CN103163530B - Phase modulation direct detection laser Doppler velometer and velocity measuring method thereof - Google Patents

Abstract

The invention discloses a phase modulation direct detection laser Doppler velometer and a velocity measuring method thereof, and relates to a direct detection laser Doppler velometer. In order to solve the problem that a method of converting frequency change of back scattering light into the change of transmittance by utilizing edge filters of a Fabry-Perot (F-P) interferometer in the current direct detection mode to obtain Doppler frequency shift is low in measuring accuracy relative to a coherent detection mode, the invention provides the phase modulation direct detection laser Doppler velometer and the velocity measuring method thereof. According to the method, a beat frequency signal of which the vibration amplitude is changed with the Doppler frequency shift of a moving target is generated by an electric-optical phase modulator and the FP interferometer; a vibration amplitude item is extracted by a phase shifter, a multiplying unit and a low-pass filter, and optical wave frequency information is identified by utilizing the vibration amplitude item; and the frequency of emitted laser and target back scattering light is measured by utilizing the turning-on state and turning-off state of a mechanical switch, and difference of two-time frequency measuring values is used as a measuring value of the Doppler frequency shift. According to the phase modulation direct detection laser Doppler velometer, the influence of the change of light intensity on a measuring result is removed by the energy detection of backward waves, so that the phase modulation direct detection laser Doppler velometer is used for measuring the movement velocity of targets in the field of optics.

Description

Phase-modulation direct detection Laser Doppler Velocimeter and speed-measuring method thereof

Technical field

The present invention relates to a kind of direct detection Laser Doppler Velocimeter, particularly a kind of phase-modulation direct detection Laser Doppler Velocimeter and speed-measuring method thereof.

Background technology

The Ear Mucosa Treated by He Ne Laser Irradiation of a branch of frequency stabilization is to moving target, because the rear orientation light of Doppler effect target will produce certain frequency displacement, by just obtaining moving target along the velocity information of beam direction to the measurement of rear orientation light Doppler shift, the ultimate principle of Here it is Doppler anemometer.Because so the beyond challenge measuring accuracy of Laser Doppler Velocimeter is with a wide range of applications in the every field such as military, industrial.According to measuring principle Laser Doppler Velocimeter, mainly can be divided into two types of direct detection and coherent detections.Coherent detection is to utilize the beat frequency of intrinsic light and rear orientation light to measure Doppler shift, this kind of method is owing to having very high sensitivity and signal to noise ratio (S/N ratio), so velocity survey precision is high, but this kind of method is very high to the wavefront of echo beam and space distribution requirement, so the processing of system and manufacture difficulty are very large.In direct detection mode, the main method of a class is for utilizing as this class boundary filter of F-P interferometer, thereby the variation that the frequency change of rear orientation light is converted into transmitance is obtained to Doppler shift.This kind of method is less demanding to echo beam, and system difficulty of processing is little, but not high with respect to coherent detection mode measuring accuracy.

Summary of the invention

The object of the invention is to utilize as this class boundary filter of FP interferometer in order to solve in current direct detection mode, thereby the frequency change of rear orientation light is converted into method that the variation of transmitance obtains Doppler shift with respect to the not high problem of coherent detection mode measuring accuracy, the invention provides a kind of phase-modulation direct detection Laser Doppler Velocimeter and speed-measuring method thereof.

Phase-modulation direct detection Laser Doppler Velocimeter of the present invention, it comprises single longitudinal mode frequency stabilized laser, polarization spectro sheet, mechanical switch, the first convex lens, the second convex lens, multimode optical fiber, the 3rd convex lens, polaroid, beam expander, beam splitting chip, FP interferometer, the 4th convex lens, the 5th convex lens, the first detector, the second detector and computing machine, and it also comprises electro-optic phase modulator, driver, phase shifter, multiplier and low-pass filter;

