CN111551951A - Laser Doppler velocimeter capable of automatically adjusting signal size and signal size control strategy thereof - Google Patents

Abstract

The invention discloses a laser Doppler velocimeter capable of automatically adjusting the signal size and a signal size control strategy, including an infrared semiconductor laser, a red light indicating semiconductor laser, a coupler, a lithium niobate phase modulator, and a first collimating lens , second collimating lens, receiving lens, infrared photodetector, infrared polarization maintaining fiber, DC signal amplification and acquisition module, Doppler signal amplification and acquisition module, detector working voltage output module, laser current output module, Doppler signal amplification and acquisition module Le signal solution and control module. By adjusting the output optical power and detector voltage in real time, and adopting an appropriate control strategy, a stable laser Doppler signal can be obtained for objects with different reflectivity.

Description

A Laser Doppler Velocimeter That Automatically Adjusts Signal Size and Its Signal Size Control control strategy

technical field

The invention relates to the field of optical measurement, in particular to a laser Doppler velocimeter capable of automatically adjusting the signal size and a signal size control strategy thereof, so that the laser Doppler velocimeter can automatically adapt to different surface reflectances when measuring the moving speed of an object object.

Background technique

The laser Doppler frequency shift is that when the laser is incident on the surface of the moving object and is scattered by the moving object, there is a difference between the light wave frequency of the scattered light and the incident light wave frequency, and the difference is proportional to the moving speed of the object. Therefore, By detecting the shift of the laser frequency, the moving speed of the object can be detected.

The optical path structure of double beam and double scattering is the optical path structure commonly used in laser velocimeters at present. The optical path structure is simple, the received light intensity signal is large, and it can be adapted to speed detection in most cases.

Since the laser Doppler velocimeter relies on the reflected laser light from the surface of the object to be measured, obtaining a stable reflected laser light is essential to achieve high-quality laser Doppler velocity measurement. In actual use, since the reflectivity of the surface of the object to be measured cannot be known in advance, and the reflectivity of the part of the object that is in contact with the laser during the moving process may also change greatly, it is necessary to obtain stable reflected laser light. , it is necessary to adjust the received light intensity to obtain a stable Doppler signal.

By adjusting the transmitted optical power or the optical power received by the photodetector, the size of the Doppler signal can be adjusted. Adjusting the light intensity usually requires adding an extra light intensity control device. How to not add an extra light power control device and ensure the stability of the Doppler signal is a difficult problem. At the same time, the adjustment range of the light intensity control device is also limited. In actual use, when the light intensity control device is adjusted to the maximum or minimum output, a satisfactory signal cannot be obtained. Therefore, it is necessary to add additional adjustment methods so that the laser velocimeter can do its best. Possibly more adaptable to objects with different reflectivity.

The existing laser Doppler velocimetry cannot adjust the output power and detector voltage in real time, and because no proper control method is used, it is impossible to obtain stable laser Doppler signals for objects with different reflectivity.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the above technical defects, and to provide a laser Doppler velocimeter that can automatically adjust the signal size and a signal size control strategy thereof.

In order to solve the above problems, the technical scheme of the present invention is: a laser Doppler velocimeter that automatically adjusts the signal size and a signal size control strategy, including an infrared semiconductor laser, a red light indicating semiconductor laser, a coupler, a lithium niobate phase Modulator, first collimating lens, second collimating lens, receiving lens, infrared photodetector, infrared polarization maintaining fiber, DC signal amplification and acquisition module, Doppler signal amplification and acquisition module, detector working voltage output module , a laser current output module, a Doppler signal calculation and control module, characterized in that: the infrared laser output by the infrared semiconductor laser and the red visible light output by the red light indicating semiconductor laser are converged into the same infrared light through the coupler Polarization maintaining fiber, when the infrared laser passes through the lithium niobate phase modulator, the light wave is evenly divided into two equal parts, and its phase is applied to the sawtooth wave modulation signal on the lithium niobate phase modulator Modulation, the light divided into two equal parts by the lithium niobate phase modulator is guided by the infrared polarization-maintaining fiber to the first collimating lens and the second collimating lens respectively, and the light reflected by the moving object is transmitted by the The receiving lens is focused on the infrared light detector, and the light intensity signal is converted into an electrical signal through the infrared light detector. The Doppler signal calculation and control module, the AC part of the electrical signal is input to the Doppler signal calculation and control module after passing through the Doppler signal amplification and acquisition module, the Doppler signal calculation and control module The output of the control module is used to control the detector working voltage output module and the laser current output module, and the detector working voltage output module is connected to the infrared light detector for controlling the operation of the infrared light detector voltage, the laser current output module is connected to the infrared semiconductor laser for controlling the working current of the infrared semiconductor laser.

