CN102680118B - A kind of measuring method of laser frequency stability and device - Google Patents

Abstract

The invention discloses a method and device for measuring the frequency stability of a laser. The method includes: selecting a radio frequency signal with a frequency of 0 for frequency calibration and setting a radio frequency signal with a sampling time τ of a frequency of ; calculating and reading the output of the laser The mapping relationship between frequency and time is obtained to obtain the mapping relationship between frequency and time of spectral hole burning; the radio frequency signal with the frequency is modulated onto the laser to be tested with the nominal frequency to form a modulated light signal with a carrier frequency of , measure the time t corresponding to the hole burning of the side frequency spectrum of the dimmed signal, obtain the side frequency frequency of the dimmed signal, and then obtain the i-th frequency drift within the sampling time τ; perform statistics on the frequency drift, The measurement of the frequency stability of the laser to be tested within the sampling time τ is realized. The invention solves the problem in the prior art that measuring the stability of the laser requires a reference light source with ultra-high stability and a small frequency difference with the laser to be measured.

Description

A method and device for measuring laser frequency stability

technical field

The invention relates to laser frequency stability measurement technology, in particular to a laser frequency stability measurement method and device.

Background technique

Laser is a kind of optical frequency electromagnetic wave, which has excellent coherence, is similar to radio waves, and is easy to modulate; in addition, laser has the advantages of high frequency, wide frequency bandwidth, large transmission information capacity, good directionality, and long transmission distance. , so it is an ideal light source for light to transmit information. It plays an increasingly important role in the fields of optical communication, optical information processing, and optical measurement. For example, precision interferometry uses the laser wavelength as a "ruler" and uses the interference principle of light to measure various physical quantities such as length, angle, displacement, and speed. Therefore, the accuracy of laser frequency will directly affect the accuracy of measurement. In laser communication, in order to improve its receiving sensitivity, coherent heterodyne receiving method is generally used, and the stability of its laser frequency will directly affect the quality of receiving. Therefore, it is particularly important to measure the laser frequency stability.

At present, the commonly used laser frequency stability measurement method is to beat the laser to be tested with a high-stability reference light source, and obtain the frequency of the light to be measured by measuring the beat frequency. This method requires that the frequency stability of the reference light source is higher than that of the laser to be tested. It is more than 2 orders of magnitude higher, which limits its application in measurement. In addition, due to the limitation of the response rate of the detector, this method cannot directly measure the frequency stability of the frequency difference between the reference light source and the laser to be measured at several GHz, and generally needs to be measured by sum frequency, difference frequency or parametric oscillation. Change the frequency of the laser to be tested. R.KrishnaMohan, T.Chang, M.Tian et al. published an article in JournalofLuminescence: Ultra-widebandspectralanalysisusingS2technology gave an ultra-wideband spectral analysis technology based on S2 crystal, but did not expand the specific application field of this technology. Merkel et al. provided a distance detection method based on crystal inhomogeneously broadened absorption spectrum in the invention patent of "MethodAndApparatusForProcessingHighTime-BandwidthSignalsUsingAMaterialWithInhomogeneouslyBroadenedAbsorptionSpectrum" on September 4, 2007, the application number is: US7265712B2, and the invention name is: . Both of the above two technologies involve signal processing technology based on non-uniformly broadened absorption spectrum of crystals, but this technology has not been extended to the field of laser frequency stability measurement.

Contents of the invention

The purpose of the present invention is to provide a method and device for measuring the frequency stability of lasers based on spectral hole burning, which overcomes the defects in the prior art that a high-stability reference light source is required for measuring the frequency stability of lasers and the frequency difference with the laser to be measured is small . The device of the invention is simple, and is beneficial to meet the requirement of measuring the frequency stability of the laser without a reference light source with high stability and small frequency difference with the laser to be measured.

The technical scheme of the present invention is: the present invention provides a kind of measuring method of laser frequency stability, and this method comprises:

Step 1: Selecting a radio frequency signal with a frequency of f _D for frequency calibration and a radio frequency signal with a frequency of f _RF for setting the sampling time τ;

Step 2: Calculate the mapping relationship f(t) between the output frequency and time of the reading laser, and obtain the mapping relationship f _h (t) between the frequency and time of spectral hole burning, wherein the reading laser refers to the laser used to generate chirped optical signals; The radio frequency signal whose frequency is f _RF is modulated onto the laser to be tested with the nominal frequency f _c to form a dimmed signal with a carrier frequency f _c (t), and the side frequency spectrum burning of the modulated signal is measured. The time t corresponding to the hole is obtained to obtain the edge frequency f _b (t) of the dimmed signal, and further obtain the i-th frequency drift Δf _{c (i)} within the sampling time τ;

Step 3: making statistics on the frequency drift Δf _c(i) to realize the measurement of the frequency stability of the laser to be tested within the sampling time τ.

