阅读说明：本技术 相位生成载波反正切中载波相位延迟和伴生调幅消除方法 (Carrier phase delay and associated amplitude modulation elimination method in phase generation carrier arc tangent ) 是由 胡鹏程 董祎嗣 付海金 张洪铭 于 2019-10-28 设计创作，主要内容包括：相位生成载波反正切中载波相位延迟和伴生调幅消除方法属于光纤干涉测量技术领域；本发明利用提取干涉信号中的正交分量,粗略地计算和补偿载波相位延迟,完成载波相位延迟的预补偿。在预补偿后,获取残余非线性误差的参数,进而实现对载波相位解调反正切算法中载波相位延迟和伴随光强调制影响的消除。该方法能够有效地同时解决载波相位延迟和光强伴随调制带来的非线性误差的问题。弥补现存载波相位延迟补偿方法会受到光强伴随调制的影响,有利于提高载波相位解调精度。(A method for eliminating carrier phase delay and associated amplitude modulation in phase generation carrier arc tangent belongs to the technical field of optical fiber interferometry; the invention utilizes the orthogonal component extracted from the interference signal to roughly calculate and compensate the carrier phase delay, thus completing the pre-compensation of the carrier phase delay. After pre-compensation, parameters of residual nonlinear errors are obtained, and then the carrier phase delay and the accompanying light intensity modulation influence in the carrier phase demodulation arc tangent algorithm are eliminated. The method can effectively solve the problem of nonlinear errors caused by carrier phase delay and light intensity accompanying modulation at the same time. The method compensates the influence of the light intensity accompanying modulation on the existing carrier phase delay compensation method, and is beneficial to improving the carrier phase demodulation precision.)

1. A method for eliminating carrier phase delay and associated amplitude modulation in phase generation carrier arc tangent demodulation is applied to a modulation type optical fiber Michelson interferometer in laser wavelength, and the optical fiber Michelson interferometer comprises the following steps:

a laser wavelength modulatable light source;

an optical path structure, comprising: the device comprises a beam splitting device, a first reflecting device and a second reflecting device, wherein the beam splitting device is used for splitting laser emitted by the wavelength-modulatable light source into a reference beam and a measuring beam, the first reflecting device is used for reflecting the reference beam, and the second reflecting device is used for reflecting the measuring beam;

a photodetector capable of detecting an interference signal formed by interference of a reference beam reflected by said first reflecting means and a measuring beam reflected by said second reflecting means;

characterized in that the method comprises:

the method comprises the following steps: multiplying interference signals detected by the photoelectric detector with two paths of orthogonal signals coswt and sinwt respectively, and obtaining a signal U through a low-pass filter₁(t) and U₂(t)；

Step two: judging whether the absolute value of U is satisfied₁(t)|≥Max[U₁(t)]The interval of t of the condition and the signal U of the interval of t₁(t) and U₂(t) partial sectionTaken out as a function U_m1(t) and U_m2(t) applying the function U_m1(t) and U_m2(t) the following operations are performed:

step three: calculating the average value of the function theta (t) to obtain an initial phase delay theta, compensating the initial phase delay theta into an original frequency doubling carrier cos (wt) and a frequency doubling carrier cos (2wt), and obtaining a frequency doubling carrier cos (wt + theta) and a frequency doubling carrier cos (2wt +2 theta) after phase delay compensation to finish initial phase delay pre-compensation;

step four: multiplying the detection signal of the photoelectric detector with the compensated frequency doubling carrier cos (wt + theta) and the frequency doubling carrier cos (2wt +2 theta), and obtaining two paths of signals S through a low-pass filter₁(t) and S₂(t) extracting the two signals S₁(t) and S₂(t) a non-linear characteristic parameter;

step five: eliminating the influence of residual initial phase delay and associated amplitude modulation by utilizing nonlinear characteristic parameters to obtain S₁ ^*(t) and S₂ ^*And (t), finishing fine error correction.

