700 may be performed by one or more LIDAR systems, such as LIDAR system 200 in FIG. 2, LIDAR system 300 in FIG. 3, LIDAR system 500a in FIG.
• a transceiver e.g., a LIDAR system
• a transceiver is configured to transmit phase-encoded optical signals based, at least in part, on input of a phase code sequence.
• a portion e.g., 1% to 10%
• the unmodulated input optical signal from the laser, or the phase- encoded transmitted signal is also directed to a reference optical path.
• the phase encode optical signal or the reference signal includes a NC pilot tone, but not both.
• the LIDAR is configured as depicted in FIG. 5A or FIG. 5B or some combination.
• the transceiver is also configured to receive a backscattered optical signal from any external object illuminated by the transmitted signals.
• a code made up of a sequence of M*N symbols is generated for use in ranging, representing M blocks of N symbols each selected from the n symbol alphabet, with no duplicate series of N symbols among the M blocks.
• the Fourier transform of an RF signal with such phase encoding is also determined during operation 703 for use in determining the Doppler shift, as described in Crouch I.
• a first portion of the laser output is modulated using code received from digital code module 372 with a single-sideband phase modulator, such as a SSBSC phase modulator, to produce a transmitted single-sideband phase-encoded signal with non-carrier pilot tone, as represented by Equation 6, and directed to a spot in a scene where there might be, or might not be, an object or a part of an object.
• a second portion of the laser output is directed as a reference signal, as represented by Equation 5a or Equation 5c, also called a local oscillator (LO) signal, along a reference path.
• LO local oscillator
• the backscattered returned signal, R with any travel time delay At and Doppler shift wo, as represented by Equation 7a or Equation 7b, is mixed with the reference signal LO, as represented by Equation 5a or Equation 5c, to output one or more mixed optical signals 362.
• the mixed signal informs on the in-phase and quadrature components.
• averaging and internal reflection subtraction is performed over several different return signals S(7) to remove spurious copies of the transmitted optical signal produced at internal optical components along the return signal path, such as circulator 323.
• spurious copies can decrease the correlation with the actual return from an external object and thus mask actual returns that are barely detectable. If the averaging is performed over a number P of different illuminated spots, and returns such that a single object is not in all those illuminated spots, then the average is dominated by the spurious copy of the code produced by the internal optical components. This spurious copy of the code can then be removed from the returned signal to leave just the actual returns in a corrected complex electrical signal S(t). P is a number large enough to ensure that the same object is not illuminated in all spots.
• P is about 100. In other embodiments, depending on the application, P can be in a range from about 10 to about 5000.
• operation 708 it is determined whether P returns have been received. If not, control passes back to operation 705 to illuminate another spot. If so, then the average signal is computed, doing phase weighting in some embodiments, and the average is subtracted from the returned signal to remove the effect of internal reflections.
• the signed Doppler shift is determined and used to correct the return signal. If separate I/Q detection and processing is not used, then the frequencies of two peaks fpsi and fpsu are found in the electrical signal based on the mixture of the reference and returned signals; and, the signed Doppler shift is determined using Equation 8a, or Equation 8b or Equation 8c. If separate EQ detection and processing is used, then the frequency of the single dominant peaks fps is found in the returned spectrum; and, the signed Doppler shift is determined using Equation 9.
• the signed Doppler shift is used to correct the time domain or spectrum of the returned signal.
• the estimate should be within the frequency resolution of the system set by the duration of processing interval.
• the Doppler shifted, time delayed code term (after downmixing) for the electric field and kth return is given by Equation 10a,
• the correction with the Doppler estimate is achieved by a vector multiplication in the time domain (or the CIRCSHIFT method in the frequency domain). This vector multiplication is depicted in Equation 10b.
• Equation 10b one can see residual phase terms remain, but the oscillating Doppler component of the argument is removed (compensated out).
• a corrected return signal is used to detect the range or relative speed or both.
