WO2024140884A1

WO2024140884A1 - Light source linearity monitoring method and system, linear frequency modulation control method and control system and lidar

Info

Publication number: WO2024140884A1
Application number: PCT/CN2023/142613
Authority: WO
Inventors: Jianhao MAO; Zhengqing PAN; Zhaoyu Lu; Shaoqing Xiang
Original assignee: Hesai Technology Co., Ltd.
Priority date: 2022-12-28
Filing date: 2023-12-28
Publication date: 2024-07-04

Abstract

A light source linearity monitoring method for an FMCW LiDAR, a light source linear frequency modulation control method, a light source linearity monitoring system, a light source linear frequency modulation control system, and an FMCW LiDAR include: determining a portion of a transmitted optical signal as a monitoring optical signal; splitting the monitoring optical signal into two monitoring optical signals and apply unequal delays to the two monitoring optical signals, and determining a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals; and determining a linearity monitoring result based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

Description

LIGHT SOURCE LINEARITY MONITORING METHOD AND SYSTEM, LINEAR FREQUENCY MODULATION CONTROL METHOD AND CONTROL SYSTEM AND LIDAR

CROSS-REFERENCE TO RELATED APPLICATION (S)

This application claims priority to Chinese Patent Application No. 202211698253.1, filed on December 28, 2022, the content of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to the technical field of light detection and ranging ( “LiDAR” ) and, in particular, to a light source linearity monitoring method for a frequency modulated continuous wave ( “FMCW” ) LiDAR, a light source linear frequency modulation control method, a light source linearity monitoring system, a light source linear frequency modulation control system, and an FMCW LiDAR.

BACKGROUND

A frequency modulated continuous wave ( “FMCW” ) LiDAR transmits continuous frequency modulated laser light as detection light, the echo signal reflected by an object has a certain frequency shift with respect to the corresponding detection optical signal, and the distance and speed information of the object can be determined by measuring the frequency shift. By doing so, the spatial detection can be achieved.

To efficiently and accurately perform the ranging, it is beneficial to improve or ensure the linearity of the frequency of the detection optical signal over time. The light source of the FMCW LiDAR generates the linear frequency swept optical signal primarily by means of external modulation or direct modulation. The external modulation light source loads a modulation signal on the laser beam outputted by the laser through an independent electro-optic modulator disposed downstream of the laser to determine linear frequency modulated light. On the basis of the fact that the output frequency of the laser is affected by current and temperature, the direct modulation light source modulates the laser by controlling the current.

The electro-optic modulator needs to be equipped with a corresponding drive signal source. Thus, this is not conductive for mass production and application. Furthermore, the operation temperature range of the electro-optic modulator is relatively narrow.

The direct modulation light source is susceptible to temperature, noise, or the like, for example, the temperature or the noise can degrade the linearity of the frequency of the optical signal over time. To alleviate this problem, in the existing technology, an optical phase-locked loop can monitor the linearity of the light source. However, the monitoring period is increased, and the accuracy of the real-time linearity of the light source can be affected.

Therefore, how to efficiently monitoring the linearity of the light source of the FMCW LiDAR in real time at a low cost to improve or ensure the reliability of the detection result of the LiDAR is to be solved by those skilled in the art.

SUMMARY

In view of this, some embodiments of this disclosure provide a light source linearity monitoring method for an FMCW LiDAR, a light source linear frequency modulation control method, a light source linearity monitoring system, a light source linear frequency modulation control system, and an FMCW LiDAR. The linearity of the light source of the FMCW LiDAR can be monitored in real time. By doing so the reliability of the detection result of the LiDAR can be improved or ensured.

In a first aspect, some embodiments of this disclosure provide a light source linearity monitoring method for an FMCW LiDAR. The light source linearity monitoring method includes:

determining a portion of a transmitted optical signal as a monitoring optical signal; splitting the monitoring optical signal into two monitoring optical signals, applying unequal delays to the two monitoring optical signals, and determining a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals; and determining a linearity monitoring result based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

Optionally, the determining the linearity monitoring result based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal includes: determining an instantaneous phase of the beat frequency signal; determining a deviation between the instantaneous phase of the beat frequency signal and an instantaneous phase of the predetermined standard beat frequency signal at a same sampling time; and determining the linearity monitoring result based on the deviation.

Optionally, the determining the instantaneous phase of the beat frequency signal includes: generating a time domain beat frequency signal based on the beat frequency signal, and applying a phase shift to the time domain beat frequency signal in the time domain to determine an orthogonal signal of the beat frequency signal; and determining the instantaneous phase of the beat frequency signal based on the orthogonal signal.

Optionally, the generating a time domain beat frequency signal based on the beat frequency signal and applying the phase shift to the time domain beat frequency signal to determine the orthogonal signal of the beat frequency signal includes: representing the beat frequency signal by a cosine curve of the beat frequency signal having a phase varies over time; and applying the phase shift to the cosine curve of the beat frequency signal through a finite impulse response filter to determine a sine curve of the beat frequency signal where the phase varies over time as the orthogonal signal of the beat frequency signal.

Optionally, the determining the instantaneous phase of the beat frequency signal based on the orthogonal signal includes: determining a tangent curve of the beat frequency signal based on the cosine curve of the beat frequency signal and the sine curve of the beat frequency signal; and determining, based on the tangent curve of the beat frequency signal, an inverse tangent curve of the beat frequency signal as the instantaneous phase of the beat frequency signal.

Optionally, the determining, based on the tangent curve of the beat frequency signal, the inverse tangent curve of the beat frequency signal as the instantaneous phase of the beat frequency signal further includes: generating a continuously varying association based on a periodic association between a phase of the beat frequency signal and time.

Optionally, the generating a continuously varying association based on a periodic association between a phase of the beat frequency signal and time includes: when determining that a jump occurs in the phase of the beat frequency signal, superimposing a phase of the beat frequency signal of a time period after a time of the jump with a periodic phase difference of the beat frequency signal.

In a second aspect, some embodiments of this disclosure provide another light source linearity monitoring method for an FMCW LiDAR. The light source linearity monitoring method includes: determining a beat frequency signal by a beat frequency processing on two delayed monitoring optical signals; determining a linearity monitoring result based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal; wherein the two delayed monitoring optical signals are split from a portion of a transmitted optical signal, and unequal delays are applied to the two delayed monitoring optical signals.

In a third aspect, some embodiments of this disclosure also provide a light source linear frequency modulation control method. The light source linear frequency modulation control method includes: determining a portion of a transmitted optical signal as a monitoring optical signal; splitting the monitoring optical signal into two monitoring optical signals, applying unequal delays to the two monitoring optical signals, and determining a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals; and adjusting the transmitted optical signal based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

Optionally, the adjusting the transmitted optical signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal includes: determining a correction signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal; superimposing the correction signal with a predetermined pre-correction signal to determine a drive signal; and adjusting the transmitted optical signal based on the drive signal.

Optionally, the determining the correction signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal includes: determining the correction signal through a linear controller. Some embodiments of this disclosure also provide another light source linear frequency modulation control method. The light source linear frequency modulation control method includes: determining a beat frequency signal by a beat frequency processing on two delayed monitoring optical signals; adjusting a transmitted optical signal based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal; wherein the two delayed monitoring optical signals are split from a portion of the transmitted optical signal, and unequal delays are applied to the two delayed monitoring optical signals.

