Real-time scale factor compensation method based on online monitoring of optical fiber parameters

Abstract

The invention discloses a scale factor real-time compensation method based on online monitoring of optical fiber parameters, which comprises the following steps of: 1, confirming variables of a closed-loop optical fiber gyroscope scale factor, including optical fiber length in an optical fiber ring, average diameter of the optical fiber ring and average wavelength of working light waves of an optical fiber gyroscope; 2, determining the change rule of the optical fiber length of the optical fiber ring and the average diameter of the optical fiber ring along with temperature; 3, determining the change rule of the fiber length of the fiber ring and the average wavelength of the working light wave of the fiber-optic gyroscope along with the temperature; and 4, compensating the calibration factor based on the change rule of the fiber length of the fiber ring, the average diameter of the fiber ring and the average wavelength of the working light wave of the fiber-optic gyroscope along with the temperature. According to the method, the width of the peak signal can be effectively controlled to be unchanged, the zero offset repeatability of the fiber-optic gyroscope in a full temperature range is improved, meanwhile, the problem of long-term consistency of scale factors of the fiber-optic gyroscope is solved, and unified calibration and compensation of the same batch can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber-optic gyroscope, in particular to a scale factor real-time compensation method based on fiber parameter online monitoring. BACKGROUND

[0002] Temperature environmental conditions will affect the performance parameters of fiber-optic gyroscope subassembly, resulting in changes in scale factor, which makes the scale factor repeatability decrease. The temperature range of fiber-optic gyroscope working environment is usually -40℃~+70℃, and the actual measurement results show that the change amount of scale factor of fiber-optic gyroscope in this temperature range is 400ppm~1500ppm, which cannot meet the demand of high-precision inertial navigation (the scale factor repeatability is less than 50ppm). In order to improve the scale factor repeatability of fiber-optic gyroscope under temperature environment, the measures usually taken at home and abroad are to improve the scale factor repeatability by temperature compensation after fine modeling of fiber-optic gyroscope. The factors affecting the scale factor repeatability under temperature environment include fiber length in fiber coil, average diameter of fiber coil, average wavelength, etc. Since the wavelength variation law of each gyroscope is different, the traditional method must model each fiber-optic gyroscope, which seriously affects the production efficiency of fiber-optic gyroscope and increases the production cost.

[0003] In addition, the SLD light source of fiber-optic gyroscope is determined by its material properties, and its light-emitting wavelength will change year by year, so high-precision application scenarios need to be recalibrated every 1~2 years, which brings inconvenience to users. SUMMARY

[0004] The purpose of the present application is to propose a scale factor real-time compensation method based on fiber parameter online monitoring, which not only eliminates the difference in wavelength variation of each gyroscope under temperature environment, makes the modeling compensation simpler, but also makes the wavelength variation and fiber length variation maintain a fixed proportion, so that the scale factor of fiber-optic gyroscope can remain unchanged for a long time, and solves the problem of recalibration due to the year-by-year change of light source wavelength.

[0005] Specifically, the present application proposes a scale factor real-time compensation method based on fiber parameter online monitoring, which comprises the following steps:

[0006] Step 1, confirming the variables of closed-loop fiber-optic gyroscope scale factor, including fiber length in fiber coil, average diameter of fiber coil and average wavelength of fiber-optic gyroscope working light wave;

[0007] Step 2, determining the temperature variation law of fiber length in fiber coil and average diameter of fiber coil;

[0008] Step 3, determining the temperature variation law of fiber length in fiber coil and average wavelength of fiber-optic gyroscope working light wave;

[0009] Step 4, compensate the calibration factor based on the fiber length of the fiber coil, the average diameter of the fiber coil and the average wavelength of the working light wave of the fiber optic gyroscope changing with temperature.

