CN113406657B - Laser Doppler speed measuring device and measuring method - Google Patents
Laser Doppler speed measuring device and measuring method Download PDFInfo
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- CN113406657B CN113406657B CN202110682794.4A CN202110682794A CN113406657B CN 113406657 B CN113406657 B CN 113406657B CN 202110682794 A CN202110682794 A CN 202110682794A CN 113406657 B CN113406657 B CN 113406657B
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
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- G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
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Abstract
The invention belongs to the laser Doppler velocity measurement technology, and particularly relates to a device for measuring laser Doppler velocity and a closed-loop control method. The device comprises: the seed laser 1, the first beam splitter 2, the modulator module 3, the optical fiber amplifier module 4, the circulator module 5 and the optical antenna module 6 are sequentially connected through optical fibers; the first beam splitter 2 is connected with an optical fiber attenuator 7, a coupler module 8, a balance photoelectric detector module 9 and a signal processing module 10 in sequence through optical fibers; the circulator module 5 is connected with the coupler module 8 through optical fibers, the frequency shift of the modulator is changed, closed-loop control of signals is realized, and the problems of wide signal spectrum range, difficult data processing and the like in an open-loop control scheme are solved.
Description
Technical Field
The invention belongs to the laser Doppler velocity measurement technology, and particularly relates to a device for measuring laser Doppler velocity and a closed-loop control method.
Background
The laser Doppler velocity measurement technology is based on Doppler effect, calculates the motion velocity value of an object by utilizing the linear relation between the motion velocity and Doppler frequency shift of the measured object, has the advantages of high measurement precision, high spatial resolution, quick dynamic response, wide velocity measurement range, non-contact measurement and the like, is widely applied to various fields, such as measurement of fluid velocity and solid movement velocity in industrial sites and scientific research, is used for monitoring blood vessel velocity in medical fields, is used for measuring wind speed, turbulence, wind shear, speed measurement and positioning of automobiles and the like in the safety monitoring field, is used for measuring aircraft velocity, engine tail flame airflow flow field, airspeed measurement and the like in the aerospace field, and has wide application market and prospect.
Various laser velocimetry apparatuses developed at present are various, for example, a laser doppler velocimetry apparatus developed by sweden Perimed corporation is used for measuring dynamic changes of single-point blood flow perfusion quantity, a Windwire laser anemometry radar developed by Lockheed Martin corporation in the United states is used for detection of airport turbulence, wind shear and the like, a 1.5 μm laser anemometry radar developed by Mitsubishi corporation in japan is used for detection of atmospheric three-dimensional wind field and the like, but the reported laser Doppler velocimetry schemes are all open-loop working modes, namely, the velocity is obtained by calculating Doppler frequency shift quantity related to the velocity, and no corresponding feedback control exists for the change of the frequency shift quantity.
According to the principle of laser speed measurement, the measured speed value is in direct proportion to Doppler frequency shift, when the measured speed value is large, for example, the flying speed, the vacuum speed or the tail flame flow speed of an engine of an aircraft are measured, the Doppler frequency shift of an optical signal is large (can reach the order of hundreds of MHz), the frequency range of an intermediate frequency signal is wide, the requirements on a photoelectric detector, the circuit bandwidth, the AD sampling frequency and the like are high, and large data volume causes great pressure to signal processing, even signal acquisition and processing are difficult to realize.
Disclosure of Invention
The purpose of the invention is that: the invention provides a closed-loop control scheme for laser speed measurement, which uses a part of Doppler frequency shift quantity for feedback control of a modulator, changes the frequency shift quantity of the modulator, realizes closed-loop control of signals, and solves the problems of wide signal spectrum range, difficult data processing and the like in the open-loop control scheme.