Further, in step 1:

First select frequency as f _D frequency calibration radio frequency signal, carry out frequency calibration; then select frequency as the radio frequency signal of f _RF , set sampling time τ;

Further, in step 2:

According to the initial frequency _f of the read laser and the PZT tuning coefficient γ, the mapping relationship _f (t)= f ₀ +γu(t), set the f _h (t)=f(t) to obtain the frequency-time mapping relationship f _h (t) of the spectral hole burning, wherein the read laser is used to generate chirp Optical signal laser; measure the time tc _,1 and t corresponding to the spectral hole burning formed by the modulated light signal carrier and the first upper lobe within N cycles of the read laser chirp control signal u(t) _b,1 ... t _{c, i} , t _{b, i} ... t _c,2N , t _b,2N , i∈Z ⁺ ; according to the f _h (t), the corresponding spectral hole burning formed by the laser to be measured is obtained Frequency f _h (t _c,1 ), f _h (t _b,1 )…f _h (t _c,i ), f _h (t _b,i )…f _h (t _c2,N ), f _h (t _{b2, N} ; according to the relationship f _c (t _c ) of the carrier frequency f _c (t) of the dimmed signal, the first upper lobe frequency f _b (t) and the frequency f _h (t) corresponding to the spectral hole burning _,i )=f _h (t _c,i ), f _b (t _b,i )=f _h (t _b,i ), get f _c (t _c,1 ), f _b (t _b,1 )… f _c (t _c,i ), f _b (t _b,i )…f _c (t _c,2N ), f _b (t _b,2N ); according to the sampling time τ≈u of the output frequency of the laser to be tested ^-1 (U ₀ )-u ^-1 (U ₀ -f _RF /γ), and further obtain the i-th frequency drift within the sampling time τ Δf _c(i) = f _c (t _{c, 2i-1} ) -f _b (t _{b, 2i-1} )-f _RF ;

Further, in step 3:

The measurement of the frequency stability S _f (τ) of the laser to be tested within the sampling time τ is realized according to the Allan variance, $S_f\left(\mathrm{\τ}\right)=\frac{1}{f_c}\sqrt{\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\frac{{{\mathrm{\Δ\; f}}_{c\left(i\right)}}^2}{2}},$ Number of statistics N≥100;

The invention provides a measuring device for laser frequency stability, which device comprises:

The sampling time setting module is used to select the radio frequency signal that is used for frequency calibration and setting the frequency of sampling time τ as f _D and f _RF respectively;

The frequency drift extraction module is used to calculate the mapping relationship f(t) between the output frequency and time of the read laser, and obtain the mapping relationship f _h (t) between the frequency and time of spectral hole burning, where the read laser is used to generate chirp A laser of optical signal; the radio frequency signal whose frequency is f _RF is modulated onto the laser to be tested with the nominal frequency f _c to form a modulated light signal with a carrier frequency f _c (t), and the measured The time t corresponding to the hole burning of the side frequency spectrum of the dimming signal is obtained to obtain the side frequency frequency f _b (t) of the dimmed signal, and further obtain the frequency drift Δf _c within the sampling time τ;

The frequency stability calculation module is used to make statistics on the frequency drift Δf _c(i) , so as to realize the measurement of the frequency stability of the laser to be tested within the sampling time τ.

Further, the calibration and sampling time setting module is used to select a radio frequency signal with a frequency of f _D for frequency calibration and a radio frequency signal with a frequency of f _RF for setting the sampling time τ;

Further, the frequency drift extraction module includes:

The write light source module is used to generate a beam of light signals to be measured;

The signal input module is used to modulate the calibrated radio frequency signal or the radio frequency signal to the light signal to be measured generated by the writing light source module to form a calibrated dimmed signal or a dimmed signal;

A reading light source module, which includes an arbitrary signal generator and a reading laser; the reading light source module is used to generate a chirped optical signal to detect spectral hole burning;