In a fourth aspect, some embodiments of this disclosure also provide a light source linearity monitoring system coupled to a light source. The light source linearity monitoring system includes an interference processor module and a data processor module. The interference processor module is configured to split a monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals. The monitoring optical signal is a portion of an optical signal transmitted by the light source. The data processor module is configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal, and determine a linearity monitoring result based on the deviation.

In a fifth aspect, some embodiments of this disclosure also provide a light source linear frequency modulation control system coupled to a light source. The light source linear frequency modulation control system includes an interference processor module, a data processor module and a feedback controller module. The interference processor module is configured to split a monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals. The monitoring optical signal is a portion of an optical signal transmitted by the light source. The data processor module is configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal. The feedback controller module is configured to adjust the transmitted optical signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal to determine a linear frequency modulated optical signal.

In a sixth aspect, some embodiments of this disclosure also provide an FMCW LiDAR. The FMCW LiDAR includes a light source, an interference processor module, and a data processor module. The light source is configured to transmit an optical signal. A portion of the optical signal is determined as a monitoring optical signal. A portion of the optical signal is determined as a detection optical signal. The interference processor module is configured to split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals. The data processor module is configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal, and determine a linearity monitoring result based on the deviation.

Optionally, the LiDAR further includes a detector. The light source is configured to transmit a linear frequency modulated optical signal as the detection optical signal. A portion of the linear frequency modulated optical signal is transmitted to the detector as a local oscillator light. The detector is configured to receive a detection echo signal determined when the detection optical signal is reflected to the LiDAR by an object. The data processor module is further configured to determine a distance and a speed of the object based on the local oscillator light and the detection echo signal.

Optionally, the data processor module is further configured to calculate the distance and the speed of the object based on a Doppler frequency shift of the detection echo signal with respect to the local oscillator light.

Optionally, the interference processor module includes a fiber interferometer with unequal arms.

Optionally, the determining the deviation between the beat frequency signal and the predetermined standard beat frequency signal includes: determining an instantaneous phase of the beat frequency signal; and determining a deviation between the instantaneous phase of the beat frequency signal and an instantaneous phase of the predetermined standard beat frequency signal at a same sampling time.

Optionally, the determining the instantaneous phase of the beat frequency signal includes: generating a time domain beat frequency signal based on the beat frequency signal, and applying a phase shift to the time domain beat frequency signal to determine an orthogonal signal of the beat frequency signal; and determining the instantaneous phase of the beat frequency signal based on the orthogonal signal.

In a seventh aspect, some embodiments of this disclosure also provide an FMCW LiDAR. The FMCW LiDAR includes a light source, an interference processor module, a data processor module, and a feedback controller module. The light source is configured to transmit an optical signal. A portion of the optical signal is determined as a monitoring optical signal. A portion of the optical signal is determined as a detection optical signal. The interference processor module is configured to split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals. The data processor module is configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal. The feedback controller module is configured to adjust the optical signal transmitted by the light source based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal to determine a linear frequency modulated optical signal.

Optionally, the LiDAR further includes a detector. The light source is configured to transmit the linear frequency modulated optical signal as the detection optical signal. A portion of the linear frequency modulated optical signal is transmitted to the detector as a local oscillator light. The detector is configured to receive a detection echo signal determined when the detection optical signal is reflected to the LiDAR by an object. The data processor module is further configured to determine a distance and a speed of the object based on the local oscillator light and the detection echo signal.

Optionally, the determining the instantaneous phase of the beat frequency signal includes: generating a time domain beat frequency signal based on the beat frequency signal, and applying phase shift to the time domain beat frequency signal to determine an orthogonal signal of the beat frequency signal; and determining the instantaneous phase of the beat frequency signal based on the orthogonal signal.

With the light source linearity monitoring method provided by some embodiments of this disclosure, a portion of a transmitted optical signal is determined as a monitoring optical signal; the monitoring optical signal is split into two monitoring optical signals, unequal delays are applied to the two monitoring optical signals, and a beat frequency signal is determined by a beat frequency processing on the two delayed monitoring optical signals; and a linearity monitoring result is determined based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal. When the linearity of the light source is detected using the method, in one aspect, the detection cost is reduced because the need for additional device is reduced (e.g., no additional device is required) ; in another aspect, since the monitoring is performed with a portion of the optical signal transmitted by the light source as the monitoring optical signal, the detection using the light source is not affected. Furthermore, the real-time performance of the monitoring can be improved or ensured, the reliability of the detection result of the LiDAR can be improved or ensured.

Further, the association between the phase of the beat frequency signal and time is determined, the instantaneous phase of the beat frequency signal and the instantaneous phase of the predetermined standard beat frequency signal at the same time (e.g., at the sampling time of the beat frequency signal) can be compared with each other, to determine a deviation between them, and the linearity monitoring result can be determined based on the deviation. Since the beat frequency signal can be sampled at any time based on the association between the phase of the beat frequency signal and time, the real-time deviation between the beat frequency signal and the predetermined standard beat frequency signal is determined. By doing so, the real-time performance of the monitoring can be improved.

Further, a time domain beat frequency signal is generated based on the beat frequency signal, the time domain beat frequency signal is phase shifted in the time domain to determine an orthogonal signal of the beat frequency signal, and the instantaneous phase of the beat frequency signal is determined based on the orthogonal signal, and noise in the beat frequency signal can be quantified. By doing so, the accuracy of the determined instantaneous phase and the accuracy of the monitoring result can be improved.

Further, since the time domain beat frequency signal can be phase shifted in real time through a finite impulse response filter without the need for a complete frequency sweep band, the time domain signal is represented by a cosine curve of the beat frequency signal having a phase varies over time and the cosine curve of the beat frequency signal is phase shifted through the finite impulse response filter to determine a sine curve of the beat frequency signal where a phase varies over time as the orthogonal signal of the beat frequency signal. The orthogonal signal of the beat frequency signal can be determined in real time. By doing so, the real-time performance of the monitoring can be improved.

Further, a tangent curve of the beat frequency signal is determined based on the cosine curve of the beat frequency signal and the sine curve of the beat frequency signal, and an inverse tangent curve of the beat frequency signal is determined based on the tangent curve of the beat frequency signal as the instantaneous phase of the beat frequency signal. By doing so, the influence of noise on the monitoring result can be reduced or avoided, and the accuracy of the monitoring result can be improved.

Further, a continuously varying association is generated based on a periodic association between the phase of the beat frequency signal and time. The error or abnormality in the phase of the beat frequency signal at the time when a periodic jump occurs can be reduced or avoided, and the accuracy of the monitoring result can be improved.

Further, when determining that a jump occurs in the phase of the beat frequency signal, the phase of the beat frequency signal of a time period after the time of the jump is superimposed with a periodic phase difference of the beat frequency signal to cause the generation of the continuously varying association based on the association between the phase of the beat frequency signal and time. By doing so, the error or abnormality in the phase of the beat frequency signal at the time when the periodic jump occurs can be reduced or avoided. The accuracy of the monitoring result can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the technical solutions in some embodiments of this disclosure or the technical solutions in the existing technology more clearly, drawings used in the description of some embodiments or the existing technology is described below.

