Polarization property detection method and implementation system for polarization-maintaining hollow-core microstructure optical fiber loop

Abstract

The present application relates to the technical field of fiber-optic gyroscopes, and in particular to a polarization property detection method and implementation system for a polarization-maintaining hollow-core microstructure optical fiber loop. The method comprises: continuously changing the wavelength of linearly polarized detection light to obtain a polarization-state Stokes parameter of emergent light of an optical fiber loop; drawing a circular trajectory on the Poincaré sphere on the basis of the polarization-state Stokes parameter of emergent light of the optical fiber loop, wherein in the circular trajectory, an arc angle from the circle center point of the circular trajectory to the circumference point of the circular trajectory or the radius of the circular trajectory represents the accuracy of the alignment of the incident linearly polarized detection light with respect to an axis, and the angular offset of the center of the circular trajectory from the equator of the Poincaré sphere represents the deterioration of a polarization property in the optical fiber loop; and calculating the polarization property on the basis of the angular offset from the equator.

Description

Method for detecting polarization characteristics of polarization maintaining hollow microstructure fiber coil and implementation system

[0001] Related Applications

[0002] The present application claims priority to the Chinese patent application No. 202411075570.7 filed on August 7, 2024, and incorporates by reference the entire disclosure of the above patent application as part of the present application. TECHNICAL FIELD

[0003] The present application belongs to the technical field of fiber-optic gyroscope, and particularly relates to a method for detecting polarization characteristics of polarization maintaining hollow microstructure fiber coil and an implementation system. BACKGROUND

[0004] Polarization maintaining hollow microstructure fiber utilizes a specific cladding structure to construct photonic bandgap effect or anti-resonant reflection effect, thereby efficiently confining light waves in air core to propagate, taking air as the transmission medium. Light waves are no longer sensitive to the influence of heat, magnetism and irradiation in the environment, and ideal high-stability light transmission can be achieved, which can effectively improve the environmental adaptability of fiber-optic gyroscope.

[0005] The optical fiber used in the fiber-optic gyroscope fiber coil usually has strong polarization maintaining capability to achieve stable transmission of linearly polarized light, thereby effectively suppressing the gyro noise caused by polarization coupling in the interference optical path. The polarization maintaining capability of the optical fiber is characterized by birefringence Δn. When light waves propagate in two mutually orthogonal polarization directions of the optical fiber, they exhibit different refractive indices. The higher the birefringence, the stronger the polarization maintaining capability.

[0006] Polarization maintaining hollow microstructure fiber usually forms anti-cross coupling effect by controlling the thickness difference (nanometer level) of the light-guiding air core glass wall in two perpendicular directions, thereby achieving high birefringence to have polarization maintaining transmission capability. This nanometer-level structural difference requires high level of fiber drawing for polarization maintaining hollow microstructure fiber, and also requires high level of stress and strain control for the optical fiber in the process of manufacturing the fiber-optic gyroscope fiber coil. The winding tension stress, transverse extrusion stress, bending stress and filling colloid solidification shrinkage stress during the manufacturing process of the fiber-optic gyroscope fiber coil will cause deformation of the micro-nanometer level cladding microstructure in the polarization maintaining hollow microstructure fiber, which will further have uncertain influence on the polarization characteristics of the polarization maintaining hollow microstructure fiber coil.

[0007] The extinction ratio instrument is usually used to measure the extinction ratio of the polarization maintaining fiber coil to evaluate the polarization characteristics of the fiber coil. This method must accurately couple the linearly polarized detection light into the polarization mode transmitted by the polarization maintaining fiber. If the detection light energy is coupled into the orthogonal polarization mode, it will seriously affect the measurement accuracy of the polarization maintaining characteristics of the polarization maintaining fiber coil. For traditional polarization maintaining fiber such as panda polarization maintaining fiber, polarization alignment can be completed with high precision by using polarization maintaining fusion splicer.

