Array VCSEL self-mixing interference depth measurement method and system based on double sinusoidal current modulation

Abstract

The invention discloses an array VCSEL (Vertical Cavity Surface Emitting Laser) self-mixing interference depth measurement method and system based on double sinusoidal current modulation, and the system comprises an optical part, an analog circuit processing part and a digital domain signal processing part, the analog circuit processing part comprises an array probe laser driving module and a weak signal amplification module, and the digital domain signal processing part comprises a data acquisition card and a software processing module of an upper computer. According to the laser self-mixing interference principle, the needed self-mixing signal is more conveniently obtained by detecting the junction voltage at the two ends of each laser in the laser array, the phase of the self-mixing interference signal is accurately analyzed by combining a high-frequency and low-frequency superposed double-sine current modulation method with an orthogonal demodulation technology, the measurement precision is improved, and the measurement accuracy is improved. Parallel acquisition of surface depth information of different positions can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of laser sensing technology and relates to a self-mixing interference depth measurement technology, and in particular to an array-type VCSEL self-mixing interference depth measurement method and system based on dual-sinusoidal current modulation. Background Art

[0002] Laser self-mixing interference effect is a feedback effect of laser. After the light output by the laser is reflected or scattered by an external object, part of the light is fed back to the laser resonant cavity. The feedback light carries the information of the external object and mixes with the light in the laser cavity, affecting the parameter characteristics of the laser itself and modulating the output power and frequency of the laser. Since the laser self-mixing interference technology has the advantages of simple and compact structure, no need for reference optical path, and the ability to identify the direction of motion, it has been successfully applied to the measurement of physical quantities such as micro-displacement, vibration, distance, laser line width, refractive index, and rotation speed. Among different types of lasers, vertical-cavity surface-emitting lasers (VCSELs) have their unique advantages: wide modulation bandwidth, extremely high photoelectric conversion efficiency, and vertical substrate emission, etc., and can be arranged into linear and planar laser arrays over a large area and with high density. Combining the VCSEL array with the self-mixing interference effect can form an array self-mixing interferometer measurement system that is both a light source and a receiving source. Whether it is multi-parameter measurement or imaging of multiple targets, it can be carried out without the need for additional collimation devices and sensors. It has important research value and application significance for the realization of miniaturized and integrated array laser self-mixing interferometer sensors.

[0003] Laser ranging is mainly used in aerospace, industry, public security and other fields that require long-distance and high-precision measurements. Depth measurement is mainly used to obtain depth information of irregular surface objects at close range. It is currently widely used in face recognition, intelligent driving and 3D reconstruction. There are three typical optical ranging methods: time difference ranging, multi-wavelength interferometry and current modulation. The outstanding advantages of the first two methods are large measurement range and high accuracy, but the performance requirements of the laser are very high, and even high-precision calibration tools are required. Although the current modulation method does not have an absolute advantage in terms of measurement accuracy and measurement range, its application to VCSEL will help further leverage the advantages of low cost and easy integration of the interferometric measurement system, and is particularly suitable for the development of various precision measurement technologies based on laser arrays. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, a method and system for self-mixing interference depth measurement of an arrayed VCSEL based on dual sinusoidal current modulation is provided. The principle of laser self-mixing interference is utilized to more conveniently obtain the required self-mixing signal by detecting the junction voltage across each laser in the laser array. The phase of the self-mixing interference signal is accurately analyzed by combining a dual sinusoidal current modulation method with high and low frequency superposition and orthogonal demodulation technology, thereby improving the measurement accuracy and realizing the parallel acquisition of surface depth information at different positions.

