Inverse wavelength filter and application method thereof

Abstract

The invention relates to an inverse wavelength filter and a use method thereof. The inverse wavelength filter comprises a Lyot filter and a variable stress controller, wherein the Lyot filter consists of a polarization maintaining optical fiber with the length of 0.25 m and a polarizer with a high extinction ratio; the variable stress controller is connected with a section of polarization-maintaining tail fiber with the length of 0.05 m at the tail end of the polarization-maintaining optical fiber through a holder; the variable stress controller is used for continuously twisting and bending the polarization maintaining optical fiber; the distortion angle and the bending angle of the polarization-maintaining optical fiber are used for respectively controlling the central wavelength and the waveform left-right symmetry degree of an optical path passing through the polarization-maintaining optical fiber; the distortion angle and the bending angle of the polarization maintaining optical fiber are in linear relation with the driving current of the variable stress controller. According to the invention, spectral shape online correction of other optical paths such as fiber-optic gyroscopes can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of online wavelength calibration of fiber optic gyroscopes, and particularly relates to an inverse wavelength filter and an application method thereof. Background Art

[0002] Fiber optic gyroscopes have the advantages of being all-solid-state, free of mechanical noise, and high reliability, meeting the requirements of underwater stealth and noise reduction, and are an excellent choice for the inertial navigation system to sail stealthily. The accuracy of the fiber optic gyroscope is proportional to the fiber length. In theory, the accuracy of the gyroscope can be increased infinitely by increasing the fiber length. However, the increase in fiber length also brings huge technical challenges: the ultra-long optical path leads to an exponential increase in the optical path stress and a sharp increase in the optical path loss, resulting in the gyro noise and scale index not meeting the accuracy requirements; the ring is vulnerable to the influence of the external environment (heat, force, magnetism), causing the gyro to drift and affecting the high-precision maintenance during long-term navigation. An important reason for achieving high precision lies in the use of a broadband light source. In an interferometric fiber optic gyroscope, the broadband light source has the advantage of suppressing the errors caused by back reflection and scattering, polarization coupling, Faraday effect, Kerr effect, etc. With the rapid improvement of the performance requirements of high-precision inertial navigation systems, the requirements for fiber optic gyroscopes have also been greatly improved. Especially the scale factor performance is the key to whether the system accuracy can be maintained and the retuning time can be extended. The scale factor of the fiber optic gyroscope can be expressed by the following formula:

[0003]

[0004] where L is the length of the ring, D is the diameter of the ring, is the average wavelength. It can be seen that the wavelength stability of the optical path is one of the most important factors affecting the stability of the gyro scale factor, which puts forward higher requirements for the wavelength stability of the erbium-doped fiber light source. At the same time, the operating environments such as UUA (Unmanned Underwater Vehicle) and underwater platforms require the inertial navigation system to operate silently for a long time, and require the wavelength to have a long-term stable and automatic calibration function. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides an inverse wavelength filter and an application method thereof.

[0006] One of the purposes of the present invention is achieved by the following technical solutions:

[0007] An inverse wavelength filter, characterized in that: it includes a Lyot filter and a variable stress controller; wherein the Lyot filter is composed of a 0.25 m long polarization-maintaining fiber and a polarizer with a high extinction ratio; the variable stress controller is connected to a 0.05 m long polarization-maintaining pigtail at the end of the polarization-maintaining fiber through a clamp; the variable stress controller is used to continuously twist and bend the polarization-maintaining fiber; the twist angle and bend angle of the polarization-maintaining fiber are used to control the central wavelength and the left-right symmetry of the waveform of the optical path passing through it respectively; the twist angle and bend angle of the polarization-maintaining fiber have a linear relationship with the driving current of the variable stress controller.

[0008] Moreover, the variable stress controller adopts an optoelectronic control method. After the controller inputs current, a force is generated in the torque coil of the controller, and this force drives the gripper to apply a torsional effect and a bending effect to the polarization-maintaining optical fiber.

[0009] The second object of the present invention is achieved by the following technical solution:

[0010] An online correction method for the optical path spectrum type of a fiber optic gyroscope. This method extracts the spectral type change amount of the entire optical path of the fiber optic gyroscope through an inverse wavelength filter, and uses a line driving method to perform negative feedback adjustment on the wavelength change to achieve the stability of the average center wavelength and waveform symmetry of the optical path. The waveform changes include: (a) the offset of the center wavelength of the light wave, which includes the left shift and decrease of the center wavelength and the right shift and increase of the center wavelength; (b) the asymmetry of the spectral type of the light wave, which includes the spectral type containing positive odd components and negative odd components.

