Apparatus and method for measuring the ratio of circular to linear birefringence of an elliptical optical fiber

Abstract

The application relates to the technical field of optical fiber performance testing, and particularly discloses a device and a method for measuring the ratio of circular birefringence to linear birefringence of a polarization-maintaining optical fiber, which comprises a 1310 nm waveband light source array assembly, an optical path assembly and a monitoring assembly, the optical path assembly is connected with the 1310 nm waveband light source array assembly through optical fibers, the monitoring assembly is connected with the optical path assembly through optical fibers, the 1310 nm waveband light source array assembly comprises an N*1 optical switch, N 1310 nm waveband lasers with different wavelengths, a current controller and a temperature controller, the N 1310 nm waveband lasers with different wavelengths are connected with the N*1 optical switch through optical fibers respectively, and the current controller and the temperature controller are electrically connected with the N 1310 nm waveband lasers with different wavelengths respectively. The phase difference and the fixed point of the polarization-maintaining optical fiber under different wavelengths are measured, the circular birefringence to linear birefringence ratio and beat length of the polarization-maintaining optical fiber under the 1310 nm waveband are measured, and the performance of the polarization-maintaining optical fiber to be measured is evaluated.

Description

Technical Field

[0001] This invention relates to the field of optical fiber performance testing technology, and in particular to a device and method for measuring the ratio of circular to linear birefringence of elliptical optical fibers. Background Technology

[0002] Currently, with the rapid development of optical technology, current transformers have evolved from traditional electromagnetic structures to fiber optic transformers. Fiber optic current transformers utilize the magneto-optical effect in optical fibers to measure current. Electromagnetic current transformers suffer from drawbacks such as limited measurement range, low accuracy, and poor safety performance. In contrast, fiber optic current transformers offer advantages such as a large measurement range, high accuracy, good safety, and small size and light weight. Elliptic-preserving optical fibers are extensively used as sensing elements in fiber optic current transformers. However, due to manufacturing limitations, elliptic-preserving fibers exhibit significant residual line birefringence, becoming a major source of measurement error. Therefore, elliptic-preserving fibers are required to have greater circular birefringence and less residual line birefringence; the ratio of circular birefringence to residual line birefringence becomes one of the key parameters for evaluating the quality of the elliptic-preserving fiber.

[0003] However, existing measurement techniques can only measure the overall beat length of elliptic fiber, which consists of both circular and linear birefringence, and cannot distinguish the proportions of circular birefringence and residual linear birefringence; or can only make a preliminary theoretical estimate based on the linear beat length and rotation pitch of the fiber preform before twisting, and cannot accurately evaluate the performance of elliptic fiber. Summary of the Invention

[0004] The purpose of this invention is to provide a measuring device and method for the ratio of circular to linear birefringence in elliptical optical fibers. This invention aims to solve the technical problem that existing measurement technologies can only measure the overall beat length of elliptical optical fibers composed of both circular and linear birefringence, and cannot distinguish the proportions of circular birefringence and residual linear birefringence. It also changes the current situation where only the linear beat length and rotation pitch of the fiber preform before twisting can be theoretically estimated, which cannot accurately evaluate the performance of elliptical optical fibers.

[0005] To achieve the above objectives, the present invention employs a measuring device for the ratio of circular to linear birefringence of an elliptical optical fiber, comprising a 1310nm band light source array assembly, an optical path assembly, and a monitoring assembly. The optical path assembly is optically connected to the 1310nm band light source array assembly, and the monitoring assembly is optically connected to the optical path assembly and located at one end of the optical path assembly. The 1310nm band light source array assembly includes an N×1 optical switch, N lasers of different wavelengths in the 1310nm band, a current controller, and a temperature controller. The N lasers of different wavelengths in the 1310nm band are respectively optically connected to the N×1 optical switch, and the current controller and the temperature controller are respectively optically connected to the N lasers of different wavelengths in the 1310nm band.

[0006] The optical path assembly includes a first optical coupler, a polarization controller, a second optical coupler, and a fixed fiber optic connector. The input end of the first optical coupler is optically connected to the output end of the N×1 optical switch. The input end of the polarization controller is optically connected to the first output end of the first optical coupler. The input end of the second optical coupler is optically connected to the output end of the polarization controller. The input end of the fixed fiber optic connector is optically connected to the output end of the second optical coupler. The fixed connector is optically connected to the optical device under test.

