Hollow-core microstructure optical fiber ring polarization-maintaining enhanced winding system and method

Abstract

The invention relates to a polarization-maintaining enhanced winding system and method for a hollow-core microstructure optical fiber ring. The polarization-maintaining enhanced winding system comprises a ring winding device and an optical fiber birefringence detection module. The winding equipment comprises two fiber releasing wheels, a winding framework and two groups of tension adjusting mechanisms; the optical fiber birefringence detection module comprises a wavelength tunable laser, a polarization state generator, a polarization state analyzer and an upper computer; the method comprises the following steps: starting an optical fiber birefringence detection module in the winding process of an optical fiber ring; the precise value of the optical fiber group delay inequality delta tau is obtained through an optical fiber birefringence detection module, and the birefringence value of the optical fiber is reversely deduced; the optical fiber birefringence is used as a feedback signal to control the tensile force applied to the hollow optical fiber by the tensile force adjusting mechanism, and the high-stability optical fiber birefringence is obtained. The polarization-maintaining enhancement effect can be achieved, and polarization-dependent noise in the interference type hollow-core microstructure fiber-optic gyroscope can be inhibited.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber gyroscopes, and relates to a hollow-core microstructure optical fiber ring polarization-maintaining enhancement winding system and method. Background Art

[0002] Hollow-core microstructured optical fibers use a specific cladding structure to establish a new light-guiding mechanism that efficiently confines light waves to the air core for propagation. Using air as the transmission medium, light waves are no longer sensitive to the effects of heat, magnetism, and radiation in the environment, and can achieve ideal high-stability light transmission, which can fundamentally solve the problem of improving the environmental adaptability of fiber-optic gyroscopes. There are two main types of hollow-core microstructured optical fibers: one is hollow-core photonic crystal fibers with periodic lattice structure characteristics that construct a light-guiding mechanism based on the photonic bandgap effect; the other is hollow-core antiresonant optical fibers with uniform glass wall thickness structure characteristics that form a light-guiding mechanism based on the antiresonant reflection effect.

[0003] Polarization-related error is one of the main errors of fiber optic gyroscopes. Usually, fiber optic gyroscopes use a full polarization-maintaining optical path solution to achieve efficient suppression of polarization-related amplitude and intensity noise. In the best case, the optical fiber used for the gyroscope, especially the optical fiber used in the fiber optic loop, should have polarization-maintaining capabilities to achieve stable transmission of linearly polarized light, thereby effectively suppressing the gyroscope noise caused by polarization crosstalk in the interference optical path. In general, the polarization-maintaining ability of an optical fiber is characterized by the birefringence (Δn). When light waves propagate in two mutually orthogonal polarization directions in the optical fiber, they exhibit different refractive indices, that is, Δn = n x -n y , the higher the birefringence, the stronger the polarization maintaining ability.

[0004] The traditional solid core polarization-maintaining optical fiber used in gyroscopes obtains high polarization-maintaining capability by introducing stress birefringence at the core. However, it is difficult to achieve high birefringence in hollow core microstructure optical fiber to have excellent polarization-maintaining capability. Hollow core microstructure optical fiber binds light waves in the air for transmission. The elastic-optic effect is invalid for air, and stress birefringence cannot be applied. Hollow core microstructure optical fiber can only achieve high birefringence by controlling the thickness difference (nanometer level) of the light-guiding air core glass wall in two perpendicular directions to form an anti-cross-coupling effect, or by controlling the ellipticity (micrometer level) of the light-guiding air core to stimulate the structural birefringence effect to achieve high polarization-maintaining light transmission. This micro-nanoscale structural difference requires extremely high drawing level of hollow core microstructure optical fiber, which is difficult to stably achieve in the preparation of long-distance hollow core microstructure optical fiber of several thousand meters, and cannot meet the demand for polarization-related noise suppression in interferometric hollow core microstructure optical fiber gyroscopes. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a hollow-core microstructure fiber ring polarization-maintaining enhancement winding system and method, which enables a non-polarization-maintaining hollow-core microstructure fiber to form a stable structural birefringence when wound into a ring, thereby achieving a polarization-maintaining enhancement effect, thereby being beneficial for suppressing polarization-related noise in an interferometric hollow-core microstructure fiber gyroscope.