[0010] Further, in step 1, the output of the fiber optic gyroscope is expressed as:

[0011] y = kx + G;

[0012] Where G is the zero bias, x is the input angular velocity, y is the digital value of the gyroscope output, K is the scale factor, and the scale factor expression of the closed-loop fiber optic gyroscope is ; N is the number of turns of the fiber coil, c is the speed of light, both are constants, λ is the average wavelength of the working light wave of the fiber optic gyroscope, L is the fiber length in the fiber coil, D is the average diameter of the fiber coil.

[0013] The derivative of the scale factor of the fiber optic gyroscope is:

[0014]

[0015] ΔK is the scale factor change, ΔL is the fiber length change, ΔD is the diameter change of the fiber coil, Δλ is the change of the working wavelength;

[0016] The scale factor change of the fiber optic gyroscope is determined by the average wavelength of the working light wave of the fiber optic gyroscope , the fiber length in the fiber coil , and the average diameter of the fiber coil .

[0017] Further, in step 2, assuming the number of fiber layers in the fiber coil is M, the diameters of the fiber coils in each layer are equal and the number of turns is N turns, and the diameter of the fiber coil in the th layer at temperature point is , then the total length of the fiber in the layer at the temperature point is:

[0018] ;

[0019] The average diameter of the fiber coil at the temperature point is

[0020] ;

[0021] Where is the total length of the fiber in the fiber coil, and the derivative of the formula is:

[0022] ;

[0023] Thus, the relative change in diameter of the fiber loop is the same as the relative change in length.

[0024] Further, in step 3, the fiber optic gyroscope comprises a detector, a temperature control circuit and an FPGA controller;

[0025] The detector is connected with the coupler of the fiber optic gyroscope, and is used to collect the spike signal generated by the fiber optic gyroscope between two adjacent modulation periods under square wave modulation;

[0026] The FPGA controller is connected with the output signal of the detector through an ADC, and judges whether the pulse of the detected spike pulse is widened or not according to the sampling value of the ADC, i.e. whether the length of the fiber in the fiber loop is increased or reduced;

[0027] The FPGA controller adjusts the temperature control point of the SLD light source in the fiber optic gyroscope according to whether the length of the fiber is increased or reduced, and the average wavelength of the SLD light source will become longer as the temperature control point is raised;

[0028] When the length of the fiber in the fiber optic gyroscope is increased, the temperature control point is raised, the average wavelength becomes longer, the speed of light in the fiber is increased, and the time of light passing through the fiber loop is reduced; when the length of the fiber is reduced, the temperature control point is lowered, the average wavelength becomes shorter, the speed of light in the fiber is reduced, and the time of light passing through the fiber loop is increased; through such feedback control, the time of light passing through the fiber loop is unchanged, i.e. the width of the spike is unchanged.

[0029] Further, in step 3, according to Cauchy formula, the relationship between the refractive index of the medium and the wavelength can be expressed as:

[0030] ;

[0031] wherein A and B are constants related to the material, n is the refractive index, and λ is the wavelength;

[0032] The speed of light in the fiber can be expressed as:

[0033] ;

[0034] is the speed of light;

[0035] The time of the light beam passing through the fiber loop is:

[0036] ;

[0037] Taking the derivative of the expression for the time of the light beam passing through the fiber loop can obtain:

[0038] ;

[0039] Since the time t remains unchanged, i.e. dt=0, it is derived that:

[0040] ;

[0041] Since A is much greater than , there is:

[0042] ;

[0043] That is, in the process of controlling the temperature control point, the relative change amount of the optical fiber length and the relative change amount of the wavelength are in a linear relationship:

[0044] ;

[0045] After online compensation, the scale factor change is only related to one parameter of the optical fiber length change.

[0046] Further, in step 4, when the temperature ℃, the optical fiber length is , the scale factor is , and the thermal expansion coefficient of the optical fiber ring of this batch is measured to be ppm / ℃;

[0047] When the temperature is T, the optical fiber length change amount is , and the scale factor change amount is:

[0048] ;

[0049] Currently ;

[0050] Let the compensation coefficient be , and the real-time output of the gyroscope is:

[0051] Divide the real-time output y of the fiber optic gyroscope by the compensation coefficient z, and output, that is, the scale factor remains unchanged.

