High sensitivity vibration sensing system and method employing a broadband light source

Abstract

The application discloses a high-sensitivity vibration sensing system and method using a broadband light source, wherein after broadband light passes through a fiber grating, the spectrum width of the light source is compressed, the coherence length is controlled, and two beams of light with an optical path difference within a specific range interfere, so that the noise of the sensing system can be significantly reduced; a heterodyne modulation and demodulation method is adopted, a fiber delay module and an acousto-optic frequency shifter are introduced into a reference path, the fiber length is compensated by controlling the cavity length, the high-order reflected detection light in the fiber Fabry-Perot resonant cavity interferes with the first-order reflected reference light, and the effect of improving the sensitivity is achieved. The application utilizes the advantages of the spectrum width of the broadband light source and the wavelength characteristics of the fiber grating, and realizes the dynamic signal modulation and demodulation of the broadband light source heterodyne interference with the advantages of reusability, high sensitivity and low cost.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more specifically to a high-sensitivity vibration sensing system and method using a broadband light source. Background Technology

[0002] Fiber optic sensing systems have been widely used in many practical applications and scientific research fields, such as environmental monitoring, resource exploration, biomedicine, and aerospace, due to their unique advantages such as strong resistance to electromagnetic interference, no electricity at the detection end, and resistance to harsh environments. Interferometric fiber optic vibration sensors utilize optical fibers that can both transmit and sense external signals. When a vibration signal is applied to the sensing unit of the system, the phase of the light wave transmitted in the fiber changes accordingly; therefore, detecting the returned phase change yields relevant information about the vibration signal. Phase-modulated fiber optic vibration systems mainly come in several types: Mach-Zehnder, Michelson, Sagnac, and Fabry-Perot, with flexible and diverse structural configurations. Fiber optic sensing systems used in conjunction with fiber optic Fabry-Perot interferometers, compared to traditional fiber optic sensing systems, offer advantages such as high resolution, simple structure, and ease of arraying, making them highly favored by researchers and a research hotspot in the design of large-scale, lightweight fiber optic sensor arrays.

[0003] Currently, most high-resolution fiber optic sensing systems and demodulation methods rely on highly coherent, narrow-linewidth kilohertz or even 100 Hz light sources. These light sources are expensive, and narrow-linewidth lasers are incompatible with wavelength division multiplexing (WDM) sensing systems. Increasing the number of light source wavelengths requires increasing the number of lasers, which greatly increases the cost and complexity of the sensing system. Therefore, although laser-driven fiber optic sensors achieve very high measurement accuracy, their applications are very limited. Currently, some broadband light source-driven sensing systems use PDH technology, which can achieve piscis-strain resolution. However, since each sensing unit requires closed-loop real-time feedback control, it cannot fully utilize the inherent wavelength division multiplexing performance of broadband light sources (Shuangxiang Zhao, White-light-driven resonant fiber-opticstrain sensor[J], Optics Letters, 2020, 45(18), 5217-5220). Some sensing systems driven by broadband light sources have a resolution of nanostrain, but still cannot meet the requirements of high-sensitivity vibration sensing (Li Enbang, Low-cost high-resolution multi-channel wavelength demodulator for fiber optic grating sensing [J], Journal of Instrumentation, 2007, 28(1), 1-6).

[0004] Existing fiber optic vibration sensing systems and methods struggle to simultaneously achieve low cost, high sensitivity, and ease of array formation. Therefore, it is necessary to develop a system and demodulation method that combines these characteristics to improve the dynamic signal demodulation capabilities of fiber optic sensing systems and arrays. Summary of the Invention

[0005] To address the aforementioned technical problems and shortcomings in this field, this invention provides a high-sensitivity vibration sensing system employing a broadband light source. The broadband light is narrowed by passing through a fiber optic grating, and the coherence length is controlled to allow interference between two beams with optical path differences within a specific range, significantly reducing the noise of the sensing system. A heterodyne modulation and demodulation method is used, introducing an optical fiber delay module and an acousto-optic frequency shifter into the reference path. By controlling the cavity length to compensate for the fiber length, interference between the higher-order reflected probe light and the first-order reflected reference light in the fiber Fabry-Perot resonator is achieved, thereby enhancing sensitivity. This invention utilizes the advantages of the broadband light source's spectral width and the wavelength characteristics of the fiber optic grating to achieve reusable, high-sensitivity, and low-cost broadband light source heterodyne interference dynamic signal modulation and demodulation.

[0006] A high-sensitivity vibration sensing system employing a broadband light source includes:

[0007] Broadband light source module, used to emit broadband light;

[0008] A fiber grating filter for bandwidth filtering of broadband light includes a first circulator, which outputs broadband light to one or more fiber gratings with different center wavelengths and the same bandwidth located on the same optical fiber, and the reflected broadband light is output through the first circulator.

[0009] The first coupler is used to split the broadband light after bandwidth filtering into two optical signals. One optical signal is used as the probe light and passes through the probe path, while the other optical signal is used as the reference light and passes through the reference path.