[0011] The third object of the present invention is achieved by the following technical solution:

[0012] A method for stabilizing the scale factor of a fiber optic gyroscope. This method realizes the stability of the wavelength by online closed-loop negative feedback control of the wavelength of the gyroscope optical path, and realizes the stable maintenance of the scale factor; it includes: extracting spectral signals from both ends of the coupler of the fiber optic gyroscope and performing synchronous waveform spectral subtraction operation; the inverse wavelength filter generates a spectral type correction amount according to the spectral subtraction operation value, the photodetector picks up the spectral type correction amount, and through a programmable electric controller, current drive is performed to send the correction amount into the light source to realize the adjustment of the wavelength of the light source; among them, both ends of the gyroscope coupler correspond to the front end of the detector and the output end of the gyroscope light source respectively.

[0013] Moreover, the extraction of spectral signals from both ends of the coupler of the fiber optic gyroscope and the synchronous waveform spectral subtraction operation are performed using a spectrometer or an optical path device with a spectral type extraction function.

[0014] The fourth object of the present invention is achieved by the following technical solution:

[0015] An online correction method for the optical path spectrum type, which uses a line driving method to perform negative feedback adjustment on the wavelength change to achieve the stability of the average center wavelength and waveform symmetry of the optical path. The waveform changes include: (a) the offset of the center wavelength of the light wave, which includes the left shift and decrease of the center wavelength and the right shift and increase of the center wavelength; (b) the asymmetry of the spectral type of the light wave, which includes the spectral type containing positive odd components and negative odd components; among them, the spectral negative feedback amount involved in the negative feedback adjustment is the spectral type change amount extracted online through the inverse wavelength filter or the spectral type change amount obtained by offline modeling in advance; the offline spectral type change amount establishes the output change law of the spectral type by testing parameters under different environmental conditions, and then extracts the environmental parameter waveform online, and inputs the change law into the inverse wavelength filter for online negative feedback.

[0016] The advantages and positive effects of the present invention are as follows:

[0017] 1. The present invention uses an inverse wavelength filter to generate a spectral correction amount. The spectrum picks up the correction amount through a photodetector, and the correction amount is sent into the light source through current drive by a controller, achieving the adjustment of the light source wavelength so as to improve the stability of the gyro scale factor. It has the advantages of on-line adjustment, automatic compensation, and high reliability, meeting the long-term navigation requirements of underwater stealth.

[0018] 2. The present invention is not limited to the correction of the light source spectrum, but is a global correction of the spectrum including all optical fiber path components of the fiber optic gyroscope, that is, the global spectral correction compensation including the light source, polarization maintaining coupler, integrated Y waveguide, and loop.

[0019] 3. The inverse wavelength filter of the present invention is not only applicable to the on-line correction of the fiber optic gyroscope spectrum, but also applicable to the correction of other optical path spectra, with good practicability. Brief Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of the inverse wavelength filter of the present invention;

[0021] Figure 2 is a diagram showing the control of the polarization maintaining fiber torsion and bending states by the variable stress controller of the present invention;

[0022] Figure 3 is a simulation diagram of the filter with a continuous modulation of 40 nm wide from 1530 to 1570 nm of the present invention. Among them, in each of the figures (a)-(c), the controller continuously twists from -5° to 5°, with a step of 2° each time. In figure (a), the waveform movement simulation of the upper deviation bending angle α = -1.5°, in figure (b), the bending angle α = 0°, and in figure (c), the lower deviation bending angle α = 1.5°;

[0023] Figure 4 is a schematic diagram of the fiber optic gyroscope waveform on-line correction method of the present invention;

[0024] Figure 5 is a negative feedback correction loop diagram of the inverse wavelength filter of the present invention for the spectral distortion of the gyro optical path. Detailed Embodiments

[0025] The structure of the present invention will be further described below with reference to the drawings and through embodiments. It should be noted that this embodiment is narrative rather than restrictive.

[0026] An inverse wavelength filter, not limited to grating filters and flat filters. One implementation of the inverse wavelength filter is as follows Figure 1 shown.

[0027] The working principle of a Lyot filter is mainly based on the birefringence effect. Birefringence means that when light propagates in certain media, it will split into two beams of light with perpendicular vibration directions and different propagation speeds. In a Lyot filter, by appropriately selecting the thickness and orientation of the birefringent crystal, the phase of one beam of light can be made to lag behind that of the other beam, thereby achieving light filtering.

[0028] The main parameter indicators of a Lyot filter include the central wavelength, bandwidth, and transmittance. The central wavelength refers to the wavelength at which the filter has the highest transmittance rate; the bandwidth is the wavelength range at which the filter's transmittance rate drops to half of its maximum value; the transmittance refers to the light transmission ability.

