One-to-six-path polarization maintaining optical fiber beam splitter based on free space integration and application of one-to-six-path polarization maintaining optical fiber beam splitter

Abstract

The invention relates to the field of optical fiber sensing, and particularly discloses a one-to-six-path polarization maintaining optical fiber beam splitter based on free space integration and application, the one-to-six-path polarization maintaining optical fiber beam splitter comprises a structural member, an optical assembly and a rubber plug, the structural member comprises a metal shell and a metal upper cover covering the metal shell, the optical assembly comprises a substrate, three light splitting sheets and seven single-core polarization-maintaining optical fiber collimators which are arranged in the metal shell, the substrate is fixed in the metal shell, two of the three light splitting sheets are symmetrically arranged on one side of the substrate, the other light splitting sheet is arranged on the other side of the substrate, and the seven single-core polarization-maintaining optical fiber collimators are arranged on the substrate. The seven single-core polarization-maintaining optical fiber collimators are respectively fixed on the substrate, and optical fibers of the seven single-core polarization-maintaining optical fiber collimators respectively penetrate out of the holes of the corresponding rubber plugs and extend out of the metal shell. Wiring can be simplified, the size is reduced, the number of discrete devices in a shunt scheme is reduced, welding points are reduced, and optical path loss and cost are reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing, and in particular to a 1-to-6-way polarization-maintaining optical fiber beam splitter based on free space integration and its application. Background Art

[0002] The three-axis fiber optic gyroscope is an inertial sensing instrument that measures angular velocity based on the Sagnac effect. It has many advantages, such as fast startup, large dynamic range, small electromagnetic influence, and good vibration and shock resistance. Therefore, it is widely used in aviation, aerospace, navigation, inertial guidance, UAV and other fields, and has great development prospects. With the rapid industrialization development of domestic three-axis fiber optic gyroscopes, the application end has put forward more stringent volume and weight requirements for inertial measurement and navigation systems while ensuring measurement accuracy. The miniaturization of gyroscopes is the basis and prerequisite for realizing the lightweight and miniaturization of inertial systems.

[0003] In the prior art, the three-axis integrated fiber optic gyroscope assembly usually adopts a modular structure design of an optoelectronic separation structure, which integrates advanced design and manufacturing concepts such as high-precision fiber optic light source technology and low-stress fiber optic winding technology. It usually adopts a shared SLD light source design to divide the light output by the SLD light source into three paths. The branching scheme adopts a cascade scheme of five 1-to-2-path polarization-maintaining fiber beam splitters. The port definition of the 1-to-2-path polarization-maintaining fiber beam splitter and the direction of optical path signal transmission (arrow direction) are shown in Figure 7 , the prior art uses the principle of a 1-to-2-way polarization-maintaining fiber beam splitter, such as Figure 6The connection of the optical path shown in the figure has a working principle that the signal of the SLD light source is input to the input end of the beam splitter (13-1), and is input to the transmission end of the beam splitter (13-3) through the transmission end of the beam splitter (13-1). Then, the input end of the beam splitter (13-3) transmits the signal to the input end of the first Y-waveguide lithium niobate modulator (14-1). After the signals at the output ends of the first Y-waveguide lithium niobate modulator (14-1) are respectively transmitted to the two ends of the first optical fiber ring (16-1), they are cross-returned to the first Y-waveguide lithium niobate modulator ( The signal is then transmitted from the input end of the first Y-guide lithium niobate modulator (14-1) back to the input end of the beam splitter (13-3), and then transmitted to the reflection end of the beam splitter (13-3), thereby being received by the first detector (15-1); similarly, the reflection end signal of the beam splitter (13-1) is transmitted to the input end of the beam splitter (13-2), and then it transmits the reflection end signal to the transmission end of the beam splitter (13-5), and transmits the transmission end signal to the transmission end of the beam splitter (13-4). The input end signal of the beam splitter (13-4) is then transmitted to the input end of the second Y-waveguide lithium niobate modulator (14-2), and then the output end signals of the second Y-waveguide lithium niobate modulator (14-2) are transmitted to the two ends of the optical fiber ring (16-2) and then cross-returned to the output ends of the second Y-waveguide lithium niobate modulator (14-2), and then transmitted from the input end of the second Y-waveguide lithium niobate modulator (14-2) to the input end of the beam splitter (13-4), and then transmitted from the reflection end of the beam splitter (13-4) to the third detector (15-3); the input end signal of the beam splitter (13-5) is transmitted to the input end of the third Y-waveguide lithium niobate modulator (14-3), and then transmitted from the output ends of the third Y-waveguide lithium niobate modulator (14-3) to the two ends of the third optical fiber ring (16-3), cross-transmitted back to the two ends, and then the input end signal of the third Y-waveguide lithium niobate modulator (14-3) is transmitted to the input end of the beam splitter (13-5), and finally output from the reflection end of the beam splitter (13-5) and transmitted to the detector (15-3).