[0005] Technical solution: To achieve the above-mentioned purpose, the present invention provides an array-type VCSEL self-mixing interference depth measurement system based on dual-sinusoidal current modulation, including an optical part, an analog circuit processing part, and a digital domain signal processing part. The optical part is composed of a self-made linear array laser probe and a target to be measured, the analog circuit processing part includes an array probe laser driving module and a weak signal amplification module, and the digital domain signal processing part includes a data acquisition card and a software processing module of a host computer;

[0006] The self-made linear array laser probe is used to emit a light beam to the target to be measured and receive part of the returned light beam, thereby generating a self-mixing interference effect;

[0007] The array probe laser driving module is used to control the bias current of each channel of the laser probe and inject a double sine modulation signal into the probe laser at the same time;

[0008] The weak signal amplification module is used to remove the DC part of the modulated self-mixing interference signal and filter and amplify the useful signal;

[0009] The data acquisition card is used to collect the self-mixed interference signal and send it to the host computer;

[0010] The software processing module is used for phase demodulation to obtain measurement data.

[0011] Furthermore, the weak signal amplification module includes a high-pass filter, an instrumentation amplifier and a low-pass filter.

[0012] Furthermore, the self-made linear array laser probe is a 1×4 linear array VCSEL laser probe. The 1×4 linear array VCSEL laser probe controls the bias voltage of each channel through four laser drive circuit modules, and injects a double-sine modulated current signal with the same parameters into the laser, so that the modulated laser of each channel is emitted to the steps of the corresponding level, and scattered back to the laser cavity through the step surface to generate a self-mixing interference effect.

[0013] Furthermore, the modulation end of the array probe laser driving module adopts a two-stage cascade mode, and the front-stage input bandwidth is 1kHz-150MHz, and the modulation signal with an amplitude within 1V is input to the driving module through the coupling capacitor, and a dual-sine modulation signal is injected into the laser based on the DC bias current.

[0014] The present invention also provides a measurement method of an array-type VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation, comprising the following steps:

[0015] S1: Provide bias current to the VCSEL laser of each channel in the self-made linear array laser probe through the array probe laser driver module;

[0016] S2: injecting a double-sine modulation signal into the VCSEL laser through the array probe laser driver module to tune the output light wavelength of the VCSEL laser;

[0017] S3: The tuned outgoing light is directed toward the target to be measured, and the VCSEL laser receives part of the return beam, resulting in a self-mixing interference effect;

[0018] S4: Based on the consistency of the change of the junction voltage and the self-mixing interference signal, the self-mixing interference signal is picked up by extracting the terminal voltage of the PN junction on the VCSEL;

[0019] S5: amplifying and filtering the self-mixing interference signal through the weak signal amplification module;

[0020] S6: collect the processed self-mixing interference signal through the data acquisition card and send it to the host computer;

[0021] S7: Phase demodulate the self-mixing interference signal through the software processing module to obtain measurement data.

[0022] Furthermore, the bias current in step S1 is determined by measuring the variation of the wavelength of the VCSEL laser with the current, determining the linear working area in which the wavelength depends on the injected current, and setting the static working point of the laser to the midpoint of the linear area, i.e., the optimal bias current, to ensure continuous tuning of the laser output wavelength.

[0023] Furthermore, the dual-sine modulation signal in step S2 is generated by using direct digital frequency synthesis technology to generate the dual-sine modulation signal through software control.

[0024] Furthermore, the self-mixing interference signal generated in step S4 is led out through the positive and negative electrodes of the laser, and the self-mixing interference signal V LD The expression is:

[0025]

[0026] Where m is the modulation coefficient, L is the distance between the target object and the laser light output position, λ is the laser wavelength, V 0 is the voltage across the laser PN junction without feedback light;

[0027] When the laser is modulated by injecting current using a double sine modulation signal with high and low frequencies superimposed, the injected current will cause the laser wavelength to change, and the instantaneous wavelength change of the output is:

[0028] λ(t)=λ 0 +Δλ(t)=λ 0 +g·I L sin(ω L t+θ)+g·I H sin(ω H t+θ) (2)

[0029] In the formula, I L is the low frequency current modulation amplitude, ω L is the low frequency modulation angular frequency, I H is the high frequency current modulation amplitude, ω H is the high-frequency modulation angular frequency, g is the proportional coefficient of the wavelength changing with the current, and its specific value is determined by the laser itself;