The technical scheme of the invention is as follows: in one aspect, a laser doppler velocimetry device is provided, the device comprising: the seed laser 1, the first beam splitter 2, the modulator module 3, the optical fiber amplifier module 4, the circulator module 5 and the optical antenna module 6 are sequentially connected through optical fibers;
the first beam splitter 2 is connected with an optical fiber attenuator 7, a coupler module 8 and a balance photoelectric detector module 9 in sequence through optical fibers; the circulator module 5 is in optical fiber connection with the coupler module 8; the balance photoelectric detector module (9) is electrically connected with the signal processing module (10);
the signal processing module 10 is electrically connected with the modulator module 3; the signal processing module 10 is configured to calculate a doppler shift from the signal sent by the balanced photodetector module 9, and calculate a radio frequency signal loaded to the modulator module 3 according to the doppler shift, so as to change the frequency shift of the modulator module 3.
Optionally, the modulator module 3 comprises at least one modulator; the regulator is an acousto-optic modulator or an electro-optic modulator.
The modulator can be a phase modulator or an intensity modulator when the modulator is an electro-optic modulator, the intensity modulator can be a Mach-Zehnder type or a cascade, parallel, orthogonal or other deformation structure based on the Mach-Zehnder type, and the purpose of the phase or intensity modulator is to make the frequency of the seed laser generate a certain variation.
Optionally, the modulator module 3 comprises at least one acousto-optic modulator; the acousto-optic modulator comprises a first lens 30, an acousto-optic crystal 31 and a second lens 32;
the first lens 30 and the optical fiber constitute a first optical fiber collimator; the second lens 32 and the optical fiber form a coupling system; the acousto-optic crystal 31 is spatially coupled with the first optical fiber collimator and the coupling system respectively;
the second lens 32 is used for receiving the light beam modulated by the acousto-optic crystal 31 and coupling into an optical fiber.
Optionally, the light transmission aperture and numerical aperture of the second lens 32 are larger than those of the first lens 30, and the light spot output by the second lens 32 is not larger than 2 times of the fiber mode field diameter, and the numerical aperture of the second lens 32 is not larger than 2 times of the fiber numerical aperture.
Alternatively, the laser power of the seed laser 1 is 10-100 mW.
Optionally, the circulator module 5 comprises a circulator, the optical antenna module 6 comprises an optical antenna, the coupler module 8 comprises a coupler, and the balanced photodetector module 9 comprises a balanced photodetector.
Optionally, the device further comprises a second beam splitter 11 and a third beam splitter 12;
a third beam splitter is connected between the first beam splitter 2 and the coupler module 8;
the circulator module 5 comprises a plurality of circulators, the optical antenna module 6 comprises a plurality of optical antennas, the coupler module 8 comprises a plurality of couplers, and the balanced photodetector module 9 comprises a plurality of balanced photodetectors; the modulator module 3 comprises a plurality of modulators; the optical fiber amplifier module 4 includes a plurality of optical fiber amplifiers;
a second beam splitter is connected between the first beam splitter 2 and each modulator; the plurality of modulators are correspondingly connected with the plurality of optical fiber amplifiers 4; the optical fiber amplifiers 4, the circulators and the optical antennas are sequentially connected in a one-to-one correspondence manner;
the circulators are connected with the couplers and the balance photoelectric detectors in sequence in a one-to-one correspondence mode.
Alternatively, if the third beam splitter is connected between the first beam splitter 2 and the optical fiber attenuators 7, the apparatus comprises a plurality of optical fiber attenuators 7; the plurality of optical fiber attenuators 7 are connected to the plurality of couplers in one-to-one correspondence.
In another aspect, there is provided a laser doppler velocimetry method, using the measuring device as described above, the measuring method comprising:
the signal processing module 10 is used for calculating the signal sent by the balanced photoelectric detector module 9 to obtain a signal frequency f1; setting the working frequency point of the modulator as f0; the feedback quantity of the signal processing module (10) is (f 1-f 0) K;
the feedback quantity is used as a negative feedback signal to be added to a modulation signal of the modulator, so that the frequency of the modulation signal actually loaded by the modulator is f0+ [ K× (f 0-f 1) ];
after multiple feedback, the frequency of the signal obtained by the signal processing module (10) for resolving the signal sent by the balanced photoelectric detector module (9) is close to the working point f0;
the final Doppler shift is the accumulated value Deltaf of each feedback quantity [ K× (f 0-f 1) ]]Calculating the motion speed V of the target, wherein a calculation formula is as followsWhere is the lambda laser wavelength.