[0004] In summary, the existing system design of the three-axis integrated fiber optic gyroscope assembly in the prior art has the problems of more discrete components, more fusion points, large loss, relatively complex wiring, and larger volume, and the signals obtained by the three detectors are weak. Therefore, it is urgent to propose a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a 1-to-6-way polarization-maintaining fiber optic splitter based on free space integration and its application, which can reduce the number of discrete components in the branching scheme while ensuring the application function of the existing three-axis integrated fiber optic gyroscope assembly, thereby reducing the number of fusion points, reducing losses, simplifying wiring, reducing volume, and achieving the purpose of reducing costs.

[0006] In order to solve the above technical problems, the present invention provides a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration, comprising a structural member, an optical component and a rubber plug, wherein the structural member comprises a metal shell and a metal upper cover arranged on the metal shell, the optical component comprises a substrate arranged in the metal shell, three beam splitters and seven single-core polarization-maintaining fiber collimators, the substrate is fixed in the metal shell, two of the three beam splitters are symmetrically arranged on one side of the substrate, and the other beam splitter is arranged on the other side of the substrate, and the two light-transmitting surfaces of the three beam splitters are respectively coated with a beam splitting film and an anti-reflection film;

[0007] The seven single-core polarization-maintaining fiber collimators are respectively fixed on the substrate, and one of the single-core polarization-maintaining fiber collimators serves as an input end and faces one of the two symmetrical beam splitters, and the other six single-core polarization-maintaining fiber collimators serve as output ends and are located on the outsides of the three beam splitters in a group of two. The rubber plugs have seven and are respectively fixed at the openings on the outer wall of the metal shell, and the optical fibers of the seven single-core polarization-maintaining fiber collimators pass through the corresponding holes of the rubber plugs and extend out of the metal shell.

[0008] Furthermore, the splitting ratio of the three beam splitters ranges from 1% to 99%, and they are respectively the first beam splitter 6 - 1 , the second beam splitter 6 - 2 and the third beam splitter 6 - 3 , and the first beam splitter 6 - 1 and the third beam splitter 6 - 3 are symmetrically arranged on the substrate 7 .

[0009] Furthermore, the splitting ratio of the first beam splitter 6-1 is 55:45, the splitting ratio of the second beam splitter 6-2 is 61:39, and the splitting ratio of the third beam splitter 6-3 is 3:97.

[0010] Furthermore, the incident angle formed between the single-core polarization-maintaining fiber collimator 5 - 1 as the input end and the first beam splitter 6 - 1 ranges from 0° to 90°.

[0011] Furthermore, the incident angle formed between the single-core polarization-maintaining fiber collimator 5 - 1 as the input end and the first beam splitter 6 - 1 is 13.5°.

[0012] Furthermore, the single-core polarization-maintaining optical fiber collimator is manufactured by coupling a single-core polarization-maintaining pigtail with a collimating lens through a reflector method or a light spot method and then fixing the pigtail with glue in a glass tube.

[0013] Furthermore, the single-core polarization-maintaining pigtail is manufactured by removing a certain length of coating from one end of a single polarization-maintaining optical fiber, inserting the end of the end into a capillary after cleaning and fixing it with glue, and then grinding and polishing the end face of the capillary into an 8° bevel and coating it with an anti-reflection film.

[0014] Furthermore, the collimating lens is a self-focusing lens or a ball lens, and both light-transmitting surfaces of the collimating lens are coated with anti-reflection films, and one of the light-transmitting surfaces is ground into an 8° inclined surface.

[0015] Furthermore, the metal shell and the metal upper cover are fixed by glue.

[0016] On the other hand, the present invention also provides an application of a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration, which is applied to a three-axis integrated fiber optic gyroscope assembly. The optical structure of the three-axis integrated fiber optic gyroscope assembly includes an SLD light source, a first Y-waveguide lithium niobate modulator, a second Y-waveguide lithium niobate modulator, a third Y-waveguide lithium niobate modulator, a first detector, a second detector, a third detector, a first fiber ring, a second fiber ring and a third fiber ring. The seven rubber plugs of the 1-to-6-way polarization-maintaining fiber beam splitter are respectively a first rubber plug, a second rubber plug, a third rubber plug, a fourth rubber plug, a fifth rubber plug, a sixth rubber plug and a seventh rubber plug;

[0017] The SLD light source is connected to the optical fiber output from the first rubber plug, the second detector is connected to the optical fiber output from the second rubber plug, the second optical fiber ring is connected to the second Y-waveguide lithium niobate modulator and then connected to the optical fiber output from the third rubber plug, the first detector is connected to the optical fiber output from the fourth rubber plug, the first optical fiber ring is connected to the first Y-waveguide lithium niobate modulator and then connected to the optical fiber output from the fifth rubber plug, the third detector is connected to the optical fiber output from the sixth rubber plug, and the third optical fiber ring is connected to the third Y-waveguide lithium niobate modulator and then connected to the optical fiber output from the seventh rubber plug.

