Double-interferometer system demodulation method and device

Abstract

The invention provides a double-interferometer system demodulation method and device, and the method comprises the steps: generating laser through a modulation laser, and inputting the laser into a signal interferometer and a reference interferometer, determining a first orthogonal signal and a second orthogonal signal corresponding to the signal interferometer, and a third orthogonal signal and a fourth orthogonal signal corresponding to the reference interferometer; the arm length differences of the signal interferometer and the reference interferometer are equal; solving a first modulation depth of the signal interferometer and a second modulation depth of the reference interferometer through an ellipse fitting algorithm, calculating Bessel function values of the first modulation depth and the second modulation depth, and obtaining an orthogonal signal without the modulation depth according to the orthogonal signal; and constructing a product sum-difference formula according to the orthogonal signal of which the modulation depth is eliminated, and obtaining an optical phase signal of which the noise is eliminated through arc tangent operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a dual-interferometer system demodulation method and device. BACKGROUND

[0002] Optical fiber interferometer is widely used in optical systems such as optical fiber vibration sensor, optical fiber accelerometer, optical fiber hydrophone, etc. The phase noise introduced by the laser in the optical fiber interferometer poses a serious challenge to the accurate demodulation of optical phase information, and restricts the application range of optical systems based on optical fiber interferometer. Especially for the detection of low-frequency optical phase signals, the existence of laser self-noise seriously interferes with the accurate demodulation of signals in the low-frequency band.

[0003] Therefore, a dual-interferometer system demodulation method is needed. SUMMARY

[0004] The purpose of the present application is to provide a dual-interferometer system demodulation method and device, which estimates the modulation depth by an ellipse fitting algorithm, compensates for the distortion introduced by the modulation depth based on the estimated value of the modulation depth, and can obtain more accurate optical phase noise measurement.

[0005] To achieve the above purpose, in a first aspect, the present application provides a dual-interferometer system demodulation method, comprising:

[0006] generating laser by modulating laser, inputting the laser into a signal interferometer and a reference interferometer, determining a first quadrature signal and a second quadrature signal corresponding to the signal interferometer, and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer; the arm length difference of the signal interferometer and the reference interferometer is equal;

[0007] solving the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer by an ellipse fitting algorithm, and calculating the Bessel function value of the first modulation depth and the second modulation depth, obtaining the first quadrature signal excluding the modulation depth, the second quadrature signal excluding the modulation depth, the third quadrature signal excluding the modulation depth, and the fourth quadrature signal excluding the modulation depth according to the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal;

[0008] constructing the sum and difference formula according to the first quadrature signal excluding the modulation depth, the second quadrature signal excluding the modulation depth, the third quadrature signal excluding the modulation depth, and the fourth quadrature signal excluding the modulation depth, and obtaining the optical phase signal excluding noise by arctangent operation.

[0009] Specifically, the laser is generated by modulating a laser, the laser is input into a signal interferometer and a reference interferometer, first and second quadrature signals corresponding to the signal interferometer and third and fourth quadrature signals corresponding to the reference interferometer are determined, and the first and second quadrature signals corresponding to the signal interferometer and the third and fourth quadrature signals corresponding to the reference interferometer are determined.

[0010] The laser is generated by modulating a laser, the laser is split into two paths by a beam splitter and enters a reference interferometer and a signal interferometer respectively, a first light intensity is output by the signal interferometer and a second light intensity is output by the reference interferometer, a first Bessel function expansion formula of the first light intensity and a second Bessel function expansion formula of the second light intensity are obtained by performing Bessel function expansion on the first light intensity and the second light intensity respectively, first and second quadrature signals of the signal interferometer are obtained by performing low-pass filtering on a calculation result of multiplying the first Bessel function expansion formula by a first fundamental frequency signal and a first second-harmonic signal, and third and fourth quadrature signals of the reference interferometer are obtained by performing low-pass filtering on a calculation result of multiplying the second Bessel function expansion formula by a second fundamental frequency signal and a second second-harmonic signal.

