CN106247930B - The residual compensation method of phase carrier formula laser interferometer closed loop demodulating algorithm - Google Patents

Abstract

The present invention is to provide a kind of residual compensation methods of phase carrier formula laser interferometer closed loop demodulating algorithm.Interference light signal is multiplied with additional carrier signal, low-pass filtering, is removed, arc tangent obtains system residual error, the phase signal weighted sum that system residual error and closed loop are demodulated corrects measurement result with this.In phase carrier formula laser interferometer closed loop demodulating process, system can have different degrees of residual error because of the limitation of disturbance factor or tracking ability.The present invention has the advantages that phase-modulation high-ranking military officer's interference signal closed loop demodulation method, while also having higher demodulation accuracy.

Description

Residual Compensation Method of Phase Carrier Laser Interferometer Closed-loop Demodulation Algorithm

technical field

The invention relates to an optical interferometry method, in particular to a method for residual error compensation of phase carrier laser interference signals.

Background technique

The phase demodulation algorithm widely used in optical interference sensors is the PGC algorithm. Its principle is to use the input signal and the local phase modulation wave to perform frequency difference processing to obtain the quadrature value of the two measured phases, and then use the quadrature value and the original The signal is multiplied by cross differential, and the measured phase value is obtained through trigonometric function relationship and integral processing. In the 1980s, when digital circuits were not very developed, the algorithm was proposed to solve the problem of engineering practice. However, there are several problems with this algorithm. First, the dynamic range of its work is greatly affected by the phase-modulated wave signal. In addition, the system works in an open-loop state, and there is no feedback loop to ensure the long-term stability of the system. Another serious problem in the PGC algorithm is that it is easily affected by the associated amplitude modulation. Since the PGC algorithm requires a phase-modulated wave signal to modulate the interferometer, it is easy to cause accompanying amplitude changes in the process of directly modulating the laser phase. Variations can produce large harmonic distortions in the final data result. On the other hand, the closed-loop demodulation algorithm for the phase-carrier laser interference signal also has different degrees of residual error due to disturbance factors or tracking capability limitations.

Contents of the invention

The purpose of the present invention is to provide a residual error compensation method of a phase carrier type laser interferometer closed-loop demodulation algorithm with higher demodulation accuracy.

The purpose of the present invention is achieved like this:

The phase carrier laser interference signal is multiplied with G cosω ₀ t and H cos2ω ₀ t after photoelectric conversion, where: ω ₀ is the phase modulation frequency, G and H are the amplitudes of the external loading wave;

Use a low-pass filter to filter out the AC component containing ω ₀ , and get and Among them: B is the AC component of the light intensity after interference, J ₁ (C) and J ₂ (C) are the Bessel function expansion coefficients related to the modulation depth of the light source, and the ratio of the two is

The system residual error of the closed-loop demodulation algorithm is obtained by arctangent calculation It is used to compensate the closed-loop phase demodulation result.

The present invention may also include:

When the phase variation range of the signal under test is less than or equal to plus or minus 45 degrees, the obtained residual term is the phase of the signal under test.

The invention introduces a closed-loop residual error compensation mechanism on the basis of a closed-loop demodulation algorithm of a phase carrier test laser interference signal.

Specifically, the interference signal after the photodetector is:

Among them: I ₁ , I ₂ are the light intensity of the two beams of interference light respectively, A is the DC component of the light intensity after interference, B is the AC component of the light intensity after interference, is the interferometric phase change value, the expression is:

where in the above formula are the initial phase of interference, the phase change caused by light source modulation, respectively. Phase change due to light source modulation It is related to the light source modulation frequency ν.

Where n is the refractive index of the fiber, l is the length difference between the two arms, c is the speed of light, and the modulation current is i=i ₀ cosω ₀ t, then the frequency change caused by the light source is ν=Δνcosω ₀ t, and the phase change caused by the modulation signal is obtained The amount is:

Where C is the modulation depth, which is a fixed constant related to the fiber interferometer and modulation, then the form of the interference signal is:

Performing Bessel expansion on it, we get:

Where J _m (C) is a high-order coefficient at a certain modulation depth C.

Multiply the Bessel expanded formula with the external loading wave signals G cosω ₀ t and H cos2ω ₀ t generated by the signal generator, and use low-pass filtering to remove the AC term including ω ₀ respectively, and we can get:

After doing the division operation, we get:

Remove the constant term and use the arctangent calculation to obtain the system phase residual of the closed-loop phase demodulation algorithm The residual is added to the closed-loop demodulation result as the final demodulation result.

The invention has the advantages of having the advantages of the closed-loop demodulation method of the phase modulation general interference signal, and at the same time having higher demodulation precision.