[0010] The fiber Fabry-Perot resonant cavity array comprises several groups of fiber gratings for multiple reflections of the probe optical signal. The reflected signal is transmitted to a second coupler via a first coupler. Each group of fiber gratings in the array consists of a pair of fiber gratings with the same bandwidth and center wavelength. The number of fiber gratings and their center wavelengths on each fiber in the array are set according to the number and center wavelengths of the fiber gratings in the fiber grating filter. The fiber gratings on each fiber in the array and their corresponding fiber gratings in the fiber grating filter have the same center wavelength. The bandwidth of the fiber gratings in the array is greater than that in the fiber grating filter, which can reduce insertion loss attenuation caused by reflection in the optical path, increase sensitivity, and achieve improved equivalent resolution.

[0011] The second circulator is used to output the reference optical signal to the fiber Bragg grating array, and the reflected signal reflected back from the fiber Bragg grating array is output to the acousto-optic frequency shifter through the second circulator.

[0012] A fiber grating array comprising several fiber gratings is used to reflect reference path optical signals; the fibers in the fiber grating array are arranged in a one-to-one correspondence with the fibers in the fiber Fabry-Perot resonator array; the number of fiber gratings and the center wavelength on each fiber in the fiber grating array are arranged in a corresponding manner to the number of fiber grating groups and the center wavelength on the corresponding fibers in the fiber Fabry-Perot resonator array; the fiber gratings in the fiber grating array and the corresponding fiber grating groups in the fiber Fabry-Perot resonator array have the same bandwidth and center wavelength;

[0013] An acousto-optic frequency shifter is used to reduce noise by shifting the frequency of the signal returned by a fiber Bragg grating array.

[0014] The fiber delay module, including an electrically adjustable fiber delay line and a cavity length compensation fiber, is located between the acousto-optic frequency shifter and the second coupler. It is used to make small-amplitude precise and large-amplitude coarse adjustments to the length of the reference path fiber to match the optical path difference between the reference path and the probe path, respectively.

[0015] The second coupler is used to perform cavity length-matched heterodyne interference on the reflected light from the probe path and the reference path, and outputs an interference signal;

[0016] An interference light power adjustment device is disposed between the second coupler and the photodetector to adjust the light power of the interference light so that the light power operates in the linear operating region of the photodetector.

[0017] Several photodetectors are used to detect the beat frequency signal of the interference signal between the detection path and the reference path, convert the photoelectric signal, and output it to the bandpass filter; the number of photodetectors is consistent with the number of fiber gratings in the fiber grating filter, the number of fiber grating groups in the fiber Fabry-Perot resonator array, and the number of center wavelength types of fiber gratings in the fiber grating array.

[0018] A bandpass filter is used to filter frequency-shifted signals in electrical signals and extract radio frequency signals carrying sensing phase shift information;

[0019] Real-time data acquisition module, used for real-time acquisition of radio frequency signals;

[0020] The data processing module is used to process the acquired radio frequency signals, demodulate the interference signals, and obtain the detection results of the broadband light source high-sensitivity cavity length matched heterodyne interference signals.

[0021] In this invention, "several" refers to one or more quantities.

[0022] In one embodiment, the high-sensitivity vibration sensing system employing a broadband light source includes a first erbium-doped fiber amplifier for power amplification of broadband light, disposed between the fiber grating filter and the first coupler.

[0023] In one embodiment, the high-sensitivity vibration sensing system employing a broadband light source includes an interference optical power adjustment device comprising a second erbium-doped fiber amplifier and an optical attenuator.

[0024] In one embodiment, the high-sensitivity vibration sensing system employing a broadband light source includes a fiber grating filter comprising multiple fiber gratings with different center wavelengths and the same bandwidth located on the same optical fiber.

[0025] Each fiber in the fiber Fabry-Perot resonant cavity array is equipped with multiple sets of fiber gratings with different center wavelengths, corresponding one-to-one with the fiber gratings in the fiber grating filter.

[0026] Each fiber in the fiber grating array is equipped with multiple fiber gratings of different center wavelengths that correspond one-to-one with the fiber gratings in the fiber grating filter.

[0027] A wavelength division multiplexing device is set between the interference optical power adjustment device and the photodetector to separate signal light of different wavelengths and transmit them to the photodetector that processes the corresponding wavelength signal.

[0028] In one embodiment, the high-sensitivity vibration sensing system employing a broadband light source includes a fiber optic Fabry-Perot resonator array comprising a first fiber optic beam splitter and multiple fibers connected to the first fiber optic beam splitter. Each fiber of the fiber optic Fabry-Perot resonator array is independently provided with several sets of fiber gratings, and the fibers of the fiber optic Fabry-Perot resonator array are time-division multiplexed through delay fibers.