[0052] The beneficial effects achieved by the present application are:

[0053] The present application not only effectively controls the invariant peak signal width, improves the fiber optic gyroscope zero bias repeatability in the whole temperature range, but also solves the long-term consistency problem of the scale factor of the fiber optic gyroscope, and can realize long-term calibration-free. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 A flowchart of a scale factor real-time compensation method based on online monitoring of optical fiber parameters is provided.

[0055] Figure 2A structure diagram of a fiber optic gyroscope corresponding to a scale factor real-time compensation method based on online monitoring of fiber parameters according to the present application is provided.

[0056] Figure 3 A schematic diagram of the relationship between the scale factor of a fiber optic gyroscope and temperature in a scale factor real-time compensation method based on online monitoring of fiber parameters according to the present application is provided.

[0057] Figure 4 A schematic diagram of a spike signal generated by square wave modulation in a scale factor real-time compensation method based on online monitoring of fiber parameters according to the present application is provided.

[0058] Figure 5 A comparison diagram between the scale factor real-time compensation method based on online monitoring of fiber parameters according to the present application and existing compensation technologies is provided.

[0059] Figure 6 A schematic diagram of the modulation effect of a modulation signal on two beams of light in a fiber optic gyroscope in a scale factor real-time compensation method based on online monitoring of fiber parameters according to the present application is provided. DETAILED DESCRIPTION

[0060] The technical solutions of the present application will be described in more detail below with reference to the accompanying drawings, and the present application includes but is not limited to the following embodiments.

[0061] As shown in the accompanying Figure 1 , the present application provides a scale factor real-time compensation method based on online monitoring of fiber parameters, which includes the following steps:

[0062] Step 1: confirming the variables of the scale factor of a closed-loop fiber optic gyroscope, including the number of turns of the fiber ring, the average diameter of the fiber ring, and the average wavelength of the working light wave of the fiber optic gyroscope;

[0063] The output of the fiber optic gyroscope can be represented as y=kx+G, where G is the zero bias, K is the scale factor, x is the input angular velocity, and y is the digital value of the output of the gyroscope; the scale factor of the closed-loop fiber optic gyroscope can be expressed as .

[0064] In the formula, is the number of turns of the fiber ring, is the speed of light, both of which are constants, is the average wavelength of the working light wave of the fiber optic gyroscope, is the length of the fiber in the fiber ring, is the average diameter of the fiber ring.

[0065] Taking the derivative of the scale factor of the fiber optic gyroscope can obtain:

[0066]

[0067] Thus the scale factor variation of fiber optic gyroscope is determined by , , three parameters variation.

[0068] Step 2, determine the fiber length and the average diameter of the fiber coil change with temperature;

[0069] Assume the number of fiber layers in the fiber coil is M, the diameter of the fiber coil in each layer is equal and the number of turns is N turns, at a certain temperature point the diameter of the fiber coil in the first layer is , then the total length of the fiber in this layer at this temperature point is:

[0070]

[0071] The average diameter of the fiber coil at this temperature point is

[0072]

[0073] where is the total length of the fiber in the fiber coil, and the derivative of the formula is:

[0074]

[0075] It can be seen that the average diameter of the fiber coil is proportional to the length of the fiber, and at any temperature point is always true, so the relative change in the average diameter of the fiber coil in the temperature environment is equal to the relative change in the length of the fiber.

