Distributed optical fiber sound wave sensing chip and system based on polarization state detection

Abstract

The utility model provides a distributed optical fiber sound wave sensing chip and system based on polarization state detection. The chip comprises an optical pulse source module, a first spot size converter, a second spot size converter and a high-speed polarization analysis module, the optical pulse source module generates pulse light and outputs the pulse light to the optical fiber circulator and the sensing optical fiber through the first spot size converter; the second spot size converter receives scattered light returned from the sensing optical fiber and the optical fiber circulator and inputs the scattered light into the high-speed polarization analysis module; the high-speed polarization analysis module comprises a polarization beam splitting rotator, four interference structures and six photoelectric sensors; the polarization beam splitting rotator divides the scattered light into a TE mode and a TM mode, rotates the TM mode to the corresponding TE mode and then outputs the scattered light through two output ports of the polarization beam splitting rotator; each output end of the polarization beam splitting rotator is connected to one photoelectric sensor and one input end of the four-way interference structure; the four-way interference structure is provided with four output ends which are respectively connected to the rest photoelectric sensors.

Description

Technical Field

[0001] This application relates to the field of distributed optical fiber sensing, and in particular to a distributed optical fiber acoustic wave sensing chip and system based on polarization state detection. Background Technology

[0002] Distributed acoustic sensing (DAS) systems can be implemented using optical sensing systems based on coherent optical time domain reflectometers (OTDRs). These systems detect local phase disturbances in optical signals caused by acoustic waves or vibrations at different locations along the sensing fiber. Distance information is determined by the pulse duration of backscattered Rayleigh (RBS) light within the fiber. A typical DAS system consists of three parts: a sensing fiber, a demodulator, and a data processing unit.

[0003] A Direct Optical Array (DAS) system for extracting local optical signal phase perturbations caused by vibrations or sound waves can be implemented using various devices. For example, a DAS system can be designed to interfere with backscattered light within the sensing fiber and reference light generated by a laser source; that is, the laser source generates both the sensing light and the reference light within the sensing fiber. In this design, due to the limitations of the interferometer's properties, the coherence length of the laser source must be at least twice the detection length. Another DAS system design involves interfering backscattered light from two different locations within the sensing fiber, determined by a specific fiber length (e.g., several meters in some applications). Because the backscattered light signals at the two locations along the sensing fiber are extremely low, the laser source typically requires extremely low phase noise to ensure the interference signal intensity is above the system's noise floor, which is primarily determined by the laser's phase noise. Therefore, in both of these DAS system designs, the laser source requires an extremely narrow linewidth, possibly kHz or narrower, to achieve high sensitivity and ultra-long sensing range in certain sensing applications.

[0004] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Utility Model Content

[0005] This invention provides a distributed fiber optic acoustic wave sensing chip and system based on polarization state detection, which can greatly relax the linewidth requirements of the laser source and reduce the cost of the laser source. In addition, by designing a photonic integrated high-speed polarization analysis module, the size of the sensing system is greatly reduced, achieving a high degree of integration.

[0006] Other objects and advantages of this utility model can be further understood from the technical features disclosed herein.

[0007] To address some or all of the aforementioned problems, firstly, a distributed fiber optic acoustic wave sensing chip based on polarization state detection is provided, comprising an optical pulse source module, a first mode spot converter, a second mode spot converter, and a high-speed polarization analysis module.

[0008] The optical pulse source module is used to generate pulsed light and output it to the external fiber optic circulator and sensing fiber through the first mode converter; the second mode converter is used to receive the scattered light returned from the sensing fiber and the fiber optic circulator and input it into the high-speed polarization analysis module.

[0009] The high-speed polarization analysis module includes a polarization beam splitter rotator, a four-way interference structure, and six photoelectric sensors. The polarization beam splitter rotator splits the received scattered light into TE mode signal light and TM mode signal light, rotates the TM mode signal light to the corresponding TE mode signal light, and then outputs the light through the two output ports of the polarization beam splitter rotator.

