Long-range and wide-frequency-response distributed acoustic sensing system and method based on photonic integration

Abstract

The present invention relates to the technical field of optical fiber sensing. Disclosed are a long-range and wide-frequency-response distributed acoustic sensing (DAS) system and method based on photonic integration. The system comprises: a low-voltage direct-current integrated power drive module, and an optical transmitter chip, an optical amplification and coupling module, an optical receiver chip, a signal conditioning and acquisition chip, and a digital signal processing chip which are connected in sequence. The DAS system based on photonic integration provided in the present invention exhibits characteristics such as a long range, a wide frequency response, high fidelity, ultra-high sensitivity, low power consumption, a compact size, and strong environmental adaptability.

Description

Long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system and method based on photonic integration TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system and method based on photonic integration. BACKGROUND

[0002] The sensing parameter of distributed acoustic sensing (DAS) is vibration acoustic wave signal, therefore, the sensing optical cable does not need to be in close contact with the measured object, and the sensing of the target state can be realized through the medium propagated acoustic field signal. Through the detection of the vibration acoustic wave of large-scale infrastructure, not only the structural damage information can be captured, but also the characteristics and information of the vibration source can be accurately restored, and the damage evolution law and failure mechanism of these large-scale facilities during service can be quantitatively revealed. Therefore, DAS is considered as the most practical value distributed optical fiber sensing technology for nondestructive testing of large-scale infrastructure.

[0003] There is a large mismatch between the performance envelope of the current DAS equipment based on discrete devices and the demand of typical applications. The sensing distance, frequency response, dynamic range and sensitivity in the DAS system are limited by the underlying mechanism, and there is always a mutual restraining relationship. Early risk warning of various large-scale facilities usually requires dynamic response, large dynamic range and high sensitivity, in addition, in some complex environments, higher requirements are put forward for the signal fidelity, sensing sensitivity, volume, weight, power consumption, environmental adaptability and other performances of the system.

[0004] Therefore, a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system and method based on photonic integration are proposed to solve the problems existing in the prior art, which is a problem that needs to be solved by the person skilled in the art.

[0005] SUMMARY

[0006] Therefore, the present application provides a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system and method based on photonic integration to solve the problems existing in the prior art.

[0007] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0008] A long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration, comprising: a low-voltage direct-current comprehensive electric drive module, and an optical transmitting chip, an optical amplification coupling module, an optical receiving chip, a signal conditioning and acquisition chip, and a digital signal processing chip connected in sequence.

[0009] The optical transmitting chip is used to synthesize the pulse sequence required by the DAS system, which contains multiple different wavelengths.

[0010] The optical amplification coupling module comprises an optical power amplifier, an optical circulator and an optical low noise amplifier connected in sequence, wherein the optical circulator is further connected with a sensing optical fiber; the optical power amplifier is connected with the pulse light modulator and is used for improving the pulse peak power; the backscattering signal returned through the optical circulator also contains multiple wavelengths due to the interleaving injection of multiple wavelengths of pulses into the sensing optical fiber; and the backscattering light signal is amplified by the optical low noise amplifier to obtain the multi-wavelength light signal after optical low noise amplification.

[0011] The optical receiving chip is used for separating and detecting the multi-channel scattered light under the wavelength division multiplexing mechanism to obtain a photoelectric detection signal.

[0012] The signal conditioning and acquisition chip is used for amplifying, filtering and quantizing the photoelectric detection signal to obtain independent n-channel demodulation results.

[0013] The digital signal processing chip is used for demodulation of the physical parameters carried by the backscattering light signal, high-dimensional feature extraction and pattern recognition, human-computer interaction and data communication.

[0014] The low-voltage direct-current integrated electric drive module is used for driving and controlling the optical transmitting chip, the optical amplification coupling module, the optical receiving chip, the signal conditioning and acquisition chip and the digital signal processing chip.

[0015] Optionally, the optical transmitting chip comprises a narrow linewidth light source array and a pulse light modulator connected in sequence.

[0016] The narrow linewidth light source array is used for outputting pulse light of different frequencies.

[0017] The pulse light modulator is used for processing the pulse light of different frequencies output by the narrow linewidth light source array, so as to obtain a detection light pulse under the wavelength division interleaving multi-domain multiplexing measurement mechanism, which includes single sideband frequency modulation and intensity modulation pulse shaping.

[0018] Optionally, the pulse light is processed based on a serial cascade modulation mode, so that the extinction ratio meets the requirements of the DAS system, and the method comprises the following steps:

[0019] 1) Each laser in the narrow linewidth light source array is alternately turned on at equal intervals in the time domain to form a pulse with a width of us level, so as to reconstruct an equivalent chirped grating REC technology and realize accurate control of the center wavelength of the laser.

[0020] 2) The n wavelengths of pulses generated by the multi-wavelength laser array are combined by a wavelength division multiplexer and interleaved into a single pulse sequence.