An optical path module, which includes a half-wave plate, a polarizing beam splitter, and a convex lens; the optical path module and the material module are used to inject the calibrated dimmed signal or the modulated dimmed signal output by the signal input module into the rare earth doped crystal In addition, it is also used to divide a beam of chirped optical signals output by the reading light source module into two beams, wherein one beam of chirped optical signals is used to read out the spectral burnt signal of the calibrated dimmed signal or the modulated light signal. hole, another chirped optical signal is used to obtain the background absorption spectrum of the rare earth doped crystal. The light spot formed by the incident crystal of a beam of chirped optical signals used to read out the calibrated dimmed signal or the spectral hole burning of the modulated signal and the calibrated dimmed signal or the light spot formed by the incident crystal of the modulated light signal Consistent; the light spot formed by the incident crystal of a beam of chirped optical signals used to read the background absorption spectrum of the rare earth doped crystal is near the light spot formed by the calibrated dimmed signal or the incident crystal of the modulated light signal;

A signal output module, which includes a photodetector, a differential signal processor and an A/D sampler; the signal output module is used for the photodetector to detect two beams of light transmitted through the rare earth doped crystal and pass through the differential signal processor Perform differential processing, and finally obtain the calibrated dimmed signal or the spectral hole burnt at the frequency corresponding to the modulated dimmed signal on the A/D sampler.

Further, the frequency stability calculation module is configured to perform 100 statistics on the frequency drift amount within each sampling time, so as to realize the measurement of the frequency stability of the laser to be tested within the sampling time.

The beneficial effect of the present invention is: the selected frequency that is used for frequency calibration is the radio frequency signal of f _D and the frequency of setting sampling time τ is the radio frequency signal of f _RF ; Calculation reads the mapping relationship f(t of laser device output frequency and time ), to obtain the mapping relationship f _h (t) of the frequency and time of spectral hole burning, wherein the read laser refers to the laser used to generate the chirped optical signal; the radio frequency signal whose frequency is f _RF is modulated to the nominal On the laser to be tested with a frequency fc, a dimmed signal is formed, and the time _t corresponding to the hole burning of the side frequency spectrum of the dimmed signal is measured to obtain the side frequency frequency f _b (t) of the dimmed signal, and further obtain the obtained The i-th frequency drift Δf _c(i) within the sampling time τ; the frequency drift Δf _c(i) is counted to realize the measurement of the frequency stability of the laser to be tested within the sampling time τ. The present invention can directly obtain the frequency at the hole-burning part of the spectrum of the laser to be tested; solves the problem in the prior art that a high-stability reference light source is required for measuring the frequency stability of the laser and has a small frequency difference with the laser to be tested, and expands the frequency and frequency of the laser to be tested. The frequency difference range of the reference frequency improves the accuracy of laser frequency stability measurement.

Description of drawings

Fig. 1 is the schematic flow chart of the measurement method of laser frequency stability in the embodiment of the present invention;

FIG. 2 is a schematic flowchart of a method for extracting frequency drift in an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a measuring device for laser frequency stability provided by an embodiment of the present invention;

Fig. 4 is the device diagram of the frequency calibration and sampling time setting module provided by the embodiment of the present invention;

FIG. 5 is a schematic diagram of a frequency drift extraction structure provided by an embodiment of the present invention;

Fig. 6 is a device diagram of the writing light source module in the frequency drift amount extraction module provided by the embodiment of the present invention;

7 is a device diagram of a signal input module in a frequency drift extraction module provided by an embodiment of the present invention;

FIG. 8 is a device diagram of a reading light source module in the frequency drift amount extraction module provided by an embodiment of the present invention;

9 is a device diagram of an optical path module and a material module in the frequency drift extraction module provided by an embodiment of the present invention;

Fig. 10 is the processed calibrated dimming signal spectral hole burning obtained in the embodiment of the present invention;

Fig. 11 is the processed dimming signal spectral hole burning obtained in the embodiment of the present invention.

Among them, 10-frequency calibration and sampling time setting module: 100-radio frequency signal generator;

20-frequency drift extraction module: 210-write light source module, 2100-write laser; 220-signal input module, 2200-electro-optic phase modulator; 230-read light source module, 2300-arbitrary signal generator and 2301-read laser; 240-optical path module, 2400-half wave plate, 2401-polarization beam splitter and 2402-convex lens; 250-material module, 2500-rare earth doped crystal; 260-signal output module, 261-photodetector, 262-differential signal processor and 263-A/D sampler;

30-frequency stability calculation module: 002, 003, 005, 006, 007 and 008 are light beams; 001 and 004 are electrical signals.

Detailed ways

Specific embodiments of the present invention will be described below with reference to FIGS. 1-11 .