[0011] Preferably, the first light intensity output by the signal interferometer and the second light intensity output by the reference interferometer are represented as:

[0012]

[0013] wherein A s , A r is a direct current light intensity, B s is a modulation amplitude of the signal interferometer, B r is a modulation amplitude of the reference interferometer, C s , C r is a modulation depth, ω0 is a carrier angular frequency, is an optical phase signal, is an optical phase noise, is an introduced additional low-frequency sinusoidal signal, I s is the first light intensity output by the signal interferometer, I r is the second light intensity output by the reference interferometer.

[0014] The first and second quadrature signals of the signal interferometer and the third and fourth quadrature signals of the reference interferometer are represented as:

[0015]

[0016] wherein S S1 is the first quadrature signal of the signal interferometer, S S2 is the second quadrature signal of the signal interferometer, S R1 is the first quadrature signal of the reference interferometer, S R2 is the second quadrature signal of the reference interferometer, Cs , C r is a modulation depth, B s is a modulation amplitude of the signal interferometer, B r is a modulation amplitude of the reference interferometer, G, H are gain factors, J1(C s ), J1(C r ) are first order Bessel function values, J2(C s ), J2(C r ) are second order Bessel function values, is an optical phase signal, is an optical phase noise, is an introduced additional low frequency sinusoidal signal.

[0017] Specifically, the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer are solved by an ellipse fitting algorithm, and the Bessel function values of the first modulation depth and the second modulation depth are calculated, and the first quadrature signal excluding the modulation depth, the second quadrature signal excluding the modulation depth, the third quadrature signal excluding the modulation depth, and the fourth quadrature signal excluding the modulation depth are obtained according to the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal, comprising:

[0018] The first quadrature signal and the second quadrature signal of the signal interferometer, and the third quadrature signal and the fourth quadrature signal of the reference interferometer are constituted into an ellipse fitting curve by an ellipse fitting algorithm, the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer are calculated by the ellipse fitting curve, and the first order Bessel function value and the second order Bessel function value of the first modulation depth and the first order Bessel function value and the second order Bessel function value of the second modulation depth are calculated, and the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal are divided by the known constant modulation amplitude of the signal interferometer, the modulation amplitude of the reference interferometer, the gain factor, the first order Bessel function value and the second order Bessel function value of the first modulation depth, and the first order Bessel function value and the second order Bessel function value of the second modulation depth to obtain the first quadrature signal excluding the modulation depth, the second quadrature signal excluding the modulation depth, the third quadrature signal excluding the modulation depth, and the fourth quadrature signal excluding the modulation depth.

[0019] Preferably, the ellipse fitting curve is expressed as:

[0020]

[0021] wherein, C s is the first modulation depth of the signal interferometer, C r is the second modulation depth of the reference interferometer, S S1 is the first quadrature signal of the signal interferometer, SS2 second quadrature signal of the signal interferometer, S R1 first quadrature signal of the reference interferometer, S R2 second quadrature signal of the reference interferometer, J1(C s ), J1(C r ) is a first order Bessel function value, J2(C s ), J2(C r ) is a second order Bessel function value;

[0022] The first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer are calculated by the ellipse fitting curve, including:

[0023] J1(C) / J2(C) is obtained by the coefficients a1, a2, b1, b2 in the ellipse curve, and the modulation depth C of the signal interferometer and the modulation depth C of the reference interferometer are obtained according to the relationship f of the modulation depth C and J1(C) / J2(C) s ; r ;

[0024] The first quadrature signal of the modulation depth, the second quadrature signal of the modulation depth, the third quadrature signal of the modulation depth, and the fourth quadrature signal of the modulation depth are represented as:

[0025]

[0026] Wherein, S S1 ' is the first quadrature signal of the modulation depth, S S2 ' is the second quadrature signal of the modulation depth, S R1 ' is the third quadrature signal of the modulation depth, S R2 ' is the fourth quadrature signal of the modulation depth, is an optical phase signal, is an optical phase noise, is an introduced additional low-frequency sinusoidal signal.