As an improvement, the output pigtail of the infrared semiconductor laser is packaged with an infrared polarization-maintaining fiber, and the laser current output module is a constant current source circuit with adjustable current size.

As an improvement, the input and output pigtails of the coupler are packaged with infrared polarization-maintaining fibers.

As an improvement, the lithium niobate phase modulator is a Y-type lithium niobate phase modulator.

As an improvement, the first collimating lens, the second collimating lens and the receiving lens may be general biconvex lenses, plano-convex lenses, meniscus lenses, achromatic lenses or aspherical lenses.

As an improvement, the infrared detector is an avalanche photodiode infrared semiconductor photodetector (APD).

As an improvement, the sawtooth wave modulation signal is a sawtooth wave with a duty cycle of 0 or 1, and the modulation depth of the sawtooth wave is 0.5π.

As an improvement, the DC signal amplifying and collecting module is composed of an amplifying circuit, an analog-to-digital conversion chip (AD chip) and necessary resistors and capacitors.

As an improvement, the Doppler signal amplification and acquisition module is composed of a DC blocking circuit, a signal amplification circuit, an analog-to-digital conversion chip and necessary resistors and capacitors, and the Doppler signal calculation and control module is a general digital The signal processing chip may be a field programmable logic gate array chip (FPGA), a single chip microcomputer (MCU) or a digital signal processor chip (DSP).

As an improvement, the detector working voltage output module is a high-voltage output circuit composed of a DC-DC conversion chip.

Compared with the prior art, the present invention has the advantages that: by adjusting the output optical power and detector voltage in real time, and adopting an appropriate control strategy, stable laser Doppler signals can be obtained for objects with different reflectivity.

Description of drawings

Figure 1 is a schematic diagram of a laser Doppler velocimeter that automatically adjusts the signal size.

Fig. 2 is the first decision flow chart of adjusting the size of the Doppler signal in real time.

Fig. 3 is the second decision flow chart for adjusting the size of the Doppler signal in real time.

As shown in the figure: 1. Infrared semiconductor laser, 2. Red light indicating semiconductor laser, 3. Coupler, 4. Lithium niobate phase modulator, 5. First collimating lens, 6. Second collimating lens, 7 , receiving lens, 8, infrared photodetector, 9, object to be measured, 10, infrared polarization maintaining fiber, 201, DC signal amplification and acquisition module, 202, detector working voltage output module, 203, Doppler signal amplification and Acquisition module, 204, laser current output module, 205, Doppler signal calculation and control module, I, drive current of infrared semiconductor laser 1, V, working voltage of infrared photodetector 8, IL, infrared semiconductor laser The lower limit of driving current of 1, the upper limit of driving current of IH and infrared semiconductor laser 1, the lower limit of VL, the operating voltage of infrared photodetector 8, the upper limit of VH, the operating voltage of infrared photodetector 8, F, the use of FFT algorithm to solve the Dopp The signal amplitude obtained from the frequency signal, FL, the lower limit of the signal amplitude, FH, the upper limit of the signal amplitude, ΔI, the incremental value of the current I for each adjustment, ΔV, the incremental value of the voltage V for each adjustment, A, DC Signal size, AH, DC signal upper limit.

Detailed ways

The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. Wherein the same parts are denoted by the same reference numerals.

It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to the directions in the drawings, and the words "inner" and "outer" ” refer to directions towards or away from the geometric center of a particular part, respectively.