[0021] 3) by time-synchronized external modulation, the pulse light internal frequency stable region is cut into two symmetrical halves, and the latter half of the pulse frequency is shifted Δf, thus forming a frequency continuously changing chirp region and two stable regions with frequencies f and f+Δf within a single pulse;

[0022] 4) using a broadband Mach-Zehnder MZ modulator structure, by precisely balancing the loss of the two arms of the Mach-Zehnder interferometer, the multiple wavelength pulse signals provided by the laser array chip are simultaneously pulse-shaped with high extinction ratio, the chirp region is cut off, and the frequency stable region is further chopped into two sub-pulses with better rectangular coefficients and frequencies f and f+Δf, the two sub-pulses generated each have a pulse width reduced to the order of tens of ns and an interval of the order of hundreds of ns.

[0023] The above system, optionally, the frequency difference Δf and the pulse width τ of the two sub-pulses satisfy the following relationship:

[0024]

[0025] The above system, optionally, the optical receiving chip includes a wavelength division demultiplexer and a plurality of photodetectors connected in parallel with the wavelength division demultiplexer;

[0026] The wavelength division demultiplexer is connected with an optical low noise amplifier;

[0027] The wavelength division demultiplexer separates the multi-wavelength optical signal after optical low noise amplification into independent n-way outputs, and then the photoelectric conversion into electrical signals is performed by a plurality of parallel photodetectors.

[0028] The above system, optionally, the signal conditioning and acquisition chip includes a plurality of signal conditioning and acquisition branches equal in number to the photodetectors, each signal conditioning and acquisition branch includes a transimpedance amplifier, a bandpass filter and an analog-to-digital converter connected in turn; the transimpedance amplifier is connected with the photodetector in correspondence.

[0029] The above system, optionally, the digital signal processing chip includes a digital demodulation, a reconfigurable neural network and a microprocessor kernel connected in turn.

[0030] The above system, optionally, the optical transmitting chip is generated by a compound semiconductor process, the optical receiving chip is generated by a silicon optical process, and the optical transmitting chip and the optical receiving chip are both generated by a photonic wire bonding (PWB) method between the internal functional components of the optical transmitting chip and the optical receiving chip and between the optical transmitting chip and the optical receiving chip and a single mode optical fiber;

[0031] The optical transmitting chip and the optical receiving chip are close in space and merged into a unified package; the electrical pins of the packaged chip are directly bound on the circuit board by a soldering machine.

[0032] The light emitting chip, the light receiving chip, and the pump light source in the optical amplification coupling module are concentrated in a set area on the circuit board, and are uniformly controlled at a constant temperature.

[0033] The low-voltage direct-current integrated electric drive module centrally schedules the light emitting chip, the optical amplification coupling module, the light receiving chip, the signal conditioning and acquisition chip, and the digital signal processing chip in the system, and functions including temperature control, abnormal protection, gain stabilization, power drive, timing control, and special functions including human-computer interface, watchdog, low-power sleep, and high-precision reference.

[0034] Optionally, the signal conditioning and acquisition chip and the digital signal processing chip are in the form of two single chips of mixed circuits and pure digital circuits, and are welded on the circuit board and interconnected through microstrip lines of the circuit board.

[0035] A long-distance wide-frequency-response distributed optical fiber acoustic wave sensing method based on photon integration, applied to the long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photon integration, comprises the following steps:

[0036] S1: The light emitting chip outputs light signals of n wavelengths with a certain sequence in the time dimension, and each wavelength of the light signal is a sub-pulse with two components of frequencies f and f+Δf, and there is a gap of hundreds of nanoseconds.

[0037] S2: The light signal passes through a power amplifier to improve the pulse peak power, and is injected into a sensing optical cable after passing through an optical circulator.

[0038] S3: The backscattered light signal carrying event information is returned through the optical circulator and is amplified by an optical low-noise amplifier.

[0039] S4: In the optical receiving chip, the wave division demultiplexer separates the light signal into independent n-way outputs, and the light signal output by each way is the superposition of backscattered light signals of two frequency components of f and f+Δf.

[0040] S5: In the optical receiving chip, the detector array respectively performs photoelectric conversion on the signals of each wavelength, and records the beat frequency signal carrying phase information.

[0041] S6: The electric signal after photoelectric conversion is amplified, filtered, and quantized by the signal conditioning and acquisition chip, and is sent to the digital signal processing chip.

[0042] S7: The sensing data obtained by the digital signal processing chip through frequency division interleaving is processed and reconstructed.

[0043] Compared with the prior art, the application provides a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system and method based on photon integration, which has the following beneficial effects:

[0044] (1) The core functional components of the DAS system are integrated in a single chip, and the chips are connected through optical wire bonding, which greatly improves the requirements of the DAS in different application scenarios in terms of volume, weight, power consumption, reliability, environmental adaptability and the like.

