CN104682187A - Automatic compensation device of phase noise of Raman laser system based on closed loop feedback and method thereof - Google Patents

Abstract

The invention discloses an automatic compensation device of a phase noise of a Raman laser system based on closed loop feedback and a method thereof. The device comprises a laser source, a beam splitter, an electrooptical modulator, an acoustic optical modulator, a beam combiner, a half-transparent half-reflecting mirror, a phase modulator, a polarizer, a photoelectric detector, a low noise microwave amplifier, a frequency mixer, a low pass filter, an analog-digital converter, an FPGA, a digital-to-analog converter, a low frequency amplifier and a phase shifter. The automatic compensation device and method provided by the invention are capable of automatically adjusting and compensating a phase difference in the Raman laser system and reducing the phase noise caused by the vibration of a light path of the Raman laser system. By adopting the circuit control mode, the advantages of integration, modularization and easy debugging of a control system are achieved.

Description

A kind of raman laser system phase noise autocompensation installation based on closed loop feedback and method

Technical field

The present invention relates to a kind of raman laser system phase noise autocompensation installation based on closed loop feedback and method, belong to atomic interferometer technical field.

Background technology

Atomic interferometer is based on matter wave interference principle, utilizes laser to carry out beam splitting, reflection, conjunction bundle thus realize the interference of atom to cold atomic beam.Atomic interferometer can accurate measurement physical constant, basic physical theory such as inspection quantum mechanics and general theory of relativity etc.Because atom has quality, atomic interferometer as sensitive inertial sensor, accurately can also can measure acceleration of gravity, angular speed etc., thus has important application in navigation, mine locating, earthquake prediction, environmental inspection.

Usual use raman laser carries out beam splitting, reflection to atomic beam and closes bundle.Raman laser is the laser that two harness have fixed frequency difference and phase difference.A laser can be used to produce laser, be then divided into two bundles, respective path use acousto-optic modulator and electrooptic modulator carry out shift frequency to laser, obtain the raman laser with fixed frequency difference.The whether constant certainty of measurement to atomic interferometer of phase difference between this two bundles laser has a great impact, and the phase noise therefore reducing raman laser system is particularly important.

In light path, optics vibrates the phase noise of phase noise on raman laser system caused certain impact, for reducing the phase noise of raman laser system as much as possible, traditional method laser system is carried out passive vibration isolation or utilizes accelerometer to measure vibration noise, finally compensate when measuring, obvious above-mentioned compensation method more complicated, but also need extra device subsidiary.

Summary of the invention

The object of the invention is to solve the problem, proposing a kind of raman laser system phase noise autocompensation installation based on closed loop feedback and method, may be used for the detection of phase difference in raman laser system, adjustment and compensation.

Based on a raman laser system phase noise autocompensation installation for closed loop feedback, comprise LASER Light Source, beam splitter, electrooptic modulator, acousto-optic modulator, bundling device, semi-transparent semi-reflecting lens, phase-modulator, the polarizer, photodetector, reactatron, frequency mixer, low pass filter, analog to digital converter, FPGA, digital to analog converter, low frequency amplifier, phase shifter;

The laser that LASER Light Source sends enters beam splitter, one end output of beam splitter is connected with the input of electrooptic modulator, other one end output of beam splitter is connected with the input of acousto-optic modulator, the output of electrooptic modulator and the output of acousto-optic modulator together input bundling device, the raman laser that bundling device exports enters semi-transparent semi-reflecting lens, semi-transparent semi-reflecting lens forms transmission laser and reflects laser, reflects laser enters phase-modulator, the output of phase-modulator is connected with the input of the polarizer, the Output of laser of the polarizer enters photodetector, the output of photodetector is connected with the input of reactatron, the output of reactatron is connected with the input of frequency mixer, the output of frequency mixer is connected with the input of low pass filter, the output of low pass filter is connected with the input of analog to digital converter, the output signal of analog to digital converter enters FPGA, the output signal of FPGA enters digital to analog converter, the output of digital to analog converter is connected with the input of low frequency amplifier, the output signal of low frequency amplifier enters phase shifter, the output of phase shifter is connected with the input of acousto-optic modulator.