[0006] One of the above objects of the present invention is achieved by the following technical solution:

[0007] A hollow core microstructure optical fiber loop polarization-maintaining enhanced winding system, comprising a loop winding device and an optical fiber birefringence detection module;

[0008] The ring winding device comprises two fiber supply wheels, a winding skeleton and two sets of tension adjustment mechanisms; the two fiber supply wheels are used to store the hollow core optical fibers to be wound, and during the optical fiber winding process, the optical fibers are continuously released at a linear speed matching the ring winding speed in an alternating manner; the two sets of tension adjustment mechanisms are respectively arranged between the two fiber supply wheels and the winding skeleton, and are used to adjust the tension of the optical fiber winding; the winding skeleton is installed on the main shaft of the ring winding machine, and continuously collects the fibers and winds the optical fibers into rings as the main shaft rotates;

[0009] The optical fiber birefringence detection module includes a wavelength tunable laser, a polarization state generator, a polarization state analyzer, and a host computer;

[0010] The wavelength tunable laser is used to generate the required corresponding optical power within a specific wavelength range. The optical energy will sequentially pass through the polarization state generator, the hollow core microstructure optical fiber to be wound, and the polarization state analyzer to provide the optical power input for measuring the birefringence of the optical fiber using the Jones matrix method;

[0011] The polarization state generator is composed of a polarizer, a magneto-optical rotator and a quarter wave plate, and is used to adjust the direction of light passing through by controlling the magneto-optical rotator, and correspondingly generate linear polarized light and left-handed and right-handed circularly polarized light in multiple angular directions;

[0012] The polarization state analyzer is used for high-speed detection of the polarization state of light, uses four channels to simultaneously obtain four Stokes parameters, and measures the instantaneous polarization state of the input light and sends it to the host computer;

[0013] The host computer is used to receive the polarization state detection signal of the polarization state analyzer, control the output wavelength of the tunable laser, adjust the polarization state switching of the polarization state generator, calculate the fiber transmission Jones matrix and obtain the fiber birefringence, and send a tension adjustment instruction to the ring winding device with the fiber birefringence as a feedback signal.

[0014] Moreover, the two sets of tension adjustment mechanisms are composed of two fixed pulleys and one movable pulley. The two movable pulleys are respectively arranged on both sides of the two fixed pulleys. The optical fiber winding tension is adjusted by moving the movable pulley up and down.

[0015] The second objective of the present invention is achieved by the following technical solutions:

[0016] A winding method using the above hollow core microstructure optical fiber loop polarization-maintaining enhanced winding system comprises the following steps:

[0017] Step 1: During the process of winding the optical fiber loop, the optical fiber birefringence detection module is started simultaneously;

[0018] Step 2: Obtain the precise value of the fiber group delay difference Δτ through the fiber birefringence detection module, and use Δτ=ΔnL / c to infer the fiber birefringence value, where Δn is the fiber birefringence, L is the fiber length, and c is the speed of light;

[0019] Step 3: Using the birefringence of the optical fiber as a feedback signal, control the tensioning force applied to the hollow optical fiber by the tensioning force adjustment mechanism to obtain a highly stable birefringence of the optical fiber.