Step six: fine correction of error S₁ ^*(t) and S₂ ^*(t) performing arc tangent operation to obtain phase demodulation value

Technical Field

The invention belongs to the field of optical fiber interferometric displacement measurement, and mainly relates to a method for eliminating phase delay and associated amplitude modulation influence in anti-tangential phase of a phase-generated carrier.

Background

With the rapid development of scientific research and the rapid improvement of industrial production level, the scientific research and industrial fields also put forward higher requirements on displacement measurement, and the minimum variation of displacement measurement is developing towards the nanometer magnitude direction. The optical fiber Michelson interferometer is an instrument for performing high-precision displacement measurement by utilizing a laser interference principle, and compared with other laser interferometers, the optical fiber Michelson interferometer has the advantages of simple structure, easiness in circuit processing, lower requirement on environment and the like, so that the optical fiber Michelson interferometer is more widely applied to the field of displacement measurement. The optical fiber Michelson interferometer has two modulation modes, one mode is to modulate a reference arm by using an electro-optic phase modulator, but in the method, because the electro-optic phase modulator is added at the reference arm, the anti-electromagnetic interference capability of the interferometer is reduced, and meanwhile, the multi-axis interference measurement is not facilitated; another modulation method is laser current internal modulation, i.e. applying a modulation signal to a wavelength-modulatable laser so that the laser output wavelength is modulated, which is beneficial to the miniaturization and wavelength division multiplexing of interferometers, and is widely used.

For an interference signal processing method of a modulation type optical fiber Michelson interferometer in a light source, a Phase Generation Carrier (PGC) technology is widely adopted, and the method has the advantages of high sensitivity, high dynamic range, good linearity and the like. Nowadays, there are two main PGC demodulation methods, one is a phase generation carrier differential cross multiplication algorithm (PGC-DCM), and the other is a phase generation carrier arc tangent algorithm (PGC-Arctan). In a PGC demodulation system, a high frequency carrier phase signal applied to fiber optic interferometric sensing converts the desired phase shifted signal to a sideband of the carrier frequency. By extracting the first and second harmonics of the interference signal, the quadrature component containing the phase shifted signal can be obtained. To extract the phase shift from the quadrature component obtained, PGC-Arctan and PGC-DCM have been rapidly developed. However, since the laser needs to be modulated within the wavelength, the light intensity is inevitably modulated during the laser output wavelength modulation, which results in light intensity accompanying modulation, and the PGC is also affected by the accompanying modulation, so that the demodulation accuracy is lowered. While considering the accompanying amplitude modulation, the optical path delay, the photoelectric conversion, the circuit delay, and the like in the optical fiber sensing system cause a phase delay between the carrier component of the detected signal and the modulation signal, and such a delay will also adversely affect the demodulation result of the PGC. Therefore, researches on phase delay and concomitant amplitude modulation influence elimination technologies are imperative.

Fig. 1 is a typical light source modulation type optical fiber michelson interferometer structure, a sinusoidal signal generating device 1 generates a sinusoidal signal to a wavelength-tunable laser 2, and performs sinusoidal modulation on the wavelength of the laser output by the wavelength-tunable laser 2, and the laser emitted by the wavelength-tunable laser 2 is split into a reference beam and a measuring beam by an optical fiber coupler 3; wherein the reference beam is collimated by the first collimator 4, reflected by the first reflector 5, the measuring beam is collimated by the second collimator 6, reflected by the second reflector 7, the reference beam and the measuring beam return to the optical fiber coupler 3 in the original path to interfere, and are output by the other end of the optical fiber coupler 3 and are merged into the photoelectric detector 8, and the ideal form of the output signal of the photoelectric detector 8 is as follows:

the signal phase generation carrier demodulation unit 9 obtains U_m1And U_m2A signal; ideally, U_m1And U_m2Can be expressed as:

wherein B is the AC amplitude of the interference signal, C is the sum of the phase modulation depths, J₁(C) And J₂(C) In order to be a function of the Bessel function,and

is a frequency-doubled and frequency-doubled carrier, and is expressed in the form of:

ideally, the amplitude of the phase carrier is adjusted so that J₁(C)＝J₂(C) Setting the carrier fundamental frequency signal and the frequency multiplication signal in the multiplier to have the same amplitude, i.e. K₁＝K₂，