The laser of single longitudinal mode frequency stabilized laser transmitting sees through polarization spectro sheet successively, mechanical switch and the first convex lens are incident to moving target, through moving target rear orientation light, be incident to the first convex lens, light after the first convex lens are assembled is incident to polarization spectro sheet through mechanical switch, light through the reflection of polarization spectro sheet is incident to the second convex lens, light after the second convex lens are assembled is introduced into one end of multimode optical fiber, the light of being exported by the other end of multimode optical fiber is incident to the 3rd convex lens, directional light through the 3rd convex lens outgoing is incident to polaroid, polarized light through polaroid outgoing is incident to electro-optic phase modulator, light through electro-optic phase modulator outgoing is incident to beam expander, the light incident beam splitting chip that expands and collimate through beam expander,

The light beam that in the two-beam being divided into through beam splitting chip, energy is less is incident to the 4th convex lens, and the light after the 4th convex lens are assembled is incident to the second detector, and the second detector sends to computing machine after converting light signal to electric signal;

The light beam that in the two-beam being divided into through beam splitting chip, energy is larger is incident to FP interferometer, and the light of exporting through FP interferometer is incident to the 5th convex lens, and the light after the 5th convex lens are assembled is incident to the first detector; The first detector converts light signal to electric signal;

Driver drives electro-optic phase modulator and phase shifter work simultaneously,

The electric signal of the electric signal of the first detector conversion and phase shifter output sends to low-pass filter simultaneously after multiplier computing, and the electric signal of low-pass filter output terminal sends to computing machine;

Meanwhile, computer control drives FP interferometer;

Computer control single longitudinal mode frequency stabilized laser.

Speed-measuring method based on above-mentioned phase-modulation direct detection Laser Doppler Velocimeter, it comprises the steps:

Step 1: when mechanical switch is closed condition, the Ear Mucosa Treated by He Ne Laser Irradiation that single longitudinal mode frequency stabilized laser sends is on the switch wall of static mechanical switch, again the rear orientation light without Doppler shift of the switch wall of mechanical switch is carried out to frequency measurement, obtain a frequency measurement;

The described method that obtains a frequency measurement is: utilize FP interferometer and electro-optic phase modulator to produce the beat signal that the tested moving target Doppler shift of amplitude changes; And by phase shifter, multiplier and low-pass filter, the term amplitude of described beat signal is extracted, utilize this term amplitude to obtain a frequency measurement;

Step 2: when mechanical switch is open mode, tested moving target back scattering light frequency is measured, obtained another frequency measurement;

The described method that obtains another frequency measurement is: utilize FP interferometer and electro-optic phase modulator to produce the beat signal that the tested moving target Doppler shift of amplitude changes; By phase shifter, multiplier and low-pass filter, the term amplitude of described beat signal is extracted, utilized this term amplitude to obtain another frequency measurement;

Step 3: the measured value of the Doppler shift that the value that the frequency measurement that the frequency measurement that step 2 is obtained and step 3 obtain obtains after subtracting each other is tested moving target;

Step 4: the electric signal that computing machine utilizes the second detector 17 to send carries out energy measuring to the measured value of the Doppler shift described in step 3, removes light intensity and changes the impact on described measured value.

Described step 1 also comprises:

By computing machine, the sharp light frequency of single longitudinal mode frequency stabilized laser transmitting is adjusted, the sharp light frequency of transmitting is overlapped with the transmitance peak point of F-P interferometer.

In the detection process of described phase-modulation direct detection Laser Doppler Velocimeter, constantly repeating step one is to step 4.

The invention has the advantages that, the present invention has increased electro-optic phase modulator target backscattering echo has been modulated on the basis of the direct detection Doppler anemometer principle based on FP interferometer, thereby under the condition that does not increase system process and assemble difficulty, improves the signal to noise ratio (S/N ratio) raising measuring accuracy of direct detection mode.Utilize electro-optic phase modulator to make tested moving target rear orientation light produce the sideband light at two equifrequent intervals.Carrier and sideband light will produce one times of modulation frequency domain beat signal through amplitude and the phase-modulation of FP interferometer, because the amplitude of this beat signal can be along with the position change of carrier wave with respect to FP interferometer transmittance curve, so can utilize the amplitude of this beat frequency item to differentiate Doppler shift.This kind of method handed over the little advantage while of assembly difficulty in reservation direct detection mode system, because so being measures this system to the amplitude of the beat signal of fixed frequency can effectively avoid a large amount of noise of circuit medium and low frequency part, simultaneity factor has extremely narrow bandwidth of operation, so relatively original direct detection mode has very high measurement signal to noise ratio (S/N ratio), thereby has improved measuring accuracy.