[0027] Preferably, the product and difference formula is represented as:

[0028]

[0029]

[0030] Wherein, is an optical phase signal, is an optical phase noise, is an introduced additional low-frequency sinusoidal signal, is the first quadrature signal of the modulation depth, is the second quadrature signal of the modulation depth, a third quadrature signal for removing the modulation depth, a fourth quadrature signal for removing the modulation depth;

[0031] The arctangent operation is represented as:

[0032]

[0033] wherein, is an optical phase signal.

[0034] In a second aspect, the present application provides a dual-interferometer system demodulation device, comprising:

[0035] a modulation unit configured to generate laser light by modulating a laser, input the laser into a signal interferometer and a reference interferometer, determine a first quadrature signal and a second quadrature signal corresponding to the signal interferometer, and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer, and the arm length difference of the signal interferometer and the reference interferometer is equal;

[0036] an ellipse fitting unit configured to solve a first modulation depth of the signal interferometer and a second modulation depth of the reference interferometer by an ellipse fitting algorithm, calculate the Bessel function value of the first modulation depth and the second modulation depth, and obtain a first quadrature signal for removing the modulation depth, a second quadrature signal for removing the modulation depth, a third quadrature signal for removing the modulation depth, and a fourth quadrature signal for removing the modulation depth according to the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal;

[0037] an operation unit configured to construct a product and difference formula according to the first quadrature signal for removing the modulation depth, the second quadrature signal for removing the modulation depth, the third quadrature signal for removing the modulation depth, and the fourth quadrature signal for removing the modulation depth, and obtain an optical phase signal for removing noise by an arctangent operation.

[0038] In a third aspect, the present application provides a computer readable storage medium having a computer program stored thereon, when the computer program is executed in a computer, the computer executes the method of the first aspect.

[0039] In a fourth aspect, the present application provides a computing device comprising a memory and a processor, the memory having executable code stored therein, and the processor executes the executable code to implement the method of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 a flowchart of a dual-interferometer system demodulation method provided by an embodiment of the present application;

[0041] Figure 2An example diagram of a dual-interferometer system demodulation method provided for an embodiment of the present application is shown in the figure;

[0042] Figure 3 A structure diagram of a dual-interferometer hydrophone probe extracted for an embodiment of the present application is shown in the figure;

[0043] Figure 4 A structure diagram of a dual-interferometer system demodulation device provided for an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0044] The technical solutions of the present application will be further described in detail below with the aid of the accompanying drawings and embodiments.

[0045] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below with the aid of the accompanying drawings. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0046] In the description of the embodiments of the present application, the words "exemplary", "for example", or "for instance" are used to mean serving as an example, instance or illustration. Any embodiment or design presented as "exemplary", "for example" or "for instance" in the embodiments of the present application should not be interpreted as being more preferred or advantageous than other embodiments or design solutions. Rather, the use of the words "exemplary", "for example" or "for instance" is intended to present the relevant concept in a specific manner.

[0047] Traditional optical phase noise suppression techniques mainly rely on precise control of the laser, such as active frequency stabilization technology based on PDH, or phase-locked technology based on external cavity injection, etc. However, these methods usually require the introduction of complex and high-cost hardware systems, such as super-stable cavities, micro-ring resonant cavities, etc. In practical applications, these methods have high requirements for the stability of the working environment, so the application scenarios of these methods are usually limited.

[0048] In recent years, significant progress has been made in noise cancellation methods based on reference interferometers. These methods use a reference interferometer to obtain a homologous noise signal, and use a signal interferometer to subtract the measurement noise to achieve noise suppression, without the need for precise control of the laser. However, these methods usually require the modulation depth of the system to be kept at the optimal position to eliminate the nonlinear effect of the modulation depth on the demodulation signal. In actual situations, the dynamic changes of the environment will cause the arm length difference of the interferometer to change in real time, making it difficult to keep the modulation depth at the optimal position, thereby introducing nonlinear distortion. The distorted signal without compensation will exist after subtraction, affecting the noise cancellation effect.

[0049] In order to overcome the deficiencies in the prior art, and based on the above, a dual-interferometer system demodulation method and device are provided. A laser is emitted by a modulated laser into a dual-interferometer system with equal arm length difference, the modulation depth of the dual-interferometer is solved by an ellipse fitting algorithm and eliminated, the optical phase signal of the eliminated noise is solved by the sum and difference formula and the arctangent operation, so as to obtain more accurate optical phase noise measurement.

