Optical fiber polarization measurement system and method

Abstract

The invention relates to the technical field of optical signal transmission, in particular to an optical fiber polarization measurement system and method. The optical fiber polarization measurement system comprises a light source which is located at the light incident side of a to-be-measured optical fiber and is used for inputting detection laser to the to-be-measured optical fiber; the optical fiber temperature control assembly is circumferentially arranged along the periphery of the to-be-measured optical fiber and is used for adjusting the temperature of the to-be-measured optical fiber; the light-emitting optical fiber is the same as the optical fiber to be detected in model and is welded with the output end of the optical fiber to be detected through polarization-maintaining welding; the heat preservation rotating assembly is arranged close to the output end of the light-emitting optical fiber and used for providing a constant-temperature environment for the light-emitting optical fiber and driving the light-emitting optical fiber to rotate concentrically. The polarization analyzing assembly is located at the output end of the light-emitting optical fiber and used for screening the output laser output by the light-emitting optical fiber based on the polarization direction; the photoelectric detection assembly is located on the side, away from the light outlet optical fiber, of the polarization detection assembly and used for detecting the optical power of the polarized laser screened by the polarization detection assembly. The measuring efficiency can be effectively improved, the cost is reduced, and the structure is simplified.

Description

Technical Field

[0001] This invention relates to the field of optical signal transmission technology, and in particular to an optical fiber polarization measurement system and method. Background Technology

[0002] In fields such as optical fiber communication and optical fiber sensing, the polarization extinction ratio is a core indicator for evaluating the transmission performance of polarization-maintaining fibers and related devices. Its measurement accuracy directly affects device selection, system optimization, and overall performance stability. Among the current mainstream optical fiber polarization measurement schemes, the Poincaré sphere scheme, based on the principle of complete polarization state characterization, has the advantage of high detection accuracy and is widely mentioned in high-precision testing scenarios.

[0003] However, the Bonga sphere solution has significant drawbacks: on the one hand, it has stringent requirements for the monochromaticity and stability of the incident light source, requiring a high-precision single-wavelength laser light source; on the other hand, it relies on complex optical interference structures and precise phase control components, resulting in high equipment integration difficulty, large overall size, and high processing and debugging costs for core components, making it difficult to meet the low-cost and high-efficiency requirements for batch device testing in industrial production. Summary of the Invention

[0004] This invention provides an optical fiber polarization measurement system to solve the problems of high cost, complex structure, and low measurement efficiency.

[0005] This invention discloses an optical fiber polarization measurement system for measuring the polarization extinction ratio of an optical fiber under test; The fiber polarization measurement system includes: A light source, located on the light-incident side of the optical fiber under test, is used to input probe laser light into the optical fiber under test; An optical fiber temperature control component is arranged circumferentially around the outer periphery of the optical fiber under test, and is used to adjust the temperature of the optical fiber under test. The output optical fiber is of the same type as the optical fiber under test, and is fused to the output end of the optical fiber under test by polarization-maintaining fusion splicing; A heat-insulating rotating assembly is positioned close to the output end of the optical fiber to provide a constant temperature environment for the optical fiber and to drive the optical fiber to rotate concentrically. A polarization analyzer, located at the output end of the optical fiber, is used to filter the output laser light from the optical fiber based on its polarization direction. A photoelectric detection component is located on the side of the polarization analyzer away from the output optical fiber, and is used to detect the optical power of the polarized laser that has been filtered by the polarization analyzer.

[0006] Optionally, the heating / cooling rate of the fiber optic temperature control component is >3℃ / s; the fiber optic temperature control component can cover a region of 15~20cm in length of the fiber optic cable under test.

[0007] Optionally, the fiber optic temperature control assembly includes multiple semiconductor cooling chips connected in series in multiple stages.

[0008] Optionally, the length of the output optical fiber is >50m; the coaxial error of the output optical fiber and the optical fiber under test after fusion splicing is <0.05mm; and the difference between the polarization extinction ratio of the reverse incident light test and the fiber's limiting polarization extinction ratio is <1dB.