In order to make the content of the present invention easier to understand clearly, the technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

As shown in Figure 1 to Figure 3, a laser Doppler velocimeter that can automatically adjust the signal size and its signal size control strategy Laser 2, coupler 3, lithium niobate phase modulator 4, first collimating lens 5, second collimating lens 6, receiving lens 7, infrared photodetector 8, infrared polarization maintaining fiber 10, DC signal amplification and acquisition Module 201 , Doppler signal amplification and acquisition module 203 , detector working voltage output module 202 , laser current output module 204 , and Doppler signal calculation and control module 205 are composed. Its structure diagram is shown in Figure 1.

The red light from the red light indicating semiconductor laser 2 is coupled into the lithium niobate phase modulator 4 through the coupler 3, and then divided into two beams, which are collimated into space by the first collimating lens 5 and the second collimating lens 6 respectively. The area where the two beams overlap in space is the detection area of the velocimeter. The red light indicates that the light emitted by the semiconductor laser 2 does not need to be used for the calculation of the laser Doppler signal, but is simply used to indicate the detection area of the velocimeter, which is convenient for practical operation.

The light emitted by the semiconductor laser 1 enters the lithium niobate phase modulator 4 after passing through the coupler 3. The light is modulated by the modulation signal applied to the lithium niobate phase modulator and divided into two equal parts with equal power. After the light wave passes through the infrared polarization maintaining fiber 10, it reaches the first collimating lens 5 and the second collimating lens 6 respectively. After the light wave enters the first collimating lens 5 and the second collimating lens 6, it becomes two beams with a certain spot size. space beam. The first collimating lens 5 and the second collimating lens 6 form a certain angle when installed, so that the two spatial beams intersect at a certain distance in front of the velocimeter. The area where the two spatial beams intersect is the detection area of the velocimeter. When the measured object 9 is in the detection area, the two spatial beams both generate scattered light with Doppler frequency shift on the surface of the measured object 9 . The scattered light is focused on the infrared light detector 8 after passing through the receiving lens 7 . The infrared light detector 8 converts the beat frequency signal of the scattered light with Doppler frequency shift and the received light intensity signal into an electrical signal. The DC component in the electrical signal represents the average light intensity received on average, and the AC component in the electrical signal represents the magnitude of the beat frequency signal.

The DC signal amplification and collection module 201 collects the DC component in the electrical signal, and the magnitude of the DC component is denoted as A. The Doppler signal amplification and collection module 203 collects the AC component in the electrical signal, and the Doppler signal calculation and control module 205 performs FFT (fast Fourier transform) operation on the collected AC signal to obtain the amplitude of the AC signal , and denote the amplitude of the AC signal as F.

Based on the values of A and F, the Doppler signal calculation and control module 205 adjusts the drive current I of the infrared semiconductor laser 1 and the operating voltage V of the infrared photodetector 8 according to the decision process described in FIGS. 2 and 3 , thereby achieving Real-time adjustment of Doppler signal size during measurement.

The decision-making process for automatically adjusting the signal size of the present invention will be further described below with reference to FIG. 2 and FIG. 3 .

After booting, the system enters the first step S101 to perform necessary initialization. Then enter S102, and set the drive current I of the infrared semiconductor laser 1 to the minimum value IL. Then enter S103, and set the working voltage of the working voltage V of the infrared photodetector 8 to the maximum value VH. Then the system enters S104, collects the Doppler signal in real time at a fixed interval and performs FFT operation, and calculates the amplitude F of the Doppler signal in real time;

Based on the Doppler signal amplitude F and the DC signal magnitude A obtained in real time, the system enters the decision-making process S201. S201 judges whether the DC signal A is greater than the upper limit AH of the DC signal, if A>AH, it means that the DC signal is too large, the detector is close to saturation, and the system enters the decision-making process S202. S202 judges whether the laser current I is greater than the current lower limit IL, and if I>IL, the system enters the decision process S204. In S204, the system subtracts a fixed value ΔI from the current laser current value, that is, I _i+1 =I _i -ΔI, and then the system enters the decision-making process S205, outputs the new laser current value to the laser, ends the current decision-making process, and waits for S104 outputs the new signal amplitude F and DC signal size A.