[0030] In the presence of optical feedback, the change in wavelength leads to the effective output of laser self-mixing interference. Substituting equation (2) into equation (1), considering that the amplitude of the modulation signal is very small Δλ(t)<<λ 0 , in the case of first-order approximation, formula (1) can be rewritten as:

[0031]

[0032] Among them, T L is the modulation depth of the low-frequency sinusoidal current, which is T H Phase modulation depth achieved for high frequency sinusoidal currents

[0033] Furthermore, the phase demodulation process in step S7 includes:

[0034] (1) performing Fourier transform on the modulated self-mixing signal;

[0035] (2) Using a rectangular window function, the first harmonic of the high-frequency current modulation signal (center frequency f H ) and the second harmonic (center frequency 2f H), perform inverse Fourier transform on the filtered first harmonic and second harmonic respectively, and obtain the sine function and cosine function corresponding to the channel phase change after removing the carrier;

[0036] (3) Use the inverse tangent operation to calculate the phase change curve over time, unwrap the phase, and obtain the phase fluctuation amplitude T from the phase time domain diagram L , phase amplitude T L The relationship between the external cavity length L is expressed as Where g is the modulation coefficient of the laser wavelength depending on the injected current, I L is the amplitude of the low-frequency modulated sinusoidal current, λ 0 It is the laser wavelength in the absence of light feedback, thereby accurately obtaining the absolute distance and realizing depth measurement. Finally, the measured depths of the corresponding four layers of steps are displayed in real time on the interface.

[0037] Furthermore, in step (2), By expanding equation (2) into Bessel function, we can obtain:

[0038]

[0039] In the formula, J n (T H ) is the value of the n-order Bessel function; from the above formula, it can be seen that the modulated self-mixing signal contains two parts, DC and AC, and its AC component can be expanded into the form of n-th harmonic. Further analysis shows that the amplitude expressions of the first harmonic and the second harmonic modulated by the phase sine and cosine functions respectively are:

[0040]

[0041]

[0042] Dividing the two equations, we can get the phase

[0043]

[0044] The present invention adopts dual sinusoidal injection current modulation and VCSEL junction voltage detection technology, combined with orthogonal phase demodulation technology based on fast Fourier transform to realize the measurement function. The overall system structure is simple and the research and development cost is greatly reduced.

[0045] In the present invention, the high- and low-frequency superimposed dual-sinusoidal signals can be flexibly generated by the host computer software, and are widely applicable. The waveform generated by the software is read by an oscilloscope to verify the consistency of the waveform. The interference signal is modulated by using two superimposed sinusoidal currents of high frequency and low frequency. The high-frequency sinusoidal signal has the effect of phase modulation, and the superimposed dual-sinusoidal signal as a whole plays the role of tuning the wavelength.

[0046] The present invention combines the semiconductor laser rate equation theory with the structural characteristics and working characteristics of VCSEL lasers, and establishes a theoretical model of self-mixing interference effect based on junction voltage detection. When the self-mixing interference effect occurs, feedback light is injected into the VCSEL to re-establish a steady state, causing the voltage at the laser tube end to change. The fringe signal obtained by junction voltage detection has excellent signal-to-noise ratio and fringe resolution, and signal acquisition can be achieved without an external photodetector.

[0047] The software program used in the present invention is a graphical program development environment that can make programming clearer and simpler. Therefore, an acquisition program, an FFT phase demodulation program, and a 4-channel depth calculation program are developed for this measurement system based on the graphical programming software.

[0048] The present invention designs a 1×4 VCSEL laser array and proposes a self-mixing interference distance measurement system based on dual-sinusoidal current modulation. Signal acquisition is achieved by replacing the external photodetector with the voltage across the laser junction. The array probe is both a light source and a receiver, and also a narrowband filter. No additional detector is required, thereby simplifying the device. The dual-sinusoidal current modulation and demodulation technology is used to reconstruct the phase of the interference signal and realize multi-channel synchronous depth measurement.