[0009] Optionally, the fiber polarization measurement system further includes: A collimating lens, located between the output end of the optical fiber and the polarization analyzer, is used to collimate the output laser.

[0010] Optionally, the focal length of the collimating lens is >5mm, and the output end of the light-emitting optical fiber is located at the front focal plane of the collimating lens.

[0011] Optionally, the polarization analyzer is located at the beam waist of the collimated laser after collimation by the collimating lens, and the optical plane of the polarization analyzer is perpendicular to the optical axis of the collimated beam.

[0012] Optionally, the extinction ratio of the polarization analyzer is >40dB, and the photodetector is located within the Rayleigh range of the polarized laser.

[0013] Optionally, the light source is a narrowband amplified spontaneous emission light source.

[0014] This invention also discloses a fiber polarization measurement method, applied to the fiber polarization measurement system described above, the fiber polarization measurement method comprising: The driving light source directs the probe laser into the input end of the optical fiber under test; The fiber optic temperature control component is activated to perform heating / cooling cycle modulation on the fiber under test, and the heat preservation rotation component is activated at the same time to ensure that the light-emitting end of the light-emitting fiber is in a constant temperature state. The heat-insulating rotating component is driven to rotate the output end of the light-emitting optical fiber, and the photoelectric detection component collects optical power data corresponding to light with different polarization directions. The polarization extinction ratio of the optical fiber under test is obtained based on the optical power data.

[0015] The beneficial effects of the fiber polarization measurement system and method provided in this invention are as follows: Based on the temperature-sensitive characteristics of the stress region of the polarization-maintaining fiber, the difference in polarization energy coupling between the fast and slow axes of the fiber under test is broken and amplified by rapidly and periodically modulating the fiber's birefringence through temperature control. Subsequently, by precisely rotating the output fiber in conjunction with a fixed analyzer, the maximum and minimum values ​​of the output optical power are directly and objectively scanned and locked, thereby calculating the polarization extinction ratio. The entire system does not require a complex programmable polarization controller and real-time algorithm fitting; it only relies on basic optoelectronic and mechanical components to achieve complete measurement. This not only significantly simplifies the system structure and greatly reduces hardware and operating costs, but also provides stronger anti-interference capabilities and a stable and reliable operating procedure. It is particularly suitable for batch testing scenarios on efficiency- and cost-sensitive production lines, ultimately achieving accurate and efficient measurement of the polarization extinction ratio. Attached Figure Description

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic diagram of an embodiment of the fiber polarization measurement system provided by the present invention; Figure 2 This is a schematic diagram of an embodiment of the fiber optic temperature control component provided by the present invention; Figure 3 This is a flowchart illustrating an embodiment of the fiber polarization measurement method provided by the present invention.

[0017] The labels for the attached figures are as follows: 10. Fiber optic polarization measurement system; 11. Light source; 12. Fiber optic temperature control assembly; 13. Optical fiber output; 14. Insulation and rotation assembly; 15. Polarization analyzer assembly; 16. Photoelectric detection assembly; 17. Collimation assembly; 20. Fiber optic cable to be tested. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] Please see Figure 1 , Figure 1 This is a schematic diagram of an embodiment of the fiber polarization measurement system provided by the present invention. The fiber polarization measurement system 10 provided by the present invention includes: a light source 11, a fiber temperature control component 12, a light-emitting fiber 13, a heat-insulating rotation component 14, a polarization analyzer component 15, and a photoelectric detection component 16. The fiber polarization measurement system 10 is used to measure the polarization extinction ratio of the fiber under test 20.

