Three-axis integrated PLC coupler for fiber-optic gyroscope and fiber-optic three-axis gyroscope system

Abstract

This invention relates to a three-axis integrated PLC coupler for fiber optic gyroscopes, comprising a PLC beam splitter chip. The PLC beam splitter chip has three photodetector receiving ports, three integrated optical chip docking output ports, and a light source input port for receiving input light. The input light is output from the three integrated optical chip docking output ports, and the externally received light returning through the three integrated optical chip docking output ports is returned to the PLC beam splitter chip and coupled to the three photodetector receiving ports respectively. A fiber optic three-axis gyroscope system is also provided, comprising a light source, three integrated optical chips, and three photodetectors, and also including the aforementioned three-axis integrated PLC coupler for fiber optic gyroscopes. This invention enables integrated beam splitting and interference signal reception for three-axis gyroscopes, eliminating a large number of discrete couplers and fusion splices, reducing the number of discrete components, reducing device size, and lowering losses and reflection noise introduced by fusion splicing.

Description

Technical Field

[0001] This invention relates to the field of fiber optic gyroscope technology, specifically to a three-axis integrated PLC coupler for fiber optic gyroscopes and a fiber optic three-axis gyroscope system. Background Technology

[0002] In a fiber optic gyroscope (FOG) system, a three-axis gyroscope needs to simultaneously achieve beam splitting from three SLD light sources, receiving signals from multiple photodetectors via PIN-FETs, and interfacing the optical path of the MIOC integrated optical chip. Traditional solutions use multiple discrete couplers in combination, which has the following drawbacks:

[0003] 1. The number of discrete components is large, and a large number of optical fibers need to be spliced ​​between the components. The splice points introduce additional insertion loss and return reflection, resulting in large size and high assembly complexity.

[0004] 2. The dispersion of multi-path beam splitting and detection beams, inconsistent temperature drift of multiple devices, and poor zero-bias stability of the three-axis optical path directly degrade the gyroscope's core performance indicators such as angle random walk and zero-bias drift.

[0005] 3. The discrete couplers are independent of each other, with numerous fiber optic cables, and the devices have poor vibration and shock resistance, which cannot meet the harsh military-grade environment of wide temperature range and strong vibration of gyroscopes.

[0006] 4. Existing integrated coupler solutions have unreasonable port allocation, which cannot simultaneously accommodate SLD light source input, multi-channel PIN-FET detector reception, and multi-channel MIOC chip optical path input and output. The packaging stress control is poor, the insertion loss varies greatly under high and low temperature environments, the splitting ratio drift is large, the PDL index deteriorates, and the overall performance of the gyroscope is restricted. Summary of the Invention

[0007] The purpose of this invention is to provide a three-axis integrated PLC coupler for fiber optic gyroscopes and a fiber optic three-axis gyroscope system, which can at least solve some of the defects in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a three-axis integrated PLC coupler for fiber optic gyroscopes, comprising a PLC beam splitter chip. The PLC beam splitter chip has three photodetector receiving ports, three integrated optical chip docking output ports, and a light source input port for receiving input light. The input light is output from the three integrated optical chip docking output ports respectively. Externally received light is transmitted back to the PLC beam splitter chip through the three integrated optical chip docking output ports respectively, and coupled to the three photodetector receiving ports respectively.

[0009] Furthermore, the first waveguide end face of the PLC beam splitter chip is provided with four ports, which are the light source input port and the three photodetector receiving ports, respectively.

[0010] Furthermore, the first waveguide end face is connected to a four-core fiber array, and the four fibers of the four-core fiber array are respectively connected to the light source input port and the three photodetector receiving ports.

[0011] Furthermore, the four-core fiber array is bonded to the end face of the first waveguide.

[0012] Furthermore, the second waveguide end face of the PLC beam splitter chip is provided with three ports, which are the three docking output ports of the integrated optical chip.

[0013] Furthermore, the second waveguide end face is connected to a three-core fiber array, and the three fibers of the three-core fiber array are respectively connected to the output ports of the three integrated optical chips.

