Cooperative communication and sensing optical transmission system based on elliptical core few-mode fiber

Abstract

The invention provides a cooperative communication and sensing optical transmission system based on an elliptical core few-mode optical fiber. The system comprises a transmitting end, the elliptical core few-mode optical fiber and a receiving end. The transmitting end converts a digital signal into a mode encoding sequence through a mode encoder and couples the mode encoding sequence into the elliptical core few-mode optical fiber; the elliptical core few-mode optical fiber effectively reduces crosstalk between modes by utilizing a relatively large effective refractive index difference between different mode groups of the elliptical core few-mode optical fiber, and effectively improves the security of information transmission by utilizing a mode coding mode; the receiving end detects the position of the end face of the output optical fiber through an imaging system and a camera, compensates the position of the end face of the optical fiber through an electric displacement table to improve the mode demodulation performance of the receiving end, and recovers a mode coding sequence into original digital information through a mode decoder and a signal processor. According to the invention, the security of the optical fiber communication system can be effectively improved, crosstalk between modes is reduced, the robustness of mode demodulation of the receiving end is increased, and the performance of the space division multiplexing optical fiber communication system is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical fields of optical fiber communication and optical sensing, and particularly relates to an optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber. Background Art

[0002] Optical sensing and optical fiber communication are studied around multiple physical dimensions of the optical field, mainly including amplitude, phase, polarization, time, frequency, wavelength, etc., and have become two major application directions in the optical field. In recent years, with the development of technologies such as 5G, optical interconnection in data centers, and the Internet of Things, the sharp increase in communication data volume has gradually brought the traditional optical fiber communication technology to the communication capacity bottleneck. To solve the communication capacity bottleneck problem, the optical fiber communication system can utilize the transverse spatial dimension of the optical field in addition to the traditional physical dimensions of the optical field to further increase the transmission capacity in the optical fiber, which is called the space division multiplexing (SDM) technology.

[0003] In the optical fiber communication system based on SDM, many studies mainly focus on few-mode fibers or multi-mode fibers. The effective refractive index difference between different mode groups of this kind of fiber is small, and the modes between different mode groups are prone to mutual coupling when multiplexed and transmitted in the optical fiber, resulting in a large inter-mode crosstalk. Therefore, multi-input multi-output digital signal processing technology is required to equalize different multiplexing modes and reduce inter-mode crosstalk. However, this digital signal processing technology will increase the electrical domain complexity at the transmitting and receiving ends and increase the system power consumption. On the other hand, in the optical fiber communication system based on SDM, many studies mainly use multiplexing multiple modes to improve the communication system capacity, and the loading of digital information is still achieved by modulating traditional dimensions such as the amplitude and phase of the optical field. This digital information modulation method is easy to be eavesdropped by eavesdroppers on the transmission link of the optical fiber communication system. The eavesdropper only needs to intercept the optical field and restore the amplitude and phase modulation information of the optical field into an electrical signal through a detector to easily obtain the original digital information. In addition, the optical fiber communication system based on SDM also needs to demodulate multiple modes multiplexed in the optical fiber at the receiving end, and a high coupling and alignment characteristic between the optical fiber and the demodulation device is required during demodulation. Once a large deviation occurs in this coupling and alignment, the demodulation characteristic and communication performance of the system will be greatly reduced. Therefore, it is of great significance to study an SDM optical transmission system with low inter-mode crosstalk, high security, and both communication and sensing functions. Summary of the Invention

[0004] The object of the present invention is to provide an optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber, which can convert digital signals into a mode encoding sequence at the transmitting end and couple it into the elliptical core few-mode fiber for transmission. By utilizing the large effective refractive index difference between different mode groups of the elliptical core few-mode fiber, the crosstalk between modes can be effectively reduced. At the receiving end, an imaging system and a camera are used to detect the position of the output fiber end face, and an electric displacement stage is used to compensate the position of the fiber end face to improve the mode demodulation performance at the receiving end. The specific technical solutions are as follows:

[0005] An optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber, the system includes a transmitting end, an elliptical core few-mode fiber and a receiving end. The transmitting end is used to generate a laser beam and perform mode encoding modulation on it, and couple the modulated mode encoding sequence into the elliptical core few-mode fiber. The elliptical core few-mode fiber is used to support the transmission of multiple mode groups. The receiving end is used to receive the mode encoding sequence in the elliptical core few-mode fiber and perform mode position detection and signal restoration on it to obtain the original digital information.