[0020] A light source 11 is located on the incident light side of the optical fiber under test 20, used to input a probe laser into the optical fiber under test 20; an optical fiber temperature control component 12 is arranged circumferentially around the optical fiber under test 20, used to adjust the temperature of the optical fiber under test 20; an output optical fiber 13 is of the same type as the optical fiber under test 20, and is fused to the output end of the optical fiber under test 20 by polarization-maintaining fusion splicing; a heat-preserving rotation component 14 is arranged close to the output end of the output optical fiber 13, used to provide a constant temperature environment for the output optical fiber 13 and drive the output optical fiber 13 to rotate concentrically; a polarization analyzer 15 is located at the output end of the output optical fiber 13, used to filter the output laser output from the output optical fiber 13 based on the polarization direction; a photoelectric detection component 16 is located on the side of the polarization analyzer 15 away from the output optical fiber 13, used to detect the optical power of the polarized laser filtered by the polarization analyzer 15.

[0021] Specifically, the light source 11 is a narrowband ASE (amplified spontaneous emission) light source 11, fixedly mounted on the light-incident side of the fiber under test 20. The light-out port of the light source 11 is precisely coaxially aligned with the input end face of the fiber under test 20, and the two achieve signal transmission through a non-contact optical coupling method. This light source 11 is used to stably input probe laser into the fiber under test 20. It has non-single-wavelength, narrowband spectral characteristics, which can effectively avoid the wavelength-dependent error of single-wavelength light sources 11 and adapt to the testing requirements of different models and specifications of fiber under test 20.

[0022] The fiber optic temperature control assembly 12 includes a high-response-speed TEC (thermal energy storage device) and an integrated temperature sensor and temperature control drive module, which are tightly fitted around the periphery of the fiber optic cable 20 under test. The fiber optic temperature control assembly 12 covers a length of 15-20 cm of the fiber optic cable 20 under test, with the wrapped section located between the input and output ends of the fiber optic cable 20 under test, avoiding the input coupling area and the output fusion splice area to prevent interference with laser transmission.

[0023] The fiber optic temperature control component 12 is used to precisely adjust the temperature of the fiber optic cable 20 under test. It outputs a control signal through the temperature control drive module to drive the TEC to achieve rapid heating and cooling cycles, and the temperature change rate can be stably maintained at >3℃ / s. At the same time, the temperature sensor collects the temperature data of the fiber optic cable 20 under test in real time and feeds it back to the temperature control module to form a closed-loop temperature control, which actively changes the stress distribution inside the fiber optic cable 20 under test through temperature changes.

[0024] In one embodiment, the fiber optic temperature control assembly 12 includes multiple semiconductor cooling chips connected in series in multiple stages. Please refer to [reference needed]. Figure 2 , Figure 2This is a schematic diagram of an embodiment of the fiber optic temperature control component 12 provided by the present invention. Multiple independent TEC semiconductor cooling chips are used as heating units, arranged in segments and coaxially in series along the length direction (i.e., the optical transmission direction) of the fiber optic cable 20 under test. Each TEC is controlled collaboratively through the same temperature control drive module, while each TEC can independently adjust its own heating / cooling power. This series design is not a simple circuit series connection, but a dual collaboration of spatial arrangement and control logic. On the one hand, the segmented stacking of multiple TECs ensures uniform temperature distribution within the 15-20cm heating section, avoiding local overheating or excessive temperature gradients caused by concentrated power in a single TEC. On the other hand, the number of TECs in operation in the cascade can be flexibly increased or decreased according to actual testing needs, expanding or shrinking the effective heating length. Therefore, the fiber optic temperature control component 12 can flexibly adjust the heating power and temperature control range according to parameters such as the diameter and material of the fiber optic cable 20 under test, improving system adaptability.

[0025] The core design of polarization-maintaining fiber is to artificially create a birefringence effect through internal stress regions. These stress regions cause refractive index differences in the fiber core in different directions: the refractive index is higher along the stress-dominant direction, resulting in slower light propagation in this direction, known as the slow axis; the refractive index is lower in the direction perpendicular to the stress-dominant direction, resulting in faster light propagation, known as the fast axis. Ideally, incident polarized light propagates independently along the fast and slow axes, with no energy coupling. However, in practical applications, the fiber under test (20) may experience partial coupling of polarization energy between the fast and slow axes due to manufacturing defects, installation stress, bending deformation, etc. (i.e., some slow axis energy is transferred to the fast axis, or vice versa), forming a mixed polarization state. This makes it impossible to directly distinguish the energy difference between the two directions through subsequent detection.

