A method for measuring and compensating for Y waveguide waveform slope

Abstract

The present application provides a Y waveguide waveform slope measurement and compensation method to solve the problem that the existing high-precision fiber-optic gyroscope Y waveguide waveform slope measurement method is based on the characteristics of the Y waveguide itself, ignoring the error of the fiber-optic gyroscope closed loop modulation wave when resetting caused by the Y waveguide waveform slope after the Y waveguide is connected with the optical path of the fiber-optic gyroscope. The present application uses the existing optical path and circuit for testing the performance of the fiber-optic gyroscope, uploads the Y waveguide waveform slope test results to the upper computer through the circuit, and when a ±23 / 8π square wave is used as a digital demodulation circuit to apply a waveform slope trigger signal, the pressure difference of the fiber-optic gyroscope demodulation signal before and after resetting is the largest. The upper computer calculates the Y waveform slope error, compensates for the error of the fiber-optic gyroscope closed loop modulation wave when resetting, improves the gyroscope precision of the fiber-optic gyroscope at a small rate of rotation, and improves the application range of the fiber-optic gyroscope.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of measurement, in particular to a Y waveguide waveform slope measurement and compensation method. BACKGROUND

[0002] At present, the performance detection of high-precision fiber optic gyroscope generally adopts a full-digital closed-loop detection method. As a special modulation device of fiber optic gyroscope, the Y waveguide phase modulator, referred to as Y waveguide, has a great relationship with the performance of the fiber optic gyroscope. The Y waveguide has a wide application in the field of optical fiber sensing and photoelectric signal processing. The principle of the Y waveguide is that an external voltage signal generates a modulation electric field through the electrodes on both sides of the Y waveguide, thereby changing the effective refractive index of the Y waveguide, and realizing the phase modulation of the transmitted optical signal.

[0003] Phase change of light wave after phase modulation which can be expressed as:

[0004]

[0005] where Δβ is the constant change amount of the Y waveguide caused by the voltage; n e is the refractive index of LiNbO3 crystal; γ 33 is the Pockels electro-optic coefficient; λ is the wavelength in vacuum; L is the electrode length of the modulator; T is the overlap factor of the electric field and the optical field; V is the external bias voltage; G is the spacing of the planar electrodes; Δn e is the change of the refractive index of LiNbO3 crystal caused by the external electric field;

[0006] Δn e =γ 33 E+κE 2 +… (2)

[0007] where E is the intensity of the modulation electric field; κ is the Kerr electro-optic coefficient.

[0008] The second term in formula (2) is a second-order high-order term. In actual engineering applications, the electro-optic effect of LiNbO3 crystal has high-order nonlinear electro-optic effect. When a square wave modulation is applied to the Y waveguide of the closed-loop fiber optic gyroscope, nonlinear distortion of the actual electro-optic effect will be caused, and eventually a slope wave at the bottom of the comb wave will be generated in the output of the closed-loop fiber optic gyroscope detector.

[0009] As shown in (a) and (b), the slope of the output waveform of the fiber optic gyroscope detector will produce an error voltage Figure 1 compared with the ideal output. After AD sampling, an additional phase error Finally, it leads to the insensitivity of the gyroscope at a small angular rate, and the dead zone phenomenon occurs, and the error voltage will affect the scale factor of the fiber-optic gyroscope at a small angular rate, and affect the performance of the high-precision fiber-optic gyroscope in the application of inertial measurement unit calibration and alignment.

[0010] The ideal modulation signal is applied to the Y waveguide of the high-precision fiber-optic gyroscope, and the nonlinearity of the Y waveguide electro-optic effect leads to the slope of the fiber-optic gyroscope detector waveform, and finally leads to the additional phase in the demodulation of the fiber-optic gyroscope.

[0011] The traditional Y waveguide waveform slope measurement method is based on the characteristics of the Y waveguide itself, and does not consider the measurement method and compensation method of the Y waveguide waveform slope in the actual application after the Y waveguide is connected with the optical path of the fiber-optic gyroscope. Therefore, the measurement error and compensation method of the Y waveguide waveform slope leading to the modulation wave of the fiber-optic gyroscope closed loop in the reset is an urgent research topic. SUMMARY

[0012] The purpose of the present application is to solve the problem that the existing Y waveguide waveform slope measurement method for high-precision fiber-optic gyroscope is based on the characteristics of the Y waveguide itself, and ignores the error caused by the Y waveguide waveform slope leading to the modulation wave of the fiber-optic gyroscope closed loop in the reset after the Y waveguide is connected with the optical path of the fiber-optic gyroscope, and provides a Y waveguide waveform slope measurement and compensation method.