FIG. 1 shows a flowchart of an example light source linearity monitoring method for an FMCW LiDAR, consistent with some embodiments of this disclosure.

FIG. 2a shows a schematic diagram of the frequency of two example monitoring optical signals determined after a same linear frequency swept optical signal is unequally delayed, consistent with some embodiments of this disclosure.

FIG. 2b shows a schematic diagram of the beat frequency signal of the two monitoring optical signals shown in FIG. 2a.

FIG. 3 shows a flowchart of an example method for determining a linearity monitoring result, consistent with some embodiments of this disclosure.

FIG. 4 shows a flowchart of an example method for determining the instantaneous phase of the beat frequency signal, consistent with some embodiments of this disclosure.

FIG. 5 shows a flowchart of an example method for determining the orthogonal signal of the beat frequency signal, consistent with some embodiments of this disclosure.

FIG. 6 shows a schematic diagram of the phase of the example beat frequency signal of the two monitoring optical signals and the orthogonal signal of the beat frequency signal, consistent with some embodiments of this disclosure.

FIG. 7 shows a flowchart of an example method for determining the instantaneous phase of the beat frequency signal based on the orthogonal signal, consistent with some embodiments of this disclosure.

FIG. 8 shows a schematic diagram of an example periodic association between the phase of the beat frequency signal of the two monitoring optical signals and time, consistent with some embodiments of this disclosure.

FIG. 9 shows a schematic diagram of the example continuously varying association between the phase of the beat frequency signal and time, consistent with some embodiments of this disclosure.

FIG. 10 shows a structural schematic diagram of an example light source linearity monitoring system, consistent with some embodiments of this disclosure.

FIG. 11 shows a flowchart of an example light source linear frequency modulation control method, consistent with some embodiments of this disclosure.

FIG. 12 shows a flowchart of an example method for adjusting a transmitted optical signal, consistent with some embodiments of this disclosure.

FIG. 13 shows a structural schematic diagram of an example light source linear frequency modulation control system, consistent with some embodiments of this disclosure.

FIG. 14 shows a structural schematic diagram of an example FMCW LiDAR, consistent with some embodiments of this disclosure.

FIG. 15 shows a structural schematic diagram of another example FMCW LiDAR, consistent with some embodiments of this disclosure.

FIG. 16 shows a structural schematic diagram of an example FMCW LiDAR, consistent with some embodiments of this disclosure.

FIG. 17 shows a diagram of the example beat frequency signal of local oscillator light and a detection echo signal of an FMCW LiDAR, consistent with some embodiments of this disclosure.

DETAILED DESCRIPTION

As described in the BACDGROUND, the light source of the FMCW LiDAR generates the linear frequency swept optical signal mainly by means of external modulation or direct modulation. However, an independent electro-optic modulator disposed downstream of the laser is needed for the external modulation light source. The independent electro-optic modulator can load a modulation signal on laser light outputted by the laser. The electro-optic modulator also needs to be equipped with a drive signal source. Thus, this is not conductive for mass production and application. The direct modulation light source is susceptible to temperature, noise, or the like. In the existing technology, an optical phase-locked loop can monitor the linearity of the light source. However, the monitoring period is increased, and the accuracy of the real-time linearity of the light source can be affected.

In view of the above-mentioned problems, some embodiments of this disclosure provide a light source linearity monitoring method for an FMCW LiDAR. A portion of a transmitted optical signal is determined as a monitoring optical signal; the monitoring optical signal is split into two monitoring optical signals, unequal delays are applied to the two monitoring optical signals, and a beat frequency signal is determined by a beating frequency processing on the two delayed monitoring optical signals; and a linearity monitoring result is determined based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal. When the linearity of the light source is monitored using the method, in one aspect, the monitoring cost is reduced because the need for additional device is reduced (e.g., no additional device is required) ; in another aspect, since the monitoring is performed with a portion of the optical signal transmitted by the light source as the monitoring optical signal, the detection using the light source is not affected. In addition, the above solution can improve or ensure the real-time performance of the monitoring, and the reliability of the detection result of the LiDAR can be improved or ensured.

To enable those skilled in the art to better understand and implement some embodiments of this disclosure, the ideas, solutions, principles, and advantages of some embodiments of this disclosure are described below in conjunction with the accompanying drawings and by means of some application examples.

In a first aspect, some embodiments of this disclosure provide a light source linearity monitoring method for an FMCW LiDAR. For example, referring to FIG. 1 which shows a flowchart of an example light source linearity monitoring method for an FMCW LiDAR, consistent with some embodiments of this disclosure. The light source linearity monitoring can be performed through the following steps.

In step A, a portion of a transmitted optical signal is determined as a monitoring optical signal.

In some embodiments, the optical signal transmitted by the light source can be split using a coupler, a portion of the transmitted optical signal can be determined as the monitoring optical signal, and the other portion can be determined as a detection optical signal and outputted to the external space for detection.

In step B, the monitoring optical signal is split into two monitoring optical signals, unequal delays are applied to the two monitoring optical signals, and a beat frequency signal is determined by a beat frequency processing on the two delayed monitoring optical signals.

In some embodiments, a variety of different forms of interferometers can apply unequal delays to the two monitoring optical signals, and a coupler can perform the beat frequency processing on the two delayed monitoring optical signals to determine the beat frequency signal.

For example, a Mach-Zehnder interferometer can apply the unequal delays on the two monitoring optical signals. The unequal delay time τ is related to the magnitude of the gain of an interferometer on the phase of the laser. In some embodiments, the unequal delay time τ can be determined in conjunction with the parameters of the LiDAR system to enable the frequency of the beat frequency signal to be within a reasonable range. In addition, the delay can introduce a delay in the control loop of the laser to influence the control effect.

In step C, a linearity monitoring result is determined based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

In some embodiments, for example, referring to FIGS. 2a and 2b, where FIG. 2a shows a schematic diagram of the frequency of two example monitoring optical signals (e.g., a first optical signal 1 and a second optical signal 2) determined after a same linear frequency swept optical signal is unequally delayed, the two monitoring optical signals are determined from an ideal linear frequency modulated optical signal. FIG. 2b shows a schematic diagram of the beat frequency signal of the two monitoring optical signals shown in FIG. 2a. As can be seen from the figure, due to the unequal delays, although the initial phases of the first optical signal 1 and the second optical signal 2 are different, the scanning frequency ranges, slopes, and periods of the two signals are consistent with each other. For example, when the optical signal transmitted by the light source is a linear frequency modulated optical signal, the frequency of the beat frequency signal of the two optical signals is a fixed value f0 during the periods when the two optical signals are both rising or falling, for example, the period t1-t2 or t3-t4.

In some embodiments of this disclosure, the fixed value f0 can be determined to the frequency of the predetermined standard beat frequency signal during the period t1-t2, the beat frequency signal is compared with the predetermined standard beat frequency signal to determine a deviation between the beat frequency signal and the predetermined standard beat frequency signal, and the linearity monitoring result can be determined based on the deviation.