[0026] The stress region of polarization-maintaining optical fiber is highly sensitive to temperature. During rapid heating, the temperature of the fiber under test (20) increases, and the material in the stress region (such as borosilicate glass) expands due to heat. This reduces the compressive stress on the fiber core, directly causing a controllable change in the refractive index difference (birefringence) of the core along the fast and slow axes. During rapid cooling, the temperature of the fiber under test (20) decreases, and the material in the stress region contracts, increasing the compressive stress on the core. This, in turn, reverses the adjustment of the refractive index difference along the fast and slow axes.

[0027] The core of PER (Performance Ratio) is the ratio of maximum optical power (Pmax) to minimum optical power (Pmin) (PER = 10lg(Pmax / Pmin)), where Pmax corresponds to the slow axis (dominant polarization direction) and Pmin corresponds to the fast axis (orthogonal polarization direction). Without temperature modulation, the fast and slow axis polarization energies of the fiber under test (20) are in a coupled, mixed state. The energies of the two axes are superimposed and the difference is slight, making it impossible for the photodetector to distinguish which power comes from the slow axis and which from the fast axis. Therefore, the true Pmax and Pmin cannot be captured, and PER measurement is impossible. However, after temperature modulation amplifies the energy difference, the mixed state transforms into a clear state where the slow axis energy is significantly higher than the fast axis energy. This allows the polarization energies of the two axes to change from being superimposed and masked to being independently discernible, providing a detectable signal basis for subsequent identification of Pmax and Pmin.

[0028] In this embodiment, temperature modulation dynamically changes the refractive index difference, which can quickly break energy coupling and amplify energy differences within a single heating-cooling cycle, obtaining a clear polarization signal without multiple iterations. Combined with subsequent rotating scanning of the output fiber 13, Pmax and Pmin can be quickly captured, ultimately achieving efficient PER measurement. This design not only improves the testing efficiency of a single fiber but also meets the needs of industrial batch testing scenarios, avoiding multiple cycle adjustments due to insufficient energy differences and reducing testing time costs.

[0029] The output fiber 13 is a polarization-maintaining fiber identical in model to the fiber under test 20. Its input end is fixedly fused to the output end of the fiber under test 20 using a high-precision polarization-maintaining fusion splicing process. The fusion splicing process strictly controls coaxiality and splice loss, ensuring that the difference between the PER value of the output fiber 13 after fusion splicing and the limiting PER value of the output fiber 13 itself is <1dB. This effectively avoids introducing additional polarization crosstalk at the splice interface, ensuring that the polarized light signal output from the fiber under test 20 can be transmitted completely and without distortion to the output fiber 13. The total length of the output fiber 13 is designed to be >50m. Utilizing the polarization-maintaining characteristics of the polarization-maintaining fiber, long-distance separation of orthogonal polarization energy is achieved, allowing the fast-axis and slow-axis polarized light, which are manifested after temperature modulation, to be completely separated during transmission, avoiding secondary coupling of polarization states.

[0030] The thermal insulation and rotation assembly 14 is an integrated structure, mainly composed of a constant temperature environment chamber, a concentric rotation drive mechanism, and an optical fiber fixing clamp. It is positioned close to the output end of the optical fiber 13, which is completely housed inside the chamber. The output end of the optical fiber 13 extends outside the chamber and connects to the concentric rotation drive mechanism. Its core functions are twofold: first, to provide a stable constant temperature environment for the optical fiber 13. The chamber incorporates high-precision heating, cooling, and insulation modules, which can stably control the internal temperature at a set value, effectively eliminating interference from external temperature changes on the polarization retention characteristics of the optical fiber 13 and ensuring the stability of the orthogonal polarization energy state after separation; second, to drive the optical fiber 13 to perform high-precision concentric rotation. The concentric rotation drive mechanism, driven by a stepper motor and equipped with an angle positioning module, can control the optical fiber 13 to rotate slowly and smoothly around its own axis. This rotation synchronously changes the direction of the polarized light output by the optical fiber 13, providing conditions for subsequent multi-directional polarization screening and power acquisition.

