An online manufacturing method for λ / 4 wave plate of all-fiber microcurrent sensor

Abstract

The present invention discloses an online manufacturing method of a λ / 4 wave plate for an all-fiber microcurrent sensor, which completes the fusion splicing of optical devices other than the λ / 4 wave plate, uses a polarization-maintaining fiber fusion splicer to complete the axial fusion splicing of the wave plate fiber and the sensing fiber, completes the 1 / 4 beat length cutting of the wave plate fiber, and uses online fusion splicing to fusion splice the wave plate fiber and the polarization-maintaining fiber. The present invention overcomes the influence of device errors such as a polarization-maintaining fiber fusion splicer, a polarization state analyzer, and an extinction ratio measuring instrument on the manufacture of the λ / 4 wave plate, improves the manufacturing accuracy of the system, and enhances the sensitivity of the system.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber current measurement, and in particular relates to an online manufacturing method of a λ / 4 wave plate of an all-optical fiber micro-current sensor. Background Art

[0002] Fiber optic current sensors are based on the Faraday effect and Ampere's loop theorem. Compared with traditional electromagnetic current transformers, they have advantages in terms of volume, weight, response speed, and test bandwidth. They have been applied to large current measurement fields such as ultra-high voltage power systems, metallurgy, and lightning current measurement, and have broad application prospects in the field of weak current detection. At present, the problem with the application of fiber optic current sensors in the field of weak current detection is sensitivity. The incompleteness of optical devices and the axial angle deviation during the polarization-maintaining fiber fusion process, especially the manufacturing deviation of the λ / 4 wave plate, are the main factors affecting the sensitivity of the system.

[0003] Usually, the manufacturing method of λ / 4 wave plate is to weld the polarization-maintaining fiber and the wave plate fiber at 45°, and then cut the wave plate fiber to 1 / 4 of the length to complete the manufacturing of λ / 4 wave plate. In "Manufacturing Industry of λ / 4 Wave Plate for All-Fiber Current Transformer" (Infrared and Laser Engineering, 2013, 42(8): 2167-2172.), Li Jianzhong proposed a method of testing the extinction ratio of linear polarized light passing through the 45° welding point to improve the accuracy of axis welding, and to accurately measure the length of the fiber cut by a vernier caliper in "Manufacturing Industry of λ / 4 Wave Plate for All-Fiber Current Transformer" (Infrared and Laser Engineering, 2013, 42(8): 2167-2172.), aiming at the problems of motor rotation accuracy and CCD camera resolution of the fiber fusion machine. The method improves the accuracy of axis welding, and uses a vernier caliper to accurately measure the length of the fiber cut. This method relies on the accuracy of the extinction ratio tester, and the vernier caliper is prone to introduce errors when measuring, which affects the manufacturing accuracy.

[0004] The Chinese invention patent "A method for making an all-fiber quarter-wave plate" (application number 200810040208.0) realizes the production of a quarter-wave plate through the steps of wave plate selection, welding of the wave plate with the transmission optical path and the sensing optical path, and protection of the welding points. However, this production scheme relies on the accuracy of the fiber fusion splicer and the extinction ratio tester, and it is difficult to achieve optimal performance.

[0005] The Chinese invention patent "Optimization Method for Fabrication of λ / 4 Wave Plate for All-Fiber Current Transformer" (application number 202110458772.X) uses a polarization state detector for real-time monitoring during the 45° axial welding process to improve the axial accuracy, and uses a one-dimensional displacement platform, fiber chuck, fiber cleaver and electron microscope to complete the fiber length cutting to achieve the fabrication of λ / 4 wave plate. The fabrication accuracy of this solution depends on the accuracy of the polarization state detector, and it is difficult to achieve optimal performance.