[0020] Furthermore, step 2 includes:

[0021] 2.1. Under the tunable laser input wavelength, the host computer first controls the polarization state generator to sequentially generate three different polarization states. At the same time, the polarization state analyzer detects the three output polarization states of the three sequentially generated polarization states after passing through the hollow-core microstructured optical fiber: light fields h, v and q;

[0022] 2.2, then the x- and y-direction components of the light fields h, v and q are used to calculate the Jones transmission matrix of the hollow-core microstructured optical fiber, as shown in equation (1);

[0023]

[0024] Where β is a complex constant

[0025] 2.3. Then the host computer controls the wavelength tunable laser to scan the wavelength and detects the Jones transmission matrix at other wavelengths. The fiber group delay difference Δτ within a specific wavelength range can be accurately obtained using formula (2);

[0026]

[0027] Where ρ1 and ρ2 are matrices T(ω+Δω)T -1 (ω) is the eigenvalue, and Δω is the frequency change of the light source.

[0028] The advantages and positive effects of the present invention are:

[0029] 1. The hollow-core microstructured optical fiber ring polarization-maintaining enhanced winding system of the present invention adds an optical fiber birefringence detection module on the basis of the existing ring winding equipment, thereby realizing real-time detection of the optical fiber birefringence during the optical fiber ring winding process. According to the detection result, the tension of the optical fiber is adjusted in real time by adjusting the tension adjustment mechanism of the ring winding equipment, thereby realizing the formation of a stable winding tension-induced structural birefringence of the hollow-core microstructured optical fiber with a non-polarization-maintaining design when it is wound into a ring, and the polarization-maintaining enhanced effect can be obtained, which is beneficial to suppressing the polarization-related noise in the interferometric hollow-core microstructured optical fiber gyroscope.

[0030] 2. The optical fiber birefringence detection module provided on the loop winding device of the present invention measures the optical fiber birefringence based on the optical fiber transmission Jones matrix. The measurement time is extremely short (measurement time <15s), and the loop winding working hours are not increased, so the winding efficiency of the optical fiber loop can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the elliptical deformation of the core of a hollow-core microstructured optical fiber under stress;

[0032] Figure 2 is a graph showing the effect of elliptical deformation of the core of a hollow-core microstructure optical fiber on the birefringence index according to an embodiment of the present invention;

[0033] Figure 3 This is a diagram of the polarization-maintaining and enhanced winding system of the hollow-core microstructure optical fiber loop of the present invention;

[0034] In the figure: 1. Wavelength tunable laser; 2. Polarization state generator; 3. Fiber supply wheel 1; 4. Winding tension adjustment mechanism 1; 5. Hollow core microstructure optical fiber ring winding skeleton; 6. Winding tension adjustment mechanism 2; 7. Fiber supply wheel 2; 8. Polarization state analyzer; 9. Host computer; 10. Winding equipment spindle DETAILED DESCRIPTION

[0035] The structure of the present invention is further described below with reference to the accompanying drawings and by way of examples. It should be noted that the present examples are descriptive rather than restrictive.

[0036] Aiming at the problem that the polarization maintaining ability of a hollow-core microstructured optical fiber without polarization maintaining design is insufficient and polarization-related noise is easily generated when the hollow-core microstructured optical fiber with non-polarization maintaining design is applied to an optical fiber gyroscope, the present invention proposes a hollow-core microstructured optical fiber ring polarization maintaining enhancement winding system and winding method. The system is provided with an optical fiber birefringence detection module, which is constructed by a wavelength tunable laser, a polarization state generator and a polarization state analyzer. The group delay difference Δτ that can characterize the birefringence of the optical fiber is measured based on the optical fiber transmission Jones matrix within a certain wavelength range. The system uses the group delay difference Δτ as a feedback signal. During the optical fiber winding process, the system adjusts and selects a suitable winding tension with the help of a winding tension adjustment mechanism to ensure that the light-guiding air core in the microstructured optical fiber produces a consistent elliptical deformation, so as to form a stable winding tension-induced structural birefringence, thereby achieving the effect of enhancing the polarization maintaining ability of the hollow-core microstructured optical fiber ring without polarization maintaining design.