[0031] The polarization analyzer 15 can be a high extinction ratio analyzer (extinction ratio > 40dB). The polarization analyzer 15 is used to selectively filter the laser output from the output fiber 13 based on the polarization direction. The divergent polarized light output from the output fiber 13 is first converted into parallel light by a collimating lens group to avoid uneven energy distribution in the polarization direction caused by beam divergence. Then, the parallel polarized light is incident on the analyzer, which only allows polarized light consistent with its own transmission direction to pass through, and strongly suppresses light with orthogonal polarization directions. This allows the separated fast-axis and slow-axis polarized light to be filtered out one by one and converted into monochromatic polarized light signals that can be detected individually.

[0032] In other implementation scenarios, the fiber optic polarization measurement system 10 further includes a collimating lens located between the output end of the output fiber 13 and the polarization analyzer 15, used to collimate the output laser. The collimating lens is installed behind the output end of the output fiber 13, wherein the front focal plane of the collimating lens group is precisely aligned with the output end of the output fiber 13, and the polarization analyzer is precisely located at the beam waist position (the region where the beam is thinnest and the polarization state is most stable) of the collimated laser emitted from the collimating lens group, and the optical plane of the polarization analyzer is perpendicular to the optical axis of the collimated beam.

[0033] The photoelectric detection component 16 consists of a high-sensitivity photoelectric probe, a signal amplification module, and a data acquisition module. It is fixedly installed on the side of the polarization analyzer 15 away from the output optical fiber 13. The photosensitive surface of the photoelectric probe is precisely aligned with the polarization laser transmission path filtered by the polarization analyzer 15, and the photosensitive surface is located within the Rayleigh range of the beam (the region where the light intensity is stable before and after the beam waist). Its core function is to detect the optical power of the polarization laser filtered by the polarization analyzer 15. The photoelectric probe can quickly convert the received optical signal into an electrical signal, which is amplified and filtered by the signal amplification module before being transmitted to the data acquisition module. The data acquisition module records and stores the optical power data corresponding to different polarization directions in real time, focusing on capturing and retaining the maximum optical power (Pmax) in the dominant polarization direction and the minimum optical power (Pmin) in the orthogonal polarization direction. At the same time, it can synchronously transmit the data to the subsequent data processing unit to provide core raw data for the calculation of the polarization extinction ratio.

[0034] In the fiber optic polarization measurement system 10, the polarization analyzer 15 is fixed, with a unique transmission direction, and can only filter polarized light in a specific direction. The output fiber 13 transmits completely separated fast-axis and slow-axis orthogonally polarized light. These two polarization directions are fixed. If the fiber does not rotate, only the optical power in one direction (aligned with the analyzer's transmission direction) can be detected, and the power in the other orthogonal direction cannot be obtained. By concentrically rotating the output fiber 13, the polarization direction of its output light can be synchronously rotated around the optical axis, allowing the directions of the fast-axis and slow-axis polarized light to sequentially align with the analyzer's transmission direction. During this process, the photodetector continuously collects optical power data at different rotation angles, thus completely covering all polarization directions and ensuring no critical extreme values ​​are missed.

[0035] The photoelectric detection component 16 consists of a high-sensitivity photoelectric probe, a signal amplification module, and a data acquisition module. It is fixedly installed on the side of the polarization analyzer 15 away from the output optical fiber 13. The photosensitive surface of the photoelectric probe is precisely aligned with the transmission path of the polarized laser after being filtered by the polarization analyzer 15, and the photosensitive surface is located within the Rayleigh range of the polarized beam emitted by the polarization analyzer (the region where the light intensity is stable before and after the beam waist). The photoelectric detection component 16 is used to detect the optical power of the polarized laser after being filtered by the polarization analyzer 15. The photoelectric probe can quickly convert the received optical signal into an electrical signal, which is amplified and filtered by the signal amplification module before being transmitted to the data acquisition module. The data acquisition module records and stores the optical power data corresponding to different polarization directions in real time, focusing on capturing and retaining the maximum optical power (Pmax) in the dominant polarization direction and the minimum optical power (Pmin) in the orthogonal polarization direction, and calculates the polarization extinction ratio of the optical fiber 20 under test using the formula PER=10lg(Pmax / Pmin).