A kind of raman laser system phase noise automatic compensating method based on closed loop feedback, the laser that LASER Light Source exports is divided into two bundle laser through beam splitter, beam of laser is by electrooptic modulator shift frequency, another beam of laser is by acousto-optic modulator shift frequency, two bundle laser after shift frequency synthesize raman laser through bundling device, install a semi-transparent semi-reflecting lens at the output of raman laser, obtain the input of fraction laser as reponse system, the form of this raman laser signal is as follows:

I(t)＝I ₀[1+cos(2πft+φ _L(t)+φ _S(t))] (1.1)

Wherein: I ₀for the amplitude of photoelectric current, f=6.834GHz is the difference on the frequency of two bundle laser, φ _lt phase noise that () is light path, φ _st phase noise that () is microwave source;

In order to extract the phase difference of two bundle laser, first need to carry out phase square wave modulation to raman laser, modulation makes the phase difference of two bundle laser to be or then be polarized the laser after modulation, play light signal to the rear and enter detector, light signal is converted to microwave signal by detector, and after ignoring optical frequency item, this tested microwave signal form is as follows:

U(t)＝U ₀cos(2πft+φ _L(t)+φ _S(t)+φ _M(t)) (1.2)

Wherein: U ₀for voltage magnitude, f=6.834GHz is the difference on the frequency of two bundle laser, φ _lt phase noise that () is light path, φ _st phase noise that () is microwave source, φ _mt () is modulation signal, modulation signal form is as follows:

${\mathrm{\&phi;}}_M\left(t\right)=\left\{\begin{array}{c}\mathrm{\&pi;}/2,\mathrm{kT}\&le;t<(k+1/2)T\\ 3\mathrm{\&pi;}/2,(k+1/2)T\&le;t<(k+1)t\end{array}\right.,k=\mathrm{0,1,2}...---\left(1.3\right)$

Wherein: T is the cycle of modulation signal;

For extracting φ _l(t) component, introduce with reference to microwave signal, by frequency mixer, tested microwave signal is carried out down-conversion, this reference microwave signal and tested microwave signal are produced by same microwave source, ignore with reference to the time delay between microwave signal and tested microwave signal, as follows with reference to microwave signal form:

U _R(t)＝U _Rcos[2πft+φ _S(t)] (1.4)

Wherein: U _rfor voltage magnitude, f=6.834GHz is the frequency with reference to microwave signal, φ _st phase noise that () is microwave source;

Tested microwave signal, after down-conversion, carries out filtering through low pass filter, can obtain tested microwave signal filtered versions as follows by (1.2) and (1.4):

$U\left(t\right)=\frac{1}{2}{U}_0{U}_R\cos [{\mathrm{\&phi;}}_L\left(t\right)-{\mathrm{\&phi;}}_M\left(t\right)]---\left(1.5\right)$

Known φ _m(t) be or so tested microwave signal can be reduced to:

$U\left(t\right)=\frac{1}{2}{U}_0{U}_R\sin {\mathrm{\&phi;}}_L\left(t\right)\sin {\mathrm{\&phi;}}_M\left(t\right)=\&PlusMinus;\frac{1}{2}{U}_0{U}_R\sin {\mathrm{\&phi;}}_L\left(t\right)---\left(1.6\right)$

Consider φ _lt () is the signal of a faint slow change, so tested microwave signal can be reduced to following form:

$U\left(t\right)=\&PlusMinus;\frac{1}{2}{U}_0{U}_R{\mathrm{\&phi;}}_L\left(t\right)---\left(1.7\right)$

In order to obtain φ _lt voltage signal that () is corresponding, analog to digital converter is utilized to be converted into digital signal, by FPGA, tested microwave signal is processed, recycling digital to analog converter is converted into analog voltage signal, in order to obtain enough power drive phase shifters, the power of low frequency amplifier to tested microwave signal is utilized to amplify, analog signal through power amplification exports phase signal corresponding with it as the input of phase shifter to control phase shifter, this phase signal is coupled into light path as feedback signal by acousto-optic modulator, the form obtained through the raman laser signal of closed loop feedback is as follows:

I(t)＝I ₀[1+cos(2πft+φ _S(t))] (1.8)

From formula (1.1) and (1.8), closed-loop feedback control system can reach the object suppressing raman laser system light path to vibrate the phase noise caused.