[0018] The beneficial effects of the present invention are:

[0019] 1. The 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration of the present invention can simplify wiring and reduce volume. Compared with the 1-to-2-way polarization-maintaining beam splitter in the prior art, the minimum volume of a single device can be Φ3mm*25mm. After 5 devices are ideally stacked, the volume occupied is approximately width*height*length: 6*9*25mm, while the present invention can achieve width*height*length of 6*4*20mm, which greatly reduces the volume of the beam splitter, reduces the number of discrete devices in the branching scheme, reduces the fusion points with external devices, reduces the optical path loss, and reduces the cost.

[0020] 2. The free-space integrated 1-to-6-way polarization-maintaining fiber beam splitter of the present invention is applied to a three-axis fiber optic gyroscope. Compared with the current method of cascading and welding five 1-to-2-way polarization-maintaining fiber beam splitters as discrete devices, it has the advantages of fewer welding points, low power consumption, compact structure, small size, fewer components and low cost.

[0021] 3. The present invention adopts a first beam splitter with a splitting ratio of 55:45, a second beam splitter with a splitting ratio of 61:39, and a third beam splitter with a splitting ratio of 3:97, which can ensure that the signals finally received by the first detector, the second detector, and the third detector in the optical circuit of the three-axis integrated fiber optic gyroscope assembly are strong and the optical signal powers of the three detectors are similar, and the three detectors can all receive optical signals of about 20% of the light source emission power. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is an overall external schematic diagram of the 1-to-6-way polarization-maintaining fiber splitter based on free-space integration of the present invention: 1 is a metal upper cover, 2 is a metal lower shell, and 3-1 / 3-2 / 3-3 / 3-4 / 3-5 / 3-6 / 3-7 are the first / second / third / fourth / fifth / sixth / seventh rubber plugs, respectively.

[0024] Figure 2 This is a schematic diagram of the internal structure of the 1-to-6-way polarization-maintaining fiber splitter based on free-space integration of the present invention: wherein 2 is a metal lower shell, 3-1 / 3-2 / 3-3 / 3-4 / 3-5 / 3-6 / 3-7 are the first / second / third / fourth / fifth / sixth / seventh rubber plugs respectively, 5-1 / 5-2 / 5-3 / 5-4 / 5-5 / 5-6 / 5-7 are the first / second / third / fourth / five / sixth / seventh single-core polarization-maintaining fiber collimators respectively, 6-1 / 6-2 / 6-3 are the first / second / third beam splitters respectively, and 7 is a substrate.

[0025] Figure 3 This is a schematic diagram of the optical component structure and optical path of the free-space integrated 1-to-6-way polarization-maintaining fiber splitter of the present invention: 5-1 / 5-2 / 5-3 / 5-4 / 5-5 / 5-6 / 5-7 are respectively the first / second / third / fourth / fifth / sixth / seventh single-core polarization-maintaining fiber collimators, 6-1 / 6-2 / 6-3 are respectively the first / second / third beamsplitters, 7 is a substrate, and the dotted line is a geometric optical simplified optical path.

[0026] Figure 4 This is a schematic structural diagram of the single-core polarization-maintaining fiber collimator of the free-space integrated 1-to-6-way polarization-maintaining fiber splitter of the present invention: 8 is a glass tube, 9 is a collimating lens, and 10 is a single-core polarization-maintaining pigtail.

[0027] Figure 5 This is a schematic diagram of the single-core polarization-maintaining pigtail structure of the 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration of the present invention: wherein 4 is a polarization-maintaining fiber, and 11 is a capillary.

[0028] Figure 6 Schematic diagram of line connection and signal transmission direction of an existing system of a three-axis integrated fiber optic gyroscope assembly in the prior art: 12 is an SLD light source, 13-1 / 13-2 / 13-3 / 13-4 / 13-5 are respectively the first / second / third / fourth / fifth 1-to-2-way polarization-maintaining fiber splitters, 14-1 / 14-2 / 14-3 are respectively the first / second / third Y-waveguide lithium niobate modulators, 15-1 / 15-2 / 15-3 are respectively the first / second / third detectors, and 16-1 / 16-2 / 16-3 are respectively the first / second / third fiber rings.

[0029] Figure 7 This is the port definition and signal transmission direction of the 1-to-2-way polarization-maintaining fiber splitter in the prior art. Since the optical path can be transmitted in the reverse direction, when a signal is input to the reflection end or the transmission end, it can also be output from the input end; but the reflection end and the transmission end are isolated and cannot transmit signals to each other.

[0030] Figure 8 Schematic diagram of the optical path connection structure of the three-axis integrated fiber optic gyroscope assembly equipped with the free-space integrated 1-to-6-way polarization-maintaining fiber beam splitter of the present invention: digital code and Figure 2 and Figure 6 The objects represented by the numeric codes are the same. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In a specific embodiment of the present invention, Figure 1-5 As shown, a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration includes structural parts, optical components and rubber plugs 3. The structural parts include a metal shell 2 and a metal upper cover 1 covered on the metal shell 2. The metal shell and the metal upper cover are fixed by glue. The optical components include a substrate 7, three beam splitters 6 and seven single-core polarization-maintaining fiber collimators 5 arranged in the metal shell 2. The substrate 7 is fixed in the metal shell 2. Two of the three beam splitters 6 are symmetrically arranged on one side of the substrate, and the other beam splitter is arranged on the other side of the substrate 7. The two light-transmitting surfaces of the three beam splitters 6 are respectively coated with a beam splitting film and an anti-reflection film.