[0013] To achieve the above purpose, the technical scheme adopted by the present application is:

[0014] A Y waveguide waveform slope measurement and compensation method, which is characterized by comprising the following steps:

[0015] Step 1), build a Y waveguide waveform slope measurement loop;

[0016] The Y waveguide waveform slope measurement loop comprises an ASE light source, a 2*2 coupler, a fiber ring, a photodetector, a digital demodulation circuit and a host computer.

[0017] The output end of the ASE light source is connected with the input end of the 2*2 coupler, the first output end of the 2*2 coupler is connected with the input end of the Y waveguide optical path to be measured; the two bifurcated ends of the Y waveguide are respectively connected with the two ends of the fiber ring; the second output end of the 2*2 coupler is connected with the input end of the photodetector, the output end of the photodetector is connected with the first input end of the digital demodulation circuit, the first output end of the digital demodulation circuit is connected with the input end of the host computer, the output end of the host computer is connected with the second input end of the digital demodulation circuit, and the second output end of the digital demodulation circuit is respectively connected with the two modulation electrode ends of the Y waveguide.

[0018] Step 2), a modulating square wave with amplitude A is continuously applied to the two modulation electrodes of the Y waveguide through a digital demodulation circuit, an electric field is generated to make the light emitted by the ASE light source interfere with the 2*2 coupler and the Y waveguide, a phase shift is generated, and after propagating through the fiber ring, interference occurs, the interference light passes through the 2*2 coupler and reaches the photodetector for photoelectric conversion to form a comb wave with a waveform slope;

[0019] Step 3), a high-speed AD acquisition card is used to collect the waveform of the comb wave, and the waveform is recorded and transmitted to the upper computer;

[0020] Step 4), the upper computer calculates the digital quantity of the waveform slope of the comb wave and calculates the waveform slope value;

[0021] Step 5), the waveform slope values sampled in a waveform slope period are normalized to obtain a quadratic fitting waveform slope curve, and the waveform slope compensation parameters are solved;

[0022] Step 6), the waveform slope compensation parameters are configured into the digital demodulation circuit to compensate for the additional phase caused by the waveform slope in the fiber optic gyroscope demodulation process.

[0023] Further, in step 2), the amplitude A of the modulating square wave is ±23 / 8π.

[0024] Further, step 5) is specifically:

[0025] 5.1), the waveform slope values sampled in a waveform slope period are normalized to obtain a quadratic fitting waveform slope curve;

[0026] 5.2), the compensation parameters

[0027] Define a set of N sampling points in a waveform slope period as 1≤k≤N, the quadratic fitting curve is represented as: f(x)=At 2 +Bt+C, which is converted to:

[0028]

[0029]

[0030]

[0031] where, t k is the sampling time corresponding to the kth sampling point; y k is the signal amplitude corresponding to the kth sampling point; A, B and C are all waveform slope compensation parameters;

[0032] ​Solve the equation set to obtain the waveform slope compensation parameters A, B and C.

[0033] Compared with the prior art, the application has the beneficial technical effects as follows:

[0034] 1. The Y waveguide waveform slope measurement and compensation method provided by the application is aimed at the error of the modulation wave of the closed loop of the fiber optic gyroscope when resetting, quantitatively tests the waveform slope of the Y waveguide under the condition, and compensates for the error. The Y waveguide waveform slope test result is collected and uploaded to the host computer through the existing optical circuit and circuit for testing the performance of the fiber optic gyroscope, and the host computer calculates the Y waveform slope error and compensates for the error of the modulation wave of the closed loop of the fiber optic gyroscope when resetting, so as to improve the precision of the fiber optic gyroscope at a small rate of rotation and expand the application range of the fiber optic gyroscope.

[0035] 2. When the Y waveguide waveform slope measurement and compensation method provided by the application adopts ±23 / 8π square wave as the waveform slope trigger signal of the digital demodulation circuit, the pressure difference of the fiber optic gyroscope demodulation signal before and after resetting is the largest, and the waveform slope effect is the most obvious, and the ±23 / 8π square wave modulation takes into account the cross-stripe working condition in the application process of the high-precision fiber optic gyroscope, and also meets the over-modulation technical requirement of the high-precision fiber optic gyroscope. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The ideal output and actual output waveform diagram of the modulation square wave is applied to the closed loop fiber optic gyroscope and sampled; wherein (a) is the ideal output and actual output waveform diagram of the applied modulation square wave; (b) is the ideal output and actual output waveform diagram of the sampled modulation square wave;