[0010] Each output of the polarization beam splitter is connected to a photoelectric sensor and an input of the four-way interference structure; the four-way interference structure has four outputs, which are respectively connected to the remaining photoelectric sensors.

[0011] This invention uses a high-speed polarization analysis module to monitor the polarization state of scattered light returned from a self-sensing fiber. This method can analyze changes or disturbances in the fiber by measuring the different polarization states of backscattered light from a single pulse at a certain position and nearby positions. Compared with existing phase detection methods, it can greatly relax the linewidth requirements of the laser source and significantly reduce the cost of the laser source. In addition, by designing and using a photonic integrated high-speed polarization analysis module, the size of the sensing system is greatly reduced, achieving a high degree of integration.

[0012] The four-way interference structure is a 4x4 multimode interferometer. Two input ports of the 4x4 multimode interferometer are connected to the two output ports of the polarization beam splitter, and the four output ports of the 4x4 multimode interferometer are each connected to a photoelectric sensor. This application provides a photonic integrated high-speed polarization analysis module capable of demodulating scattered light signals into electrical signals.

[0013] The four-way interference structure is a 90° mixer, which includes a first coupler, a second coupler, a third coupler, and a fourth coupler. The input terminals of the first and second couplers are respectively the two input terminals of the four-way beam splitting structure. The output terminals of the first and second couplers are connected to the third and fourth couplers, respectively. A π / 2 phase delay is provided between the first and third couplers. The third and fourth couplers each have two output terminals, each connected to a photoelectric sensor. Another photonic integrated high-speed polarization analysis module provided in this application can demodulate scattered light signals into electrical signals.

[0014] The optical pulse source module includes a laser source, an optical pulse generator, and a semiconductor amplifier connected in sequence; the optical pulse generator includes an optical modulator or an optical switch. It is used to generate and amplify optical pulses, providing detection sensitivity.

[0015] The optical pulse source module includes a laser source and a semiconductor amplifier connected in sequence. By applying a reverse voltage to the semiconductor amplifier to give it high absorption, it can function as both an optical amplifier and an optical pulse generator with a high extinction ratio.

[0016] A bandpass filter is also connected between the optical pulse source module and the first mode converter. This further filters out additional spontaneous emission noise from the semiconductor amplifier.

[0017] Between the second mode converter and the high-speed polarization analysis module, a second amplifier and a second bandpass filter are connected in sequence. This further amplifies the scattered light and filters out additional spontaneous emission noise from the optical amplifier.

[0018] The second amplifier is a semiconductor amplifier or an erbium-doped fiber amplifier.

[0019] The photoelectric sensor is a PIN diode or an avalanche photodiode.

[0020] A coherent amplification optical path is also provided, which includes a fifth coupler connected to the laser source. The output of the fifth coupler is connected to the input of the polarization beam splitter. By providing a coherent amplification optical path, a small portion of the light from the laser is directly injected into the polarimeter, interfering with the scattered light returned from the sensing fiber. This significantly enhances the scattered light returned from the fiber and improves the measurement sensitivity.

[0021] A coherent amplification optical path is also provided, comprising a fifth coupler connected to the laser source and a sixth coupler disposed between the fifth coupler and the polarization beam splitter. The sixth coupler has two output terminals, respectively connected to the two output terminals of the polarization beam splitter. By providing a coherent amplification optical path, a small portion of the light from the laser is directly injected into the polarimeter, interfering with the scattered light returned from the sensing fiber, thereby greatly enhancing the scattered light returned by the fiber and improving the measurement sensitivity.

[0022] On the other hand, this utility model provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, including a sensing chip, a fiber optic circulator, a sensing fiber, and a data acquisition and processing module as described in any of the first aspects.

[0023] The output port of the first mode converter is connected to the first port of the fiber optic circulator, the second port of the fiber optic circulator is connected to the sensing fiber, and the third port of the fiber optic circulator is connected to the input of the second mode converter.