Accompanying drawing explanation

Fig. 1 is the principle schematic of phase-modulation direct detection Laser Doppler Velocimeter of the present invention.

Fig. 2 is the frequency discrimination curve of the Doppler shift of the present invention while testing the speed.

Fig. 3 is the transmittance curve schematic diagram of FP interferometer of the present invention.

Fig. 4 is the schematic diagram of the light signal through electro-optic phase modulator of the present invention through the beat signal of FP interferometer.

The schematic diagram of Fig. 5 signal that to be beat signal in Fig. 4 obtain with signal through phase shifter output after multiplier multiplies each other.

Fig. 6 is for carrying out the signal of Fig. 5 the schematic diagram of the signal after Fourier transform.

Fig. 7 is the schematic diagram of the flip-flop signal of the signal in Fig. 6.

Embodiment

Embodiment one: in conjunction with Fig. 1, present embodiment is described, the phase-modulation direct detection Laser Doppler Velocimeter described in present embodiment,

It comprises single longitudinal mode frequency stabilized laser 1, polarization spectro sheet 2, mechanical switch 3, the first convex lens 4, the second convex lens 6, multimode optical fiber 7, the 3rd convex lens 8, polaroid 9, beam expander 11, beam splitting chip 12, FP interferometer 13, the 4th convex lens 14, the 5th convex lens 15, the first detector 16, the second detector 17 and computing machine 22, and it also comprises electro-optic phase modulator 10, driver 18, phase shifter 19, multiplier 20 and low-pass filter 21;

The laser of single longitudinal mode frequency stabilized laser 1 transmitting sees through polarization spectro sheet 2 successively, mechanical switch 3 and the first convex lens 4 are incident to moving target, through moving target rear orientation light, be incident to the first convex lens 4, light after the first convex lens 4 are assembled is incident to polarization spectro sheet 2 through mechanical switch 3, light through 2 reflections of polarization spectro sheet is incident to the second convex lens 6, light after the second convex lens 6 are assembled is introduced into one end of multimode optical fiber 7, the light of being exported by the other end of multimode optical fiber 7 is incident to the 3rd convex lens 8, directional light through the 3rd convex lens 8 outgoing is incident to polaroid 9, polarized light through polaroid 9 outgoing is incident to electro-optic phase modulator 10, light through electro-optic phase modulator 10 outgoing is incident to beam expander 11, the light incident beam splitting chip 12 that expands and collimate through beam expander 11,

The light beam that in the two-beam being divided into through beam splitting chip 12, energy is less is incident to the 4th convex lens 14, and the light after the 4th convex lens 14 are assembled is incident to after the second detector 17, the second detectors 17 convert light signal to electric signal and sends to computing machine;

The light beam that in the two-beam being divided into through beam splitting chip 12, energy is larger is incident to FP interferometer 13, and the light of exporting through FP interferometer 13 is incident to the 5th convex lens 15, and the light after the 5th convex lens 15 are assembled is incident to the first detector 16; The first detector 16 converts light signal to electric signal;

Driver 18 drives electro-optic phase modulator 10 and phase shifter 19 work simultaneously,

The electric signal of the electric signal of the first detector 16 conversions and phase shifter 19 outputs sends to low-pass filter 21 simultaneously after multiplier 20 computings, and the electric signal of low-pass filter 21 output terminals sends to computing machine 22;

Meanwhile, computing machine 22 is controlled and is driven FP interferometer 13;

Computing machine 22 is controlled single longitudinal mode frequency stabilized laser 1.