[0049] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0050] (1) By using junction voltage detection and a homemade 1×4 linear array VCSEL laser source, an interferometric measurement structure is realized without the need for additional sensors and photoelectric detection devices. The VCSEL laser simultaneously plays the role of light source, interferometer, detector, and narrowband filter. By expanding it into a one-dimensional linear array arrangement, the multi-dimensional detection capability of the laser self-mixing interferometer is increased; the structure of the entire system is greatly simplified, which is conducive to high-density and large-scale system integration, and can realize integrated, miniaturized, and portable measurement equipment.

[0051] (2) An array VCSEL laser self-mixing interferometer depth measurement technology based on dual sinusoidal current modulation was proposed, a portable and easily expandable measurement system was developed, and a software processing program for real-time acquisition, high-speed phase demodulation processing, and synchronous display of distance measurement results was designed, realizing real-time synchronous measurement of multi-channel step depth information and improving measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a flow chart of the array VCSEL self-mixing interferometry depth measurement system based on dual sinusoidal current modulation provided by the present invention;

[0053] Figure 2This is a schematic diagram of absolute distance measurement using dual sinusoidal current modulation;

[0054] Figure 3 It is a flow chart of self-mixed signal demodulation. DETAILED DESCRIPTION

[0055] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0056] like Figure 1 As shown, the present invention provides an array-type VCSEL self-mixing interference depth measurement system based on dual-sinusoidal current modulation, comprising an optical part, an analog circuit processing part, and a digital domain signal processing part. The optical part is composed of a self-made linear array laser probe and a target to be measured, the analog circuit processing part comprises an array probe laser driving module and a weak signal amplification module, and the digital domain signal processing part comprises a data acquisition card and a software processing module of a host computer; the self-made linear array laser probe is used to send a light beam to the target to be measured, and the receiving part returns the light beam, so that a self-mixing interference effect occurs; the array probe laser driving module is used to control the bias current of each channel of the laser probe, and at the same time inject a dual-sinusoidal modulation signal into the probe laser; the weak signal amplification module comprises a high-pass filter, an instrument amplifier and a low-pass filter, which are used to remove the DC part of the modulated self-mixing interference signal and filter and amplify the useful signal; the data acquisition card is used to collect the self-mixing interference signal and send it to the host computer; the software processing module is used for phase demodulation to obtain measurement data.

[0057] VCSEL has advantages that traditional edge-emitting lasers do not have, such as lower threshold current, small beam divergence angle, circular spot, single longitudinal mode operation, and easy on-chip integration. In this embodiment, the array laser probe uses 4 VCSEL laser modules of the same batch, with a typical threshold current of about 1.3mA, an output power of 4mW, a working center wavelength of 850nm, and a beam divergence angle of about 7mrad. The laser module comes with a collimating lens with a focal length of 3.6mm to constrain laser divergence and achieve beam collimation. The single VCSEL module is arranged into a 1×4 linear array with a center spacing of 8mm by fixing the mold. The target adopts 8 steps with a total height of 40mm (20mm×8mm×5mm per layer), which can be fixed on an electric translation stage. The laser array is stabilized by a laser driver to emit a laser beam with uniform lateral distribution and stable frequency. The 1×4 linear array VCSEL laser probe controls the bias voltage of each channel through four laser drive circuit modules. At the same time, it injects a double-sine modulated current signal with the same parameters into the laser, so that the modulated laser of each channel is emitted to the steps of the corresponding layer, and scattered back to the laser cavity through the step surface to produce a self-mixing interference effect.

[0058] The modulation end of the array probe laser driver module adopts a two-stage cascade method. The front-stage input bandwidth is 1kHz-150MHz, and the modulation signal with an amplitude within 1V is input to the driver module through a coupling capacitor. A dual-sine modulation signal is injected into the laser based on the DC bias current.

[0059] The laser driving circuit independently controls the bias current of each channel VCSEL. The output beams of each channel converge to different positions of the external target object. Part of the scattered light returns along the original optical path and is coupled into the resonant cavity to produce a self-mixing interference effect. Each laser unit in the array laser can be addressed independently, and the self-mixing interference signal is extracted through the junction voltage. Direct digital frequency synthesis technology is used to generate a double-sine modulation wave through software control and input it to the laser driving circuit to provide double-sine current modulation for each channel to tune the wavelength of the VCSEL output light. When the self-mixing interference effect occurs, the carrier concentration on the PN junction of the VCSEL laser changes due to the injection of feedback light, and the junction voltage is consistent with the change of the self-mixing interference signal. Therefore, the interference signal can be picked up by extracting the terminal voltage of the PN junction on the VCSEL.