[0033] Seven single-core polarization-maintaining fiber collimators 5 are respectively fixed on the substrate 7, and one of the single-core polarization-maintaining fiber collimators 5-1 is used as an input end and faces one of the two symmetrical beam splitters, and the other six single-core polarization-maintaining fiber collimators are used as output ends and are located on the outsides of the three beam splitters in a group of two. There are seven rubber plugs and they are respectively fixed on the openings of the outer wall of the metal shell. The optical fibers of the seven single-core polarization-maintaining fiber collimators pass through the corresponding holes of the rubber plugs and extend out of the metal shell, and then the holes are sealed with glue;

[0034] Specifically, the splitting ratio range of the three beam splitters is 1% to 99%, the material of the beam splitters is NBK7 glass, the refractive index is 1.5036, and they are respectively the first beam splitter 6-1, the second beam splitter 6-2 and the third beam splitter 6-3, and the first beam splitter 6-1 and the third beam splitter 6-3 are symmetrically arranged on the substrate 7; in this embodiment, the splitting ratio of the first beam splitter 6-1 is 55:45, the splitting ratio of the second beam splitter 6-2 is 61:39, and the splitting ratio of the third beam splitter 6-3 is 3:97, and the first beam splitter 6-1 and the third beam splitter 6-3 are symmetrically arranged.

[0035] Specifically, the seven single-core polarization-maintaining fiber collimators 5 are respectively a first single-core polarization-maintaining fiber collimator 5-1, a second single-core polarization-maintaining fiber collimator 5-2, a third single-core polarization-maintaining fiber collimator 5-3, a fourth single-core polarization-maintaining fiber collimator 5-4, a fifth single-core polarization-maintaining fiber collimator 5-5, a sixth single-core polarization-maintaining fiber collimator 5-6, and a seventh single-core polarization-maintaining fiber collimator 5-7. Figure 2 As shown, the first single-core polarization-maintaining fiber collimator 5-1 is used as the input end and is arranged toward the first beam splitter 6-1. The incident angle Φ formed between the first single-core polarization-maintaining fiber collimator 5-1 as the input end and the first beam splitter 6-1 ranges from 0 to 90°;

[0036] In this embodiment, the first collimator 5-1 adopts an incident angle of 13.5°, and the corresponding 1-to-6-way polarization-maintaining fiber optic beam splitter based on free space integration has the most compact internal structure and a small volume. At present, the minimum volume of a single device of the 1-to-2-way polarization-maintaining beam splitter can be Φ3mm*25mm, and the volume of 5 devices after ideal stacking is approximately width*height*length: 6*9*25mm, while the present invention can achieve width*height*length of 6*4*20mm, which greatly reduces the volume of the beam splitter and minimizes the size of the overall beam splitter.

[0037] In this embodiment, the manufacturing method of the free-space integrated 1-to-6-way polarization-maintaining fiber beam splitter of the present invention comprises the following steps:

[0038] S1. Making single-core polarization-maintaining pigtail

[0039] A certain length of coating is removed from one end of a single polarization-maintaining optical fiber 4, which is cleaned and inserted into the capillary 11 and fixed with glue. The end face of the capillary 11 is then ground and polished into an 8° bevel and coated with an anti-reflection film. Specifically, this embodiment uses panda polarization-maintaining optical fiber, and the capillary 11 uses a glass capillary with an outer diameter of 1.0 mm and a length of 5 mm.

[0040] S2. Fabrication of single-core polarization-maintaining fiber collimator

[0041] A single-core polarization-maintaining pigtail 10 is coupled with a collimating lens 9 by a reflector method or a spot method, and then fixed in a glass tube 8 by glue, wherein the collimating lens 9 is a self-focusing lens or a ball lens, and both light-transmitting surfaces of the collimating lens are coated with an anti-reflection film, one of which is ground into an 8° bevel, and the bevel is arranged parallel to the 8° bevel of the capillary;

[0042] Specifically, in this embodiment, the collimating lens 9 adopts a ball lens with an outer diameter of 1.0 mm, a radius of curvature of 1.419 mm, and a length of 2.98 mm, and the glass tube 8 adopts a glass tube with an outer diameter of 1.4 mm, an inner diameter of 1.2 mm, and a length of 7 mm. The collimator coupling method adopts a reflector method, and its principle is to set the distance between the mirror surface of the reflector and the spherical surface of the ball lens to half of the required collimator working distance, and the collimator adjusted by coupling is the required collimator; see here Figure 3 The incident angle of the first single-core polarization-maintaining fiber collimator 5-1 relative to the first beam splitter 6-1 is 13.5°, and the distance between each collimator and the beam splitter is 3 mm. Figure 3 From the geometric optics diagram, we estimate the optical path of each collimator, that is, the working distances of the first single-core polarization-maintaining fiber collimator 5-1 / the second single-core polarization-maintaining fiber collimator 5-2 / the third single-core polarization-maintaining fiber collimator 5-3 / the fourth single-core polarization-maintaining fiber collimator 5-4 / the fifth single-core polarization-maintaining fiber collimator 5-5 / the sixth single-core polarization-maintaining fiber collimator 5-6 / the seventh single-core polarization-maintaining fiber collimator 5-7 are 35mm / 10mm / 21mm / 10mm / 10mm / 10mm / 35mm respectively;