• operation 711 includes associating each delay time with one of the signed Doppler shifts, assuming that a particular return is based on an object or part of an object moving at a particular average speed over the duration of one transmitted signal. For a given signed Doppler correction, only those range peaks associated with that signed Doppler correction will be present in the cross correlation. So it is improbable to incorrectly pair a given range and signed Doppler in the case of multiple instances.
• operation 731 it is determined if another spot is to be illuminated. If so, control passes back to operation 703 and following. If not, control passes to operation 733.
• a device is operated based on the corrected ranges or speeds or both. In some embodiments, this involves presenting on a display device an image that indicates a Doppler corrected position of any object at a plurality of spots illuminated by the transmitted optical signal. In some embodiments, this involves communicating, to the device, data that identifies at least one object based on a point cloud of corrected positions at a plurality of spots illuminated by transmitted optical signals. In some embodiments, this involves moving a vehicle to avoid a collision with an object, wherein a closing speed between the vehicle and the object is determined based on a size of the Doppler effect at a plurality of spots illuminated by the transmitted optical signal. In some embodiments, this involves identifying the vehicle or identifying the object on the collision course based on a point cloud of corrected positions at a plurality of spots illuminated by the transmitted optical signal.
• This waveform D is used to drive the SSB phase modulator.
• FIG. 9A is a flow chart that illustrates an example method for using phase-encoded LIDAR system to determine and compensate for internal reflection effects on ranges, according to an embodiment.
• operations are depicted in FIG. 9A, and subsequent flow diagram FIG. 11 and FIG. 12, as integral operations in a particular order for purposes of illustration, in other embodiments, one or more operations, or portions thereof, are performed in a different order, or overlapping in time, in series or in parallel, or are omitted, or one or more additional operations are added, or the method is changed in some combination of ways.
• some or all operations of method 900a may be performed by one or more LIDAR systems, such as LIDAR system 200 in FIG. 2, LIDAR system 300 in FIG.
• LIDAR system 500a in FIG. 5A and/or LIDAR system 500b in FIG. 5B.
• operations 903a and 910a through 933a may be performed by processing system 350 in FIG. 3 and/or processing system 550 in FIG. 5A and FIG. 5B.
• a transceiver e.g., a LIDAR system
• a transceiver is configured to transmit phase-encoded optical signals based on input of a phase code sequence.
• a portion e.g., 1% to 10%
• the transceiver is also configured to receive a backscattered optical signal from any external object illuminated by the transmitted signals.
• operation 901a includes configuring other optical components in hardware to provide the functions of one or more of the following operations as well.
• the transmitted signal need not be a beam. A diverging signal will certainly see a lot of different ranges and Doppler values within a single range profile; but, provide no cross range resolution within an illuminated spot. However, it is
• a code made up of a sequence of M*N symbols is generated for use in ranging, representing M blocks of N symbols each selected from the n symbol alphabet, with no duplicate series of N symbols among the M blocks.
• the Fourier transform of an RF signal with such phase encoding is also determined during operation 903a for use in determining the Doppler shift, as described in WO2018/144853.
• a first portion of the laser output is phase-encoded using code received from digital code module 372 to produce a transmitted phase-encoded signal, as represented by Equation 6a, and directed to a spot in a scene where there might be, or might not be, an object or a part of an object.
• a second portion of the laser output is directed as a reference signal, as represented by Equation 5a or Equation 5b, also called a local oscillator (LO) signal, along a reference path.
• LO local oscillator
• the backscattered returned signal, R with any travel time delay At and Doppler shift wo, as represented by Equation 7a, is mixed with the reference signal LO, as represented by Equation 5a or Equation 5b, to output one or more mixed optical signals 362.
• the mixed signal informs on the in-phase and quadrature components.
• the mixed optical signals are directed to and detected at one or more optical detectors to convert the optical signals to one or more corresponding electrical signals.
• one electrical signal on one channel (Ch 1) indicates down-mixed in-phase component I; and the other electrical signal on a different channel (CH 2) indicates down-mixed quadrature component Q.
