CN113594859A

CN113594859A - Injection locking correction method and device

Info

Publication number: CN113594859A
Application number: CN202010441649.2A
Authority: CN
Inventors: 潘政清; 向少卿; 孙恺
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2020-04-30
Filing date: 2020-05-22
Publication date: 2021-11-02
Anticipated expiration: 2040-05-22
Also published as: CN113594859B

Abstract

An injection locking correction method and apparatus thereof, the method comprising: changing the magnitude of the injection current of the slave laser, and controlling the injection locking state of the slave laser to be continuously changed between an out-of-lock state and a locking state; performing delay coupling and beat frequency processing on the laser signal output from the laser to obtain a beat frequency signal; determining a corresponding injection current range when the slave laser is in a locked state based on the beat frequency signal, and taking a central value of the injection current range as a correction current value; and adjusting the magnitude of the injection current of the slave laser to the correction current value. By adopting the scheme, the stability of injection locking can be improved, and the slave laser is in a locked state for a long time.

Description

Injection locking correction method and device

The present application claims priority of chinese patent application entitled "injection locking correction method and apparatus thereof" filed in china patent office at 30/04/2020, application number 202010368451.6, which is incorporated herein by reference in its entirety.

Technical Field

The embodiment of the specification relates to the field of photoelectric technology, in particular to an injection locking correction method and device.

Background

A LIDAR (Light Detection And Range, LIDAR or Laser Detection And Range, LADAR) is an active Detection device, which is provided with a Light source, And can obtain parameter data of a target by transmitting a Detection signal to the target And performing data processing on an echo signal reflected back from the target.

Frequency Modulated Continuous Wave (FMCW) laser radars generally require a high-coherence, high-power Frequency Modulated laser source. However, the output power of a conventional tunable narrow linewidth laser is weak, and the power requirement of the laser radar cannot be met. If the amplification is forced by an optical amplifier, the signal-to-noise ratio of the light source is reduced. And by adopting the injection locking technology, the low-noise amplification characteristic can be obtained, and the method has strong side mode inhibition capability and good application prospect.

However, the locking range of injection locking is only several GHz, and strict wavelength alignment of the master and slave lasers is usually required, and due to the influence of factors such as temperature drift or laser internal stress release, wavelength mismatch of the master and slave lasers can cause lock loss, and at this time, manual adjustment can be usually performed, so that the slave laser enters the locked state again.

Disclosure of Invention

In view of this, embodiments of the present disclosure provide an injection locking correction method and apparatus thereof, which can improve stability of injection locking and enable a slave laser to be in a locked state for a long time.

The embodiment of the specification provides an injection locking correction method, which is applied to a light source, wherein the light source comprises a master laser and a slave laser, the master laser is suitable for injection locking the slave laser, and the injection locking correction method comprises the following steps:

A1) changing the magnitude of the injection current of the slave laser, and controlling the injection locking state of the slave laser to be continuously changed between an out-of-lock state and a locking state;

A2) performing delay coupling and beat frequency processing on the laser signal output from the laser to obtain a beat frequency signal;

A3) determining a corresponding injection current range when the slave laser is in a locked state based on the beat frequency signal, and taking a central value of the injection current range as a correction current value;

A4) and adjusting the magnitude of the injection current of the slave laser to the correction current value.

Optionally, the step a1) includes the following steps:

A11) and continuously changing the magnitude of the injection current based on a preset current change interval, returning the magnitude of the injection current to the initial injection current value after the magnitude of the injection current reaches end point current values at two ends of the current change interval in sequence, controlling the slave laser to change between an out-of-lock state and a lock state, and finally returning to the initial lock state.

Optionally, the step a11) includes the following steps:

A111) and continuously changing the magnitude of the injection current along a specified direction based on the current change interval until reaching an endpoint current value at one end of the current change interval, reversely and continuously changing the magnitude of the injection current until reaching an endpoint current value at the other end of the current change interval, reversely and continuously changing the magnitude of the injection current to return to the initial injection current value, controlling the secondary laser to sequentially enter a primary lock losing state, a secondary lock losing state and a secondary lock losing state from the initial locking state, and finally returning to the initial locking state.

Optionally, the step a3) includes the following steps:

A31) performing analog-to-digital conversion processing on the beat frequency signal to obtain a time domain diagram of the beat frequency signal;

A32) performing short-time Fourier transform on the time domain graph of the beat frequency signal to obtain a spectrogram sequence of the beat frequency signal;

A33) and determining a secondary locking state region based on the spectrogram sequence of the beat signal, and acquiring an injection current value corresponding to the central position of the secondary locking state region as a correction current value.

Optionally, the step a33) includes the following steps:

A331) determining a secondary locking state region and time information of the central position of the secondary locking state region based on the spectrogram sequence of the beat signal, and acquiring an injection current value corresponding to the time information;

A332) calculating the offset between the initial injection current value of the slave laser and the injection current value corresponding to the central position of the locking state area, and determining an injection current adjustment value between the initial injection current value and the correction current value;

the step A34) comprises the following steps:

A341) and adjusting the magnitude of the injection current of the slave laser to the correction current value based on the injection current adjustment value.

Optionally, the step a332) includes the following steps:

a3321) And comparing the offset with a preset current adjustment threshold, and if the offset is greater than the current adjustment threshold, taking the offset as the injection current adjustment value.

Optionally, the step a2) includes the following steps:

A21) dividing the laser signal output from the laser into two paths, and performing delay processing on the laser signal of one path;

A22) and coupling the laser signals divided into two paths and then carrying out beat frequency processing to obtain the beat frequency signals.

The present specification also provides an injection locking correction device, connected to a light source, the light source including a master laser and a slave laser, the master laser being adapted to injection lock the slave laser through an injection locking device, the injection locking device outputting an injection current to the slave laser so that the slave laser is in a locked state, the injection locking correction device including:

the injection current control module is used for responding to a trigger signal, controlling the injection locking device to change the magnitude of the output injection current so as to control the injection locking state of the slave laser to be continuously changed between an unlocking state and a locking state, and outputting a corresponding current adjusting signal to the injection locking device according to a determined correction current value so that the magnitude of the injection current output by the injection locking device is adjusted to the correction current value;

and the signal processing module is suitable for performing delay coupling and beat frequency processing on the laser signal output by the slave laser to obtain a beat frequency signal, determining a corresponding injection current range when the slave laser is in a locked state according to the beat frequency signal, and taking a central value of the injection current range as a correction current value.