[0076] Step 3, determine the fiber length and the average wavelength of the fiber optic gyroscope working light change with temperature;

[0077] There are many factors affecting the variation of the average wavelength of the fiber optic gyroscope working light, such as the temperature of the light source chip, the driving current of the light source, the parameters of the optical devices in the optical path, and many other factors, which vary greatly due to individual differences. Figure 3 The scale factor variation curve of the same batch of traditional fiber optic gyroscope in the range of-30℃~+65℃, the scale factor variation is 1400~2400ppm, and the difference between each individual is large, which cannot be perfectly compensated by using the same set of parameters, so in high precision requirement occasions, the traditional method is to fine modeling compensation for each gyroscope.

[0078] The thermal expansion and contraction effect of materials cannot be changed. If the change in operating wavelength is consistent with the thermal expansion and contraction of the material, the same parameters can be used for compensation for the same batch of fiber optic gyroscopes. Therefore, this project proposes a real-time scaling factor compensation technology based on online monitoring of fiber optic parameters to improve the repeatability of the scaling factor of fiber optic gyroscopes.

[0079] Fiber optic gyroscopes commonly use square wave modulation, which generates spike signals between two adjacent modulation periods, such as... Figure 4 As shown, at room temperature, the time it takes for light to pass through the fiber optic ring is almost equal to the modulation period, and the peak signal width is the narrowest. When the temperature changes, the fiber length increases, and the peak will broaden.

[0080] The generation mechanism of spike signals is as follows:

[0081] Currently, fiber optic gyroscopes commonly use square wave signals (including four-state and eight-state modulation methods) to modulate the optical path. If the waveform of the modulation signal is as follows... Figure 6 As shown in (a), the modulation period is T, and the modulation phase of the modulation signal on the two beams of light in the fiber optic gyroscope is as follows: Figure 6 As shown in (b) and (c), the delay time between the modulation phases of the two beams is the intrinsic period of the fiber loop. Because the modulation signal period T is different from the intrinsic period of the fiber optic gyroscope's fiber loop. They cannot be strictly equal, therefore the modulation signal causes a phase difference between the interfering beams as follows: Figure 6 As shown in (d), the interference intensity of the Sagnac optical path can be expressed as:

[0082]

[0083] in The light intensity of a single beam of light, To generate a phase difference for rotational speed, The phase difference generated by the modulated signal, according to the above formula, when At that time, under the action of the modulation signal, the interference intensity of the two beams is as follows: Figure 6 As shown in (e).

[0084] As can be seen from the above analysis, since the period of the modulation signal cannot be exactly equal to the intrinsic period of the fiber optic gyroscope's fiber ring, the modulation signal causes the interference light intensity to produce periodic "spiks" at the step of the modulation signal.

[0085] This invention utilizes the width of a spike signal to monitor changes in optical fiber length. The technical solution of this invention is as follows: Figure 2 As shown, the FPGA controller is connected to the detector output signal through the ADC. It judges whether the pulse of the detection spike pulse is broadened by the sampled value of the ADC, that is, whether the fiber length in the fiber loop is increased or decreased.

[0086] The FPGA controller adjusts the temperature control point of the SLD light source in the fiber optic gyroscope according to whether the fiber length increases or decreases, and the average wavelength of the SLD light source will become longer as the temperature control point increases;

[0087] When the fiber length increases in the fiber optic gyroscope, the temperature control point temperature is increased, the average wavelength becomes longer, the speed of light in the fiber increases, and the time of light passing through the fiber ring decreases; when the fiber length decreases, the temperature control point temperature is decreased, the average wavelength becomes shorter, the speed of light in the fiber decreases, and the time of light passing through the fiber ring increases; through such feedback control, the time of light wave passing through the fiber ring is unchanged, that is, the peak width is unchanged.

[0088] In this closed-loop control process, the relative change amount of the wavelength and the change amount of the fiber length are in a fixed proportion.

[0089] According to the Cauchy formula, the relationship between the refractive index of the medium and the wavelength can be expressed as

[0090]

[0091] where A is the refractive index of the material at zero wavelength (or infinite wavelength), B is the degree of change of the refractive index with wavelength, n is the refractive index, and λ is the wavelength.