• a complex down-mixed signal S is computed based on the two electrical signals. In any case one or more electrical signals are produced in operation 908a.
• averaging and internal reflection subtraction is performed over several different return signals S(/) to remove spurious copies of the phase-encoded signal produced at internal optical components along the return signal path, such as scanning optics 322.
• spurious copies can decrease the correlation with the actual return from an external object and thus mask actual returns that are barely detectable. If the averaging is performed over a number P of different illuminated spots, and returns such that a single object is not in all those illuminated spots, then the average is dominated by the spurious copy of the code produced by the internal optical components. This spurious copy of the code can then be removed from the returned signal to leave just the actual returns in a corrected complex electrical signal S(t).
• P is a number large enough to ensure that the same object is not illuminated in all spots.
• P is about 100. In other embodiments, depending on the application, P can be in a range from about 10 to about 5000.
• FIG. 11 is a block diagram that illustrates example multi-spot averaging to remove returns from internal optics, according to an embodiment. Operations 909a and 910a perform this correction.
• This average signal is used to correct each of the received signals S / ,(t) to produce corrected signals S c:(t) to use as received signal S(t) in subsequent operations, as given by Equation (6b)
• the internal optics are calibrated once under controlled conditions to produce fixed values for Ss(/) that are stored for multiple subsequent deployments of the system.
• operation 910a includes only applying Equation 12b.
• the spurious copies of the code produced by the internal optics are small enough, or the associated ranges different enough from the ranges to the external objects, that operation 909a and 910a can be omitted.
• operations 909a and 910a are omitted, and control passes directly from operation 908a to operation 911a, using S(t) from operation 908a rather than from Equation 12b in operation 910a.
• a corrected return signal is used to detect the range or Doppler shift or both.
• a device is operated based on the corrected ranges or speeds or both. In some embodiments, this involves presenting on a display device an image that indicates a Doppler corrected position of any object at a plurality of spots illuminated by the transmitted optical signal. In some embodiments, this involves communicating, to the device, data that identifies at least one object based on a point cloud of corrected positions at a plurality of spots illuminated by transmitted optical signals. In some embodiments, this involves moving a vehicle to avoid a collision with an object, wherein a closing speed between the vehicle and the object is determined based on a size of the Doppler effect at a plurality of spots illuminated by the transmitted optical signal. In some embodiments, this involves identifying the vehicle or identifying the object on the collision course based on a point cloud of corrected positions at a plurality of spots illuminated by the transmitted optical signal.
• Range bins are distinguished by a range bin index that increases with distance (lag time).
• a distance (range) associated with an index is the index number multiplied by the range bin size.
• the range bin size is given by the time lag increment multiplied by the speed of light in the medium. In the examples given below, unless otherwise stated, the range bin size is 1 meter.
• FIG. 9B is a flow chart that illustrates an example method for using phase-encoded LIDAR system to determine and compensate for internal reflection effects on ranges, according to an embodiment.
• operations are depicted in FIG. 9B, and subsequent flow diagram FIG. 11 and FIG. 12, as integral operations in a particular order for purposes of illustration, in other embodiments, one or more operations, or portions thereof, are performed in a different order, or overlapping in time, in series or in parallel, or are omitted, or one or more additional operations are added, or the method is changed in some combination of ways.
• some or all operations of method 900b may be performed by one or more LIDAR systems, such as LIDAR system 200 in FIG. 2, LIDAR system 300 in FIG. 3, LIDAR system 500a in FIG. 5A, and/or LIDAR system 500b in FIG. 5B.
• FIG. 10A through FIG. 10E are graphs that illustrate example range signals before and after corrections to remove returns from internal optics, according to an embodiment.
• the horizontal axis indicates range bins in meters from zero to over 4000m; and, the vertical axis indicates cross correlation power in decibels (dB, log(y/yo) relative to reference yo).
• the trace shows the correlation peaks before subtracting the average of P spots. A large peak appears about 100 m and a smaller peak at about 2000m.