[0045] (2) The system uses a laser array chip and an array detector to realize a wavelength division interleaving mechanism, breaks through the restriction between the sensing distance and the detection pulse light emission frequency, and can use a higher pulse emission frequency to improve the upper limit of the frequency response, the dynamic range and the detection sensitivity of the sensing instrument.

[0046] (3) By optimizing the top-level sensing system scheme, using external modulation pulse shaping and serial cascade modulation schemes, the stringent requirements of the prior art on the linewidth of the light source are greatly reduced, and high extinction ratio detection light pulses are obtained, so that the performance indicators of the photon integrated chip meet the requirements of the DAS system.

[0047] (4) The demodulated information of the system contains three dimensions of wavelength, space and time, and through continuous dynamic optimization between multiple synchronous independent measurement results, the influence of fading noise can be suppressed, the signal can be reconstructed with high precision, and the sensitivity of the signal is improved.

[0048] (5) The driving and power supply of each module in the system are merged from the functional point of view, and low-voltage direct current power supply is used, and each module is centrally scheduled, which avoids the functional redundancy of the existing scheme, suppresses the interference, and reduces the volume and power consumption. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the drawings needed in the embodiment or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the application, and those skilled in the art can obtain other drawings according to the provided drawings without creating any creative labor.

[0050] Fig. 1 is a structural block diagram of a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photon integration;

[0051] Fig. 2 is a flow chart of a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing method based on photon integration disclosed by the application;

[0052] Fig. 3 is a schematic diagram of a detection pulse light synthesis scheme under a wavelength division interleaving multi-domain multiplexing measurement mechanism.

[0053] Figure 4 is a flow chart of DAS signal processing under the wave division interleaving multi-domain multiplexing measurement mechanism of the application. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0055] In the present application, the relationship 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 the entities or operations, the term "comprising", "containing" or any other variant thereof is intended to cover non-exclusive containing, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or equipment including the element.

[0056] In view of the insurmountable technical obstacles faced by the DAS technology relying on discrete devices in the present stage in improving the sensing distance, frequency response, signal guarantee degree, sensing sensitivity, volume, weight, power consumption, environmental adaptability and the like, the application is based on a photonic integration route, the light emitting chip in the core functional components of the system is generated by using a compound semiconductor process, and the light receiving chip is generated by using a silicon light process; the top sensing system scheme is optimized, and through multi-domain interleaving multiplexing, serial cascade modulation and the like, the performance requirements of the photonic integrated components meet the DAS system; in terms of data processing, parallel demodulation, time slot interleaving, phase demodulation, signal interpolation and the like are performed on the multi-path sensing data, and the methods in three dimensions of wavelength, space and time are comprehensively utilized, so as to realize continuous dynamic optimization between multi-path synchronous independent measurement results, suppress the influence of fading noise, and reconstruct the signal with high precision; the driving and power supply of each module in the system are merged from the functional point of view, and are centrally scheduled by a low-voltage direct-current comprehensive electric drive module to other modules in the system, so as to reduce redundancy, suppress interference, and reduce volume and power consumption. The specific technical solutions are as follows:

[0057] Referring to Figure 1, the application discloses a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photon integration, comprising: a low-voltage direct-current comprehensive electric drive module, and an optical transmitting chip, an optical amplification coupling module, an optical receiving chip, a signal conditioning and acquisition chip, and a digital signal processing chip connected in sequence;

[0058] The optical transmitting chip is used for synthesizing a pulse sequence containing multiple different wavelengths required by the DAS system.

[0059] The optical amplification coupling module comprises an optical power amplifier, an optical circulator, and an optical low-noise amplifier connected in sequence, wherein the optical circulator is further connected with a sensing optical fiber; the optical power amplifier and the optical low-noise amplifier are simply referred to as optical power amplifier and optical low-noise amplifier in Figure 1.

[0060] The optical power amplifier is connected with a pulse light modulator and is used for improving the pulse peak power; the sensing optical fiber is injected through the optical circulator; since multiple wavelengths of pulses are injected into the sensing optical fiber in an interleaved manner, the backscattering signals returned through the optical circulator also contain multiple wavelengths; the backscattering light signals are amplified through the optical low-noise amplifier to obtain the multi-wavelength light signals after optical low-noise amplification.

[0061] The optical receiving chip is used for separating and detecting the multiple scattered light under the wavelength division multiplexing mechanism to obtain photoelectric detection signals.

[0062] The signal conditioning and acquisition chip is used for amplifying, filtering, and quantizing the photoelectric detection signals to obtain independent n-way demodulation results.

[0063] The digital signal processing chip is used for demodulating the physical parameters carried by the backscattering light signals, extracting high-dimensional features, performing pattern recognition, and realizing human-computer interaction and data communication.

[0064] The low-voltage direct-current comprehensive electric drive module is used for driving and controlling the optical transmitting chip, the optical amplification coupling module, the optical receiving chip, the signal conditioning and acquisition chip, and the digital signal processing chip; the timing synchronization, driving, and control requirements between the modules in the system are centrally scheduled in a high-integration manner to realize low power consumption and low noise.

[0065] Further, the optical transmitting chip comprises a narrow linewidth light source array and a pulse light modulator connected in sequence.

[0066] The narrow linewidth light source array is used for outputting pulse light of different frequencies.

[0067] Specifically, the narrow linewidth light source array is developed based on the reconstruction equivalent chirped grating (REC) technology, and the linewidth, center wavelength and stability of the array are mainly determined by the sampling grating in the laser cavity. The REC technology uses the apodization of the sampling function combined with the chirp of the sampling period to obtain the target reflection (or transmission) spectrum with the same performance as the real apodization and real grating period chirp. The preparation of a uniform seed grating is realized by one-step holographic exposure, and the sampling structure is formed by one-step micrometer-level photolithography process. The equivalent implementation of complex grating structures such as chirp, phase shift and apodization, which require nanometer-level process, can reduce the requirements for grating preparation. If the +1 order sub-grating is selected as the resonant wavelength range of the laser, the relative change of the period of the +1 order sub-grating is:

[0068] In the formula, P is the sampling period, ΔP is the length of the mutation at a certain position in the sampling grating, and Λ0 is the grating period.

[0069] On the laser cavity structure, the REC technology is used to realize a high-performance feedback cavity structure; and the process can be compatible with the traditional DFB semiconductor laser by adding a micrometer-level photolithography process.

[0070] The pulse light modulator is used for processing the pulse light of different frequencies output by the narrow linewidth light source array, so as to obtain the probe light pulse under the wave division interleaved multi-domain multiplexing measurement mechanism, including single sideband frequency modulation and intensity modulation pulse shaping.

[0071] Further, the single sideband frequency modulation is composed of a nested Mach-Zehnder interference structure composed of multiple electro-optic phase shifters. By applying an external electric signal to change the refractive index of the optical waveguide, the phase of the output optical signal changes with the change of the external electric signal, and finally the electro-optic modulation is completed.

[0072] The intensity modulation pulse shaping adopts a broadband Mach-Zehnder (MZ) modulator structure. By balancing the loss of the two arms of the Mach-Zehnder interferometer, a high extinction ratio is realized at multiple wavelengths. The extinction ratio ER and the ratio r of the light transmittance of the two arms satisfy the following relationship:

[0073] Further, FIG. 3 is a light emitting chip structure and working principle: the pulse light is processed based on a serial cascade modulation mode (specifically implemented in the pulse light modulator), so that the extinction ratio meets the requirements of the DAS system, and specifically includes the following steps:

[0074] 1) Each laser in the narrow linewidth light source array is turned on at equal intervals in the time domain to form a pulse with a width of us level, so as to realize precise control of the center wavelength of the laser by using the reconstruction equivalent chirped grating (REC) technology;

[0075] 2) The n-wavelength pulses generated by the multi-wavelength laser array are combined by a wavelength division multiplexer and interleaved into a single pulse sequence;

[0076] 3) By external modulation in time, the pulse light is divided into two symmetrical halves in the frequency stable region, and the latter half of the pulse frequency is shifted by Δf, thus forming a frequency continuously changing chirp region and two stable regions with frequencies f and f+Δf within a single pulse;

[0077] 4) A broadband Mach-Zehnder MZ modulator structure is used to accurately balance the loss of the two arms of the Mach-Zehnder interferometer, to simultaneously provide high extinction ratio pulse shaping for the multiple wavelength pulse signals provided by the laser array chip, to cut off the chirp region, and to further chop the frequency stable region into two sub-pulses with better rectangular coefficients and frequencies f and f+Δf, and to generate two sub-pulses with pulse widths reduced to tens of ns and intervals of hundreds of ns.

[0078] Wherein, the frequency difference Δf and the pulse width τ of the two sub-pulses satisfy the following relationship:

[0079] Specifically, to meet the miniaturization requirement of the system, the optical amplification coupling module is integrated in a common pump and drive manner, and is realized in a compact module based on discrete devices. The optical amplification coupling module adopts a two-stage control manner to realize flexible control and adjustment of the gain of the power amplifier and the low-noise amplifier. The first-stage control is the output and output light intensity control of the pump light source by the control module, and the second-stage control is the attenuation size control of the power amplifier by the two-stage constant power control signal and the attenuation size control of the low-noise amplifier by the two-stage constant gain control signal.

[0080] Further, the optical receiving chip includes a wavelength division demultiplexer, a plurality of photodetectors (PD1, PD2,..., PD n ) connected in parallel with the wavelength division demultiplexer;

[0081] The wavelength division demultiplexer is connected with the optical low-noise amplifier;

[0082] The wavelength division demultiplexer separates the multi-wavelength optical signal after the optical low-noise amplification into independent n-way outputs, and then the photoelectric conversion into electrical signals is performed by the plurality of parallel photodetectors.

[0083] Specifically, for the wavelength division multiplexer of the DAS system, a series of micro resonant cavity filters are adopted, and the ring-shaped micro resonant cavity is constructed with a small turning radius of 3-5 microns based on the large refractive index difference of the silicon optical waveguide. A larger free spectral range is obtained through a smaller resonant cavity perimeter. Each micro resonant cavity filter can separate the signals of a wavelength channel. The resonant wavelength of each micro resonant cavity filter is adjusted by a heater through the thermo-optic effect, so as to accurately and stably control the center wavelength of each micro resonant cavity filter. The design of coupling multiple resonant cavities realizes the characteristics of steep roll-off between spectral passband and bandgap, low crosstalk between different wavelength channels, etc.

[0084] Further, the signal conditioning and acquisition chip includes a plurality of signal conditioning and acquisition branches corresponding to the number of photodetectors, each signal conditioning and acquisition branch includes a transimpedance amplifier (TIA), a bandpass filter (BPF) and an analog-to-digital converter (ADC) connected in sequence; the transimpedance amplifier is connected with the photodetector in correspondence.

[0085] Specifically, the photoelectric current is subjected to signal conditioning, acquisition and processing to obtain independent n-way demodulation results. If the pulse repetition frequency of a single channel is f s , after interpolation processing, the equivalent pulse repetition frequency of nf s can be obtained, and the theoretical upper limit of the frequency response will reach nf s / 2.

[0086] Further, the digital signal processing chip includes a digital demodulation, a reconfigurable neural network and a microprocessor kernel connected in sequence. The microprocessor kernel is a RISC-V architecture microprocessor kernel.

[0087] Specifically, the DAS signal processing procedure based on the photonic integrated system includes the following steps:

[0088] 1) Parallel demodulation is performed on different wavelength electrical signals to obtain phase data varying with space for each wavelength;

[0089] 2) The phase data obtained for different wavelengths are spliced and combined in the time dimension according to the time interval of switching between different wavelengths in the optical chip array and the sampling recovery time of the digital signal; at this time, data in three dimensions of wavelength, space and time can be obtained;

[0090] 3) Interpolation operation is performed on the phase data demodulated for multiple wavelengths in the time domain to obtain the distribution of phase changes along the time axis;

[0091] 4) According to the low probability characteristic that multiple independent measurement results simultaneously appear fading at adjacent time and same position, the three-dimensional method of wavelength, space and time is comprehensively utilized to realize continuous dynamic optimization between multiple synchronous independent measurement results; high-precision reconstruction of the signal is completed;

[0092] 5) Reconfigurable network can identify and classify events; adjust the structure and parameters of the network to identify and classify different monitoring tasks of the sensing system, etc., to improve the scene adaptability.

[0093] Further, the light emitting chip is generated by using a compound semiconductor process, the light receiving chip is generated by using a silicon light process, and the light emitting chip and the light receiving chip are connected by using optical wire bonding (Photonic Wire Bonding, PWB) between the internal functional components of the light emitting chip and the light receiving chip and between the light emitting chip and the light receiving chip and a single-mode optical fiber; the volume, weight, and power consumption of the system are greatly reduced, and the environmental adaptability is enhanced.

[0094] The light emitting chip and the light receiving chip are arranged close to each other and merged into a unified package; the electrical pins of the package are directly bound to the circuit board by using a soldering machine;

[0095] The light emitting chip, the light receiving chip, and the pump light source in the optical amplification and coupling module are concentrated in a set area on the circuit board and are uniformly controlled at a constant temperature;

[0096] The low-voltage direct-current integrated electric drive module centrally schedules the light emitting chip, the optical amplification and coupling module, the light receiving chip, the signal conditioning and acquisition chip, and the digital signal processing chip in the system, and the functions include temperature control, abnormal protection, gain stabilization, power supply driving, timing control, and also include special functions such as human-computer interface, watchdog, low-power sleep, and high-precision reference.

[0097] Further, the signal conditioning and acquisition chip and the digital signal processing chip are in the form of two single chips of a mixed circuit and a pure digital circuit and are welded on the circuit board and interconnected through microstrip lines on the circuit board.

[0098] Corresponding to the system described in FIG. 1, the application also discloses a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing method based on photonic integration, which is applied to the long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration described in FIG. 1, and specific steps are shown in FIG. 2.

[0099] S1: the light emitting chip outputs n light signals with a certain sequence in the time dimension, and each light signal is a sub-pulse with two components of frequency f and f+Δf, and there is a gap of about 100 ns;

[0100] S2: the light signal passes through a power amplifier to improve the pulse peak power, and is injected into a sensing optical cable after passing through an optical circulator;

[0101] S3: the backscattering light signal carrying event information is returned through an optical circulator and is amplified by an optical low-noise amplifier;

[0102] S4: separate into independent n-way outputs in the optical receiving chip with a wavelength division demultiplexer, and the optical signal of each output is the superposition of backscattering light signals of two frequency components f and f+Δf;

[0103] S5: photoelectric conversion of signals of each wavelength is carried out with a detector array in the optical receiving chip, and beat frequency signals carrying phase information are recorded;

[0104] S6: the electrical signal after photoelectric conversion is amplified, filtered and quantized by a signal conditioning and collection chip, and is sent to a digital signal processing chip;

[0105] S7: the sensing data obtained by the digital signal processing chip is processed and reconstructed.

[0106] When the system starts measuring, the light emitting chip first synthesizes a pulse sequence containing multiple different wavelengths required by the DAS system, as shown in Figure 3, which is a detection pulse light synthesis scheme under the wavelength division interleaved multi-domain multiplexing measurement mechanism, which is divided into four functional areas in series in the light emitting chip:

[0107] 1) Functional area 1 - laser internal modulation: composed of an array of n lasers with different wavelengths. When the system starts measuring, each laser in the array alternately opens at equal intervals in the time domain, and a pulse with a width of μs level is formed through internal modulation. There is a certain length of chirp area in the short time gap after the laser is turned on, but the frequency of the pulse light will soon stabilize and maintain at f. When the laser is turned off, a certain degree of leakage light will be generated.

[0108] 2) Functional area 2 - multi-wavelength interleaving: the pulses of n wavelengths are combined by a wavelength division multiplexer and interleaved into a single pulse sequence, realizing the multiplexing of the measurement system in the time domain and the wavelength domain. Since there is leakage light for each wavelength output, the leakage light level of the combined pulse light sequence will be increased by n times, causing the extinction ratio to decrease. However, from any single wavelength, this decrease should not be very obvious.

[0109] 3) Functional area 3 - external modulation pulse frequency shift: realized by a single sideband frequency modulator. Through time-synchronous external modulation, this area will divide the internally frequency-stable region of the pulse light into approximately symmetric halves, and shift the frequency of the latter half of the pulse by Δf. Thus, within a single pulse, a chirp region with continuously varying frequency and two stable regions with frequencies f and f+Δf are formed. The modulator has a certain suppression effect on the leakage light, which can improve the extinction ratio.

[0110] 4) Functional Area 4 - External Modulation Pulse Shaping: Pulse shaping is achieved by an intensity modulator, removing the chirped region and further chopping the frequency-stable region into a rectangular coefficient, resulting in two sub-pulses with frequencies of f and f+Δf. The pulse width of each sub-pulse is reduced to the tens of nanoseconds range, with an interval of hundreds of nanoseconds. This modulator further suppresses leakage light.

[0111] The control of the pulse width and repetition frequency of the pulsed light is achieved by an embedded control circuit. The host computer obtains the values ​​of the pulse width and repetition frequency to be changed through serial communication, and writes these values ​​into an electrically erasable programmable read-only memory (EEPROM). 2 The PROM (Programmable Logic ROM) is used to send the pulses to a Complex Programmable Logic Device (CPLD). The CPLD obtains its master clock from an active crystal oscillator and outputs two pulses based on the received information. One is a control pulse, whose pulse width and repetition frequency are consistent with the control information issued by the controller. This pulse is received by the AOM (Analog Memory Operator) after passing through a buffer. The other is a synchronization pulse, which is completely synchronized with the control pulse, but with a fixed pulse width. This pulse is used as a synchronization trigger signal for the data acquisition card. The system pulse width adjustment step is 10ns, implemented using a 100MHz pulse width modulation (PWM) peripheral module. The CPLD to be used is the CompactPGC4KLS from the domestic manufacturer Ziguang Tongchuang. The EEPROM to be used is the FM24C08A from Fudan Microelectronics, used to store the pulse width and repetition frequency values. Even if the microcontroller does not receive control commands from the controller after power-on, it can still control the CPLD to output pulses normally using the default values ​​set during the last power-on.

[0112] After the probe pulse light sequence is synthesized, it enters the optical amplification and coupling module, where the peak power of the pulses is increased by a power amplifier and injected into the sensing optical fiber through an optical circulator. Since multiple wavelengths of pulses are interleaved and injected into the sensing fiber, the backscattered signal returned by the optical circulator will also contain multiple wavelengths. These scattered lights are amplified by an optical low-noise amplifier.