[0037] Figure 1 This is a schematic diagram of the elliptical deformation of the core of a hollow-core microstructured optical fiber under stress. The structural material of the hollow-core microstructured optical fiber is silicon dioxide. Several micron-scale microstructure units (the example shows 6 two-nested circular tube microstructure units) are evenly distributed on the inside of the large hollow circular structure. The function of the micron-scale microstructure units is to completely confine the light to be transmitted in the air core. The thin lines in the figure represent the original position of the end face structure of the hollow-core microstructured optical fiber. The displacement of the pressure plate toward the hollow-core optical fiber generates a lateral extrusion force on the hollow-core optical fiber. The tension applied during the process of winding the hollow-core microstructured optical fiber into a ring can also generate similar lateral extrusion forces between the layers of the optical fiber ring. Due to the high proportion of air in the hollow-core microstructured optical fiber and the use of single-point suspension to connect the cladding microstructure units, the mechanical strength of the optical fiber structure is limited. Under the application of lateral extrusion force, the hollow-core microstructured optical fiber will deform, and the cladding microstructure units will undergo relative displacement deformation. The optical fiber will shrink inward due to the force in the extrusion direction, and will form an outward stretching deformation effect in the orthogonal direction of the extrusion. As a result, the air core composed of multiple cladding microstructure units is no longer circular, but becomes elliptical, where a represents the short semi-axis length of the elliptical core, and b represents the long semi-axis length of the elliptical core.

[0038] Figure 2It is the influence of the elliptical deformation of the hollow core microstructure fiber core on the birefringence. When the hollow core microstructure fiber core is elliptical, geometric birefringence will be formed. According to numerical simulation calculation, the structural birefringence of the hollow core microstructure fiber will first increase with the increase of the core elliptical deformation degree. After the core elliptical deformation degree reaches a specific value, the structural birefringence of the hollow core microstructure fiber will decrease with the increase of the core elliptical deformation degree. As can be seen from the figure, in the embodiment of the present invention, when the semi-axis length of the hollow core microstructure fiber core ellipse a=10um and the elliptical deformation ratio b / a=1.8, the generated structural birefringence is the largest. In the hollow core microstructure fiber, since the light wave is efficiently bound by the light guiding mechanism constructed by the microstructure unit to propagate in the hollow core, the light transmission medium is air, and the air has no elastic light effect and cannot form stress birefringence. Therefore, when the hollow core microstructure fiber produces stable structural birefringence, there will be no stress-induced birefringence degradation mechanism.

[0039] Figure 3 This is a schematic diagram of the polarization-maintaining enhanced winding system for a hollow-core microstructure optical fiber ring of the present invention. The system applies a specific tensioning force during the process of winding the hollow-core microstructure optical fiber into a ring to cause the light-guiding air core to ellipse and deform, so as to form a winding tension-induced structural birefringence, thereby enhancing the polarization-maintaining ability of the hollow-core microstructure optical fiber ring. The system has a birefringence detection function, which is used for the selection and re-inspection of the magnitude of the winding tension force applied to ensure the optimality and consistency of the ellipticalization of the hollow-core microstructure optical fiber core. In order to solve the problem of inconsistent core elliptical direction caused by optical fiber torsion during winding, the optical fiber winding back-twist method in the invention patent "A hollow-core microstructure optical fiber winding back-twist method and system, ZL 202210671935.7" can be used to circumvent it.

[0040] The winding system of the present invention is mainly composed of a wavelength tunable laser 1, a polarization state generator 2, a polarization state analyzer 8, a host computer 9 and related mechanisms of the ring winding equipment.