Optionally, the injection current control module is adapted to control the injection locking device to continuously change the magnitude of the injection current along the designated direction according to a preset current change interval, and reversely and continuously change the magnitude of the injection current until reaching an end point current value at one end of the current change interval, and reversely and continuously change the magnitude of the injection current until reaching an end point current value at the other end of the current change interval, so as to control the slave laser to sequentially enter a primary lock losing state, a secondary lock losing state and a secondary lock losing state from the initial lock state, and finally return to the initial lock state.

Optionally, the signal processing module further includes:

the beat frequency processing unit is suitable for carrying out delay coupling and beat frequency processing on the laser signal output from the laser to obtain a beat frequency signal;

the analog-to-digital conversion unit is suitable for performing analog-to-digital conversion processing on the beat frequency signal to obtain a time domain diagram of the beat frequency signal;

a frequency domain conversion unit for converting the frequency domain signal,

the time domain graph of the beat frequency signal is subjected to short-time Fourier transform to obtain a spectrogram sequence of the beat frequency signal;

and the correction current acquisition unit is suitable for determining a secondary locking state area according to the spectrogram sequence of the beat signal and acquiring an injection current value corresponding to the central position of the secondary locking state area as a correction current value.

Optionally, the correction current obtaining unit includes:

the injection current value acquisition subunit is suitable for determining a secondary locking state region and time information of the central position of the secondary locking state region according to the spectrogram sequence of the beat signal, and acquiring an injection current value corresponding to the time information;

an offset amount operator unit adapted to calculate an offset amount between the injection current value initially from the laser and an injection current value corresponding to a center position of the lock-up state region;

the injection current control module is suitable for transmitting a current adjusting signal containing the injection current adjusting value to the injection locking device.

Optionally, the adjustment value obtaining subunit is further adapted to compare the offset with a preset current adjustment threshold, and if the offset is greater than the current adjustment threshold, take the offset as the injection current adjustment value.

Optionally, the beat processing unit includes: a first optical coupler, a second optical coupler and a photodetection subunit, wherein:

the first optical coupler is suitable for receiving the laser signals output by the laser and transmitting the laser signals to the second optical coupler through a transmission line and a delay line respectively;

the second optical coupler is suitable for respectively receiving the laser signals transmitted by the transmission line and the laser signals transmitted by the delay line, and coupling and transmitting the two paths of laser signals to the photoelectric detection subunit;

the photoelectric detection subunit is adapted to perform beat frequency processing on the coupled laser signal transmitted by the second optical coupler to obtain the beat frequency signal.

By adopting the injection locking correction scheme of the embodiment of the specification, the injection current range corresponding to the locking state area of the slave laser can be determined by acquiring the laser signal output by the slave laser when the slave laser changes between the out-of-lock state and the locking state and performing delay coupling and beat frequency processing, the central value of the injection current range is used as the correction current value, and the injection current of the slave laser is adjusted. In other words, according to the scheme of the embodiment of the present specification, the injection current of the slave laser can be feedback-controlled according to the laser signal output from the laser, so that the injection current value of the slave laser is automatically corrected, the problem of the slave laser losing lock caused by release of the environmental temperature and stress is avoided, the stability of injection locking is improved, and the slave laser is in a locked state for a long time.

Further, the magnitude of the injection current is continuously changed according to a preset current change interval, so that the magnitude of the injection current returns to an initial injection current value after reaching end point current values at two ends of the current change interval in sequence, the slave laser is controlled to change between an out-of-lock state and a lock state, and finally returns to the initial lock state. The injection current change process of the injection current is continuously changed, so that the slave laser can be ensured to enter an out-of-lock state when the injection current becomes smaller and the injection current becomes larger, and more accurate correction current value can be obtained subsequently.

Further, in the change process of the injection current, according to the current change interval, the magnitude of the injection current is continuously changed along a specified direction, after the end point current value at one end of the current change interval is reached, the magnitude of the injection current is continuously changed in a reverse direction, and after the end point current value at the other end of the current change interval is reached, the magnitude of the injection current is continuously changed in a reverse direction to return to the initial injection current value, so that the secondary laser can be controlled to sequentially enter a primary lock losing state, a secondary lock losing state and a secondary lock losing state from the initial lock state, and finally return to the initial lock state. Therefore, whether the time range of the secondary locking state is positioned in the middle of the whole correction period or not can be accurately judged, namely whether the time ranges respectively corresponding to the primary unlocking state and the secondary unlocking state are symmetrical left and right relative to the time range of the secondary locking state or not can be accurately judged, and therefore the optimal injection current can be accurately determined.

Further, whether the injection current value needs to be adjusted or not can be determined by comparing the offset with a preset current adjustment threshold, and the injection current value is adjusted when the offset is larger than the preset current adjustment threshold, so that the adjustment times of the injection current can be reduced under the condition that the slave laser is ensured to be in a locked state for a long time.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present specification, the drawings needed to be used in the embodiments of the present specification or in the description of the prior art will be briefly described below, it is obvious that the drawings described below are only some embodiments of the present specification, and it is also possible for a person skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a flow chart of a method for injection locking correction in an embodiment of the present disclosure;

FIG. 2 is a flow chart of a method for obtaining a corrected current value in an embodiment of the present disclosure;

FIG. 3a is a time domain diagram of a beat signal when the slave laser is in a locked state in an embodiment of the present disclosure;

FIG. 3b is a spectrum diagram corresponding to FIG. 3a in an embodiment of the present disclosure;

FIG. 4a is a time domain diagram of a beat signal when the slave laser is in an out-of-lock state in an embodiment of the present disclosure;

FIG. 4b is a spectrum diagram corresponding to FIG. 4b in an embodiment of the present disclosure;

FIG. 5 is a graph illustrating the amplitude of a beat signal versus the frequency of the center of the slave laser over time in an embodiment of the present disclosure;

FIG. 6 is a schematic structural diagram of a lidar in an embodiment of the present disclosure;

FIG. 7 is a schematic diagram of an injection locking correction apparatus according to an embodiment of the present disclosure;

FIG. 8 is a schematic structural diagram of a beat frequency processing unit in an embodiment of the present disclosure;

FIG. 9 is a schematic diagram of an injection locking circuit according to an embodiment of the present disclosure;

fig. 10 is a schematic view of an application scenario of an injection locking correction apparatus in an embodiment of the present disclosure.