[0008] For the nanoscale structural differences on the end face of polarization maintaining hollow microstructure optical fiber, the axial identification function of polarization maintaining fusion splicer or high-power optical microscope cannot be used to locate the polarization axis of polarization maintaining hollow microstructure optical fiber. At present, there is no convenient technical means to ensure that the linearly polarized detection light is accurately coupled into the polarization mode of the polarization maintaining hollow microstructure optical fiber. Therefore, how to realize the polarization characteristic evaluation of the polarization maintaining hollow microstructure optical fiber ring is a new problem. SUMMARY

[0009] To meet the demand of polarization characteristic evaluation of polarization maintaining hollow microstructure optical fiber ring, a polarization characteristic detection method and system configuration of polarization maintaining hollow microstructure optical fiber ring without polarization axis are provided. The wavelength-continuous incident linearly polarized detection light is collimated and coupled into the tail fiber of the polarization maintaining hollow microstructure optical fiber ring without considering the polarization axis. The polarization characteristic degradation in light transmission will make the center of the circular track of the outgoing light polarization state Stokes parameter deviate from the equator of Poincare sphere by a corresponding angle. The polarization maintaining characteristic of the polarization maintaining hollow microstructure optical fiber ring can be evaluated by the deviation angle. Therefore, the polarization characteristic of the polarization maintaining microstructure optical fiber ring can be detected without polarization axis, which has the advantages of simple and convenient operation.

[0010] A polarization characteristic detection method of polarization maintaining hollow microstructure optical fiber ring, comprising the following steps:

[0011] The outgoing light polarization state Stokes parameter of the fiber ring is obtained by continuously changing the wavelength of the linearly polarized detection light.

[0012] A circular track is drawn on the Poincare sphere by the outgoing light polarization state Stokes parameter of the fiber ring.

[0013] In the circular track, the arc angle 2φ of the center point of the circular track to the circumferential point or the radius of the circular track represents the accuracy of the incident linearly polarized detection light axis, and the deviation angle 2δ of the center of the circular track from the equator of the Poincare sphere represents the polarization characteristic degradation in the fiber ring.

[0014] The polarization characteristic is calculated by the equatorial deviation angle, and the polarization characteristic is the extinction ratio PER, which is -20log(tan|δ|).

[0015] Further, the outgoing light polarization state Stokes parameter of the fiber ring is realized by a polarization state detection module.

[0016] Further, the polarization state detection module comprises a four-cornered pyramid lens, a polarizer, a quarter-wave plate and a four-quadrant detector. The four-cornered pyramid lens divides the light beam intensity of the fiber ring into four equal parts and refracts them in four directions. After the combination of the polarizer and the wave plate, the four-quadrant detector synchronously detects the four light intensity information to obtain the outgoing light polarization state Stokes parameter.

[0017] The implementation system for detecting the polarization characteristics of a polarization maintaining hollow microstructure fiber ring includes a wavelength tunable laser, a first lens, a second lens, a third lens, a polarizer, a polarization state detection module, and a host computer. The wavelength tunable laser is used to generate a corresponding required optical power in a specific wavelength range. The emitted light waves are processed by the first lens, the polarizer, and the second lens to achieve collimation, polarization, and focusing. The focused light waves are coupled into a polarization maintaining hollow microstructure fiber ring tail fiber. After the light waves are transmitted in the fiber ring for one round, the light waves are emitted from the other end of the fiber ring tail fiber. The emitted light waves are expanded and collimated into parallel light beams by the third lens, and then projected onto the polarization state detection module to convert the optical signals into electrical signals to obtain the Stokes parameters of the light polarization state. The polarization state detection module sends four voltage signals representing the Stokes parameters of the light polarization state to the host computer.

[0018] Further, the host computer processes the Stokes parameters of the light polarization state, stores and draws the trajectory of the Stokes parameters on the Poincare sphere, and sends instructions to control the wavelength tunable laser to perform wavelength scanning. After the Stokes parameters of the light polarization state form a circular trajectory, the host computer fits the circle to determine the coordinates of the center of the circle, and evaluates the polarization characteristics of the polarization maintaining hollow microstructure fiber ring by the angle of the center of the circle deviating from the equator of the Poincare sphere.

[0019] Further, the polarization state detection module includes a four-cornered pyramid lens, a polarizer, a quarter-wave plate, and a four-quadrant detector. The four-cornered pyramid lens divides the light beam intensity of the fiber ring into four equal parts and refracts them in four directions. After the combination of the polarizer and the wave plate, the four-quadrant detector synchronously detects the four light intensity information to obtain the Stokes parameters of the light polarization state.