[0007] The monitoring component includes a wavelength meter, a first polarization analyzer, a first computer, a second polarization analyzer, and a second computer. The wavelength meter is connected to the second output terminal 52 of the first optical coupler of the optical path component. The first polarization analyzer is connected to the first output terminal 71 of the second optical coupler of the optical path component. The first computer is connected to the first polarization analyzer via a data cable. The input terminal of the second polarization analyzer is connected to the output terminal of the optical device under test. The second computer is connected to the second polarization analyzer via a data cable.

[0008] The polarization controller is an electric polarization controller.

[0009] The present invention also provides a method for measuring the ratio of circular to linear birefringence of an elliptic optical fiber, applied in the measuring device for the ratio of circular to linear birefringence of an elliptic optical fiber as described above, comprising the following steps: The first step is to use the N×1 optical switch to coarsely select the output wavelength of the 1310nm band light source array component, and then use the current controller and the temperature controller to finely adjust the output light wavelength. The second step is to record the polarization state received by the first polarization analyzer, which is defined as the initial input polarization state, and at the same time record the polarization state received by the second polarization analyzer. The third step is to adjust the output wavelength of the 1310nm band light source array component so that it differs from the previous output wavelength by 5nm, and then repeat the first step. Fourth step: Adjust the polarization controller until the polarization state received by the first polarization analyzer is the same as the polarization state of the initial input in the second step; Fifth step: Record the polarization state received by the second polarization analyzer; Step 6: Repeat steps 3, 4, and 5 4 to 5 times; The seventh step is to use the three-point method to fit the polarization state recorded multiple times by the second polarization analyzer to obtain the circular trajectory of the polarization state change, and at the same time calculate the center of the circle. Step 8: Adjust the polarization controller so that the polarization state received by the second polarization analyzer is close to the center of the circular trajectory fitted in step 7, and repeat steps 3 to 6. Step 9: Repeat step 7 until the circular trajectory fitted by the polarization state recorded in the second polarization analyzer approaches a point. The point obtained at this time is called the fixed point.

[0010] The polarization state of the fixed point on the Poincaré sphere of the second polarization analyzer is recorded; denoted as [S1 S2 S3], the ratio of the circular birefringence to the birefringence in the elliptical fiber under test is obtained as follows: .

[0011] The beneficial effects of the device and method for measuring the circular to linear birefringence ratio of an elliptic fiber according to the present invention are as follows: by measuring the phase difference and the fixed point of the elliptic fiber at different wavelengths, the circular to linear birefringence ratio and beat length of the elliptic fiber at the 1310nm band can be measured to evaluate the performance of the elliptic fiber under test. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the structure of the measuring device for the ratio of circular to linear birefringence of the elliptic optical fiber according to the present invention.

[0014] Figure 2 This is a flowchart of the method steps for measuring the ratio of circular to linear birefringence of an elliptical optical fiber according to the present invention.

[0015] 1-N×1 optical switch, 2-N lasers of different wavelengths in the 1310 band, 3-current controller, 4-temperature controller, 5-first optical coupler, 6-polarization controller, 7-second optical coupler, 8-fixed fiber optic connector, 9-wavelength meter, 10-first polarization analyzer, 11-first computer, 12-optical device under test, 13-second polarization analyzer, 14-second computer. Detailed Implementation

[0016] Please see Figure 1This invention provides a device for measuring the ratio of circular to linear birefringence of an elliptical optical fiber, comprising a 1310nm band light source array assembly, an optical path assembly, and a monitoring assembly. The optical path assembly is optically connected to the 1310nm band light source array assembly, and the monitoring assembly is optically connected to the optical path assembly and located at one end of the optical path assembly. The 1310nm band light source array assembly includes an N×1 optical switch 1, N lasers 2 of different wavelengths in the 1310nm band, a current controller 3, and a temperature controller 4. The N lasers 2 of different wavelengths in the 1310nm band are respectively optically connected to the N×1 optical switch 1, and the current controller 3 and the temperature controller 4 are respectively optically connected to the N lasers 2 of different wavelengths in the 1310nm band.