[0036] During a measurement, the fiber optic temperature control component 12 is activated, and the temperature control drive module outputs a control signal to drive the TEC semiconductor cooler into a rapid heating-cooling cycle mode. During heating, the material in the stress zone expands, reducing the compressive stress on the core layer; during cooling, the material in the stress zone contracts, increasing the compressive stress. Through this dynamic stress adjustment, the polarization energy coupling balance (mixed polarization state) between the fast and slow axes within the fiber under test 20 can be fully disrupted within a single complete heating-cooling cycle, allowing the originally coupled orthogonal polarization energy to be fully manifested. No multiple iterations are required; only one complete cycle is needed to fully manifest the polarization energy, providing a distinguishable polarized light signal for subsequent measurements.

[0037] Temperature changes cause the stress zone to expand or contract, altering the refractive index difference (Δn) between the fast and slow axes. This change in refractive index difference (Δn) directly leads to a continuous and periodic change in the phase difference (Δφ) between the two beams of light after propagation (because Δφ∝Δn×L). Therefore, the phase difference changes from a fixed value to a cyclically varying Δφ(t) that changes with time and temperature.

[0038] The light emitted from the end of the fiber under test 20 is the vector combination of two coherent beams: a fast-axis beam (strong) and a slow-axis beam (weak). According to optical principles, the polarization state (linear, elliptically, or circularly polarized) of the combined beam of two orthogonally polarized beams depends entirely on their phase difference (Δφ) and amplitude ratio. When Δφ = 0° or 180°, the combined light is linearly polarized, but its vibration direction changes. When Δφ is other values, the combined light is elliptically polarized. Temperature modulation causes Δφ(t) to change continuously, thus the polarization state of the combined light also evolves continuously and periodically.

[0039] The polarization analyzer 15 only allows electric field components parallel to its transmission direction to pass through. For any incident polarization ellipse, the light intensity (I) that can pass through the analyzer is equal to the square of the projected length of the ellipse in its transmission direction. Therefore, the continuous evolution of the polarization state (driven by temperature modulation) is converted into the continuous fluctuations I(t) of the polarized light power passing through the analyzer.

[0040] Slowly rotating the optical fiber 13 one revolution is equivalent to scanning the entire polarization ellipse in space at each instant of temperature (i.e., at each specific Δφ value). Through this rotation, the system can align the major axis (strongest direction) of the polarization ellipse with the analyzer at a certain rotation angle, measure the maximum possible light intensity at that Δφ, and measure the minimum possible light intensity in the vertical direction.

[0041] After the entire temperature cycle and complete rotation scan, the maximum value among all the maximum light intensities recorded by the system corresponds to the worst-case Pmax; the minimum value among all the minimum light intensities corresponds to the worst-case Pmin. The PER calculated using these values ​​is the most rigorous and realistic evaluation of the device performance. The photodetector 16 continuously operates, converting the filtered polarized light signal into an electrical signal, which is then amplified, filtered, and transmitted to the data acquisition module. The data acquisition module records the rotation angle-optical power data in real time. When the output fiber 13 rotates to the point where the slow axis (dominant polarization direction) is completely aligned with the transmission direction of the analyzer, the maximum optical power (Pmax) is captured; when it rotates to the point where the fast axis (orthogonal polarization direction) is orthogonal to the transmission direction of the analyzer, the minimum optical power (Pmin) is captured, and these two core extreme values ​​are stored. The polarization extinction ratio of the fiber under test 20 is calculated based on the formula PER=10lg(Pmax / Pmin).