An embodiment of the present invention provides a method for measuring the frequency stability of a laser, as shown in FIG. 1 , which specifically includes the following steps:

Step 1, the selected frequency for frequency calibration is the radio frequency signal of f _D and the frequency of setting the sampling time τ is the radio frequency signal of f _RF ;

Wherein, the method of frequency calibration and sampling time setting in step 1 specifically comprises: first select the frequency to be the radio frequency signal of f _D frequency calibration, carry out frequency calibration; Then the radio frequency signal that the selected frequency is f _RF , set the sampling time τ;

Step 2, calculate the mapping relationship f(t) between the output frequency and time of the read laser, and obtain the mapping relationship f _h (t) between the frequency and time of spectral hole burning, wherein the read laser refers to the laser used to generate chirped optical signals; Modulate the radio frequency signal whose frequency is _fRF onto the laser to be tested with the nominal frequency fc to form a dimmed signal with a carrier frequency of fc _{( t} ), and measure the side frequency of the modulated signal The time t corresponding to the spectral hole burning is obtained to obtain the edge frequency f _b (t) of the dimmed signal, and further obtain the i-th frequency drift Δf _{c (i)} within the sampling time τ;

Wherein, as shown in Figure 2, the frequency drift extraction method in step 2 specifically includes the following steps:

Step 1, using a laser to be tested with a nominal frequency f _c to generate a beam of optical signals to be measured;

Step 2, judging whether it is used for frequency calibration, if so, then modulate the radio frequency signal with the selected frequency f _D onto the optical signal to be measured with the nominal frequency f _c generated by the writing light source module to form a calibration have been dimmed signal; otherwise, modulate the radio frequency signal that the selected frequency is f _RF to the optical signal to be measured that the nominal frequency f _c produced by described write light source module, form the carrier frequency that is f _c (t) Dimming signal;

Step 3, the read laser chirp read laser chirp control signal that the selected period is T and the amplitude is U ₀ is used to control the read laser to generate a bunch of chirp optical signals;

Step 4. Inject the calibrated dimmed signal or the modulated signal into the rare earth doped crystal through the control of the optical path, and divide the chirped optical signal into two beams at the same time, one of which is incident on the spot of the crystal Consistent with the calibrated dimmed signal or the spot of the incident crystal of the calibrated dimmed signal, it is used to read the spectral hole burning formed by the calibrated dimmed signal or the spectral hole burning formed by the calibrated dimmed signal; another Other places where the beam is incident on the crystal are used to obtain the background absorption spectrum of the rare earth-doped crystal;

Step 5. Use a photodetector to detect the two beams of light transmitted through the rare earth-doped crystal, and sample the signal output by the photodetector to obtain the spectral hole burning or Spectral hole burning formed by the dimmed signal;

Step 6. Determine whether it is used for frequency calibration. If so, measure and calibrate the optical carrier of the spectral hole burning formed by the dimmed signal, and the time t _c and t _b of the spectral hole burning formed by the first upper lobe, and then sequentially Execute step 7; otherwise, measure the time t _c and t _b of the optical carrier of the spectral hole-burning formed by the dimmed signal, and the first upper lobe where the spectral hole-burning is formed, and execute step 8;

Step 7. According to the frequency difference Δv=f _h at the frequency f _h (t _c ) at the spectral hole-burning position formed by the optical carrier and the frequency f _h (t _b ) at the spectral hole-burning position formed by the first upper lobe (t _c )-f _h (t _b )=-f _D , and the voltage difference Δu=u(t _c )-u(t _b ) at the place where the scanning optical carrier and the first upper lobe form a spectral hole burnt, calculate the Read the PZT tuning coefficient of the laser The initial frequency obtained under the action of the read laser chirp control signal u(t) is f ₀ the mapping relationship between the read laser output frequency and time f(t)=f ₀ +γu(t); make the f _h ( t)=f(t) to obtain the mapping relationship f _h (t) of the frequency and time of the spectral hole burning, and then return to step 1;

Step 8. Measure the times tc _,1 and tb _, corresponding to the spectral hole burning formed by the modulated signal carrier and the first upper lobe within N periods of the read laser chirp control signal u(t). ₁ ...t _c,i , t _b,i ...t _c,2N , t _b,2N , i∈Z ⁺ ;

Step 9. Obtain the frequency f _h (t _c,1 ), f _h (t _b,1 )...f _h (t _c,i ) corresponding to the spectral hole burning formed by the laser to be measured according to the f _h (t) ), f _h (t _b,i )...f _h (t _c,2N ), f _h (t _b,2N ); according to the carrier frequency f _c (t) of the dimmed signal, the first upper frequency f The relationship between _b (t) and the frequency f _h (t) corresponding to the spectral hole burning f _c (t _c,i )=f _h (t _c,i ), f _b (t _b,i )=f _h ( t _b,i ), get f _c (t _c,1 ), f _b (t _b,1 )…f _c (t _c,i ), f _b (t _b,i )…f _c (t _c,2N ), f _b (t _{b, 2N} ); according to the sampling time τ≈u ^-1 (U ₀ )-u ^-1 (U ₀ -f _RF /γ) of the output frequency of the laser to be measured, the sampling The i-th frequency drift within time τ Δf _c(i) = f _c (t _{c, 2i-1} )-f _b (t _{b, 2i-1} )-f _RF ;

Step 3, making statistics on the frequency drift Δf _c(i) to realize the measurement of the frequency stability of the laser to be tested within the sampling time τ.

Wherein, the method for measuring the frequency stability of the laser to be tested in step 3 specifically includes: realizing the measurement of the frequency stability S _f (τ) of the laser to be tested within the sampling time τ according to the Allan variance, $S_f\left(\mathrm{\τ}\right)=\frac{1}{f_c}\sqrt{\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\frac{{{\mathrm{\Δf}}_{c\left(i\right)}}^2}{2}},$ Statistical times N≥100.

The embodiment of the present invention provides a measuring device for laser frequency stability, as shown in Figure 3, the measuring device for laser frequency stability provided by the embodiment of the present invention includes: frequency calibration and sampling time setting module 10, frequency drift Quantity extraction module 20 and frequency stability calculation module 30.

Frequency calibration and sampling time setting module 10, the frequency that is used for the selected frequency calibration is the radio frequency signal of f _D and the frequency of setting sampling time τ is the radio frequency signal of f _RF ;

It should also be noted that: the specific device of the frequency calibration and sampling time setting module 10 is shown in Figure 4;

The frequency calibration and sampling time setting module 10 is used to generate the radio frequency signal 001;

The frequency drift extraction module 20 is connected with the frequency stability calculation module 30, and is used to extract the laser frequency drift, and specifically includes: a write light source module 210, a signal input module 220, a read light source module 230, an optical path module 240, a material module 250 and Signal output module 260, as shown in Figure 5;

Wherein, the writing light source module 210 is connected with the signal input module 220, and is used to generate a beam of optical signals to be measured by using the laser to be tested 211;

It should also be explained that: the specific device of the writing light source module 210 is shown in Figure 6;

The writing light source module 210 is used to form the optical signal 002 to be measured;

The signal input module 220 is connected with the writing light source module 210, and is used for modulating the calibration radio frequency signal or the radio frequency signal generated by the radio frequency signal generator 100 to the optical signal to be measured generated by the writing light source module 210 through the electro-optic phase modulator 221 to form Scaling the dimmed signal or the dimmed signal;

It should also be noted that: the specific device of the signal input module 220 is shown in Figure 7;

The signal input module 220 is used to form a scaled dimmed signal or a dimmed signal 003;

The electro-optical phase modulator 2200 modulates the calibrated radio frequency signal or the radio frequency signal generated by the radio frequency signal generator 100 on the optical signal 002 to be measured output by the laser to be tested 2100 to form a calibrated dimmed signal or a dimmed signal 003;

The reading light source module 230 is connected with the optical path module 240, and is used to generate a chirped optical signal to detect spectral hole burning;

It should also be noted that: the specific device of the reading light source module 230 is shown in Figure 8;

The reading light source module 230 specifically includes: an arbitrary signal generator 2300 and a reading laser 2301 for generating chirped optical signals;

The optical path module 240 is connected to the signal input module 220, the reading light source module 230, and the material module 250, and is used to inject the calibrated dimmed signal or the dimmed signal output by the signal input module 220 into the material module 250 through the optical path 241. The rare earth doped crystal 251 is also used to divide a beam of chirped optical signals output by the reading light source module 230 into two beams through the optical path 241, and the light spot formed by one beam of chirped optical signals entering the crystal 251 is aligned with the calibration. The light spot formed by the incident crystal of the optical signal or the dimmed signal is consistent; the light spot formed by the incident crystal of another beam of chirped optical signal is near the light spot formed by the incident crystal of the calibrated dimmed signal or the dimmed signal;

The material module 250 is connected with the optical circuit module 240 and the signal output module 260, and is used for forming in the rare earth doped crystal 251 when the calibrated dimmed signal or the dimmed signal output by the optical circuit module 240 enters the rare earth doped crystal 251 Scaling the spectral hole burning of the dimmed signal or the spectral hole burning of the dimmed signal; the light spot formed by a beam of chirped optical signal entering the crystal 251 and the calibration of the dimmed signal or the light spot formed by the incident crystal 251 of the dimmed signal consistent, used to read out the calibrated dimmed signal or the spectral hole burnt of the calibrated light signal; the light spot formed by the incident crystal 251 of another chirped optical signal The vicinity of the formed light spot is used to obtain the background absorption spectrum of the rare earth doped crystal 251;

It should also be noted that: the specific devices of the optical path module 240 and the material module 250 are shown in FIG. 9 ;

The optical path module 240 and the material module 250 specifically include a half-wave plate 2400, a polarizing beam splitter 2401, a convex lens 2402, and a rare earth-doped crystal 2500;

The calibrated dimming signal or the 003 dimming signal is focused to the rare earth doped crystal 2500 through 2402, and a spectral burning hole formed by the calibrated dimming signal or the 003 dimming signal is formed in the rare earth doped crystal 2500; chirp The optical signal 005 is divided into two beams by the half-wave plate 2400 and the polarization beam splitter 2401, respectively 007 and 008, wherein the beam 007 is used to read out the spectral hole burnt formed by the calibration dimmed signal or the modulated dimmed signal 003 , the beam 008 is used to obtain the background absorption spectrum of the rare earth doped crystal 2500 . The light spot formed by the beam 007 irradiating the crystal is consistent with the light spot formed by the calibrated dimming signal or the 003 incident crystal; near the spot;

The signal output module 260 is connected with the material module 250, and is used for the photodetector 261 to detect the two beams of light transmitted through the material module 250 to perform differential processing through the differential signal processor 262, and finally obtain the fixed value on the A/D sampling 263. Mark the dimmed signal or the spectral hole burning formed by the dimmed signal.

It should also be noted that: the specific device of the signal output module 260 includes a photodetector 261, a differential signal processor 262 and an A/D sampler 263; the photodetector detects the two beams of light 007 and 008, and perform differential signal processing on the signal output by the optical detector, and obtain the spectral hole burning of the optical signal on the A/D sampler 263 .

The frequency stability calculation module 30 is configured to make statistics on the frequency drift, so as to realize the measurement of the frequency stability of the laser to be tested within the sampling time.

The embodiment of the present invention takes the sampling time τ=3.1ms as an example to describe the present invention in detail:

The description of the instrument used in the embodiment of the present invention is shown in Table 1.

Table 1 Instructions for using the instrument

model Laser under test NEWFOCUS-TLB-6017 read laser NEWFOCUS-TLB-6017 electro-optic phase modulator EOSPACE-PM-5K1-20-PFA-830-UV-UL RF signal generator Agilent-E4447A Arbitrary Signal Generator Agilent-33250A crystal material Tm ³⁺ :YAG

The concrete steps of the example of the present invention:

1. First select the frequency f _D = 100MHz to calibrate the radio frequency signal, and perform frequency calibration; use the laser to be tested with the nominal frequency f _c to generate a beam of optical signals to be measured; use the radio frequency with the selected frequency f _D The signal is modulated onto the optical signal to be measured with a nominal frequency f _c generated by the write light source module to form a calibrated dimmed signal; the selected read laser with a cycle of T=200m and an amplitude of U ₀ =170mV The cosine chirped read laser chirp control signal is used to control the read laser to generate a bunch of chirped optical signals; the calibrated modulated optical signal is incident into the rare earth doped crystal through optical path control, and the chirped optical signal is divided into Two beams, one of which the chirped optical signal incident crystal spot is consistent with the calibrated dimmed signal incident crystal spot, used to read out the spectral hole burning formed by the calibrated dimmed signal; the other beam Other places of the incident crystal are used to obtain the background absorption spectrum of the rare earth-doped crystal; a photodetector is used to detect the two beams of light transmitted through the rare earth-doped crystal, and the output signal of the photodetector is Sampling to obtain the spectral hole burning formed by the calibrated dimming signal; measuring the optical carrier of the spectral hole burning formed by the calibrated dimming signal, and the time t _c and t _b at which the first upper lobe forms the spectral hole burning; According to the frequency difference Δv=-f _D between the frequency fc at the spectral hole-burning place formed by the optical carrier and the frequency _fc + _fD at the spectral hole-burning place formed by the first upper _lobe , and the formation of the scanning optical carrier and the first upper lobe The voltage difference at the burning hole of the spectrum Δu=U ₀ cos(10π·t _c )-U ₀ cos(10π·t _b ), calculate the PZT tuning coefficient of the read laser The initial frequency obtained under the action of the read laser chirp control signal u(t) is f ₀ the mapping relationship between the read laser output frequency and time f(t)=f ₀ +γu(t); make the f _h ( t)=f(t) obtains the mapping relationship f _h (t) of the frequency and time of the spectral hole burning, as shown in Figure 10 after the signal obtained from the experiment is processed;

2. Modulate the radio frequency signal with the selected frequency f _RF = 500MHz onto the optical signal to be measured with the nominal frequency f _c generated by the writing light source module to form a dimmed signal, and then set the sampling time τ≈u ^-1 (U ₀ )-u ^-1 (U ₀ -f _RF /γ)=3.1ms; measure the modulated light signal carrier within N periods of the read laser chirp control signal u(t), The time t _{c, 1} , t _{b, 1} ... t _{c, i} , t _{b, i} ... t _c,2N , t _{b, 2N} , i∈Z ⁺ corresponding to the spectral hole burning formed by the first upper lobe; f _h (t) Obtain the frequency f _h (t _{c, 1} ), f _h (t _{b, 1} ) ... f _h (t _{c, i} ), f _h (t _{b, i} )... f _h (t _{c, 2N} ), f _h (t _{b, 2N} ); according to the carrier frequency f _c (t) of the dimmed signal, the first upper side frequency f _b (t) and the The relationship f _c (t _c,i )=f _h (t _c,i ) and f _b (t _b,i )=f _h (t _b,i ) of the frequency f _h (t) corresponding to the above spectral hole burning, Get f _c (t _{c, 1} ), f _b (t _{b, 1} )... f _c (t _{c, i} ), f _b (t _{b, i} )... f _c (t _{c, 2N} ), f _b (t _{b, 2N} ); further obtain the i-th frequency drift Δf _c(i) = f _c (t _{c, 2i-1} )-f _b (t _{b, 2i-1} )-f _RF within the sampling time τ, The signal obtained from the experiment is processed as shown in Figure 11.

3. Realize the measurement of the frequency stability S _f (τ) of the laser to be tested within the sampling time τ according to the Allan variance, $S_f\left(\mathrm{\τ}\right)=\frac{1}{f_c}\sqrt{\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\frac{{{\mathrm{\Δf}}_{c\left(i\right)}}^2}{2}},$ Number of statistics N=100;

In the embodiment of the present invention, the laser frequency stability result S _f (τ)≈1.19×10 ⁻⁹ for the sampling time τ=3.1 ms.

Claims (7)

1. a method for measuring laser frequency stability, is characterized in that, the method comprises: Step 1: Selecting a radio frequency signal with a frequency of f _D for frequency calibration and a radio frequency signal with a frequency of f _RF for setting the sampling time τ; Step 2: Calculate the mapping relationship f(t) between the output frequency and time of the reading laser, and obtain the mapping relationship f _h (t) between the frequency and time of spectral hole burning, wherein the reading laser refers to the laser used to generate chirped optical signals; The radio frequency signal whose frequency is f _RF is modulated onto a laser to be tested with a nominal frequency f _c to form a modulated signal with a carrier frequency f _c (t), and the side frequency spectrum burn of the modulated signal is measured The time t corresponding to the hole is obtained to obtain the edge frequency f _b (t) of the dimmed signal, and further obtain the i-th frequency drift Δf _{c (i)} within the sampling time τ; Step 3: Perform statistics on the frequency drift Δf _c(i) to realize the measurement of the frequency stability of the laser to be tested within the sampling time τ. 2. measuring method as claimed in claim 1, it is characterized in that, in step 1: first selected frequency is _f frequency calibration radio frequency signal, carries out frequency calibration; Then selected frequency is the radio frequency signal of f _RF , set Set the sampling time τ. 3. measuring method as claimed in claim 1, it is characterized in that, in step 2: according to the starting frequency _f of reading laser and the PZT tuning coefficient γ, obtain the read laser chirp control signal u(t that amplitude is U ₀ ) under the action of the read laser output frequency and time mapping relationship f(t)=f ₀ +γu(t), let the f _h (t)=f(t) to obtain the frequency and The mapping relationship of time f _h (t), wherein the read laser refers to the laser used to generate the chirped optical signal; measure the modulated optical signal within N periods of the read laser chirp control signal u(t) Time t _c,1 , t _b,1 ...t _c,i , t _b,i ...t _c,2N , t _b,2N corresponding to the spectral hole burning formed by the carrier wave and the first upper lobe, i∈Z ⁺ ; According to the f _h (t), the frequencies f _h (t _c,1 ), f _h (t _b,1 )...f _h (t _c,i ), f h (t c,i ) corresponding to the spectral hole burning formed by the laser to be measured are obtained _h (t _b,i )...f _h (t _c,2N ), f _h (t _b,2N ); according to the carrier frequency f _c (t) of the dimmed signal, the first upper side lobe frequency f _b (t ) and the frequency f _h (t) corresponding to the spectral hole burning f _c (t _c,i )=f _h (t _c,i ), f _b (t _b,i )=f _h (t _{b, i} ), get f _c (t _c,1 ), f _b (t _b,1 )…f _c (t _c,i ), f _b (t _b,i )…f _c (t _c,2N ), f _b (t _b,2N ); according to the sampling time τ≈u ^-1 (U ₀ )-u ^-1 (U ₀ -f _RF /γ) of the output frequency of the laser to be measured, further obtain the The i-th frequency drift Δf _c(i) =f _c (t _c,2i-1 )-f _b (t _b,2i-1 )-f _RF . 4. measuring method as claimed in claim 1, it is characterized in that, in step 3: realize the measurement of the frequency stability S _f (τ) of the described laser to be measured in the described sampling time τ according to Allan variance, $S_f\left(\mathrm{\τ}\right)=\frac{1}{f_c}\sqrt{\frac{1}{N}\underset{i=1}{\overset{N}{\Σ}}\frac{{{\mathrm{\Δf}}_{c\left(i\right)}}^2}{2}},$ Statistical times N≥100. 5. A measuring device for laser frequency stability, characterized in that the device comprises: Frequency calibration and sampling time setting module (10), the frequency that is used for the selected frequency calibration is the radio frequency signal of f _D and the frequency of setting sampling time τ is the radio frequency signal of f _RF ; The frequency drift extraction module (20) is used to calculate the mapping relationship f(t) between the output frequency and time of the reading laser, and obtain the mapping relationship f _h (t) between the frequency and time of spectral hole burning, wherein the reading laser is used to A laser that generates a chirped optical signal; the radio frequency signal whose frequency is f _RF is modulated onto a laser to be tested with a nominal frequency f _c to form a modulated optical signal with a carrier frequency f _c (t), and the measurement of the The time t corresponding to the edge frequency spectrum of the dimmed signal is burned to obtain the edge frequency f _b (t) of the dimmed signal, and further obtain the i-th frequency drift Δf _{c (i)} within the sampling time τ; A frequency stability calculation module (30), configured to make statistics on the frequency drift Δf _c(i) , so as to realize the measurement of the frequency stability of the laser to be tested within the sampling time τ. 6. measuring device as claimed in claim 5, is characterized in that, described frequency drift extraction module (20) comprises: The writing light source module (210) is used to form and generate a beam of optical signals to be measured; The signal input module (220) is used to modulate the calibrated radio frequency signal or the radio frequency signal onto the light signal to be measured generated by the writing light source module to form a calibrated dimmed signal or a dimmed signal; A reading light source module (230), which includes an arbitrary signal generator (2300) and a reading laser (2301); the reading light source module (230) is used to generate a chirped optical signal (005) to detect spectral hole burning; An optical path module (240), which includes a half-wave plate (2400), a polarizing beam splitter (2401) and a convex lens (2402); the optical path module (240) and the material module (250) are used to input the signal into the module ( The calibrated dimmed signal or the dimmed signal output by 220) is incident into the rare earth doped crystal, and is also used to divide a beam of chirped optical signals output by the reading light source module (230) into two beams, wherein One beam of chirped optical signals is used to read out the calibration modulated signal or the spectral hole burning of the modulated signal, and the other beam of chirped optical signals is used to obtain the background absorption spectrum of rare earth doped crystals; The light spot formed by a beam of chirped optical signal entering the crystal of the calibrated dimmed signal or the spectral hole burning of the dimmed signal is consistent with the light spot formed by the calibrated dimmed signal or the incident crystal of the dimmed signal; The light spot formed by a chirped light signal entering the crystal to obtain the background absorption spectrum of the rare earth doped crystal is near the light spot formed by the calibration dimmed signal or the light spot formed by the incident crystal of the modulated light signal; A signal output module (260), which includes a photodetector (261), a differential signal processor (262) and an A/D sampler (263); the signal output module (260) is used for photodetector (261) detection The two beams of light transmitted through the rare earth-doped crystal are differentially processed by a differential signal processor (262), and finally the calibrated dimmed signal or the dimmed signal is obtained on the A/D sampler (263) Spectral hole burning at the corresponding frequency. 7. measuring device as claimed in claim 5, is characterized in that, described frequency stability calculating module (30) is used for carrying out 100 statistics of described frequency drift amount in each described sampling time, realizes described The measurement of the frequency stability of the laser to be tested within the sampling time.