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

Abstract

The invention provides a distributed optical fiber sound wave sensing chip, system and method 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] The present application relates to the field of distributed optical fiber sensing, and in particular to a distributed optical fiber acoustic wave sensing chip, system and method based on polarization state detection. Background Art

[0002] Distributed acoustic sensing (DAS) systems can be implemented through optical sensing systems based on coherent optical time domain reflectometry (OTDR), which are used to detect local phase disturbances of optical signals caused by acoustic waves or vibrations at different locations along the sensing fiber. The distance information is determined by the pulse duration of the Rayleigh backscattered (RBS) light in the fiber. DAS systems usually include three parts: sensing fiber, demodulator, and data processing unit.

[0003] DAS systems for extracting local optical signal phase disturbances caused by vibrations or sound waves can be implemented by a variety of devices. For example, the DAS system can be designed to interfere the backscattered light in the sensing fiber with the reference light generated by the laser light source, that is, the laser light source generates both the sensing light in the sensing fiber and the reference light. In this design, due to the nature of the interferometer, the coherence length of the laser light source is at least twice the detection length range. Another design of the DAS system is to interfere the backscattered light from two different positions in the sensing fiber, and the two positions are determined by a specific length of the fiber (for example, several meters in some applications). Since the backscattered light signals at the two positions along the sensing fiber are extremely low, the phase noise of the laser light source is usually required to be extremely low, in order to make the intensity of the interference signal higher than the noise floor of the system, which is mainly determined by the phase noise of the laser. Therefore, in the above two DAS system designs, the laser light source needs an extremely narrow linewidth, which may be 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 convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0005] The present invention provides a distributed optical fiber acoustic wave sensor chip, system and method based on polarization state detection, which can greatly relax the line width requirements of laser light sources and reduce the cost of laser light sources; in addition, by designing a photon-integrated high-speed polarization analyzer, the size of the sensing system is greatly reduced, achieving high integration.

[0006] Other purposes and advantages of the present invention can be further understood from the technical features disclosed in the present invention.

[0007] In order to solve some or all of the above problems, in the first aspect, a distributed optical fiber acoustic wave sensor chip based on polarization state detection is first provided, including an optical pulse source module, a first spot mode converter, a second spot mode converter and a high-speed polarization analysis module;

[0008] The optical pulse source module is used to generate pulsed light and output it to an external optical fiber circulator and a sensing optical fiber through the first spot mode converter; the second spot mode converter is used to receive scattered light returned from the sensing optical fiber and the optical fiber 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 and rotates the TM mode signal light to the corresponding TE mode signal light and then outputs them respectively through the two output ports of the polarization beam splitter rotator;

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

[0011] The present invention sets a high-speed polarization analyzer to monitor the polarization state of scattered light returned from the self-sensing optical fiber. This method can analyze changes or disturbances on the optical fiber by measuring the different polarization states of backscattered light at a certain position and an adjacent position of a single pulse light. Compared with the existing phase detection method, it can greatly relax the line width requirements of the laser light source and significantly reduce the cost of the laser light source. In addition, by designing and using a photon-integrated high-speed polarization analyzer, 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 of whose input ports are respectively connected to two output ports of a polarization beam splitter rotator, and four output ports of the 4x4 multimode interferometer are respectively connected to a photoelectric sensor. The present application provides a photon-integrated high-speed polarization analyzer that can demodulate scattered light signals into electrical signals.

[0013] The four-way interference structure is a 90° mixer, and the 90° mixer includes a first coupler, a second coupler, a third coupler and a fourth coupler, the input ends of the first coupler and the second coupler are respectively two input ends of the four-way beam splitting structure, the output ends of the first coupler and the second coupler are respectively connected to the third coupler and the fourth coupler, a π / 2 phase delay is arranged between the first coupler and the third coupler, and the third coupler and the fourth coupler each have two output ends, respectively connected to a photoelectric sensor. Another photon integrated high-speed polarization analyzer provided by the present 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, which is used to generate and amplify optical pulses and provide detection sensitivity.

[0015] The optical pulse source module comprises a laser source and a semiconductor amplifier connected in sequence. By applying a reverse voltage to the semiconductor amplifier to make it have a higher absorption degree, it can be used as an optical amplifier and also as 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 spot converter, so as to further filter out the additional spontaneous radiation noise of the semiconductor amplifier.