[0017] Furthermore, the optical path assembly includes a first optical coupler 5, a polarization controller 6, a second optical coupler 7, and a fixed fiber optic connector 8. The input end of the first optical coupler 5 is optically connected to the output end of the N×1 optical switch 1. The input end of the polarization controller 6 is optically connected to the first output end 51 of the first optical coupler 5. The input end of the second optical coupler 7 is optically connected to the output end of the polarization controller 6. The input end of the fixed fiber optic connector 8 is optically connected to the second output end 72 of the second optical coupler 7. The fixed connector 8 is optically connected to the optical device under test 12.

[0018] Furthermore, the monitoring component includes a wavelength meter 9, a first polarization analyzer 10, a first computer 11, a second polarization analyzer 13, and a second computer 14. The wavelength meter 9 is connected to the second output terminal 52 of the first optical coupler 5 of the optical path component. The first polarization analyzer 10 is connected to the first output terminal 71 of the second optical coupler 7 of the optical path component. The first computer 11 is connected to the first polarization analyzer 10 via a data cable. The input terminal of the second polarization analyzer 13 is connected to the output terminal of the optical device under test. The second computer 14 is connected to the second polarization analyzer 13 via a data cable.

[0019] Furthermore, the polarization controller 6 is an electric polarization controller.

[0020] Please see Figure 2 The present invention also provides a method for measuring the ratio of circular to linear birefringence of an elliptic optical fiber, applied in the measuring device for the ratio of circular to linear birefringence of an elliptic optical fiber as described above, comprising the following steps: S1: First, use the N×1 optical switch 1 to coarsely select the output wavelength of the 1310nm band light source array component, and then use the current controller 3 and the temperature controller 4 to finely adjust the output light wavelength. S2: The second step is to record the polarization state received by the first polarization analyzer 10, which is defined as the initial input polarization state, and at the same time record the polarization state received by the second polarization analyzer 13. S3: The third step is to adjust the output wavelength of the 1310nm band light source array component so that it differs from the previous output wavelength by 5nm, and repeat the first step operation. S4: Fourth step, adjust the polarization controller 6 until the polarization state received by the first polarization analyzer 10 is the same as the polarization state of the initial input in the second step; S5: Fifth step, record the polarization state received by the second polarization analyzer 13; S6: Step 6, repeat steps 3, 4 and 5 4 to 5 times; S7: The seventh step is to fit the polarization state recorded multiple times by the second polarization analyzer 13 into a circular trajectory of polarization state change using the three-point method, and at the same time calculate the center of the circle. S8: Eighth step, adjust the polarization controller 6 so that the polarization state received by the second polarization analyzer 13 is close to the center of the circular trajectory fitted in the seventh step, and repeat the operations from the third to the sixth step. S9: Step 9, repeat step 7 until the circular trajectory fitted by the polarization state recorded in the second polarization analyzer approaches a point. The point obtained at this time is called the fixed point.

[0021] Furthermore, the polarization state of the fixed point on the Poincaré sphere of the second polarization analyzer is recorded; denoted as [S1 S2 S3], the ratio of the circular birefringence to the birefringence in the elliptical fiber under test is obtained as follows: (8).

[0022] In the apparatus and method for measuring the ratio of circular to linear birefringence of an elliptic fiber according to the present invention, the total beat length of the elliptic fiber under test is measured by wavelength scanning. ; When measuring the beat length of an elliptic fiber, the wavelength scanning method is used. The trajectory of the output polarization state of the elliptic fiber on the Poincaré sphere of the second polarization analyzer 13 as the light frequency changes is a circle that rotates around the polarization vector. When the polarization controller 6 adjusts the circle of the trajectory to be smaller and smaller until it becomes a point, the output polarization state remains at this point no matter how the light frequency changes. According to the theory of the dominant polarization state, the polarization state at this time corresponds to the dominant polarization state. The total birefringence of an elliptic fiber can be determined by measuring the total beat length of the elliptic fiber using the wavelength scanning method. To calculate: (1); Total birefringence in elliptic fiber Circular birefringence Linear birefringence The relationship is (2); The ratio of circular birefringence to linear birefringence can be determined by the polarization vector. Calculations are performed on the polarization vector. The relationship between the ratio of circular birefringence to linear birefringence is as follows: (3); (4); (5); The specific values ​​of circular and linear birefringence for elliptic fiber have now been calculated. The values ​​of circular and linear birefringence can also be used to calculate the values ​​of the circular beat length and linear beat length. Round racket length : (6); Line length : (7); As can be seen from the above, the values ​​of circular birefringence and linear birefringence of the elliptical fiber under test can be obtained from the total beat length and polarization vector of the elliptical fiber under test, and the values ​​of circular beat length and linear beat length can also be obtained.