[0029] The fiber grating array includes a second fiber beam splitter and multiple fibers connected to the second fiber beam splitter and corresponding one-to-one with each fiber in the fiber Fabry-Perot resonator array. The number of fiber gratings and the center wavelength on each fiber in the fiber grating array are set according to the number of fiber grating groups and the center wavelength on the corresponding fiber in the fiber Fabry-Perot resonator array. The fibers in the fiber grating array are time-division multiplexed in the same way as the fiber Fabry-Perot resonator array through delay fibers.

[0030] Furthermore, the high-sensitivity vibration sensing system using a broadband light source can combine wavelength division multiplexing with time division multiplexing on the basis of the above time division multiplexing scheme. That is, on the basis of the above time division multiplexing scheme, the fiber grating filter includes multiple fiber gratings with different center wavelengths and the same bandwidth located on the same optical fiber.

[0031] Each fiber in the fiber Fabry-Perot resonant cavity array is equipped with multiple sets of fiber gratings with different center wavelengths, corresponding one-to-one with the fiber gratings in the fiber grating filter.

[0032] Each fiber in the fiber grating array is equipped with multiple fiber gratings of different center wavelengths that correspond one-to-one with the fiber gratings in the fiber grating filter.

[0033] A wavelength division multiplexing device is set between the interference optical power adjustment device and the photodetector to separate signal light of different wavelengths and transmit them to the photodetector that processes the corresponding wavelength signal.

[0034] In one embodiment, when the high-sensitivity vibration sensing system employing a broadband light source involves time-division multiplexing, the broadband light is pulsed light. In other cases, the broadband light can be continuous light or pulsed light. The pulsed light can be generated using any of the pulse modulation devices such as acousto-optic modulators, electro-optic modulators, and semiconductor optical amplifiers (SOAs).

[0035] The high-sensitivity vibration sensing system employing a broadband light source involves wavelength division multiplexing, where the absolute value of the optical path difference between each wavelength is required to be less than or equal to λ. FBG 2 / Δλ FBG , λ FBG , Δλ FBG These represent the center wavelength and bandwidth of the fiber Bragg grating array, respectively, and the optical path difference must be consistent for interference at each wavelength.

[0036] In one embodiment, the high-sensitivity vibration sensing system employing a broadband light source has a broadband light bandwidth Δλ. ASE satisfy:

[0037] Δλ ASE ≥Δλ FBG1 +…+Δλ FBGn

[0038] Where n is a positive integer, Δλ FBG1 , …, Δλ FBGn These represent the bandwidth of each fiber grating in the fiber grating array.

[0039] In one embodiment, the bandwidth Δλ of any fiber grating in the fiber grating filter, fiber Fabry-Perot resonator array, and fiber grating array is... FBG satisfy:

[0040] Δλ FBG ≤λ FBG 2 / δL

[0041] Where, λ FBGδL is the center wavelength of the corresponding fiber grating, and δL is the optical path difference between the probe light and the reference light in cavity length matched heterodyne interference.

[0042] The high-sensitivity vibration sensing system using a broadband light source can use any one of broadband light sources such as ASE, SLD, or LED light sources.

[0043] The high-sensitivity vibration sensing system employing a broadband light source can use a fiber optic grating that is any one or a combination of uniform fiber Bragg gratings and apodized fiber gratings.

[0044] The high-sensitivity vibration sensing system employing a broadband light source comprises a cavity length-matched interferometer consisting of a first coupler, a fiber optic Fabry-Perot resonant cavity array, a second circulator, a fiber optic grating array, an acousto-optic frequency shifter, a fiber optic delay module, and the second coupler. The cavity length-matched interferometer can adopt a Michelson-type structure or a Mach-Zehnder-type structure and uses heterodyne interferometry. By adjusting the cavity length compensation fiber length in the reference path, the optical path of the reflected light from the fiber optic grating in the reference path is made approximately the same as the optical path of the higher-order reflected light participating in the interference of the Fabry-Perot cavity in the probe path, thereby improving the sensitivity.

[0045] The high-sensitivity vibration sensing system using a broadband light source incorporates a reference optical path in its optical path structure. By rationally controlling the optical path difference and coherence length between the sensing optical path and the reference optical path, path noise can be effectively reduced, while avoiding the noise increase problem caused by interference from other multi-order reflected light in the sensing optical path.

[0046] The fiber Fabry-Perot resonator employs asymmetric high-reflectivity fiber grating pairs. When the cavity length-matched interferometer uses a Michelson-type structure, to enhance the intensity of higher-order reflected light, in a set of fiber gratings, when i≥2, the reflectivity of the first fiber grating contacting the probe light is (i-1) / (i+1), and when i=1, the reflectivity is 1. Here, i represents the reflection order of the fiber Fabry-Perot resonator participating in the interference, and the reflectivity of the second fiber grating contacting the probe light is 1. The fiber grating in the reference path only serves a reflective function, and the sensing element is the fiber between the fiber gratings. Simultaneously, the reflectivity of the fiber grating array in the reference path and the coupling ratio of the second coupler change according to the reflection order of the interfering light, requiring the reference light and probe light power to be essentially the same to achieve optimal sensitivity enhancement.