[0020] Further, the polarization maintaining hollow microstructure fiber ring is made of a polarization maintaining hollow microstructure fiber. The polarization maintaining hollow microstructure fiber is a whole fiber in which air holes with end face periodic structure are arranged along the axial direction in a single dielectric material.

[0021] Further, the polarization maintaining hollow microstructure fiber utilizes four cladding microstructure units to construct an anti-resonance reflection effect to efficiently confine the light waves in the air core for transmission.

[0022] The above one or more technical solutions in the embodiments of the present application have at least the following technical effects:

[0023] 1. The incident linearly polarized detection light does not need to be accurately aligned with the axial direction of the polarization transmission mode of the polarization maintaining hollow microstructure fiber ring, so that the polarization characteristics of the polarization maintaining hollow microstructure fiber ring can be effectively evaluated, the problem of identifying the nanoscale structural difference of the orthogonal polarization principal axes of the polarization maintaining hollow microstructure fiber is avoided, and the method is convenient and simple to operate.

[0024] 2. The polarization state detection module is compact, and the unique four-cornered pyramid lens is easy to collimate and couple with the polarization-maintaining hollow microstructure optical fiber. The light beam intensity is equally divided and refracted in four directions by the cone surface. The four light intensity information is synchronously detected by the four-quadrant detector after the combination of the corresponding polarizer and wave plate, so as to obtain the Stokes parameters of the light polarization state. The four signals are completely synchronized without relative delay, which is beneficial to the fast and accurate measurement of the Stokes parameters of the light polarization state. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0026] Fig. 1 is a schematic diagram of a polarization characteristic detection system of a polarization-maintaining hollow microstructure optical fiber provided by the present application.

[0027] Fig. 2 is a schematic diagram of an end face of a polarization-maintaining hollow microstructure optical fiber provided by the present application.

[0028] Fig. 3 is a schematic diagram of the variation trajectory of the Stokes parameters of the light polarization state of the light emitted by the polarization-maintaining hollow microstructure optical fiber ring provided by the present application.

[0029] Fig. 4 is a schematic diagram of the composition of a polarization state detection module provided by the present application.

[0030] Fig. 5 is a schematic diagram of the test results of the variation trajectory of the Stokes parameters of the light polarization state provided by the present application.

[0031] In the drawings: 1. Wavelength tunable laser; 2. First lens; 3. Polarizer; 4. Second lens; 5. Polarization-maintaining hollow microstructure optical fiber ring; 6. Third lens; 7. Polarization state detection module; 8. Upper computer; 9. Light input port; 10. Four-cornered pyramid lens; 11. Polarizer; 12. Wave plate and polarizer set; 13. Four-quadrant detector. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions in the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, but not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application. The following embodiments are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0033] In the description of the embodiments of the present application, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0034] In the description of the embodiments of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0035] In the embodiments of the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0036] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms is not necessarily for the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the present application and the features of different embodiments or examples without contradiction.

[0037] A polarization characteristic detection method and implementation system of a polarization maintaining hollow microstructure optical fiber ring are described below in conjunction with FIGS. 1-5.