[0014] Furthermore, the three-core fiber array is bonded to the end face of the second waveguide.

[0015] Furthermore, it also includes a protective casing for housing the PLC beam splitter chip.

[0016] Furthermore, the two ends of the protective shell are sealed with sealing elements.

[0017] This invention provides another technical solution: a fiber optic three-axis gyroscope system, including a light source, three integrated optical chips, and three photodetectors, and also including the aforementioned three-axis integrated PLC coupler for the fiber optic gyroscope. The input light from the light source enters through the input port of the light source and passes through the output ports of the three integrated optical chips to enter the three integrated optical chips respectively. The interference light signals returned by the three integrated optical chips are respectively transmitted back to the PLC beam splitter through the output ports of the three integrated optical chips, and are respectively coupled to the receiving ports of the three photodetectors, and then output to the three photodetectors.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: by using a PLC beam splitter chip with seven ports, the light source beam splitter optical path, the detector receiving optical path, and the MIOC output optical path are integrated on a single chip, and the optical transmission path is set, which can realize the integration of beam splitting of the three-axis gyroscope light source and interference signal reception. This eliminates a large number of discrete couplers and fusion splices, reduces the number of discrete components, reduces the size of the components, and reduces the loss and reflection noise introduced by the fusion splice. Moreover, all optical paths are integrated into the same PLC beam splitter chip, the three beam splitter optical paths share a common substrate, the temperature environment is completely consistent, the beam splitting ratio, insertion loss, and temperature drift of the three paths are consistent, which greatly improves the zero-bias stability of the three-axis gyroscope optical path. Attached Figure Description

[0019] Figure 1 An exploded view of a three-axis integrated PLC coupler for a fiber optic gyroscope, provided in an embodiment of the present invention;

[0020] Figure 2 A cross-sectional structural diagram of a three-axis integrated PLC coupler for a fiber optic gyroscope provided in an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of a PLC beam splitter chip for a three-axis integrated PLC coupler for a fiber optic gyroscope, provided for an embodiment of the present invention;

[0022] In the attached diagram, the following labels are used: 1-PLC splitter chip; 2-four-core fiber array; 3-three-core fiber array; 4-sealing component; 5-protective shell; 6-light source; 7-first photodetector; 8-second photodetector; 9-third photodetector; 10-first integrated optical chip; 11-second integrated optical chip; 12-third integrated optical chip; 13-fiber ring. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1 , Figure 2 and Figure 3This invention provides a three-axis integrated PLC coupler for fiber optic gyroscopes, including a PLC beam splitter chip 1. The PLC beam splitter chip 1 has three photodetector receiving ports, three integrated optical chip docking output ports, and a light source input port for receiving input light. The input light is output from the three integrated optical chip docking output ports respectively. The externally received light is transmitted back to the PLC beam splitter chip 1 through the three integrated optical chip docking output ports respectively, and is coupled to the three photodetector receiving ports respectively. In this embodiment, by employing a seven-port PLC beam splitter chip 1, the light source beam splitting path, detector receiving path, and MIOC output path are monolithically integrated, and the optical transmission path is set. This enables the integration of three-axis gyroscope light source beam splitting and interference signal reception, eliminating a large number of discrete couplers and fusion splices, reducing the number of discrete components, decreasing device size, and lowering losses and reflection noise introduced by fusion splicing. Moreover, since all optical paths are integrated into the same PLC beam splitter chip 1, the three beam splitting paths share a common substrate, ensuring a completely consistent temperature environment. This results in good consistency in the beam splitting ratio, insertion loss, and temperature drift of the three paths, greatly improving the zero-bias stability of the three-axis gyroscope optical path. Specifically, in traditional fiber optic three-axis coupling systems, to simultaneously achieve beam splitting of three SLD light sources, reception of multiple PIN-FET signals from photodetectors, and optical path docking of the MIOC integrated optical chip, multiple discrete couplers are mostly used. However, this approach faces many drawbacks. This embodiment ingeniously improves the PLC beam splitter chip 1 by integrating a 1×3 beam splitter optical path within it. A total of seven ports are designed, and the light source beam splitter optical path, detector receiving optical path, and MIOC output optical path are monolithically integrated. After setting the optical path of each port, the beam splitter of the three-axis gyroscope light source and the interference signal receiving can be integrated, eliminating a large number of discrete couplers and fusion splices, reducing the number of discrete components, and reducing the size of the device.For ease of description, the three photodetector receiving ports are defined as the first photodetector receiving port, the second photodetector receiving port, and the third photodetector receiving port, respectively. The three integrated optical chip output ports are also defined as the first integrated optical chip output port, the second integrated optical chip output port, and the third integrated optical chip output port, respectively. Input light from the light source input port is output through the first, second, and third integrated optical chip output ports, respectively. Received light from the outside is transmitted back through the first, second, and third integrated optical chip output ports, respectively, to the PLC beam splitter chip 1, and then coupled to the first, second, and third photodetector receiving ports. This allows one PLC beam splitter chip 1 to achieve three optical path connections. When this fiber optic gyroscope is used with a three-axis integrated PLC coupler in a fiber optic three-axis gyroscope system, the system can achieve three-way SLD light source beam splitting, multi-channel photodetector PIN-FET signal reception, and MIOC using only one coupler. The integrated optical chip optical path docking avoids several defects caused by the traditional combination of multiple discrete couplers to achieve the function.