[0006] Further, the transmitting end includes a laser, a mode encoder connected to the output end of the laser, and a coupler connected to the output end of the mode encoder. The laser is used to generate and emit a collimated fundamental mode Gaussian beam. The mode encoder is used to map the original digital information onto multiple high-order laser modes through mode encoding modulation to obtain a mode encoding sequence transmitted in free space. The coupler is used to couple the mode encoding sequence transmitted in free space into the elliptical core few-mode fiber.

[0007] Further, the mode encoder converts the original m-ary digital sequence into an m-ary mode encoding sequence by switching the phase diagram for modulating the fundamental mode Gaussian beam.

[0008] Further, different characters of each symbol in the original m-ary digital sequence have specific corresponding phase diagrams. Each of the phase diagrams modulates the fundamental mode Gaussian beam to generate a beam of a specific mode. Each of the beams of specific modes excites modes in a specific mode group in the elliptical core few-mode fiber. The m-ary characters of each symbol correspond to m mode groups in the elliptical core few-mode fiber.

[0009] Further, the elliptical core few-mode fiber includes a circular cladding structure on the outermost layer, an elliptical annular low refractive index core structure in the middle layer, and an elliptical high refractive index core structure in the innermost layer. The refractive index of the elliptical high refractive index core structure is greater than the refractive index of the circular cladding structure, and the refractive index of the circular cladding structure is greater than the elliptical annular low refractive index core structure, so as to support multiple mode groups with a high effective refractive index difference.

[0010] Further, the receiving end includes an electric displacement stage, a beam splitter, an imaging lens group, a camera, a coupler, a mode decoder, and a signal processor;

[0011] The electric displacement stage is used to fix and control the position of the output fiber end face of the elliptical core few-mode fiber;

[0012] The beam splitter is used to divide the divergent beam from the output fiber end face of the elliptical core few-mode fiber into two beams according to the power ratio;

[0013] The imaging lens group is used to image one of the two beams onto the camera;

[0014] The camera is used to detect and analyze the light spot of the beam to obtain the position information of the output fiber end face of the elliptical core few-mode fiber;

[0015] The coupler is used to couple the other of the two beams into the mode decoder;

[0016] The mode decoder is used to perform mode recognition and optoelectronic conversion on the mode encoding sequence, and convert the optical signal into an electrical signal;

[0017] The signal processor is used to restore the electrical signal to obtain the original digital information.

[0018] Further, in the mode decoder, a beam splitter, m reverse phase diagrams, and m optoelectronic detectors are sequentially arranged according to the transmission direction when the m-ary mode encoding sequence enters, and the m-ary mode encoding sequence is converted into m electrical signals after being transmitted forward through the mode decoder.

[0019] Further, the camera determines the initial center position of the camera field of view through the maximum value of the current output by the optoelectronic detector in the mode decoder.

[0020] Further, the camera determines the positions of the x-axis and y-axis of the output fiber end face of the elliptical core few-mode fiber by identifying that the geometric center of the beam deviates from the initial center position of the camera field of view, determines the position of the z-axis of the output fiber end face of the elliptical core few-mode fiber by identifying the size of the beam envelope, and determines the rotation angle of the output fiber end face of the elliptical core few-mode fiber by identifying the angle between the major axis or minor axis of the beam and the x-axis.

[0021] Further, the output end of the camera is connected to the electric displacement stage to form a feedback control loop, and the camera sends the measured positions of the x-axis, y-axis, and z-axis and the rotation angle of the output fiber end face of the elliptical core few-mode fiber to the electric displacement stage, causing the electric displacement stage to move in the reverse direction.