With the above embodiment, a portion of a transmitted optical signal is determined as the monitoring optical signal; the monitoring optical signal is split into two monitoring optical signals, unequal delays are applied to the two monitoring optical signals, and a beat frequency signal is determined by performing a beat frequency processing on the two delayed monitoring optical signals; and a linearity monitoring result can be determined based on the deviation between the beat frequency signal and a predetermined standard beat frequency signal. Therefore, in one aspect, the monitoring cost is low because the need for additional device is reduced (e.g., no additional device is required) ; in another aspect, since the monitoring is performed with a portion of the optical signal transmitted by the light source as the monitoring optical signal, the detection using the light source is not affected. Furthermore, the real-time performance of the monitoring can also be improved or ensured, the reliability of the detection result of the LiDAR can be improved or ensured.

For a better understanding and implementation by those skilled in the art, the following is described by way of some examples and in conjunction with example application scenarios.

For step C, an example method of determining a linearity monitoring result based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal is described below in conjunction with some examples. For example, referring to FIG. 3 which shows a flowchart of an example method for determining a linearity monitoring result, as an example, the linearity monitoring result can be determined, for example, through the following steps.

In step C1, an instantaneous phase of the beat frequency signal is determined.

In some embodiments, the variation of the beat frequency signal over time is reflected through the phase. The beat frequency signal of a time point can be defined. By doing so, the real-time variation of the beat frequency signal can be reflected.

In some embodiments, the time point can include one or more time points, or each time point.

In step C2, a deviation between the instantaneous phase of the beat frequency signal and an instantaneous phase of the predetermined standard beat frequency signal at a same sampling time is determined.

In some embodiments, the beat frequency signal can be sampled at any time based on the association between the phase of the beat frequency signal and time to determine the instantaneous phase of the beat frequency signal. Since the beat frequency signal is already an approximate sine signal rather than a linear signal, and the phase of a standard sine varies linearly, the deviation between the instantaneous phase of the beat frequency signal at the sampling time and the instantaneous phase of the predetermined standard beat frequency signal can be determined.

In step C3, a linearity monitoring result is determined based on the deviation.

In some embodiments, the real-time deviation between the beat frequency signal and the predetermined standard beat frequency signal can be determined based on the association between the phase of the beat frequency signal and time. The real-time linearity monitoring result can be determined.

With the above embodiment, the association between the phase of the beat frequency signal and time is determined, the deviation between the instantaneous phase of the beat frequency signal and the instantaneous phase of the predetermined standard beat frequency signal at the same time (e.g., at the sampling time of the beat frequency signal) can be compared with each other, to determine a deviation between them, and the linearity monitoring result can be determined based on the deviation. Since the beat frequency signal can be sampled at any time based on the association between the phase of the beat frequency signal and time, the real-time deviation between the beat frequency signal and the predetermined standard beat frequency signal is determined. By doing so, the real-time performance of the monitoring can be improved.

In some embodiments, for example, referring to FIG. 4 which shows a flowchart of an example method for determining the instantaneous phase of the beat frequency signal, as an example, the instantaneous phase of the beat frequency signal can be determined, for example, through the following steps.

In step C11, a time domain beat frequency signal is generated based on the beat frequency signal, and the time domain beat frequency signal is phase shifted in the time domain to determine an orthogonal signal of the beat frequency signal.

In some embodiments, a beat frequency signal at a certain time point can be represented as a time domain beat frequency signal. The time domain beat frequency signal can include, for example, a curve where the phase varies over time in the time domain. The time domain beat frequency signal can be phase shifted based on the curve with the amplitude unchanged to determine an orthogonal signal of the beat frequency signal, for example, two signals with a phase difference of 90°. For example, the signal determined by phase shifting the time domain beat frequency signal by 90° is the orthogonal signal of the beat frequency signal.

In step C12, the instantaneous phase of the beat frequency signal is determined based on the orthogonal signal.

In some embodiments, since the noise in the beat frequency signal is difficult to be predicted, the phase of the beat frequency signal at a certain time point is difficult to be determined, and thus the instantaneous phase of the beat frequency signal can be determined based on the orthogonal signal.

With the above embodiment, the time domain beat frequency signal is generated based on the beat frequency signal. The time domain beat frequency signal, which is an approximate standard sine signal for example, referring to FIG. 6, is phase shifted in the time domain to determine the orthogonal signal of the beat frequency signal, and the instantaneous phase of the beat frequency signal is determined based on the orthogonal signal, and noise in the beat frequency signal can be quantified. By doing so, the accuracy of the determined instantaneous phase and the accuracy of the monitoring result can be improved.

In some embodiments, for example, referring to FIG. 5 which shows a flowchart of an example method for determining the orthogonal signal of the beat frequency signal, as an example, the orthogonal signal of the beat frequency signal can be determined, for example, through the following steps.

In step C111, the beat frequency signal is represented by a cosine curve where the phase varies over time.

In some embodiments, the beat frequency signal can be represented by a cosine curve where the phase varies over time and for example, can be represented as where represents the noise in the beat frequency signal, and represents the instantaneous phase. Since the value of is difficult to be predicted, the instantaneous phase of the beat frequency signal can be represented by

In step C112, the cosine curve of beat frequency signal is phase shifted through a finite impulse response filter to determine a sine curve of beat frequency signal where the phase varies over time, as the orthogonal signal of the beat frequency signal.

For example, still referring to FIG. 2a, the monitoring optical signal shown in FIG. 2a includes two adjacent frequency sweep bands, for example, an up-sweep band where the frequency increases over time and a down-sweep band where the frequency decreases over time. In the existing technology, the Hilbert transform method can typically calculate the above-mentioned instantaneous phase However, the Hilbert transform method requires a complete frequency sweep band Δf to calculate the result and thus cannot satisfy the real-time requirement of the light source linearity monitoring.

In some embodiments, in response to the above drawback, the time domain beat frequency signal is phase shifted in real time through a finite impulse response filter in some embodiments of this disclosure. For example, still referring to FIG. 6 which shows a schematic diagram of the phase of the example beat frequency signal of the two monitoring optical signals and the orthogonal signal of the beat frequency signal, the solid line shown in the figure represents the phase diagram of an example original beat frequency signal, and the original time domain beat frequency signal is phase shifted by 90° through the finite impulse response filter to determine a sine curve of the beat frequency signal where the phase varies over time in real time, for example, as shown by the dashed line in the figure, as the example orthogonal signal of the beat frequency signal.

With the above embodiment, since the finite impulse response filter can phase shift the time domain beat frequency signal in real time without the need for a complete frequency sweep band, the orthogonal signal of the beat frequency signal can be determined in real time. By doing so, the real-time performance of the monitoring can be improved.

In some embodiments, for example, referring to FIG. 7 which shows a flowchart of an example method for determining the instantaneous phase of the beat frequency signal based on the orthogonal signal, as an optional example, the instantaneous phase of the beat frequency signal can be determined, for example, through the following steps.

In step C121, a tangent curve of the beat frequency signal is determined based on the cosine curve of the beat frequency signal and the sine curve of the beat frequency signal.