Single longitudinal mode frequency stabilized laser 1 shoot laser is irradiated on moving target through polarization spectro sheet, target rear orientation light is collected Hou Yuan road through lens and is returned, through same polarization spectro sheet, reflect and utilize convex lens to assemble and collect multimode optical fiber again, scatter echo thus multimode optical fiber is introduced Doppler range rate measuring system.Optical fiber emergent light becomes directional light by convex lens, then successively through polaroid and electro-optic phase modulator.The light of phase-modulator outgoing is further expanded and collimates it by beam expander, then by beam splitting chip, is divided into two-beam, and the light beam that wherein energy is less enters energy measuring passage, and the air-gap FP interferometer that passes through that energy is larger carries out frequency measurement.In this system, electro-optic phase modulator is driven by the sinusoidal voltage of additional fixed frequency, rear orientation light after ovennodulation will produce the sideband light at two equifrequent intervals on the basis of original frequency content, after F-P interferometer, the light wave amplitude of these three frequencies and phase place all can change, will on the detector of square law, produce with the beat signal identical with modulating frequency, and along with the amplitude of this beat signal of variation of back scattering light frequency will change.Thereby utilize multiplier and low-pass filter to detect to this beat signal amplitude information the light beam radial velocity that the Doppler shift that just can obtain rear orientation light can obtain target.Because this kind of method is so the amplitude of the beat signal of fixed frequency to be measured to this system can effectively avoid a large amount of noise of circuit medium and low frequency part, simultaneity factor has extremely narrow bandwidth of operation, so relatively original direct detection mode has very high measurement signal to noise ratio (S/N ratio).

Embodiment two: the speed-measuring method of the phase-modulation direct detection Laser Doppler Velocimeter described in present embodiment, it comprises the steps:

Step 1: when mechanical switch 3 is closed condition, the Ear Mucosa Treated by He Ne Laser Irradiation that single longitudinal mode frequency stabilized laser 1 sends is on the switch wall of static mechanical switch 3, again the rear orientation light without Doppler shift of the switch wall of mechanical switch 3 is carried out to frequency measurement, obtain a frequency measurement;

The described method that obtains a frequency measurement is: utilize FP interferometer 13 and electro-optic phase modulator 10 to produce the beat signal that the tested moving target Doppler shift of amplitude changes; And extracted by the term amplitude of the beat signal described in 21 pairs of phase shifter 19, multiplier 20 and low-pass filters, utilize this term amplitude to obtain a frequency measurement;

Step 2: when mechanical switch 3 is open mode, tested moving target back scattering light frequency is measured, obtained another frequency measurement;

The described method that obtains another frequency measurement is: utilize FP interferometer 13 and electro-optic phase modulator 10 to produce the beat signal that the tested moving target Doppler shift of amplitude changes; Term amplitude by phase shifter 19, multiplier 20 and 21 pairs of described beat signals of low-pass filter is extracted, and utilizes this term amplitude to obtain another frequency measurement;

Step 3: the measured value of the Doppler shift that the value that the frequency measurement that the frequency measurement that step 2 is obtained and step 3 obtain obtains after subtracting each other is tested moving target;

Step 4: the electric signal that computing machine utilizes the second detector 17 to send carries out energy measuring to the measured value of the Doppler shift described in step 3, removes light intensity and changes the impact on described measured value.

The light field of the laser of single longitudinal mode frequency stabilized laser 1 transmitting after electro-optic phase modulator 10 modulation is

E _in＝E ₀e ^{i(ωt+βsinΩt)} (1)

The circular frequency that wherein ω is incident laser, the modulating frequency that Ω is electro-optic phase modulator, β is degree of modulation (relevant with the voltage of Sine Modulated).Utilize Bessel's function that formula (1) is launched,

$E_{\mathrm{in}}=E_0[\underset{n=0}{\overset{\∞}{\mathrm{\Σ}}}{J}_n\left(\mathrm{\β}\right)\exp \left(i(\mathrm{\ω}+\mathrm{n\Ω})t\right)+\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}{(-1)}^n{J}_n\left(\mathrm{\β}\right)\exp \left(i(\mathrm{\ω}-\mathrm{n\Ω})t\right)]---\left(2\right)$

By formula (2), can be found out after sinusoidal phase modulation, incident light has increased the sideband light at a series of equifrequents interval on the basis of original carrier frequency.The amplitude of these different frequency light is determined by the Bessel's function of not at the same level time.When adjusting modulation voltage and make degree of modulation β≤0.9, second order and be almost reduced to zero with the amplitude of upper side band light, so now formula (2) formula can only be considered first-order bessel function, therefore