[0025] Please see Figure 1 , Figure 2 and Figure 3 The PLC beam splitter chip 1 has four ports on its first waveguide end face, which are the light source input port and three photodetector receiving ports, respectively. A four-core fiber array 2 is connected to the first waveguide end face, and the four fibers of the four-core fiber array 2 are respectively connected to the light source input port and the three photodetector receiving ports. The four-core fiber array 2 is bonded to the first waveguide end face. The PLC beam splitter chip 1 has three ports on its second waveguide end face, which are the three integrated optical chip docking output ports, respectively. A three-core fiber array 3 is connected to the second waveguide end face, and the three fibers of the three-core fiber array 3 are respectively connected to the three integrated optical chip docking output ports, respectively. The three-core fiber array 3 is bonded to the second waveguide end face. In this embodiment, the two waveguide end faces of the PLC beam splitter chip 1 each have multiple ports. For ease of description, the first waveguide end face and the second waveguide end face are defined. Specifically, four ports are designed on the first waveguide end face, which are the light source input port, the first photodetector receiving port, the second photodetector receiving port, and the third photodetector receiving port, respectively corresponding to… Figure 3Ports 3, 1, 2, and 4 are located on the first waveguide. The second waveguide endface has three ports: the first integrated optical chip docking output port, the second integrated optical chip docking output port, and the third integrated optical chip docking output port, corresponding to... Figure 3 Ports 5, 6, and 7 are used in the optical path design. Input light enters through port 3, passes through PLC beam splitter 1, and is then split and output from ports 5, 6, and 7. This process is the output light. Received light comes from the integrated optical chips. The light from the reverse return chip of one integrated optical chip (defined as the first integrated optical chip 10) passes through port 5 and is coupled to ports 1 and 3 respectively. The light from the reverse return chip of another integrated optical chip (defined as the second integrated optical chip 11) passes through port 6 and is coupled to ports 2 and 3 respectively. Finally, the light from the reverse return chip of the first integrated optical chip (defined as the third integrated optical chip 12) passes through port 7 and is coupled to ports 3 and 4 respectively. In this way, a single PLC beam splitter 1 can achieve the same technical effect as multiple discrete couplers used in traditional technology. Preferably, in the PLC beam splitter chip 1, the channels corresponding to each port are isolated, specifically in adjacent channels. This avoids optical crosstalk between adjacent channels. The isolation design can adopt a Rowland circle layout, utilizing the aberration-correcting optical properties of the Rowland circle to achieve beam splitting and focusing in the free propagation area of ​​the flat plate. This allows different wavelengths of light to be accurately separated into each output waveguide, achieving wavelength division multiplexing / demultiplexing. It also reduces insertion loss and channel crosstalk, thus achieving the purpose of isolation. Preferably, the three integrated optical chips have a Y-type waveguide structure. Using a Y-type waveguide structure, the light from ports 5, 6, and 7 can be split into two beams and their polarization states adjusted. After passing through the fiber optic ring 13, a phase difference is formed, resulting in a time difference in reception by the three photodetectors. Light within a single fiber will not interfere or conflict. The integrated optical chip outputs two beams, one clockwise and one counterclockwise, propagating in opposite directions within the fiber optic ring 13. When the gyroscope housing rotates, a slight difference in the optical path length of the two beams occurs, generating a Sagnac phase. The phase difference is proportional to the angular velocity Ω, the total length of the fiber L, and the area A enclosed by the loop. The longer the optical fiber and the larger the loop area, the stronger the Sagnac phase signal and the higher the gyroscope sensitivity. Preferably, an isolation structure is set on the optical path between the light source input port and the light source 6, or on the channel corresponding to port 3 in the PLC beam splitter chip 1, to prevent the returned light from entering the light source 6 and damaging it. This isolation structure uses a coated glass sheet or a unidirectional online isolator, both of which can serve an isolation function. Preferably, the first waveguide end face and the four-core fiber array 2 are bonded together with UV adhesive using low-stress coupling, and the second waveguide end face and the three-core fiber array 3 are bonded together with UV adhesive using low-stress coupling.

