A hollow-core microstructure optical fiber loop polarization-maintaining enhanced winding system and method

Abstract

The present invention relates to a hollow-core microstructure optical fiber loop polarization-maintaining and enhanced winding system and method, comprising a loop winding device and an optical fiber birefringence detection module; the loop winding device comprises two pay-off wheels, a winding skeleton, and two sets of tension adjustment mechanisms; the optical fiber birefringence detection module comprises a wavelength tunable laser, a polarization state generator, a polarization state analyzer, and a host computer; the method comprises: simultaneously activating the optical fiber birefringence detection module during the optical fiber loop winding process; obtaining the precise value of the optical fiber group delay difference Δτ through the optical fiber birefringence detection module, and inferring the optical fiber birefringence value; and using the optical fiber birefringence as a feedback signal, controlling the tension applied to the hollow-core optical fiber by the tension adjustment mechanism to obtain a highly stable optical fiber birefringence. The present invention can achieve a polarization-maintaining and enhanced effect, which is beneficial for suppressing polarization-dependent noise in an interferometric hollow-core microstructure optical fiber gyroscope.

Description

Technical Field

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

[0002] Hollow-core microstructured optical fibers utilize a specific cladding structure to establish a novel 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 environmental influences such as heat, magnetism, and radiation, enabling ideal, highly stable optical transmission and fundamentally addressing the challenge of further improving the environmental adaptability of fiber-optic gyroscopes. There are two main types of hollow-core microstructured optical fibers: hollow-core photonic crystal fibers with a periodic lattice structure, which utilize the photonic bandgap effect to create a light-guiding mechanism; and hollow-core antiresonant fibers with a uniform glass wall thickness, which utilize the antiresonant reflection effect to create a light-guiding mechanism.

[0003] Polarization-related error is one of the main errors in fiber optic gyroscopes. Fiber optic gyroscopes usually use a full polarization-maintaining optical path solution to effectively suppress 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 ability to achieve stable transmission of linearly polarized light, thereby effectively suppressing the gyroscope noise caused by polarization crosstalk in the interference optical path. Generally, the polarization-maintaining ability of the optical fiber is determined by the birefringence ( ) to characterize that when light waves propagate in two mutually orthogonal polarization directions in the optical fiber, they exhibit different refractive indices, namely , the higher the birefringence, the stronger the polarization maintaining ability.

[0004] Traditional solid-core polarization-maintaining fibers used in gyros achieve high polarization-maintaining capability by introducing stress-induced birefringence into the fiber core. However, achieving high birefringence and excellent polarization-maintaining capability in hollow-core microstructured fibers is challenging. Hollow-core microstructured fibers confine light waves for transmission in air, where the elasto-optic effect is ineffective and stress-induced birefringence cannot be applied. Hollow-core microstructured fibers can only achieve high birefringence by controlling the thickness difference (nanometer-scale) between the glass walls of the light-guiding air core in two perpendicular directions to create an anti-cross-coupling effect, or by controlling the ellipticity (micrometer-scale) of the light-guiding air core to induce a structural birefringence effect to achieve highly polarization-maintaining light transmission. These micro-nanoscale structural differences require extremely high levels of hollow-core microstructured fiber drawing technology, making them difficult to reliably achieve over long distances of several thousand meters. Consequently, they cannot meet the requirements for polarization-dependent noise suppression in interferometric hollow-core microstructured fiber gyros. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention proposes a hollow-core microstructured optical fiber loop polarization-maintaining enhancement winding system and method, which enables a non-polarization-maintaining hollow-core microstructured optical fiber to form stable structural birefringence when wound into a loop, thereby achieving a polarization-maintaining enhancement effect, thereby being beneficial for suppressing polarization-dependent noise in an interferometric hollow-core microstructured optical fiber gyroscope.

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

[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 includes 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 fiber to be wound, and during the fiber winding process, the optical fiber is continuously released in an alternating manner at a linear speed that matches the ring winding speed; 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 fiber and winds the optical fiber into a ring 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 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.

[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, thereby generating linearly 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. It 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 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 at the same time send a tension adjustment instruction to the ring winding device using 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 object of the present invention is achieved by the following technical solutions:

[0016] A winding method using the aforementioned 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 fiber group delay difference through the fiber birefringence detection module The exact value of , inversely deduce the fiber birefringence value, where is the birefringence of the optical fiber, is the fiber length, is the speed of light;

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

[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 polarization states generated sequentially and the corresponding three output polarization states after passing through the hollow-core microstructured optical fiber. 、 and ;

[0022] 2.2, then use the light field 、 and of 、 The Jones transmission matrix of the hollow-core microstructured optical fiber is obtained by the directional component, as shown in formula (1);

[0023] (1)

[0024] Where, is a complex constant

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

[0026] (2)

[0027] Where, and is a matrix The eigenvalue of 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 tensioning force of the optical fiber is adjusted in real time by adjusting the tensioning force 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 during the ring winding, thereby achieving the effect of polarization-maintaining enhancement, which is beneficial to suppressing the polarization-related noise in the interferometric hollow-core microstructured optical fiber gyroscope.