[0042] Please refer to the following: Figure 3 , Figure 3 This is a schematic flowchart of an embodiment of the fiber polarization measurement method provided by the present invention. The fiber polarization measurement method includes the following steps: S101: The driving light source directs the probe laser into the input end of the optical fiber under test.

[0043] S102: Activate the fiber optic temperature control component to perform heating / cooling cycle modulation on the fiber under test, and simultaneously activate the heat preservation rotation component to ensure that the light-emitting end of the light-emitting fiber is in a constant temperature state.

[0044] S103: Drive the heat preservation rotating component to rotate the output end of the light-emitting optical fiber, and collect the optical power data corresponding to light with different polarization directions through the photoelectric detection component.

[0045] S104: Obtain the polarization extinction ratio of the optical fiber under test based on the optical power data.

[0046] In a specific implementation scenario, the fiber polarization measurement system is set up, a narrowband ASE light source (not single-wavelength) is started, and the output power of the light source is adjusted to a stable state to ensure that the emitted light spectrum has narrowband characteristics and is suitable for the transmission requirements of the fiber / device under test. The probe light emitted by the narrowband ASE light source is accurately incident on the input end of the fiber / device under test, ensuring that the incident light is perpendicular to the fiber end face to reduce incident loss.

[0047] The fiber heating assembly is activated to rapidly heat / cool the fiber under test in a cyclic modulation process. A temperature control system monitors temperature changes in real time during modulation to ensure the temperature change rate remains stable at >3℃ / s. By actively altering the internal stress distribution of the fiber under test through temperature changes, and utilizing the temperature sensitivity of the polarization-maintaining fiber's stress region, the polarization energy balance between the fast and slow axes is disrupted, laying the foundation for subsequent polarization direction differentiation.

[0048] The temperature-modulated polarized light is transmitted from the output end of the fiber under test to the polarization-maintaining fusion spliced ​​output fiber. During the long-distance transmission of the polarized light in the output fiber (length > 50m), the polarization-maintaining characteristics of the polarization-maintaining fiber ensure that the orthogonal polarization energies of the fast axis and slow axis are completely separated. At the same time, the temperature is continuously maintained by the temperature-maintaining rotating component to avoid polarization coupling caused by ambient temperature fluctuations, thus ensuring the stability of the separated polarization energy state.

[0049] Polarized light exits from the optical fiber and is incident on the collimating lens. A long focal length lens (focal length > 5mm) is used to convert the diverging polarized light into parallel light, reducing the problem of uneven energy distribution in the polarization direction caused by the beam divergence angle.

[0050] The collimated beam is transmitted to the polarizer located at the beam waist. The polarizer only allows polarized light in a specific direction to pass through, thus achieving selective filtering of orthogonally polarized light.

[0051] Activate the photodetector to detect optical power. Positioning the detector within the Rayleigh ray of the collimated beam effectively avoids detection errors caused by uneven light intensity distribution. Initiate the concentric rotation function of the thermal insulation rotation component, controlling the output end of the optical fiber to rotate slowly. During rotation, the photodetector continuously collects optical power data corresponding to different polarization directions, focusing on recording the maximum optical power (Pmax) in the dominant polarization direction (e.g., the slow axis) and the minimum optical power (Pmin) in orthogonal polarization directions (e.g., the fast axis), ensuring the completeness and accuracy of the collected data. Based on the definition of polarization extinction ratio (PER), substitute the collected Pmax and Pmin data, and calculate the polarization extinction ratio using the formula PER = 10lg(Pmax / Pmin).