[0024] The data acquisition and processing module is used to acquire the demodulated electrical signal from the sensor chip and perform algorithm processing to calculate the polarization state information of the scattered light.

[0025] The data acquisition and processing module includes analog circuits and digital circuits. The data acquisition and processing module receives the electrical signal from the photoelectric sensor and processes it through the analog circuits and digital circuits to calculate the polarization state information of the scattered light.

[0026] The sensing fiber is a scattering-enhanced fiber, which includes femtosecond laser pulse-enhanced fiber or ultraviolet radiation-treated enhanced fiber.

[0027] Compared with the prior art, the beneficial effects of this utility model mainly include the following: This utility model sets up a high-speed polarization analysis module to monitor the polarization state of the scattered light returned by the self-sensing fiber. It can analyze the changes or disturbances on the fiber by measuring the different polarization states of the backscattered light at a certain position and the adjacent position of a single pulse light. Compared with the existing phase detection method, it can greatly relax the linewidth requirements of the laser source and significantly reduce the cost of the laser source. In addition, by designing and using a photonic integrated high-speed polarization analysis module, the size of the sensing system is greatly reduced, and a high degree of integration is achieved. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is one embodiment of the present invention.

[0030] Figure 2 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is a second embodiment of the present invention.

[0031] Figure 3 Four different polarization analyzers are provided for this utility model.

[0032] Figure 4 The photon integrated polarization analyzer provided by this utility model.

[0033] Figure 5 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is the third embodiment of the present invention.

[0034] Figure 6 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is the fourth embodiment of the present invention. Detailed Implementation

[0035] The foregoing and other technical contents, features, and effects of this utility model will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are only for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the scope of this utility model.

[0036] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0037] Existing distributed acoustic sensing (DAS) systems monitor vibrations or sound waves at a specific point on an optical fiber by detecting the phase of the signal light. The phase information is typically obtained by interfering the backscattered light from the sensing fiber with a local reference light, or by demodulating the interference of backscattered light from two different locations. Currently, phase detection-based systems place high demands on the laser source, requiring extremely narrow linewidths to achieve high sensitivity and ultra-long sensing range in applications.

[0038] This application provides a distributed acoustic wave sensing system based on polarization state detection. This system is based on the fact that the polarization state (SOP) of an optical pulse in a sensing fiber changes upon encountering vibration or sound waves. These changes or disturbances occur within the duration of a single pulse, and the system senses changes in vibration or sound waves by detecting these polarization state changes. Specifically, this technology primarily measures the different polarization states of backscattered light from a single pulse within the sensing fiber at a specific location and adjacent locations, where the propagation distance within the pulse duration is very short. Compared to the two DAS systems mentioned above that rely on the interference of backscattered light and reference light, or backscattered light signals from different locations in the sensing fiber (arriving at the photodetector at different times), this system, because the different polarization components originate from backscattered light from adjacent locations within the same pulse duration in the sensing fiber, has virtually no or very low relative delay between the different polarization components. Their interference allows for a relatively shorter coherence length (i.e., a wider laser linewidth) in the laser source, thus significantly relaxing the linewidth requirements and substantially reducing the cost of the laser source. For example, low-cost lasers from OTDRs can be used directly in polarization DAS, and these lasers can be single-mode or multi-mode in some applications. Example 1

[0039] Figure 1 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is one embodiment of the present invention.

[0040] refer to Figure 1 In the A section, a basic DAS system includes a laser, a fiber optic circulator, a sensing fiber, a high-speed polarization analysis module, and a data acquisition and processing module.

[0041] In this embodiment, a semiconductor laser is used as the optical pulse signal source. The bulk laser is driven by an electrical pulse signal (V1) to generate optical pulses, which are then input into the fiber optic circulator connected to it. It can be understood that the fiber optic circulator is a multi-port non-reciprocal optical device that has a light guiding function. The fiber optic circulator in this embodiment has three ports. When light is input from any one of the ports (generally the first port), it can be output from the next port (the second port) in numerical order with almost no loss, while there is almost no light output at the other ports (the third port). Similarly, when light is input from the second port, it can also be output from the third port with almost no loss. At the same time, there is no light output at the first port or other ports.