[0043] Specifically: In this embodiment, a 50:50 coupler is selected, and the data of one output end of the coupler is tested to be 3.3dB. The other output end is fused with the lead-out pigtail of the light source, the input end of the coupler is inserted into the optical power meter and zeroed, and then the 3.3dB output end of the coupler is inserted into the optical power meter;

[0044] Then clean the glass tube 8 and the collimating lens 9, fix the glass tube 8 on the fixture, and then insert the 8° surface end of the collimating lens 9 into the glass tube 8, leaving a certain length outside, and fix it with glue. Among them, clean the side wall and end face of the capillary 11 of the single-core polarization-maintaining pigtail 10, and then insert it into the glass tube 8 and fix it on the coupling adjustment frame, so that the 8° inclined surface on it is parallel to the 8° inclined surface of the collimating lens 9;

[0045] Then move the reflector to the distance between the spherical surface of the collimating lens 9, which is half the working distance of the collimator. Then, fuse the single-core polarization-maintaining fiber pigtail 10 with the optical fiber at the input end of the coupler. Adjust the coupling adjustment frame, monitor the optical power meter reading, find the minimum reading that is less than 3.55dB, and glue to fix the position of the capillary 11 and the glass tube 8. The single-core polarization-maintaining fiber collimator is completed.

[0046] S3. Fabrication of optical components

[0047] In this embodiment, the substrate adopts a ceramic substrate with a length*width*thickness of 33mm*12.5mm*0.45mm. In order to ensure that the optical signal power finally received by the three detectors 15-1 / 15-2 / 15-3 is similar, the splitting ratio of the first beam splitter 6-1 is 55:45, the splitting ratio of the second beam splitter 6-2 is 61:39, and the splitting ratio of the third beam splitter 6-3 is 3:97. The first beam splitter 6-1 and the third beam splitter 6-3 are symmetrically arranged up and down, so that the detectors can finally receive the optical signal with a transmission power of about 20% of the light source;

[0048] According to the direction of the optical path, in order to facilitate positioning and prevent the collimators from touching and interfering with each other during coupling, in this embodiment, the distances X1, Y1, X2, Y2, X3, and Y3 from the edge of the substrate 7 of the first beam splitter 6-1, the second beam splitter 6-2, and the third beam splitter 6-3 are 9 mm, 2.5 mm, 9 mm, 2.75 mm, 9 mm, and 2.5 mm, respectively. In specific implementation, positioning marks are made in advance on the substrate 7;

[0049] Then clean the beam splitter and the substrate, stick the three beam splitters 6 on the substrate 7 to mark the positions, and fix them with glue; connect the optical fiber leading out of the light source to the optical power meter and return it to zero, then fix the substrate 7 with the beam splitter attached to the platform of the coupling table, fix the first single-core polarization-maintaining fiber collimator 5-1 to the coupling table fixture, and fuse the optical fiber of the collimator with the optical fiber leading out of the light source, then move the collimator to about 3mm above the first beam splitter 6-1, adjust the angle knob to make the incident angle of the first single-core polarization-maintaining fiber collimator 5-1 relative to the first beam splitter 6-1 13.5°, fix the seventh single-core polarization-maintaining fiber collimator 5-7 to the coupling table fixture, move it to about 3mm of the third beam splitter 6-3, and at the same time adjust the angle knob to make the incident angle between the seventh single-core polarization-maintaining fiber collimator 5-7 and the third beam splitter 6-3 The angle is 13.5°, and the optical fiber of the seventh single-core polarization-maintaining fiber collimator 5-7 is connected to the optical power meter, and then the coupling adjustment frame knobs of the first single-core polarization-maintaining fiber collimator 5-1 and the seventh single-core polarization-maintaining fiber collimator 5-7 are adjusted to monitor the optical power reading. When the reading is minimum and less than 7.3dB, the first single-core polarization-maintaining fiber collimator 5-1 is fixed on the substrate 7 by glue, and the optical fiber of the seventh single-core polarization-maintaining fiber collimator 5-7 is connected to the extinction ratio tester, and the rotary key knob of the adjustment frame of the seventh single-core polarization-maintaining fiber collimator 5-7 is adjusted until the monitored extinction ratio is maximum and meets the requirement of being greater than 24dB; then the seventh single-core polarization-maintaining fiber collimator 5-7 is connected to the optical power meter, and the knob of the adjustment frame is fine-tuned. When the reading is minimum and less than 7.3dB, the seventh single-core polarization-maintaining fiber collimator 5-7 is fixed on the substrate by glue;