Is the phase difference between the reference and measurement optical paths. It can be seen that U_m1And U_m2Appear to relate to

The sine and cosine functions of (1) are equal in amplitude and zero in direct current bias and are orthogonal to each other under an ideal state.

In practical situations, however, due to optical path delay in the fiber interferometer measurement system, delay caused by the photoelectric converter, circuit delay, filter delay, etc., the modulation term in the interference signal and the phase of the carrier reference signal may not be consistent, and thus additional phase delay error may be generated. Therefore, the interference signal form becomes:

wherein θ ═ w_cΔ t is the phase delay error introduced by the time delay Δ t, and it can be found that the phase delay error increases with the increase of the carrier frequency, and the quadrature component corresponding to the phase-locked amplification becomes:

the corresponding phase demodulation result becomes:

it can be seen that the phase demodulation result is directly affected by the phase delay amount θ, and even when cos θ is 0 and cos2 θ is 0, PGC-Arctan cannot demodulate correctly. Therefore, phase delay compensation related to the phase generation carrier demodulation arc tangent algorithm has been regarded as the main point and hot spot in research of all parties.

In 1987, a phase shifter of a Composite amplifier structure was proposed in W.Mikhael and S.Michael to achieve synchronization between a carrier signal and a modulation signal (W.Mikhael and S.Michael, "Composite operation amplifiers: Generation and fine-gain applications," IEEE trans.C.Syst.34 (5), 449-460 (1987)). However, the design of a fully analog circuit is rather complex and at the same time susceptible to electromagnetic interference and temperature variations.

In 2007, s.c. huang and h.lin proposed a phase delay compensation method that uses two phase compensators to act on the fundamental square wave and the second harmonic square wave, respectively, to set the required carrier phase delay by adjusting the phase compensators to provide the maximum amplitude of the sensed phase signal (s.c. huang and h.lin, "Modified phase-generated carrier modulation compensated for the propagation delay of the fiber," applied.opt, vol.46, No.31, pp. 7594-. This method has proven effective, but requires readjustment of the phase compensator when the parameters somewhere in the optical path change.

In 2008, t.lan et al proposed a carrier phase advance technique. The method eliminates phase delay errors by estimating the system loop time delay in advance and generating corresponding phase advance carriers according to the estimated time delay in advance (T.Lan, C.Zhang, L.Li, G.Luo, and C.Li, "Carrier phase advance technology for digital PGC modulation," Opto-Electronic Eng.35(7), 49-52 (2008)). However, the introduced time delay of each part (e.g., amplifier, phase modulator, photodetector) cannot be accurately measured for the demodulation system, which limits the accuracy of the phase delay compensation to some extent.

In 2017, the task group of Chen Ben Yong professor of Zhejiang industry university provides a method for realizing phase delay compensation of PGC, extra phase shift is added into a reference signal, the phase shift variable is adjusted to judge the correct phase shift amount by judging whether the output value of a low-pass filter is the maximum value, and the scheme is verified to be effective experimentally. (S.Zhang, L.Yan, B.Chen, Z.xu, and J.Xie, "Real-time phase delay compensation of PGC modulation in vivo phase-modulation interferometer for nanometer displacement measurement," Opt.Exp.vol.25, No.1, pp.472-485, Jan.2017.) this approach may result in greater complexity of the demodulation system for large-scale fiber optic sensing arrays.

However, the above method can only be applied to out-of-laser wavelength modulation, and for in-laser wavelength modulation, there is an intensity-dependent modulation in addition to the phase carrier delay.