[0037] Figure 2 The principle diagram of the Y waveguide waveform slope measurement and compensation method of the application;

[0038] Figure 3 The Y waveguide waveform slope curve diagram collected by the host computer in the embodiment of the application;

[0039] Figure 4 The waveform slope curve diagram after Y waveguide waveform slope compensation in the embodiment of the application;

[0040] REFERENCE NUMERALS:

[0041] 1-ASE light source, 2-2*2 coupler, 3-Y waveguide, 4-optical fiber ring, 5-optoelectronic detector, 6-digital demodulation circuit, 7-host computer. DETAILED DESCRIPTION

[0042] In order to make the purposes, advantages and characteristics of the present application more clear, a Y waveguide waveform slope measurement and compensation method is further described in detail below in combination with the drawings and specific embodiments. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and are not intended to limit the protection scope of the present application.

[0043] As shown in Figure 2 , the Y waveguide waveform slope measurement circuit includes an ASE light source 1, a 2*2 coupler 2, a fiber ring 4, a photodetector 5, a digital demodulation circuit 6 and a host computer 7. The output end of the ASE light source 1 is connected with the input end of the 2*2 coupler 2, the first output end of the 2*2 coupler 2 is connected with the input end of the Y waveguide 3 to be measured, the two bifurcated ends of the Y waveguide 3 are respectively connected with the two ends of the fiber ring 4, the second output end of the 2*2 coupler 2 is connected with the input end of the photodetector 5, the output end of the photodetector 5 is connected with the first input end of the digital demodulation circuit 6, the first output end of the digital demodulation circuit 6 is connected with the input end of the host computer 7, the output end of the host computer 7 is connected with the second input end of the digital demodulation circuit 6, and the second output end of the digital demodulation circuit 6 is connected with the modulation electrode end of the Y waveguide 3.

[0044] The ASE light source 1 provides light for generating a signal, which is introduced into the input end of the Y waveguide 3 to be measured after being split by the 2*2 coupler 2. The Y waveguide 3 integrates the functions of polarization, beam splitting and phase modulation. The transmitted light signal forms a polarized light after passing through the Y waveguide 3, and then propagates in opposite directions in the fiber ring 4. Due to the beam combining and polarization of the Y waveguide 3 to be measured, the light signals propagating in opposite directions through the fiber ring 4 meet at the Y waveguide 3 and form interference waves. The interference waves enter the photodetector 5 after being split by the 2*2 coupler 2, and are converted into electrical signals as the input of the digital demodulation circuit 6. The electrical signals are transmitted to the host computer 7 after AD acquisition and demodulation, and are fed back to the digital demodulation circuit 6 after compensation in the host computer 7. The digital demodulation circuit 6 simultaneously applies a trigger modulation signal to the Y waveguide 3.

[0045] The specific steps of measuring and compensating the Y waveguide waveform slope to be measured by using the above-mentioned Y waveguide measurement circuit are as follows:

[0046] Step 1), build the above-mentioned Y waveguide waveform slope measurement circuit, and power on the ASE light source 1 and the digital demodulation circuit 6;

[0047] Step 2), continuously apply a square wave modulation of a certain amplitude to the two modulation electrodes of the Y waveguide 3 through the digital demodulation circuit 6, so that the light emitted by the ASE light source 1 produces a phase shift of after passing through the 2*2 coupler 2 and the Y waveguide 3, and then propagates through the fiber ring 4 to produce interference. The interference light reaches the photodetector 5 after passing through the 2*2 coupler 2 to perform photoelectric conversion, forming a waveform as shown inFigure 1 The comb wave shown in the figure has a waveform slope;

[0048] Step 3), collect the shape of the comb wave by using a high-speed AD acquisition card, record and transmit to the upper computer 7;

[0049] Step 4), the upper computer 7 calculates the waveform slope digital quantity of the restored comb wave, and calculates the waveform slope value;

[0050] Step 5), normalize the waveform slope value data sampled in a waveform slope period, obtain the waveform slope curve after quadratic fitting, and solve the waveform slope compensation parameters;

[0051] The data normalization processing is to accumulate the original data, compare the accumulated value with the normal acquisition value, and directly calculate the real waveform slope value of the waveguide through the upper computer 7;

[0052] Suppose the set of N sampling points in a waveform slope period is 1≤k≤N, the quadratic fitting curve is expressed as: f(x)=At 2 +Bt+C, which is converted to:

[0053]

[0054]

[0055]

[0056] Where, t k is the sampling time corresponding to the kth sampling point; y k is the signal amplitude corresponding to the kth sampling point; A, B and C are all waveform slope compensation parameters;

[0057] Solve the equation set to obtain the waveform slope compensation parameters A, B and C.