[0017] A second amplifier and a second bandpass filter are connected in sequence between the second spot mode converter and the high-speed polarization analyzer, so as to further amplify the scattered light and filter out the additional spontaneous radiation noise of 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, and the coherent amplification optical path includes a fifth coupler connected to the laser source, and the output end of the fifth coupler is connected to the input end of the polarization beam splitter rotator. By providing the coherent amplification optical path, a small portion of the light from the laser is directly injected into the polarizer, and interferes with the scattered light returned by the sensing optical fiber, thereby greatly enhancing the scattered light returned by the optical fiber and improving the measurement sensitivity.

[0021] A coherent amplification optical path is also provided. The coherent amplification optical path includes a fifth coupler connected to the laser source and a sixth coupler disposed between the fifth coupler and the polarization beam splitting rotator. The sixth coupler has two output ends, which are respectively connected to the two output ends of the polarization beam splitting rotator. By providing the coherent amplification optical path, a small part of the light from the laser is directly injected into the polarimeter, where it interferes with the scattered light returned from the sensing optical fiber, thereby greatly enhancing the scattered light returned from the optical fiber and improving the measurement sensitivity.

[0022] In a second aspect, the present invention provides a distributed optical fiber acoustic wave sensing system based on polarization state detection, including a sensing chip, an optical fiber circulator, a sensing optical fiber, and a data acquisition and processing module as described in any one of the first aspects;

[0023] 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 end of the second mode field converter;

[0024] The data acquisition and processing module is used to collect the demodulated electrical signals of the sensing chip and perform algorithm processing to calculate the polarization state information of the scattered light.

[0025] The data acquisition and processing module includes an analog circuit and a digital circuit. The data acquisition and processing module receives the electrical signals of the photoelectric sensor and processes them through the analog circuit and the digital circuit to calculate the polarization state information of the scattered light.

[0026] 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.

[0027] In a third aspect, the present invention provides a distributed optical fiber acoustic wave sensing method based on polarization state detection, which is implemented based on the sensing system described in any one of the second aspects, and includes the following steps:

[0028] The optical pulse source module generates optical pulses and delivers them to the first port of the optical fiber circulator through the first mode field converter, and then transmits them to the sensing optical fiber through the second port of the optical fiber circulator;

[0029] The optical pulses generate scattered light in the sensing optical fiber. The scattered light is input into the high-speed polarization analysis module through the third port of the optical fiber circulator and the second mode field converter;

[0030] The high-speed polarization analysis module is used to demodulate the received scattered light into electrical signals and output them to the data acquisition and processing module, and the polarization state information of the scattered light is obtained through algorithm processing by the data acquisition and processing module.

[0031] Compared with the prior art, the beneficial effects of the present invention mainly include the following: By providing a high-speed polarization analyzer to monitor the polarization state of the scattered light returned from the self-sensing optical fiber, this method can analyze the changes or disturbances on the optical fiber by measuring the different polarization states of the backward scattered light of a single pulsed light at a certain position and adjacent positions. Compared with the existing phase detection methods, the line width requirement for the laser light source can be greatly relaxed, and the cost of the laser light source can be significantly reduced. In addition, by designing and using a photon-integrated high-speed polarization analyzer, the size of the sensing system is greatly reduced, achieving high integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 A distributed optical fiber acoustic wave sensing system based on polarization state detection provided in Embodiment 1 of the present invention.

[0034] Figure 2 A distributed optical fiber acoustic wave sensing system based on polarization state detection provided in Embodiment 2 of the present invention.

[0035] Figure 3 Four different polarization analyzers provided by the present invention.

[0036] Figure 4 The photon-integrated polarization analyzer provided by the present invention.

[0037] Figure 5 A distributed optical fiber acoustic wave sensing system based on polarization state detection provided in Embodiment 3 of the present invention.

[0038] Figure 6 A distributed optical fiber acoustic wave sensing system based on polarization state detection provided in Embodiment 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] Regarding the foregoing and other technical contents, features and effects of the present invention, they will be clearly presented in the following detailed description of a preferred embodiment with reference to the drawings. The directional terms mentioned in the following embodiments, such as: up, down, left, right, front or back, etc., are only references to the directions of the attached drawings. Therefore, the directional terms used are for illustration and not for limiting the present invention.