[0038] The present application is directed to the need for convenient evaluation of the polarization characteristics of a polarization maintaining hollow microstructure fiber ring, and proposes a polarization maintaining hollow microstructure fiber ring polarization characteristic detection method and system configuration based on the polarization state Stokes parameter variation trajectory. The incident linearly polarized detection light does not need to be accurately aligned with the axial direction of the polarization transmission mode of the polarization maintaining hollow microstructure fiber ring. In this embodiment, the wavelength of the linearly polarized detection light is continuously changed. The existence of the birefringence Δn of the polarization maintaining hollow microstructure fiber causes the polarization state Stokes parameter to rotate around the S1 axis on the Poincare sphere. If there is polarization coupling in the fiber ring, the Stokes parameter will rotate around the S2 axis on the Poincare sphere. The polarization state Stokes parameter of the light exiting the fiber ring will form a circular trajectory on the Poincare sphere. The accuracy of the axial alignment of the incident linearly polarized detection light determines the arc angle 2φ of the center point of the circle to the circumference point of the circular trajectory or the radius of the circular trajectory. The polarization characteristics in the fiber ring determine the offset angle 2δ of the center of the circular trajectory from the equator of the Poincare sphere. The polarization characteristics of the polarization maintaining hollow microstructure fiber ring, i.e. the polarization extinction ratio PER, can be estimated by PER≈-20log(tan|δ|). The polarization state detection module of the system configuration realizes accurate measurement of the polarization state Stokes parameter of the exiting light. The polarization state detection module is composed of a four-cornered pyramid lens, a polarizer, a quarter-wave plate, and a four-quadrant detector. The four-cornered pyramid lens can divide the beam intensity of the fiber ring exiting light into four equal parts and refract them in four directions. After passing through the corresponding polarizer and wave plate combination, the four-quadrant detector synchronously detects the four light intensity information to quickly obtain the polarization state Stokes parameter of the exiting light.

[0039] Figure 1 is a schematic diagram of a polarization maintaining hollow microstructure fiber polarization characteristic detection system. The system is composed of a wavelength tunable laser, a first lens, a second lens, a third lens, a polarizer, a polarization state detection module, and an upper computer.

[0040] The wavelength tunable laser is used to generate corresponding required optical power in a specific wavelength range. The emitted light waves are processed by collimation, polarization and focusing through the first lens 2, the polarizer and the second lens 4. The focused light waves are coupled into the polarization maintaining hollow micro-structured fiber coil and tail fiber. The light waves are transmitted in the fiber coil for one round and then exit from the other end of the fiber coil tail fiber. The exiting light waves are expanded and collimated into parallel light beams through the third lens 6, and then projected to the polarization state detection module for photoelectric signal conversion to obtain the optical polarization state Stokes parameters. The polarization state detection module sends four voltage signals representing the optical polarization state Stokes parameters to the host computer for calculation of the optical polarization state Stokes parameters. The host computer stores and draws the optical polarization state Stokes parameter change trajectory on the Poincare sphere. At the same time, the host computer sends instructions to control the wavelength tunable laser to perform wavelength scanning. After the optical polarization state Stokes parameters form a circular trajectory, the host computer fits the circle to determine the center coordinates, and the angle of the center from the equator of the Poincare sphere can be used to evaluate the polarization characteristics of the polarization maintaining hollow micro-structured fiber coil.

[0041] Figure 2 is a schematic view of the end face of the polarization maintaining hollow micro-structured fiber. The polarization maintaining hollow micro-structured fiber is an air hole that penetrates the whole fiber along the axial direction with the end face periodic structure arranged on a single dielectric material (usually pure silica material). It uses four cladding micro-structured units to construct the anti-resonant reflection effect, so that the light waves are efficiently confined in the air core for transmission. Each cladding micro-structured unit on the fiber end face is composed of two small circles and one large semicircle structure. The four cladding micro-structured units are uniformly distributed on the fiber cladding structure. The space surrounded by the four cladding micro-structured units forms a negative curvature core (at the center of the fiber end face) for air light guiding. The large semicircle structure glass wall at the negative curvature core has a nanoscale thickness difference in two orthogonal directions to excite mode anti-cross coupling effect and achieve high birefringence, thereby forming high polarization maintaining effect.

[0042] Figure 3 is a schematic diagram of the change trajectory of the Stokes parameters of the output light polarization state of the polarization-maintaining hollow microstructured fiber coil, when the incident linearly polarized light is misaligned with the polarization axis of the polarization-maintaining hollow microstructured fiber coil, part of the light energy will be coupled into the orthogonal polarization mode of the polarization-maintaining hollow microstructured fiber. In this case, the linearly polarized light will be divided into two orthogonal polarization components, which will be transmitted in the slow axis and fast axis of the polarization-maintaining hollow microstructured fiber, respectively. The phase delay Δφ between the two orthogonal polarization components is determined by 2πlΔn / λ, where l is the length of the polarization-maintaining hollow microstructured fiber coil, Δn is the birefringence of the polarization-maintaining hollow microstructured fiber, and λ is the wavelength of the transmitted light. When the two orthogonal polarization components are transmitted along the polarization-maintaining hollow microstructured fiber coil, the real-time polarization state Stokes parameters S(l) = S1(l)i + S2(l)j + S3(l)k of the combined synthesis will form a continuous circular trajectory on the Poincare sphere around an axis Ω = Ω1i + Ω2j + Ω3k as the fiber length dl increases, as shown in equations (1) and (2).