[0042] In this embodiment, specifically, the optical pulse is input from the first port of the fiber optic circulator and then transmitted into the sensing fiber through the second port. During the transmission of the optical pulse in the sensing fiber, backscattered Rayleigh light is continuously generated. This backscattered light from the sensing fiber is then input through the second port of the fiber optic circulator and then output through the third port, ultimately reaching the high-speed polarization analysis module (Polarimeter). The high-speed polarization analysis module demodulates the input backscattered light and converts it into an electrical signal, which is then input into the data acquisition and processing module for algorithm processing. In this embodiment, the data acquisition and processing module includes analog circuits and digital circuits, such as A / D (analog-to-digital converter), FPGA (Field-Programmable Gate Array), and D / A (digital-to-analog converter).

[0043] It is understandable that Rayleigh scattering occurs during the transmission of a light pulse in a sensing fiber. When a disturbance occurs at a certain position z in the sensing fiber, the polarization state (SOP) of the scattered light generated at position z is rapidly changed due to the disturbance, and thus, at time T... z When the value is 2nz / c, it is detected by a high-speed polarization meter, based on the detection time T. z The location of the event point can be determined as z=cT z / (2n), where c is the speed of light and n is the refractive index of the sensing fiber, such as Figure 1 As shown in B in the diagram.

[0044] The local SOP change at position z in the sensing fiber during the pulse duration can be represented by the changes in three Stokes parameters s1, s2, and s3, or by the solid angle on the Poincaré sphere. The changes are represented as follows:

[0045]

[0046] The Stokes vector of SOP at position z and time t is represented as follows:

[0047]

[0048] Where T represents transpose, and τ is the time delay of the polarization component within the optical pulse, i.e., the duration of the optical pulse.

[0049] In this design, the amount of local stress or vibration at position z in the sensing fiber can be represented by the change in the polarization state of the scattered light, i.e., the solid angle. The changes in the three Stokes parameters s1, s2, and s3 of the SOP. Example 2

[0050] Figure 2 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is a second embodiment of the present invention.

[0051] refer to Figure 2 The distributed fiber optic acoustic wave sensing system in this embodiment is based on the first embodiment and includes a laser, a modulator / switch, a semiconductor amplifier (SOA), a bandpass filter (BPF), a fiber optic circulator, a sensing fiber, a high-speed polarization analysis module, and a data acquisition and processing module.

[0052] In this embodiment, the laser, modulator / switch, and semiconductor optical amplifier together constitute an optical pulse source module. After the laser generates a laser signal, it is first modulated into an optical pulse by an optical pulse generator (i.e., modulator or switch), and then amplified by a semiconductor optical amplifier before being output. The generated optical pulse can first pass through a bandpass filter (BPF) to filter out the amplifier's additional spontaneous emission noise, and then be input into the sensing fiber through an optical fiber circulator. The scattered light returning from the sensing fiber is separated from the output light by the optical fiber circulator. In order to enhance the scattered light signal returning from the sensing fiber, an amplifier and a bandpass filter can be sequentially set between the optical fiber circulator and the high-speed polarization analysis module to amplify the scattered light and input it into the high-speed polarization analysis module to detect fluctuations in SOP caused by sound waves or vibrations.

[0053] It is understandable that the bandpass filter between the optical pulse source module and the fiber optic circulator is not necessary; similarly, the amplifier and bandpass filter between the fiber optic circulator and the high-speed polarization analysis module are not necessary either; the amplifier can be an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA).

[0054] In various DAS applications, optical pulses may require a high extinction ratio (ER), for example, an ER in the order of 50-70 dB to achieve the desired detection sensitivity. Such a high ER may not be easily achievable in various instances, including the modulator / switching devices used in some DAS systems. Since an SOA can have high absorbance by applying a reverse voltage, it can function as both an optical amplifier and a high-extinction-ratio optical pulse generator. Therefore, in some embodiments, the modulator / switching device can be removed, and the optical pulse switching function can be accomplished solely by driving the SOA with a pulsed electrical signal.