[0047] The present invention also provides a high-sensitivity vibration sensing method using a broadband light source, and employs the aforementioned high-sensitivity vibration sensing system using a broadband light source;

[0048] The high-sensitivity vibration sensing method using a broadband light source includes:

[0049] The broadband light source module emits broadband light, which is filtered by a fiber optic grating filter. After passing through the first coupler, it is split into two optical signals. One optical signal is used as the probe light and passes through the probe path, while the other optical signal is used as the reference light and passes through the reference path.

[0050] The probe light is transformed into a beam with cavity length-matched interference sensing information by the fiber optic Fabry-Perot resonant cavity array, and then reflected and transmitted to the second coupler via the first coupler.

[0051] The reference light enters the first port of the second circulator and exits from the second port of the second circulator. It is reflected by the fiber grating array and becomes a beam with cavity length matching interference eigenvalues. Then, it exits from the third port of the second circulator and passes through the acousto-optic frequency shifter and the fiber delay module to the second coupler.

[0052] The probe light and the reference light undergo cavity-length matched heterodyne interference, and an interference signal is output.

[0053] The output interference signal is sequentially processed by an interference optical power adjustment device for power adjustment, a photoelectric detector for photoelectric signal conversion, and a bandpass filter to filter the frequency shift signal in the electrical signal, thereby extracting the radio frequency signal carrying the sensing phase shift information.

[0054] The real-time data acquisition module and data processing module acquire and process radio frequency signals, demodulate interference signals, and obtain the detection results of broadband light source high-sensitivity cavity length matched heterodyne interference signals.

[0055] This invention provides a high-sensitivity vibration sensing system and method using a broadband light source with a resolution of up to skin strain, which can solve the problems mentioned in the background art above: 1) Narrow linewidth lasers are expensive as light sources for sensing systems and are incompatible with wavelength division multiplexing sensing systems; 2) Problems such as low sensitivity and poor optical path matching versatility faced in the application of interferometric sensing systems.

[0056] Compared with the prior art, the beneficial effects of this invention are as follows:

[0057] 1. Compared to existing Fabry-Perot interferometric vibration sensing systems that require narrow-linewidth laser light sources, are expensive, and are incompatible with wavelength division multiplexing systems, this invention can use low-cost broadband light sources to reduce multi-order optical noise introduced by multiple reflections in Fabry-Perot interferometers, enabling dynamic sensing array measurements while reducing system cost and complexity.

[0058] 2. A cavity length matching interferometer was fabricated using an electrically adjustable fiber delay line, cavity length compensation fiber, acousto-optic frequency shifter, and fiber optic grating to achieve heterodyne modulation and demodulation. This improved the detection sensitivity of the sensing system while ensuring that the matching interferometer had good cavity length matching capability.

[0059] 3. The system and method of the present invention are applicable to demodulation of a single sensing unit, and can also realize time division multiplexing, wavelength division multiplexing, and time division and wavelength division hybrid multiplexing demodulation of multiple sensing units. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the high-sensitivity Fabry-Perot vibration sensing system using a broadband light source according to Embodiment 1 of the present invention;

[0061] Figure 2 This is a comparison chart of the spectrum of optical interference output signals of different orders in the sensing system of Embodiment 1 of the present invention.

[0062] Figure 3 This is a schematic diagram of the structure of the wavelength division multiplexing, time division multiplexing, and time division and wavelength division hybrid multiplexing system of Embodiment 2 of the present invention;

[0063] Figure 4 This is a schematic diagram of the broadband light source module structure of the time-division and time-division and wavelength-division hybrid multiplexing system in Embodiment 2 of the present invention. Detailed Implementation

[0064] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0065] Example 1

[0066] See Figure 1 A high-sensitivity vibration sensing system employing a broadband light source includes a broadband light source module 1, a fiber optic grating filter 2, a first erbium-doped fiber amplifier 3, a first coupler 4, a fiber optic Fabry-Perot resonator array 5, a second circulator 6, a fiber optic grating array 7, an acousto-optic frequency shifter 8, an electrically adjustable fiber delay line 9, a cavity length compensation fiber 10, a second coupler 11, a second erbium-doped fiber amplifier 12, an optical attenuator 13, a wavelength division multiplexing device 14, two photodetectors 15 and 16, a bandpass filter 17, a real-time data acquisition module 18, and a data processing module 19.

[0067] Broadband light source module 1 is used to emit broadband light.

[0068] The fiber Bragg grating filter 2 is used for bandwidth filtering of broadband light, and includes a first circulator 203 and two fiber Bragg gratings 201 and 202 with the same bandwidth but different center wavelengths located on the same optical fiber. The first circulator 203 is used to output the broadband light to the two fiber Bragg gratings 201 and 202 located on the same optical fiber with center wavelengths of λ1 and λ2 respectively. The fiber Bragg gratings 201 and 202 have the same bandwidth, and the reflected broadband light is output through the first circulator 203.