[0041] Wavelength tunable laser (model: WSL-110): used to generate the required optical power within a specific wavelength range. The optical energy will pass through the polarization state generator, the hollow core microstructured optical fiber to be wound, and the polarization state analyzer in sequence to provide the optical power input for measuring the birefringence of the optical fiber using the Jones matrix method;

[0042] Polarization state generator (model: PSG-101): It consists of a polarizer, a magneto-optical rotator and a quarter wave plate. By controlling the magneto-optical rotator to adjust the direction of light passing through, it can generate 0°, 90°, 45° linear polarized light and left-handed and right-handed circularly polarized light;

[0043] Polarization state analyzer (model: PAX1000IR2 / M): used for high-speed detection of light polarization state. It uses four channels to obtain four Stokes parameters at the same time, and can measure the instantaneous polarization state of the input light and send it to the host computer.

[0044] Host computer: used to receive polarization state detection signals from the polarization state analyzer, control the output wavelength of the tunable laser, adjust the polarization state switching of the polarization state generator, calculate the fiber transmission Jones matrix and obtain the fiber birefringence, and send tension adjustment instructions to the ring winding device with the fiber birefringence as feedback signal;

[0045] Ring winding equipment: mainly includes the first fiber supply wheel 3, the second fiber supply wheel 7, the winding skeleton 5, the first tension adjustment mechanism 4 and the second tension adjustment mechanism 6. The two fiber supply wheels are used to store the hollow core optical fiber to be wound. During the fiber winding process, the optical fiber is continuously released at a linear speed that matches the ring winding speed in an alternating manner. The tension adjustment mechanism consists of two fixed pulleys and a movable pulley. The movable pulley moves up and down to adjust the tension of the optical fiber winding. The winding skeleton is installed on the main shaft 10 of the ring winding machine, and the fiber is continuously collected and wound into a ring as the main shaft rotates.

[0046] Among them, the method for measuring the fiber group delay difference Δτ based on the fiber transmission Jones matrix to characterize the birefringence of hollow core microstructure fiber is as follows:

[0047] The light emitted by the wavelength tunable laser passes through the polarization state generator and the hollow core microstructure fiber on the winding device in sequence, and finally reaches the polarization state analyzer for detection of the light polarization state. Under the input wavelength of the tunable laser, the host computer first controls the polarization state generator to sequentially generate three different polarization states, such as 0°, 90° and 45° linear polarization light. At the same time, the polarization state analyzer detects the three polarization states generated sequentially after passing through the hollow core microstructure fiber. The corresponding three output polarization states of the light field h, v and q, and then the x and y direction components of the hollow core microstructure fiber can be used to calculate the Jones transmission matrix of the hollow core microstructure fiber, as shown in formula (1). Subsequently, the host computer controls the wavelength tunable laser to scan the wavelength and detects the Jones transmission matrix at other wavelengths. Formula (2) can be used to accurately obtain the fiber group delay difference Δτ within a specific wavelength range. Since the fiber group delay difference Δτ=ΔnL / c, Δn is the fiber birefringence, L is the fiber length, and c is the speed of light, it can be seen that the fiber birefringence can be inferred by accurately obtaining the fiber group delay difference Δτ.

[0048]

[0049] Where β is a complex constant.

[0050]

[0051] Where ρ1 and ρ2 are matrices T(ω+Δω)T -1 (ω) is the eigenvalue, and Δω is the frequency change of the light source.

[0052] Based on the relationship between the elliptical deformation and birefringence of the hollow core microstructured optical fiber, the optimal elliptical deformation is selected to obtain the optimal high birefringence effect. The high birefringence represents a high polarization maintaining ability. For example, in the embodiment of the present invention, it can be selected Figure 2 The maximum birefringence caused by the structure can be obtained at the elliptical deformation ratio b / a=1.8. The birefringence of the optical fiber is used as a feedback signal to control the tension adjustment mechanism to apply a specific hollow-core optical fiber ring winding tension to obtain a stable optical fiber birefringence, and the size of the optical fiber birefringence increases proportionally with the increase of the optical fiber winding length, and finally the hollow-core microstructure optical fiber ring has a good polarization maintenance ability as a whole.