• FIG. IOC shows a solid trace that indicates multiple spurious reflections between 60 and 90 meters, which are nearly completely removed in the dashed trace that indicates the corrected range profile.
• optical back reflection is often made up of multiple reflections.
• the circulator has several back reflecting surfaces which manifest as separate peaks in FIG. IOC uncorrected.
• FIG. 10D shows a solid trace that indicates an actual peak at about 1850m, which is enhanced about 10% in the dashed trace that indicates the corrected range profile.
• the laser dither often goes over several hundred megahertz at a frequency of several hundred hertz. This can cause challenges relative to the internal reflection average subtraction techniques discussed above, because the phase may drift by >2p during a typical circulator averaging duration of 20 to 30 measurements used in some embodiments, or between 10 and 5000 measurements used in various other embodiments.
• the internal reflection average subtraction method is modified to take account of laser phase changes during the internal reflection averaging period.
• the phase sensitivity of coherent LIDAR systems can be leveraged to solve this problem.
• phase corrections e.g., multiplying by a unitary complex number
• FIG. 11 is a flow chart that illustrates an example method for phase tracking internal reflections before subtraction, according to an embodiment. This method 1100 is
• phase associated with this peak for the /ith spot is a complex number given by Equation 13c.
• Angle ⁇ x ⁇ is a function that computes the four quadrant inverse tangent, basically the [-p, p] wrapped angle between the real and imaginary parts of the complex number x.
• the return signal is corrected in the time domain by the phase determined in operation 1111, as given by Equation 14a.
• Equation 14b the complex sum of the phase corrected signals and number n of signals summed is accumulated and stored in memory or a special register or on some other computer-readable medium as a time series of complex numbers.
• the summation is given by Equation 14b.
• operation 1139 it is determined whether there is another returned signal in the averaging ensemble to correct for internal reflections. If so, control passes back to operation 1131. If not, control passes to operation 1141. In some embodiments, the returned signal to be corrected for internal reflections is outside the averaging ensemble and operation 1139 is omitted and control passes directly from operation 1137 to operation 1141.
• FIG. 12 is a flow chart that illustrates an example method for phase tracking internal reflections before subtraction, according to a different embodiment.
• the phase can be efficiently measured by calculating the inner product of the transmitted code and received signal circularly shifted by the expected range index of the back-reflected signal.
• the inner product will compute the same amplitude and phase result as the full cross correlation but only at the range bin of interest.
• This method 1200 saves many computations. From this phase calculation, the received signal is phase corrected in the time domain.
• the corrected time domain signal is then averaged with other phase-corrected temporal measurements. This averaged temporal signal will be used as the back-reflected signal to be subtracted from future temporal measurements as above.
• phase of this entry is computed.
• the phase associated with this range index for the /ith spot, designated fI R is a complex number given by Equation 13c, as described above.
• the return signal is corrected in the time domain by the phase determined in operation 1215, as given by Equation 14a, described above, and a sum or average is accumulated over P returned signals as described above with respect to Equations 14b and 14c.
• both the phase corrected signal Sp(t) and the phase correction are stored on a computer-readable medium for later retrieval.
• the phase corrected signal Sp(t ) and phase correction fI R are stored instead of the received signal Ek P ( t).
• the complex sum of the phase corrected signals and number n of signals summed is accumulated and stored in memory or a special register or on some other computer-readable medium.
• Equation 14c provides the time domain internal reflection subtraction signal Ss(t) given by Equation 12a. This equivalence is expressed in Equation 14d. If P signals have not been accumulated then control passes back to operation 905a to illuminate the next spot.
• the suppression is always >20dB and routinely >30dB.
• the target for this operation is often for a noise floor of about 15dB to 20dB.
• the code is subdivided into sections (say 256 sample chunks) before performing one or more of the above operations (e.g., estimating and tracking phase with the inner product trick.
• the phase evolution (and hence the frequency of the laser) can be tracked digitally at faster timescales. This can improve phase tracking circulator subtraction a bit.