Detailed Description

As mentioned above, the lidar is an active detection device, and is provided with a light source, and the lidar can obtain parameter data of a target by transmitting a detection signal to the target and performing data processing according to an echo signal reflected by the target.

In order to enable the tunable narrow linewidth laser to output a high-power laser signal, an injection locking technique may be employed. Specifically, a master Laser which is required to be a Seed Laser (Seed Laser) and a slave Laser which emits a high-power Laser signal are required to realize injection locking, the master Laser emits an injection Laser signal to the slave Laser through an injection locking device, the slave Laser can establish stable oscillation at the frequency of the injection Laser signal under a certain condition, the free running mode of the slave Laser is suppressed, and the slave Laser enters a locking state so as to run along with the frequency of the master Laser.

The injection locking system can be regarded as a narrow-bandwidth amplifying system, the amplifying bandwidth is extremely narrow, and the width can be several GHz near the wavelength of a laser signal output by the free running laser, so that a certain-order sideband can be selectively amplified, a carrier wave and other sidebands are suppressed, and single-frequency laser is obtained.

Although the injection locking technology can be adopted to enable the slave laser to output a high-power single-mode narrow-linewidth laser signal, the master laser and the slave laser lose lock due to the influence of factors such as temperature drift or internal stress release of the laser, and at the moment, only manual adjustment can be carried out to enable the slave laser to enter a locking state again.

In view of the above problem, embodiments of the present disclosure provide an injection locking correction scheme, where a laser signal output when the slave laser changes between an out-of-lock state and a lock state is obtained, and delayed coupling and beat frequency processing are performed, so as to determine an injection current range corresponding to the slave laser in the lock state, and adjust the injection current of the slave laser by using a central value of the injection current range, thereby automatically correcting the injection current value of the slave laser, improving stability of injection locking, and enabling the slave laser to be in the lock state for a long time.

For the purpose of enabling those skilled in the art to more clearly understand and practice the concepts, implementations and advantages of the embodiments of the present disclosure, detailed descriptions are provided below through specific application scenarios with reference to the accompanying drawings.

Referring to a flow chart of an injection locking correction method in an embodiment of the present specification shown in fig. 1, in the embodiment of the present specification, the injection locking correction method may be applied to a light source including a master laser and a slave laser, the master laser being adapted to injection lock the slave laser, the injection locking correction method including the steps of:

A1) and changing the magnitude of the injection current of the slave laser, and controlling the injection locking state of the slave laser to be continuously changed between the out-of-lock state and the locking state.

Wherein, according to the injection locking result of the slave laser, the injection locking state of the slave laser may include: a locked state and an unlocked state.

The master laser is a linear frequency modulation laser, the slave laser is injected and locked at the same time, and once the injection and locking are successful, the slave laser outputs linear frequency modulation light with the same frequency as the master laser.

In a specific implementation, the current input to the slave laser is referred to as the injection current.

The magnitude of the injection current for bringing the slave laser into the lock state is made different depending on the type of the slave laser, and the slave laser allows the injection current to vary in the lock state within a certain interval, and adjusting the magnitude of the injection current up and down within the current interval allowed in the lock state does not change the lock state of the slave laser, but only the oscillation amplitude (amplitude) of the laser signal output from the slave laser changes with the variation of the injection current.

Therefore, when the value of the injection current falls within the current interval allowed by the locking state, the slave laser can enter or maintain the locking state, and the frequency and the wavelength of the laser signal output by the slave laser are controlled by the master laser.

When the injection current of the slave laser is changed and exceeds the current interval allowed by the locking state, the slave laser enters the unlocking state, and the frequency and the wavelength of a laser signal output by the slave laser are determined by the free running mode of the slave laser and are not controlled by the master laser.

A2) And performing delay coupling and beat frequency processing on the laser signal output from the laser to obtain a beat frequency signal.

In a specific implementation, the laser signal output from the laser is delayed, and then coupled with an undelayed laser signal, so as to obtain a coupled laser signal with periodically changing amplitude, and the coupled laser signal is subjected to beat frequency processing, so as to obtain a beat frequency signal. The beat frequency processing may adopt any beat frequency detection method to process the coupled laser signal.

In the locked state, the slave laser outputs linearly modulated light having the same frequency as that of the master laser, and in the unlocked state (i.e., out-of-lock state), the slave laser is in a free-running state and outputs laser light having its own free-running frequency, and at this time, no beat signal or a beat signal is extremely weak.

A3) And determining the corresponding injection current range when the slave laser is in a locking state based on the beat frequency signal, and taking the central value of the injection current range as a correction current value.

In a specific implementation, as the injection current changes, the slave laser changes between a locked state and an unlocked state, and the oscillation amplitude of the laser signal output by the slave laser also changes. The spectrogram can be obtained by performing Fast Fourier Transform (FFT) on the beat signal to obtain the corresponding amplitude at the desired frequency. Since the beat frequency signal is obtained by processing the laser signal output from the laser, it is possible to determine whether the slave laser is in an injection locking state or not by the amplitude of the beat frequency signal. When the slave laser is in the locked state, the beat signal amplitude is maximum. And through the time corresponding relation, after a time period corresponding to the maximum amplitude of the beat frequency signal is determined, acquiring an injection current range of the time period, wherein an injection current value positioned in the middle of the current range is an optimal injection current value of the laser, and acquiring the optimal injection current value as a correction current value.

In a specific implementation, after the magnitude of the injection current is adjusted to the correction current value, the slave laser can keep a locking state.

By adopting the scheme, the injection current of the slave laser can be subjected to feedback control according to the laser signal output by the slave laser, so that the injection current value of the slave laser is automatically corrected, the problem of unlocking of the slave laser caused by environmental temperature and stress release is avoided, the stability of injection locking is improved, and the slave laser is in a locked state for a long time.