[0050] Figure 1 A flow chart of a dual-interferometer system demodulation method provided by an embodiment of the present application is shown in FIG. 1. Figure 1 The method mainly includes the following steps:

[0051] Step S101: A laser is generated by a modulated laser, and the laser is input into a signal interferometer and a reference interferometer, to determine a first quadrature signal and a second quadrature signal corresponding to the signal interferometer, and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer; the arm length difference of the signal interferometer and the reference interferometer is equal.

[0052] For example, a laser is generated by a modulated laser, and the laser is divided into two paths by a beam splitter and enters a reference interferometer and a signal interferometer respectively, a first light intensity is output by the signal interferometer, and a second light intensity is output by the reference interferometer, a first Bessel function expansion formula of the first light intensity and a second Bessel function expansion formula of the second light intensity are obtained by performing Bessel function expansion on the first light intensity and the second light intensity respectively, the first quadrature signal and the second quadrature signal of the signal interferometer are obtained by performing low-pass filtering on the calculation result of multiplying the first Bessel function expansion formula by a first fundamental frequency signal and a first second-harmonic signal, and the third quadrature signal and the fourth quadrature signal of the reference interferometer are obtained by performing low-pass filtering on the calculation result of multiplying the second Bessel function expansion formula by a second fundamental frequency signal and a second second-harmonic signal.

[0053] Figure 2 An example diagram of a dual-interferometer system demodulation method provided by an embodiment of the present application is shown in FIG. 2. Figure 2 As shown in FIG. 2, an arbitrary waveform generator (AWG) generates an electrical signal to drive a laser diode (LD) to generate a laser, the laser is divided into two paths by a beam splitter and enters a reference interferometer and a signal interferometer respectively, and the reference interferometer is in a quiet environment.

[0054] Figure 3A structure diagram of a double-interferometer hydrophone probe provided by an embodiment of the present application is shown in the figure, and the hydrophone probe will adopt a core shaft type push-pull structure, which is composed of an inner cylinder, an air cavity and an outer cylinder. The inner cylinder is used to wind the reference arm optical fiber of the signal interferometer, and the outer cylinder is used to wind the sensing arm optical fiber of the signal interferometer. When the underwater acoustic signal propagates to the sensing unit, the inner cylinder and the outer cylinder will be deformed under the action of the sound pressure, and cause the surrounding optical fiber to be slightly deformed. The deformation causes the refractive index of the optical fiber to change, and finally reflects on the phase of the optical signal in the sensing arm. The air cavity is used to store the reference interferometer, and the layer will be made of a material with high Young's modulus (such as tungsten steel / graphene), so that external signals are difficult to cause the layer to be deformed, thereby ensuring the accuracy of the reference interferometer system noise measurement.

[0055] The PGC (Phase Generated Carrier) demodulation technology is an active phase demodulation method. The core principle is that: first, a high-frequency phase modulation signal (whose frequency is outside the frequency band of the signal to be measured) is loaded onto the interference optical signal. Then, the modulated interference optical signal is multiplied (mixed) with two reference signals: one is a base frequency signal with the same frequency as the phase modulation signal, and the other is a frequency-doubled signal with double the frequency. The mixed signals are filtered by a low-pass filter to remove all high-frequency components, and finally a pair of orthogonal signals containing the measured information is output. By a specific signal processing algorithm (such as differential cross-multiplication method, arctangent method, etc.), the measured phase information contained in the pair of orthogonal signals can be demodulated.