• FIG. 14 is a block diagram that illustrates a computer system 1400 upon which an embodiment of the invention may be implemented.
• Computer system 1400 includes a communication mechanism such as a bus 1410 for passing information between other internal and external components of the computer system 1400.
• Information is represented as physical signals of a measurable phenomenon, typically electric voltages, but including, in other embodiments, such phenomena as magnetic, electromagnetic, pressure, chemical, molecular atomic and quantum interactions. For example, north and south magnetic fields, or a zero and non-zero electric voltage, represent two states (0, 1) of a binary digit (bit). Other phenomena can represent digits of a higher base.
• a superposition of multiple simultaneous quantum states before measurement represents a quantum bit (qubit).
• a sequence of binary digits constitutes digital data that is used to represent a number or code for a character.
• a bus 1410 includes many parallel conductors of information so that information is transferred quickly among devices coupled to the bus 1410.
• One or more processors 1402 for processing information are coupled with the bus 1410.
• a processor 1402 performs a set of operations on information.
• the set of operations include bringing information in from the bus 1410 and placing information on the bus 1410.
• the set of operations also typically include comparing two or more units of information, shifting positions of units of information, and combining two or more units of information, such as by addition or multiplication.
• a sequence of operations to be executed by the processor 1402 constitutes computer instructions.
• Computer system 1400 also includes a memory 1404 coupled to bus 1410.
• the memory 1404 such as a random access memory (RAM) or other dynamic storage device, stores information including computer instructions. Dynamic memory allows information stored therein to be changed by the computer system 1400. RAM allows a unit of information stored at a location called a memory address to be stored and retrieved independently of information at neighboring addresses.
• the memory 1404 is also used by the processor 1402 to store temporary values during execution of computer instructions.
• the computer system 1400 also includes a read only memory (ROM) 1406 or other static storage device coupled to the bus 1410 for storing static information, including instructions, that is not changed by the computer system 1400.
• ROM read only memory
• Also coupled to bus 1410 is a non-volatile (persistent) storage device 1408, such as a magnetic disk or optical disk, for storing information, including instructions, that persists even when the computer system 1400 is turned off or otherwise loses power.
• Information is provided to the bus 1410 for use by the processor from an external input device 1412, such as a keyboard containing alphanumeric keys operated by a human user, or a sensor.
• a sensor detects conditions in its vicinity and transforms those detections into signals compatible with the signals used to represent information in computer system 1400.
• bus 1410 Other external devices coupled to bus 1410, used primarily for interacting with humans, include a display device 1414, such as a cathode ray tube (CRT) or a liquid crystal display (LCD), for presenting images, and a pointing device 1416, such as a mouse or a trackball or cursor direction keys, for controlling a position of a small cursor image presented on the display 1414 and issuing commands associated with graphical elements presented on the display 1414.
• a display device 1414 such as a cathode ray tube (CRT) or a liquid crystal display (LCD)
• LCD liquid crystal display
• pointing device 1416 such as a mouse or a trackball or cursor direction keys
• special purpose hardware such as an application specific integrated circuit (IC) 1420
• IC application specific integrated circuit
• the special purpose hardware is configured to perform operations not performed by processor 1402 quickly enough for special purposes.
• application specific ICs include graphics accelerator cards for generating images for display 1414, cryptographic boards for encrypting and decrypting messages sent over a network, speech recognition, and interfaces to special external devices, such as robotic arms and medical scanning equipment that repeatedly perform some complex sequence of operations that are more efficiently implemented in hardware.
• Computer system 1400 also includes one or more instances of a communications interface 1470 coupled to bus 1410.
• Communication interface 1470 provides a two-way communication coupling to a variety of external devices that operate with their own processors, such as printers, scanners and external disks. In general the coupling is with a network link 1478 that is connected to a local network 1480 to which a variety of external devices with their own processors are connected.
• communication interface 1470 may be a parallel port or a serial port or a universal serial bus (USB) port on a personal computer.
• USB universal serial bus
• Signals include man-made variations in amplitude, frequency, phase, polarization or other physical properties of carrier waves.