Optionally, the feedback coefficient K takes a value of 0.01-0.5.
Optionally, the value of the working frequency point f0 is 20-100 MHz.
The invention has the advantages that: the invention provides a speed measuring device and a closed-loop control method based on a laser Doppler speed measuring and coherent detection principle, which have the following advantages:
1. after closed-loop control, heterodyne signal frequency is changed in a small range all the time, so that the frequency spectrum estimation range is greatly reduced, and the frequency spectrum estimation precision and the speed measurement precision can be improved;
2. the signal frequency range is greatly reduced, the requirements on photoelectric detectors, circuit bandwidth and AD sampling frequency are low, and meanwhile, the design difficulty of a filter, an amplifier and other circuits is reduced;
3. a fixed band-pass filter can be arranged to filter useless spectrum information, so that the signal-to-noise ratio of the system is improved;
4. the nonlinearity of measurement is reduced, and the measurement precision is improved;
5. the AD data collection amount is greatly reduced, the back-end data processing pressure is reduced, the hardware calculation power consumption is reduced, and the calculation speed is improved.
Description of the drawings:
FIG. 1 is a block diagram of a closed loop control scheme for laser Doppler velocimetry;
FIG. 2 is a schematic diagram of the power spectrum of the acquired signal;
FIG. 3 is a closed loop control flow diagram;
FIG. 4 shows Bragg conditions satisfied by an acousto-optic modulator, k1 being an incident light wave vector, k2 being an acoustic wave vector, and k3 being an outgoing light wave vector;
FIG. 5 is a block diagram of an acousto-optic modulator, (a) a conventional acousto-optic modulator, and (b) a modified acousto-optic modulator;
FIG. 6 is a block diagram of a closed loop control scheme for multi-path laser Doppler velocimetry
Reference numerals illustrate: a 1-seed laser, a 2-first beam splitter, a 3-modulator module, a 4-optical fiber amplifier module, a 5-circulator module, a 6-optical antenna module, a 7-optical fiber attenuator, an 8-coupler module, a 9-balanced photoelectric detector module and a 10-signal processing module; a 5-1-incident optical fiber, a 5-3-exit end coupling optical fiber, a 5-4-self-focusing lens, a 5-5-self-focusing lens; 31-acousto-optic crystal, 11-second beam splitter, 12-third beam splitter.
The specific embodiment is as follows:
example 1
In this embodiment, referring to fig. 1, a laser doppler velocity measurement device is provided, where the device includes: the seed laser 1, the first beam splitter 2, the modulator module 3, the optical fiber amplifier module 4, the circulator module 5 and the optical antenna module 6 are sequentially connected through optical fibers; the first beam splitter 2 is connected with an optical fiber attenuator 7, a coupler module 8 and a balance photoelectric detector module 9 in sequence through optical fibers; the circulator module 5 is connected with a coupler module 8 by optical fibers. The balanced photodetector module 9 and the signal processing module 10 are electrically connected.
Wherein the signal processing module 10 is electrically connected with the modulator module 3; the signal processing module 10 is configured to calculate a doppler shift from the signal sent by the balanced photodetector module 9, and calculate a frequency shift amount of the radio frequency signal loaded to the modulator module 3 according to the doppler shift, so as to adjust the frequency shift amount of the modulator module 3.
As one of the preferred implementation of the present embodiment, the modulator module 3 comprises at least one modulator, which may be an acousto-optic modulator or an electro-optic modulator.