[0040] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are proposed to help readers better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0041] In existing distributed acoustic sensing (DAS) systems, the vibration or acoustic wave at a certain location on the optical fiber is monitored by detecting the phase of the signal light. The phase information is usually obtained by interfering the backscattered light of the sensing optical fiber with the local reference light, or by interfering the backscattered lights at two different positions and then demodulating. Currently, phase detection has relatively high requirements for the laser light source, requiring an extremely narrow linewidth to achieve high sensitivity and ultra-long sensing range in sensing applications.

[0042] The present application provides a distributed acoustic sensing system based on polarization state detection. In this system, when an optical pulse in the sensing optical fiber encounters vibrations or acoustic waves, the state of polarization (SOP) of the optical signal will change. These changes or perturbations occur within the duration of a single pulse. By detecting the change in the polarization state, the change in vibration or acoustic wave can be sensed. Specifically, this technology mainly measures the different polarization states of the backscattered light of a single pulse of light in the sensing optical fiber at a certain position and adjacent positions. The propagation distance within the duration of the optical pulse at this position is very short. Compared with the above two DAS systems based on the interference of backscattered light and reference light or the backscattered light signals from different positions of the sensing optical fiber (and arriving at the photodetector at different times), since different polarization components are the backscattered light from adjacent positions within the same pulse duration of the sensing optical fiber, there is actually no or very low relative delay between different polarization components. They interfere with each other, enabling the coherence length of the laser light source to be relatively short (i.e., a wider laser linewidth). Therefore, the requirement for the linewidth of the laser light source can be greatly relaxed, and the cost of the laser light source can be significantly reduced. For example, low-cost lasers in OTDR can be directly used in polarization DAS, and these lasers can be single-longitudinal-mode or multi-longitudinal-mode in some applications.

[0043] Embodiment 1

[0044] Figure 1 A distributed optical fiber acoustic sensing system based on polarization state detection provided in Embodiment 1 of the present invention.

[0045] Refer to Figure 1 In A of, a basic DAS system includes a laser, a fiber optic circulator, a sensing fiber, a high-speed polarimeter, and a data acquisition and processing module.

[0046] 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 an optical pulse and input it into the connected optical fiber circulator. It can be understood that an optical fiber circulator is a multi-port non-reciprocal optical device with an optical guiding function. The optical fiber 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) almost without loss in numerical order, and there is almost no light output at other ports (the third port). And so on, when light is input from the second port, it can also be output from the third port with almost no loss, and at the same time, there is no light output at the first port or other ports.

[0047] In this embodiment, specifically, the optical pulse is input from the first port of the optical fiber circulator and then transmitted from the second port into the sensing optical fiber. During the transmission of the optical pulse in the sensing optical fiber, backward Rayleigh scattered light will be continuously generated. Then, the backward scattered light from the sensing optical fiber will be input from the second port of the optical fiber circulator and then output from the third port, and then transmitted into the high-speed polarimeter. The high-speed polarimeter will demodulate the input backward scattered light and convert it into an electrical signal and input it 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), etc.

[0048] It can be understood that Rayleigh scattering will occur during the transmission of the optical pulse in the sensing optical fiber. When a disturbance occurs at a certain position z in the sensing optical fiber, due to the influence of the disturbance, the polarization state (SOP) of the scattered light generated at this position z will be quickly changed, and then it will be detected by the high-speed polarimeter at time T z = 2nz / c. According to the detected time T z , the position 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 optical fiber, as shown in B in Figure 1 .

[0049] The local SOP change at position z in the sensing optical fiber during the pulse duration can be represented by the changes of the three Stokes parameters s1, s2, and s3, or by the change of the solid angle Ω on the Poincare sphere:

[0050]

[0051] Among them, the Stokes vector of the SOP at position z and time t is expressed as:

[0052]

[0053] Among them, T represents the transpose, and τ is the time delay of the polarization component within the optical pulse, that is, the duration of the optical pulse.

[0054] Under this design, the amount of local stress or vibration at position z in the sensing optical fiber can be represented by the change in the polarization state of the scattered light, that is, the change in the solid angle Ω or the change in the three Stokes parameters s1, s2, and s3 of the SOP.