[0060] In this embodiment, the above-mentioned array VCSEL self-mixing interference depth measurement system based on double sinusoidal current modulation is used to Figure 1 The scattering target in the image is used to measure the 4-layer corresponding step depth. The specific measurement method is as follows:

[0061] S1: Provide bias current to the VCSEL laser of each channel in the self-made linear array laser probe through the array laser driving module; measure the variation of the wavelength of the VCSEL laser with the current, and determine the linear working area where the wavelength depends on the injected current. To ensure continuous tuning of the laser output wavelength, the static working point of the laser can be set to the midpoint of the linear area, that is, the optimal bias current.

[0062] S2: injecting a double-sine modulation signal into the VCSEL laser through the array probe laser driver module to tune the output light wavelength of the VCSEL laser;

[0063] The dual-sine modulation signal is generated by using direct digital frequency synthesis technology and software control to generate the dual-sine modulation signal.

[0064] S3: The tuned outgoing light is directed toward the target to be measured, and the VCSEL laser receives part of the return beam, resulting in a self-mixing interference effect;

[0065] S4: Based on the consistency of the change of the junction voltage and the self-mixing interference signal, the self-mixing interference signal is picked up by extracting the terminal voltage of the PN junction on the VCSEL;

[0066] In the array laser self-mixing interference system, the driving circuit module provides the appropriate bias current to each channel of the VCSEL laser to make it work normally, and the output laser is incident on the stationary target object at a distance L from the laser. Under weak light feedback conditions, the multiple feedback of the external cavity can be ignored. At this time, the gain change in the cavity is approximately linear and uniform. The junction voltage detection method can be used to detect the laser output optical power. The generated self-mixing interference signal is led out through the positive and negative electrodes of the laser. The self-mixing interference signal V LD The expression is:

[0067]

[0068] Where m is the modulation coefficient, L is the distance between the target object and the laser light output position, λ is the laser wavelength, V 0 is the voltage across the laser PN junction without feedback light;

[0069] Reference Figure 2 When the laser is modulated by injecting current using a double sine modulation signal with high and low frequencies superimposed, the injected current will cause the laser wavelength to change, and the instantaneous wavelength change of the output is:

[0070] λ(t)=λ 0 +Δλ(t)=λ 0 +g·I L sin(ω L t+θ)+g·I H sin(ωH t+θ) (2)

[0071] In the formula, I L is the low frequency current modulation amplitude, ω L is the low frequency modulation angular frequency, I H is the high frequency current modulation amplitude, ω H is the high-frequency modulation angular frequency, and g is the proportional coefficient of the wavelength changing with the current. Its specific value is determined by the laser itself. When the current flows through the laser tube, the thermal effect generated will change the refractive index of the laser. When the refractive index changes, the working wavelength of the laser will also change accordingly. When the current change is relatively small, g has nothing to do with the current. It depends on the specific parameters of the laser and can be determined through experiments.

[0072] In the presence of optical feedback, the change in wavelength leads to the effective output of laser self-mixing interference. Substituting equation (2) into equation (1), considering that the amplitude of the modulation signal is very small Δλ(t)<<λ 0 , in the case of first-order approximation, formula (1) can be rewritten as:

[0073]

[0074] Among them, T L is the modulation depth of the low-frequency sinusoidal current, which is T H Phase modulation depth achieved for high frequency sinusoidal currents

[0075] S5: amplifying and filtering the self-mixing interference signal through the weak signal amplification module;

[0076] The detected junction voltage signal is input to the input of the high-pass filter, and the output of the high-pass filter is output to the input of the instrument amplifier through an AC coupling signal. The instrument amplifier outputs the amplified signal to the low-pass filter, and after filtering out the DC component and low and high-frequency noise in the signal, the 4-way signal output by the filter amplifier circuit is simultaneously output to the data acquisition card.