Specifically, in this embodiment, the modulator module 3 includes at least one acousto-optic modulator. The acousto-optic modulator includes an incident end optical fiber, a first lens 30, an acousto-optic crystal 31, a second lens 32 and an emergent end coupling optical fiber, as shown in fig. 4 and 5;
the first lens 30 and the incident end optical fiber form a first optical fiber collimator; the second lens 32 and the outgoing end optical fiber form a coupling system; the acousto-optic crystal 31 is spatially coupled with the first optical fiber collimator and the coupling system respectively;
the second lens 32 is used for receiving the light beam modulated by the acousto-optic crystal 31 and coupling into an optical fiber.
In this embodiment, the acousto-optic modulator is based on the acousto-optic bragg diffraction principle, as shown in fig. 4, the incident light vector k1, the acoustic wave vector k2 and the diffracted light vector k3 satisfy the bragg condition, so that if the frequency of the acoustic wave is changed to change the frequency shift amount of the acousto-optic modulator, the magnitude and direction of the diffracted light vector k3 will change. As shown in FIG. 5 (a), a conventional acousto-optic modulator structure is shown, wherein 5-1 is an incident end optical fiber, 31 is an acousto-optic crystal, and 5-3 is an emergent end coupling optical fiber; 5-4 and 5-5 are both self-focusing lenses or spherical lenses. 5-1 and 5-4, 5-3 and 5-5 respectively constitute optical fiber collimators for collimating the optical signals and then making them incident into the acousto-optic crystal, and at the same time coupling the diffracted light beams in the acousto-optic crystal into the optical fibers. The traditional acousto-optic modulator works under specific acoustic wave frequency, the k3 direction is fixed, the direction and the position of the corresponding diffracted light are fixed, and the ideal coupling efficiency can be obtained by adopting an optical fiber collimator coupling mode, but if the acoustic wave frequency is changed, the direction and the position of the diffracted light are changed, the optical fiber coupling efficiency is required to be rapidly reduced, even no light is output, and the modulation frequency range corresponding to 90% of the power reduction of the acousto-optic modulator of a certain model is actually measured to be 22MHz. Therefore, the modulation frequency of the acousto-optic modulator can only be changed within a small range, limiting the application of the closed-loop scheme.
In order to expand the modulation frequency variation range of the acousto-optic modulator, this embodiment proposes a modification as shown in fig. 5 (b), in which the optical fiber collimator composed of 5-3 and 5-5 is changed to a coupling system composed of the outgoing end coupling optical fiber 5-3 and the second lens 32, so as to improve the optical fiber coupling efficiency when the modulation frequency is varied. The first lens 30 is a self-focusing lens or a spherical lens, and the 5-1 and 30 constitute a fiber collimator.
Specifically, in this embodiment, the second lens 32 may be a combined lens system or a single lens, and its input has a larger aperture and numerical aperture, and its output matches the numerical aperture and mode field of the optical fiber.
Further, the light transmission aperture and numerical aperture of the second lens 32 are larger than those of the first lens 30, the light spot output by the second lens 32 is not larger than 2 times of the optical fiber mode field diameter, and the numerical aperture of the second lens 32 is not larger than 2 times of the optical fiber numerical aperture.
As one of the preferred embodiments of the present example, the laser power of the seed laser 1 is 10 to 100mW.
As one of the preferred implementations of the present embodiment, as shown in connection with fig. 1, the circulator module 5 comprises a circulator, the optical antenna module 6 comprises an optical antenna, the coupler module 8 comprises a coupler, the balanced photodetector module 9 comprises a balanced photodetector, and the fiber amplifier module 4 comprises a fiber amplifier.
The seed laser 1, the first beam splitter 2, the acousto-optic modulator, the optical fiber amplifier, the circulator and the optical antenna are sequentially connected; the input end 1 of the coupler is connected with the three ports of the circulator, the input end of the optical fiber attenuator 7 is connected with the other output end of the first beam splitter 2, and the output end of the optical fiber attenuator is connected with the input end 2 of the coupler; the two output ends of the coupler are connected with a balance photoelectric detector which is connected with the signal processing module 10. The signal processing module 10 is connected with the seed laser 1, the acousto-optic modulator and the optical fiber amplifier through electrical interfaces for supplying power, and of course, other ways of supplying power are also possible. The optical devices are all in butt joint through flanges by using polarization maintaining optical fiber fusion or using joints such as FC/APC and the like.