Advantage of the present invention:

(1) by adopting closed loop feedback control loop, achieving automatic adjustment and the compensation of phase difference in raman laser system, reducing the light path phase noise of raman laser system, reducing the light path phase noise of raman laser system;

(2) by adopting circuit control mode, achieving integrated, the modularization of control system and being easy to the advantages such as debugging;

Accompanying drawing explanation

Fig. 1 is the phase difference automatic compensating method block diagram based on closed loop feedback;

In figure:

1-LASER Light Source 2-beam splitter 3-electrooptic modulator

4-acousto-optic modulator 5-bundling device 6-semi-transparent semi-reflecting lens

7-phase-modulator 8-polarizer 9-photodetector

10-reactatron 11-frequency mixer 12-low pass filter

13-analog to digital converter 14-FPGA 15-digital to analog converter

16-low frequency amplifier 17-phase shifter

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The present invention is a kind of phase difference autocompensation installation based on closed loop feedback, as shown in Figure 1, LASER Light Source 1, beam splitter 2, electrooptic modulator 3, acousto-optic modulator 4, bundling device 5, semi-transparent semi-reflecting lens 6, phase-modulator 7, the polarizer 8, photodetector 9, reactatron 10, frequency mixer 11, low pass filter 12, analog to digital converter 13, FPGA 14, digital to analog converter 15, low frequency amplifier 16, phase shifter 17 is comprised.

The laser that LASER Light Source 1 sends enters beam splitter 2, one end output of beam splitter 2 is connected with the input of electrooptic modulator 3, other one end output of beam splitter 2 is connected with the input of acousto-optic modulator 4, the output of electrooptic modulator 3 and the output of acousto-optic modulator 4 together input bundling device 5, the raman laser that bundling device 5 exports enters semi-transparent semi-reflecting lens 6, semi-transparent semi-reflecting lens 6 forms transmission laser and reflects laser, reflects laser enters phase-modulator 7, the output of phase-modulator 7 is connected with the input of the polarizer 8, the Output of laser of the polarizer 8 enters photodetector 9, the output of photodetector 9 is connected with the input of reactatron 10, the output of reactatron 10 is connected with the input of frequency mixer 11, the output of frequency mixer 11 is connected with the input of low pass filter 12, the output of low pass filter 12 is connected with the input of analog to digital converter 13, the output signal of analog to digital converter 13 enters FPGA14, the output signal of FPGA14 enters digital to analog converter 15, the output of digital to analog converter 15 is connected with the input of low frequency amplifier 16, the output signal of low frequency amplifier 16 enters phase shifter 17, the output of phase shifter 17 is connected with the input of acousto-optic modulator 4.

Based on a raman laser system phase noise automatic compensating method for closed loop feedback, as described below:

The laser that LASER Light Source 1 exports is divided into two bundle laser through beam splitter 2, beam of laser is by electrooptic modulator 3 shift frequency, another beam of laser is by acousto-optic modulator 4 shift frequency, two bundle laser after shift frequency synthesize raman laser through bundling device 5, at the output of raman laser, a semi-transparent semi-reflecting lens 6 is installed, obtain the input of fraction laser as reponse system, the form of this raman laser signal is as follows:

I(t)＝I ₀[1+cos(2πft+φ _L(t)+φ _S(t))] (1.1)

Wherein: I ₀for the amplitude of photoelectric current, f=6.834GHz is the difference on the frequency of two bundle laser, φ _lt phase noise that () is light path, φ _st phase noise that () is microwave source;

In order to extract the phase difference of two bundle laser, first need to carry out phase square wave modulation to raman laser, modulation makes the phase difference of two bundle laser to be or then be polarized the laser after modulation, play light signal to the rear and enter photodetector 9, light signal is converted to microwave signal by photodetector 9, and after ignoring optical frequency item, this tested microwave signal form is as follows:

U(t)＝U ₀cos(2πft+φ _L(t)+φ _S(t)+φ _M(t)) (1.2)