[0077] S6: The data acquisition card performs analog-to-digital conversion on the processed self-mixing interference signal and inputs it into the host computer;

[0078] S7: Phase demodulate the self-mixing interference signal through the software processing module to obtain measurement data;

[0079] Reference Figure 3 , the phase demodulation process includes:

[0080] (1) performing Fourier transform on the modulated self-mixing signal;

[0081] (2) Using a rectangular window function, the first harmonic of the high-frequency current modulation signal (center frequency f H ) and the second harmonic (center frequency 2f H ), perform inverse Fourier transform on the filtered first harmonic and second harmonic respectively, and obtain the sine function and cosine function corresponding to the channel phase change after removing the carrier;

[0082] make By expanding equation (2) into Bessel function, we can obtain:

[0083]

[0084] In the formula, J n (T H ) is the value of the n-order Bessel function; from the above formula, it can be seen that the modulated self-mixing signal contains two parts, DC and AC, and its AC component can be expanded into the form of n-th harmonic. Further analysis shows that the amplitude expressions of the first harmonic and the second harmonic modulated by the phase sine and cosine functions respectively are:

[0085]

[0086]

[0087] Dividing the two equations, we can get the phase

[0088]

[0089] (3) The phase variation curve over time is calculated by using the inverse tangent operation. The phase obtained by solving the above equation is wrapped between [-π,π]. To obtain a continuous phase value, it is necessary to unwrap the above equation and then obtain the phase fluctuation amplitude T from the phase time domain diagram. L , phase amplitude T L The relationship between the external cavity length L is expressed as Where g is the modulation coefficient of the laser wavelength depending on the injected current, I L is the amplitude of the low-frequency modulated sinusoidal current, λ 0 It is the laser wavelength in the absence of light feedback, thereby accurately obtaining the absolute distance, realizing depth measurement, and the depth is displayed in real time on the interface.

Claims

1. An array VCSEL self-mixing interferometry depth measurement system based on dual sinusoidal current modulation, characterized in that: It includes an optical part, an analog circuit processing part, and a digital domain signal processing part. The optical part is composed of a self-made linear array laser probe and a target to be measured. The analog circuit processing part includes an array probe laser driving module and a weak signal amplification module. The digital domain signal processing part includes a data acquisition card and a software processing module of a host computer. The self-made linear array laser probe is used to emit a light beam to the target to be measured and receive part of the returned light beam, thereby generating a self-mixing interference effect; The array probe laser driving module is used to control the bias current of each channel of the laser probe and inject a double sine modulation signal into the probe laser at the same time; The weak signal amplification module is used to remove the DC part of the modulated self-mixing interference signal and filter and amplify the useful signal; The data acquisition card is used to collect the self-mixed interference signal and send it to the host computer; The software processing module is used for phase demodulation to obtain measurement data.

2. The array-type VCSEL self-mixing interferometry depth measurement system based on dual sinusoidal current modulation according to claim 1, characterized in that: The weak signal amplification module includes a high-pass filter, an instrumentation amplifier and a low-pass filter.

3. The array-type VCSEL self-mixing interferometry depth measurement system based on dual sinusoidal current modulation according to claim 1, characterized in that: The self-made linear array laser probe is a 1×4 linear array VCSEL laser probe.

4. The array-type VCSEL self-mixing interferometry depth measurement system based on dual sinusoidal current modulation according to claim 1, characterized in that: The modulation end of the array probe laser driving module adopts a two-stage cascade mode, the modulation signal is input into the front stage, and is input into the driving module through the coupling capacitor, and a double-sine modulation signal is injected into the laser based on the DC bias current.