[0006] The above schemes all adopt the offline production scheme of λ / 4 wave plate. Although the production process is convenient to a certain extent, the λ / 4 wave plate will introduce certain errors during the process of welding with the optical path, which will affect the sensitivity of the system. At the same time, the pigtails of each optical component in the optical fiber microcurrent sensor are welded through a polarization-maintaining fiber connector or a polarization-maintaining fiber fusion splicer. For commercial polarization-maintaining fiber connectors, there is an axial angle deviation of about ±3° for the optical axis. For a polarization-maintaining fiber fusion splicer, the axial angle deviation can be reduced to about ±1°. Therefore, in the case of axial angle deviation in other optical paths, even if the offline-made λ / 4 wave plate is very perfect, the sensitivity improvement of the system is limited. Therefore, it is necessary to consider the production of the λ / 4 wave plate together with the overall sensitivity of the optical device to maximize the sensitivity of the system. Summary of the invention

[0007] The purpose of the present invention is to provide an online manufacturing method of a λ / 4 wave plate capable of improving the sensitivity of an optical fiber microcurrent sensor in view of the shortcomings of the above-mentioned technology.

[0008] To achieve the above object, the online manufacturing method of the all-fiber micro-current sensor λ / 4 wave plate designed by the present invention comprises the following steps:

[0009] Step 1, completing the welding of optical components except the λ / 4 wave plate;

[0010] Step 2: Use a polarization-maintaining fiber fusion splicer to complete the axial fusion splicing of the wave plate fiber and the sensor fiber;

[0011] Step 3, completing 1 / 4 beat length cutting of the wave plate optical fiber;

[0012] Step 4: Use online fusion splicing to fusion-splice the wave plate fiber and the polarization-maintaining fiber.

[0013] Furthermore, the specific process of step four is: placing the tail end of the wave plate fiber and the polarization-maintaining fiber in the fiber clamps on the left and right sides of the polarization-maintaining fiber fusion splicer respectively, selecting the working mode of the polarization-maintaining fiber fusion splicer as the PAS mode, and manually adjusting the axial angle between the polarization-maintaining fiber and the wave plate fiber, powering on the optical fiber microcurrent sensor, and outputting a constant current through the DC regulated power supply. The axial angle between the wave plate fiber and the polarization-maintaining fiber is determined by testing the Faraday rotation angle caused by the current. When the axial angle between the wave plate fiber and the polarization-maintaining fiber is 45°, the fusion of the optical fibers is completed, and the online production of the λ / 4 wave plate is completed.

[0014] Furthermore, in step one, a single-mode fusion splicer is used to complete the fusion of the broadband light source and the coupler, and the coupler and the polarizer; a polarization-maintaining fiber fusion splicer is used to complete the 45° axial fusion of the polarizer and the phase modulator pigtail, and the 0° axial fusion of the phase modulator and the polarization-maintaining fiber, and the sensor fiber and the reflector pigtail.

[0015] Furthermore, in step 2, the axis angle is 0°.

[0016] Furthermore, in the step three, the high-precision optical fiber cutting knife includes a fixed platform, and a one-dimensional displacement platform and an optical fiber cutting knife arranged on the fixed platform, and the optical fiber clamp is fixed on the one-dimensional displacement platform; one end of the wave plate optical fiber is fixed on the fiber clamp, and the fusion point of the wave plate optical fiber and the sensing optical fiber is observed through a high-definition electron microscope, and aligned with the tool, and the screw is rotated to a distance of 1 / 4 beat length to complete the cutting of 1 / 4 beat length of the wave plate optical fiber.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1) Based on the high-precision cutting of the wave plate fiber at 1 / 4 of the beat length, the present invention completes the 45° online fusion of the wave plate fiber and the polarization-maintaining fiber, and determines the optimal response capability by observing the changes in the data processing system, thereby improving the sensitivity of the system;

[0019] 2) The present invention overcomes the influence of the errors of components such as polarization-maintaining optical fiber fusion splicer, polarization state analyzer and extinction ratio measuring instrument on the production of λ / 4 wave plate;

[0020] 3) The present invention is not limited to optical fiber current sensors, but is also applicable to any other occasions where a λ / 4 wave plate needs to be manufactured. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of the high-precision optical fiber cutting knife of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] The online manufacturing method of the λ / 4 wave plate of the all-fiber micro-current sensor comprises the following steps:

[0024] Step 1: Complete the welding of optical components except the λ / 4 wave plate

[0025] A single-mode fusion splicer is used to complete the fusion of the broadband light source and the coupler, and the coupler and the polarizer; a polarization-maintaining fiber fusion splicer is used to complete the 45° axial fusion of the polarizer and the phase modulator pigtail, as well as the 0° axial fusion of the phase modulator and the polarization-maintaining fiber, and the sensor fiber and the reflector pigtail, thus completing the connection between the optical components of the optical path except the λ / 4 wave plate.