Wherein: U ₀for voltage magnitude, f=6.834GHz is the difference on the frequency of two bundle laser, φ _lt phase noise that () is light path, φ _st phase noise that () is microwave source, φ _mt () is modulation signal, modulation signal form is as follows:

${\mathrm{\&phi;}}_M\left(t\right)=\left\{\begin{array}{c}\mathrm{\&pi;}/2,\mathrm{kT}\&le;t<(k+1/2)T\\ 3\mathrm{\&pi;}/2,(k+1/2)T\&le;t<(k+1)t\end{array}\right.,k=\mathrm{0,1,2}...---\left(1.3\right)$

Wherein: T is the cycle of modulation signal;

For extracting φ _l(t) component, introduce with reference to microwave signal, by frequency mixer 11, tested microwave signal is carried out down-conversion, this reference microwave signal and tested microwave signal are produced by same microwave source, ignore with reference to the time delay between microwave signal and tested microwave signal, as follows with reference to microwave signal form:

U _R(t)＝U _Rcos[2πft+φ _S(t)] (1.4)

Wherein: U _rfor voltage magnitude, f=6.834GHz is the frequency with reference to microwave signal, φ _st phase noise that () is microwave source;

Tested microwave signal, after down-conversion, carries out filtering through low pass filter 12, can obtain tested microwave signal filtered versions as follows by (1.2) and (1.4):

$U\left(t\right)=\frac{1}{2}{U}_0{U}_R\cos [{\mathrm{\&phi;}}_L\left(t\right)-{\mathrm{\&phi;}}_M\left(t\right)]---\left(1.5\right)$

Known φ _m(t) be or so tested microwave signal can be reduced to:

$U\left(t\right)=\frac{1}{2}{U}_0{U}_R\sin {\mathrm{\&phi;}}_L\left(t\right)\sin {\mathrm{\&phi;}}_M\left(t\right)=\&PlusMinus;\frac{1}{2}{U}_0{U}_R\sin {\mathrm{\&phi;}}_L\left(t\right)---\left(1.6\right)$

Consider φ _lt () is the signal of a faint slow change, so tested microwave signal can be reduced to following form:

$U\left(t\right)=\&PlusMinus;\frac{1}{2}{U}_0{U}_R{\mathrm{\&phi;}}_L\left(t\right)---\left(1.7\right)$

In order to obtain φ _lt voltage signal that () is corresponding, analog to digital converter is utilized to be converted into digital signal, by FPGA, tested microwave signal is processed, recycling digital to analog converter is converted into analog voltage signal, in order to obtain enough power drive phase shifters, the power of low frequency amplifier to tested microwave signal is utilized to amplify, analog signal through power amplification exports phase signal corresponding with it as the input of phase shifter to control phase shifter, this phase signal is coupled into light path as feedback signal by acousto-optic modulator, the form obtained through the raman laser signal of closed loop feedback is as follows:

I(t)＝I ₀[1+cos(2πft+φ _S(t))] (1.8) 。

Claims (2)

1., based on a raman laser system phase noise autocompensation installation for closed loop feedback, comprise LASER Light Source, beam splitter, electrooptic modulator, acousto-optic modulator, bundling device, semi-transparent semi-reflecting lens, phase-modulator, the polarizer, photodetector, reactatron, frequency mixer, low pass filter, analog to digital converter, FPGA, digital to analog converter, low frequency amplifier, phase shifter;

The laser that LASER Light Source sends enters beam splitter, one end output of beam splitter is connected with the input of electrooptic modulator, other one end output of beam splitter is connected with the input of acousto-optic modulator, the output of electrooptic modulator and the output of acousto-optic modulator together input bundling device, the raman laser that bundling device exports enters semi-transparent semi-reflecting lens, semi-transparent semi-reflecting lens forms transmission laser and reflects laser, reflects laser enters phase-modulator, the output of phase-modulator is connected with the input of the polarizer, the Output of laser of the polarizer enters photodetector, the output of photodetector is connected with the input of reactatron, the output of reactatron is connected with the input of frequency mixer, the output of frequency mixer is connected with the input of low pass filter, the output of low pass filter is connected with the input of analog to digital converter, the output signal of analog to digital converter enters FPGA, the output signal of FPGA enters digital to analog converter, the output of digital to analog converter is connected with the input of low frequency amplifier, the output signal of low frequency amplifier enters phase shifter, the output of phase shifter is connected with the input of acousto-optic modulator.