[0055] Embodiment 2:

[0056] Figure 2 A distributed optical fiber acoustic wave sensing system based on polarization state detection provided by Embodiment 2 of the present invention.

[0057] Reference Figure 2 , the distributed optical fiber acoustic wave sensing system of this embodiment is obtained on the basis of Embodiment 1, and includes a laser (Laser), a modulator (Modulator) / switch (Switch), a semiconductor optical amplifier (SOA), a band-pass filter (BPF), an optical fiber circulator (Circulator), a sensing optical fiber (Sensing fiber), a high-speed polarimeter (Polarimeter), and a data acquisition and processing module.

[0058] In this embodiment, the laser, the modulator / switch, and the 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., the modulator or the switch), and then amplified by the semiconductor optical amplifier and output. The generated optical pulse can first pass through the band-pass filter (BPF) to filter out the additional spontaneous emission noise of the amplifier, and then be input into the sensing optical fiber through the optical fiber circulator; the scattered light returned from the sensing optical fiber is separated from the output light through the optical fiber circulator. In order to enhance the scattered light signal returned from the sensing optical fiber, an amplifier and a band-pass filter can be sequentially arranged between the optical fiber circulator and the high-speed polarimeter, and the scattered light is amplified and then input into the high-speed polarimeter to detect the fluctuation of the SOP caused by acoustic waves or vibrations.

[0059] It can be understood that the band-pass filter between the optical pulse source module and the optical fiber circulator is not necessary; similarly, the amplifier and the band-pass filter between the optical fiber circulator and the high-speed polarimeter are not necessary; the amplifier can be an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA).

[0060] In various DAS applications, optical pulses may require a relatively high extinction ratio (ER). For example, an ER on the order of 50 - 70 dB can achieve the required detection sensitivity. Such a high ER may not be easily achieved in various instances, including the modulator / switching devices used in certain DAS systems. Since an SOA can have a high absorbance by applying a reverse voltage, the SOA can be an optical amplifier and at the same time an optical pulse generator with a high extinction ratio. Therefore, in some embodiments, the modulator / switch can be removed, and the switching function of the optical pulse can be completed by driving the SOA only with a pulsed electrical signal.

[0061] In the above structure, a high-speed polarization analyzer is an important device for realizing the demodulation of the polarization state of scattered light. The structure of the high-speed polarization analyzer will be introduced below. Both amplitude-splitting polarimeters and wavefront-splitting polarimeters can be used to quickly detect changes in the SOP. Taking the wavefront-splitting polarimeter as an example, its basic principle is to divide the wavefront of the scattered light returned from the sensing fiber into separate light beams, then process them separately through different optical polarization components, and detect them by different optical detectors to obtain the Stokes vector elements.

[0062] Figure 3 Four different polarization analyzers are provided by the present invention. Referring to Figure 3 a and b in, the structures of the two provided polarimeters are similar, and both are composed of a polarizer array, a focusing lens, and a photodetector array (PD array) arranged in sequence along the light propagation direction. Specifically, it includes a wedged substrate for transmitting light, a plurality of polarization elements located on the substrate, and the polarization elements are arranged at different positions and are spatially separated from each other to receive different parts of the common input light to generate transmitted light beams with different polarization states; and a plurality of optical detectors, each detector corresponding to a polarization element and receiving the transmitted light beam from the corresponding polarization element. The difference between the two is that in Figure 3 a in, the polarizer is arranged on the planar side of the wedged substrate, while Figure 3 b in is to place the polarizer array on the wedged side of the wedged substrate. Generally, for ease of use, the polarizer array, the focusing lens, and the photodetector array are encapsulated in a housing to form a polarization analyzer.

[0063] Referring to Figure 3 a and b in, in this embodiment, the polarizer array is a 2x2 array, including three polarizers with different polarization directions, whose orientations are 0°, 45°, 90° and one right-handed circular polarization (RHC) or left-handed circular polarization (LHC) polarizer. Alternatively, one of the 0° or 90° polarizers can be replaced with a planar optical thin film.