[0092] The speed of light in the fiber can be expressed as:

[0093]

[0094] The time of the light beam passing through the fiber ring is:

[0095]

[0096] Taking the derivative of both sides of the above equation gives:

[0097]

[0098] Since the time t remains unchanged, that is, dt=0; the above equation can be derived as:

[0099]

[0100] In the above formula, since A is much larger than , we have:

[0101] According to the Cauchy formula, the A and B parameters of the 1310nm fiber core are 1.45 and 0.003 respectively; A=1.45, =0.003 / 1.31 / 1.31=0.00174815, so A is much larger than .

[0102]

[0103] That is, in the process of controlling the peak width, the relative change in fiber length is linearly related to the relative change in wavelength:

[0104]

[0105] As can be seen from the above formula, the change in scaling factor is only related to one parameter: the change in fiber length.

[0106] Step 4: Compensate for calibration factors based on the temperature variation of fiber ring length, average fiber ring diameter, and average wavelength of the working light wave of the fiber optic gyroscope.

[0107] At temperature At ℃, the fiber length is The scaling factor is The measured coefficient of thermal expansion of this batch of fiber optic rings is: ppm / ℃.

[0108] When the temperature is T, the change in fiber length is: The change in the scaling factor is:

[0109] ;

[0110] current ;

[0111] Let the compensation coefficient Gyroscope real-time output:

[0112] By dividing the real-time output y of the fiber optic gyroscope by the compensation coefficient z, the scaling factor can be kept constant.

[0113] In summary, the thermal expansion and contraction properties of materials determine... The scaling factor of fiber optic gyroscopes of the same batch can be perfectly compensated using the same parameters because the scaling factor has a fixed relationship with temperature and the same structure and material of fiber optic rings.

[0114] Comparative tests were conducted on the complete fiber optic gyroscope unit; detailed test results can be found [link to test results]. Figure 5 The gyroscope employing online monitoring and real-time compensation technology for fiber optic parameters exhibits a scale factor variation of only about 50 ppm across the entire temperature range, while the fiber optic gyroscope without this technology shows a scale factor variation of 1200 ppm. This demonstrates that the technology can effectively improve the scale factor repeatability of fiber optic gyroscopes.

[0115] The application is not limited to the above specific embodiments, and those skilled in the art can implement the application in other various specific embodiments according to the content disclosed in the embodiments and the drawings, therefore, any design using the design structure and the idea of the application and making some simple changes or alterations falls within the protection scope of the application.

[0116] The above is only the preferred embodiment of the application, and does not constitute any limitation on the protection scope of the application; any technical solution formed by equivalent transformation or equivalent replacement falls within the protection scope of the application; the part not described in the application is the known technology of those skilled in the art.

Claims

1. A method for real-time scaling factor compensation based on online monitoring of fiber optic parameters, characterized in that, The scaling factor real-time compensation method based on online monitoring of fiber optic parameters includes the following steps: Step 1: Identify the variables of the closed-loop fiber optic gyroscope scaling factor, including the fiber length in the fiber loop, the average diameter of the fiber loop, and the average wavelength of the working light wave of the fiber optic gyroscope. Step 2: Determine the variation of fiber length and average diameter of the fiber ring with temperature; Step 3: Determine the fiber length of the fiber loop and the temperature variation of the average wavelength of the working optical wave of the fiber optic gyroscope. Step 4: Compensate for calibration factors based on the temperature variation of fiber ring length, average fiber ring diameter, and average wavelength of the working light wave of the fiber optic gyroscope.