2. the raman laser system phase noise automatic compensating method based on closed loop feedback, be specially: the laser that LASER Light Source exports is divided into two bundle laser through beam splitter, beam of laser is by electrooptic modulator shift frequency, another beam of laser is by acousto-optic modulator shift frequency, two bundle laser after shift frequency synthesize raman laser through bundling device, be provided with semi-transparent semi-reflecting lens at the output of raman laser system, fetching portion raman laser is as the input of closed loop feedback system, and raman laser signal is:

I(t)＝I ₀[1+cos(2πft+φ _L(t)+φ _S(t))] (1.1)

Wherein: I ₀for the amplitude of photoelectric current, f=6.834GHz is the difference on the frequency of two bundle laser, φ _lt phase noise that () is light path, φ _st phase noise that () is microwave source;

First carry out phase square wave modulation to raman laser, modulation makes the phase difference of two bundle laser to be or then be polarized the laser after modulation, play light signal to the rear and enter detector, light signal is converted to microwave signal by detector, ignores optical frequency item, and tested microwave signal is:

U(t)＝U ₀cos(2πft+φ _L(t)+φ _S(t)+φ _M(t)) (1.2)

Wherein: U ₀for voltage magnitude, f=6.834GHz is the difference on the frequency of two bundle laser, φ _lt phase noise that () is light path, φ _st phase noise that () is microwave source, φ _mt () is modulation signal, modulation signal is:

${\mathrm{\&phi;}}_M\left(t\right)=\left\{\begin{array}{c}\mathrm{\&pi;}/2,\mathrm{kT}\&le;t<(k+1/2)T\\ 3\mathrm{\&pi;}/2,(k+1/2)T\&le;t<(k+1)t\end{array}\right.,k=\mathrm{0,1,2}...\left(1.3\right)$

Wherein: T is the cycle of modulation signal;

Introduce with reference to microwave signal, by frequency mixer, tested microwave signal carried out down-conversion, produced by same microwave source with reference to microwave signal and tested microwave signal, ignore with reference to the time delay between microwave signal and tested microwave signal, with reference to microwave signal be:

U _R(t)＝U _Rcos[2πft+φ _S(t)] (1.4)

Wherein: U _rfor voltage magnitude, f=6.834GHz is the frequency with reference to microwave signal, φ _st phase noise that () is microwave source;

Tested microwave signal, after down-conversion, carries out filtering through low pass filter, obtains tested microwave signal filtered versions to be by (1.2) and (1.4):

$U\left(t\right)=\frac{1}{2}{U}_0{U}_R\cos [{\mathrm{\&phi;}}_L\left(t\right)-{\mathrm{\&phi;}}_M\left(t\right)]---\left(1.5\right)$

Known φ _m(t) be or tested microwave signal is reduced to:

$U\left(t\right)=\frac{1}{2}{U}_0{U}_R\sin {\mathrm{\&phi;}}_L\left(t\right)\sin {\mathrm{\&phi;}}_M\left(t\right)=\&PlusMinus;\frac{1}{2}{U}_0{U}_R\sin {\mathrm{\&phi;}}_L\left(t\right)---\left(1.6\right)$

Because φ _lt () is the signal of faint slow change, then tested microwave signal is reduced to:

$U\left(t\right)=\&PlusMinus;\frac{1}{2}{U}_0{U}_R{\mathrm{\&phi;}}_L\left(t\right)---\left(1.7\right)$

Utilize analog to digital converter by φ _lt () is converted to digital signal, by FPGA, tested microwave signal is processed, recycling digital to analog converter is converted into analog voltage signal, the power of low frequency amplifier to tested microwave signal is utilized to amplify, analog signal through power amplification exports phase signal corresponding with it as the input of phase shifter to control phase shifter, this phase signal is coupled into light path as feedback signal by acousto-optic modulator, and the form obtained through the raman laser signal of closed loop feedback is:

I(t)＝I ₀[1+cos(2πft+φ _S(t))] (1.8)

。