[0056] According to the PGC demodulation algorithm, the signal interferometer outputs a first light intensity, and the reference interferometer outputs a second light intensity, which is represented as:

[0057]

[0058] wherein A s , A r is the direct current light intensity, B s is the modulation amplitude of the signal interferometer, B r is the modulation amplitude of the reference interferometer, C s , C r is the modulation depth, ω0 is the carrier angular frequency, is the optical phase signal, is the optical phase noise, is an additional low-frequency sinusoidal signal introduced, I s is the first light intensity output by the signal interferometer, I r is the second light intensity output by the reference interferometer;

[0059] The Bessel function expansion of the first light intensity and the second light intensity is carried out to obtain the Bessel function expansion of the first light intensity and the Bessel function expansion of the second light intensity, which is represented as:

[0060]

[0061] where I s ′ is the Bessel function expansion of the first light intensity, I r ′ is the Bessel function expansion of the second light intensity, A s , A r is the direct current light intensity, B s is the modulation amplitude of the signal interferometer, B r is the modulation amplitude of the reference interferometer, C s , C r is the modulation depth, is the optical phase signal, is the optical phase noise, is the introduced additional low frequency sinusoidal signal, J 2k+1 (C r ) is the odd order Bessel function, J 2k (C r ) is the even order Bessel function, (-1) k is the sign change of the phase reflecting the periodicity of the modulation process.

[0062] By multiplying I s ′, I r ′ with the fundamental frequency signal G cos(ω0t) and the double frequency signal H cos(2ω0t) respectively, and then passing through low pass filters (LPF) with a cut-off frequency of 1 / 2 of the modulation frequency, the first quadrature signal S S and the second quadrature signal S S2 of the signal interferometer, and the third quadrature signal S R1 and the fourth quadrature signal S R2 of the reference interferometer are obtained, which are expressed as:

[0063]

[0064] where S S1 is the first quadrature signal of the signal interferometer, S S2 is the second quadrature signal of the signal interferometer, S R1 is the third quadrature signal of the reference interferometer, S R2 is the fourth quadrature signal of the reference interferometer, C s , C r is the modulation depth, B s is the modulation amplitude of the signal interferometer, B r is the modulation amplitude of the reference interferometer, G, H are gain factors, J1(C s ), J1(C r ) are first order Bessel function values, J2(C s ), J2(C r) is the second order Bessel function value, is the optical phase signal, is the optical phase noise, is the introduced extra low frequency sinusoidal signal. In practice, the system noise is proportional to the difference of the arm lengths, and the difference of the arm lengths of the two interferometers will be controlled within 50 cm to further reduce the system noise.

[0065] Step S102: solving the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer by the ellipse fitting algorithm, and calculating the Bessel function values of the first modulation depth and the second modulation depth, obtaining the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth, and the fourth quadrature signal without modulation depth from the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal.

[0066] For example, the first quadrature signal and the second quadrature signal of the signal interferometer, and the third quadrature signal and the fourth quadrature signal of the reference interferometer are constituted into an ellipse fitting curve by the ellipse fitting algorithm, the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer are calculated by the ellipse fitting curve, and the first order Bessel function value and the second order Bessel function value of the first modulation depth and the first order Bessel function value and the second order Bessel function value of the second modulation depth are calculated, the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal are divided by the known constant modulation amplitude of the signal interferometer, the modulation amplitude of the reference interferometer, the gain factor, the first order Bessel function value and the second order Bessel function value of the first modulation depth, and the first order Bessel function value and the second order Bessel function value of the second modulation depth to obtain the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth, and the fourth quadrature signal without modulation depth.

[0067] For example, Figure 2 As shown, the electrical signal passing through the low-pass filter (LPF) enters the ellipse fitting algorithm (EFA) for further signal processing, and the first quadrature signal and the second quadrature signal of the signal interferometer, and the third quadrature signal and the fourth quadrature signal of the reference interferometer are constituted into an ellipse fitting curve, and the ellipse fitting curve is represented as:

[0068]

[0069] Wherein, C s , C r is the modulation depth, S S1 is the first quadrature signal of the signal interferometer, S S2 is the second quadrature signal of the signal interferometer, S R1is the third orthogonal signal of the reference interferometer, S R2 The fourth orthogonal signal of the reference interferometer, J1(C s )、J1(C r ) is the first-order Bessel function value, J2(C s )、J2(C r ) is the value of the second-order Bessel function;

[0070] The relevant parameters J2(C s ) / J1(C s )、J2(C r ) / J1(C r ), Expressed as:

[0071]

[0072] The first modulation depth C of the reference interferometer is obtained according to the relationship f between the modulation depth C and J1(C) / J2(C) s The second modulation depth C of the sum signal interferometer r , expressed as:

[0073] C s =f(J2(C s ) / J1(C s ))

[0074] C r =f(J2(C r ) / J1(C r ))

[0075] Calculate the first-order Bessel function value J1(C s ) and the second-order Bessel function value J2(C s ) and the first-order Bessel function value J1(C r ) and the second-order Bessel function value J2(C r ), the first orthogonal signal S S1 and the second orthogonal signal S S2 , the third orthogonal signal S R1 and the fourth orthogonal signal S R2 Divide the modulation amplitude of the interferometer signal by the known constant B s , the modulation amplitude B of the reference interferometer r , gain factor G, H, first order Bessel function value J1(C s ) and the second-order Bessel function value J2(C s ) and the first-order Bessel function value J1(C r ) and the second-order Bessel function value J2(Cr ), a first quadrature signal of the removed modulation depth, a second quadrature signal of the removed modulation depth, a third quadrature signal of the removed modulation depth, and a fourth quadrature signal of the removed modulation depth are obtained, and are expressed as:

[0076]

[0077] wherein S S1 ' is the first quadrature signal of the removed modulation depth, S S2 ' is the second quadrature signal of the removed modulation depth, S R1 ' is the third quadrature signal of the removed modulation depth, and S R2 ' is the fourth quadrature signal of the removed modulation depth, is the optical phase signal, is the optical phase noise, is an introduced additional low-frequency sinusoidal signal.

[0078] Step S103: Constructing a product-sum difference formula according to the first quadrature signal of the removed modulation depth, the second quadrature signal of the removed modulation depth, the third quadrature signal of the removed modulation depth, and the fourth quadrature signal of the removed modulation depth, and obtaining the optical phase signal of the removed noise through an arctangent operation.

[0079] For example, the product-sum difference formula is expressed as:

[0080]

[0081] wherein, is the optical phase signal, is the optical phase noise, is the introduced additional low-frequency sinusoidal signal, is the first quadrature signal of the removed modulation depth, is the second quadrature signal of the removed modulation depth, is the third quadrature signal of the removed modulation depth, is the fourth quadrature signal of the removed modulation depth.

[0082] The arctangent operation is expressed as:

[0083]

[0084] wherein, is the optical phase signal.

[0085] For example, Figure 2 As shown, a series of multipliers and adders are used to operate the sinusoidal and cosine signals of different phases to obtain and and further calculate Finally, the phase of the signal is extracted by an "Arctan" (inverse tangent function operation)

[0086] According to an embodiment of the present application, a dual-interferometer system demodulation device is provided. Figure 4 A structure diagram of a dual-interferometer system demodulation device provided by an embodiment of the present application is shown in FIG. 4, which comprises: Figure 4

[0087] A modulation unit 401 is configured to generate laser by modulating a laser, input the laser into a signal interferometer and a reference interferometer, determine a first quadrature signal and a second quadrature signal corresponding to the signal interferometer and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer, and the arm length difference of the signal interferometer and the reference interferometer is equal.

[0088] An ellipse fitting unit 402 is configured to solve a first modulation depth of the signal interferometer and a second modulation depth of the reference interferometer by an ellipse fitting algorithm, calculate the Bessel function value of the first modulation depth and the second modulation depth, and obtain a first quadrature signal without modulation depth, a second quadrature signal without modulation depth, a third quadrature signal without modulation depth, and a fourth quadrature signal without modulation depth according to the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal.

[0089] An operation unit 403 is configured to construct a product and difference formula according to the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth, and the fourth quadrature signal without modulation depth, and obtain a noise-removed optical phase signal by an inverse tangent operation.

[0090] ​It can be understood that the method steps in the embodiments of the present application can be implemented by hardware, or by a combination of software and hardware executed by a processor. The software instructions can be composed of a corresponding software module, and the software module can be stored in a random access memory (RAM), a flash memory, a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically EPROM (EEPROM), a register, a hard disk, a mobile hard disk, a CD-ROM, or any other form of storage medium well known in the art. An exemplary storage medium is coupled to the processor, so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an ASIC.