[0030] 2. The fiber birefringence detection module provided on the loop winding equipment of the present invention measures the fiber birefringence based on the fiber transmission Jones matrix. The measurement time is extremely short (measurement time <15s), which does not increase the loop winding working hours and can improve the winding efficiency of the optical fiber loop. 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 microstructured optical fiber on the birefringence in an embodiment of the present invention;

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

[0034] Figure: 1. Wavelength tunable laser; 2. Polarization state generator; 3. Fiber supply reel 1; 4. Winding tension adjustment mechanism 1; 5. Hollow-core microstructured optical fiber ring winding frame; 6. Winding tension adjustment mechanism 2; 7. Fiber supply reel 2; 8. Polarization state analyzer; 9. Host computer; 10. Winding equipment spindle DETAILED DESCRIPTION

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

[0036] The present invention addresses the problem of insufficient polarization maintenance capability and the generation of polarization-dependent noise when hollow-core microstructured optical fibers with non-polarization-maintaining design are used in optical fiber gyros. A hollow-core microstructured optical fiber loop polarization-maintaining enhanced winding system and winding method are proposed. The system is equipped 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 that can characterize the optical fiber birefringence is measured based on the optical fiber transmission Jones matrix within a certain wavelength range. , the system is based on group delay difference In order to provide feedback signals, the winding tension adjustment mechanism is used to adjust and select the appropriate winding tension during the fiber winding process to ensure that the light-guiding air core in the microstructured optical fiber produces consistent elliptical deformation, thereby forming a stable winding tension-induced structural birefringence, thereby achieving the effect of enhancing the polarization maintenance ability of the non-polarization-maintaining hollow-core microstructured optical fiber ring.

[0037] Figure 1 This diagram illustrates the ovalization of the core of a hollow-core microstructured optical fiber under stress. The structural material of the hollow-core microstructured optical fiber is silica. Several micron-scale microstructure units (six nested circular tubes in the example) are uniformly distributed within the large hollow circular structure. These micron-scale microstructure units function to completely confine light transmission within the air core. The thin lines in the diagram represent the original position of the hollow-core microstructured optical fiber end face. The displacement of the pressure plate toward the hollow-core fiber exerts a lateral compressive force on the hollow-core fiber. The tension applied during the ring winding of the hollow-core microstructured optical fiber also produces similar lateral compressive forces between the layers of the fiber ring. Due to the high proportion of air in the hollow-core microstructured optical fiber and the use of a 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 inwards 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 elliptical deformation occurs. represents the length of the semi-minor axis of the elliptical core, Represents the length of the semi-major axis of the elliptical fiber core.

[0038] Figure 2 It is the effect of the elliptical deformation of the hollow core microstructured optical fiber on the birefringence. When the hollow core microstructured optical fiber core is elliptical, geometric birefringence will be formed. According to numerical simulation calculations, the birefringence caused by the hollow core microstructured optical fiber structure will first increase with the increase of the core elliptical deformation degree. After the core elliptical deformation degree reaches a specific value, the birefringence caused by the hollow core microstructured optical fiber structure 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 elliptical core of the hollow core microstructured optical fiber is and ellipse deformation ratio When the structure-induced birefringence is the largest, the generated structure-induced birefringence is the largest. In hollow-core microstructured optical fibers, light waves are efficiently confined and propagated in the hollow core by the light-guiding mechanism constructed by the microstructure units. The light transmission medium is air, which has no elastic-optical effect and cannot form stress-induced birefringence. Therefore, when the hollow-core microstructured optical fiber generates stable structure-induced 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 the hollow-core microstructured optical fiber ring of the present invention. The system applies a specific tensioning force during the process of winding the hollow-core microstructured optical fiber into a ring to cause the light-guiding air core to ellipse and deform, thereby forming a winding tension-induced structural birefringence and thereby enhancing the polarization-maintaining ability of the hollow-core microstructured optical fiber ring. The system has a birefringence detection function, which is used for selecting and rechecking the magnitude of the winding tension applied to ensure the optimality and consistency of the ellipticalization of the hollow-core microstructured 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 backtwist method in the invention patent "A hollow-core microstructured optical fiber winding backtwist method and system, ZL 202210671935.7" can be used to circumvent it.