[0029] The specific implementation of the inverse wavelength filter is as Figure 2 shown. The twist angle θ is:

[0030] θ = kIL

[0031] where k is the twist stiffness coefficient of the polarization-maintaining fiber, L is the length of the polarization-maintaining fiber, I is the current of the variable stress controller, α is the bending angle, and σ is the flexural section modulus;

[0032]

[0033] The basic principle of this inverse wavelength filter is based on a dynamically tunable Lyot filter. However, different from an ordinary Lyot filter, this filter adds a twisted type variable stress controller, uses a twisted optical fiber with a fiber length L, and adds a spring strainer at the bottom of the fiber. The force applied by the strainer is controlled by a programmable controller. Therefore, by controlling the variable stress controller to adjust the direction and amplitude of the twisting force, the central wavelength position of the inverse wavelength filter can be adjusted. Adjusting the stress controller generates a bending force, and the bending of the polarization-maintaining fiber can change the left-right symmetry of the waveform. During the continuous control of the twist angle and bending angle, the spectral pattern of the filter will produce an offset of the central wavelength and a slight change in the symmetry degree. The direction of the left-right movement of the central wavelength depends on the direction of the twisting force, and the distance of the waveform offset from the center position is proportional to the amplitude of the twisting force. The degree of left-right asymmetry of the waveform is linearly related to the bending angle α of the fiber, and the degree of left-right tilt depends on the bending direction.

[0034] Figure 3 It is a simulation diagram of a filter with continuous modulation from 1530 to 1570 nm and a width of 40 nm. During the entire modulation process, the length of the polarization-maintaining fiber is 0.25 m, and the twist angle is continuously adjusted from 0° to 10°.

[0035] Application 1 of the inverse wavelength filter:

[0036] Based on the above inverse wavelength filter, the theoretical basis of the method for dynamically adjusting the spectrum pattern of a fiber optic gyroscope is as follows: The erbium-doped fiber light source, coupler, Y waveguide, and loop in the optical path of the fiber optic gyroscope are affected by environmental temperature and stress, resulting in changes in the refractive index of the optical path, and thus causing changes in the waveform of the optical path. The above changes lead to instability of the scale factor, which is a core index of the gyroscope. Inspired by the fact that the polarization-maintaining fiber undergoes phase changes under high stress, combined with the working principle that the inverse wavelength filter can continuously adjust the waveform, a method for dynamically adjusting the spectrum pattern of a fiber optic gyroscope based on the inverse wavelength filter is proposed to dynamically correct the gyroscope spectrum pattern to achieve the effect of stabilizing the scale factor.

[0037] The main idea of the invention: As Figure 4 , in a traditional gyroscope, the light wave emitted by a broadband light source passes through a polarization-maintaining coupler, then through a Y waveguide, then through a fiber optic loop, and then back through the Y waveguide and coupler to form an interference signal that reaches a photodetector. The signal output by the modulation and demodulation control circuit is the output of the gyroscope. Because the spectrum pattern changes during the transmission of light through the coupler, Y waveguide, and loop, including the shift of the central wavelength and the change in the symmetry of the spectrum pattern. In the present invention, the above-mentioned inverse wavelength filter is added between the polarization-maintaining coupler and the photodetector of the existing fiber optic gyroscope. The inverse wavelength filter can be designed to only pass the waveform of the set central wavelength and correct the symmetry of the distorted waveform, and can output the distortion amount in the form of difference (negative feedback is the compensation amount). Then, the driving current of the light source and the temperature are controlled by a programmable controller to adjust the wavelength of the light source, so as to improve the average wavelength of the optical path and achieve the effect of stabilizing the scale factor of the fiber optic gyroscope.

[0038] The core content for realizing the stability of the scale factor of the fiber optic gyroscope includes:

[0039] (1) Extract the spectrum pattern change amount of the entire optical path of the fiber optic gyroscope through the inverse wavelength filter, and use the line driving method to perform negative feedback adjustment on the wavelength change to achieve wavelength stability.

[0040] (2) In the solution, the waveform changes in the optical path include but are not limited to: (a) The amplitude of the light wave changes, including an increase and a decrease in amplitude. (b) The central wavelength of the light wave shifts, including a left shift and a decrease in the central wavelength and a right shift and an increase in the central wavelength. (c) The spectrum pattern of the light wave is asymmetric, including positive odd components and negative odd components in the spectrum pattern.

[0041] This inverse wavelength filter is applicable not only to the online correction of the spectrum pattern of the fiber optic gyroscope, but also to the correction of the spectrum patterns of other optical paths. In addition, the spectral negative feedback amount involved in the negative feedback adjustment can be obtained from the spectrum pattern change amount extracted online by the inverse wavelength filter or from the spectrum pattern change amount obtained by offline modeling in advance.