In step C122, an inverse tangent curve of the beat frequency signal is determined based on the tangent curve of the beat frequency signal as the instantaneous phase of the beat frequency signal.

With the above embodiment, the tangent curve of the beat frequency signal is determined based on the cosine curve of the beat frequency signal and the sine curve of the beat frequency signal, and the inverse tangent curve of the beat frequency signal is determined based on the tangent curve of the beat frequency signal as the instantaneous phase of the beat frequency signal. The influence of noise on the monitoring result can be reduced or avoided. By doing so, the accuracy of the monitoring result can be improved.

As an example, referring to FIG. 8 which shows a schematic diagram of an example periodic association between the phase of the beat frequency signal of the two monitoring optical signals and time, the sampling frequency is 80 MHz, and the phase of the beat frequency signal varies periodically within a range of [-π, +π] .

As an example, still referring to FIG. 7, the method for determining the instantaneous phase of the beat frequency signal based on the orthogonal signal shown in FIG. 7 can further include the following steps.

In step C123, a continuously varying association is generated based on a periodic association between the phase of the beat frequency signal and time.

For example, for example, still referring to FIG. 8, since the phase of the beat frequency signal varies periodically, errors or abnormalities can occur at the time when the periodic jump occurs, affecting the accuracy of the monitoring result. Therefore, the continuously varying association is generated based on a periodic association between the phase of the beat frequency signal and time. By doing so, the error or abnormality in the phase of the beat frequency signal at the time when the period jump occurs can be reduced or avoided, and the accuracy of the monitoring result can be improved.

In some embodiments, in response to determining that a jump occurs in the phase of the beat frequency signal, the phase of the beat frequency signal of a time period after the time of the jump is superimposed with a periodic phase difference of the beat frequency signal.

As an example, referring to FIG. 8 and FIG. 9 which shows a schematic diagram of the example continuously varying association between the phase of the beat frequency signal and time, in FIG. 8 where the horizontal axis represents the time and the vertical axis represents the phase, since the instantaneous phase of the beat frequency signal is represented by the inverse tangent curve, the phase of the beat frequency signal varies within a range of [-π, +π] , the periodic phase difference is 2π. When the phase jump between two consecutive time points is greater than π, the phase of the beat frequency signal of a time period after the two consecutive time points is superimposed with the periodic phase difference 2π of the beat frequency signal. The periodic association between the phase of the beat frequency signal and time the continuously varying association can be generated based on the periodic association between the phase of the beat frequency signal and time. For example, still referring to FIG. 9 where the horizontal axis represents the time and the vertical axis represents the radian rad, the error or abnormality in the phase of the beat frequency signal at the time when the periodic jump occurs can be reduced or avoided, and the accuracy of the monitoring result can be improved.

In some embodiments, the beat frequency signal can be sampled at a predetermined sampling frequency. When the optical signal transmitted by the light source is a linear frequency modulated optical signal, the variation amount of the phase of the beat frequency signal at a sampling time should be a fixed value, and the starting phase of the beat frequency signal is denoted as Accordingly, the phase of the predetermined standard beat frequency signal of the Nth sampling time is the phase of the actually sampled beat frequency signal is represented by and when the phase deviation between the two is not zero, it can be determined that the optical signal at the sampling time does not satisfy the linearity requirement.

To carry out the light source linearity monitoring more conveniently, this disclosure further provides a light source linearity monitoring system corresponding to the light source linearity monitoring method described above. For example, referring to FIG. 10 which shows a structural schematic diagram of an example light source linearity monitoring system, the light source linearity monitoring system T is coupled to a light source L and includes an interference processor module T1 and a data processor module T2.

The interference processor module T1 can split a monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals. The monitoring optical signal is a portion of an optical signal transmitted by the light source.

The data processor module T2 can determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal, and determine a linearity monitoring result based on the deviation.

With the above monitoring system T, a portion of an optical signal Ls transmitted by the light source L can be determined as a monitoring optical signal, the monitoring optical signal Ls can be guided to the interference processor module T1, the interference processor module T1 can split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal Ds by a beat frequency processing on the two delayed monitoring optical signals. The interference processor module T1 can further guide the beat frequency signal Ds into the data processor module T2, and the data processor module T2 can determine a deviation between the beat frequency signal and the predetermined standard beat frequency signal and can determine a linearity monitoring result based on the deviation. With the above monitoring system, in one aspect, the monitoring cost is reduced because the need for additional device is reduced (e.g., no additional device is required) ; in another aspect, since the monitoring is performed with a portion of the optical signal transmitted by the light source as the monitoring optical signal, the normal detection using the light source is not affected. Furthermore, the real-time performance of the monitoring can be improved or ensured, the reliability of the detection result of the LiDAR can be improved or ensured.

Some embodiments of this disclosure further provide a light source linear frequency modulation control method. For example, referring to FIG. 11 which shows a flowchart of an example light source linear frequency modulation control method, the light source linear frequency modulation control can be performed through the following steps.

In S1, a portion of a transmitted optical signal is determined as a monitoring optical signal.

In some embodiments, reference can be made to the examples of the light source linearity monitoring method described above.

In S2, the monitoring optical signal is split into two monitoring optical signals, unequal delays are applied to the two monitoring optical signals, and a beat frequency signal is determined by a beat frequency processing on the two delayed monitoring optical signals.

In S3, the transmitted optical signal is adjusted based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

In some embodiments, the drive current of the light source can be adjusted based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal so that the optical signal transmitted by the light source can be adjusted.

With the above embodiment, a portion of a transmitted optical signal is determined as a monitoring optical signal; the monitoring optical signal is split into two monitoring optical signals, unequal delays are applied to the two monitoring optical signals, and a beat frequency signal is determined by a beat frequency processing on the two delayed monitoring optical signals; and the transmitted optical signal can be adjusted based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal. With the above control method, the transmitted optical signal can be adjusted in real time to ensure that the optical signal satisfies or substantially satisfies the linearity requirement, and the control cost is reduced because the need for additional device is reduced (e.g., no additional device is required) .

For step S3 in the above embodiment, an example method of adjusting the transmitted optical signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal is described below in conjunction with an example. For example, referring to FIG. 12 which shows a flowchart of an example method for adjusting the transmitted optical signal, as an example, the transmitted optical signal can be adjusted, for example, through the following steps.

In S31, a correction signal is determined based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal.

In some embodiments, the drive signal of the light source can be corrected based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal, and the corrected drive signal is determined as the correction signal.

In S32, the correction signal is superimposed with a predetermined pre-correction signal to determine a drive signal.

In some embodiments, the pre-correction signal is used for controlling the frequency of the optical signal transmitted by the light source to be consistent with a target frequency.

In some embodiments of this disclosure, the pre-correction signal is used for enabling the light source to output a linear frequency modulated optical signal. It is to be understood that the pre-correction signal can also be used for enabling the light source to output a non-linear frequency modulated optical signal. The non-linear frequency modulated optical signal satisfies a predetermined requirement. The shape and value of the pre-correction signal are not limited in the embodiments of this disclosure.

In S33, the transmitted optical signal is adjusted based on the drive signal.