• the communications interface 1470 sends and receives electrical, acoustic or electromagnetic signals, including infrared and optical signals, that carry information streams, such as digital data.
• Non-volatile media include, for example, optical or magnetic disks, such as storage device 1408.
• Volatile media include, for example, dynamic memory.
• Transmission media include, for example, coaxial cables, copper wire, fiber optic cables, and waves that travel through space without wires or cables, such as acoustic waves and electromagnetic waves, including radio, optical and infrared waves.
• the term computer- readable storage medium is used herein to refer to any medium that participates in providing information to processor 1402, except for transmission media.
• Computer-readable media include, for example, a floppy disk, a flexible disk, a hard disk, a magnetic tape, or any other magnetic medium, a compact disk ROM (CD-ROM), a digital video disk (DVD) or any other optical medium, punch cards, paper tape, or any other physical medium with patterns of holes, a RAM, a programmable ROM (PROM), an erasable PROM (EPROM), a FLASH-EPROM, or any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.
• the term non-transitory computer-readable storage medium is used herein to refer to any medium that participates in providing information to processor 1402, except for carrier waves and other signals.
• Network link 1478 typically provides information communication through one or more networks to other devices that use or process the information.
• network link 1478 may provide a connection through local network 1480 to a host computer 1482 or to equipment 1484 operated by an Internet Service Provider (ISP).
• ISP equipment 1484 in turn provides data communication services through the public, world-wide packet-switching communication network of networks now commonly referred to as the Internet 1490.
• a computer called a server 1492 connected to the Internet provides a service in response to information received over the Internet.
• server 1492 provides information representing video data for presentation at display 1414.
• the invention is related to the use of computer system 1400 for implementing the techniques described herein. According to one embodiment of the invention, those techniques are performed by computer system 1400 in response to processor 1402 executing one or more sequences of one or more instructions contained in memory 1404. Such instructions, also called software and program code, may be read into memory 1404 from another computer-readable medium such as storage device 1408. Execution of the sequences of instructions contained in memory 1404 causes processor 1402 to perform the method operations described herein.
• hardware such as application specific integrated circuit 1420, may be used in place of or in combination with software to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware and software.
• instructions and data may initially be carried on a magnetic disk of a remote computer such as host 1482.
• the remote computer loads the instructions and data into its dynamic memory and sends the instructions and data over a telephone line using a modem.
• a modem local to the computer system 1400 receives the instructions and data on a telephone line and uses an infra-red transmitter to convert the instructions and data to a signal on an infra-red a carrier wave serving as the network link 1478.
• An infrared detector serving as communications interface 1470 receives the instructions and data carried in the infrared signal and places information representing the instructions and data onto bus 1410.
• Bus 1410 carries the information to memory 1404 from which processor 1402 retrieves and executes the instructions using some of the data sent with the instructions.
• the instructions and data received in memory 1404 may optionally be stored on storage device 1408, either before or after execution by the processor 1402.
• the chip set 1500 includes a communication mechanism such as a bus 1501 for passing information among the components of the chip set 1500.
• a processor 1503 has connectivity to the bus 1501 to execute instructions and process information stored in, for example, a memory 1505.
• the processor 1503 may include one or more processing cores with each core configured to perform independently.
• a multi-core processor enables multiprocessing within a single physical package. Examples of a multi-core processor include two, four, eight, or greater numbers of processing cores.
• the processor 1503 may include one or more microprocessors configured in tandem via the bus 1501 to enable independent execution of instructions, pipelining, and multithreading.
• the processor 1503 and accompanying components have connectivity to the memory 1505 via the bus 1501.
• the memory 1505 includes both dynamic memory (e.g., RAM, magnetic disk, writable optical disk, etc.) and static memory (e.g., ROM, CD-ROM, etc.) for storing executable instructions that when executed perform one or more operations of a method described herein.
• the memory 1505 also stores the data associated with or generated by the execution of one or more operations of the methods described herein.

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