Optical fiber vibration sensing system based on polarization state and application

Abstract

The invention discloses a polarization-state-based optical fiber vibration sensing system and application, and relates to the technical field of optical fiber sensing, and the polarization-state-based optical fiber vibration sensing system mainly comprises a transmitting end and a receiving end. The transmitting end comprises a laser diode, a first erbium-doped optical fiber amplifier, a first circulator, a polarization scrambler, a single-mode optical fiber link, a second circulator and a second erbium-doped optical fiber amplifier which are connected in sequence; and the receiving end comprises a polarization beam splitter, a first shunt module, a second shunt module, an optical mixer, a first balanced photoelectric detector, a second balanced photoelectric detector, a third balanced photoelectric detector and a polarization analysis module. According to the optical fiber vibration sensing system based on the polarization state and the application, the vibration monitoring performance and reliability in a long-distance and high-noise environment can be improved.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more specifically, to a fiber optic vibration sensing system and its application based on polarization state. Background Technology

[0002] Submarine fiber optic cables, serving as the backbone of global communication networks, possess the unique advantage of natural electromagnetic shielding in the deep-sea environment. Leveraging their high capacity, low latency, and high reliability, submarine optical cables widely support global real-time communication and critical data transmission services. These widely deployed fiber optic infrastructures will form a collaborative global sensing and transmission network, providing stable, high-speed, and comprehensive data connectivity and environmental sensing capabilities to support future intelligent applications such as smart cities, intelligent manufacturing, and the global Internet of Things.

[0003] In recent years, with the deepening development of fields such as smart ocean, earthquake monitoring, and seabed resource exploration, the demand for long-distance, high-precision, and real-time vibration sensing has been increasing. Traditional seabed vibration monitoring methods mainly rely on point-based sensing devices such as seabed seismometers and pressure sensor arrays. These methods suffer from high deployment costs, limited spatial coverage, complex maintenance, and difficulty in achieving large-scale continuous sensing, which severely limits their application effectiveness in practical engineering. In contrast, distributed fiber optic sensing technology based on mechanisms such as Rayleigh scattering and Brillouin scattering can transform existing submarine communication optical cables into continuously distributed vibration sensor arrays, eliminating the need for additional dedicated sensors and significantly improving the spatial resolution, response speed, and system coverage of monitoring.

[0004] However, existing distributed fiber optic vibration sensing technologies have limitations in addressing weak vibration signal identification, polarization state change tracking, and environmental noise suppression in complex deep-sea environments. The inherent birefringence in optical fibers and environmental factors cause random changes in the polarization state of optical signals, making accurate vibration signal extraction difficult. Summary of the Invention

[0005] The purpose of this invention is to provide a fiber optic vibration sensing system and its application based on polarization state, which can improve the vibration monitoring performance and reliability in long-distance, high-noise environments.

[0006] This invention provides a fiber optic vibration sensing system based on polarization state, comprising a transmitter and a receiver; the transmitter includes a laser diode, a first erbium-doped fiber amplifier, a first circulator, a polarization scrambler, a single-mode fiber link, a second circulator, and a second erbium-doped fiber amplifier connected in sequence; the receiver includes a polarization beam splitter, a first splitting module, a second splitting module, and... Optical mixer, first balanced photodetector, second balanced photodetector, third balanced photodetector, and polarization analysis module.

[0007] The present invention also provides an application of the above-described polarization-state-based fiber optic vibration sensing system for seabed vibration monitoring.