In the decision-making process S202, if the laser current I is less than the current lower limit IL, it indicates that the laser current has been adjusted to the minimum value and cannot be reduced further. To further reduce the DC voltage A, the APD working voltage needs to be reduced, so the decision-making process S203 is entered. . S203 judges whether the current APD working voltage V is greater than the lower voltage limit VL, and if V>VL, the system enters the decision-making process S206. In S206, the system subtracts a fixed value ΔV from the current APD working voltage V, that is, V _i+1 =V _i -ΔV, and then the system enters the decision-making process S207, outputs the new APD working voltage to the APD, and ends the current decision-making process, Wait for S104 to output the new signal amplitude F and DC signal size A.

In S201, if the DC signal A is less than the upper limit AH of the DC signal, that is, A<AH, it indicates that the detector is not saturated, and the system enters the decision-making process S301. In S301, it is judged whether the Doppler signal amplitude F is less than the lower limit FL of the amplitude. If F<FL, it indicates that the current Doppler signal amplitude is too small and the Doppler signal amplitude needs to be increased, so the system enters the decision-making process S302 . In S302, it is determined whether the laser current I is less than the current upper limit IH, and if I<IH, it means that the current laser current can continue to increase, so the system enters the decision-making process S304. In S304, add a fixed value ΔI to the laser current I, that is, I _i+1 =I _i +ΔI, then the system enters the decision-making process S307, outputs the new laser current value to the laser, ends the current decision-making process, and waits for S104 Output new signal amplitude F and DC signal size A.

In S302, if the laser current I is greater than the current upper limit IH, that is, I>IH, it indicates that the laser current has increased to the maximum value, and the Doppler signal amplitude F cannot be increased by increasing the laser current. It is necessary to adjust the APD working voltage V to increase the Doppler signal amplitude F, so the system enters the decision process S303. In S303, it is determined whether the APD operating voltage V is less than the upper voltage limit VH, and if V<VH, the system enters the decision-making process S305. In S305, a fixed value ΔV is added to the APD working voltage, that is, V _i+1 =V _i +ΔV, then the system enters the decision-making process S306, outputs the new laser current value to the laser, ends the current decision-making process, and waits for S104 Output new signal amplitude F and DC signal size A.

In S301, if the Doppler signal amplitude F is greater than the lower amplitude limit FL, that is, F>FL, the system enters the decision-making process S308. In S308, the system determines whether the Doppler signal amplitude F is greater than the upper limit FH of the amplitude, and if F>FH, the system enters the decision-making process S309. In S309, the system judges whether the laser current I is greater than the current lower limit IL, and if I>IL, it indicates that the laser current can be reduced, and the system enters the decision process S311. In S311, the system subtracts a fixed value ΔI from the current laser current value, that is, I _i+1 =I _i −ΔI, and then the system enters the decision-making process S312, outputs the new laser current value to the laser, and ends the current decision-making process, Wait for S104 to output new signal amplitude F and DC signal size A.

In S309, if the laser current I is less than the current lower limit IL, that is, I<IL, the laser current cannot be further reduced, and the system enters the decision-making process S310. In S310, the system determines whether the APD operating voltage V is greater than the lower voltage limit VL, and if V>VL, the system enters the decision-making process S313. In S313, the system subtracts a fixed value ΔV from the current APD working voltage V, that is, V _i+1 =V _i -ΔV, and then the system enters the decision-making process S314, outputs the new APD working voltage to the APD, and ends the current decision-making process. Wait for S104 to output the new signal amplitude F and DC signal size A.

The present invention and its embodiments have been described above, and the description is not restrictive, and what is shown in the accompanying drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. All in all, if those of ordinary skill in the art are inspired by it, and without departing from the purpose of the present invention, any structural modes and embodiments similar to this technical solution are designed without creativity, all should belong to the protection scope of the present invention.