[0055] In the above structure, the high-speed polarization analysis module is a crucial device for demodulating the polarization state of scattered light. The structure of the high-speed polarization analysis module is described below. Both amplitude-splitting polarimeters and wavefront-splitting polarimeters can be used to quickly detect changes in SOP (Sensitive Point of Optimization). Taking the wavefront-splitting polarimeter as an example, its basic principle is to split the wavefront of the scattered light returning from the sensing fiber into separate beams, which are then processed by different optical polarization elements and detected by different optical detectors to obtain the Stokes vector elements.

[0056] Figure 3 Four different polarization analyzers are provided for this utility model. (Reference) Figure 3 The two polarizers described in examples a and b have similar structures, both consisting of a polarizer array, a focusing lens, and a photodetector array arranged sequentially along the light propagation direction. Specifically, they include a wedge-shaped substrate for transmitting light, multiple polarization elements located on the substrate, these elements being spatially separated and positioned at different locations to receive different portions of the common input light, thus generating transmitted beams with different polarization states; and multiple optical detectors, each corresponding to a polarization element and receiving the transmitted beam from its respective element. The difference between the two lies in... Figure 3 In part 'a', the polarizer is a planar side with a wedge-shaped substrate, while Figure 3 In this context, 'b' refers to placing the polarizer array on the wedge side of the wedge-shaped substrate. Typically, for ease of use, the polarizer array, focusing lens, and photodetector array are encapsulated in a housing to form a polarization analyzer.

[0057] refer to Figure 3 In this embodiment, the polarizer array is a 2x2 array, including three polarizers with different polarization directions, namely 0°, 45°, and 90°, and a right-handed circularly polarized (RHC) or left-handed circularly polarized (LHC) polarizer. Alternatively, one of the 0° or 90° polarizers can be replaced with a planar optical sheet.

[0058] In operation, the fiber collimator amplifies the input light from the fiber pigtail, then splits it into four sub-beams with different polarizations by a 2x2 polarizer array, which are then guided in four different directions by a wedge-shaped substrate. Finally, the four sub-beams are focused by a focusing lens onto different photodiodes (PDs) on a 2x2 PD array to generate corresponding photocurrents or photovoltages. In some embodiments, each PD is followed by a transimpedance amplifier to amplify the converted electrical signal before it is input to the data acquisition and processing module.

[0059] Figure 3 Figure c shows a polarimeter consisting of a 2x2 lens array, a 2x2 polarizer array, and a 2x2 PD array. The lens array splits the input beam into four sub-beams and focuses them onto four different PDs on the PD array. Between the lens array and the PD array is the 2x2 polarizer array, which can be placed behind the lens array or directly in front of the PD array to detect light with different polarization states.

[0060] Figure 3 Figure d illustrates a polarimeter consisting of a collimator, a pair of cylindrical lenses, a 1x4 lens array, a 1x4 polarizer array, and a 1x4 photodiode array. The beam from the fiber collimator is linearly extended by the cylindrical lens pair, then passes through the 1x4 polarizer array, and is finally focused by the 1x4 lens array onto four different photodiodes (PDs) on the 1x4 PD array. The scattered light's SOP can be determined by detecting the photocurrent Ii (i = 1, 2, 3, 4).

[0061] Please note that the photodetector (PD) can be a PIN diode or an avalanche photodiode (APD) to improve detection sensitivity.

[0062] The above describes a DAS system composed of discrete optical components. In fact, silicon photonics technology can also be used to fabricate on-chip integrated DAS systems. Example 3

[0063] The polarization analyzers described above typically include polarizer arrays, lenses, and photodetector arrays, and are mostly discrete optical components. Their large size makes them difficult to integrate into a photonic DAS system. To achieve a photonic DAS system, improvements to the polarization analyzer are needed.