In practical applications, the master laser may be a semiconductor laser, a fiber laser or a solid-state laser, and the slave laser may be a semiconductor laser, a fiber laser or a solid-state laser. The master laser may injection lock the slave laser by any injection locking method.

In a specific implementation, in order to ensure that the injection locking state of the slave laser can be changed between the out-locking state and the locking state by changing the injection current, a current change interval can be preset, and the magnitude of the injection current can be changed according to the current change interval.

The end point current values of the two ends of the current change interval are larger than the end point current values of the two ends of the current interval allowed by the locked state of the slave laser, so that when the injection current value is adjusted to be part of current values in the preset current change interval, the slave laser can be controlled to enter the unlocked state from the locked state, and when the injection current value is adjusted to be other part of current values in the preset current change interval, the slave laser can be controlled to enter the locked state from the unlocked state.

For example, the preset current variation interval may be [ x ]₁，x₂]The current interval allowed from the laser lock-up state may be [ x ]₃，x₄]Wherein x is₁Less than x₃And x is₂Greater than x₄. When the slave laser is in a locked state, and the injection current value is adjusted to [ x ]₁，x₃)∪(x₄，x₂]When the current value is any one, the slave laser can be controlled to enter an unlocking state from a locking state; when the slave laser is in an out-of-lock state, and the injection current value is adjusted to be x₃，x₄]At any current value, the slave laser can be controlled to enter a locking state from an unlocking state.

In a specific implementation, the master laser may perform injection locking on the slave laser, the slave laser is in a locked state, in order to distinguish between a locked state before the injection current is not changed and a locked state after the injection current is changed, the locked state before the injection current is not changed may be regarded as an initial locked state, and the magnitude of the injection current in the initial locked state may be regarded as an initial injection current value.

In practical application, in order to facilitate changing the magnitude of the injection current, an initial injection current value may be used as an initial value, an additional current for adjusting the magnitude of the injection current is superimposed on the initial injection current value, and the magnitude of the additional current is set according to the initial injection current value and a preset current variation interval. For example, if the initial injection current value is 5ma and the preset current variation interval is [2.5, 7.5] ma, an additional current with a magnitude of 2.5 ma may be superimposed.

It can be understood that, according to an actual situation, the additional current may be a current signal with an arbitrary waveform, and the amplitude of the additional current may be adjusted according to a preset current variation interval, which is not limited in this embodiment of the present specification.

In a specific implementation, since the correction current value may be smaller than the initial injection current value and may also be larger than the initial injection current value, in order to ensure that the laser can enter the locked state when the injection current becomes small and large, the step a1) may include the following steps:

According to the scheme, the injection current change process of continuously changing the injection current can ensure that the slave laser can enter an out-of-lock state when the injection current becomes smaller and the injection current becomes larger, and is favorable for obtaining more accurate correction current values subsequently.

In a specific implementation, the injection locking correction efficiency is influenced by the change efficiency of the injection locking state of the slave laser, and in order to improve the change efficiency of the injection locking state of the slave laser, the step a11) may include the following steps:

Wherein, the designated direction may be a direction in which the current becomes larger or a direction in which the current becomes smaller. For example, if the initial injection current value is 5ma and the preset current change interval is [2.5, 7.5] ma, the injection current may be continuously increased until the injection current value becomes 7.5 ma, the injection current may be continuously decreased in the reverse direction until the injection current becomes 2.5 ma, and then the injection current may be increased in the reverse direction until the injection current value returns to 5 ma.

Therefore, whether the time range of the secondary locking state is positioned in the middle of the whole correction period or not can be accurately judged, namely whether the time ranges respectively corresponding to the primary unlocking state and the secondary unlocking state are bilaterally symmetrical relative to the time range of the secondary locking state or not can be accurately judged, and therefore the optimal injection current can be accurately determined.

In specific implementation, through the time correspondence relationship, when the slave laser continuously changes in the out-of-lock state and the lock state, a time period corresponding to the maximum amplitude of the beat signal is determined, and the injection current value of the time period is obtained. In order to determine the injection current value more quickly, Short-Time Fourier Transform (or Short-Term Fourier Transform, STFT) is performed on the beat signal according to the correspondence between the injection current and the beat signal, so that the correction current value can be determined by obtaining the injection current range corresponding to the maximum amplitude of the beat signal.

Specifically, as shown in fig. 2, the step a3) may specifically include the following steps:

A31) and performing analog-to-digital conversion processing on the beat frequency signal to obtain a time domain diagram of the beat frequency signal.

Any Analog-to-Digital Converter (ADC) module may be adopted to perform Analog-to-Digital conversion processing on the beat signal.

A32) And carrying out short-time Fourier transform on the time domain graph of the beat frequency signal to obtain a spectrogram sequence of the beat frequency signal.

In specific implementation, since the injection locking state of the slave laser continuously changes between the unlocking state and the locking state, the amplitude of the beat frequency signal in the locking state is higher than that in the unlocking state, the amplitude of the beat frequency signal under the specified frequency is obtained according to short-time Fourier transform to obtain an amplitude sequence, and the amplitude sequence is arranged into a curve to obtain a spectrogram sequence of the beat frequency signal.

In specific implementation, because the amplitude is high in the locked state and low in the unlocked state, the secondary locked state region and the center position of the secondary locked state region can be determined according to the shape of a curve formed by the amplitude sequence, and therefore the injection current value corresponding to the center position serves as the correction current value.

By adopting the scheme, the acquisition efficiency of the correction current value can be improved by acquiring the injection current range corresponding to the maximum amplitude of the beat frequency signal.

In practical applications, when the slave laser is in a locked state, as shown in fig. 3a, it is a time domain diagram of a beat signal when the slave laser is in the locked state, and the beat signal p (t) obtained from the laser signal output from the slave laser in the locked state has a stable frequency and waveform in the time domain. And performing fast Fourier transform on the beat frequency signal in the graph in FIG. 3a to obtain a spectrogram as in FIG. 3b, wherein the beat frequency signal p (omega) after the fast Fourier transform has a highest single peak in a frequency domain, and side modes are suppressed, and a frequency value corresponding to the highest single peak is an output frequency value when locking is injected.