[0022] The optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention has the following beneficial effects compared with the prior art:

[0023] 1. The optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention can simultaneously perform digital information transmission and measure the position of the output fiber end face of the elliptical-core few-mode fiber, combining the functions of communication and sensing.

[0024] 2. The optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention uses mode-encoding modulation for digital information transmission, which has higher security compared with the traditional modulation method using the amplitude and phase dimensions of the optical field and is not easily eavesdropped by eavesdroppers.

[0025] 3. The optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention effectively increases the effective refractive index difference between different mode groups. The modes of different mode groups will not couple with each other during transmission in the elliptical-core few-mode fiber and effectively reduce mode crosstalk, effectively reducing the complexity of digital signal processing at the sending and receiving ends.

[0026] 4. The optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention measures the position of the output fiber end face of the elliptical-core few-mode fiber through a camera at the receiving end, and adjusts the position of the output fiber end face of the few-mode fiber through a feedback loop and an electric displacement stage, so that the mode decoder at the receiving end remains in the optimal working state, improving the robustness of the receiving-end system performance. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of the optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention;

[0028] Figure 2 is the refractive index distribution diagram of the elliptical-core few-mode fiber in the embodiment of the present invention;

[0029] Figure 3 is a schematic structural diagram of the mode encoder and mode decoder of the optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode fiber proposed by the present invention;

[0030] Figure 4 is a schematic diagram of measuring the position of the output fiber end face and the camera receiving the light spot map at the receiving end in the embodiment of the present invention;

[0031] Figure 5 is the experimental test result diagram of transmitting information through the mode-encoding sequence and measuring the position of the fiber end face at the receiving end in the embodiment of the present invention. Detailed Embodiments

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings provided by the present invention. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the objectives of the embodiments of the present invention.

[0033] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connection" and "connection" shall be interpreted in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral one; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium. It may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] In the description of the present invention, the orientation or positional relationships such as "upper", "lower", "left", "right", "front", "rear", "center", "horizontal", "vertical", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings, only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0035] Embodiment: Refer to Figure 1 As shown, this embodiment provides an optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber. The system includes a transmitting end, an elliptical core few-mode fiber connected to the output end of the transmitting end, and a receiving end connected to the output end of the elliptical core few-mode fiber. The transmitting end is used to generate a laser beam and perform mode encoding modulation on the laser beam, and couple the modulated mode encoding sequence into the elliptical core few-mode fiber. The core refractive index of the elliptical core few-mode fiber is elliptically distributed and is used to support the transmission of multiple mode groups; the receiving end is used to receive the mode encoding sequence in the elliptical core few-mode fiber and perform mode position detection and signal restoration on it to obtain the original digital information.

[0036] In a specific embodiment of the present invention, the transmitting end includes a laser, a mode encoder, and a coupler. The input end of the mode encoder is connected to the output end of the laser, the input end of the coupler is connected to the output end of the mode encoder, and the output end of the coupler is connected to the input fiber end face of the elliptical core few-mode fiber. The laser is used to generate and emit a collimated fundamental mode Gaussian beam in the C band. The mode encoder is used to map the binary original digital information to two laser modes through mode encoding modulation to obtain a mode encoding sequence transmitted in free space. The coupler is a high-power objective lens and is used to couple the mode encoding sequence transmitted in free space into the elliptical core few-mode fiber.

[0037] In a specific embodiment of the present invention, referring to Figure 2 as shown, the elliptical core few-mode fiber includes a circular cladding structure in the outermost layer, an elliptical annular low-index core structure in the middle layer, and an elliptical high-index core structure in the innermost layer. The radius of the circular cladding structure is 61.4 μm, the width of the elliptical annular low-index core structure is 10 μm, and the major axis and minor axis lengths of the elliptical high-index core structure are 7.6 μm and 4.9 μm, respectively. The refractive indices of the three are such that the elliptical high-index core structure > the circular cladding structure > the elliptical annular low-index core structure. The refractive index of the elliptical high-index core structure is 0.47% higher than that of the circular cladding structure, and the refractive index of the elliptical annular low-index core structure is 0.63% lower than that of the circular cladding structure. This elliptical core few-mode fiber supports 2 mode groups, and the effective refractive index difference between its LP01 mode and LP11 a mode is 2.23×10 -3 , and the length of the elliptical core few-mode fiber can be 1.1 km.