E _in＝E ₀[J ₀(β)exp(iωt)+J ₁(β)exp(i(ω+Ω)t)-J ₁(β)exp(i(ω-Ω)t)] (3)

Be that light after phase-modulation comprises the carrier wave that a frequency is ω, and frequency is respectively the positive and negative single order sideband that ω+Ω and ω-Ω and amplitude equal phase are contrary.Obviously the photocurrent equal and opposite in direction single spin-echo that upper side band (ω+Ω) and carrier wave (ω) beat frequency and lower sideband (ω-Ω) and carrier wave (ω) beat frequency produce, after stack, just offsetting completely and making output is zero just.When this bundle light modulated input FP interferometer 13, will cause amplitude and the phase place of two sidebands to change, the symmetry of sideband be destroyed, and has beat frequency output.And along with their frequency changes with respect to FP interferometer 13 transmittance curve relative positions, the amplitude of beat signal also will change.

FP interferometer 13 sees through filter formula:

$T=A_{\mathrm{\δ}}{e}^{i{A}_{\mathrm{\φ}}}---\left(4\right)$

Wherein $A_{\mathrm{\δ}}=\frac{(1-R-A)}{\sqrt{1-2R\cos \left(\mathrm{\φ}\right)+R^2}},A_{\mathrm{\φ}}=\arctan \left(\frac{(1+R)}{(1-R)}\tan \left(\frac{\mathrm{\φ}}{2}\right)\right),$

R and A are respectively FP interferometer 13 surface reflectance and absorption (scattering) coefficient. wherein λ represents optical wavelength, and n represents air refraction, and h represents FP interferometer 13 thickness, and θ represents light wave incident angle.

Utilize formula (3) and (4) can obtain the light field expression formula of the light process FP interferometer 13 after ovennodulation

$E_{\mathrm{out}}=$

$E_0[J_0\left(\mathrm{\β}\right)T\left(\mathrm{\ω}\right)\exp \left(\mathrm{i\ωt}\right)+J_1\left(\mathrm{\β}\right)T(\mathrm{\ω}+\mathrm{\Ω})\exp (i+(\mathrm{\ω}+\mathrm{\Ω})t)-J_1\left(\mathrm{\β}\right)Te(\mathrm{\ω}-\mathrm{\Ω})\exp (i-(\mathrm{\ω}-\mathrm{\Ω})t)---\left(5\right)$

The optical heterodyne beat signal obtaining at the first detector 16 is:

i(Ω)∝|E _out| ² (6)

Above formula is arranged and comprises three heterogeneities in can discovery signals: DC terms, one times of modulating frequency beat frequency item and two times of modulating frequency beat frequency items.Wherein

DC terms is:

$E_0^2{J}_0^2{\left|T\left(\mathrm{\ω}\right)\right|}^2+E_0^2{J}_1^2|{T(\mathrm{\ω}+\mathrm{\Ω})|}^2+E_0^2{J}_1^2{\left|T(\mathrm{\ω}-\mathrm{\Ω})\right|}^2,$

One times of modulating frequency beat frequency item is:

$2E_0^2{J}_0{J}_1\mathrm{Re}(T\left(\mathrm{\ω}\right)T^{*}(\mathrm{\ω}+\mathrm{\Ω})-T(\mathrm{\ω}-\mathrm{\Ω})T^{*}\left(\mathrm{\ω}\right))\cos \left(\mathrm{\Ωt}\right),$

Two times of modulating frequency beat frequency items are:

$E_0^2{J}_0{J}_{1}T\left(\mathrm{\ω}\right)T^{*}(\mathrm{\ω}+\mathrm{\Ω})\exp (-\mathrm{i\Ωt})+e_0^2{J}_0{J}_{1}T(\mathrm{\ω}+\mathrm{\Ω})T^{*}\left(\mathrm{\ω}\right)\exp \left(\mathrm{i\Ωt}\right)$