[0064] In operation, the fiber collimator expands the input light from the fiber pigtail, and then divides it into four sub-beams with different polarizations through a 2x2 polarizer array, and then the sub-beams are directed to four different directions by the wedge-shaped substrate. Finally, the four sub-beams are focused by the focusing lens onto different PDs on the 2x2 PD array to generate corresponding photocurrents or photovoltages. In some embodiments, a transimpedance amplifier is connected after each PD to amplify the converted electrical signal and then input it into the data acquisition and processing module.

[0065] Figure 3 Figure c shows a polarimeter, which consists of a 2x2 lens array, a 2x2 polarizer array, and a 2x2 PD array. The lens array divides 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.

[0066] Figure 3 Figure d shows a polarimeter, which consists of a collimator, a pair of cylindrical lenses, a 1x4 lens array, a 1x4 polarizer array, and a 1x4 PD array. The beam from the fiber collimator is linearly expanded by the pair of cylindrical lenses, and then after passing through the 1x4 polarizer array, it is focused by the 1x4 lens array onto four different PDs on the 1x4 PD array. The SOP of the scattered light can be determined by the detected photocurrents Ii (i = 1, 2, 3, 4).

[0067] Note that the photodetector (PD) can be a PIN diode or an avalanche photodiode (APD) to improve the detection sensitivity.

[0068] The above is the DAS system composed of discrete optical devices. In fact, currently, an on-chip integrated DAS system can also be prepared using silicon photonics technology.

[0069] Embodiment III

[0070] The polarimeters provided above usually include a polarizer array, lenses, and a photodetector array, mostly discrete optical devices, which are relatively large in size and difficult to implement a photonic integrated DAS system. To implement a photonic integrated DAS system, the polarimeter needs to be improved.

[0071] Figure 4 This is the photonic integrated polarimeter provided by the present invention. Refer to Figure 4In a, an example of a polarization analyzer device configured for a first type of photonic integrated circuit (PIC). Figure 4 In a, a 4x4 multimode interferometer (MMI)-based polarimeter is shown, where a polarization beam splitting rotator (PSR) splits the input light into two orthogonally polarized states (TE and TM) and rotates the TM mode to the corresponding TE mode. Approximately 1 / 3 of the power in each of the two light beams (i.e., the original TE mode and the TE mode converted from TM) is coupled out, and the power of the two orthogonally polarized states is measured using photodetectors PDx and PDy. The remaining light of the two light beams then enters ports 1 and 3 of the 4x4 MMI, is split into 4 light beams, and detected by PD1, PD2, PD3, and PD4. Finally, information on the SOP and DOP is extracted using the six detected photocurrents. The PD can be a PIN diode or an avalanche photodiode.

[0072] Figure 4 In b, an example of a 90° mixer-based polarimeter is shown. Its structure is similar to that of the 4x4 MMI-based polarimeter, except that the 4x4 MMI is replaced by a 90° mixer. The structure of the 90° mixer is shown in the figure, where the first coupler (C1), the second coupler (C2), the third coupler (C3), and the fourth coupler (C4) are couplers with a coupling ratio of approximately 50%. The input ends of the first coupler and the second coupler receive the two scattered light beams separated by the PSR. The output ends of the first coupler and the second coupler are respectively connected to the third coupler and the fourth coupler. A phase retarder of π / 2 is provided between the first coupler and the third coupler. Each of the third coupler and the fourth coupler has two output ends, which are respectively connected to a photoelectric sensor.

[0073] Based on the above polarization analyzer, the polarization state of the scattered light, i.e., the Stokes parameters, can be obtained from the detected photocurrents as follows:

[0074] S0 = a(I x +I y ), S1 = a(I x -I y ), S2 = α(I1 - I2), S3 = α(I3 - I4) (2a)

[0075]

[0076] Figure 5 A distributed fiber optic acoustic wave sensing system based on polarization state detection provided in Embodiment 3 of the present invention.

[0077] Figure 5A photon-integrated distributed fiber optic acoustic sensing system is shown, which uses a high-speed polarization analyzer to obtain sensing signals from the optical fiber. This device is similar to that shown in the second embodiment, except that most of the functional components are integrated on a PIC chip (which can be called a photon-integrated DAS demodulation chip), and only the sensing optical fiber and the circulator are outside the chip.

[0078] This embodiment provides a distributed fiber optic acoustic 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 optical fiber, and a data acquisition and processing module.

[0079] Reference Figure 5 , the distributed fiber optic acoustic sensing system of this embodiment includes a photon-integrated DAS demodulation chip (i.e., the sensing chip), an optical fiber circulator (Circulator), a sensing optical fiber (Sensing fiber), and a data acquisition and processing module. The chip has an optical pulse output end and a scattered light input end, and the optical pulse output end and the scattered light input end are respectively connected to the first port and the third port of the optical fiber circulator; the optical pulse output end outputs an optical pulse signal to the optical fiber circulator and the sensing optical fiber, and the scattered light input end receives the scattered light returned from the sensing optical fiber and the optical fiber circulator.

[0080] Specifically, the photon-integrated DAS demodulation chip includes an optical pulse source module composed 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 a semiconductor optical amplifier and 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 enter the optical fiber circulator and then the sensing optical fiber through the first mode spot converter (SSC). Here, the output port of the first mode spot converter is the optical pulse output end of the demodulation chip; the scattered light returned from the sensing optical fiber enters from the scattered light input end of the demodulation chip after being separated from the output light by the optical fiber circulator. Here, a second mode spot converter is provided, and the input port of the second mode spot converter is the scattered light input end of the demodulation chip; in order to enhance the scattered light signal returned from the sensing optical fiber, a second amplifier and a second bandpass filter are sequentially provided after the second mode spot converter, and the scattered light can be amplified and then input into the high-speed polarization analyzer to detect the fluctuation of the SOP caused by sound waves or vibrations. Among them, there is a section of single-mode (SM) optical fiber between the optical fiber circulator and the scattered light input end of the demodulation chip, and the second mode spot converter is connected to the high-speed polarimeter through a waveguide that supports TE and TM modes. It can be understood that the high-speed polarimeter for measuring light here needs to be a photon-integrated polarimeter, such as Figure 4 one of the two types of photon-integrated polarization analyzers shown.

[0081] In this embodiment, the first band - pass filter between the optical pulse source module and the first mode spot converter is not necessary; similarly, the second amplifier and the second band - pass filter are not necessary either; in this embodiment, the amplifier can be an erbium - doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA).

[0082] Similar to the situation in Embodiment 2, in this embodiment, the modulator / switch in the optical pulse source module can also be removed, and a high extinction ratio optical pulse can be obtained by only driving the first amplifier with a pulsed electrical signal.

[0083] In the embodiments of the present application, the sensing optical fiber can be a scattering - enhanced optical fiber. For example, it can be processed by femtosecond laser pulses or ultraviolet radiation to enhance backscattering, thereby improving the detection sensitivity.

[0084] Embodiment 4:

[0085] Figure 6 A distributed fiber optic acoustic sensing system based on polarization state detection provided for Embodiment 4 of the present invention. This system is basically similar to that shown in Embodiment 3. The DAS system includes a photonic integrated DAS demodulation chip, an optical fiber circulator, a sensing optical fiber, and a data acquisition and processing module. The photonic integrated DAS demodulation chip has an output end and an input end, and the output end and the input end are respectively connected to the first port and the third port of the optical fiber circulator; the output end outputs an optical pulse signal to the sensing optical fiber, and the input end receives the scattered light returned from the sensing optical fiber and...

[0086] The difference is that, based on the chip shown in Embodiment 3, an additional set of coherent amplification optical paths is provided, that is, a part of the light from the laser is directly injected into the polarimeter to interfere with the scattered light returned from the sensing optical fiber. Through this coherent amplification, the scattered light returned from the optical fiber can be greatly enhanced, and the measurement sensitivity can be improved. Specifically, in this embodiment, a fifth coupler is added between the laser and the modulator / switch, which can divide the laser signal emitted by the laser into two paths of 50% and 50%. One path is used to generate an optical pulse, and the other path is used to generate coherent amplification light. Among them, the other path is divided into two paths through the additional sixth coupler and respectively input to the two output ends of the polarization beam splitting rotator; in this embodiment, the polarization analyzer adopts the structure shown in Figure 4 b shown in, and in other embodiments, the structure shown in Figure 4 a can also be adopted. In other embodiments, the sixth coupler may not be used, and the coherent amplification light and the scattered light can be input together from the input end of the polarization beam splitting rotator, and the function of coherent amplification can also be realized.