[0008] Implementing the fiber optic vibration sensing system and application based on polarization state provided by this invention has the following beneficial effects: This invention utilizes the sensitivity between polarization state and fiber vibration caused by environmental disturbances to extract polarization state from polarization multiplexed signals. By defining the characteristic fluctuations of polarization state, different vibration events can be identified and located, enhancing the system's ability to identify vibration events and improving monitoring performance and reliability in long-distance, high-noise environments. This provides a more effective technical means for monitoring vibration in the seabed environment. Attached Figure Description

[0009] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a flowchart of the fiber optic vibration sensing system based on polarization state provided by the present invention; Figure 2 This is a schematic diagram of the time-varying response of the polarization rotation angle provided by the present invention; Figure 3 This is a schematic diagram of the phase delay response provided by the present invention. Detailed Implementation

[0010] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0011] Figure 1 A schematic diagram of the polarization-state-based fiber optic vibration sensing system of this embodiment is shown. In this embodiment, the polarization-state-based fiber optic vibration sensing system includes a transmitter and a receiver; the transmitter includes a laser diode, a first erbium-doped fiber amplifier, a first circulator, a polarization scrambler, a single-mode fiber link, a second circulator, and a second erbium-doped fiber amplifier connected in sequence; the receiver includes a polarization beam splitter, a first splitting module, a second splitting module, and... Optical mixer, first balanced photodetector, second balanced photodetector, third balanced photodetector, and polarization analysis module.

[0012] In one exemplary embodiment, the first port of the first circulator is connected to the output of the first erbium-doped fiber amplifier, the second port of the first circulator is connected to the polarization scrambler, and the third port of the first circulator is connected to the receiver; the first port of the second circulator is connected to the output of the second erbium-doped fiber amplifier, the second port of the second circulator is connected to the single-mode fiber link, and the third port of the second circulator is connected to the input of the second erbium-doped fiber amplifier.

[0013] In one exemplary embodiment, the output of the polarization beam splitter serves as the input of the receiver, and the output of the polarization beam splitter is connected to the inputs of the first splitting module and the second splitting module; the output of the first splitting module is connected to the input of the receiver. The optical mixer is connected to the first input terminal of the third balanced photodetector; the output terminal of the second splitter module is connected to the... The optical mixer is connected to the second input terminal of the third balanced photodetector; The first and second input terminals of the optical mixer are connected to the input terminals of the first balanced photodetector and the second balanced photodetector, respectively; the first balanced photodetector, the second balanced photodetector, and the third balanced photodetector are connected to the polarization analysis module.

[0014] In one exemplary embodiment, the laser diode is used to emit a continuous light wave; the erbium-doped fiber amplifier is used to amplify the optical power of the continuous light wave; and the polarization scrambling device is used to introduce polarization perturbations twice in conjunction with a circulator, so as to achieve positioning by detecting the time delay characteristics of the two polarization abrupt changes caused by vibration.

[0015] In one exemplary embodiment, the polarization beam splitter is used to decompose the optical signal into... and Two polarization components; the splitting module is used to split the optical signal into two outputs; the balanced photodetector is used to convert the optical signal into an electrical signal; the polarization analysis module is used to calculate the polarization rotation angle based on the electrical signal output by the balanced photodetector. and phase delay To determine the vibration event and its location.

[0016] In one exemplary embodiment, the calculation process for the polarization rotation angle and phase delay is as follows: Based on the distribution characteristics of the electrical signal output by the balanced photodetector and the Stokes vector on the Poincaré sphere, the optimal plane is found using the singular value decomposition algorithm and the least squares fitting method. Based on the normal of the optimal plane, the polarization rotation angle and phase delay are obtained.

[0017] In one exemplary embodiment, the optimal plane is found using a singular value decomposition algorithm and a least squares fitting method. Based on the normal of the optimal plane, the polarization rotation angle and phase delay are obtained, as shown in the formula:

[0018]

[0019]

[0020]

[0021]

[0022] in, Indicates minimization. For the first The distance from each Stokes vector to the plane; The equation of the least squares plane is given by the normal vector. ; For the first Stokes vectors; The number of Stokes vectors; It is the polarization rotation angle; For phase delay; The normal to the least squares plane obtained using the singular value decomposition algorithm; It is the arctangent function.

[0023] In some embodiments, the above-described polarization-state-based fiber optic vibration sensing system can also be implemented in the following ways.