When the injection current deviates from the current interval allowed by the locked state, the slave laser is in the unlocked state, as shown in fig. 4a, it is a time domain diagram of the beat signal when the slave laser is in the unlocked state, and the beat signal p (t) obtained from the laser signal output from the slave laser in the unlocked state is spread in spectrum, energy is dispersed, and quality is deteriorated. The beat frequency signal in fig. 4a is subjected to fast fourier transform to obtain a spectrogram as in fig. 4b, and the waveform of the beat frequency signal p (ω) subjected to fast fourier transform in the frequency domain is disordered, and the peak value corresponding to the highest single peak is reduced, even without obvious peak frequency.

Therefore, the injection locking state of the slave laser can be reflected more intuitively through the spectrogram of the beat frequency signal, and the corresponding current value range when the slave laser is in the locking state can be determined through the corresponding relation between the spectrogram and the time domain diagram, so that the current interval allowed by the locking state can be obtained.

In particular implementations, the correction is obtained for better understanding by those skilled in the artThe flow process, as shown in FIG. 5, is a beat signal amplitude E_p(t) and the slave laser center frequency F_I(t) graph plot over time t. Wherein the solid line part represents the amplitude E of the beat signal_p(t) the waveform that changes with time t, whose amplitude may be any Unit (a.u.), may specifically perform short-time fourier transform on the beat frequency time domain diagram, obtain the amplitude of the beat frequency signal at a specified frequency, obtain an amplitude sequence, arrange the amplitude sequence into a curve, and obtain a spectrogram sequence of the beat frequency signal. The hatched part indicates the free-running frequency F of the slave laser_I(t) a time-varying waveform, which may be in gigahertz (GHz). The unit of the time axis t may be microseconds (μ s).

As shown in fig. 5, an additional current is superimposed at 150 microseconds, the frequency of the injected current is changed, so that the magnitude of the injected current can be changed, the magnitude of the additional current can be selected from 5-20 milliamperes (mA), the amplitude of the additional current is assumed to be 15mA, the laser is in an initial locked state, as the injected current becomes larger, the free running frequency of the laser becomes larger, the locked state is changed to an unlocked state at a mark a, and the unlocked state enters a primary unlocked state; the injected current changes to the maximum value and then starts to decrease in the reverse direction, and the slave laser is still in an out-of-lock state at the moment; as the injection current becomes smaller, the free running frequency of the slave laser becomes smaller, the slave laser changes from an unlocking state to a locking state at a mark B and enters a secondary locking state; the frequency of the injected current is continuously reduced, the slave laser is changed from the locking state to the unlocking state again at the mark C, and the secondary unlocking state is entered; after the injection current changes to the minimum value, the reverse direction starts to increase, the free running frequency of the laser becomes high, the state is changed to the locking state again from the unlocking state at the mark D until the injection current value is changed to the initial injection current value, and the laser returns to the initial locking state.

In the process of the change of the injection current, the frequency is shifted by 15GHz from the central wavelength of the laser, the frequency change time of the injection current is 80 mus, and 4 dot frequency periods are consumed. According to the amplitude of the beat signal, the injection locking state of the laser can be reflected, so that a secondary locking state area B → C is obtained, a corresponding injection current range can be obtained according to the secondary locking state area B → C, and the central position of the secondary locking state area B → C corresponds to the central value of the injection current range, so that the obtained injection current value corresponding to the central position of the secondary locking state area is the central value of the injection current range.

In a specific implementation, the step a33) may include the following steps:

A331) and determining a secondary locking state region and time information of the central position of the secondary locking state region based on the spectrogram sequence of the beat signal, and acquiring an injection current value corresponding to the time information.

As shown in FIG. 5, from the spectrogram sequence of the beat signal, the time information of the center position of the secondary lock state region B → C, denoted as t, can be obtained₁Time of day, thereby by determining t₁The magnitude of the injection current at the moment can be obtained as t₁The injection current value at that time is used as a correction current value.

A332) Calculating the offset between the initial injection current value of the slave laser and the injection current value corresponding to the central position of the locking state area, and determining the injection current adjustment value between the initial injection current value and the correction current value.

Accordingly, according to the injection current adjustment value obtained in the above steps, the step a34) may include the steps of:

When the injection current adjusting value is a negative value, the injection current of the slave laser is reduced to the correction current value; and when the injection current adjusting value is a positive value, increasing the injection current of the slave laser to the correction current value.

In the specific implementation, frequent adjustment of the injection current is not beneficial to the operation of the laser radar, and under the condition that the slave laser is ensured to be in a locked state for a long time, in order to reduce the adjustment times of the injection current, a current adjustment threshold value is preset, and whether the injection current is adjusted or not is determined through the current adjustment threshold value.

In an embodiment of the present specification, the step a332) may include the following steps:

a3321) And adjusting the magnitude of the injection current of the slave laser to the correction current value based on the injection current adjustment value.

By adopting the above scheme, when the offset is greater than the current adjustment threshold, it is determined that the offset of the injection current reaches the current adjustment condition, the offset can be used as the injection current adjustment value to adjust the injection current, and when the offset is not greater than the current adjustment threshold, it is determined that the offset of the injection current does not reach the current adjustment condition, the injection current adjustment value is zero, and the injection current does not need to be adjusted.

In a specific implementation, in order to ensure that the delayed laser signal and the undelayed laser signal have the same frequency and wavelength, the laser signal output from the laser may be branched and then subjected to a delay coupling process, and specifically, the step a2) may include the following steps:

A21) and dividing the laser signal output from the laser into two paths, and performing delay processing on the laser signal of one path.

The delay line may be used to delay one of the laser signals.

For example, the laser signal output from the laser is divided into two paths, one of the two paths is transmitted by using a transmission line to obtain an undelayed laser signal, and the other path can be transmitted by using a 10m delay line to obtain a delayed laser signal. It should be understood that the foregoing embodiments are merely examples, and delay lines with other lengths may be adopted according to practical application scenarios, and the embodiments of the present specification are not limited thereto.