In some embodiments, the correction signal can be determined through a linear controller.

In some embodiments, if an analog drive signal is generated based on a digital drive signal through a digital-to-analog converter DAC by the light source to achieve the adjustment of the transmitted optical signal, the output of the digital-to-analog converter DAC can be corrected through a linear controller, and the correction amount can be expressed as:

where representing that the phase deviation between the phase of the predetermined standard beat frequency signal corresponding to the Nth sampling time and the phase of the actually sampled beat frequency signal. K_G represents the gain coefficient of the linear controller, and Kf represents the coefficient of the integral term.

With the above embodiment, the drive signal of the light source is corrected through the linear controller based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal. By doing so, the linearity of the optical signal transmitted by the light source can be adjusted.

To carry out the light source linear frequency modulation control more conveniently, this disclosure further provides a light source linear frequency modulation control system corresponding to the light source linear frequency modulation control method described above. For example, referring to FIG. 13 which shows a structural schematic diagram of an example light source linear frequency modulation control system. The light source linear frequency modulation control system M is coupled to a light source L. The example light source linear frequency modulation control system includes an interference processor module M1, a data processor module M2, and a feedback controller module M3.

The interference processor module M1 can split a monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals. The monitoring optical signal can be a portion of an optical signal transmitted by the light source.

The data processor module M2 can determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

The feedback controller module M3 can adjust the transmitted optical signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal to determine a linear frequency modulated optical signal.

With the above control system M, a portion of an optical signal transmitted by the light source L is determined as a monitoring optical signal LS, the monitoring optical signal Ls is guided to the interference processor module M1, the interference processor module M1 splits the monitoring optical signal Ls into two monitoring optical signals, applies unequal delays to the two monitoring optical signals, determines a beat frequency signal Ds by a beat frequency processing on the two delayed monitoring optical signals, and further guides the beat frequency signal Ds into the data processor module M2. The data processor module M2 determines a deviation Ws between the beat frequency signal and a predetermined standard beat frequency signal and guides the deviation Ws into the feedback controller module M3. The feedback controller module M3 adjusts the optical signal transmitted by the light source L based on the deviation Ws.With the above light source linear frequency modulation control system M, the optical signal transmitted by the light source can be adjusted in real time to ensure that the optical signal satisfies or substantially satisfies the linearity requirement, and the control cost is reduced because the need for additional device is reduced (e.g., no additional device is required) .

Some embodiments of this disclosure further provide an FMCW LiDAR. For example, referring to FIG. 14 which shows a structural schematic diagram of an example FMCW LiDAR, the FMCW LiDAR LA can include a light source LA1, an interference processor module LA2, and a data processor module LA3.

The light source LA1 can transmit an optical signal. A portion of the optical signal is determined as a monitoring optical signal, and a portion of the optical signal is determined as a detection optical signal.

The interference processor module LA2 can split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals.

The data processor module LA3 can determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal and determine a linearity monitoring result based on the deviation.

In some embodiments, the instantaneous phase of the beat frequency signal is determined, a deviation between the instantaneous phase of the beat frequency signal and the instantaneous phase of a predetermined standard beat frequency signal at a same sampling time is determined, and a linearity monitoring result can be determined based on the deviation. Since the real-time deviation between the beat frequency signal and the predetermined standard beat frequency signal can be determined based on the instantaneous phase of the beat frequency signal, the real-time performance of the monitoring can further be improved.

In some embodiments of this disclosure, a time domain beat frequency signal is generated based on the beat frequency signal, the time domain beat frequency signal is phase shifted in the time domain to determine an orthogonal signal of the beat frequency signal, and the instantaneous phase of the beat frequency signal is determined based on the orthogonal signal. By doing so, the influence of noise on the monitoring result can be reduced or avoided, and the accuracy of the monitoring result can be improved.

When the above FMCW LiDAR LA is started, a portion of an optical signal transmitted by the light source LA1 is determined as a monitoring optical signal and enters the interference processor module LA2. The interference processor module LA2 splits the monitoring optical signal into two monitoring optical signals, applies unequal delays to the two monitoring optical signals, determines a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals, and further guides the beat frequency signal into the data processor module LA3. The data processor module LA3 determines a deviation between the beat frequency signal and a predetermined standard beat frequency signal and can determine a linearity monitoring result based on the deviation. With the above LiDAR, in one aspect, since the LiDAR can achieve the monitoring based on the hardware system of the LiDAR itself. The need for additional device is reduced (e.g., no additional device is required) , the monitoring cost is reduced. In another aspect, since the monitoring is performed with a portion of the optical signal transmitted by the light source as the monitoring optical signal, the detection using the light source is not affected. Furthermore, the real-time performance of the monitoring can be improved or ensured, and the reliability of the detection result of the LiDAR can be improved or ensured.

Some embodiments of this disclosure further provide an FMCW LiDAR. For example, referring to FIG. 15 which shows a structural schematic diagram of another example FMCW LiDAR, the FMCW LiDAR LB can include a light source LB1, an interference processor module LB2, a data processor module LB3, and a feedback controller module LB4.

The light source LB1 can to transmit an optical signal. A portion of the optical signal is determined as a monitoring optical signal, and a portion of the optical signal is determined as a detection optical signal.

The interference processor module LB2 can split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals.

The data processor module LB3 can determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal.

In some embodiments, for the example of determining the deviation between the beat frequency signal and the predetermined standard beat frequency signal, reference can be made to the above embodiments.

The feedback controller module LB4 can adjust the optical signal transmitted by the light source based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal to determine a linear frequency modulated optical signal.

When the above FMCW LiDAR LB is started, a portion of an optical signal transmitted by the light source LB1 is determined as a monitoring optical signal and enters the interference processor module LB2. The interference processor module LB2 splits the monitoring optical signal into two monitoring optical signals, applies unequal delays to the two monitoring optical signals, determines a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals, and further guides the beat frequency signal into the data processor module LB3. The data processor module LB3 determines a deviation between the beat frequency signal and a predetermined standard beat frequency signal and guides the deviation into the feedback controller module LB4. The feedback controller module LB4 adjusts the optical signal transmitted by the light source LB1 based on the deviation. With the above LiDAR, the optical signal transmitted by the light source can be adjusted in real time to ensure that the optical signal satisfies or substantially satisfies the linearity requirement, and since the LiDAR can achieve the control based on the hardware system of the LiDAR itself. The need for additional device is reduced (e.g., no additional device is required) , the control cost is reduced.

In some embodiments, still referring to FIGS. 14 and 15, the FMCW LiDAR LA and the FMCW LiDAR LB can also include a detector. As an example, still referring to FIG. 15, the FMCW LiDAR LB can include a detector LB5.

The light source LB1 can transmit a linear frequency modulated optical signal as the detection optical signal and a portion of the linear frequency modulated optical signal is transmitted to the detector LB5 as a local oscillator light.

The detector LB5 can receive a detection echo signal determined when the detection optical signal is reflected to the LiDAR by an object.

The data processor module LB3 can further determine a distance and a speed of the object based on the local oscillator light and the detection echo signal.