[0050] Similarly, the third single-core polarization-maintaining fiber collimator 5-3 is coupled, adjusted and fixed with the first single-core polarization-maintaining fiber collimator 5-1, and the optical power meter is required to monitor the minimum reading and be less than 5.2dB, and the extinction ratio tester is required to monitor the data to be the maximum and greater than 24dB; the fifth single-core polarization-maintaining fiber collimator 5-5 is coupled, adjusted and fixed with the first single-core polarization-maintaining fiber collimator 5-1, and the optical power meter is required to monitor the reading and be less than 3.95dB, and the extinction ratio tester is required to monitor the data to be the maximum and greater than 24dB; the optical fiber of the third single-core polarization-maintaining fiber collimator 5-3 is fused with the optical fiber led out of the light source, the second single-core polarization-maintaining fiber collimator 5-2 is adjusted and fixed, and the optical power meter is required to monitor the reading and be less than 3.95dB, and the extinction ratio tester is required to monitor the data to be the maximum and greater than 24dB; The reading is minimum and less than 2.6dB, and the extinction ratio tester monitors the maximum and greater than 24dB; then the optical fiber of the fifth single-core polarization-maintaining fiber collimator 5-5 is fused with the optical fiber led out of the light source, the fourth single-core polarization-maintaining fiber collimator 5-4 is adjusted and fixed, and the optical power meter monitors the minimum reading and is less than 3.95dB, and the extinction ratio tester monitors the maximum data and is greater than 24dB; finally, the seventh single-core polarization-maintaining fiber collimator 5-7 is fused with the optical fiber led out of the light source, the sixth single-core polarization-maintaining fiber collimator 5-6 is adjusted and fixed, and the optical power meter monitors the minimum reading and is less than 0.6dB, and the extinction ratio tester monitors the maximum data and is greater than 24dB, and the production is completed.

[0051] S4. Packaging production

[0052] In this embodiment, the structural parts are made of aluminum alloy: Figure 2 , use glue to fix the seven rubber plugs on the seven holes of the metal shell 2 respectively, clean the bottom surface of the substrate 7 and the inner bottom surface of the metal shell. For the convenience of operation, the substrate 7 only needs to be fixed with glue in the center of the inner bottom surface of the metal shell 2, and then the optical fiber of the first single-core polarization-maintaining optical fiber collimator 5-1 is connected through the hole of the first rubber plug 3-1, the optical fiber of the second single-core polarization-maintaining optical fiber collimator 5-2 is connected through the hole of the second rubber plug 3-2, the optical fiber of the third single-core polarization-maintaining optical fiber collimator 5-3 is connected through the hole of the third rubber plug 3-3, and the optical fiber of the fourth single-core polarization-maintaining optical fiber collimator 5-1 is connected through the hole of the first rubber plug 3-1. The optical fiber of the straightener 5-4 is extended out from the hole of the fourth rubber plug 3-4, the optical fiber of the fifth single-core polarization-maintaining optical fiber collimator 5-5 is extended out from the hole of the fifth rubber plug 3-5, the optical fiber of the sixth single-core polarization-maintaining optical fiber collimator 5-6 is extended out from the hole of the sixth rubber plug 3-6, and the optical fiber of the seventh single-core polarization-maintaining optical fiber collimator 5-7 is extended out from the hole of the seventh rubber plug 3-7, and the holes of the seven rubber plugs are filled with glue to fix the optical fibers; finally, a circle of glue is applied to the inner edge step of the metal shell 2, and the metal cover 1 is covered and sealed to complete the beam splitter.

[0053] The free-space integrated 1-to-6-way polarization-maintaining fiber beam splitter of the present invention greatly reduces material costs and labor costs. Specifically, the optical component of the present invention only requires 7 single-core polarization-maintaining fiber collimators and 3 beam splitters; while a single 1-to-2-way polarization-maintaining beam splitter in the prior art requires 1 collimator, 1 dual-core collimator, and 1 beam splitter. The overall system (such as Figure 6-7 ) requires the use of 5 single-core collimators, 5 dual-core collimators, and 5 beam splitters. The cost of the dual-core collimator is that 3 more collimators and two more beam splitters are needed just from the quantity. The price of the dual-core collimator is much higher than that of the single-core collimator, and the cost is higher. In addition, the less materials used in the present invention, the less times and difficulty of patching are required, which can greatly reduce the manual operation cost and improve the operation efficiency.

[0054] The present invention is applied to a three-axis fiber optic gyroscope. Compared with the current method of using five 1-to-2-way polarization-maintaining fiber beam splitters as discrete devices for cascade welding, it has the advantages of fewer welding points, low power consumption, compact structure, small size, fewer components, and low cost.