$-E_0^2{J}_0{J}_{1}T\left(\mathrm{\ω}\right)T^{*}(\mathrm{\ω}-\mathrm{\Ω})\exp \left(\mathrm{i\Ωt}\right)-E_0^2{J}_0{J}_{1}T(\mathrm{\ω}-\mathrm{\Ω})T^{*}\left(\mathrm{\ω}\right)\exp (-\mathrm{i\Ωt}).$

By observing, can find that the envelope of one times of modulating frequency beat frequency item is that amplitude is along with frequency of light wave ω and light intensity E ₀change and change.So can random there is shake in order not affect measuring accuracy in target back scattering light intensity in actual velocity-measuring system, should be by itself and the impact divided by the variation of removal light intensity of the signal of energy channel before beat signal amplitude extraction.Its simulation result of removing field intensity impact as shown in Figure 2, so it can be used as the frequency discrimination curve of Doppler shift.

We suppose that the thickness of FP interferometer 13 is d ≈ 43mm, and surface reflectivity and absorption coefficient are R=0.866, A=0.0025, and optical maser wavelength is λ=1064nm.In Fig. 2,0MHz position is FP interferometer 13 transmitance peaks, and when back scattering light frequency changes, the amplitude of beat frequency will change.Between the peak-to-peak value of Doppler shift at this enveloping curve, be just can by this curve, identify.

The term amplitude of one times of modulating frequency beat signal can be passed through phase-shifter, and multiplier and low-pass filter extract.The driving signal extraction of an electro-optic phase modulator part, then the phase shift through phase shifter generation pi/2 makes it become cosine signal.Recycling multiplier is the driving signal multiplication with process phase shift detector signal, and then through low-pass filter, just can obtain the amplitude amount of one times of modulating frequency beat signal.The emulation of this process is as shown in Fig. 3, Fig. 4, Fig. 5, Fig. 6 and Fig. 7.

Fig. 3 is the transmittance curve of FP interferometer 13, and the beat signal of the light wave process FP interferometer 13 of process phase-modulator as shown in Figure 4.This beat signal and the modulation signal through phase shift after multiplying each other, multiplier are obtained to signal as shown in Figure 5.This signal is carried out to Fourier transform as shown in Figure 6.Wherein flip-flop is the amplitude composition of one times of modulating frequency.Finally utilize low-pass filter to obtain this flip-flop, as shown in Figure 7, it is consistent with the frequency discrimination curve form of Fig. 2.

Embodiment three: present embodiment is the further restriction to the speed-measuring method of the phase-modulation direct detection Laser Doppler Velocimeter described in embodiment two, and described step 1 also comprises:

Sharp light frequency by 1 transmitting of 22 pairs of single longitudinal mode frequency stabilized lasers of computing machine is adjusted, and the frequency that the sharp light frequency of transmitting and the transmitance peak point of FP interferometer 13 are corresponding is overlapped.

By computing machine, the output light frequency of single longitudinal mode frequency stabilized laser 1 is adjusted, making one times of modulating frequency term amplitude that final system obtains is zero, even if outgoing light frequency overlaps with the transmitance peak point of FP interferometer, can make like this system there is best measurement range.

Embodiment four: present embodiment is the further restriction to the speed-measuring method of the phase-modulation direct detection Laser Doppler Velocimeter described in embodiment two, in the detection process of described phase-modulation direct detection Laser Doppler Velocimeter, constantly repeating step one is to step 4.

Owing to there is frequency displacement in the frequency of shoot laser, so want continuous repeating step one to step 4 in carrying out velocity survey process for a long time.

Claims (4)

1. phase-modulation direct detection Laser Doppler Velocimeter, it comprises single longitudinal mode frequency stabilized laser (1), polarization spectro sheet (2), mechanical switch (3), the first convex lens (4), the second convex lens (6), multimode optical fiber (7), the 3rd convex lens (8), polaroid (9), beam expander (11), beam splitting chip (12), FP interferometer (13), the 4th convex lens (14), the 5th convex lens (15), the first detector (16), the second detector (17) and computing machine (22), it is characterized in that, it also comprises electro-optic phase modulator (10), driver (18), phase shifter (19), multiplier (20) and low-pass filter (21),