[0043] Ω represents the axial center vector, and S represents the real-time polarization state vector, where S(l) represents the real-time polarization state at the fiber length l, S1(l) represents the S1-axis real-time polarization state at the fiber length l, S2(l) represents the S2-axis real-time polarization state at the fiber length l, S3(l) represents the S3-axis real-time polarization state at the fiber length l, Ω1 represents the projection of the axial center vector Ω on the S1-axis, Ω2 represents the projection of the axial center vector Ω on the S2-axis, Ω3 represents the projection of the axial center vector Ω on the S3-axis, i is the unit vector on the S1-axis, j is the unit vector on the S2-axis, and k is the unit vector on the S3-axis.

[0044] The circular change trajectory process of the real-time polarization state S(l) in the above-mentioned polarization-maintaining hollow microstructured fiber coil can be represented by the circular change trajectory Mueller transmission matrix dM Fiber (l) / dl, as shown in equation (3), the polarization-maintaining hollow microstructured fiber coil is equivalent to a wave plate in terms of light transmission, and provides a phase delay that is proportional to the fiber length. If there are manufacturing defects in the fiber itself or external environmental disturbances that cause the polarization characteristics of the fiber to degrade, polarization coupling will occur at the defect or disturbance location. The two orthogonal polarization components are polarized coupled at this point. The subsequent fiber after the polarization coupling point can be regarded as a wave plate that rotates by an angle θ, and the size of θ is determined by the polarization coupling rate ρ, ρ = sin 2 θ.

[0045] The phase delay Δφ and the rotation angle θ between the two orthogonal polarization components transmitted in the polarization-maintaining hollow microstructured fiber coil can be represented by Mueller matrix equations (4) and (5), respectively.

[0046] The 3x3 sub-matrix which has influence on the real-time polarization states S1, S2 and S3 is extracted from the formula (4) and (5), and in order to obtain the differential form of polarization-maintaining hollow micro-structured fiber loop Mueller transmission matrix dM Fiber (l) / dl, then the phase delay Mueller transmission matrix M WP (Δφ) and the rotation Mueller transmission matrix M ROT (θ) can be simplified to formula (6) and (7) respectively.

[0047] Substitute Δφ = 2πlΔn / λ and into formula (6) and (7) respectively, formula (8) and (9) can be obtained.

[0048] The polarization coupling Mueller transmission matrix M Fiber (l) can be obtained by formula (10). Fiber (l) = M ROT (-θ)M WP (Δφ)M ROT (θ) (10)

[0049] Substitute formula (8) and (9) into formula (10), formula (11) can be obtained.

[0050] Derivate formula (11) with respect to l, formula (12) can be obtained.

[0051] By comparing formula (2) with formula (12), Ω1 = 2πΔn / λ, Ω3 = 0, then the rotation axis Ω of the polarization state Stokes parameter S(l) on the Poincare sphere can be expressed as formula (13). It can be seen from this that the birefringence Δn of the polarization-maintaining hollow micro-structured fiber causes the polarization state Stokes parameter S(l) to rotate around the i-axis (i.e. the S1 axis on the Poincare sphere), and if the polarization coupling phenomenon exists in the polarization-maintaining hollow micro-structured fiber loop, the Stokes parameter S(l) will be excited to rotate around the j-axis (i.e. the S2 axis on the Poincare sphere).

[0052] The rotation coefficients of the i-axis and the j-axis in formula (13) both contain the birefringence Δn and the wavelength λ, which means that when the birefringence of the polarization-maintaining hollow micro-structured fiber changes due to the influence of the external environment or the transmission wavelength λ changes, the polarization state Stokes parameter of the light emitted from the polarization-maintaining hollow micro-structured fiber loop will also form a circular track around an axis on the Poincare sphere.