[0038] In a specific embodiment of the present invention, the receiving end includes an electric displacement stage, a beam splitter, an imaging lens group, a camera, a coupler, a mode decoder, and a signal processor. The electric displacement stage is used to fix and control the position of the output fiber end face of the elliptical core few-mode fiber, and can translate the output fiber end face along the x-axis, y-axis, and z-axis, and control the rotation angle θ of the output fiber end face; the beam splitter is used to split the divergent beam from the output fiber end face of the elliptical core few-mode fiber into two beams according to a specific power ratio. The imaging lens group images one of the beams onto the camera. The camera detects and analyzes the spot of the captured beam to obtain the x-axis, y-axis, z-axis positions and rotation angle θ information of the output fiber end face of the elliptical core few-mode fiber. At the same time, the output end of the camera is connected to the electric displacement stage to form a feedback control loop with the electric displacement stage, and sends the measured x-axis, y-axis, z-axis positions and rotation angle θ information of the output fiber end face of the elliptical core few-mode fiber to the electric displacement stage, so that the electric displacement stage moves in the reverse direction according to the measured position and rotation angle information to ensure that the output fiber end face of the elliptical core few-mode fiber and the mode decoder work in the best coupling state. The coupler is an objective lens or a lens group, its input end is connected to the output end of the beam splitter, and its output end is connected to the mode decoder. The coupler is used to couple the other beam into the mode decoder. The mode decoder performs mode recognition and optoelectronic conversion on the mode coding sequence, converts the optical signal into an electrical signal, and the signal processor restores the electrical signal to obtain the original digital information.

[0039] Referring to Figure 3As shown in the figure, it is a schematic structural diagram of a mode encoder and a mode decoder. In the mode encoder, two phase diagrams are provided in the transmission direction of the fundamental mode Gaussian beam. After passing through the mode encoder, the fundamental mode Gaussian beam is converted from the original binary digital sequence into a binary mode encoding sequence. In the mode decoder, a beam splitter, two reverse phase diagrams, and two photodetectors are sequentially arranged in the transmission direction when the binary mode encoding sequence enters. After the binary mode encoding sequence passes through the mode decoder in the forward direction, it is converted into two electrical signals.

[0040] The specific working process and working principle of the optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber provided in this embodiment are specifically as follows:

[0041] The laser generates and emits a collimated fundamental mode Gaussian beam in the C band. The mode encoder converts the original binary digital sequence into a binary mode encoding sequence by switching the phase diagram for modulating the fundamental mode Gaussian beam. Each different character of each symbol in the original binary digital sequence has a specific corresponding phase diagram. The symbol character 0 corresponds to the phase plate of the fundamental mode Gaussian beam generating an elliptical envelope, and the symbol character 1 corresponds to the phase plate of the Hermite Gaussian beam HG01 generating an elliptical envelope, obtaining a mode encoding sequence transmitted in free space. The coupler couples the mode encoding sequence transmitted in free space into the elliptical core few-mode fiber.

[0042] The mode encoding sequence is transmitted in the elliptical core few-mode fiber. The fundamental mode Gaussian beam with an elliptical envelope excites the LP01 mode in the elliptical core few-mode fiber, and the Hermite Gaussian beam HG01 with an elliptical envelope excites the LP11a mode in the elliptical core few-mode fiber, and finally outputs from the elliptical core few-mode fiber.