[0064] Figure 4 This utility model provides a photonic integrated polarization analyzer. (Reference) Figure 4In the example of 'a', there is a polarization analyzer device configured with the first type of photonic integrated circuit (PIC). Figure 4 Figure 'a' illustrates a polarimeter based on a 4x4 multimode interferometer (MMI), where a polarization beam splitter (PSR) splits the input light into two orthogonal polarization states (TE and TM) and rotates the TM mode to the corresponding TE mode. Approximately one-third of the power of each of the two beams (i.e., the original TE mode and the TE mode converted from TM) is coupled out, and the power of the two orthogonal polarization states is measured using photodetectors PDx and PDy. The remaining light from both beams then enters ports 1 and 3 of the 4x4 MMI, is split into four beams, and detected by PD1, PD2, PD3, and PD4. Finally, information on the SOP and DOP is extracted using the six detected photocurrents. PDs can be PIN diodes or avalanche photodiodes.

[0065] Figure 4 Figure b illustrates an example of a polarimeter based on a 90° mixer. Its structure is similar to that of a polarimeter based on a 4x4 MMI, except that the 4x4 MMI is replaced by a 90° mixer. The figure shows the construction of the 90° mixer, where the first coupler (C1), second coupler (C2), third coupler (C3), and fourth coupler (C4) have a coupling ratio of approximately 50%. The inputs of the first and second couplers receive two scattered beams from the PSR. The outputs of the first and second couplers are connected to the third and fourth couplers, respectively. A π / 2 phase delay is placed between the first and third couplers. The third and fourth couplers each have two outputs, each connected to a photoelectric sensor.

[0066] Based on the polarization analyzer described above, the polarization state of the scattered light, i.e., the Stokes parameter, can be obtained by detecting the photocurrent, as shown below:

[0067]

[0068] Figure 5 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, which is the third embodiment of the present invention.

[0069] Figure 5 A photonic integrated distributed fiber optic acoustic wave sensing system is demonstrated, which uses a high-speed polarization analysis module to acquire sensing signals from the optical fiber. This device is similar to that shown in Embodiment 2, except that most of the functional components are integrated on a PIC chip (which can be called a photonic integrated DAS demodulation chip), with only the sensing fiber and circulator outside the chip.

[0070] This embodiment provides a distributed fiber optic acoustic wave sensing chip and sensing system based on polarization state detection. The sensing chip includes an optical pulse source module, a first mode spot converter, a second mode spot converter, and a high-speed polarization analysis module, while the sensing system includes a sensing chip, an optical fiber circulator, a sensing fiber, and a data acquisition and processing module.

[0071] refer to Figure 5 The distributed fiber optic acoustic wave sensing system of this embodiment includes a photonic integrated DAS demodulation chip (i.e., a sensing chip), a fiber optic circulator, a sensing fiber, and a data acquisition and processing module. The chip has an optical pulse output terminal and a scattered light input terminal, which are respectively connected to the first port and the third port of the fiber optic circulator. The optical pulse output terminal outputs an optical pulse signal to the fiber optic circulator and the sensing fiber, and the scattered light input terminal receives the scattered light returned from the sensing fiber and the fiber optic circulator.

[0072] Specifically, the photonic integrated DAS demodulation chip includes an optical pulse source module consisting of a laser, a modulator / switch, and a first amplifier. After the laser generates a laser signal, it is first modulated into an optical pulse by the modulator / switch, and then amplified by the semiconductor optical amplifier before being output. The generated optical pulse can first pass through a first bandpass filter to filter out the additional spontaneous emission noise of the first amplifier, and then be input into the sensing fiber through a first mode-spot converter (SSC). Here, the output port of the first mode-spot converter is the optical pulse output terminal of the demodulation chip. The scattered light returning from the sensing fiber is separated from the output light by the fiber circulator and enters the scattered light input terminal of the demodulation chip. Here, a second mode-spot converter is provided, and the input port of the second mode-spot converter is the scattered light input terminal of the demodulation chip. In order to enhance the scattered light signal returning from the sensing fiber, a second amplifier and a second bandpass filter are set sequentially after the second mode-spot converter. The scattered light can be amplified and input into the high-speed polarization analysis module to detect the fluctuation of SOP caused by sound waves or vibration. In this system, a single-mode (SM) fiber connects the fiber optic circulator and the scattered light input of the demodulation chip, while the second mode converter is connected to the high-speed polarizer via a waveguide supporting TE and TM modes. It is understood that the high-speed polarizer used here needs to be a photonic integrated polarizer, such as... Figure 4 One of the two types of photonic integrated polarization analyzers shown.