[0053] The arc angle of the center of the circular track of the Stokes parameter of the polarization state of the emergent light from the center to the circumference The CrossTalk of the incident linearly polarized light can be estimated by equation (14) with the strong correlation to the incident linearly polarized light axis.

[0054] The polarization coupling in the PM-HCSF loop will make the center of the circular track of the Stokes parameter of the polarization state of the emergent light deviate from the equator of the Poincare sphere by an angle of 2δ. Therefore, the polarization property of the PM-HCSF loop can be estimated by equation (15). PER≈-20log(tan|δ|) (15)

[0055] Fig. 4 is a schematic diagram of the polarization state detection module, which is composed of a four-cornered pyramid lens 10, a wave plate and polarizer group 12, and a four-quadrant detector 13. The light input port of the four-cornered pyramid lens 10 is coated with an anti-reflection film to improve the light projection efficiency. The output port of the four-cornered pyramid lens is divided into four quadrants, and the four equal planes are ground to be at an angle of α with the light input port 9. Therefore, the four-cornered pyramid lens can divide the input light beam intensity into four equal parts and refract them in four directions. By adjusting the angle α, the refractive direction can be adjusted. The output of the four-cornered pyramid lens passes through the wave plate and polarizer group 12, which includes four polarizers 11. The first quadrant plane is pasted with a polarizer, and its pass axis is horizontal. The second quadrant plane is pasted with a polarizer, and its pass axis is vertical. The third quadrant plane is pasted with a polarizer, and its pass axis is at an angle of 45°. The fourth quadrant plane is pasted with a quarter wave plate and a polarizer in sequence. The birefringent axis of the quarter wave plate is horizontal, and the pass axis of the polarizer is at an angle of 45°. After the input light passes through the four-cornered pyramid lens and the corresponding quadrant polarizer and wave plate, four spatially distributed and ordered light intensity signals P1, P2, P3 and P4 are formed. By substituting the four light intensity signals into equations (16) to (19), the polarization state of the input light, i.e. the Stokes parameters, can be calculated. The four-quadrant detector is used to convert the four light intensity signals into voltage signals and send them to the modulation and demodulation circuit board for polarization state and polarization state change angle calculation. The polarization state detection module is compact in design, which is conducive to the construction of a small-sized fiber optic gyroscope based on polarization detection. S0 represents the initial light intensity, s1 represents the polarization state detected by the S1 axis, s2 represents the polarization state detected by the S2 axis, and s3 represents the polarization state detected by the S3 axis. S0=P1+P2(16) s1=(P1-P2) / S0(17) s2=(2P3-S0) / S0(18) s3=(2P4-S0) / S0(19)

[0056] Figure 5 is a test result of the change trajectory of the Stokes parameter of the polarization state of the outgoing light, the polarization axis is random, when the incident detection light is coupled into the same polarization-maintaining hollow microstructure fiber coil three times, and the polarization coupling of the incident detection light at the fiber coil port is-16dB, -24dB and-30dB respectively, the center coordinates of the circular change trajectory of the Stokes parameter of the polarization state of the outgoing light of the fiber coil do not change, the center is offset from the equator of the Poincare sphere by about 1°, and the polarization-maintaining hollow microstructure fiber coil can be estimated to be 35.2dB. As can be seen, the evaluation of the polarization characteristics of the polarization-maintaining hollow microstructure fiber coil using the method of the present application does not need to strictly control the polarization axis of the incident light, and provides a simple and convenient detection technique for the study of the influence of temperature changes, fiber coil colloid parameters, etc. on the polarization characteristics of the polarization-maintaining hollow microstructure fiber coil.

[0057] In summary, the present application proposes a polarization characteristic detection method and system configuration for polarization-maintaining hollow microstructure fiber coils without polarization axis, which evaluates the polarization characteristics of the fiber coil from the angle of the offset of the center of the circular trajectory of the Stokes parameter of the polarization state of the outgoing light of the fiber coil from the equator of the Poincare sphere, and no longer needs precise polarization axis operation of the incident light, which avoids the problem of difficult identification of the polarization axis of the polarization-maintaining hollow microstructure fiber, and has the advantages of simple and convenient operation.