[0023] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A measuring device for the ratio of circular to linear birefringence of an elliptical optical fiber, characterized in that, The device includes a 1310nm band light source array assembly, an optical path assembly, and a monitoring assembly. The optical path assembly is optically connected to the 1310nm band light source array assembly, and the monitoring assembly is optically connected to the optical path assembly. The 1310nm band light source array assembly includes an N×1 optical switch, N lasers of different wavelengths in the 1310nm band, a current controller, and a temperature controller. The N lasers of different wavelengths in the 1310nm band are each optically connected to the N×1 optical switch, and the current controller and the temperature controller are each electrically connected to the N lasers of different wavelengths in the 1310nm band.

2. The measuring device for the ratio of circular to linear birefringence of an elliptical optical fiber as described in claim 1, characterized in that, The optical path assembly includes a first optical coupler, a polarization controller, a second optical coupler, and a fixed fiber optic connector. The input end of the first optical coupler is connected to the output fiber of the N×1 optical switch. The input end of the polarization controller is connected to the first output fiber of the first optical coupler. The input end of the second optical coupler is connected to the output fiber of the polarization controller. The input end of the fixed fiber optic connector is connected to the first output fiber of the second optical coupler. An elliptic fiber is placed between the fiber optic connector and the monitoring component.

3. The measuring device for the ratio of circular to linear birefringence of an elliptical optical fiber as described in claim 2, characterized in that, The monitoring component includes a wavelength meter, a first polarization analyzer, a first computer, a second polarization analyzer, and a second computer. The wavelength meter is connected to the second output terminal of the first optical coupler of the optical path component. The first polarization analyzer is connected to the first output terminal of the second optical coupler of the optical path component. The first computer is connected to the first polarization analyzer via a data cable. The input terminal of the second polarization analyzer is connected to the output terminal of the optical device under test. The second computer is connected to the second polarization analyzer via a data cable.

4. The measuring device for the ratio of circular to linear birefringence of an elliptical optical fiber as described in claim 2, characterized in that, The polarization controller is an electric polarization controller.

5. A method for measuring the ratio of circular to linear birefringence of an elliptical optical fiber, applied in the measuring device for the ratio of circular to linear birefringence of an elliptical optical fiber as described in claim 3, characterized in that... Includes the following steps: The first step is to use the N×1 optical switch to coarsely select the output wavelength of the 1310nm band light source array component, and then use the current controller and the temperature controller to finely adjust the output light wavelength. The second step is to record the polarization state received by the first polarization analyzer, which is defined as the initial input polarization state, and at the same time record the polarization state received by the second polarization analyzer. The third step is to adjust the output wavelength of the 1310nm band light source array component so that it differs from the previous output wavelength by 5nm, and then repeat the first step. Fourth step: Adjust the polarization controller until the polarization state received by the first polarization analyzer is the same as the polarization state of the initial input in the second step; Fifth step: Record the polarization state received by the second polarization analyzer; Step 6: Repeat steps 3, 4, and 5 4 to 5 times; The seventh step is to use the three-point method to fit the polarization state recorded multiple times by the second polarization analyzer to obtain the circular trajectory of the polarization state change, and at the same time calculate the center of the circle. Step 8: Adjust the polarization controller so that the polarization state received by the second polarization analyzer is close to the center of the circular trajectory fitted in step 7, and repeat the operations from step 3 to step 6. Step 9: Repeat step 7 until the circular trajectory fitted by the polarization state recorded in the second polarization analyzer approaches a point. The point obtained at this time is called the fixed point.

6. The method for measuring the ratio of circular to linear birefringence in an elliptical optical fiber as described in claim 5, characterized in that, Record the polarization state of the fixed point on the Poincaré sphere of the second polarization analyzer; denoted as [S1 S2 S3], the ratio of the circular birefringence to the birefringence in the elliptical fiber under test is obtained as follows: .

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