U due to light intensity accompanying modulation_m1And U_m2Can be expressed as: (Kai Wang, Min Zhang, FajieDuan, Shantran Xie, and Yanbiao Liao, "Measurement of the phase shift between measures and frequency modulations with in DFB-LD and its inflections on PGCconstituent in a fiber-optical sensor system," applied. Opt,52(29), 7194. Olympic 7199(2013).)

Where m is the light intensity modulation factor, P₁、P₂、θ₁And theta₂The expression is as follows:

the previous method can solve the problem of carrier phase delay, but cannot simultaneously solve the problem of light intensity concomitant modulation.

In summary, a method capable of effectively realizing real-time detection without adding any additional phase compensation device and simultaneously solving the carrier phase delay and associated amplitude modulation influence in carrier phase demodulation is absent in the field of optical fiber interferometric sensing measurement detection.

Disclosure of Invention

1. A method for eliminating carrier phase delay and associated amplitude modulation in phase generation carrier arc tangent demodulation is applied to a modulation type optical fiber Michelson interferometer in laser wavelength, and the optical fiber Michelson interferometer comprises the following steps:

a laser wavelength modulatable light source;

an optical path structure, comprising: the device comprises a beam splitting device, a first reflecting device and a second reflecting device, wherein the beam splitting device is used for splitting laser emitted by the wavelength-modulatable light source into a reference beam and a measuring beam, the first reflecting device is used for reflecting the reference beam, and the second reflecting device is used for reflecting the measuring beam;

a photodetector capable of detecting an interference signal formed by interference of a reference beam reflected by said first reflecting means and a measuring beam reflected by said second reflecting means;

characterized in that the method comprises:

the method comprises the following steps: multiplying interference signals detected by the photoelectric detector with two paths of orthogonal signals coswt and sinwt respectively, and obtaining a signal U through a low-pass filter₁(t) and U₂(t)；

Step two: judging whether the absolute value of U is satisfied₁(t)|≥Max[U₁(t)]The interval where t of the condition is located, and the interval where t is locatedSignal U₁(t) and U₂(t) is partially truncated as a function U_m1(t) and U_m2(t) applying the function U_m1(t) and U_m2(t) the following operations are performed:

step three: calculating the average value of the function theta (t) to obtain an initial phase delay theta, compensating the initial phase delay theta into an original frequency doubling carrier cos (wt) and a frequency doubling carrier cos (2wt), and obtaining a frequency doubling carrier cos (wt + theta) and a frequency doubling carrier cos (2wt +2 theta) after phase delay compensation to finish initial phase delay pre-compensation;

step four: multiplying the detection signal of the photoelectric detector with the compensated frequency doubling carrier cos (wt + theta) and the frequency doubling carrier cos (2wt +2 theta), and obtaining two paths of signals S through a low-pass filter₁(t) and S₂(t) extracting the two signals S₁(t) and S₂(t) a non-linear characteristic parameter;

step five: eliminating the influence of residual initial phase delay and associated amplitude modulation by utilizing nonlinear characteristic parameters to obtain S₁ ^*(t) and S₂ ^*And (t), finishing fine error correction.

Step six: fine correction of error S₁ ^*(t) and S₂ ^*(t) performing arc tangent operation to obtain phase demodulation value

The invention has the following characteristics and beneficial effects:

the invention utilizes the orthogonal component extracted from the interference signal to roughly calculate and compensate the carrier phase delay, thus completing the pre-compensation of the carrier phase delay. After pre-compensation, parameters of residual nonlinear errors are obtained, and then the carrier phase delay and the accompanying light intensity modulation influence in the carrier phase demodulation arc tangent algorithm are eliminated. The method can effectively solve the problem of nonlinear errors caused by carrier phase delay and light intensity accompanying modulation at the same time. The method compensates the influence of the light intensity accompanying modulation on the existing carrier phase delay compensation method, and is beneficial to improving the carrier phase demodulation precision.