Claims (10)

1. A laser Doppler velocimeter for automatically adjusting the signal size and a signal size control strategy, comprising an infrared semiconductor laser (1), a red light indicating semiconductor laser (2), a coupler (3), a lithium niobate phase modulation device (4), first collimating lens (5), second collimating lens (6), receiving lens (7), infrared light detector (8), infrared polarization maintaining fiber (8), DC signal amplification and collection Module (201), Doppler signal amplification and acquisition module (203), detector operating voltage output module (202), laser current output module (204), Doppler signal calculation and control module (205), characterized by In that: the infrared laser output by the infrared semiconductor laser (1) and the red visible light output by the red light indicating semiconductor laser (2) are converged into the same infrared polarization-maintaining fiber through the coupler (3), and the infrared laser passes through the When the lithium niobate phase modulator (4) is used, the light wave is evenly divided into two equal parts, and at the same time, its phase is modulated by the sawtooth wave modulation signal applied on the lithium niobate phase modulator (4), and is modulated by the sawtooth wave modulation signal applied to the lithium niobate phase modulator (4). The light divided into two equal parts by the lithium niobate phase modulator (4) is guided by the infrared polarization-maintaining fiber to the first collimating lens (5) and the second collimating lens (6), respectively. The light reflected by the object is focused by the receiving lens (7) to the infrared light detector (8), the light intensity signal is converted into an electrical signal via the infrared light detector (8), and the direct current part of the electrical signal is via After the DC signal amplification and acquisition module (201) is input to the Doppler signal calculation and control module (205), the AC part of the electrical signal is passed through the Doppler signal amplification and acquisition module (203) Then, input the Doppler signal calculation and control module (205), and the output of the Doppler signal calculation and control module (205) is used for the control detector working voltage output module (202) and all The laser current output module (204), the detector operating voltage output module (202) is connected to the infrared light detector (8) for controlling the operating voltage of the infrared light detector (8), the laser The current output module (204) is connected to the infrared semiconductor laser (1), and is used for controlling the working current of the infrared semiconductor laser (2). 2. a kind of laser Doppler velocimeter and its signal size control strategy of a kind of automatic adjustment signal size according to claim 1, is characterized in that: the output pigtail of described infrared semiconductor laser (2) adopts infrared polarization maintaining fiber package, the laser current output module (204) is a constant current source circuit with adjustable current size. 3. a kind of laser Doppler velocimeter that automatically adjusts the signal size according to claim 1 and its signal size control strategy, it is characterized in that: the input and output pigtails of the coupler (3) all adopt infrared polarization maintaining fiber optic packaging. 4. a kind of laser Doppler velocimeter and signal size control strategy of a kind of automatic adjustment signal size according to claim 1, is characterized in that: described lithium niobate phase modulator (4) is Y-type lithium niobate phase modulator. 5. A kind of laser Doppler velocimeter with automatic signal size adjustment according to claim 1 and its signal size control strategy, it is characterized in that: described first collimating lens (5), second collimating lens ( 6) and the receiving lens (7) can be a common biconvex lens, plano-convex lens, meniscus lens, achromatic lens or aspheric lens. 6. A kind of laser Doppler velocimeter with automatic signal size adjustment according to claim 1 and its signal size control strategy, it is characterized in that: described infrared detector (8) is avalanche photodiode type infrared semiconductor light Detector (APD). 7. The laser Doppler velocimeter and its signal size control strategy for automatically adjusting the signal size according to claim 1, wherein the sawtooth wave modulation signal is a sawtooth wave with a duty cycle of 0 or 1 , and the modulation depth of the sawtooth wave is 0.5π. 8. A kind of laser Doppler velocimeter with automatic signal size adjustment according to claim 1 and its signal size control strategy, it is characterized in that: described DC signal amplification and acquisition module (201) is composed of amplifying circuit and module. It is composed of digital conversion chip (AD chip) and necessary resistors and capacitors. 9. A kind of laser Doppler velocimeter with automatic signal size adjustment according to claim 1 and its signal size control strategy, it is characterized in that: described Doppler signal amplification and acquisition module (203) is composed of DC blocking circuit, signal amplification circuit, analog-to-digital conversion chip and necessary resistance and capacitance, the Doppler signal calculation and control module (205) is a general digital signal processing chip, which can be a field programmable logic gate array chip ( FPGA), microcontroller chip (MCU) or digital signal processor chip (DSP). 10. The laser Doppler velocimeter with automatic signal size adjustment according to claim 1 and its signal size control strategy, wherein the detector operating voltage output module (202) is a DC-DC conversion chip Constituted high voltage output circuit.

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