[0055] like Figure 8, an application of a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration, applied to a three-axis integrated fiber optic gyroscope assembly, the optical structure of the three-axis integrated fiber optic gyroscope assembly includes a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration, an SLD light source 12, a first Y-waveguide lithium niobate modulator 14-1, a second Y-waveguide lithium niobate modulator 14-2, a third Y-waveguide lithium niobate modulator 14-3, a first detector 15-1, a second detector 15-2, a third detector 15-3, a first fiber ring 16-1, a second fiber ring 16-2 and a third fiber ring 16-3, and seven rubber plugs 3 of the 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration are respectively a first rubber plug 3-1, a second rubber plug 3-2, a third rubber plug 3-3, a fourth rubber plug 3-4, a fifth rubber plug 3-5, a sixth rubber plug 3-6 and a seventh rubber plug 3-7;

[0056] The SLD light source 12 is connected to the optical fiber output from the first rubber plug 3-1, the second detector 15-2 is connected to the optical fiber output from the second rubber plug 3-2, the second optical fiber ring 16-2 is connected to the second Y-waveguide lithium niobate modulator 14-2 and then connected to the optical fiber output from the third rubber plug 3-3, the first detector 15-1 is connected to the optical fiber output from the fourth rubber plug 3-4, the first optical fiber ring 16-1 is connected to the first Y-waveguide lithium niobate modulator 14-1 and then connected to the optical fiber output from the fifth rubber plug 3-5, the third detector 15-3 is connected to the optical fiber output from the sixth rubber plug 3-6, and the third optical fiber ring 16-3 is connected to the third Y-waveguide lithium niobate modulator 14-3 and then connected to the optical fiber output from the seventh rubber plug 3-7.

[0057] Specifically, the optical line connection of the three-axis integrated fiber optic gyroscope assembly refers to Figure 8 , the optical path working principle of this scheme:

[0058] The optical signal emitted by the SLD light source is transmitted from the first single-core polarization-maintaining fiber collimator 5-1 to the splitting surface of the first beam splitter 6-1, where reflection and transmission occur, wherein the reflected optical signal is transmitted to the splitting surface of the second beam splitter 6-2, and the transmitted optical signal is transmitted and coupled into the fifth single-core polarization-maintaining fiber collimator 5-5, and then the optical signal is transmitted into the input end of the first Y-waveguide lithium niobate modulator 14-1, and then transmitted from the output ends of the first modulator 14-1 into the two ends of the first optical fiber ring 16-1, and then cross-transmitted in the first optical fiber ring 16-1 and returned to the output ends of the first modulator 14-1, and then transmitted from the input end of the first modulator 14-1 into the fifth single-core polarization-maintaining fiber collimator 5-5, and then the optical signal is transmitted to the splitting surface of the first beam splitter 6-1, and the reflected optical signal is transmitted and coupled into the fourth single-core polarization-maintaining fiber collimator 5-4, and finally transmitted into the first detector 15-1;

[0059] Similarly, a part of the optical signal transmitted to the splitting surface of the second beam splitter 6-2 is reflected on the splitting surface of the third beam splitter 6-3, and a part is transmitted and coupled into the third single-core polarization-maintaining fiber collimator 5-3. The optical signal in the third single-core polarization-maintaining fiber collimator 5-3 is transmitted into the input end of the second Y-waveguide lithium niobate modulator 14-2, and then the optical signal is transmitted from the output ends of the second Y-waveguide lithium niobate modulator 14-2 into the two ends of the second optical fiber ring 16-2, and then returns to the output ends of the second Y-waveguide lithium niobate modulator 14-2 through cross transmission, and then is transmitted from the input end of the second Y-waveguide lithium niobate modulator 14-2 into the third single-core polarization-maintaining fiber collimator 5-3, and then transmitted to the splitting surface of the second beam splitter 6-2, and the reflected optical signal is transmitted and coupled into the second single-core polarization-maintaining fiber collimator 5-2, and finally transmitted into the second detector 15-2;

[0060] The optical signal reflected and transmitted to the splitting surface of the third beam splitter 6-3 will be transmitted and coupled into the seventh single-core polarization-maintaining fiber collimator 5-7, and then transmitted into the input end of the third Y-waveguide lithium niobate modulator 14-3, and then the optical signal is transmitted from the output ends of the fourth modulator 14-3 into the two ends of the third optical fiber ring 16-3, and after cross-transmission in the third optical fiber ring 16-3, it returns to the output ends of the third modulator 14-3, and then transmitted from the input end of the third modulator 14-3 into the quasi-seventh single-core polarization-maintaining fiber collimator 5-7, and then transmitted to the splitting surface of the third beam splitter 6-3, and reflected and coupled into the sixth single-core polarization-maintaining fiber collimator 5-6, and finally the optical signal is transmitted into the third detector 15-3;

[0061] In order to ensure that the optical signal power ultimately received by the first detector 15-1, the second detector 15-2, and the third detector 15-3 is similar and the signal is strong, this solution adopts a first beam splitter 6-1 with a splitting ratio of 55:45, a second beam splitter 6-2 with a splitting ratio of 61:39, and a third beam splitter 6-3 with a splitting ratio of 3:97, so that the three detectors can ultimately receive optical signals of about 20% of the light source's emission power; and the 1-to-6-way polarization-maintaining fiber beam splitter based on free-space integration of the present invention simplifies wiring and reduces volume, and can replace the existing technical solutions. Compared with the existing technology, it reduces the number of discrete devices in the branching solution, reduces the fusion points with external devices, reduces optical path losses, and reduces costs.