2. The method for real-time scaling factor compensation based on online monitoring of fiber optic parameters according to claim 1, characterized in that, In step 1, the output of the fiber optic gyroscope is expressed as: y = kx + G; Where G is zero bias, x is the input angular velocity, y is the digital value output by the gyroscope, and K is the scaling factor. The expression for the scaling factor of a closed-loop fiber optic gyroscope is: ; For fiber ring turns, The speed of light is a constant. The average wavelength of the working light wave for fiber optic gyroscopes, For the fiber length in the fiber optic ring, This represents the average diameter of the fiber optic ring. Differentiating the fiber optic gyroscope's scaling factor yields: ； The change in the scaling factor. This represents the change in fiber length. This represents the change in the diameter of the fiber optic ring. This is the change in the operating wavelength; The scaling factor variation of a fiber optic gyroscope is determined by the average wavelength of the working light wave of the fiber optic gyroscope. Fiber length in fiber ring Average diameter of fiber optic ring It is determined by the changes in three parameters.

3. The real-time scaling factor compensation method based on online monitoring of fiber optic parameters according to claim 2, characterized in that, In step 2, assuming the number of fiber layers in the fiber ring is M, and the fiber coils in each layer have the same diameter and N turns, at the temperature point... Next The diameter of the layer fiber coil is Then, at this temperature point, the total length of the optical fiber in this layer is: ； At this temperature point, the average diameter of the fiber optic ring is ； in Let be the total length of the optical fiber in the optical fiber loop. Differentiating the formula, we get: ； Therefore, the relative change in the diameter of the fiber optic ring is the same as the relative change in its length.

4. The method for real-time scaling factor compensation based on online monitoring of fiber optic parameters according to claim 2, characterized in that, In step 3, the fiber optic gyroscope includes a detector, a temperature control circuit, and an FPGA controller; The detector is connected to the fiber optic gyroscope via a coupler to acquire the spike signal generated by the fiber optic gyroscope between two adjacent modulation cycles under square wave modulation. The FPGA controller is connected to the detector output signal through the ADC. It judges whether the pulse of the detection spike pulse is broadened by the sampled value of the ADC, that is, whether the length of the optical fiber in the optical fiber loop is increased or decreased. The FPGA controller adjusts the temperature control point of the SLD light source in the fiber optic gyroscope based on whether the fiber length increases or decreases. The average wavelength of the SLD light source will increase as the temperature control point increases. In a fiber optic gyroscope, as the fiber length increases, the temperature of the control point is raised, the average wavelength becomes longer, the speed of light in the fiber increases, and the time it takes for light to pass through the fiber loop decreases. Conversely, as the fiber length decreases, the temperature of the control point is lowered, the average wavelength becomes shorter, the speed of light in the fiber decreases, and the time it takes for light to pass through the fiber loop increases. Through this feedback control, the time it takes for the light wave to pass through the fiber loop remains constant, i.e., the peak width remains constant.

5. The method for real-time scaling factor compensation based on online monitoring of fiber optic parameters according to claim 4, characterized in that, In step 3, according to Cauchy's formula, the relationship between the refractive index of the medium and the wavelength can be expressed as: ； Where A and B are material-related constants, and n is the refractive index. Wavelength; The speed of light in an optical fiber can be expressed as: ； It's the speed of light; The time it takes for the light beam to pass through the fiber optic loop is: ； Differentiating both sides of the time expression for the beam passing through the fiber loop, we get: ； Since time t remains constant, i.e., dt=0, we can deduce that: ； Because A is much greater than Therefore, we have: ； That is, during the process of controlling the temperature control point, the relative change in fiber length and the relative change in wavelength are linearly related: ； After online compensation, the scaling factor change is only related to one parameter: the change in fiber length.

6. The method for real-time scaling factor compensation based on online monitoring of fiber optic parameters according to claim 1, characterized in that, In step 4, at temperature At ℃, the fiber length is The scaling factor is The measured coefficient of thermal expansion of this batch of fiber optic rings is: ppm / ℃; When the temperature is T, the change in fiber length is: The change in the scaling factor is: ； current ; Let the compensation coefficient Gyroscope real-time output: By dividing the real-time output y of the fiber optic gyroscope by the compensation coefficient z, the scaling factor can be kept constant.

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