As one of the preferred modes of the present embodiment, as shown in connection with fig. 6, the apparatus further comprises a second beam splitter and a third beam splitter; a third beam splitter 12 is connected between the first beam splitter 2 and the coupler module 8; the circulator module 5 comprises a plurality of circulators, the optical antenna module 6 comprises a plurality of optical antennas, the coupler module 8 comprises a plurality of couplers, and the balanced photodetector module 9 comprises a plurality of balanced photodetectors; the modulator module 3 comprises a plurality of acousto-optic modulators. The fiber amplifier module 4 includes a plurality of fiber amplifiers.
A second beam splitter is connected between the first beam splitter 2 and each acousto-optic modulator; each acousto-optic modulator is correspondingly connected with a plurality of optical fiber amplifiers; the optical fiber amplifiers, the circulators and the optical antennas are sequentially connected in a one-to-one correspondence mode. The circulators are connected with the couplers and the balance photoelectric detectors in sequence in a one-to-one correspondence mode.
Furthermore, if the third beam splitter is connected between the optical fiber attenuators 7 of the first beam splitter 2, the apparatus comprises a plurality of optical fiber attenuators 7; the plurality of optical fiber attenuators 7 are connected to the plurality of couplers in one-to-one correspondence.
As one of the preferred embodiments of the present embodiment, the optical fiber attenuator 7 may be an optical power attenuator of any principle or an optical fiber splitter of any fractional ratio. The optical antenna can be in a focusing working mode or a collimation working mode.
As one of the preferred modes of the present embodiment, the optical antenna module 6 includes an optical antenna that can simultaneously transmit and receive a plurality of laser signals of different angles of view; the optical antenna is connected to a plurality of circulators.
The working principle of the embodiment is as follows: the laser emitted by the seed laser 1 is split into two beams of light by the first beam splitter 2, one beam enters the acousto-optic modulator as signal light, and the other beam enters the optical fiber attenuator as local oscillation light. The signal light is modulated into a pulse signal by the acousto-optic modulator, enters the optical fiber amplifier, enters the circulator after being amplified, enters the optical antenna through two ports of the circulator, and is then emitted to the air or the target object. The signal scattered by air or reflected by the target enters the circulator through the optical antenna, enters the coupler from the three ports of the circulator, and enters the coupler together with the local oscillation light output from the optical fiber attenuator to realize optical mixing. And then dividing the mixed signals into two beams of light with equal power through a coupler, respectively entering two input ends of a balance detector to realize heterodyne detection, and enabling heterodyne signals output by a balance photoelectric detector to enter a signal processing module. In this embodiment, the signal processing module provides the modulation signal and the feedback control signal for the acousto-optic modulator.
Example 2
In this embodiment, as shown in fig. 3, a laser doppler velocimetry method is provided, and the measuring device described in embodiment 1 is used, where the measuring method includes the following steps:
the signal processing module 10 is used for calculating the signal sent by the balanced photoelectric detector module 9 to obtain a signal frequency f1; setting the working frequency point of the acousto-optic modulator as f0; the feedback amount of the signal processing module 10 is (f 1-f 0) ×k;
the feedback quantity is used as a negative feedback signal to be superimposed on the modulation signal of the acousto-optic modulator, so that the frequency of the modulation signal actually loaded by the acousto-optic modulator is f0+ [ K× (f 0-f 1) ];
after multiple feedback, until the frequency of the signal obtained by the signal processing module 10 for resolving the signal sent by the balanced photoelectric detector module 9 is close to the working point f0;
the final Doppler shift is the accumulated value Deltaf of each feedback quantity [ K× (f 0-f 1) ]]Calculating the motion velocity V of the target, and calculatingThe formula isWhere is the lambda laser wavelength.