With the above embodiment, when the FMCW LiDAR LB is started, a portion of the optical signal transmitted by the light source LB1 is determined as the monitoring optical signal for the linearity monitoring of the light source, and the other portion can be determined as the detection optical signal for determining the distance and the speed of the object. Since the monitoring and the detection can be performed simultaneously and do not interfere with each other, the detection signal can be adjusted in real time based on the monitoring result. By doing so, the reliability of the detection result of the LiDAR can be improved. In some embodiments, the data processor module LA3 and the data processor module LB3 can further calculate the distance and the speed of the object based on a Doppler frequency shift of the detection echo signal with respect to the local oscillator light.

In some embodiments, the interference processor module LA2 and the interference processor module LB2 can use a variety of different forms of interferometers to apply unequal delays to two monitoring optical signals, and a coupler can perform the beat frequency processing to determine the beat frequency signal.

In some embodiments, a Mach-Zehnder interferometer can apply unequal delays to the two monitoring optical signals. The light source linear frequency modulation control process in the operation process of the light source is described through an example.

For example, referring to FIG. 16 which shows a structural schematic diagram of an example FMCW LiDAR, consistent with some embodiments of this disclosure, after the FMCW LiDAR LX is started, the light emitted by a distributed feedback semiconductor laser DFB is split by a coupler LX1. A portion of the light is outputted as a detection optical signal Ld1 to calculate the distance and the speed of an object, and the other portion of the light is inputted as a monitoring optical signal Ld2 to an optical interference processor MZI to monitor the linearity of the distributed feedback semiconductor laser DFB.

For example, for example, still referring to FIG. 16, a portion Ld11 of the detection optical signal Ld1 is transmitted to the detector PD as a local oscillator light, and the other portion Ld12 is transmitted to the object. After the other portion Ld12 is reflected by the object, a detection echo signal is formed and transmitted to the detector PD. The local oscillator light and the detection echo signal are subject to Fourier transform to determine a beat frequency signal of the two. For example, referring to FIG. 17 which shows a schematic diagram of the example beat frequency signal of the local oscillator light and a detection echo signal of an FMCW LiDAR, for example, still referring to FIG. 17, the distance information of the object can be determined based on the beat frequency signal of the local oscillator light and the detection echo signal by using the following formula:
D= (fb*c*ts) / (2Δf) (2)

where fb represents the frequency of the beat frequency signal of the local oscillator light and the detection echo signal, c represents the speed of light, ts represents the period of the frequency sweep band of the detection optical signal, and Δf represents the frequency modulation bandwidth of the frequency sweep band of the detection optical signal.

Further, the time of flight of the detection optical signal can be determined based on the following formula:
td=2D/c (3)

Further, the speed information of the object can be determined based on the time of flight.

As can be seen from formula (2) , to improve or ensure the accuracy of the determined distance information, it is beneficial to improve or ensure that the frequency of the detection optical signal varies linearly over time. It is beneficial that the detection optical signal satisfies or substantially satisfies a predetermined linearity requirement to determine the accurate distance information.

Therefore, to ensure that the linearity of the detection optical signal satisfies or substantially satisfies a detection requirement, in some embodiments of this disclosure, the other portion of the optical signal transmitted by the distributed feedback semiconductor laser DFB is transmitted to the optical interference processing instrument MZI as the monitoring optical signal. The monitoring optical signal monitors the linearity of the distributed feedback semiconductor laser DFB and adjusts the detection optical signal in real time based on the monitoring result. By doing so, the reliability of the detection result of the LiDAR can be improved.

For example, the optical interference processing instrument MZI can perform the beat frequency processing on the monitoring optical signal Ld2 to determine the beat frequency signal. A beat frequency current signal can be generated based on the detected beat frequency signal by the photodetector PD. and outputted to a transimpedance amplifier TIA coupled to the photodetector PD to determine an amplified beat frequency voltage signal. An analog-to-digital converter ADC converts the beat frequency voltage signal into a beat frequency square-wave signal. A data processor module LX3 compares the inputted beat frequency square-wave signal with a predetermined standard beat frequency signal to determine a deviation between the beat frequency signal and the predetermined standard beat frequency signal. The output of a digital-to-analog converter DAC can be corrected through a linear controller based on the deviation to determine a correction signal. A predetermined pre-correction signal of the digital-to-analog converter DAC is superimposed with the correction signal to determine a drive signal as the output of the digital-to-analog converter DAC to control the drive current of the distributed feedback semiconductor laser DFB to cause the distributed feedback semiconductor laser DFB to transmit the linear frequency modulated optical signal which satisfies the predetermined requirement.

A memory can be disposed in the data processor module LX3 to store the predetermined pre-correction signal of the digital-to-analog converter DAC.

In some embodiments, an FPGA is used for the control of the LiDAR, the processing and operation of the detection data, or the like in the LiDAR. Therefore, in some embodiments, the data processor module LX3 can be disposed in an FPGA; in one aspect, the remaining computility of the FPGA can be utilized; in another aspect, the number of peripheral circuits can be reduced. By doing so, the implementation cost can be reduced.

For example, any one of an interference processor module, a data processor module, or a feedback controller module can be implemented as a processor unit, a controller, a computer or any form of hardware components. As another example, a processor unit can include one or more hardware components and one or more software components. For example, the processor unit can include a processor (e.g., a digital signal processor, microcontroller, field programmable gate array, a central processor, an application-specific integrated circuit, or the like) and a computer program, when the computer program is run on the processor, the function of the processor module can be realized, the computer program can be stored in a memory (e.g., a random access memory, a flash memory, a read-only memory, an programmable read-only memory, a register, a hard disk, a removable hard disk, or a storage medium of any other form) or server.

For example, a light source can include a light emitting circuit, vertical-cavity surface-emitting lasers ( “VCSELs” ) , edge-emitting lasers ( “EELs” ) , distributed feedback lasers ( “DFBs” ) , fiber lasers, or the like.

For example, a detector can include a light receiving circuit, photodiodes, single photon avalanche diodes ( “SPADs” ) , avalanche photodiodes ( “APDs” ) , charged-coupled device ( “CCD” ) , complementary metal-oxide-semiconductor ( “CMOS” ) sensor, or the like.

In this disclosure, the terms “a, ” “an, ” and “the” are intended to represent singular or plural forms, unless expressly stated otherwise in the context. The term “multiple” in this disclosure refers to a number of two or more. For example, multiple objects can include two objects, or more than two objects.

Although some embodiments of this disclosure are disclosed as above, this disclosure is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the scope of this disclosure, and therefore, the scope of protection of this disclosure shall be as limited by the claims.