[0087] Some commonly used English nouns or letters adopted for the convenience of clear description in the present invention are only used for exemplary reference rather than restrictive interpretation or specific usage, and the protection scope of the present invention should not be limited by their possible Chinese translations or specific letters.

[0088] It should also be noted that, in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, 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 wave sensor chip based on polarization state detection, characterized in that: It includes an optical pulse source module, a first spot mode converter, a second spot mode converter and a high-speed polarization analysis module; The optical pulse source module is used to generate pulsed light and output it to an external optical fiber circulator and a sensing optical fiber through the first spot mode converter; the second spot mode converter is used to receive scattered light returned from the sensing optical fiber and the optical fiber circulator and input it into the high-speed polarization analysis module; 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 and rotates the TM mode signal light to the corresponding TE mode signal light and then outputs them respectively through the two output ports of the polarization beam splitter rotator; Each output end of the polarization beam splitter rotator is connected to a photoelectric sensor and an input end of the four-way interference structure; the four-way interference structure has four output ends, which are respectively connected to the remaining photoelectric sensors.

2. A distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: The four-way interference structure is a 4x4 multimode interferometer, two input ports of the 4x4 multimode interferometer are respectively connected to two output ports of the polarization beam splitter rotator, and four output ports of the 4x4 multimode interferometer are respectively connected to a photoelectric sensor.

3. A distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: 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 ends of the first coupler and the second coupler are respectively two input ends of the four-way beam splitting structure. The output ends of the first coupler and the second coupler are respectively connected to the third coupler and the fourth coupler. A π / 2 phase delay device is arranged between the first coupler and the third coupler. The third coupler and the fourth coupler each have two output ends, which are respectively connected to a photoelectric sensor.

4. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: The optical pulse source module comprises a laser source, an optical pulse generator and a semiconductor amplifier which are connected in sequence; the optical pulse generator comprises an optical modulator or an optical switch.

5. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: The optical pulse source module comprises a laser source and a semiconductor amplifier which are connected in sequence.

6. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: A bandpass filter is also connected between the optical pulse source module and the first spot converter.

7. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: A second amplifier and a second band-pass filter are connected in sequence between the second spot mode converter and the high-speed polarization analyzer.

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

9. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 1, characterized in that: The photoelectric sensor is a PIN diode or an avalanche photodiode.

10. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 4, characterized in that: A coherent amplification optical path is also provided, and the coherent amplification optical path includes a fifth coupler connected to the laser source, and the output end of the fifth coupler is connected to the input end of the polarization beam splitter rotator.

11. The distributed optical fiber acoustic wave sensor chip based on polarization state detection according to claim 4, characterized in that: A coherent amplification optical path is also provided, which includes a fifth coupler connected to the laser source and a sixth coupler provided between the fifth coupler and the polarization beam splitter rotator, wherein the sixth coupler has two output ends respectively connected to the two output ends of the polarization beam splitter rotator.

12. A distributed optical fiber acoustic wave sensing system based on polarization state detection, characterized in that: It comprises the sensor chip, optical fiber circulator, sensor optical fiber and data acquisition and processing module according to any one of claims 1 to 11; The output port of the first spot mode 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 end of the second spot mode converter; The data acquisition and processing module is used to collect the electrical signal demodulated by the sensor chip and perform algorithm processing to calculate the polarization state information of the scattered light.

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

14. The sensor system according to claim 12, characterized in that: 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-processed enhanced optical fiber.

15. A distributed optical fiber acoustic wave sensing method based on polarization state detection, characterized in that: The sensing system according to any one of claims 12 to 14 is implemented, comprising the following steps: The optical pulse source module generates an optical pulse and transmits it to the first port of the optical fiber circulator through the first spot mode converter, and then transmits it to the sensing optical fiber through the second port of the optical fiber circulator; The optical pulse generates scattered light in the sensing optical fiber, and the scattered light passes through the third port of the optical fiber circulator and the second spot mode converter and then is input into the high-speed polarization analysis module; The high-speed polarization analysis module is used to demodulate the received scattered light into an electrical signal and output it to the data acquisition and processing module, and the polarization state information of the scattered light is obtained by performing algorithm processing through the data acquisition and processing module.

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