[0042] Application 2 of the inverse wavelength filter:

[0043] The overall optical path wavelength, such as Figure 5 shown below:

[0044] The implementation process is as follows: A feedback optical path is applied to the original optical path of the fiber optic gyroscope. The feedback circuit includes a spectrometer and an inverse wavelength filter section. In the case of no optical path spectrum distortion, the inverse wavelength filter does not work. At this time, the light output by the ASE light source successively passes through the coupler end 1, the waveguide, and the loop, and then reaches the detector through the waveguide from the coupler end 2. When the spectrum of the gyro optical path is distorted due to external temperature and pressure, the spectrometer collects waveforms at both ends of the coupler end 2 and end 1 respectively, and takes the difference between the waveforms of the two paths and the waveform of the first path as the waveform change amount. Take the opposite of this change amount, that is, the difference between the first path and the second path, as the input of the inverse wavelength filter. According to the position and shape of the waveform change, the variable stress controller adjusts the twist angle and bending angle of the Lyot polarization-maintaining fiber according to Figure 3 the rule. Under the above stress control, the fiber optic filter will correct the input spectrum of the ASE light source. The correction value is the opposite of the spectrum change amount at both the output and input ends of the coupler, completing an inverse operation of the wavelength change, that is, the negative feedback of the wavelength change, so as to achieve the feedback control of the spectrum, ensure the maintenance of the average center spectrum position and shape of the overall optical path of the gyroscope, and thus achieve the stability of the overall scale factor of the fiber optic gyroscope (because the scale is inversely proportional to the wavelength).

[0045] Although embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes, and modifications are possible without departing from the spirit of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments and drawings.

Claims

1. An inverse wavelength filter, characterized in that: It includes a Lyot filter and a variable stress controller; wherein the Lyot filter is composed of a 0.25m long polarization-maintaining optical fiber and a polarizer with a high extinction ratio; the variable stress controller is connected to a 0.05m long polarization-maintaining optical fiber pigtail at the tail end of the polarization-maintaining optical fiber through a clamp; the variable stress controller is used to achieve continuous twisting and bending of the polarization-maintaining optical fiber; the twist angle and bending angle of the polarization-maintaining optical fiber are used to respectively control the central wavelength and the left-right symmetry of the waveform of the optical path passing therethrough; the twist angle and bending angle of the polarization-maintaining optical fiber are linearly related to the driving current of the variable stress controller.

2. The inverse wavelength filter according to claim 1, characterized in that: The variable stress controller adopts a photoelectric control method. When the controller inputs current, the controller torque coil generates a force to drive the clamp to exert a twisting action and a bending action on the polarization-maintaining optical fiber.

3. A method for online correction of optical path spectrum of fiber optic gyroscope, characterized in that: The method extracts the spectral change of the entire optical path of the fiber gyroscope through the inverse wavelength filter described in claim 1 or 2, and adopts a line driving method to perform negative feedback adjustment on the wavelength change to achieve the stability of the average central wavelength and waveform symmetry of the optical path. The waveform change includes: (a) the offset of the central wavelength of the light wave, which includes a decrease in the left shift of the central wavelength and an increase in the right shift; (b) the asymmetry of the light wave spectrum, which includes the spectrum containing positive odd components and negative odd components.

4. A method for stabilizing the scale factor of a fiber optic gyroscope, characterized in that: The method realizes wavelength stability by controlling the wavelength of the gyro optical path through online closed-loop negative feedback, thereby achieving stable maintenance of the scale factor; the method comprises: extracting spectral signals from both ends of the coupler of the optical fiber gyroscope and performing a synchronous waveform spectral subtraction operation; generating a spectral correction amount according to the spectral subtraction operation value through the inverse wavelength filter described in claim 1 or 2, picking up the spectral correction amount through a photoelectric detector, and sending the correction amount to a light source through current driving by a programmable electric controller, thereby achieving adjustment of the wavelength of the light source; wherein the two ends of the gyro coupler correspond to the detector front end and the gyro light source output end respectively.

5. The method for stabilizing the scale factor of an optical fiber gyroscope according to claim 4, characterized in that: A spectrometer or an optical path device with a spectrum extraction function is used to extract spectrum signals from both ends of the coupler of the fiber optic gyroscope and perform synchronous waveform spectrum subtraction operations.

6. A method for online correction of optical path spectrum, characterized in that: A line driving method is used to perform negative feedback adjustment on wavelength changes to achieve the stability of the average central wavelength of the optical path and the waveform symmetry, and the waveform changes include: (a) the shift of the central wavelength of the light wave, which includes the central wavelength shifting to the left and increasing to the right; (b) the asymmetry of the light wave spectrum, which includes the spectrum containing positive odd components and negative odd components; wherein the spectral negative feedback amount involved in the negative feedback adjustment is the spectral change amount extracted online by the inverse wavelength filter described in claim 1 or 2 or the spectral change amount obtained by offline modeling in advance; the offline spectral change amount establishes the output change law of the spectrum by testing the parameters under different environmental conditions, and then extracts the environmental parameter waveform online, and inputs the change law into the inverse wavelength filter through online negative feedback.

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