By adopting the scheme, the structure is simple, the delay processing of the laser signal is convenient to realize, and the delayed laser signal and the undelayed laser signal are both from the slave laser, so that the delayed laser signal and the undelayed laser signal can be ensured to have the same frequency and wavelength, the beat frequency processing is convenient to perform subsequently, and the beat frequency signal is obtained.

In specific implementation, a correction trigger condition may be preset according to an actual use environment, and after the correction trigger condition is met, any one of the injection locking correction methods is automatically executed to adjust an injection current of a slave laser in the laser radar, so as to ensure that the slave laser can be kept in a locked state for a long time.

For example, the correction trigger condition may be: and judging whether a correction period is met, if so, meeting the correction trigger condition, and automatically executing any injection locking correction method. The correction period may be set to any time length such as 1 second and 1 minute.

For another example, the correction triggering condition may be: and if the task of outputting the point cloud picture is finished once, the correction triggering condition is met, and any injection locking correction method is automatically executed.

It is to be understood that the injection locking correction method of the present specification can be applied to any type of laser radar using an injection locking function. For example, the injection locking correction method of the present specification may be applied to a frequency modulated continuous wave lidar. Also, the injection locking correction method of the present description may be applied to one or more slave lasers. The present description does not limit the type of lidar and the number of slave lasers.

In other words, in the whole process from the lock-out state (primary lock-out state) to the lock-in state (secondary lock-out state) to the lock-out state (secondary lock-out state), whether the slave laser is locked or not and the current range corresponding to the central lock-in state region (i.e., the region corresponding to the secondary lock-in state) can be reflected by monitoring the beat signal intensity (black solid line in fig. 5) output by the photodetector such as the reference interferometer, and the injection current is stabilized as much as possible within a certain range in the central lock-in state region, and then the injection current is adjusted to the current value corresponding to the center of the lock-in state region after the primary modulation is completed, i.e., the primary closed-loop feedback control is completed. Since the additional current for detecting injection locking is a triangular wave current with central symmetry, if it is detected that the locking state region is also left-right symmetric, i.e. the highest peak of the locking state is located at the center and the left and right unlocking state regions are symmetric, it means that the injection current given originally is more appropriate, and even if slightly shifted later, the laser is least easily unlocked because the injection current is in the relatively safest range.

To facilitate understanding and implementation by those skilled in the art, the entire injection locking correction process will be described with continued reference to fig. 5 and then fig. 10, assuming that the laser or the entire light source is already operating in a locked state, where the injection current of the DFB-LD (slave laser) is a relatively constant current, and the optical frequency (or wavelength) of the DFB-LD (slave laser) is determined by the first-order sideband frequency F1 of the seed light (i.e., the injection current signal) output by the master laser after EOM. When the correction is carried out, the magnitude of the injection current of the DFB-LD (from the laser) is actively changed by using a centrosymmetric triangular wave additional current, namely the free-running frequency F2 (or the wavelength) of the DFB-LD is changed, when the F2 and the F1 are different to a certain degree (about several GHz, which is called locking bandwidth), the DFB-LD (from the laser) is unlocked, and the frequency of the light output by the DFB-LD (from the laser) is the free-running laser frequency F2 and the first-order sideband frequency F1 of the unmodulated light. With the change of the triangular wave additional current, the F2 of the DFB-LD (slave laser) is changed, when the difference between the F2 and the F1 is smaller than the locking bandwidth again, the laser enters the locking state again, and the output frequency of the DFB-LD (slave laser) is changed to F1.

The seed light output by the master laser is converted into linear frequency modulation light after passing through the EOM, when the DFB-LD (slave laser) is locked, the interferometer (namely a photoelectric detector) can detect linear frequency modulation signals, when the linear frequency modulation light is input into the interferometer, the interferometer outputs standard sinusoidal signals, and the PSD (power spectral density) at the beat frequency in the frequency spectrum is very high. When the DFB-LD (slave laser) is unlocked, the output frequencies F2 and F2 of the DFB-LD (slave laser) are controlled by triangular wave additional current, the linearity is poor, and the frequency change speed is completely different from F1, so that the original standard sinusoidal signal cannot be detected by the interferometer. The PSD drops at the original beat frequency in the spectrum. The success or failure of injection locking can be known through the size of the PSD.

As shown in fig. 5, since the triangular wave additional current is vertically symmetrical, if the time range of the central lock state region B → C is detected to be located at the center in the entire correction period region a → D, that is, the peak of the secondary lock state is located at the center, and the left and right unlock state regions a → B and C → D are relatively symmetrical, it means that the originally given injection current is relatively most suitable, that is, the originally given constant current is the optimal injection current value in the middle of the current range corresponding to the lock state region B → C, otherwise, the magnitude of the injection current is adjusted to the optimal injection current value in the middle of the current range corresponding to the lock state region B → C, and thus, the slave laser is in a state in which it is relatively least easy to unlock. It should be noted that the peak mentioned above does not refer to a specific value, but a relative range of values. For example, the maximum value is 1, and the peak value may be a range value of (1 ± 0.01).

Embodiments of the present invention further provide a device corresponding to the injection locking correction method, so that those skilled in the art can better understand and implement the embodiments of the present invention, which will be described in detail below with reference to the accompanying drawings.

Referring to a schematic structural diagram of a lidar in an embodiment of the present invention shown in fig. 6, in this embodiment, the lidar 60 may include a light source 61, an injection locking device 62, and an injection locking correction device 63.

Wherein the light source may comprise a master laser 611 and a slave laser 612, the master laser 611 being adapted to injection lock the slave laser 612 by means of an injection locking device 62. The injection locking correction device 63 is connected to the light source 61 and the injection locking device 62, respectively.

As shown in fig. 7, a schematic structural diagram of an injection locking correction apparatus in an embodiment of the present invention, the injection locking correction apparatus 63 may include:

an injection current control module 631 adapted to control the injection locking device 62 to change the magnitude of the output injection current in response to a trigger signal so as to control the injection locking state of the slave laser 612 to continuously change between an out-of-lock state and a locked state, and to output a corresponding current adjustment signal to the injection locking device 62 according to the determined correction current value so that the magnitude of the injection current output by the injection locking device 62 is adjusted to the correction current value;

the signal processing module 632 is adapted to perform delay coupling and beat frequency processing on the laser signal output by the slave laser 612 to obtain a beat frequency signal, determine a corresponding injection current range when the slave laser 612 is in a locked state according to the beat frequency signal, and use a central value of the injection current range as a correction current value.