[0069] The first erbium-doped fiber amplifier 3 is disposed between the fiber grating filter 2 and the first coupler 4, and is used to amplify the power of broadband light.

[0070] The first coupler 4 is used to split the broadband light after bandwidth filtering into two optical signals. One optical signal is used as the probe light and passes through the probe path, while the other optical signal is used as the reference light and passes through the reference path.

[0071] The fiber Fabry-Perot resonator array 5 is used for multiple reflections of the probe optical signal. The reflected signal is transmitted to the second coupler 11 via the first coupler 4. The fiber Fabry-Perot resonator array 4 includes two sets of fiber gratings with different center wavelengths located on the same optical fiber. Each set of fiber gratings in the fiber Fabry-Perot resonator array 5 consists of a pair of fiber gratings with the same bandwidth and center wavelength. The first set of fiber gratings consists of fiber gratings 501 and 502 with a center wavelength of λ1, and the second set consists of fiber gratings 503 and 504 with a center wavelength of λ2. The bandwidth of the fiber gratings in the fiber Fabry-Perot resonator array 5 is greater than the bandwidth of the fiber gratings in the fiber grating filter 2.

[0072] The second circulator 6 is used to output the reference path optical signal to the fiber optic grating array 7. The reflected signal reflected back by the fiber optic grating array 7 is output to the acousto-optic frequency shifter 8 through the second circulator 6.

[0073] Fiber Bragg grating array 7 is used to reflect the reference path optical signal. The number and center wavelength of the fiber gratings in fiber grating array 7 are set according to the number and center wavelength of the fiber grating groups in fiber Fabry-Perot resonator array 5. The fiber gratings on fiber grating array 7 and their corresponding fiber grating groups on fiber Fabry-Perot resonator array 5 have the same bandwidth and center wavelength. Specifically, fiber grating array 7 includes two fiber gratings 701 and 702 located on the same optical fiber and corresponding to two fiber grating groups on the fiber Fabry-Perot resonator array 5, with center wavelengths of λ1 and λ2 respectively.

[0074] The acousto-optic frequency shifter 8 is used to reduce noise by shifting the frequency of the signal returned by the fiber Bragg grating array 7.

[0075] An electrically adjustable fiber delay line 9 and a cavity length compensation fiber 10 together form a fiber delay module, which is positioned between the acousto-optic frequency shifter 8 and the second coupler 11. The electrically adjustable fiber delay line 9 and the cavity length compensation fiber 10 are used to make small-amplitude precise adjustments and large-amplitude coarse adjustments to the length of the reference path fiber, respectively, to match the optical path difference between the reference path and the probe path.

[0076] The second coupler 11 is used to perform cavity length-matched heterodyne interference on the reflected light from the probe path and the reference path, and outputs an interference signal.

[0077] The second erbium-doped fiber amplifier 12 and the optical attenuator 13 form an interference optical power adjustment device, which is located between the second coupler 11 and the wavelength division multiplexing device 14. It is used to adjust the optical power of the interference light so that the optical power operates in the linear operating region of the photodetectors 15 and 16.

[0078] The wavelength division multiplexing device 14 is disposed between the interference optical power adjustment device and the photodetectors 15 and 16, and is used to separate signal light of different wavelengths and transmit them to the photodetectors 15 and 16 that process the corresponding wavelength signals respectively.

[0079] Photodetectors 15 and 16 are used to detect the beat frequency signal of the interference signal between the probe path and the reference path, convert it into a photoelectric signal, and output it to the bandpass filter 17. Photodetector 15 is used to detect signal light with wavelength λ1. Photodetector 16 is used to detect signal light with wavelength λ2.

[0080] The bandpass filter 17 is used to filter the frequency-shifted signal in the electrical signal and extract the radio frequency signal carrying the sensing phase shift information.

[0081] The real-time data acquisition module 18 is used to acquire radio frequency signals in real time.

[0082] The data processing module 19 is used to process the acquired radio frequency signals, demodulate the interference signals, and obtain the detection results of the broadband light source high-sensitivity cavity length matched heterodyne interference signals.

[0083] The high-sensitivity vibration sensing method using a broadband light source, based on the aforementioned high-sensitivity vibration sensing system employing a broadband light source, includes:

[0084] The broadband light source module 1 emits broadband light, which is filtered by the fiber optic grating filter 2, then amplified by the first erbium-doped fiber amplifier 3, and then split into two optical signals by the first coupler 4. One optical signal is used as the probe light and passes through the probe path, and the other optical signal is used as the reference light and passes through the reference path.

[0085] After the probe light passes through the fiber optic Fabry-Perot resonant cavity array 5 and is transformed into a beam with cavity length matching interference sensing information, it is reflected and transmitted to the second coupler 11 via the first coupler 4.

[0086] The reference light enters the first port of the second circulator 6, and after exiting the second port of the second circulator 6, it is reflected by the fiber grating array 7 and becomes a beam with cavity length matching interference eigenvalues. Then, it exits the third port of the second circulator 6 and passes through the acousto-optic frequency shifter 8 and the fiber delay module to the second coupler 11.