[0058] Step 6), configure the waveform slope compensation parameters to the digital demodulation circuit 6, and compensate the additional phase caused by the waveform slope in the optical fiber gyroscope demodulation process.

[0059] The Y waveguide waveform slope measurement and compensation method of the embodiment can control the acquisition rate and the square wave amplitude applied to the Y waveguide electrode through software, and test the waveguide waveform slope under different modulated square waves by repeating steps 2)-6). It is found through testing that when the waveform slope trigger signal applied by the digital demodulation circuit 6 is ±23 / 8π square wave modulation, the pressure difference of the optical fiber gyroscope demodulation signal before and after reset is the largest, the waveform slope effect is the most obvious, and the ±23 / 8π square wave modulation takes into account the cross-stripe working condition in the application process of high-precision optical fiber gyroscope, and also meets the over-modulation technology demand of high-precision optical fiber gyroscope.

[0060] Figure 3 In order to compensate the Y waveguide waveform slope waveform collected in advance, after twice fitting compensation, the Y waveguide waveform slope waveform as shown in FIG. 6 is obtained. It can be seen that the fitting curve is consistent with the change trend of the Y waveguide waveform slope, the error of the Y waveguide in the reset of the modulation wave in the closed loop of the fiber optic gyroscope is compensated, the precision of the fiber optic gyroscope at a small rate of rotation is improved, and the application range of the fiber optic gyroscope is improved. Figure 4

[0061] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.​

Claims

1. A Y waveguide wave shape skew measurement and compensation method, characterized by, The method comprises the following steps: Step 1), building a Y waveguide waveform slope measurement circuit; The Y waveguide waveform slope measurement circuit comprises an ASE light source (1), a 2*2 coupler (2), a fiber ring (4), a photodetector (5), a digital demodulation circuit (6) and a host computer (7); The output end of the ASE light source (1) is connected with the input end of the 2*2 coupler (2), the first output end of the 2*2 coupler (2) is connected with the input end of the Y waveguide (3), the two bifurcated ends of the Y waveguide (3) are connected with the two ends of the fiber ring (4) respectively, the second output end of the 2*2 coupler (2) is connected with the input end of the photodetector (5), the output end of the photodetector (5) is connected with the first input end of the digital demodulation circuit (6), the first output end of the digital demodulation circuit (6) is connected with the input end of the host computer (7), the output end of the host computer (7) is connected with the second input end of the digital demodulation circuit (6), and the second output end of the digital demodulation circuit (6) is connected with the two modulation electrode ends of the Y waveguide (3) respectively; Step 2), the modulating square wave with amplitude A is continuously applied to the two modulating electrodes of the Y waveguide (3) by the digital demodulation circuit (6), the electric field is generated to make the light emitted by the ASE light source (1) pass through the 2*2 coupler (2) and the Y waveguide (3), and the phase shift is generated After the light passes through the optical fiber ring (4) and interferes, the interfered light reaches the photoelectric detector (5) to form the comb wave with the waveform slope after the photoelectric conversion through the 2*2 coupler (2). Step 3), collecting the waveform of the comb wave by using a high-speed AD acquisition card, and recording and transmitting to the host computer (7); Step 4), the host computer (7) calculates the waveform slope digital quantity of the restored comb wave, and calculates the waveform slope value; Step 5), normalizing the waveform slope value sampled in one waveform slope period to obtain the waveform slope curve after quadratic fitting, and solving the waveform slope compensation parameters; specifically: 5.1), normalizing the waveform slope value sampled in one waveform slope period to obtain the waveform slope curve after quadratic fitting; 5.2), solving the compensation parameters A set of N sampling points within one waveform slope period is defined as The quadratic fitting curve is expressed as: f(x) = At 2 +Bt+C, which is converted to: Wherein, t k is the sampling time corresponding to the kth sampling point; y k is the signal amplitude corresponding to the kth sampling point; A, B and C are waveform slope compensation parameters; Solving the equation set to obtain the waveform slope compensation parameters A, B and C; Step 6), configure the waveform slope compensation parameter into the digital demodulation circuit (6) to compensate the additional phase caused by the waveform slope in the fiber-optic gyroscope demodulation process is made.

2. The Y waveguide waveform slope measurement and compensation method according to claim 1, wherein the amplitude A of the modulated square wave is ±23 / 8π in step 2). ​

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