[0024] This solution employs a forward optical transmission architecture combined with digital signal processing technology in fiber optic vibration sensing and monitoring scenarios to achieve highly sensitive detection and localization of vibration events. By acquiring and analyzing polarization state signals in real time and offline, the system extracts key polarization parameters and identifies their abrupt changes. It can operate stably on existing optical device platforms, providing a reliable technical means for marine vibration monitoring.

[0025] The principle of this invention is as follows: During transmission, the polarization state of an optical signal is randomly changed due to environmental factors. This system introduces polarization disturbances twice at the transmitting end using the same polarization scrambling instrument combined with a circulator. Positioning is achieved by detecting the time delay characteristics of the two polarization abrupt changes caused by the vibration. At the receiving end, the optical signal is decomposed into polarization beams by a polarization beam splitter. and Two polarization components are input to... An optical mixer then converts the signal into an electrical signal via three balanced photodetectors. The electrical signal is acquired by an oscilloscope and processed offline using a polarization analysis algorithm based on the Stokes vector. The core of this method is to construct the distribution characteristics of the Stokes vector on the Poincaré sphere. Ideally, a noise-free Stokes vector would lie entirely within a plane of the Poincaré sphere, uniquely determined by its normal vector. However, noise in the actual received signal causes the Stokes vector to deviate from the ideal plane and not fall entirely within the same plane. To accurately characterize the polarization characteristics of the signal, this invention employs a least-squares fitting method to find the optimal plane, defined as... Minimize the plane, where For the first The distances from each Stokes vector to the plane. Assume the equation of the least squares plane is... Then its normal vector is Stokes vector Distance to the plane It can be represented in the following matrix form: (1) This optimization problem can be solved using the singular value decomposition algorithm. The normal to the least squares plane is then found. Then, two key parameters characterizing the change in polarization state can be calculated: the polarization rotation angle. and phase delay The calculation formula is as follows: (2) (3) Figure 1 This is a schematic diagram of the overall system architecture implemented in this embodiment, illustrating the transmission and reception process of sensor signals under the forward transmission architecture.

[0026] At the transmitting end, the laser diode emits a continuous light wave, which is amplified by an erbium-doped fiber amplifier. The amplified optical signal is then subjected to polarization disturbance by a polarization scrambler before passing through the first circulator into a section of fiber of [length missing]. The single-mode fiber optic link. The optical signal with a changed polarization state is guided back through a second circulator and then passes through the same polarization scrambler again, creating a secondary perturbation.

[0027] At the receiving end, the optical signal is split into two parts by a polarization beam splitter, each carrying a different signal. , Two polarized light beams. These two light signals pass through... An optical mixer, in conjunction with a balanced photodetector, is used for direct detection to obtain the Stokes parameters characterizing the polarization state change. The electrical signal acquired by the oscilloscope undergoes offline digital signal processing (such as least-squares plane fitting and singular value decomposition) to finally calculate the polarization state rotation angle. and phase delay By monitoring the abrupt changes in these two parameters, it can be determined whether the system is affected by external factors and to pinpoint the location of the abrupt change. It should be noted that when an optical signal passes through the same polarization scrambler twice, polarization abrupt changes with specific intervals can be formed in the signal. By analyzing the time delay relationship between these two abrupt changes, the precise location of the vibration can be further calculated, enhancing the system's spatial positioning capability.

[0028] Figure 2 This is a schematic diagram of the time-varying response of the polarization rotation angle. The figure clearly shows the response locations where the polarization state undergoes two abrupt changes. The time interval between the two polarization abrupt changes was measured to be... According to the speed of light in an optical fiber ( The distance traveled by the light signal between the two polarization abrupt changes can be calculated as follows: The calculation result is consistent with the experimental result using twice the fiber length ( The results show good consistency, verifying that the system can effectively identify and accurately locate vibration events.