[0091] In the above embodiments, all or some of the steps can be implemented by software, hardware, firmware or any combination thereof. When implemented by software, all or some of the steps can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded into and executed by a computer, all or some of the steps described in the embodiments of the present application are performed. The computer can be a general purpose computer, a special purpose computer, a computer network, or other programmable apparatuses. The computer instructions can be stored in or transmitted from a computer readable storage medium. The computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center through a wired (such as a coaxial cable, an optical fiber, a digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.) manner. The computer readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server, data center, etc. integrated with one or more available media sets. The available media can be a magnetic medium (such as a floppy disk, a hard disk, a magnetic tape), an optical medium (such as a DVD), or a semiconductor medium (such as a solid state disk (SSD)), etc.

[0092] The above detailed description of the specific embodiments of the present application has been given to understand the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for demodulating a dual-interferometer system, comprising: generating laser light by a modulated laser, inputting the laser light into a signal interferometer and a reference interferometer, determining a first quadrature signal and a second quadrature signal corresponding to the signal interferometer, and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer, wherein the arm length difference of the signal interferometer and the reference interferometer is equal; solving a first modulation depth of the signal interferometer and a second modulation depth of the reference interferometer by an ellipse fitting algorithm, calculating the Bessel function values of the first modulation depth and the second modulation depth, and obtaining a first quadrature signal without modulation depth, a second quadrature signal without modulation depth, a third quadrature signal without modulation depth, and a fourth quadrature signal without modulation depth according to the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal; constructing a product-sum-difference formula according to the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth, and the fourth quadrature signal without modulation depth, and obtaining a noise-removed optical phase signal by an inverse tangent operation.

2. The method of claim 1, wherein, generating laser light by a modulated laser, inputting the laser light into a signal interferometer and a reference interferometer, determining a first quadrature signal and a second quadrature signal corresponding to the signal interferometer, and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer, comprising: generating laser light by a modulated laser, splitting the laser light into two paths by a beam splitter, inputting the two paths into the reference interferometer and the signal interferometer respectively, outputting a first light intensity by the signal interferometer and a second light intensity by the reference interferometer, performing Bessel function expansion on the first light intensity and the second light intensity respectively to obtain a first Bessel function expansion formula of the first light intensity and a second Bessel function expansion formula of the second light intensity, obtaining the first quadrature signal and the second quadrature signal of the signal interferometer by low-pass filtering the calculation result of multiplying the first Bessel function expansion formula by a first fundamental frequency signal and a first second-harmonic signal, and obtaining the third quadrature signal and the fourth quadrature signal of the reference interferometer by low-pass filtering the calculation result of multiplying the second Bessel function expansion formula by a second fundamental frequency signal and a second second-harmonic signal.

3. The method of claim 2, wherein, the first light intensity output by the signal interferometer and the second light intensity output by the reference interferometer are represented as: wherein A s , A r is the direct current light intensity, B s is the modulation amplitude of the signal interferometer, B r is the modulation amplitude of the reference interferometer, C s , C r is the modulation depth, ω0is the carrier angular frequency, is the optical phase signal, is the optical phase noise, is an additional low frequency sinusoidal signal introduced, I s is the first light intensity output by the signal interferometer, I r is the second light intensity output by the reference interferometer; the first quadrature signal and the second quadrature signal of the signal interferometer, and the third quadrature signal and the fourth quadrature signal of the reference interferometer are represented as: where S S1 is a first quadrature signal of the signal interferometer, S S2 is a second quadrature signal of the signal interferometer, S R1 is a third quadrature signal of the reference interferometer, S R2 is a fourth quadrature signal of the reference interferometer, C s , C r is a modulation depth, B s is a modulation amplitude of the signal interferometer, B r is a modulation amplitude of the reference interferometer, G, H are gain factors, J1(C s ), J1(C r ) are first order Bessel function values, J2(C s ), J2(C r ) are second order Bessel function values, is an optical phase signal, is an optical phase noise, is an introduced additional low frequency sinusoidal signal.