Claims

A method of light source linearity monitoring for an FMCW LiDAR, comprising:

determining a portion of a transmitted optical signal as a monitoring optical signal;

splitting the monitoring optical signal into two monitoring optical signals, applying unequal delays to the two monitoring optical signals, and determining a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals; and

determining a linearity monitoring result based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.
The method of claim 1, wherein the determining the linearity monitoring result based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal comprises:

determining an instantaneous phase of the beat frequency signal;

determining a deviation between the instantaneous phase of the beat frequency signal and an instantaneous phase of the predetermined standard beat frequency signal at a same sampling time; and

determining the linearity monitoring result based on the deviation.
The method of claim 2, wherein the determining the instantaneous phase of the beat frequency signal comprises:

generating a time domain beat frequency signal based on the beat frequency signal, and applying a phase shift to the time domain beat frequency signal in the time domain to determine an orthogonal signal of the beat frequency signal; and

determining the instantaneous phase of the beat frequency signal based on the orthogonal signal.
The method of claim 3, wherein the generating a time domain beat frequency signal based on the beat frequency signal and applying the phase shift to the time domain beat frequency signal in the time domain to determine the orthogonal signal of the beat frequency signal comprises:

representing the beat frequency signal by a cosine curve of the beat frequency signal, having a phase varies over time; and

applying the phase shift to the cosine curve of the beat frequency signal through a finite impulse response filter to determine a sine curve of the beat frequency signal having a phase varies over time as the orthogonal signal of the beat frequency signal.
The method of claim 4, wherein the determining the instantaneous phase of the beat frequency signal based on the orthogonal signal comprises:

determining a tangent curve of the beat frequency signal based on the cosine curve of the beat frequency signal and the sine curve of the beat frequency signal; and

determining, based on the tangent curve of the beat frequency signal, an inverse tangent curve of the beat frequency signal, as the instantaneous phase of the beat frequency signal.
The method of claim 5, wherein the determining, based on the tangent curve of the beat frequency signal, the inverse tangent curve of the beat frequency signal as the instantaneous phase of the beat frequency signal further comprises:

generating a continuously varying association based on a periodic association between a phase of the beat frequency signal and time.
The method of claim 6, wherein the generating a continuously varying association based on a periodic association between a phase of the beat frequency signal and time comprises:

when determining that a jump occurs in the phase of the beat frequency signal, superimposing a phase of the beat frequency signal of a time period after a time of the jump with a periodic phase difference of the beat frequency signal.
A method of light source linear frequency modulation control, comprising:

determining a portion of a transmitted optical signal as a monitoring optical signal;

splitting the monitoring optical signal into two monitoring optical signals, applying unequal delays to the two monitoring optical signals, and determining a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals; and

adjusting the transmitted optical signal based on a deviation between the beat frequency signal and a predetermined standard beat frequency signal.
The method of claim 8, wherein the adjusting the transmitted optical signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal comprises:

determining a correction signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal;

superimposing the correction signal with a predetermined pre-correction signal to determine a drive signal; and

adjusting the transmitted optical signal based on the drive signal.
The method of claim 9, wherein the determining the correction signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal comprises:

determining the correction signal through a linear controller.
A system of light source linearity monitoring coupled to a light source, comprising:

an interference processor module configured to split a monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals, wherein the monitoring optical signal is a portion of an optical signal transmitted by the light source; and

a data processor module configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal and determine a linearity monitoring result based on the deviation.
A system of light source linear frequency modulation control coupled to a light source, comprising:

an interference processor module configured to split a monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals, and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals, wherein the monitoring optical signal is a portion of an optical signal transmitted by the light source; and

a data processor module configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal; and

a feedback controller module configured to adjust the transmitted optical signal based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal to determine a linear frequency modulated optical signal.
An FMCW LiDAR, comprising a light source, an interference processor module, and a data processor module;

wherein the light source is configured to transmit an optical signal, wherein a portion of the optical signal is determined as a monitoring optical signal, and a portion of the optical signal is determined as a detection optical signal;

the interference processor module is configured to split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals;

the data processor module is configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal and determine a linearity monitoring result based on the deviation.
The LiDAR of claim 13, further comprising a detector;

wherein the light source is configured to transmit a linear frequency modulated optical signal as the detection optical signal, and a portion of the linear frequency modulated optical signal is transmitted to the detector, as a local oscillator light;

the detector is configured to receive a detection echo signal determined when the detection optical signal is reflected to the LiDAR by an object; and

the data processor module is further configured to determine a distance and a speed of the object based on the local oscillator light and the detection echo signal.
The LiDAR of claim 14, wherein the data processor module is further configured to determine the distance and the speed of the object based on a Doppler frequency shift of the detection echo signal with respect to the local oscillator light.
The LiDAR of any of claims 13 to 15, wherein the interference processor module comprises a fiber interferometer with unequal arms.
The LiDAR of any of claims 13 to 16, wherein the determining the deviation between the beat frequency signal and the predetermined standard beat frequency signal comprises:

determining an instantaneous phase of the beat frequency signal; and

determining a deviation between the instantaneous phase of the beat frequency signal and an instantaneous phase of the predetermined standard beat frequency signal at a same sampling time.
The LiDAR of claim 17, wherein the determining the instantaneous phase of the beat frequency signal comprises:

generating a time domain beat frequency signal based on the beat frequency signal, and applying a phase shift to the time domain beat frequency signal in the time domain to determine an orthogonal signal of the beat frequency signal; and

determining the instantaneous phase of the beat frequency signal based on the orthogonal signal.
An FMCW LiDAR, comprising a light source, an interference processor module, a data processor module, and a feedback controller module;

wherein the light source is configured to transmit an optical signal, wherein a portion of the optical signal is determined as a monitoring optical signal, and a portion of the optical signal is determined as a detection optical signal;

the interference processor module is configured to split the monitoring optical signal into two monitoring optical signals, apply unequal delays to the two monitoring optical signals and determine a beat frequency signal by a beat frequency processing on the two delayed monitoring optical signals;

the data processor module is configured to determine a deviation between the beat frequency signal and a predetermined standard beat frequency signal; and

the feedback controller module is configured to adjust the optical signal transmitted by the light source based on the deviation between the beat frequency signal and the predetermined standard beat frequency signal to determine a linear frequency modulated optical signal.
The LiDAR of claim 19, further comprising a detector;

wherein the light source is configured to transmit the linear frequency modulated optical signal as the detection optical signal, and a portion of the linear frequency modulated optical signal is transmitted to the detector, as a local oscillator light;

the detector is configured to receive a detection echo signal determined when the detection optical signal is reflected to the LiDAR by an object; and

the data processor module is further configured to determine a distance and a speed of the object based on the local oscillator light and the detection echo signal.
The LiDAR of claim 20, wherein the data processor module is further configured to calculate the distance and the speed of the object based on a Doppler frequency shift of the detection echo signal with respect to the local oscillator light.
The LiDAR of any of claims 19 to 21, wherein the interference processor module comprises a fiber interferometer with unequal arms.
The LiDAR of any of claims 19 to 22, wherein the determining the deviation between the beat frequency signal and the predetermined standard beat frequency signal comprises:

determining an instantaneous phase of the beat frequency signal; and

determining a deviation between the instantaneous phase of the beat frequency signal and an instantaneous phase of the predetermined standard beat frequency signal at a same sampling time.
The LiDAR of claim 23, wherein the determining the instantaneous phase of the beat frequency signal comprises:

generating a time domain beat frequency signal based on the beat frequency signal, and applying phase shift to the time domain beat frequency signal in the time domain to determine an orthogonal signal of the beat frequency signal; and

determining the instantaneous phase of the beat frequency signal based on the orthogonal signal.