5. The measurement method of the array VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation according to claim 1 is characterized in that: The steps include: S1: Provide bias current to the VCSEL laser of each channel in the self-made linear array laser probe through the array probe laser driver module; S2: injecting a double-sine modulation signal into the VCSEL laser through the array probe laser driver module to tune the output light wavelength of the VCSEL laser; S3: The tuned outgoing light is directed toward the target to be measured, and the VCSEL laser receives part of the return beam, resulting in a self-mixing interference effect; S4: Based on the consistency of the change of the junction voltage and the self-mixing interference signal, the self-mixing interference signal is picked up by extracting the terminal voltage of the PN junction on the VCSEL; S5: amplifying and filtering the self-mixing interference signal through the weak signal amplification module; S6: collect the processed self-mixing interference signal through the data acquisition card and send it to the host computer; S7: Phase demodulate the self-mixing interference signal through the software processing module to obtain measurement data.

6. The measurement method of the array VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation according to claim 5 is characterized in that: The bias current in step S1 is determined by measuring the variation of the wavelength of the VCSEL laser with the current, determining the linear working area where the wavelength depends on the injected current, and setting the static working point of the laser to the midpoint of the linear area, i.e., the optimal bias current, to ensure continuous tuning of the laser output wavelength.

7. The measurement method of the array VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation according to claim 5 is characterized in that: The dual-sine modulation signal in step S2 is generated by using direct digital frequency synthesis technology to generate the dual-sine modulation signal through software control.

8. The measurement method of the array VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation according to claim 5 is characterized in that: In step S4, the self-mixing interference signal V LD The expression is: Where m is the modulation coefficient, L is the distance between the target object and the laser light output position, λ is the laser wavelength, and V0 is the voltage across the laser PN junction without feedback light; When the laser is modulated by injecting current using a double sine modulation signal with high and low frequencies superimposed, the injected current will cause the laser wavelength to change, and the instantaneous wavelength change of the output is: λ(t)=λ0+Δλ(t)=λ0+g·I L sin(ω L t+θ)+g·I H sin(ω H t+θ) (2) In the formula, I L is the low frequency current modulation amplitude, ω L is the low frequency modulation angular frequency, I H is the high frequency current modulation amplitude, ω H is the high frequency modulation angular frequency, g is the proportional coefficient of wavelength changing with current; In the presence of optical feedback, the change in wavelength leads to the effective output of laser self-mixing interference. Substituting equation (2) into equation (1), considering that the amplitude of the modulation signal is very small Δλ(t)<<λ0, in the first-order approximation, equation (1) is rewritten as: Among them, T L is the modulation depth of the low-frequency sinusoidal current, which is T H Phase modulation depth achieved for high frequency sinusoidal currents 9. The measurement method of the array VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation according to claim 8, characterized in that: The processing of phase demodulation in step S7 includes: (1) performing Fourier transform on the modulated self-mixing signal; (2) Using a rectangular window function, the first harmonic and the second harmonic of the high-frequency current modulation signal are filtered out from the obtained spectrum, and the filtered first harmonic and the second harmonic are respectively subjected to inverse Fourier transform. After removing the carrier, the sine function and the cosine function corresponding to the channel phase change are obtained; (3) Use the inverse tangent operation to calculate the phase change curve over time, unwrap the phase, and obtain the phase fluctuation amplitude T from the phase time domain diagram L , phase amplitude T L The relationship between the external cavity length L is expressed as T L =(4πgI L / λ0 2 )L, where g is the modulation coefficient of the laser wavelength depending on the injection current, I L is the amplitude of the low-frequency modulated sinusoidal current, and λ0 is the laser wavelength in the absence of optical feedback. The absolute distance can be accurately obtained to achieve depth measurement.

10. The measurement method of the array VCSEL self-mixing interference depth measurement system based on dual sinusoidal current modulation according to claim 9, characterized in that: In step (2), By expanding equation (2) into Bessel function, we can obtain: In the formula, J n (T H ) is the value of the n-order Bessel function; from the above formula, it can be seen that the modulated self-mixing signal contains two parts, DC and AC, and its AC component can be expanded into the form of n-th harmonic. Further analysis shows that the amplitude expressions of the first harmonic and the second harmonic modulated by the phase sine and cosine functions respectively are: Dividing the two equations, we can get the phase

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