Description of drawings

FIG. 1 is a flowchart of a residual compensation method for closed-loop demodulation of a phase-carrier laser interference signal.

Fig. 2 is a device structure diagram of a residual error compensation method for closed-loop demodulation of a phase-carrier laser interference signal.

Detailed ways

The present invention will be described in more detail below with examples in conjunction with the accompanying drawings.

2, the device of the present invention includes: 1. laser light source, 2. fiber coupler, 3. fiber sensor arm, 4. fiber reference arm, 5. sensing arm reflector, 6. reference arm reflector, 7. Photodetector, 8, band-pass filter, 9, multiplier for multiplying external carrier signal, 10, multiplier, 11, low-pass filter, 12, low-pass filter, 13, divider, 14 . Arctangent operation, 15. Square root operation, 16. PID controller, 17. Adder, 18. The final demodulated phase signal output, 19. Piezoelectric ceramic driver, 20. Piezoelectric ceramic. The device of the present invention can be divided into two parts, the first part is the interference phase signal of the phase carrier generated by the laser fiber interferometer, including laser light source, fiber coupler, reference arm and sensing arm; the second part is the phase carrier provided by the present invention The residual compensation method of the laser interferometer closed-loop demodulation algorithm, wherein the phase demodulation module is composed of a band-pass filter with a center frequency ω ₀ , a multiplier, a low-pass filter, and a square root summation operation. The system residual compensation The module is composed of a multiplier, a low-pass filter, a divider, and an arctangent operation, and the closed-loop control module is composed of a PID controller and piezoelectric ceramics.

The interference signal is sent to the programmable logic device (FPGA) through photoelectric conversion and AD sampling, and the band-pass filtering, self-multiplication, low-pass filtering, square root operation, and PID operation of the optical interference signal are completed in the FPGA to generate a closed-loop control signal, namely The phase compensation signal is amplified to generate a compensation phase and fed into the optical path.

At the same time, after the photoelectric conversion interference signal is sampled by AD, it is also multiplied, divided, low-pass filtered and arctangent calculated with the single-frequency and double-frequency carrier signals in the FPGA to obtain the system residual. The residual and the phase compensation signal are added in the FPGA to obtain the final phase demodulation result, which is output by the FPGA.

During the closed-loop demodulation process of the phase-carrier laser interferometer, the system will have different degrees of residual error due to disturbance factors or limitations of tracking capabilities. The invention provides a residual error compensation method of a phase-carrier laser interference signal closed-loop demodulation algorithm, which mainly includes: multiplication of the interference optical signal and an external carrier signal, low-pass filtering, division, and arctangent to obtain the system residual , to correct the measurement result by weighting and summing the system residual and the phase signal obtained from the closed-loop demodulation.

The phase carrier laser interference signal is multiplied with G cosω ₀ t and H cos2ω ₀ t after photoelectric conversion (ω ₀ is the phase modulation frequency, G and H are the amplitude of the external loading wave respectively), and the low-pass filter is used Filter out the AC component containing ω ₀ , get and (B is the AC component of the light intensity after interference, J ₁ (C) and J ₂ (C) are the Bessel function expansion coefficients related to the modulation depth of the light source respectively), the ratio of the two is According to this formula, the system residual error of the closed-loop demodulation algorithm can be obtained by arctangent calculation And used to compensate the closed-loop phase demodulation results;

When the phase change range of the signal under test is not large (such as plus or minus 45 degrees), the closed-loop system can be converted to an open-loop state after properly adjusting the static operating point, and the obtained residual term is the signal generated by the signal under test. phase.

Claims (2)

1. A kind of residual compensation method of phase carrier type laser interferometer closed-loop demodulation algorithm, it is characterized in that: The phase carrier laser interference signal is multiplied with G cosω ₀ t and H cos2ω ₀ t after photoelectric conversion, where: ω ₀ is the phase modulation frequency, G and H are the amplitudes of the external loading wave; Use a low-pass filter to filter out the AC component containing ω ₀ , and get and Among them: B is the AC component of the light intensity after interference, J ₁ (C) and J ₂ (C) are the Bessel function expansion coefficients related to the modulation depth of the light source, and the ratio of the two is C is the modulation depth; The system residual error of the closed-loop demodulation algorithm is obtained by arctangent calculation It is used to compensate the closed-loop phase demodulation result. 2. The residual compensation method of the phase-carrier laser interferometer closed-loop demodulation algorithm according to claim 1, characterized in that: when the phase variation range produced by the measured signal is between minus 45 degrees and plus 45 degrees, The resulting residual term is the phase generated by the signal under test.