The laser of single longitudinal mode frequency stabilized laser (1) transmitting sees through polarization spectro sheet (2) successively, mechanical switch (3) and the first convex lens (4) are incident to moving target, through moving target rear orientation light, be incident to the first convex lens (4), light after the first convex lens (4) are assembled is incident to polarization spectro sheet (2) through mechanical switch (3), light through polarization spectro sheet (2) reflection is incident to the second convex lens (6), light after the second convex lens (6) are assembled is introduced into one end of multimode optical fiber (7), the light of being exported by the other end of multimode optical fiber (7) is incident to the 3rd convex lens (8), directional light through the 3rd convex lens (8) outgoing is incident to polaroid (9), polarized light through polaroid (9) outgoing is incident to electro-optic phase modulator (10), light through electro-optic phase modulator (10) outgoing is incident to beam expander (11), the light incident beam splitting chip (12) that expands and collimate through beam expander (11),

In the two-beam being divided into through beam splitting chip (12), the less light beam of energy is incident to the 4th convex lens (14), light after the 4th convex lens (14) are assembled is incident to the second detector (17), and the second detector (17) sends to computing machine after converting light signal to electric signal;

In the two-beam being divided into through beam splitting chip (12), the larger light beam of energy is incident to FP interferometer (13), light through FP interferometer (13) output is incident to the 5th convex lens (15), and the light after the 5th convex lens (15) are assembled is incident to the first detector (16); The first detector (16) converts light signal to electric signal;

Driver (18) drives electro-optic phase modulator (10) and phase shifter (19) work simultaneously,

The electric signal of the electric signal of the first detector (16) conversion and phase shifter (19) output sends to low-pass filter (21) simultaneously after multiplier (20) computing, and the electric signal of low-pass filter (21) output terminal sends to computing machine (22);

Meanwhile, computing machine (22) is controlled and is driven FP interferometer (13);

Computing machine (22) is controlled single longitudinal mode frequency stabilized laser (1).

2. the speed-measuring method based on phase-modulation direct detection Laser Doppler Velocimeter claimed in claim 1, is characterized in that, it comprises the steps:

Step 1: when mechanical switch (3) is closed condition, the Ear Mucosa Treated by He Ne Laser Irradiation that single longitudinal mode frequency stabilized laser (1) sends is on the switch wall of static mechanical switch (3), again the rear orientation light without Doppler shift of the switch wall of mechanical switch (3) is carried out to frequency measurement, obtain a frequency measurement;

The described method that obtains a frequency measurement is: utilize FP interferometer (13) and electro-optic phase modulator (10) to produce the beat signal that the tested moving target Doppler shift of amplitude changes; And by phase shifter (19), multiplier (20) and low-pass filter (21), the term amplitude of described beat signal is extracted, utilize this term amplitude to obtain a frequency measurement;

Step 2: when mechanical switch (3) is open mode, tested moving target back scattering light frequency is measured, obtained another frequency measurement;

The described method that obtains another frequency measurement is: utilize FP interferometer (13) and electro-optic phase modulator (10) to produce the beat signal that the tested moving target Doppler shift of amplitude changes; By phase shifter (19), multiplier (20) and low-pass filter (21), the term amplitude of described beat signal is extracted, utilized this term amplitude to obtain another frequency measurement;

Step 3: the measured value of the Doppler shift that the value that the frequency measurement that the frequency measurement that step 2 is obtained and step 1 obtain obtains after subtracting each other is tested moving target;

Step 4: the electric signal that computing machine utilizes the second detector (17) to send carries out energy measuring to the measured value of the Doppler shift described in step 3, removes light intensity and changes the impact on described measured value.

3. the speed-measuring method of phase-modulation direct detection Laser Doppler Velocimeter according to claim 2, is characterized in that, step 1 also comprises:

By computing machine (22), the sharp light frequency of single longitudinal mode frequency stabilized laser (1) transmitting is adjusted, the sharp light frequency of transmitting is overlapped with the transmitance peak point of FP interferometer.

4. the speed-measuring method of phase-modulation direct detection Laser Doppler Velocimeter according to claim 2, is characterized in that, in the detection process of described phase-modulation direct detection Laser Doppler Velocimeter, constantly repeating step one is to step 4.