[0087] The probe light and the reference light undergo cavity length-matched heterodyne interference to output an interference signal and achieve wavelength division multiplexing of the signal;

[0088] The output interference signal is sequentially processed by an interference optical power adjustment device for power adjustment, then by a wavelength division multiplexing device 14 for photoelectric signal conversion by photodetectors 15 and 16, and finally by a bandpass filter 17 to filter the frequency shift signal in the electrical signal and extract the radio frequency signal carrying the sensing phase shift information.

[0089] The real-time data acquisition module 18 and the data processing module 19 acquire and process the radio frequency signal, demodulate the interference signal, and obtain the detection result of the broadband light source high-sensitivity cavity length matched heterodyne interference signal.

[0090] The bandwidth Δλ of broadband light ASE satisfy:

[0091] Δλ ASE ≥Δλ FBG1 +Δλ FBG2

[0092] Where, Δλ FBG1 ,Δλ FBG2 These represent the bandwidth of each fiber grating in the fiber grating array 7.

[0093] The bandwidth Δλ of any fiber grating in fiber grating array 7 FBG satisfy:

[0094] Δλ FBG ≤λ FBG 2 / δL

[0095] Where, λ FBG λ is the center wavelength of the corresponding fiber grating, taken from λ1 or λ2, and δL is the optical path difference between the probe light and the reference light in cavity length matched heterodyne interference.

[0096] The process and principle of implementing the high-sensitivity Fabry-Perot vibration sensing method with a broadband light source in this embodiment are as follows:

[0097] The cavity length-matched interferometer consists of a first coupler 4, a fiber optic Fabry-Perot resonant cavity array 5, a second circulator 6, a fiber optic grating array 7, an acousto-optic frequency shifter 8, a fiber optic delay module, and a second coupler 11. In this embodiment, the cavity length-matched interferometer is pre-designed, and the interferometer uses a Michelson-type or Mach-Zehnder-type structure, employing heterodyne interferometry.

[0098] After broadband light passes through fiber optic grating filter 2, its bandwidth narrows, and the optical signal can be expressed as E = Ae^(-E / A). j[2πf+φ(t)] Where A is the amplitude corresponding to the transmitted optical signal, f is the center frequency of fiber gratings 201 and 202, φ(t) is the initial phase, and j represents the imaginary unit. The coherence length of the optical signal can then be expressed as... In the formula, Δλ FBGλ represents the bandwidth of fiber Bragg gratings 201 and 202. FBG L represents the center wavelength of fiber gratings 201 and 202. FBG It is the coherence length of the optical signal after the broadband light passes through fiber gratings 201 and 202.

[0099] After passing through the first coupler 4, the optical signal is split into two paths. One optical signal serves as the reference light and passes through the reference path. The reference optical signal is reflected by fiber optic gratings 701 and 702 and enters the third port of the second circulator 6. It is then transmitted through the acousto-optic frequency shifter 8 and the fiber optic delay module to the second coupler 11. At this point, the frequency-shifted reference optical signal is represented as E = A′e. j[2π[(f+Δf)]+φ(t)] , where A′ is the amplitude corresponding to the reference optical signal, Δf is the frequency shift amount of the acousto-optic frequency shifter 8, j represents the imaginary unit, f is the center frequency of fiber optic gratings 701 and 702, and φ(t) is the initial phase.

[0100] Another optical signal, acting as the probe light, passes through the probe path. As the signal passes through the probe path, it undergoes multiple reflections within the fiber Fabry-Perot resonant cavity. During this process, the nth-order reflected light is affected by vibration, resulting in a phase change. In the formula, The sensor represents the phase change, n is the number of reflections of the reflected light, j represents the imaginary unit, β is the transmission constant, and l FBG-FP Given the length of the fiber Fabry-Perot resonator, the expression for the optical signal reflected from the probe path and transmitted to the second coupler 11 is: Where A″ is the amplitude corresponding to the probe optical signal, j represents the imaginary unit, f is the center frequency of fiber gratings 501, 502, 503, and 504, and φ(t) is the initial phase. This is for sensing phase changes.

[0101] In this embodiment, a large-scale coarse adjustment is made by changing the length of the cavity length compensation fiber 10 in the reference path, while a small-scale precise adjustment is made by adjusting the electrically adjustable fiber delay line 9. The cavity length matching heterodyne interferometry technique requires that broadband light does not interfere when passing through the sensing interferometer; interference only occurs when the optical path difference between the reference path and the probe path is nearly equal, i.e., it needs to satisfy: ΔL < <L FBG ΔL is the optical path difference between the reference path and the probe path. Figure 1 It needs to satisfy l2≈l1+2i×L FBG-FP And the optical path difference ΔL=|l2-l1-2n×l FBG-FP |< <L FBGn is the number of reflections in the fiber Fabry-Perot resonator participating in the interference, i = n + 1, l1 is the distance from the first coupler 4 to the second coupler 12 after being reflected by the fiber grating 501 with wavelength λ1 in the fiber Fabry-Perot array, and l2 is the distance from the first coupler 4 to the second coupler 12 after passing through the second circulator 6 and being reflected by the fiber grating 701 with wavelength λ1 in the fiber grating array. The system sensitivity can be improved by adjusting the fiber delay module, and light of different wavelengths is separated by wavelength division multiplexing device 14.