Drawings

Fig. 1 is a schematic structural diagram of an improved optical source internal modulation type optical fiber michelson interferometer.

Description of elements and numbering in the figures: 1 sinusoidal signal generating device, 2 laser wavelength modulatable light source, 3 optical fiber circulator, 4 optical fiber collimator, 5 beam splitter, 6 reflector A, 7 reflector B, 8 photoelectric detector, 9 improved PGC demodulation unit and 10 upper computer

Fig. 2 is a schematic diagram of the general structure of the method for eliminating the influence of phase delay and associated amplitude modulation in the anti-tangential of the phase generated carrier.

Description of elements and numbering in the figures: 11 analog-to-digital converter, 12 frequency multiplication sine reference signal generating module, 13 frequency multiplication cosine reference signal generating module, 14 frequency multiplication cosine reference signal generating module, 15 multiplier A, 16 multiplier B, 17 multiplier C, 18 low-pass filter A, 19 low-pass filter B, 20 low-pass filter C, 21 arc tangent calculating module A, 22 error fine correction module, 23 arc tangent calculating module, 24 high-pass filter

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

A method for eliminating phase delay and associated amplitude modulation influence in phase generation carrier anti-tangential is applied to an optical fiber Michelson interferometer. Fig. 1 is a schematic structural diagram of an improved optical source internal modulation type optical fiber michelson interferometer, and fig. 2 is a schematic structural diagram of a general method for eliminating phase delay and associated amplitude modulation influence in phase inversion and tangential of a phase generated carrier. In fig. 1, a sinusoidal signal generating device (1) generates a sinusoidal signal and applies the sinusoidal signal to a laser wavelength modulatable light source (2), the output wavelength of the laser wavelength modulatable light source (2) is subjected to sinusoidal modulation, laser output by the laser wavelength modulatable light source (2) enters one port of an optical fiber circulator (3), is emitted from two ports of the optical fiber circulator (3), enters an optical fiber collimator (4) and is emitted to a beam splitter (5) to be divided into a reference beam and a measuring beam; the reference beam is reflected by a reflector A (6), the measuring beam is reflected by a reflector B (7), the reference beam and the measuring beam return to the optical fiber collimator (4) in a primary path to generate interference, and the reference beam and the measuring beam are output to the photoelectric detector (8) from the two ports of the optical fiber circulator (3) and from the three ports of the optical fiber circulator (3).

The output signal of the detector is multiplied by a frequency doubling sine signal and a frequency doubling cosine signal relative to the modulation frequency respectively and passes through a low-pass filter, and the obtained formula is reasonably ignored as follows:

judges that U is satisfied₁(t)≥Max[U₁(t)]The interval of t of the condition and the signal U of the interval of t₁(t) and U₂(t) is partially truncated as a function U_m1(t) and U_m2(t) applying the function U_m1(t) and U_m2(t) the following operations are performed:

and calculating the average value of the function theta (t) to obtain an initial phase delay theta, compensating the initial phase delay theta into the original frequency doubling carrier cos (wt) and the frequency doubling carrier cos (2wt), and obtaining the frequency doubling carrier cos (wt + theta) and the frequency doubling carrier cos (2wt +2 theta) after phase delay compensation to finish initial phase delay pre-compensation.

Multiplying the detection signal of the photoelectric detector with the compensated frequency doubling carrier cos (wt + theta) and the frequency doubling carrier cos (2wt +2 theta), and obtaining two paths of signals S through a low-pass filter₁(t) and S₂(t) of (d). Extracting the two signals S₁(t) and S₂(t) a non-linear characteristic parameter;

eliminating the influence of residual initial phase delay and associated amplitude modulation by utilizing nonlinear characteristic parameters to obtain S₁ ^*(t) and S₂ ^*And (t), finishing fine error correction.

After fine correction of errors

And

performing arc tangent operation to obtain phase demodulation value