[0073] In this embodiment, the first bandpass filter between the optical pulse source module and the first mode spot converter is not necessary; similarly, the second amplifier and the second bandpass filter are not necessary either; in this embodiment, the amplifier can be an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA).

[0074] Similar to Embodiment 2, this embodiment can also remove the modulator / switch in the optical pulse source module and obtain a high extinction ratio optical pulse by driving the first amplifier only through the pulse electrical signal.

[0075] In the embodiments of this application, the sensing fiber can be a scattering-enhancing fiber, for example, it can be treated with femtosecond laser pulses or ultraviolet radiation to enhance backscattering, thereby improving detection sensitivity. Example 4

[0076] Figure 6 This invention provides a distributed fiber optic acoustic wave sensing system based on polarization state detection, as described in Embodiment 4. The system is essentially similar to that shown in Embodiment 3. The DAS system includes a photonic integrated DAS demodulation chip, a fiber optic circulator, a sensing fiber, and a data acquisition and processing module. The photonic integrated DAS demodulation chip has one output terminal and one input terminal, which are respectively connected to the first and third ports of the fiber optic circulator. The output terminal outputs an optical pulse signal to the sensing fiber, and the input terminal receives the scattered light returned from the sensing fiber.

[0077] The difference lies in that, based on the chip shown in Embodiment 3, an additional coherent amplification optical path is added. This involves directly injecting a portion of the light from the laser into the polarizer, interfering with the scattered light returned from the sensing fiber. This coherent amplification significantly enhances the scattered light returned from the fiber and improves measurement sensitivity. Specifically, in this embodiment, a fifth coupler is added between the laser and the modulator / switch. This coupler splits the laser signal emitted by the laser into two 50% paths. One path generates light pulses, and the other generates coherently amplified light. The third path is then split into two by the added sixth coupler, each input to one of the two outputs of the polarization beam splitter. In this embodiment, the polarization analyzer uses... Figure 4 The structure shown in b in the figure can also be used in other embodiments. Figure 4 The structure shown in Figure a is as follows. In other embodiments, the sixth coupler may not be used, and the coherent amplified light and the scattered light can be input together from the input end of the polarization beam splitter to achieve the function of coherent amplification.

[0078] The common English terms or letters used in this utility model for the purpose of clear description are for illustrative purposes only and are not intended to be limiting or specific. They should not be used to limit the scope of protection of this utility model based on their possible Chinese translations or specific letters.

[0079] It should also be noted that in this article, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

Claims

1. A distributed optical fiber acoustic sensing chip based on polarization state detection, characterized in that, The sensor chip comprises a light pulse source module, a first mode spot converter, a second mode spot converter and a high-speed polarization analysis module. The light pulse source module is used to generate pulse light and output the pulse light to an external fiber loop and a sensing fiber through the first mode spot converter; the second mode spot converter is used to receive scattered light returned from the sensing fiber and the fiber loop and input the scattered light into the high-speed polarization analysis module. The high-speed polarization analysis module comprises a polarization beam splitting rotator, a four-way interference structure and six photoelectric sensors; the polarization beam splitting rotator divides the received scattered light into TE mode signal light and TM mode signal light and rotates the TM mode signal light to the corresponding TE mode signal light and then outputs the TE mode signal light and the TM mode signal light through two output ports of the polarization beam splitting rotator respectively. Each output port of the polarization beam splitting rotator is connected to one photoelectric sensor and one input port of the four-way interference structure; the four-way interference structure has four output ports, which are connected to the remaining photoelectric sensors respectively.