[0026] Please see Figure 1 , Figure 2 and Figure 3The three-axis integrated PLC coupler for this fiber optic gyroscope also includes a protective shell 5 for housing the PLC beam splitter chip 1. In this embodiment, the protective shell 5 can be made of stainless steel square tubing. The PLC beam splitter chip 1 is located at the center inside the protective shell 5. Then, the three-core fiber array 3 and the four-core fiber array 2 are respectively located on both sides of the PLC beam splitter chip 1, and both are also located inside the protective shell 5, receiving protection from the protective shell 5. Then, the two ends of the protective shell 5 are sealed with sealing materials 4. The sealing materials 4 can be made of sealing soft glue, which can play a stress buffering role for the internal fiber array and the PLC beam splitter chip 1. At the same time, the fiber can release stress by passing through the soft glue. Specifically, the UV glue used to couple the three-core fiber array 3, the four-core fiber array 2 and the PLC beam splitter chip 1 is a low-shrinkage, low-CTE optical UV glue. The glue application position avoids the effective waveguide light transmission area. The glue only acts on the edge of the fiber array base to avoid the glue stress being transmitted to the waveguide coupling surface. The sealing adhesive is an elastic buffer silicone that does not directly apply rigid compression to the fiber optic array, thus releasing fiber stress, suppressing stress birefringence at high and low temperatures, and reducing device PDL and splitting ratio drift. The internal fibers of the three-core fiber array 3 and the four-core fiber array 2 are single-mode fibers. The stainless steel square tube outer shell is a rectangular thin-walled stainless steel sleeve, used only for protection. A gap is left between the inner wall of the sleeve and the internal fiber optic array and PLC chip, preventing the sleeve from directly compressing the internal optical components and avoiding stress transmission caused by shell deformation. Thus, employing a low-stress FA-PLC coupling process, coupled with elastic sealing soft rubber at both ends for stress buffering, and with the stainless steel shell not directly compressing the internal optical components, it can effectively suppress birefringence caused by packaging stress. The device has a low PDL, a high and low temperature loss variation TDL ≤ 0.3dB, and a splitting ratio variation rate ≤ 2%, meeting the wide-temperature operating specifications of laser gyroscopes. The ports are specifically defined for three-axis laser gyroscope systems. Port 3 is specifically connected to the SLD light source 6, ports 1 / 2 / 4 are connected to three photodetectors (PIN-FET), and ports 5 / 6 / 7 are connected to three MIOCs (integrated optical chips). The device can be directly assembled into a gyroscope from the factory without the need for additional fiber optic jumpers to modify the circuit, improving gyroscope assembly efficiency. The overall device size is small, with a shell size of only 16.0×3.7mm. The sealed structure has strong vibration and shock resistance, achieving low insertion loss, low loss variation, and high splitting ratio stability. It is suitable for the wide-temperature operating environment of -45℃ to +85℃ for three-axis laser gyroscope systems and the harsh environment of military gyroscopes.