[0026] Step 2: Use a polarization-maintaining fiber fusion splicer to complete the axial fusion splicing of the wave plate fiber and the sensor fiber, with the axial angle being 0°;

[0027] Step 3: Complete the 1 / 4 beat length cutting of the wave plate fiber

[0028] like Figure 1 As shown, the high-precision optical fiber cutting knife includes a fixed platform 1, and a one-dimensional displacement platform 2 and an optical fiber cutting knife 3 arranged on the fixed platform 1. The optical fiber clamp 4 is fixed on the one-dimensional displacement platform 2 by four nuts; one end of the wave plate optical fiber is fixed on the fiber clamp 4; the fusion point of the wave plate optical fiber and the sensing optical fiber is observed by a high-definition electron microscope, and aligned with the cutter 6, and the screw 5 is rotated counterclockwise to a distance of 1 / 4 beat length to complete the high-precision cutting of the wave plate optical fiber 1 / 4 beat length;

[0029] Step 4: Use online fusion splicing to fusion-splice the wave plate fiber and the polarization-maintaining fiber

[0030] Place the tail end of the wave plate fiber and the polarization-maintaining fiber in the fiber clamps on the left and right sides of the polarization-maintaining fiber fusion splicer respectively, select the PAS mode of the polarization-maintaining fiber fusion splicer, and set the axis alignment method to manual; when manually adjusting the axis alignment angle between the polarization-maintaining fiber and the wave plate fiber, power on the optical fiber microcurrent sensor, set the DC regulated power supply to a constant current output, and determine the axis alignment angle between the wave plate fiber and the polarization-maintaining fiber by testing the Faraday rotation angle caused by the current. When the axis alignment angle between the wave plate fiber and the polarization-maintaining fiber is 45°, the fiber fusion is completed, and the online production of the λ / 4 wave plate is completed.

[0031] In step 1, due to the fact that there is a certain manufacturing error in the polarization-maintaining fiber fusion splicer during the axial fusion process, when the rotation matrix is ​​used to describe the influence of each fusion point of the optical device on the state of the beam,

[0032] R(θ1)·R(θ2)=R(θ1+θ2) Equation 1

[0033] Among them, θ1 is the axis-to-axis angle between the polarizer and the phase modulator pigtail optical axis, and ideally θ1 = 45°; θ2 is the axis-to-axis angle between the phase modulator pigtail and the polarization-maintaining fiber, and ideally θ2 = 0°; R(θ1) and R(θ2) are the rotation matrices corresponding to θ1 and θ2, respectively.

[0034] When there is an angular deviation of the axis,

[0035]

[0036] Δθ1 is the axis angle deviation corresponding to θ1, and Δθ2 is the axis angle deviation corresponding to θ2.

[0037] At this time, the rotation matrix can be expressed as:

[0038] R(θ1+Δθ1)·R(θ2+Δθ2)=R(θ1)·R(θ2)·R(Δθ1+Δθ2) Equation 3

[0039] In step 4, let θ3 be the axial angle between the polarization-maintaining fiber and the wave plate fiber. Ideally, θ3 = 45°. When there is an axial angle welding error,

[0040] θ3=45°+Δθ3 Formula 4

[0041] Δθ3 is the angular deviation of θ3. At this time, the rotation matrix of the system is expressed as:

[0042] R(θ1+Δθ1)·R(θ2+Δθ2)·R(θ3+Δθ3)=R(θ1)·R(θ2)·R(θ3)R(Δθ1+Δθ2+Δθ3) Equation 5

[0043] Therefore, adjusting Δθ3 can compensate Δθ1 and Δθ2, that is,

[0044] Δθ1+Δθ2+Δθ3=0 Formula 6

[0045] When equation 6 is satisfied, the rotation matrix of the system is expressed as:

[0046] R(θ1+Δθ1)·R(θ2+Δθ2)·R(θ3+Δθ3)=R(θ1)·R(θ2)·R(θ3) Equation 7

[0047] Therefore, by modulating the axial angle of the polarization-maintaining fiber and the polarization-maintaining fiber, the influence of the axial angle deviation of the optical path in the early stage on the sensitivity of the system can be compensated. In specific operation, the components of the all-fiber microcurrent (microcurrent is a current with a maximum measurement current of no more than 10A and a current resolution of mA level) sensor are powered on, and the output current of the DC regulated power supply is set to a constant value of 0.5A, and the demodulated angle information is observed by the digital signal processing system; in particular, the digital signal processing system adopts the harmonic division method or the closed-loop feedback data processing method to eliminate the influence of the light source energy fluctuation on the measurement result; that is, when the axial angle of the polarization-maintaining fiber and the wave plate fiber is manually adjusted, the angle solution of the digital signal system is observed. When the solved angle is the maximum value, the fiber fusion work is completed, that is, the online production of the λ / 4 wave plate is completed.

[0048] In the process of online welding of the λ / 4 wave plate in step 4, the principle of maximum sensitivity is adopted. By adjusting θ3, the axial angle deviation of θ1 and θ2 in the optical path is compensated. While completing the production of the λ / 4 wave plate, the axial angle deviation of the welding point in the optical path is effectively compensated, thereby improving the sensitivity of the system.

[0049] In addition to the above examples, the present invention may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope of this patent.

Claims

1. An online method for manufacturing a λ / 4 wave plate for an all-fiber microcurrent sensor, characterized in that: The following steps are involved: Step 1, completing the welding of optical components except the λ / 4 wave plate; Step 2: Use a polarization-maintaining fiber fusion splicer to complete the axial fusion splicing of the wave plate fiber and the sensor fiber; Step 3, completing 1 / 4 beat length cutting of the wave plate optical fiber; Step 4, using online fusion splicing to fusion splice the wave plate fiber and the polarization-maintaining fiber; The specific process of step four is as follows: placing the tail end of the wave plate fiber and the polarization-maintaining fiber in the fiber clamps on the left and right sides of the polarization-maintaining fiber fusion splicer respectively, selecting the working mode of the polarization-maintaining fiber fusion splicer as the PAS mode, and manually adjusting the axial angle between the polarization-maintaining fiber and the wave plate fiber, powering on the optical fiber microcurrent sensor, and outputting a constant current through the DC regulated power supply. The axial angle between the wave plate fiber and the polarization-maintaining fiber is determined by testing the Faraday rotation angle caused by the current. When the axial angle between the wave plate fiber and the polarization-maintaining fiber is 45°, the fiber fusion is completed, and the online production of the λ / 4 wave plate is completed.

2. The online manufacturing method of the λ / 4 wave plate of the all-optical microcurrent sensor according to claim 1 is characterized in that: In the step 1, a single-mode fusion splicer is used to complete the fusion of the broadband light source and the coupler, and the coupler and the polarizer; a polarization-maintaining fiber fusion splicer is used to complete the 45° axial fusion of the polarizer and the phase modulator pigtail, and the 0° axial fusion of the phase modulator and the polarization-maintaining fiber, and the sensor fiber and the reflector pigtail.

3. The online manufacturing method of the λ / 4 wave plate of the all-optical microcurrent sensor according to claim 1 is characterized in that: In the step 2, the axis angle is 0°.

4. The online manufacturing method of the λ / 4 wave plate of the all-optical microcurrent sensor according to claim 1 is characterized by: In the step three, the high-precision optical fiber cutting knife comprises a fixed platform (1), and a one-dimensional displacement platform (2) and an optical fiber cutting knife (3) arranged on the fixed platform (1), and the optical fiber clamp (4) is fixed on the one-dimensional displacement platform (2); one end of the wave plate optical fiber is fixed on the fiber clamp (4), and the fusion point between the wave plate optical fiber and the sensing optical fiber is observed through a high-definition electron microscope and aligned with the cutter (6), and the screw (5) is rotated to a distance of 1 / 4 beat length to complete the cutting of the wave plate optical fiber 1 / 4 beat length.

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