[0102] The final interference light signal can be represented as: Where Δf is the frequency shift amount of the acousto-optic frequency shifter 8, t is the time-domain independent variable, and φ(t) is the initial phase. To sense phase changes, the electrical signal after passing through photodetectors 14 and 15 and bandpass filter 16 can be represented as... B represents the amplitude of the AC term. After signal demodulation, vibration signal information can be obtained from this electrical signal.

[0103] The spectrum comparison diagram of the output signals of optical interference of different orders in this embodiment is shown below. Figure 2 As shown in the experimental results, the present invention can significantly improve the signal-to-noise ratio and sensitivity of the system, further demonstrating the feasibility of the system and method of the present invention.

[0104] Example 2

[0105] refer to Figure 3 , Figure 4 The high-sensitivity vibration sensing system using a broadband light source in this embodiment is a hybrid multiplexed link combining wavelength division multiplexing and time division multiplexing. This system is similar to that in Embodiment 1 and... Figure 1 Similar devices and connections will not be described in detail here.

[0106] The fiber Fabry-Perot resonator array 5 of this embodiment includes a first fiber beam splitter 505 and two optical fibers connected to the first fiber beam splitter 505. Each optical fiber of the fiber Fabry-Perot resonator array 5 is independently provided with two sets of fiber gratings identical to those in Embodiment 1. The two optical fibers of the fiber Fabry-Perot resonator array 5 are time-division multiplexed through a delay fiber 506.

[0107] The fiber grating array 7 in this embodiment includes a second fiber beam splitter 703 and two fibers connected to the second fiber beam splitter 703 and corresponding one-to-one with each fiber in the fiber Fabry-Perot resonator array 5. The number of fiber gratings and the center wavelength of each fiber in the fiber grating array 7 are set according to the number of fiber grating groups and the center wavelength of the corresponding fiber in the fiber Fabry-Perot resonator array 5. The two fibers of the fiber grating array 7 are time-division multiplexed in the same way as the fiber Fabry-Perot resonator array 5 through a delay fiber 506.

[0108] The working principle of the optical path structure in this embodiment is the same as that in Embodiment 1, and will not be repeated here. It should be specifically noted that, unlike Embodiment 1, the broadband light source module 1 in this embodiment adopts a pulsed form: (See reference...) Figure 4 Broadband continuous light is emitted by broadband light source 101, and arbitrary signal generator 102 generates periodic pulse signals to pulse modulation device 103. When broadband continuous light passes through pulse modulation device 103, it becomes broadband pulse signal.