2. The distributed fiber optic acoustic sensor chip based on polarization state detection of claim 1, wherein, The four-way interference structure is a 4x4 multimode interferometer, two input ports of the 4x4 multimode interferometer are connected to two output ports of the polarization beam splitting rotator respectively, and four output ports of the 4x4 multimode interferometer are connected to one photoelectric sensor respectively.

3. The distributed fiber optic acoustic sensor chip based on polarization state detection of claim 1, wherein, The four-way interference structure is a 90° mixer, the 90° mixer comprises a first coupler, a second coupler, a third coupler and a fourth coupler, input ports of the first coupler and the second coupler are two input ports of a four-way beam splitting structure respectively, output ports of the first coupler and the second coupler are connected to the third coupler and the fourth coupler respectively, a phase delay of π / 2 is arranged between the first coupler and the third coupler, the third coupler and the fourth coupler each have two output ports connected to one photoelectric sensor respectively.

4. The distributed fiber optic acoustic sensor chip based on polarization state detection of claim 1, wherein, The light pulse source module comprises a laser source, a light pulse generator and a semiconductor amplifier connected in sequence; the light pulse generator comprises an optical modulator or an optical switch.

5. The distributed fiber optic acoustic sensor chip based on state of polarization probing of claim 1, wherein, The light pulse source module comprises a laser source and a semiconductor amplifier connected in sequence.

6. The distributed fiber optic acoustic sensor chip based on state of polarization probing of claim 1, wherein, A band-pass filter is further connected between the light pulse source module and the first mode spot converter.

7. The polarization state detection based distributed optical fiber acoustic sensor chip of claim 1, wherein, A second amplifier and a second band-pass filter are further connected in sequence between the second mode spot converter and the high-speed polarization analysis module.

8. The distributed fiber optic acoustic sensor chip based on state of polarization probing according to claim 7, characterized in that, The second amplifier is a semiconductor amplifier or an erbium-doped fiber amplifier.

9. The polarization state detection based distributed optical fiber acoustic sensor chip of claim 1, wherein, The photoelectric sensor is a PIN diode or an avalanche photodiode.

10. The distributed fiber optic acoustic sensor chip based on state of polarization probing according to claim 4, wherein, A coherent amplification light path is further arranged, the coherent amplification light path comprises a fifth coupler connected to the laser source, and an output port of the fifth coupler is connected to an input port of the polarization beam splitting rotator.

11. The distributed fiber optic acoustic sensor chip based on state of polarization probing according to claim 4, wherein, A coherent amplification light path is further arranged, the coherent amplification light path comprises a fifth coupler connected to the laser source and a sixth coupler arranged between the fifth coupler and the polarization beam splitting rotator, the sixth coupler has two output ports connected to two output ports of the polarization beam splitting rotator respectively.

12. A distributed optical fiber acoustic sensor system based on state of polarization probing, characterized in that, The sensor chip, the fiber loop, the sensing fiber and a data acquisition and processing module as claimed in any one of claims 1-11 are comprised. The output port of the first mode field converter is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the sensing optical fiber, and the third port of the optical fiber circulator is connected to the input port of the second mode field converter; The data acquisition and processing module is used for acquiring the demodulated electrical signal of the sensing chip and performing algorithm processing, and calculating the polarization state information of the scattered light.

13. The sensing system of claim 12, wherein, The data acquisition and processing module includes an analog circuit and a digital circuit, receives the electrical signal of the photoelectric sensor, and processes the electrical signal through the analog circuit and the digital circuit to calculate the polarization state information of the scattered light.

14. The sensing system of claim 12, wherein, The sensing optical fiber is a scattering-enhanced optical fiber, and the scattering-enhanced optical fiber includes a femtosecond laser pulse-enhanced optical fiber or an ultraviolet radiation treatment-enhanced optical fiber.

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