Specifically, in this embodiment, the closed-loop control method based on the laser doppler velocity measurement principle is based on: the power of the seed laser is 10-100 mW, the emitted laser passes through a beam splitter with the beam splitting ratio of 90/10-50/50, one end with high power is used as signal light to enter an acousto-optic modulator module to modulate signals, a certain frequency shift f0 is generated, the frequency shift is 20-100 MHz, the signals can be modulated into pulses, a continuous mode can be maintained, and then the signals enter an optical fiber amplifier; the small-power end is taken as local oscillation light, enters an optical fiber attenuator, enters a 50/50 coupler after being attenuated by a certain amplitude, enters an circulator through an optical fiber amplifier, and then enters an optical antenna to be transmitted to a moving body. The signal light is scattered after encountering the moving body, and the backward scattered signal re-enters the fiber antenna and enters the 50/50 coupler after passing through the circulator. At this time, the local oscillation light and the signal light enter the 50/50 coupler together, after being split by the coupler, enter two light input ports of the balanced photoelectric detector respectively, heterodyne mixing detection is finally completed in the balanced photoelectric detector, and intermediate frequency signals output by the balanced photoelectric detector enter the signal acquisition, processing and driving circuit to perform signal processing and output feedback signals to the acousto-optic modulator to perform closed loop control.
The specific closed-loop control method comprises the following steps: setting the working frequency point of the acousto-optic modulator as f0, the signal processing module 10 calculates the signal frequency f1 obtained by resolving the signal sent by the balanced photoelectric detector module 9, as shown in fig. 2, calculates the Power Spectral Density (PSD) of the signal, and estimates the frequency f1 of the signal. The feedback amount of the signal processing module 10 is (f 1-f 0) ×k, K being a feedback coefficient. The Doppler frequency shift is multiplied by a certain feedback coefficient K and then is used as a negative feedback signal to be superimposed on the modulation signal of the acousto-optic modulator, and the frequency of the modulation signal actually loaded by the acousto-optic modulator is f0+ [ K× (f 0-f 1)]. After multiple feedback, until the frequency of the signal obtained by the signal processing module 10 for resolving the signal sent by the balanced photoelectric detector module 9 is close to the working point f0; the final Doppler shift isAccumulated value Δf= Σ [ k× (f 0-f 1) of individual feedback amounts]Calculating the motion speed V of the target, wherein a calculation formula is as followsWhere is the lambda laser wavelength.
As one of the preferred embodiments of the present embodiment, the feedback coefficient K takes a value of 0.01-0.5. The feedback coefficient has small value, good control stability, low closed-loop speed, narrow frequency band, large feedback coefficient, high closed-loop speed, high frequency band, poor stability and easy divergence of the control process.
The direction of the measured speed can be conveniently judged by setting the working frequency point, and sometimes the influence of removing low-frequency noise on signal calculation is considered and limited by the measuring speed range, wherein the value of the working frequency point f0 is 20-100 MHz.
Claims (8)
1. A laser doppler velocimetry method, using a laser doppler velocimetry device, the device comprising: the seed laser (1), the first beam splitter (2), the modulator module (3), the optical fiber amplifier module (4), the circulator module (5) and the optical antenna module (6) are sequentially connected through optical fibers;
the first beam splitter (2) is connected with the optical fiber attenuator (7), the coupler module (8) and the balance photoelectric detector module (9) through optical fibers in sequence; the circulator module (5) is connected with the coupler module (8) through optical fibers; the balance photoelectric detector module (9) is electrically connected with the signal processing module (10);
the signal processing module (10) is electrically connected with the modulator module (3); the signal processing module (10) is used for resolving the signals sent by the balanced photoelectric detector module (9) to obtain Doppler frequency shift, and calculating radio frequency signals loaded to the modulator module (3) according to the Doppler frequency shift so as to change the frequency shift amount of the modulator module (3); the speed measuring method is characterized by comprising the following steps:
the signal processing module (10) is used for resolving the signals sent by the balanced photoelectric detector module (9) to obtain the signal frequencyf1The method comprises the steps of carrying out a first treatment on the surface of the Setting the working frequency point of the modulator module (3) asf0The method comprises the steps of carrying out a first treatment on the surface of the The feedback quantity of the signal processing module (10) is%f1-f0)*KThe method comprises the steps of carrying out a first treatment on the surface of the Feedback coefficientKThe value is 0.01-0.5;
the feedback quantity is used as a negative feedback signal to be superimposed on the modulation signal of the modulator module (3) so that the frequency of the modulation signal actually loaded by the modulator module (3) is as followsf0+∑[K×(f0-f1)]；
The frequency of the signal obtained by solving the signal sent by the balanced photoelectric detector module (9) through multiple feedback to the signal processing module (10) approaches to the working pointf0Until that is reached;
the final Doppler shift is the accumulated value of each feedback quantityΔf=∑[K×(f0-f1)]Calculating the movement speed of the targetVThe calculation formula isWhereinλIs the laser wavelength.