[0052] Unlike existing technologies, this invention leverages the temperature-sensitive characteristics of the stress region in polarization-maintaining optical fibers. It rapidly and periodically modulates the fiber's birefringence through temperature control, breaking and amplifying the polarization energy coupling difference between the fast and slow axes of the fiber under test. Subsequently, by precisely rotating the output fiber in conjunction with a fixed analyzer, the maximum and minimum values ​​of the output optical power are directly and objectively scanned and locked, thereby calculating the polarization extinction ratio. The entire system eliminates the need for complex programmable polarization controllers and real-time algorithm fitting, relying solely on basic optoelectronic and mechanical components to achieve complete measurement. This significantly simplifies the system structure, greatly reduces hardware and operating costs, and provides stronger anti-interference capabilities and a stable and reliable operating procedure. It is particularly suitable for batch testing scenarios on efficiency- and cost-sensitive production lines, ultimately achieving accurate and efficient measurement of a single key performance indicator (polarization extinction ratio).

[0053] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features; and all such modifications and substitutions should fall within the protection scope of the appended claims of the present invention.

Claims

1. A fiber optic polarization measurement system, characterized in that, Used to measure the polarization extinction ratio of the optical fiber under test; The fiber polarization measurement system includes: A light source, located on the light-incident side of the optical fiber under test, is used to input probe laser light into the optical fiber under test; An optical fiber temperature control component is arranged circumferentially around the outer periphery of the optical fiber under test, and is used to adjust the temperature of the optical fiber under test. The output optical fiber is of the same type as the optical fiber under test, and is fused to the output end of the optical fiber under test by polarization-maintaining fusion splicing; A heat-insulating rotating assembly is positioned close to the output end of the optical fiber to provide a constant temperature environment for the optical fiber and to drive the optical fiber to rotate concentrically. A polarization analyzer, located at the output end of the optical fiber, is used to filter the output laser light from the optical fiber based on its polarization direction. A photoelectric detection component is located on the side of the polarization analyzer away from the output optical fiber, and is used to detect the optical power of the polarized laser that has been filtered by the polarization analyzer.

2. The fiber polarization measurement system according to claim 1, characterized in that, The heating / cooling rate of the optical fiber temperature control component is >3℃ / s; the optical fiber temperature control component can cover a region of 15~20cm in length of the optical fiber under test.

3. The fiber polarization measurement system according to claim 2, characterized in that, The fiber optic temperature control component includes multiple semiconductor cooling chips connected in series at multiple levels.

4. The fiber polarization measurement system according to claim 1, characterized in that, The length of the output optical fiber is >50m; the coaxial error of the output optical fiber and the optical fiber under test after fusion splicing is <0.05mm; and the difference between the polarization extinction ratio of the reverse incident light test and the fiber's limiting polarization extinction ratio is <1dB.

5. The fiber polarization measurement system according to claim 1, characterized in that, The fiber polarization measurement system also includes: A collimating lens, located between the output end of the optical fiber and the polarization analyzer, is used to collimate the output laser.

6. The fiber polarization measurement system according to claim 5, characterized in that, The focal length of the collimating lens is >5mm, and the output end of the light-emitting optical fiber is located at the front focal plane of the collimating lens.

7. The fiber polarization measurement system according to claim 5, characterized in that, The polarization analyzer is located at the beam waist of the collimated laser after collimation by the collimating lens, and the optical plane of the polarization analyzer is perpendicular to the optical axis of the collimated beam.

8. The fiber polarization measurement system according to claim 7, characterized in that, The extinction ratio of the polarization analyzer is >40dB, and the photodetector is located within the Rayleigh range of the polarized laser.

9. The fiber polarization measurement system according to claim 1, characterized in that, The light source is a narrowband amplified spontaneous emission light source.

10. A method for measuring fiber polarization, characterized in that, The fiber polarization measurement method, applied to the fiber polarization measurement system according to any one of claims 1-9, comprises: The driving light source directs the probe laser into the input end of the optical fiber under test; The fiber optic temperature control component is activated to perform heating / cooling cycle modulation on the fiber under test, and the heat preservation rotation component is activated at the same time to ensure that the light-emitting end of the light-emitting fiber is in a constant temperature state. The heat-insulating rotating component is driven to rotate the output end of the light-emitting optical fiber, and the photoelectric detection component collects optical power data corresponding to light with different polarization directions. The polarization extinction ratio of the optical fiber under test is obtained based on the optical power data.

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