Wherein the injection current control module 631 determines the injection mode by sending a control signal to the injection locking device 62, the injection locking device 62 can be controlled to change the magnitude of the output injection current according to any one of the injection current change modes, for example, the injection current control module 61 is adapted to control the injection locking device 62 to continuously change the magnitude of the injection current along a specified direction according to a preset current variation interval until reaching an endpoint current value at one end of the current variation interval, continuously changing the magnitude of the injection current in a reverse direction until reaching the end point current value at the other end of the current change interval, continuously changing the magnitude of the injection current in the reverse direction until returning to the initial injection current value, so as to control the slave laser 612 to enter the primary out-of-lock state, the secondary out-of-lock state and the secondary out-of-lock state in sequence from the initial lock state, and finally return to the initial lock state. Reference may be made to the related embodiments of the injection locking correction method, and details are not repeated herein.

According to the scheme, the injection current of the slave laser can be subjected to feedback control according to the laser signal output by the slave laser, so that the injection current value of the slave laser is automatically corrected, the problem that the slave laser is unlocked due to release of environmental temperature and stress is avoided, the stability of injection locking is improved, and the slave laser is in a locked state for a long time.

In specific implementation, through the time correspondence relationship, when the slave laser continuously changes in the out-of-lock state and the lock state, a time period corresponding to the maximum amplitude of the beat signal is determined, and the injection current value of the time period is obtained. In order to determine the injection current value more quickly, short-time Fourier transform is performed on the beat frequency signal according to the corresponding relation between the injection current and the beat frequency signal, so that the correction current value can be determined by obtaining the injection current range corresponding to the maximum amplitude of the beat frequency signal.

Specifically, with continued reference to fig. 7, the signal processing module 632 may include:

a beat frequency processing unit 6321, adapted to perform delay coupling and beat frequency processing on the laser signal output from the laser to obtain a beat frequency signal;

an analog-to-digital conversion unit 6322, adapted to perform analog-to-digital conversion on the beat frequency signal to obtain a time domain diagram of the beat frequency signal;

a frequency domain converting unit 6323, adapted to perform short-time fourier transform on the time domain diagram of the beat signal to obtain a spectrogram sequence of the beat signal;

the correction current obtaining unit 6324 is adapted to determine a secondary lock state region according to the spectrogram sequence of the beat signal, and obtain an injection current value corresponding to a center position of the secondary lock state region as a correction current value.

In a specific implementation, as shown in fig. 7, the correction current obtaining unit 6324 may include: an injection current value obtaining subunit 63241, configured to determine a secondary lock state region and time information of a center position of the secondary lock state region according to the spectrogram sequence of the beat signal, and obtain an injection current value corresponding to the time information;

an offset amount calculation subunit 63242 adapted to calculate an offset amount between the initial injection current value from the laser and the corresponding injection current value of the lock-up state region center position;

an adjustment value obtaining sub-unit 63243 adapted to determine an injection current adjustment value between the initial injection current value and the correction current value according to the offset;

the injection current control module 631 is adapted to transmit a current adjustment signal containing the injection current adjustment value to the injection locking device 63.

In a specific implementation, in order to reduce the number of adjustment times of the injection current, the adjustment value obtaining subunit 63243 is further adapted to compare the offset with a preset current adjustment threshold, and if the offset is greater than the current adjustment threshold, take the offset as the injection current adjustment value.

In a specific implementation, in order to ensure that the delayed laser signal and the undelayed laser signal have the same frequency and wavelength, as shown in fig. 8, the beat frequency processing unit 6321 may include: a first optocoupler 63211, a second optocoupler 63212, and a photodetector subunit 63213, wherein:

the first optical coupler 63211 is suitable for receiving the laser signals output by the lasers and respectively transmitting the laser signals to the second optical coupler through a transmission line and a delay line;

the second optical coupler 63212 is adapted to receive the laser signal transmitted through the transmission line and the laser signal transmitted through the delay line, respectively, couple and transmit two paths of laser signals to the photodetection subunit;

the photodetection subunit 63213 is adapted to perform beat frequency processing on the coupled laser signal transmitted by the second optical coupler to obtain the beat frequency signal.

The photodetector unit 63213 may be any kind of photodetector, for example, a Photo-Detector (PD).

In practical application, the injection locking device can adopt any injection locking circuit.

For example, as shown in fig. 9, a connection diagram of an injection locking circuit is shown. Which may include: an Electro-optical Modulator (EOM) 02, a circulator 07, a Voltage-Controlled Oscillator (VCO) 04, a power amplifier 03, an Arrayed Waveguide Grating (AWG) 05, and a Current Source (CS) 06.

The arrayed waveguide grating 05 outputs a voltage signal to the voltage-controlled oscillator 04, the voltage-controlled oscillator 04 oscillates and outputs a voltage signal of a corresponding waveform to the power amplifier 03, the amplified voltage signal is input to the electro-optical modulator 02, and the arrayed waveguide grating 05 outputs a current signal to the current source 06, so that the current source 06 constantly outputs an injection current of a corresponding magnitude to the slave laser 08.

The main laser 01 outputs an injection laser signal having a step length of λ₀After being modulated by the electro-optical modulator 02, the step length of the injection laser signal output by the electro-optical modulator 02 after being modulated is λ₁And the first order sideband frequency is f₁The modulated injection laser signal is input to the slave laser 08 via the circulator 07. The laser signal output from the laser 08 is output through the circulator 07.

The frequency of the laser signal output from the laser 08 in the free-running mode is f₂. When f is₂And f₁When the phase difference reaches a certain level (about several GHz, referred to as lock bandwidth), the lock is lost from the laser 08, and the frequency of the laser signal output from the laser 08 is f₂Not modulating the frequency f of the injected laser signal₁. Followed byWith variation of the injected current, f₂Also changes when f₂And f₁When the difference is again smaller than the lock bandwidth, the laser 08 enters the lock state, and the frequency of the laser signal output from the laser 08 becomes f₁And the amplitude of the waveform becomes large.