[0062] The above disclosure is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration, characterized in that: The invention comprises a structural part, an optical component and a rubber plug (3), wherein the structural part comprises a metal shell 2 and a metal upper cover (1) arranged on the metal shell (2), and the optical component comprises a substrate (7) arranged in the metal shell (2), three beam splitters (6) and seven single-core polarization-maintaining fiber collimators (5), wherein the substrate (7) is fixed in the metal shell (2), two of the three beam splitters (6) are arranged on one side of the substrate (7), and the other beam splitter is arranged on the other side of the substrate (7), and the two light-transmitting surfaces of the three beam splitters (6) are respectively coated with a beam splitting film and an anti-reflection film; The seven single-core polarization-maintaining fiber collimators (5) are respectively fixed on the substrate (7), and one of the single-core polarization-maintaining fiber collimators serves as an input end and faces one of the two symmetrical beam splitters, and the other six single-core polarization-maintaining fiber collimators serve as output ends and are respectively located on the outside of the three beam splitters (6) in a group of two. The rubber plugs (3) have seven holes respectively fixed on the outer wall openings of the metal shell (2), and the optical fibers of the seven single-core polarization-maintaining fiber collimators (5) respectively pass through the corresponding holes of the rubber plugs (3) and extend out of the metal shell (2).

2. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 1, characterized in that: The three beam splitters (6) have a beam splitting ratio ranging from 1% to 99%, and they are respectively a first beam splitter (6-1), a second beam splitter (6-2) and a third beam splitter (6-3); the first beam splitter (6-1) and the third beam splitter (6-3) are symmetrically arranged on the substrate (7).

3. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 2, characterized in that: The splitting ratio of the first beam splitter (6-1) is 55:45, the splitting ratio of the second beam splitter (6-2) is 61:39, and the splitting ratio of the third beam splitter (6-3) is 3:

97.

4. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 3, characterized in that: The incident angle range formed between the single-core polarization-maintaining optical fiber collimator (5-1) as the input end and the first beam splitter (6-1) is 0-90°.

5. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 4, characterized in that: The incident angle formed between the single-core polarization-maintaining optical fiber collimator (5-1) as the input end and the first beam splitter (6-1) is 13.5°.

6. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 5, characterized in that: The manufacturing method of the single-core polarization-maintaining optical fiber collimator (5) is as follows: after coupling the single-core polarization-maintaining optical fiber (10) with the collimating lens (9) through a reflector method or a light spot method, the single-core polarization-maintaining optical fiber (10) is fixed in a glass tube (8) by glue.

7. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 6, characterized in that: The manufacturing method of the single-core polarization-maintaining pigtail (10) is as follows: removing the coating layer from one end of a single polarization-maintaining optical fiber (4), inserting the end into a capillary (11) after cleaning and fixing it with glue, and then grinding and polishing the end face of the capillary (11) into an 8° bevel and coating it with an anti-reflection film.

8. The one-to-six-way polarization-maintaining fiber beam splitter based on free-space integration according to claim 6, characterized in that: The collimating lens (9) is a self-focusing lens or a spherical lens. Both light-transmitting surfaces of the collimating lens (9) are coated with anti-reflection films, and one of the light-transmitting surfaces is ground into an 8° inclined surface.

9. The method according to claim 1, characterized in that: The metal shell (2) and the metal upper cover (1) are fixed by glue.

10. An application of a 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration, using the 1-to-6-way polarization-maintaining fiber beam splitter based on free space integration according to any one of claims 1 to 9, characterized in that: Applicable to a three-axis integrated fiber optic gyroscope assembly, the optical structure of the three-axis integrated fiber optic gyroscope assembly comprises an SLD light source (12), a first Y-waveguide lithium niobate modulator (14-1), a second Y-waveguide lithium niobate modulator (14-2), a third Y-waveguide lithium niobate modulator (14-3), a first detector (15-1), a second detector (15-2), a third detector (15-3), a first fiber ring (16-1), a second fiber ring (16-2) and a third fiber ring (16-3), and the seven rubber plugs (3) of the 1-to-6-way polarization-maintaining fiber beam splitter are respectively a first rubber plug (3-1), a second rubber plug (3-2), a third rubber plug (3-3), a fourth rubber plug (3-4), a fifth rubber plug (3-5), a sixth rubber plug (3-6) and a seventh rubber plug (3-7); The SLD light source (12) is connected to the optical fiber output from the first rubber plug (3-1); the second detector (15-2) is connected to the optical fiber output from the second rubber plug (3-2); the second optical fiber ring (16-2) is connected to the second Y-waveguide lithium niobate modulator (14-2) and then connected to the optical fiber output from the third rubber plug (3-3); the first detector (15-1) is connected to the optical fiber output from the fourth rubber plug (3-4); the first optical fiber ring (16-1) is connected to the first Y-waveguide lithium niobate modulator (14-1) and then connected to the optical fiber output from the fifth rubber plug (3-5); the third detector (15-3) is connected to the optical fiber output from the sixth rubber plug (3-6); and the third optical fiber ring (16-3) is connected to the third Y-waveguide lithium niobate modulator (14-3) and then connected to the optical fiber output from the seventh rubber plug (3-7).

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