4. The method of claim 1, wherein, the solving of the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer by the ellipse fitting algorithm, the calculation of the Bessel function values of the first modulation depth and the second modulation depth, and the obtaining of the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth, and the fourth quadrature signal without modulation depth according to the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal, comprising: The first quadrature signal and the second quadrature signal of the signal interferometer and the third quadrature signal and the fourth quadrature signal of the reference interferometer are constituted into an ellipse fitting curve through an ellipse fitting algorithm, the first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer are calculated through the ellipse fitting curve, the first order Bessel function value and the second order Bessel function value of the first modulation depth and the first order Bessel function value and the second order Bessel function value of the second modulation depth are calculated, the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal are divided by known constant signals, the modulation amplitude of the signal interferometer, the modulation amplitude of the reference interferometer, a gain factor, the first order Bessel function value and the second order Bessel function value of the first modulation depth and the first order Bessel function value and the second order Bessel function value of the second modulation depth to obtain the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth and the fourth quadrature signal without modulation depth.

5. The method of claim 4, wherein, The ellipse fitting curve is expressed as: wherein C s is a first modulation depth of the signal interferometer, C r is a second modulation depth of the reference interferometer, S S1 is a first quadrature signal of the signal interferometer, S S2 is a second quadrature signal of the signal interferometer, S R1 is a third quadrature signal of the reference interferometer, S R2 is a fourth quadrature signal of the reference interferometer, J1(C s ), J1(C r ) is a first Bessel function value, J2(C s ), J2(C r ) is a second Bessel function value; The first modulation depth of the signal interferometer and the second modulation depth of the reference interferometer are calculated through the ellipse fitting curve, which includes: J1(C) / J2(C) is obtained from the coefficients a1, a2, b1, b2 in the elliptic curve, the modulation depth C of the reference interferometer is obtained according to the relationship f of the modulation depth C and J1(C) / J2(C) s and the modulation depth C of the signal interferometer r ; The first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth and the fourth quadrature signal without modulation depth are expressed as: where S S1 is the first quadrature signal with removed modulation depth, S S2 is the second quadrature signal with removed modulation depth, S R1 is the third quadrature signal with removed modulation depth, S R2 is the fourth quadrature signal with removed modulation depth, is the optical phase signal, is the optical phase noise, is the introduced additional low frequency sinusoidal signal.

6. The method of claim 1, wherein, The product-sum and difference formula is expressed as: wherein is the optical phase signal, is the optical phase noise, is an introduced additional low frequency sinusoidal signal, is a first quadrature signal with removed modulation depth, is a second quadrature signal with removed modulation depth, is a third quadrature signal with removed modulation depth, is a fourth quadrature signal with removed modulation depth; The arctangent operation is expressed as: wherein is the optical phase signal.

7. A dual-interferometer system demodulation apparatus, comprising: a modulation unit configured to generate laser light by modulating a laser, input the laser light into a signal interferometer and a reference interferometer, and determine a first quadrature signal and a second quadrature signal corresponding to the signal interferometer and a third quadrature signal and a fourth quadrature signal corresponding to the reference interferometer; the arm length difference of the signal interferometer and the reference interferometer is equal; an ellipse fitting unit configured to solve a first modulation depth of the signal interferometer and a second modulation depth of the reference interferometer through an ellipse fitting algorithm, calculate Bessel function values of the first modulation depth and the second modulation depth, and obtain a first quadrature signal without modulation depth, a second quadrature signal without modulation depth, a third quadrature signal without modulation depth and a fourth quadrature signal without modulation depth from the first quadrature signal and the second quadrature signal, the third quadrature signal and the fourth quadrature signal; an operation unit configured to construct a product-sum and difference formula according to the first quadrature signal without modulation depth, the second quadrature signal without modulation depth, the third quadrature signal without modulation depth and the fourth quadrature signal without modulation depth, and obtain a noise-removed optical phase signal through an arctangent operation.

8. An electronic device comprising: A processor, a memory and computer program instructions stored on the memory and executable on the processor, wherein the processor executes the computer program instructions to implement the method of any one of claims 1 to 6.

9. A computer readable storage medium, wherein, The computer readable storage medium stores computer execution instructions, and the computer execution instructions are executed by the processor to implement the method of any one of claims 1 to 6.

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