Fig. 10 is a schematic view of an application scenario of the injection locking correction apparatus in an embodiment of the present disclosure, and a detailed description of a correction process performed by the injection locking correction apparatus is provided below by using specific embodiments in conjunction with fig. 6 to 9.

In an embodiment of the present specification, the master laser 01 can injection-lock the slave laser 08 by forming an injection locking circuit by the electro-optical modulator 02, the circulator 07, the voltage-controlled oscillator 04, the power amplifier 03, the arrayed waveguide grating 05, and the current source 06. In the working process of the laser radar, a laser signal output from the laser 08 is transmitted to the radar detection circuit 11 through the circulator 07 and the third optical coupler 09, and is emitted as a detection signal, and data processing is performed according to an echo signal. Among them, the waveform for radar detection output from the laser 08 may be a triangular wave, a sawtooth wave, or the like.

The injection locking correction apparatus 10 may include: an injection current control module 101 and a signal processing module 102; the signal processing module 102 may include: a beat processing unit 1021, an analog-to-digital conversion unit 1022, a frequency domain conversion unit 1023, and a correction current acquisition unit 1024; the beat processing unit 1021 may include: a first optical coupler 10211, a second optical coupler 10212, and a photodetector subunit 10213.

When the injection current control module 101 responds to a trigger signal, a control signal is sent to the arrayed waveguide grating 05, the arrayed waveguide grating 05 is controlled to change the output current signal, so that the magnitude of the injection current output by the current source 06 is changed, and the injection locking state of the slave laser 08 is continuously changed between the out-of-lock state and the locking state. At this point the injection locking correction process is entered.

The laser signal emitted from the laser 08 is transmitted to the first optical coupler 10211 through the third optical coupler 09. The first optical coupler 10211 receives the laser signal output from the laser 08 and transmits the laser signal to the second optical coupler 10212 through a transmission line and a delay line, respectively. The second optical coupler 10212 receives the laser signal transmitted through the transmission line and the laser signal transmitted through the delay line, respectively, and couples and transmits two laser signals to the photodetection subunit 10213. The photodetection subunit 10213 performs beat frequency processing on the coupled laser signal transmitted by the second optical coupler 10212 to obtain the beat frequency signal.

The analog-to-digital conversion unit 1022 performs analog-to-digital conversion on the beat frequency signal to obtain a time domain diagram of the beat frequency signal. The frequency domain conversion unit 1023 performs short-time fourier transform on the time domain graph of the beat frequency signal to obtain a spectrogram sequence of the beat frequency signal. The correction current obtaining unit 1024 takes the central value of the current range as the correction current value from the current range corresponding to the laser 08 in the locked state range according to the spectrogram sequence of the beat signal.

The injection current control module 101 outputs a corresponding current adjustment signal to the arrayed waveguide grating 05 according to the correction current value, so that the arrayed waveguide grating 05 outputs a corresponding current signal, and the magnitude of the injection current output by the current source 06 is adjusted to the correction current value.

It is to be understood that the above embodiments are only examples, and in practical cases, the injection locking correction apparatus may be applied in other scenarios, and the present specification does not limit this.

Furthermore, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or imply that the number of technical features being indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of the feature. Moreover, the terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the specification described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein.

Although the embodiments of the present specification are disclosed above, the embodiments of the present specification are not limited thereto. Various changes and modifications may be effected by one skilled in the art without departing from the spirit and scope of the embodiments herein described, and it is intended that the scope of the embodiments herein described be limited only by the scope of the appended claims.

Claims

1. An injection locking correction method applied to a light source, wherein the light source comprises a master laser and a slave laser, the master laser is suitable for injection locking the slave laser, and the injection locking correction method comprises the following steps:

2. The injection locking correction method as claimed in claim 1, wherein said step a1) comprises the steps of:

3. The injection locking correction method as claimed in claim 2, wherein the step a11) comprises the steps of:

4. The injection locking correction method as claimed in claim 3, wherein the step A3) comprises the steps of:

5. The injection locking correction method as claimed in claim 4, wherein the step A33) comprises the steps of:

the step A34) comprises the following steps:

6. The injection locking correction method as claimed in claim 5, wherein the step A332) comprises the steps of:

7. Injection locking correction method according to any of claims 1-6, characterized in that said step A2) comprises the steps of:

8. An injection locking correction device connected with a light source, wherein the light source comprises a master laser and a slave laser, the master laser is adapted to injection lock the slave laser through an injection locking device, the injection locking device outputs an injection current to the slave laser so that the slave laser is in a locked state, the injection locking correction device comprises:

9. The injection locking correction device of claim 8, wherein the injection current control module is adapted to control the injection locking device to continuously change the magnitude of the injection current along a predetermined direction according to a preset current variation interval until reaching an end point current value at one end of the current variation interval, reversely and continuously change the magnitude of the injection current until reaching an end point current value at the other end of the current variation interval, and reversely and continuously change the magnitude of the injection current to return to an initial injection current value, so as to control the slave laser to sequentially enter a primary out-of-lock state, a secondary out-of-lock state, and a secondary out-of-lock state from the initial lock state, and finally return to the initial lock state.

10. The injection lock correction device of claim 9, wherein the signal processing module further comprises:

the frequency domain conversion unit is suitable for performing short-time Fourier transform on the time domain graph of the beat frequency signal to obtain a spectrogram sequence of the beat frequency signal;

11. The injection locking correction device according to claim 10, wherein the correction current obtaining unit includes:

an adjustment value obtaining subunit, adapted to determine, according to the offset, an injection current adjustment value between the initial injection current value and the correction current value;

12. The injection locking correction device of claim 11, wherein the adjustment value obtaining subunit is further adapted to compare the offset with a preset current adjustment threshold, and if the offset is greater than the current adjustment threshold, the offset is used as the injection current adjustment value.

13. An injection lock correction device as claimed in any one of claims 10 to 11, characterized in that the beat processing unit comprises: a first optical coupler, a second optical coupler and a photodetection subunit, wherein: