CN106124032A - The digital measuring method of a kind of optical frequency modulators modulate delay and device - Google Patents

Abstract

The present invention relates to digital measuring method and device that a kind of optical frequency modulators modulate postpones, belong to technical field of electro-optical measurement.This device includes frequency stabilized carbon dioxide laser, polaroid, λ/2 wave plate, spectroscope, frequency shifter, reflecting mirror, tested smooth converting modulator, modulating signal source, reflecting mirror, semi-transparent semi-reflecting lens, polaroid 11, photodetector, digital oscilloscope, electronic computer.Measurand is the optical frequency signal time delay between the two after the excitation control signal of light converting modulator and regulation and control；Use heterodyne laser interferometric measuring means to obtain the laser frequency adjustment signal waveform of light converting modulator, and convert optical signals into the signal of telecommunication.The method can obtain good convergence, has higher accuracy of measurement, and carrier wave non-stationary and the violent situation of amplitude envelops change are had good adaptivity.

Description

Digital measurement method and device for modulation delay of optical frequency modulator

Technical Field

The invention relates to a digital measurement method and a digital measurement device for modulation delay of an optical frequency modulator, and belongs to the technical field of photoelectric measurement.

Background

The laser vibration measurer is a universal, basic vibration and impact measuring instrument, has high precision, no contact and no additional interference and influence on the measured object, and has measurement and calibration as the moving quantity value (displacement, speed and acceleration) and measurement principle based on laser Doppler effect. Usually, the measurement and calibration are carried out by exciting through a standard vibration table, measuring values by a standard laser vibration meter and measuring and calibrating other laser vibration meters, so that the frequency band is narrow, the accuracy is low and the tracing problem exists.

After the optical frequency modulator appears, the optical frequency modulator performs frequency regulation on measuring light emitted by the laser vibration meter by an optical frequency regulation technology and then feeds the measuring light back to the laser vibration meter, so that the problem of measurement and calibration of the laser vibration meter is solved. However, the problem of measuring the delay characteristic of the optical frequency modulator itself is not solved, and the greatest difficulty is that the control signal of the optical frequency modulator itself is a frequency modulation signal in which a radio frequency sine wave is a carrier wave and an audio frequency sine wave is a modulation waveform, a frequency modulation effect is generated on a passing optical frequency signal through a sound wave vibration mode and a light wave diffraction effect in the middle, and finally a frequency modulation result is generated on a passing laser signal, and the optical frequency modulator belongs to an optical, mechanical and electrical system integrating mechanical, electronic and optical effects, wherein the part needing to be accurately measured is the delay time of the modulation optical frequency signal on an excited electrical modulation signal. The response is not of the same physical magnitude as the stimulus.

How to evaluate the regulation response delay of the optical frequency modulator to the excitation optical frequency and the problem of magnitude traceability are the practical problems that the technology must face. The basic object of the present invention is to solve the problem of metering the modulation delay of the optical frequency modulator itself. Namely, the modulation delay of the optical frequency modulator is quantitatively measured, and the delay time of the output optical frequency signal relative to the input optical frequency modulation signal is quantitatively measured, so that a technical basis is provided for the measurement traceability of the demodulation delay time of the laser vibrometer.

In essence, the delay time of the sinusoidal vibration waveform demodulated and output by the laser vibration meter relative to the sinusoidal modulation signal of the analog vibration comprises three delay parts of demodulation delay of the laser vibration meter, modulation delay of the optical frequency modulator and electrical modulation delay in the sinusoidal frequency modulation process, and only the modulation delay of the optical frequency modulator and the demodulation delay of the laser vibration meter are difficult to separate in the delay time. The measurement range of the invention covers a wide delay range from nanosecond to second, and the delay measurement accuracy can be better than 0.1% magnitude.

Disclosure of Invention

The invention aims to provide a digital measurement method and a digital measurement device for modulation delay of an optical frequency modulator aiming at the problems of measurement and measurement calibration of the modulation delay time of the optical frequency modulator.

The core idea of the invention is as follows: dividing the laser generated by the frequency stabilized laser into two parts, one part is directly fed into the laser with the frequency f₀The carrier frequency of the (t) sine wave modulation of (a) is f_cAnd the other path of the laser light is subjected to frequency translation f by a frequency shifter_d>f_cThen combining the two divided laser beams to perform beat frequency interference; obtaining heterodyne frequency modulation signals y (t) shifted to a radio frequency range by a photoelectric detector, simultaneously carrying out waveform measurement on FM signals x (t) and heterodyne frequency modulation signals y (t) output by the photoelectric detector in a high-speed data acquisition mode, demodulating a sequence of modulation sine waves a (t) from a measurement sequence of the signals x (t) by a delay-free digital frequency demodulation method, demodulating an optical frequency response sequence b (t) of the modulation sine waves a (t) from the measurement sequence of the signals y (t), and finally obtaining the phase delay of the optical frequency response b (t) of a measured optical frequency modulator to the modulation signals a (t)Using the time difference t corresponding to the phase delay_abThe problem of measurement and calibration of delay time of a measured optical frequency modulator is solved; if the delay time difference is large, the modulation frequency f needs to be decreased₀So that t is_ab<1/f₀；

The non-delay digital frequency demodulation method is a non-delay digital demodulation algorithm based on sine wave four-parameter waveform fitting, and is used for demodulating the instantaneous frequency of an FM signal x (t), so that a modulated sine wave a (t) and an optical frequency response sequence b (t) are respectively obtained, the method can obtain good convergence, has high measurement accuracy, and can realize good self-adaption to non-stability of a carrier wave and severe amplitude envelope change;

the purpose of the invention is realized by the following technical scheme.

A digital measurement method and device for modulation delay of an optical frequency modulator comprises a measurement device for the optical frequency modulator and a digital measurement method for modulation delay of the optical frequency modulator;

the measuring device for the optical frequency modulator is called as the device for short, and comprises a frequency stabilized laser, a polaroid, a lambda/2 wave plate, a spectroscope, a frequency shifter, a reflector, a measured optical frequency modulator, a modulation signal source, a reflector, a semi-transparent semi-reflective mirror, a polaroid, a photoelectric detector, a digital oscilloscope and an electronic computer;

a digital measurement method for modulation delay of an optical frequency modulator is called as the method for short, and comprises the following steps:

1) the frequency stabilized laser emitted by the frequency stabilized laser is divided into two parts by the polaroid, the lambda/2 wave plate and the spectroscope, and one part is frequency-shifted f by the frequency shifter_dThen, the light beam passes through the reflector, passes through the semi-transparent semi-reflecting mirror to interfere with the other path of combined beam, and enters the photoelectric detector through the polarizing film to be received; the other path of the light beam passes through a reflector and is injected into a measured optical frequency modulator, is modulated by an FM signal x (t) output by a modulation signal source in the measured optical frequency modulator and then is output, is reflected by a semi-transparent mirror, then is subjected to beam combination interference with the previous path of laser, and is received by a photoelectric detector through a polarizing film; the signal output by the photodetector is a carrier frequency equal to the shift frequency f_dHeterodyne frequency modulated signal y (t);

the FM signal is a sine modulation signal and is expressed by a formula (1):

x(t)＝A_xcos(2π×f_x(t)×t+ψ_x)+D_x； (1)

wherein A is_xIs the amplitude of x (t)，f_xFrequency of x (t)_xIs the phase of x (t), D_xAn offset of x (t);

heterodyne fm signal y (t) is represented by equation (2):

y(t)＝A_ycos(2π×f_y(t)×t+ψ_y)+D_y； (2)

wherein A is_xIs the amplitude of x (t), f_xFrequency of x (t)_xIs the phase of x (t), D_xOffset of heterodyne frequency modulation signal y (t);

2) signals x (t) and y (t) are synchronously acquired by a digital oscilloscope to respectively obtain acquisition sequences x₁,x₂,…,x_nAnd y₁,y₂,…,y_n；

3) Respectively carrying out non-delay digital frequency demodulation on the acquisition sequences of the signals x (t) and y (t) output by the step 2) by an electronic computer according to a non-delay digital frequency demodulation method, and then respectively carrying out non-delay digital frequency demodulation on the acquisition sequences of y (t)_iThe frequency demodulation waveform sequence obtained (i ═ 1,2, …, n) is called a heterodyne frequency demodulation waveform sequence, and is recorded as:acquisition sequence x of x (t)_iThe frequency demodulation waveform sequence obtained (i ═ 1,2, …, n) is referred to as an FM frequency demodulation waveform sequence, and is written as:

in order to ensure that the water-soluble organic acid,

4) respectively carrying out least square waveform fitting on the FM frequency demodulation waveform sequence and the heterodyne frequency demodulation waveform sequence output by the step 3) by using a four-parameter sine wave fitting method, which specifically comprises the following steps:

4.1) using a four-parameter sine wave fitting method to the FM frequency demodulation waveform sequence a output by the 3)₁，a₂，…，a_MPerforming least square waveform fitting, wherein the functional expression of the waveform least square fitting curve is shown as the following formula (3):

wherein A is_aIs the fitted sinusoidal waveform amplitude;fitting the sine wave frequency; phi is a_aFitting the initial phase of the sine waveform; d_aFitting a sine waveform direct current component; is called a (t)_i) FM fitting result, wherein pi is circumferential rate;

the fitted residual root mean square value of the FM frequency demodulation waveform sequence is shown in formula (4):

${\mathrm{\&rho;}}_a=\sqrt{\frac{1}{M}\underset{i=1}{\overset{M}{\&Sigma;}}{\left(a\right(t_i)-a_i)}^2}---\left(4\right)$

ρ_afitting residual root mean square values of the FM frequency demodulation waveform sequence;

4.2) demodulating waveform sequence b to heterodyne frequency by using four-parameter sine wave fitting method₁，b₂，…，b_MPerforming least square waveform fitting, wherein the functional expression of a waveform least square fitting curve is shown as the formula (5):

wherein A is_bA sinusoidal waveform amplitude fitted for a heterodyne frequency demodulation waveform sequence;fitting a sine wave frequency for the heterodyne frequency demodulation waveform sequence;a sinusoidal waveform initial phase fitted for a heterodyne frequency demodulation waveform sequence; d_bFitting a sine waveform direct current component; b (t)_i) Is the heterodyne fitting result;

the residual root mean square value of the heterodyne frequency demodulation waveform sequence fitting is as follows:

${\mathrm{\&rho;}}_b=\sqrt{\frac{1}{M}\underset{i=1}{\overset{M}{\&Sigma;}}{\left(b\right(t_i)-b_i)}^2}---\left(6\right)$

where ρ is_bA residual root mean square value fitted for the heterodyne frequency demodulation waveform sequence;

5) calculating the trigger delay to be measured and the corresponding phase difference according to the result in the step 4);

wherein, the trigger delay to be measured is marked as tau; the phase difference corresponding to the trigger delay to be measured is recorded asSpecifically, it is calculated by formula (7):

to this end, from 1) to 5), the measurement process of the delay time τ of the optical frequency modulator under test is completed, i.e.

A digital measurement method for modulation delay of an optical frequency modulator;

3) the delay-free digital frequency demodulation method comprises the following specific steps:

a. setting the sequence length n and the sampling rate v of the acquired waveform according to the carrier frequency of the detected signal; setting a principle to ensure that more than 20 sampling points are required in each carrier waveform period; limiting the lower limit value of n to 10000; wherein, the detected signal is a frequency modulation signal waveform y (t);

b. collecting the measured signal in a to obtain the number of the waveform y (t) of the frequency-modulated signalAccording to the collection sequence, record as: y is_iI is 1,2, …, n, where i represents the number of sampling points in the synchronous sampling sequence;

b. acquiring the detected signal in the step a to obtain a data acquisition sequence of a frequency modulation signal waveform y (t), and recording the data acquisition sequence as: y is_iI is 1,2, …, n, where i represents the number of sampling points in the synchronous sampling sequence;

c. in the waveform acquisition sequence y_iThe leading edge intercepts a segment of the waveform less than one carrier period, noted as: y is_i，i＝1,2,…,m₁；

Performing sine fitting on the sequence of the waveform segment of the frequency modulation signal output by the step c) by using an electronic computer according to the process of the step 4) to obtain the instantaneous frequency f of the fitted sine wave₁The method specifically comprises the following steps:

c.1 assuming that the measured waveform of the intercepted waveform segment is approximate to a sine wave with a waveform of

y_s(t)＝A_ysin(2πf_yt+ψ_y)+D_y(8)

Wherein, y_s(t) measured waveform of the intercepted waveform segment, A_yAmplitude of a sine wave, f_yIs the frequency, ψ, of a sine wave_yIs the initial phase of a sine wave, D_yAmplitude deviation of the measured waveform of the intercepted waveform segment;

a waveform segment of less than one carrier cycle is truncated at the leading edge of the waveform acquisition sequence,

$y_s^i=y_s\left(t_i\right)=y_s\left(\right(i-1)\&CenterDot;\mathrm{\&Delta;}\mathrm{\&tau;}),i=1,2,...,m_1---\left(9\right)$

wherein, the sampling time interval delta tau is 1/v;

c.2 computer Pair acquisition sequencePerforming four-parameter fitting on a sine waveform to obtain a fitting signal:

wherein, y_s(i) In order to fit the signal to the signal,in order to fit the amplitude of the sine wave,in order to fit the angular frequency of the sine wave,to fit the initial phase of the sine wave,fitting the direct current component value of the sine wave;

fitting frequencyComprises the following steps:

${\hat{f}}_1=\frac{{\widehat{\mathrm{\&omega;}}}_1\&CenterDot;v}{2\mathrm{\&pi;}}---\left(11\right)$

the frequency isIs a point (1+ m)₁) Instantaneous frequency demodulation results at/2;

c.3, fitting four parameters of a sine waveform, specifically:

assuming that the sine wave frequency target value to be estimated is f₀，ω₀＝2πf₀V, the number of signals contained in the sine wave sampling sequence to be estimated is p (0) and is less than one period<p<1) The occupied time length of the waveform is tau; then, f₀1/τ, another factor q is chosen (e.g. q 1 × 10^-5) So that the estimated sinusoidal frequency f₀>q/τ; thus, f₀∈[q/τ,2/τ]The specific process is as follows:

c3.⑴ sets the fitting iteration stop condition to h_e；

h_eHas a value range of 1 × 10^-18To 1 × 10^-20xx; preferred is h_eIs 1 × 10^-20；

c3.⑵ from a known time t₁,t₂,...,t_m1Sine wave acquisition sample y₁,y₂,...,y_m1. The signal waveform obtained by the point counting method occupies a time length of tau (m)₁-1)/v, selecting a factor q (e.g. q 1 × 10^-5) Determining the target frequency f₀Existence interval of [ q/τ,2/τ ]]；

c3.⑶ determining an iteration left boundary frequency f_L＝q/τ；ω_L＝2πf_LV,/v; iteration right boundary frequency: f. of_R＝2/τ；ω_R＝2πf_R/v；

c3.⑷ indicates the median frequency ω_M＝(ω_R+ω_L) 2; calculating respective fitting residual errors rho (omega) on the left boundary frequency, the right boundary frequency and the median frequency by using a three-parameter fitting formula_L)、ρ(ω_M) And ρ (ω)_R)；

c3, ⑸ judges whether rho (omega) is present or not_L)<η·ρ(ω_M) Wherein η is a criterion factor, and the value range is 1-1.5;

if ρ (ω)_L)<η·ρ(ω_M) Then let ω be_R＝ρ(ω_M)，ω_LRepeatedly executing ⑷ - ⑸ processes without changing;

c3, ⑹ rho (omega)_L)≥η·ρ(ω_M) Then there must be ω_R<2ω₀Determining the left boundary frequency of the iteration as omega_L(ii) a Iterative right boundary frequency omega_R(ii) a The median frequency was chosen according to the preferred method: omega_M＝ω_L+0.618×(ω_R-ω_L)

And ω_T＝ω_R-0.618×(ω_R-ω_L)；

c3, ⑺ at ω_LPerforming three-parameter sine curve fitting to obtain A_L、D_L、ρ_L(ii) a At omega_RPerforming three-parameter sine curve fitting to obtain A_R、D_R、ρ_R(ii) a At omega_MPerforming three-parameter sine curve fitting to obtain A_M、D_M、ρ_M(ii) a At omega_TPerforming three-parameter sine curve fitting to obtain A_T、D_T、ρ_T；

c3, ⑻ F_M<ρ_TThen ρ is ρ_MHas omega₀∈[ω_T,ω_R]，ω_L＝ω_T，ω_T＝ω_M；ω_M＝ω_L+0.618×(ω_R-ω_L) (ii) a If ρ_M>ρ_TThen ρ is ρ_THas omega₀∈[ω_L,ω_M]，ω_R＝ω_M，ω_M＝ω_T；ω_T＝ω_R-0.618×(ω_R-ω_L)；

c3.⑼ determines if (| (ρ |)_M(k)-ρ_T(k))/ρ_T(k)|＜h_eIf yes, the iteration is stopped, and ρ is ρ_TThen, obtaining the parameter of the four-parameter fitting sine curve as A ═ A_T、ω＝ω_T、D＝D_TRho, finishing the fitting process; ρ ═ ρ_MThen, obtaining the parameter of the four-parameter fitting sine curve as A ═ A_M、ω＝ω_M、D＝D_MAnd rho, finishing the fitting process, otherwise, repeating the processes of c3, ⑺ -c 3 and ⑼;

d. storing instantaneous frequency parameters of an output sinusoidal modelIs the frequency of the measured sinusoidal model;

e. to be less thanCycle length (e.g. of) The corresponding sequence time length is the length m of the next fitting sequence₂Sequence center position from m₁Moving a sampling point backwards at position/2, executing the processes c and d on a new data segment, and obtaining the instantaneous frequency of the output sinusoidal model

Repeatedly executing the sliding fitting process until the end point of the data sequence;

obtaining a frequency demodulation waveform sequence:a demodulated waveform output for signal waveform y (t);

to this end, from a to e, the delay-free digital frequency demodulation method is completed.

Advantageous effects

Compared with other optical frequency modulator measuring methods and devices, the optical frequency modulator delay time measuring method and device provided by the invention have the following beneficial effects:

1. the method and the device for measuring the delay time of the optical frequency modulator provided by the invention use a heterodyne laser interference measuring device to obtain the waveform of an output signal of the measured optical frequency modulator, and simultaneously carry out waveform measurement on a modulation signal x (t) of the measured optical frequency modulator and an output signal y (t) of the measured optical frequency modulator in a high-speed data acquisition mode, thereby realizing the measurement and comparison of optical quantity values aiming at the time delay among different physical quantity values of electrical quantity values;

2. the method and the device for measuring the delay time of the optical frequency modulator provided by the invention adopt a non-delay digital frequency demodulation mode, demodulate a sequence of a modulation sine wave a (t) from a measurement sequence of a signal x (t), demodulate an optical frequency response sequence b (t) of the modulation sine wave a (t) from the measurement sequence of a signal y (t), and finally obtain the optical frequency response b (t) of the measured optical frequency modulator for the phase delay of the modulation signal a (t)Higher measurement accuracy is obtained compared with other hardware demodulation methods, no extra demodulation delay error is introduced, and finally the time difference t corresponding to the phase delay is used_abThe problem of measurement and calibration of delay time of a measured optical frequency modulator is solved;

3. the method and the device for measuring the delay time of the optical frequency modulator acquire a signal waveform sequence by means of high-speed data acquisition and quantization technology, use a model section less than one carrier period to carry out delay-free digital frequency demodulation on the signal waveform, have higher time resolution and minimum filtering effect, and further can realize the accurate demodulation of instantaneous frequency on the waveform of a laser frequency modulation signal x (t) and an output signal y (t) of the measured optical frequency modulator, thereby solving the problems of accurate measurement of the delay time of the measured optical frequency modulator and magnitude tracing;

4. the method for measuring the delay time of the optical frequency modulator uses a least square optimal estimation mode, so that the method has high measurement accuracy, high model demodulation resolution and high demodulation efficiency;

5. the method and the device for measuring the delay time of the optical frequency modulator demodulate the frequency modulation signal in a sliding model mode, have high time resolution, absolutely convergent algorithm and good adaptivity to non-stationary waveforms, and can conveniently carry out traceability calibration.

Drawings

FIG. 1 is a schematic diagram of an apparatus and method for measuring delay time of an optical frequency modulator according to the present invention;

reference numbers in fig. 1: 1-frequency stabilized laser, 2-polaroid, 3-lambda/2 wave plate, 4-spectroscope, 5-frequency shifter, 6-reflector, 7-measured optical frequency modulator, 8-modulation signal source, 9-reflector, 10-semi-transparent semi-reflector, 11-polaroid, 12-photoelectric detector, 13-digital oscilloscope and 14-electronic computer.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Examples

The structure of the measuring method and the device of the optical frequency modulator is shown in figure 1, and the measuring method and the device comprise a frequency stabilized laser 1, a polaroid 2, a lambda/2 wave plate 3, a spectroscope 4, a frequency shifter 5, a reflector 6, a measured optical frequency modulator 7, a modulation signal source 8, a reflector 9, a half-transmitting and half-reflecting mirror 10, a polaroid 11, a photoelectric detector 12, a digital oscilloscope 13 and an electronic computer 14.

Specifically, in this embodiment:

firstly, the frequency stabilized laser emitted by the frequency stabilized laser 1 is divided into two parts by the polaroid 2, the lambda/2 wave plate 3 and the spectroscope 4, and one part is frequency-shifted f by the frequency shifter 5_dThen, the beam passes through the reflector 9, the semi-transparent semi-reflecting mirror 10 to interfere with the other path of combined beam, and enters the photoelectric detector 12 through the polarizing plate 11 to be received; the other path is injected into a measured optical frequency modulator 7 through a reflecting mirror 6, and the measured optical frequency modulator 7 is modulated by a sine wave output from a modulation signal source 8FM signal x (t) ═ a_xcos(2π×f_x(t)×t+ψ_x)+D_xThe modulated output is reflected by the half mirror 10, interferes with the previous laser beam, and is received by the photodetector 12 through the polarizer 11. The signal output by photodetector 12 is at a carrier frequency equal to the shift frequency f_dFrequency modulation signal y (t) a_ycos(2π×f_y(t)×t+ψ_y)+D_y；

Secondly, signals x (t) and y (t) are synchronously acquired by a digital oscilloscope 13 to respectively obtain acquisition sequences x₁,x₂,…,x_nAnd y₁,y₂,…,y_n；

Thirdly, after the computer 14 adopts the non-delay digital frequency demodulation algorithm to respectively carry out the non-delay digital frequency demodulation on x (t) and y (t), the waveform y (t) of the wave form is measured_i(i ═ 1,2, …, n) of the obtained frequency demodulation waveform sequence:the waveform x (t) of which is a measurement sequence x_i(i ═ 1,2, …, n) of the obtained frequency demodulation waveform sequence:

then the process of the first step is carried out,

fourthly, the sine wave sequence a is adjusted by a four-parameter sine wave fitting method₁,a₂,…,a_MAnd performing least square waveform fitting, wherein the function expression of a waveform least square fitting curve is as follows:

the fitted residual root mean square value is:

${\mathrm{\&rho;}}_a=\sqrt{\frac{1}{M}\underset{i=1}{\overset{M}{\&Sigma;}}{\left(a\right(t_i)-a_i)}^2}---\left(\right(13)$

wherein A is_aFitting the amplitude of the sine waveform;fitting the sine wave frequency; phi is a_aFitting the initial phase of the sine waveform; d_aFitting a sine waveform direct current component; rho_aFitting residual root mean square values;

using four-parameter sine wave fitting method to align sine wave sequence b₁,b₂,…,b_MAnd performing least square waveform fitting, wherein the function expression of a waveform least square fitting curve is as follows:

the fitted residual root mean square value is:

${\mathrm{\&rho;}}_b=\sqrt{\frac{1}{M}\underset{i=1}{\overset{M}{\&Sigma;}}{\left(b\right(t_i)-b_i)}^2}---\left(15\right)$

wherein A is_bFitting the amplitude of the sine waveform;fitting the sine wave frequency; phi is a_bFitting the initial phase of the sine waveform; d_bFitting a sine waveform direct current component; rho_bFitting residual root mean square values;

fifthly, the phase difference phi corresponding to the trigger delay tau to be measured_abCan be expressed as:

thereby completing the measurement process of the delay time tau of the measured optical frequency modulator;

the delay-free digital frequency demodulation algorithm comprises the following steps:

A. setting the sequence length n and the sampling rate v of the acquired waveform according to the carrier frequency of the detected signal; the rule is set to ensure that there are more than 20 samples per carrier waveform period. Limiting the lower limit value of n to 10000;

B. the data acquisition sequence of the frequency modulation signal waveform is as follows: y is_iI is 1,2, …, n, where i represents the number of sampling points in the synchronous sampling sequence;

C. intercepting a waveform segment, y, of less than one carrier period at the leading edge of a waveform acquisition sequence_i，i＝1,2,…,m₁

Using computer to make sine fitting on the waveform segment sequence of the modulated signal according to the process described in c.3 to obtain instantaneous frequency f of fitted sine wave₁The method specifically comprises the following steps:

c.1 supposing that the measured waveform of the intercepted waveform segment is approximate to a sine wave, and the waveform is

y(t)＝A_ysin(2πf_yt+ψ_y)+D_y(17)

Wherein A is_yAmplitude of a sine wave, f_yIs the frequency, ψ, of a sine wave_yIs the initial phase of the sine wave;

intercepting a waveform segment, y, of less than one carrier period at the leading edge of a waveform acquisition sequence_i，i＝1,2,…,m₁

y_i＝y(t_i)＝y((i-1)·Δτ)，i＝1,2,…,m₁(18)

Wherein, the sampling time interval delta tau is 1/v;

c.2 computer-to-acquisition sequence y_i，(i＝1,2,…,m₁) And performing four-parameter fitting on the sine waveform to obtain a fitting signal:

wherein,in order to fit the amplitude of the sine wave,in order to fit the angular frequency of the sine wave,to fit the initial phase of the sine wave,fitting the direct current component value of the sine wave;

fitting frequencyComprises the following steps:

${\hat{f}}_1=\frac{{\widehat{\mathrm{\&omega;}}}_1\&CenterDot;v}{2\mathrm{\&pi;}}---\left(20\right)$

the frequency isAs point (1+ m)₁) Instantaneous frequency demodulation results at/2;

c.3 sine waveform four-parameter fitting process

Assuming that the sine wave frequency target value to be estimated is f₀，ω₀＝2πf₀V, the number of signals contained in the sine wave sampling sequence to be estimated is p (0) and is less than one period<p<1) The occupied time length of the waveform is tau; then, f₀1/τ, another factor q is chosen (e.g. q 1 × 10^-5) So that the estimated sinusoidal frequency f₀>q/τ; thus, f₀∈[q/τ,2/τ]The method comprises the following steps:

⑴ setting fitting iteration stop condition as h_e(ii) a (optionally h)_e＝1×10^-20)

⑵ from a known time t₁,t₂,...,t_m1Sine wave acquisition sample y₁,y₂,...,y_m1(ii) a The signal waveform obtained by the point counting method occupies a time length of tau (m)₁-1)/v, selecting a factor q (e.g. q 1 × 10^-5) Determining the target frequency f₀Existence interval of [ q/τ,2/τ ]]；

⑶ determining an iteration left boundary frequency f_L＝q/τ；ω_L＝2πf_LV,/v; iteration right boundary frequency: f. of_R＝2/τ；ω_R＝2πf_R/v；

⑷ order the median frequency ω_M＝(ω_R+ω_L) 2; calculating respective fitting residual errors rho (omega) on the left boundary frequency, the right boundary frequency and the median frequency by using a three-parameter fitting formula_L)、ρ(ω_M) And ρ (ω)_R)；

⑸ judges whether or not ρ (ω) is present_L)<η·ρ(ω_M) Wherein η is a criterion factor, and the value range is 1-1.5;

if ρ (ω)_L)<η·ρ(ω_M) Then let ω be_R＝ρ(ω_M)，ω_LRepeatedly executing ⑷ - ⑸ processes without changing;

⑹ if ρ (ω)_L)≥η·ρ(ω_M) Then there must be ω_R<2ω₀Determining the left boundary frequency of the iteration as omega_L(ii) a Iterative right boundary frequency omega_R(ii) a The median frequency was chosen according to the preferred method: omega_M＝ω_L+0.618×(ω_R-ω_L) And ω_T＝ω_R-0.618×(ω_R-ω_L)；

⑺ at omega_LPerforming three-parameter sine curve fitting to obtain A_L、D_L、ρ_L(ii) a At omega_RPerforming three-parameter sine curve fitting to obtain A_R、D_R、ρ_R(ii) a At omega_MPerforming three-parameter sine curve fitting to obtain A_M、D_M、ρ_M(ii) a At omega_TPerforming three-parameter sine curve fitting to obtain A_T、D_T、ρ_T；

⑻ if ρ_M<ρ_TThen ρ is ρ_MHas omega₀∈[ω_T,ω_R]，ω_L＝ω_T，ω_T＝ω_M；ω_M＝ω_L+0.618×(ω_R-ω_L) (ii) a If ρ_M>ρ_TThen ρ is ρ_THas omega₀∈[ω_L,ω_M]，ω_R＝ω_M，ω_M＝ω_T；ω_T＝ω_R-0.618×(ω_R-ω_L)；

⑼ judges whether or not | (ρ |)_M(k)-ρ_T(k))/ρ_T(k)|＜h_eIf yes, the iteration is stopped, and ρ is ρ_TThen, obtaining the parameter of the four-parameter fitting sine curve as A ═ A_T、ω＝ω_T、D＝D_TRho, finishing the fitting process; ρ ═ ρ_MThen, obtaining the parameter of the four-parameter fitting sine curve as A ═ A_M、ω＝ω_M、D＝D_MRho, finishing the fitting process, otherwise, repeating the process from ⑺ to ⑼;

d. storing instantaneous frequency parameters of an output sinusoidal modelIs the frequency of the measured sinusoidal model;

e. to be less thanCycle length (e.g. of) The corresponding sequence time length is the length m of the next fitting sequence₂Sequence center position from m₁Moving a sampling point backwards at position/2, executing the processes c and d on a new data segment, and obtaining the instantaneous frequency of the output sinusoidal model

Repeatedly executing the sliding fitting process until the end point of the data sequence;

obtaining a frequency demodulation waveform sequence:is the demodulated waveform output of signal waveform y (t).

While the foregoing is directed to the preferred embodiment of the present invention, it is not intended that the invention be limited to the embodiment and the drawings disclosed herein. Equivalents and modifications may be made without departing from the spirit of the disclosure and the scope of the invention.

Claims (8)

1. A digital measurement method and device for modulation delay of an optical frequency modulator are characterized in that:

the core idea is as follows: dividing the laser generated by the frequency stabilized laser into two parts, one part is directly fed into the laser with the frequency f₀The carrier frequency of the (t) sine wave modulation of (a) is f_cAnd the other path of the laser light is subjected to frequency translation f by a frequency shifter_d>f_cThen combining the two divided laser beams to perform beat frequency interference; obtaining the frequency shift by a photodetectorA heterodyne frequency modulation signal y (t) reaching a radio frequency range, a waveform measurement is simultaneously carried out on an FM signal x (t) and the heterodyne frequency modulation signal y (t) output by a photoelectric detector in a high-speed data acquisition mode, a sequence of a modulation sine wave a (t) is demodulated from a measurement sequence of the signal x (t) by a delay-free digital frequency demodulation method, an optical frequency response sequence b (t) of the modulation sine wave a (t) is demodulated from the measurement sequence of the signal y (t), and finally the optical frequency response b (t) of a measured optical frequency modulator is obtained, wherein the phase delay of the optical frequency response b (t) to the modulation signal a (t)Using the time difference t corresponding to the phase delay_abThe problem of measurement and calibration of delay time of a measured optical frequency modulator is solved; if the delay time difference is large, the modulation frequency f needs to be decreased₀So that t is_ab<1/f₀。

2. The method and apparatus of claim 1 for digitally measuring the modulation delay of an optical frequency modulator, further characterized by:

the non-delay digital frequency demodulation method is a non-delay digital demodulation algorithm based on sine wave four-parameter waveform fitting to demodulate the instantaneous frequency of an FM signal x (t), so that a modulated sine wave a (t) and an optical frequency response sequence b (t) are obtained respectively.

3. The method and apparatus of claim 1 for digitally measuring the modulation delay of an optical frequency modulator, further characterized by:

the device comprises a measuring device of an optical frequency modulator and a digital measuring method of modulation delay of the optical frequency modulator;

the measuring device for the optical frequency modulator is called as the device for short, and comprises a frequency stabilized laser, a polaroid, a lambda/2 wave plate, a spectroscope, a frequency shifter, a reflector, a measured optical frequency modulator, a modulation signal source, a reflector, a semi-transparent semi-reflective mirror, a polaroid, a photoelectric detector, a digital oscilloscope and an electronic computer.

4. A method and apparatus for digitally measuring the modulation delay of an optical frequency modulator as claimed in claim 3, further characterized by:

a digital measurement method for modulation delay of an optical frequency modulator is called as the method for short, and comprises the following steps:

1) the frequency stabilized laser emitted by the frequency stabilized laser is divided into two parts by the polaroid, the lambda/2 wave plate and the spectroscope, and one part is frequency-shifted f by the frequency shifter_dThen, the light beam passes through the reflector, passes through the semi-transparent semi-reflecting mirror to interfere with the other path of combined beam, and enters the photoelectric detector through the polarizing film to be received; the other path of the light beam passes through a reflector and is injected into a measured optical frequency modulator, is modulated by an FM signal x (t) output by a modulation signal source in the measured optical frequency modulator and then is output, is reflected by a semi-transparent mirror, then is subjected to beam combination interference with the previous path of laser, and is received by a photoelectric detector through a polarizing film; the signal output by the photodetector is a carrier frequency equal to the shift frequency f_dHeterodyne frequency modulated signal y (t);

2) signals x (t) and y (t) are synchronously acquired by a digital oscilloscope to respectively obtain acquisition sequences x₁,x₂,…,x_nAnd y₁,y₂,…,y_n；

3) Respectively carrying out non-delay digital frequency demodulation on the acquisition sequences of the signals x (t) and y (t) output by the step 2) by an electronic computer according to a non-delay digital frequency demodulation method, and then respectively carrying out non-delay digital frequency demodulation on the acquisition sequences of y (t)_iThe frequency demodulation waveform sequence obtained (i ═ 1,2, …, n) is called a heterodyne frequency demodulation waveform sequence, and is recorded as:acquisition sequence x of x (t)_iThe frequency demodulation waveform sequence obtained (i ═ 1,2, …, n) is referred to as an FM frequency demodulation waveform sequence, and is written as:

in order to ensure that the water-soluble organic acid,

4) performing least square waveform fitting on the FM frequency demodulation waveform sequence and the heterodyne frequency demodulation waveform sequence output by the step 3) by using a four-parameter sine wave fitting method respectively;

5) calculating the trigger delay to be measured and the corresponding phase difference according to the result in the step 4);

so far, from 1) to 5), the measurement process of the delay time τ of the optical frequency modulator to be measured is completed, i.e., a digital measurement method of the modulation delay of the optical frequency modulator.

5. A method of digitally measuring the modulation delay of an optical frequency modulator as claimed in claim 4, further characterized by:

1) the FM signal is a sine modulation signal and is expressed by a formula (1):

x(t)＝A_xcos(2π×f_x(t)×t+ψ_x)+D_x； (1)

wherein A is_xIs the amplitude of x (t), f_xFrequency of x (t)_xIs the phase of x (t), D_xAn offset of x (t);

heterodyne fm signal y (t) is represented by equation (2):

y(t)＝A_ycos(2π×f_y(t)×t+ψ_y)+D_y； (2)

wherein A is_xIs the amplitude of x (t), f_xFrequency of x (t)_xIs the phase of x (t), D_xThe offset of heterodyne fm signal y (t).

6. A method of digitally measuring the modulation delay of an optical frequency modulator as claimed in claim 4, further characterized by:

4) the method specifically comprises the following steps:

4.1) using a four-parameter sine wave fitting method to the FM frequency demodulation waveform sequence a output by the 3)₁，a₂，…，a_MPerforming least square waveform fitting, wherein the functional expression of the waveform least square fitting curve is shown as the following formula (3):

wherein A is_aIs the fitted sinusoidal waveform amplitude;fitting the sine wave frequency; phi is a_aFitting the initial phase of the sine waveform; d_aFitting a sine waveform direct current component; is called a (t)_i) FM fitting result, wherein pi is circumferential rate;

the fitted residual root mean square value of the FM frequency demodulation waveform sequence is shown in formula (4):

${\mathrm{\&rho;}}_a=\sqrt{\frac{1}{M}\underset{i=1}{\overset{M}{\&Sigma;}}{\left(a\right(t_i)-a_i)}^2}---\left(4\right)$

ρ_afitting residual root mean square values of the FM frequency demodulation waveform sequence;

4.2) demodulating waveform sequence b to heterodyne frequency by using four-parameter sine wave fitting method₁，b₂，…，b_MPerforming least square waveform fitting, wherein the functional expression of a waveform least square fitting curve is shown as the formula (5):

wherein A is_bA sinusoidal waveform amplitude fitted for a heterodyne frequency demodulation waveform sequence;fitting a sine wave frequency for the heterodyne frequency demodulation waveform sequence;a sinusoidal waveform initial phase fitted for a heterodyne frequency demodulation waveform sequence; d_bFitting a sine waveform direct current component; b (t)_i) Is the heterodyne fitting result;

the residual root mean square value of the heterodyne frequency demodulation waveform sequence fitting is as follows:

${\mathrm{\&rho;}}_b=\sqrt{\frac{1}{M}\underset{i=1}{\overset{M}{\&Sigma;}}{\left(b\right(t_i)-b_i)}^2}---\left(6\right)$

where ρ is_bA residual root mean square value fitted for the heterodyne frequency demodulation waveform sequence.

7. A method of digitally measuring the modulation delay of an optical frequency modulator as claimed in claim 4, further characterized by:

5) the method specifically comprises the following steps:

the trigger delay to be measured, denoted as τ; the phase difference corresponding to the trigger delay to be measured is recorded asSpecifically, it is calculated by formula (7):

8. a method of digitally measuring the modulation delay of an optical frequency modulator as claimed in claim 4, further characterized by:

3) the delay-free digital frequency demodulation method comprises the following specific steps:

a. setting the sequence length n and the sampling rate v of the acquired waveform according to the carrier frequency of the detected signal; setting a principle to ensure that more than 20 sampling points are required in each carrier waveform period; limiting the lower limit value of n to 10000; wherein, the detected signal is a frequency modulation signal waveform y (t);

b. acquiring the detected signal in the step a to obtain a data acquisition sequence of a frequency modulation signal waveform y (t), and recording the data acquisition sequence as: y is_iI is 1,2, …, n, where i represents the number of sampling points in the synchronous sampling sequence;

b. acquiring the detected signal in the step a to obtain a data acquisition sequence of a frequency modulation signal waveform y (t), and recording the data acquisition sequence as: y is_iI is 1,2, …, n, where i represents synchronous samplingSampling point serial numbers in the sample sequence;

c. in the waveform acquisition sequence y_iThe leading edge intercepts a segment of the waveform less than one carrier period, noted as: y is_i，i＝1,2,…,m₁；

Performing sine fitting on the sequence of the waveform segment of the frequency modulation signal output by the step c) by using an electronic computer according to the process of the step 4) to obtain the instantaneous frequency f of the fitted sine wave₁The method specifically comprises the following steps:

c.1 assuming that the measured waveform of the intercepted waveform segment is approximate to a sine wave with a waveform of

y_s(t)＝A_ysin(2πf_yt+ψ_y)+D_y(8)

Wherein, y_s(t) measured waveform of the intercepted waveform segment, A_yAmplitude of a sine wave, f_yIs the frequency, ψ, of a sine wave_yIs the initial phase of a sine wave, D_yAmplitude deviation of the measured waveform of the intercepted waveform segment;

a waveform segment of less than one carrier cycle is truncated at the leading edge of the waveform acquisition sequence,i＝1,2,…,m₁

$y_s^i=y_s\left(t_i\right)=y_s\left(\left(i-1\right)\&CenterDot;\mathrm{\&Delta;}\mathrm{\&tau;}\right),i=1,2,...,m_1---\left(9\right)$

wherein the sampling time interval Δ τ is 1/v;

c.2 computer Pair acquisition sequence(i＝1,2,…,m₁) And performing four-parameter fitting on the sine waveform to obtain a fitting signal:

wherein, y_s(i) In order to fit the signal to the signal,in order to fit the amplitude of the sine wave,in order to fit the angular frequency of the sine wave,to fit the initial phase of the sine wave,fitting the direct current component value of the sine wave;

fitting frequencyComprises the following steps:

${\hat{f}}_1=\frac{{\widehat{\mathrm{\&omega;}}}_1\&CenterDot;v}{2\mathrm{\&pi;}}---\left(11\right)$

the frequency isIs a point (1+ m)₁) Instantaneous frequency demodulation results at/2;

c.3, fitting four parameters of a sine waveform, specifically:

assuming that the sine wave frequency target value to be estimated is f₀，ω₀＝2πf₀V, the number of signals contained in the sine wave sampling sequence to be estimated is p (0) and is less than one period<p<1) The occupied time length of the waveform is tau; then, f₀1/τ, another factor q is chosen (e.g. q 1 × 10^-5) So that the estimated sinusoidal frequency f₀>q/τ; thus, f₀∈[q/τ,2/τ]The specific process is as follows:

c3.⑴ sets the fitting iteration stop condition to h_e；

h_eHas a value range of 1 × 10^-18To 1 × 10^-20xx; preferred is h_eIs 1 × 10^-20；

c3.⑵ from a known time t₁,t₂,...,t_m1Sine wave acquisition sample y₁,y₂,...,y_m1. The signal waveform obtained by the point counting method occupies a time length of tau (m)₁-1)/v, selecting a factor q (e.g. q 1 × 10^-5) Determining the target frequency f₀Existence interval of [ q/τ,2/τ ]]；

c3.⑶ determining an iteration left boundary frequency f_L＝q/τ；ω_L＝2πf_LV,/v; iteration right boundary frequency: f. of_R＝2/τ；ω_R＝2πf_R/v；

c3.⑷ order median valueFrequency: omega_M＝(ω_R+ω_L) 2; calculating respective fitting residual errors rho (omega) on the left boundary frequency, the right boundary frequency and the median frequency by using a three-parameter fitting formula_L)、ρ(ω_M) And ρ (ω)_R)；

c3, ⑸ judges whether rho (omega) is present or not_L)<η·ρ(ω_M) Wherein η is a criterion factor, and the value range is 1-1.5;

if ρ (ω)_L)<η·ρ(ω_M) Then let ω be_R＝ρ(ω_M)，ω_LRepeatedly executing ⑷ - ⑸ processes without changing;

c3, ⑹ rho (omega)_L)≥η·ρ(ω_M) Then there must be ω_R<2ω₀Determining the left boundary frequency of the iteration as omega_L(ii) a Iterative right boundary frequency omega_R(ii) a The median frequency was chosen according to the preferred method: omega_M＝ω_L+0.618×(ω_R-ω_L)

And ω_T＝ω_R-0.618×(ω_R-ω_L)；

c3, ⑺ at ω_LPerforming three-parameter sine curve fitting to obtain A_L、D_L、ρ_L(ii) a At omega_RPerforming three-parameter sine curve fitting to obtain A_R、D_R、ρ_R(ii) a At omega_MPerforming three-parameter sine curve fitting to obtain A_M、D_M、ρ_M(ii) a At omega_TPerforming three-parameter sine curve fitting to obtain A_T、D_T、ρ_T；

c3, ⑻ F_M<ρ_TThen ρ is ρ_MHas omega₀∈[ω_T,ω_R]，ω_L＝ω_T，ω_T＝ω_M；ω_M＝ω_L+0.618×(ω_R-ω_L) (ii) a If ρ_M>ρ_TThen ρ is ρ_THas omega₀∈[ω_L,ω_M]，ω_R＝ω_M，ω_M＝ω_T；ω_T＝ω_R-0.618×(ω_R-ω_L)；

c3.⑼ determines if (| (ρ |)_M(k)-ρ_T(k))/ρ_T(k)|<h_eIf yes, the iteration is stopped, and ρ is ρ_TThen, obtaining the parameter of the four-parameter fitting sine curve as A ═ A_T、ω＝ω_T、D＝D_TRho, finishing the fitting process; ρ ═ ρ_MThen, obtaining the parameter of the four-parameter fitting sine curve as A ═ A_M、ω＝ω_M、D＝D_MAnd rho, finishing the fitting process, otherwise, repeating the processes of c3, ⑺ -c 3 and ⑼;

d. storing instantaneous frequency parameters of an output sinusoidal modelIs the frequency of the measured sinusoidal model;

e. to be less thanCycle length (e.g. of) The corresponding sequence time length is the length m of the next fitting sequence₂Sequence center position from m₁Moving a sampling point backwards at position/2, executing the processes c and d on a new data segment, and obtaining the instantaneous frequency of the output sinusoidal model

Repeatedly executing the sliding fitting process until the end point of the data sequence;

obtaining a frequency demodulation waveform sequence:a demodulated waveform output for signal waveform y (t);

to this end, from a to e, the delay-free digital frequency demodulation method is completed.