[0053] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A hollow core microstructure optical fiber loop polarization-maintaining enhanced winding system, characterized in that: Including loop winding equipment and optical fiber birefringence detection module; The ring winding device comprises two fiber supply wheels, a winding skeleton and two sets of tension adjustment mechanisms; the two fiber supply wheels are used to store the hollow core optical fibers to be wound, and during the optical fiber winding process, the optical fibers are continuously released at a linear speed matching the ring winding speed in an alternating manner; the two sets of tension adjustment mechanisms are respectively arranged between the two fiber supply wheels and the winding skeleton, and are used to adjust the tension of the optical fiber winding; the winding skeleton is installed on the main shaft of the ring winding machine, and continuously collects the fibers and winds the optical fibers into rings as the main shaft rotates; The optical fiber birefringence detection module includes a wavelength tunable laser, a polarization state generator, a polarization state analyzer, and a host computer; The wavelength tunable laser is used to generate the required corresponding optical power within a specific wavelength range. The optical energy will sequentially pass through the polarization state generator, the hollow core microstructure optical fiber to be wound, and the polarization state analyzer to provide the optical power input for measuring the birefringence of the optical fiber using the Jones matrix method; The polarization state generator is composed of a polarizer, a magneto-optical rotator and a quarter wave plate, and is used to adjust the direction of light passing through by controlling the magneto-optical rotator, and correspondingly generate linear polarized light and left-handed and right-handed circularly polarized light in multiple angular directions; The polarization state analyzer is used for high-speed detection of the polarization state of light, uses four channels to simultaneously obtain four Stokes parameters, and measures the instantaneous polarization state of the input light and sends it to the host computer; The host computer is used to receive the polarization state detection signal of the polarization state analyzer, control the output wavelength of the tunable laser, adjust the polarization state switching of the polarization state generator, calculate the fiber transmission Jones matrix and obtain the fiber birefringence, and send a tension adjustment instruction to the ring winding device with the fiber birefringence as a feedback signal.

2. The hollow core microstructure optical fiber loop polarization-maintaining enhanced winding system according to claim 1, characterized in that: The two sets of tension adjustment mechanisms are composed of two fixed pulleys and one movable pulley. The two movable pulleys are respectively arranged on both sides of the two fixed pulleys. The optical fiber winding tension is adjusted by moving the movable pulley up and down.

3. A winding method using the hollow core microstructure optical fiber loop polarization-maintaining enhanced winding system according to claim 1 or 2, characterized in that: The steps include: Step 1: During the process of winding the optical fiber loop, the optical fiber birefringence detection module is started simultaneously; Step 2: Obtain the precise value of the fiber group delay difference Δτ through the fiber birefringence detection module, and use Δτ=ΔnL / c to infer the fiber birefringence value, where Δn is the fiber birefringence, L is the fiber length, and c is the speed of light; Step 3: Using the birefringence of the optical fiber as a feedback signal, control the tensioning force applied to the hollow optical fiber by the tensioning force adjustment mechanism to obtain a highly stable birefringence of the optical fiber.

4. The method for winding a hollow-core microstructure optical fiber loop polarization-maintaining enhanced winding system according to claim 3, characterized in that: Step 2 includes: 2.

1. Under the tunable laser input wavelength, the host computer first controls the polarization state generator to sequentially generate three different polarization states. At the same time, the polarization state analyzer detects the three output polarization states of the three sequentially generated polarization states after passing through the hollow-core microstructured optical fiber: light fields h, v and q; 2.2, then the x- and y-direction components of the light fields h, v and q are used to calculate the Jones transmission matrix of the hollow-core microstructured optical fiber, as shown in equation (1); Where β is a complex constant 2.

3. Then the host computer controls the wavelength tunable laser to scan the wavelength and detects the Jones transmission matrix at other wavelengths. The fiber group delay difference Δτ within a specific wavelength range can be accurately obtained using formula (2); Where ρ1 and ρ2 are matrices T(ω+Δω)T -1 (ω) is the eigenvalue, and Δω is the frequency change of the light source.

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