[0058] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for detecting the polarization properties of a polarization maintaining hollow core microstructured fiber ring, characterized in that, The application comprises the following steps: The polarization state of the output light of the fiber coil is obtained by continuously changing the wavelength of the linearly polarized detection light; The polarization state of the output light of the fiber coil is obtained by continuously changing the wavelength of the linearly polarized detection light; in the circular trajectory, an arc angle of the circular trajectory from a center point of the circle to a point on the circumference The radius of the circular trajectory represents the axial accuracy of the incident linearly polarized detection light, and the center of the circular trajectory is offset from the equator of the Poincare sphere by an angle 2δ, which represents the polarization characteristic degradation in the fiber coil; and The polarization characteristic is calculated by the equatorial offset angle, and the polarization characteristic is the polarization extinction ratio PER, which is -20log(tan|δ|).

2. The method of claim 1, wherein the method is characterized by: The polarization state of the output light of the fiber coil is obtained by a polarization state detection module.

3. The method of claim 2, wherein the method further comprises: The polarization state detection module comprises a four-cornered pyramid lens, a polarizer, a quarter-wave plate and a four-quadrant detector, the four-cornered pyramid lens divides the intensity of the output light beam of the fiber coil into four equal parts and refracts them in four directions, the polarizer and the quarter-wave plate are combined, and then the four-quadrant detector synchronously detects the four light intensity information to obtain the polarization state of the output light.

4. A system for implementing a polarization property measurement of a polarization maintaining hollow core microstructured fiber loop, the system comprising: a polarization maintaining hollow core microstructured fiber loop; a light source; a polarization controller; a polarization analyzer; and a polarization rotator. The application comprises a wavelength tunable laser, a first lens, a second lens, a third lens, a polarizer, a polarization state detection module and a host computer, the wavelength tunable laser is used to generate a corresponding required optical power in a specific wavelength range, the emitted light wave sequence passes through the first lens, the polarizer and the second lens, and the light wave is collimated, polarized and focused, the focused light wave is coupled into a polarization maintaining hollow microstructure fiber coil and a fiber tail, the light wave is transmitted in the fiber coil for one round and is output from the other end of the fiber tail, the output light wave is expanded and collimated into a parallel light beam by the third lens, and then is projected onto the polarization state detection module to perform photoelectric signal conversion to obtain the light polarization state Stokes parameter, and the polarization state detection module sends four voltage signals representing the light polarization state Stokes parameter to the host computer.

5. The system for detecting the polarization properties of a polarization maintaining holey microstructure fiber coil according to claim 4, wherein, The host computer processes to calculate the light polarization state Stokes parameter, stores and draws the light polarization state Stokes parameter change trajectory on the Poincare sphere, and sends instructions to control the wavelength tunable laser to perform wavelength scanning, after the light polarization state Stokes parameter forms a circular trajectory, the host computer fits the circle to determine the center coordinates, and evaluates the polarization characteristic of the polarization maintaining hollow microstructure fiber coil through the angle of the center offset from the equator of the Poincare sphere.

6. The system for measuring the polarization properties of a polarization maintaining holey microstructure fiber coil according to claim 4, wherein The polarization state detection module comprises a four-cornered pyramid lens, a polarizer, a quarter-wave plate and a four-quadrant detector, the four-cornered pyramid lens divides the intensity of the output light beam of the fiber coil into four equal parts and refracts them in four directions, the polarizer and the quarter-wave plate are combined, and then the four-quadrant detector synchronously detects the four light intensity information to obtain the polarization state of the output light.

7. The system for detecting the polarization properties of a polarization maintaining holey microstructure fiber coil according to any one of claims 4-6, wherein, The polarization maintaining hollow microstructure fiber coil is wound by a polarization maintaining hollow microstructure fiber, the polarization maintaining hollow microstructure fiber is a whole fiber in which air holes with end face periodic structure penetrating along the axial direction are arranged on a single dielectric material.

8. The system for detecting the polarization properties of a polarization maintaining holey microstructure fiber coil according to claim 7, wherein, The polarization maintaining hollow microstructure fiber is constructed by four cladding microstructure units to construct the anti-resonance reflection effect so that the light wave is efficiently confined in the air core for transmission.

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