[0029] Figure 3 This is a schematic diagram of the phase-delay time-varying response, showing the time interval between the two abrupt changes. Figure 2 The results shown are highly consistent, further verifying the system's high sensitivity and stable response to vibration signals.

[0030] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A polarization state-based fiber optic vibration sensing system, comprising: It comprises a transmitting end and a receiving end; the transmitting end comprises a laser diode, a first erbium-doped fiber amplifier, a first circulator, a polarization scrambler, a single-mode fiber link and a second circulator and a second erbium-doped fiber amplifier connected in sequence; the receiving end comprises a polarization beam splitter, a first branching module, a second branching module, a light mixer, a first balanced photodetector, a second balanced photodetector, a third balanced photodetector and a polarization analysis module.

2. A polarization state based optical fibre vibration sensing system according to claim 1, characterized in that, The first port of the first circulator is connected with the output end of the first EDF amplifier, the second port of the first circulator is connected with the polarization scrambler, and the third port of the first circulator is connected with the receiving end; the first port of the second circulator is connected with the output end of the second EDF amplifier, the second port of the second circulator is connected with the single-mode fiber link, and the third port of the second circulator is connected with the input end of the second EDF amplifier.

3. The polarization state based optical fiber vibration sensing system of claim 1, wherein, The output end of the polarization beam splitter is connected with the input end of the first shunt module and the second shunt module as the input end of the receiving end; the output end of the first shunt module is connected with the input end of the second shunt module as the input end of the receiving end; the output end of the second shunt module is connected with the input end of the third balanced photodetector as the input end of the receiving end. The light mixer is connected with the first input end of the third balanced photodetector. The output end of the second shunt module is connected with the The second input end of the third balanced photodetector is connected with the optical mixer; and The first and second input ends of the optical mixer are respectively connected with the input ends of the first balanced photodetector and the second balanced photodetector; and the first balanced photodetector, the second balanced photodetector and the third balanced photodetector are connected with the polarization analysis module.

4. The polarization state based optical fiber vibration sensing system of claim 1, wherein, The laser diode is used to emit continuous light waves; the EDF amplifier is used to amplify the optical power of the continuous light waves; and the polarization scrambler is used to introduce polarization disturbance twice in combination with the circulator, so as to realize positioning by detecting the time delay characteristics of the two polarization mutations caused by vibration.

5. The polarization state based optical fiber vibration sensing system of claim 1, wherein, The polarization beam splitter is used to decompose the optical signal into two polarization components; the branching module is used to divide the optical signal into two output paths; the balanced photodetector is used to convert the optical signal into an electrical signal; and the polarization analysis module is used to calculate the polarization rotation angle and the phase delay according to the electrical signal output by the balanced photodetector, and to judge the vibration event and the position where the vibration event occurs.

6. A polarization state based optical fibre vibration sensing system according to claim 5, characterized in that, The calculation process of the polarization rotation angle and the phase delay is as follows: according to the electrical signal output by the balanced photodetector and the distribution characteristics of the Stokes vector on the Poincare sphere, an optimal plane is found by using the singular value decomposition algorithm and the least square fitting method, and the polarization rotation angle and the phase delay are obtained according to the normal line of the optimal plane.

7. A polarization state based optical fibre vibration sensing system according to claim 6, characterized in that, The singular value decomposition algorithm and the least square fitting method are used to find the optimal plane, and the polarization rotation angle and the phase delay are obtained according to the normal line of the optimal plane, as shown in the formula: ， ， ， ， ， wherein, represents minimization, is the equation of the least squares plane whose normal vector is ; is the distance of the stokes vector to the plane; ; is the stokes vector; ; is the number of stokes vectors; is the polarization rotation angle; is the phase delay; is the normal of the least squares plane solved using singular value decomposition algorithm; is the arctangent function.

8. Use of a polarization state based optical fiber vibration sensing system according to any one of claims 1 to 7, characterized in that, The application is applied to submarine vibration monitoring.

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