[0027] Please see Figures 1 to 3This invention provides a fiber optic three-axis gyroscope system, including a light source 6, three integrated optical chips, and three photodetectors. It also includes the aforementioned three-axis integrated PLC coupler for fiber optic gyroscopes. The input light from the light source 6 enters through the input port of the light source and passes through the output ports of the three integrated optical chips, respectively entering the three integrated optical chips. The interference light signals returned from the three integrated optical chips are respectively transmitted back through the output ports of the three integrated optical chips to the PLC beam splitter 1, and then coupled to the receiving ports of the three photodetectors, and finally output to the three photodetectors. In this embodiment, the three integrated optical chips are a first integrated optical chip 10, a second integrated optical chip 11, and a third integrated optical chip 12, and the three photodetectors are a first photodetector 7, a second photodetector 8, and a third photodetector 9. Using the aforementioned three-axis integrated PLC coupler for fiber optic gyroscopes in the fiber optic three-axis gyroscope system allows for the splitting of three SLD light sources, the reception of PIN-FET signals from multiple photodetectors, and the optical path docking of MIOC integrated optical chips with a single coupler, offering significant advantages compared to conventional methods that only use discrete couplers.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A three-axis integrated PLC coupler for fiber optic gyroscopes, characterized in that: The device includes a PLC beam splitter chip, which has three photodetector receiving ports, three integrated optical chip docking output ports, and a light source input port for receiving input light. The input light is output from the three integrated optical chip docking output ports respectively, and the externally received light is transmitted back to the PLC beam splitter chip through the three integrated optical chip docking output ports respectively, and coupled to the three photodetector receiving ports respectively.

2. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 1, characterized in that: The first waveguide end face of the PLC beam splitter chip has four ports, which are the light source input port and the three photodetector receiving ports.

3. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 2, characterized in that: The first waveguide end face is connected to a four-core fiber array, and the four fibers of the four-core fiber array are respectively connected to the light source input port and the three photodetector receiving ports.

4. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 3, characterized in that: The four-core fiber array is bonded to the end face of the first waveguide.

5. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 1, characterized in that: The second waveguide end face of the PLC beam splitter chip has three ports, which are the output ports of the three integrated optical chips.

6. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 5, characterized in that: The second waveguide end face is connected to a three-core fiber array, and the three fibers of the three-core fiber array are respectively connected to the docking output ports of the three integrated optical chips.

7. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 6, characterized in that: The three-core fiber array is bonded to the end face of the second waveguide.

8. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 1, characterized in that: It also includes a protective housing for housing the PLC beam splitter chip.

9. The three-axis integrated PLC coupler for fiber optic gyroscopes as described in claim 8, characterized in that: The protective shell is sealed at both ends with sealing elements.

10. A fiber optic three-axis gyroscope system, comprising a light source, three integrated optical chips, and three photodetectors, characterized in that: It also includes a three-axis integrated PLC coupler for fiber optic gyroscopes as described in any one of claims 1-9, wherein the input light from the light source enters through the input port of the light source and passes through the output ports of the three integrated optical chips to enter the three integrated optical chips respectively, and the interference light signals returned by the three integrated optical chips are respectively transmitted back to the PLC beam splitter through the output ports of the three integrated optical chips respectively, and are respectively coupled to the receiving ports of the three photodetectors, and then output to the three photodetectors.

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