[0113] The optical signal amplified by the optical low noise amplifier is divided into independent n-way outputs by a wavelength division demultiplexer, and is converted into electrical signals by an array of photodetectors. After the electrical signals are amplified, conditioned and collected by the signal conditioning and collection chip, independent n-way digital signals are obtained. The signal conditioning circuit mainly includes an amplifier and two bandpass filters with a center frequency of 50MHz. The electrical signals output by the photodetector are filtered by the first bandpass filter to remove most of the noise, and then amplified by the amplifier to a range close to the collection card range. Since the amplifier will inevitably introduce noise during amplification, the amplified signal is filtered by the second bandpass filter to remove the noise of the amplifier, and then collected by the collection card. The filter and the amplifier are standard devices 7BN01B5-50 filter and FD-9NH15NLF03-100 amplifier of Boya Electronics respectively, and the digital signal collection selects CBM96 / 94 series ADC of Hicmicro.

[0114] The digital signals are further processed by a digital signal processing chip carrying lightweight and migratory algorithms. The specific steps are shown in FIG. 4. The electrical signals of different wavelengths are demodulated in parallel to obtain the phase data of each wavelength varying with space. Then, the phase data of different wavelengths are spliced and combined in the time dimension according to the time interval of switching between different wavelengths in the optical chip array and the sampling recovery time of the digital signal. At this time, the data in the three dimensions of wavelength, space and time can be obtained. The phase data of multiple wavelengths are interpolated in the time domain to obtain the distribution of the phase change along the time axis. According to the low probability characteristic that multiple independent measurement results occur simultaneously at adjacent time and the same position, the three-dimensional method of wavelength, space and time is comprehensively used to realize continuous dynamic optimization between multiple synchronous independent measurement results. The high-precision reconstruction of the signal is completed. Finally, the reconstructed network can identify and classify events. The structure and parameters of the network are adjusted to identify and classify different monitoring tasks of the sensing system, etc., to improve the scene adaptability.

[0115] Each of the embodiments in the specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments. Especially, for the system or system embodiment, since it is basically similar to the method embodiment, it is described more simply, and the related parts can be referred to the part of the method embodiment. The above-described system and system embodiment are only illustrative, and the units described as separate components can be or can not be physically separated, and the components displayed as units can be or can not be physical units, i.e. they can be located in one place or distributed on multiple network units. According to the actual needs, part or all of the modules can be selected to achieve the purpose of the embodiment. Those skilled in the art can understand and implement without creative labor.

[0116] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and, while certain embodiments according to the principles set forth herein have been shown and described, various modifications and substitutions can be made thereto without departing from the spirit and scope of the application as these broadly disclosed. Therefore, the application is not to be limited only to the embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A long-range wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration, characterized in that, The system comprises a low-voltage direct-current integrated electric drive module, and a light emitting chip, a light amplification coupling module, a light receiving chip, a signal conditioning and acquisition chip, and a digital signal processing chip connected in sequence. The light emitting chip is configured to synthesize a pulse sequence containing multiple different wavelengths required by a DAS system. The light amplification coupling module comprises an optical power amplifier, an optical circulator, and an optical low-noise amplifier connected in sequence, wherein the optical circulator is further connected with a sensing optical fiber; the optical power amplifier is connected with a pulse light modulator and is configured to improve the pulse peak power; the sensing optical fiber is injected with the pulse light through the optical circulator; since the multiple wavelengths of the pulse light are interleaved and injected into the sensing optical fiber, the backscattering signal returned through the optical circulator also contains multiple wavelengths; the backscattering light signal is amplified by the optical low-noise amplifier to obtain a multi-wavelength light signal after optical low-noise amplification. The light receiving chip is configured to separate and detect the multi-channel scattered light under a wavelength division multiplexing mechanism to obtain a photoelectric detection signal. The signal conditioning and acquisition chip is configured to amplify, filter, and quantize the photoelectric detection signal to obtain independent n-channel demodulation results. The digital signal processing chip is configured to demodulate the physical parameters carried by the backscattering light signal, extract high-dimensional features, perform pattern recognition, and perform human-computer interaction and data communication. The low-voltage direct-current integrated electric drive module is configured to drive and control the light emitting chip, the light amplification coupling module, the light receiving chip, the signal conditioning and acquisition chip, and the digital signal processing chip.

2. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 1, wherein the light emitting chip comprises a narrow linewidth light source array and a pulse light modulator connected in sequence. The narrow linewidth light source array is configured to output pulse light of different frequencies. The pulse light modulator is configured to process the pulse light of different frequencies output by the narrow linewidth light source array to obtain detection light pulses under a wavelength division interleaved multi-domain multiplexing measurement mechanism, including single sideband frequency modulation and intensity modulation pulse shaping.

3. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 2, wherein the pulse light is processed based on a serial cascade modulation mode to make the extinction ratio meet the requirements of the DAS system, and the processing comprises the following steps: 1) Each laser in the narrow linewidth light source array is turned on at equal intervals in the time domain to form a pulse with a width of us level, so as to reconstruct an equivalent chirp grating (REC) technology and accurately control the center wavelength of the laser; 2) The n wavelengths of pulse light generated by the multi-wavelength laser array are combined by a wavelength division multiplexer to form a single pulse sequence; 3) The stable frequency region in the pulse light is divided into two symmetrical halves by time-synchronous external modulation, and the frequency of the latter half of the pulse is shifted by Δf, so that a chirp region with continuously changing frequency and two stable regions with frequencies of f and f+Δf are formed in a single pulse. ​ ​ ​ 4. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 3, wherein the Mach-Zehnder MZ modulator structure with a wide band is adopted to realize high-extinction-ratio pulse shaping of multiple wavelength pulse signals provided by the laser array chip by precisely balancing the loss of two arms of the Mach-Zehnder interferometer, to cut off the chirp region, and to further chop the frequency stable region into two sub-pulses with better rectangular coefficients and the frequencies of f and f+Δf, so that the two sub-pulses generated each have a pulse width reduced to tens of nanoseconds and an interval of hundreds of nanoseconds.

4. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 3, wherein, For two sub-pulses of the same wavelength and with a frequency difference Δf, the frequency difference Δf and the pulse width τ satisfy the following relationship:

5. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 1, wherein, The optical receiving chip comprises a wavelength division demultiplexer and a plurality of photodetectors connected in parallel with the wavelength division demultiplexer. The wavelength division demultiplexer is connected with an optical low-noise amplifier. The wavelength division demultiplexer separates the multi-wavelength optical signal after the optical low-noise amplification into independent n-way outputs, and then the photoelectric conversion into electrical signals is performed by the plurality of parallel photodetectors.

6. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 5, wherein, The signal conditioning and acquisition chip comprises a plurality of signal conditioning and acquisition branches in the same number as the photodetectors, each signal conditioning and acquisition branch comprising a transimpedance amplifier, a band-pass filter and an analog-to-digital converter connected in sequence; and the transimpedance amplifier is connected with the photodetector in correspondence.

7. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 6, wherein, The digital signal processing chip comprises a digital demodulation, a reconfigurable neural network and a microprocessor kernel connected in sequence.

8. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 1, wherein, The optical transmitting chip is generated by using a compound semiconductor process, the optical receiving chip is generated by using a silicon optical process, and the optical transmitting chip and the optical receiving chip are connected by using optical wire bonding Photonic Wire Bonding, PWB, between the internal functional components of the optical transmitting chip and the optical receiving chip and between the optical transmitting chip and the optical receiving chip and a single-mode optical fiber; The optical transmitting chip and the optical receiving chip are arranged close to each other and merged into a unified package; and the electrical pins of the packaged chip are directly bound on the circuit board by using a soldering machine; The optical transmitting chip, the optical receiving chip and the pump light source in the optical amplification coupling module are concentrated in a set area on the circuit board and uniformly controlled by a constant temperature device; The low-voltage direct-current integrated electric drive module centrally schedules the transmitting chip, the optical amplification coupling module, the optical receiving chip, the signal conditioning and acquisition chip and the digital signal processing chip in the system, and the functions thereof include temperature control, abnormal protection, gain stabilization, power supply driving, timing control, human-computer interface, watchdog, low-power sleep, high-precision reference and special functions.

9. The long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photonic integration according to claim 8, wherein, The signal conditioning and collection chip and the digital signal processing chip are in the form of two single chips of mixed circuit and pure digital circuit, are welded on the circuit board, and are interconnected through the microstrip line of the circuit board.

10. A long-distance wide-frequency-response distributed optical fiber acoustic wave sensing method based on photonic integration, characterized in that, The application is applied to a long-distance wide-frequency-response distributed optical fiber acoustic wave sensing system based on photon integration, The method comprises the following steps: S1: outputting optical signals of n wavelengths with a certain sequence in the time dimension from an optical emission chip, and each wavelength of the optical signals is a sub-pulse with two components of frequency f and f+Δf, and there is a gap of hundreds of nanoseconds; S2: the optical signals pass through a power amplifier to improve the pulse peak power, and are injected into a sensing optical cable after passing through an optical circulator; S3: backscattered optical signals carrying event information are returned through the optical circulator and are amplified by an optical low-noise amplifier; S4: the optical signals are separated into independent n-way outputs in an optical receiver chip through a wavelength division demultiplexer, and the optical signals output by each way are superpositions of backscattered optical signals of two frequency components of f and f+Δf; S5: the signals of each wavelength are photoelectrically converted by a detector array in the optical receiver chip, and beat signals carrying phase information are recorded; S6: the electric signals after photoelectric conversion are amplified, filtered and quantized by a signal conditioning and collection chip, and are sent to a digital signal processing chip; S7: sensing data obtained by frequency division interleaving of the multiple channels are processed and reconstructed by the digital signal processing chip.

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