[0043] The beam splitter divides the beam at the output fiber end face of the divergent elliptical core few-mode fiber into two beams according to a specific power ratio. One of the beams enters the mode decoder through the coupler. In the mode decoder, the two reverse phase diagrams can convert each mode to be detected into a fundamental mode Gaussian beam and convert it into a high level through a single-mode fiber in the photodetector, and convert each mode that does not need to be detected into a hollow beam and convert it into a low level through a single-mode fiber in the photodetector. The LP01 mode and LP11a mode in the elliptical core few-mode fiber will be respectively converted into an elliptical envelope fundamental mode Gaussian beam and a Hermite Gaussian beam HG01 in free space before entering the mode decoder. The elliptical envelope fundamental mode Gaussian beam and the Hermite Gaussian beam HG01 are respectively converted into a fundamental mode Gaussian beam and a hollow beam after passing through the upper reverse phase diagram; the elliptical envelope fundamental mode Gaussian beam and the Hermite Gaussian beam HG01 are respectively converted into a hollow beam and a fundamental mode Gaussian beam after passing through the lower reverse phase diagram. The two photodetectors on the upper and lower paths simultaneously output two binary electrical signal sequences and are restored to the original binary digital sequence through signal processing.

[0044] Another beam of light is imaged onto a camera through an imaging lens group. The camera detects and analyzes the light spot of this beam, and the position of the output fiber end face of the elliptical-core few-mode fiber along the x-axis, y-axis, and z-axis and the rotation angle θ of the end face can be obtained. Refer to Figure 4 As shown, the camera determines the positions of the x-axis and y-axis of the output fiber end face of the elliptical-core few-mode fiber by identifying that the geometric center of the captured beam deviates from the initial center position of the camera's field of view, determines the position of the z-axis of the output fiber end face of the elliptical-core few-mode fiber by identifying the size of the envelope of the captured beam, and determines the rotation angle θ of the output fiber end face of the elliptical-core few-mode fiber by identifying the angle between the major axis of the captured beam and the x-axis. Among them, the initial center position of the camera's field of view is determined by the maximum value of the output current of the photodetector in the mode decoder. At the same time, the camera and the electric displacement stage form a feedback control loop, and the measured positions of the x-axis, y-axis, and z-axis and the rotation angle θ of the output fiber end face of the elliptical-core few-mode fiber are sent to the electric displacement stage, and it is made to move in the reverse direction according to the measured positions and rotation angle, ultimately ensuring that the output fiber end face and the mode decoder work in the best coupling state.

[0045] The image information transmitted by this optical transmission system can be restored losslessly at the receiving end. Refer to Figure 5 As shown, where Figure 5 (b)-(d) show the experimental results of the system measuring the displacements of the output fiber end face of the elliptical-core few-mode fiber along the x-axis, y-axis, and z-axis. The displacement range is from -100 μm to 100 μm, and the displacement movement interval is 10 μm. It can be seen that the measured displacement values of the system coincide with the set displacement values. The measurement errors of the displacements in the x-axis and y-axis directions are within ±2 μm, and the measurement error of the displacement in the z-axis direction is about ±2.3 μm; Figure 5 (f) shows the test results of the x-axis direction displacement of the system under the bending condition of the elliptical-core few-mode fiber with a radius of 5 mm. The experimental results show that the measurement results under the bending state of the elliptical-core few-mode fiber are consistent with the measurement results under the non-bending state, indicating the low-mode crosstalk characteristics between different mode groups of the elliptical-core few-mode fiber; Figure 5 (e) shows the experimental results of the system measuring the rotation angle θ of the output fiber end face of the elliptical-core few-mode fiber. The rotation range of the rotation angle θ is from -90° to 90°, and the measurement error of the rotation angle is within ±1.5°.

[0046] Those skilled in the art of this technology should understand that the present invention can be implemented in many other specific forms without departing from the spirit and scope of the present invention. Based on the embodiments in the present invention, any changes and modifications made by those of ordinary skill in the field of the present invention according to the above disclosure shall fall within the protection scope of the claims.

Claims

1. An optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber, characterized in that: The system includes a transmitting end, an elliptical-core few-mode fiber, and a receiving end. The transmitting end is used to generate a laser beam and perform mode-encoding modulation on it, and couple the modulated mode-encoding sequence into the elliptical-core few-mode fiber. The elliptical-core few-mode fiber is used to support the transmission of multiple mode groups. The receiving end is used to receive the mode-encoding sequence in the elliptical-core few-mode fiber and perform mode-position detection and signal restoration on it to obtain the original digital information.

2. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode optical fiber according to claim 1, characterized in that: The transmitting end includes a laser, a mode encoder connected to the output end of the laser, and a coupler connected to the output end of the mode encoder. The laser is used to generate and emit a collimated fundamental-mode Gaussian beam. The mode encoder is used to map the original digital information onto multiple higher-order laser modes through mode-encoding modulation to obtain a mode-encoding sequence transmitted in free space. The coupler is used to couple the mode-encoding sequence transmitted in free space into the elliptical-core few-mode fiber.

3. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber according to claim 2, characterized in that: The mode encoder converts the original m-ary digital sequence into an m-ary mode-encoding sequence by switching the phase diagram for modulating the fundamental-mode Gaussian beam.

4. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber according to claim 3, wherein: For each symbol in the original m-ary digital sequence, there is a specific phase diagram corresponding to it. Modulating the fundamental-mode Gaussian beam with each phase diagram can generate a beam of a specific mode. Each beam of a specific mode can excite a mode in a specific mode group in the elliptical-core few-mode fiber. The m-ary symbols of each symbol correspond to m mode groups in the elliptical-core few-mode fiber.

5. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber according to claim 4, characterized in that: The elliptical-core few-mode fiber includes an outermost circular cladding structure, an intermediate elliptical-ring low-refractive-index core structure, and an innermost elliptical high-refractive-index core structure. The refractive index of the elliptical high-refractive-index core structure is greater than that of the circular cladding structure, and the refractive index of the circular cladding structure is greater than that of the elliptical-ring low-refractive-index core structure, resulting in the support of multiple mode groups with a high effective refractive index difference.

6. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode optical fiber according to claim 5, wherein: The receiving end includes a motorized displacement stage, a beam splitter, an imaging lens group, a camera, a coupler, a mode decoder, and a signal processor. The motorized displacement stage is used to fix and control the position of the output fiber end face of the elliptical-core few-mode fiber. The beam splitter is used to split the beam from the output fiber end face of the divergent elliptical-core few-mode fiber into two beams according to the power ratio. The imaging lens group is used to image one of the two beams onto the camera. The camera is used to detect and analyze the light spot of the beam to obtain the position information of the output fiber end face of the elliptical-core few-mode fiber. The coupler is used to couple the other of the two beams into the mode decoder. The mode decoder is used to perform mode recognition and optoelectronic conversion on the mode-encoding sequence, converting the optical signal into an electrical signal. The signal processor is used to restore the electrical signal to obtain the original digital information.

7. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode optical fiber according to claim 6, wherein: In the mode decoder, a beam splitter, m reverse phase diagrams, and m photodetectors are sequentially arranged according to the transmission direction when the m-ary mode-encoding sequence enters. The m-ary mode-encoding sequence is converted into m electrical signals after passing through the mode decoder in the forward direction.

8. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber according to claim 7, characterized in that: The camera determines the initial center position of the camera's field of view based on the maximum value of the output current of the photodetector in the mode decoder.

9. The optical transmission system for collaborative communication and sensing based on an elliptical core few-mode fiber according to claim 8, characterized in that: The camera determines the positions of the x-axis and y-axis of the output fiber end face of the elliptical core few-mode fiber by identifying the deviation of the geometric center of the light beam from the initial center position of the camera's field of view. The camera determines the position of the z-axis of the output fiber end face of the elliptical core few-mode fiber by identifying the size of the light beam envelope. The camera determines the rotation angle of the output fiber end face of the elliptical core few-mode fiber by identifying the angle between the major axis or minor axis of the light beam and the x-axis.

10. The optical transmission system for collaborative communication and sensing based on an elliptical-core few-mode optical fiber according to claim 9, wherein: The output end of the camera is connected to the electric displacement stage to form a feedback control loop. The camera sends the measured positions of the x-axis, y-axis, and z-axis and the rotation angle of the output fiber end face of the elliptical core few-mode fiber to the electric displacement stage, causing the electric displacement stage to move in the reverse direction.

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