[0040] The winding system of the present invention mainly consists 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 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 fiber birefringence using the Jones matrix method.

[0042] Polarization state generator (model: PSG-101): 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 polarization and left-handed and right-handed circular polarization;

[0043] Polarization State Analyzer (Model: PAX1000IR2 / M): Used for high-speed detection of the polarization state of light. It uses four channels to simultaneously obtain four Stokes parameters, can measure the instantaneous polarization state of the input light and send it to the host computer;

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

[0045] The ring winding equipment primarily comprises a first fiber supply wheel 3, a second fiber supply wheel 7, a winding frame 5, a first tension adjustment mechanism 4, and a second tension adjustment mechanism 6. The two fiber supply wheels store the hollow-core optical fiber to be wound. During the fiber winding process, the fibers are released alternately at a linear speed that matches the ring winding speed. The tension adjustment mechanism consists of two fixed pulleys and a movable pulley, which move up and down to adjust the fiber winding tension. The winding frame is mounted on the ring winding machine's main shaft 10 and continuously collects and winds the optical fiber into a ring as the main shaft rotates.

[0046] Among them, the fiber group delay difference is measured based on the fiber transmission Jones matrix The method to characterize the birefringence of hollow core microstructured optical fiber is as follows:

[0047] The light emitted by the wavelength tunable laser passes through the polarization generator and the hollow core microstructured optical fiber on the winding device in sequence, and finally reaches the polarization analyzer for polarization state detection. Under the input wavelength of the tunable laser, the host computer first controls the polarization generator to sequentially generate three different polarization states, such as 0°, 90° and 45° linear polarization. At the same time, the polarization analyzer detects the three polarization states generated sequentially after passing through the hollow core microstructured optical fiber, and the corresponding three output polarization states of the light field. 、 and , and then use them 、 The Jones transmission matrix of the hollow-core microstructured optical fiber can be obtained by the directional component, as shown in formula (1). Subsequently, the host computer controls the wavelength tunable laser to perform wavelength scanning and detects the Jones transmission matrix at other wavelengths. The fiber group delay difference within a specific wavelength range can be accurately obtained using formula (2). Due to the delay difference of the fiber group , is the birefringence of the optical fiber, is the fiber length, =The speed of light, so the fiber group delay difference The precise acquisition of the optical fiber birefringence can be used to infer the optical fiber birefringence.

[0048] (1)

[0049] In the formula is a complex constant.

[0050] (2)

[0051] In the formula and is a matrix The eigenvalue of 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. High birefringence represents high polarization maintaining ability. For example, in the embodiment of the present invention, Figure 2 Medium ellipse deformation ratio The maximum structural birefringence can be obtained at . Using the fiber birefringence as a feedback signal to control the tension adjustment mechanism and apply a specific hollow-core fiber ring winding tension can achieve a stable fiber birefringence. The fiber birefringence increases proportionally with the increase in fiber winding length, ultimately making the hollow-core microstructure fiber ring have good polarization maintaining ability.

[0053] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various replacements, 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 contents disclosed in the embodiments and drawings.

Claims

1. A hollow-core microstructured optical fiber loop polarization-maintaining enhanced winding system, characterized by: Including looping equipment and optical fiber birefringence detection module; The ring winding device includes 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 fiber to be wound, and during the fiber winding process, the optical fiber is continuously released in an alternating manner at a linear speed that matches the ring winding speed; 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 fiber and winds the optical fiber into a ring 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 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. 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, thereby generating linearly 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. It 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 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 at the same time send a tension adjustment instruction to the ring winding device using the fiber birefringence as a feedback signal.

2. The hollow-core microstructured 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 microstructured optical fiber loop polarization-maintaining enhanced winding system according to claim 1 or 2, characterized in that: The steps include: Step 1: During the fiber loop winding process, start the fiber birefringence detection module at the same time Step 2: Obtain the fiber group delay difference through the fiber birefringence detection module The exact value of , inversely deduce the fiber birefringence value, where is the birefringence of the optical fiber, is the fiber length, is the speed of light; Step 3: Using the optical fiber birefringence as a feedback signal, control the tension applied to the hollow-core optical fiber by the tension adjustment mechanism to obtain a highly stable optical fiber birefringence.

4. The method for winding a hollow-core microstructured optical fiber using the polarization-maintaining enhanced winding system of claim 1 or 2 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 polarization states generated sequentially and the corresponding three output polarization states after passing through the hollow-core microstructured optical fiber. ; 2.

3. The host computer then controls the wavelength tunable laser to scan the wavelength and detect the Jones transmission matrix at other wavelengths. The fiber group delay difference within a specific wavelength range can be accurately obtained using formula (2).

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