2. The laser doppler velocimetry method of claim 1, wherein the operating frequency pointf0The value is 20-100 MHz.
3. A laser doppler velocimetry method according to claim 1, characterized in that the modulator module (3) comprises at least one modulator, which is an acousto-optic modulator or an electro-optic modulator.
4. The laser doppler velocimetry method of claim 1, wherein the modulator module (3) comprises at least one acousto-optic modulator; the acousto-optic modulator comprises a first lens (30), an acousto-optic crystal (31) and a second lens (32);
the first lens (30) and the optical fiber form a first optical fiber collimator; the second lens (32) and the optical fiber form a coupling system; the acousto-optic crystal (31) is spatially coupled with the first optical fiber collimator and the coupling system respectively;
the second lens (32) is used for receiving the light beam modulated by the acousto-optic crystal (31) and coupling the light beam into the optical fiber.
5. The laser doppler velocimetry method of claim 4, wherein the light transmission aperture and numerical aperture of the second lens (32) are larger than those of the first lens (30), and the light spot output by the second lens (32) is not larger than 2 times of the optical fiber mode field diameter, and the numerical aperture of the second lens (32) is not larger than 2 times of the optical fiber numerical aperture.
6. The laser doppler velocimetry method of claim 1, wherein the circulator module (5) comprises a circulator, the optical antenna module (6) comprises an optical antenna, the coupler module (8) comprises a coupler, and the balanced photodetector module (9) comprises a balanced photodetector.
7. The laser doppler velocimetry method of claim 1, wherein the device further comprises a second beam splitter (11) and a third beam splitter (12);
a third beam splitter (12) is connected between the first beam splitter (2) and the coupler module (8);
the circulator module (5) comprises a plurality of circulators, the optical antenna module (6) comprises a plurality of optical antennas, the coupler module (8) comprises a plurality of couplers, and the balanced photoelectric detector module (9) comprises a plurality of balanced photoelectric detectors; the modulator module (3) comprises a plurality of modulators; the optical fiber amplifier module (4) comprises a plurality of optical fiber amplifiers;
a second beam splitter (11) is connected between the first beam splitter (2) and each modulator; the modulators are correspondingly connected with the optical fiber amplifiers; the optical fiber amplifiers, the circulators and the optical antennas are sequentially connected in a one-to-one correspondence manner;
the circulators are connected with the couplers and the balance photoelectric detectors in sequence in a one-to-one correspondence mode.
8. A laser doppler velocimetry method according to claim 7, characterized in that the device comprises a plurality of optical fiber attenuators (7) if a third beam splitter is connected between the first beam splitter (2) and the optical fiber attenuators (7); the optical fiber attenuators (7) are connected with the couplers in a one-to-one correspondence manner.
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| US7557795B2 (en) * | 2005-06-30 | 2009-07-07 | Microsoft Corporation | Input device using laser self-mixing velocimeter |
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| US5847817A (en) * | 1997-01-14 | 1998-12-08 | Mcdonnell Douglas Corporation | Method for extending range and sensitivity of a fiber optic micro-doppler ladar system and apparatus therefor |
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