[0109] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A high-sensitivity vibration sensing system employing a broadband light source, characterized in that, include: Broadband light source module (1), used to emit broadband light; The fiber grating filter (2) used for bandwidth filtering of broadband light includes a first circulator (203). The first circulator (203) is used to output broadband light to one or more fiber gratings with different center wavelengths and the same bandwidth located on the same fiber. The reflected broadband light is output through the first circulator (203). The first coupler (4) is used to split the broadband light after bandwidth filtering into two optical signals. One optical signal is used as the probe light and passes through the probe path, and the other optical signal is used as the reference light and passes through the reference path. The fiber Fabry-Perot resonant cavity array (5) includes several fiber grating groups for multiple reflections of the probe optical signal. The reflected signal is transmitted to the second coupler (11) through the first coupler (4). Each fiber grating group in the fiber Fabry-Perot resonant cavity array (5) consists of a pair of fiber gratings with the same bandwidth and center wavelength. The number of fiber grating groups and the center wavelength on each fiber in the fiber Fabry-Perot resonant cavity array (5) are set according to the number of fiber gratings and the center wavelength in the fiber grating filter (2). The fiber grating groups on each fiber in the fiber Fabry-Perot resonant cavity array (5) and the corresponding fiber gratings in the fiber grating filter (2) have the same center wavelength. The bandwidth of the fiber gratings in the fiber Fabry-Perot resonant cavity array (5) is greater than the bandwidth of the fiber gratings in the fiber grating filter (2). The second circulator (6) is used to output the reference path optical signal to the fiber optic grating array (7), and the reflected signal reflected back by the fiber optic grating array (7) is output to the acousto-optic frequency shifter (8) through the second circulator (6). A fiber grating array (7) comprising several fiber gratings is used to reflect the reference path optical signal; the optical fibers in the fiber grating array (7) are arranged in a one-to-one correspondence with the optical fibers in the fiber Fabry-Perot resonator array (5); the number of fiber gratings and the center wavelength on each optical fiber in the fiber grating array (7) are arranged in a corresponding manner with the number of fiber grating groups and the center wavelength on the corresponding optical fibers in the fiber Fabry-Perot resonator array (5); the fiber gratings in the fiber grating array (7) and the corresponding fiber grating groups in the fiber Fabry-Perot resonator array (5) have the same bandwidth and center wavelength; The acousto-optic frequency shifter (8) is used to perform optical frequency shifting on the signal returned by the fiber optic grating array (7) to achieve noise reduction; The fiber delay module includes an electrically adjustable fiber delay line (9) and a cavity length compensation fiber (10), which are located between the acousto-optic frequency shifter (8) and the second coupler (11) to make small-amplitude precise and large-amplitude coarse adjustments to the length of the reference path fiber to match the optical path difference between the reference path and the probe path. The second coupler (11) is used to perform cavity length-matched heterodyne interference on the reflected light from the probe path and the reference path, and output interference signal; An interference light power adjustment device is disposed between the second coupler (11) and the photodetector to adjust the light power of the interference light so that the light power operates in the linear operating region of the photodetector. Several photodetectors are used to detect the beat frequency signal of the interference signal between the detection path and the reference path, perform photoelectric signal conversion and output to the bandpass filter (17); the number of photodetectors is consistent with the number of center wavelength types of the fiber grating in the fiber grating filter (2), the fiber grating group in the fiber Fabry-Perot resonator array (5), and the fiber grating in the fiber grating array (7). A bandpass filter (17) is used to filter frequency-shifted signals in electrical signals and extract radio frequency signals carrying sensing phase shift information. The real-time data acquisition module (18) is used to acquire radio frequency signals in real time; The data processing module (19) is used to process the acquired radio frequency signals, demodulate the interference signals, and obtain the detection results of the broadband light source high-sensitivity cavity length matched heterodyne interference signals. The fiber Fabry-Perot resonator employs asymmetric high-reflectivity fiber grating pairs. To enhance higher-order reflected light intensity, in a set of fiber gratings, when i At that time, the reflectivity of the fiber grating of the first contact probe light is (i-1) / (i+1), when i At that time, the reflectivity of the fiber grating of the first contact probe light is 1, where i is the reflection order of the fiber Fabry-Perot resonator participating in the interference, and the reflectivity of the fiber grating of the second contact probe light is 1. The fiber grating in the reference path only serves a reflective function, while the sensing element is the optical fiber between the fiber gratings. Meanwhile, the reflectivity of the fiber grating array in the reference path and the coupling ratio of the second coupler change according to the reflection order of the interfering light. It is necessary to ensure that the optical power of the reference light and the probe light are basically the same in order to achieve the best sensitivity enhancement effect.

2. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, characterized in that, A first erbium-doped fiber amplifier (3) for power amplification of broadband light is provided between the fiber grating filter (2) and the first coupler (4).

3. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, characterized in that, The interference optical power adjustment device includes a second erbium-doped fiber amplifier (12) and an optical attenuator (13).

4. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, characterized in that, The fiber grating filter (2) includes multiple fiber gratings with different center wavelengths and the same bandwidth located on the same optical fiber; Each fiber of the fiber Fabry-Perot resonator array (5) is provided with multiple sets of fiber gratings with different center wavelengths that correspond one-to-one with the fiber gratings in the fiber grating filter (2). Each fiber of the fiber grating array (7) is provided with multiple fiber gratings with different center wavelengths that correspond one-to-one with the fiber gratings in the fiber grating filter (2); A wavelength division multiplexing device (14) is set between the interference optical power adjustment device and the photodetector to separate signal light of different wavelengths and transmit them to the photodetector that processes the corresponding wavelength signal.

5. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, characterized in that, The fiber Fabry-Perot resonant cavity array (5) includes a first fiber beam splitter (505) and multiple optical fibers connected to the first fiber beam splitter (505). Each optical fiber of the fiber Fabry-Perot resonant cavity array (5) is independently provided with several groups of fiber gratings. The optical fibers of the fiber Fabry-Perot resonant cavity array (5) are time-division multiplexed through delay fibers. The fiber grating array (7) includes a second fiber beam splitter (703) and multiple fibers connected to the second fiber beam splitter (703) and corresponding one-to-one with each fiber in the fiber Fabry-Perot resonator array (5). The number of fiber gratings and the center wavelength on each fiber in the fiber grating array (7) are set according to the number of fiber grating groups and the center wavelength on the corresponding fiber in the fiber Fabry-Perot resonator array (5). The fibers in the fiber grating array (7) are time-division multiplexed in the same way as the fiber Fabry-Perot resonator array (5) through delay fibers.

6. The high-sensitivity vibration sensing system using a broadband light source according to claim 5, characterized in that, The fiber grating filter (2) includes multiple fiber gratings with different center wavelengths and the same bandwidth located on the same optical fiber; Each fiber of the fiber Fabry-Perot resonator array (5) is provided with multiple sets of fiber gratings with different center wavelengths that correspond one-to-one with the fiber gratings in the fiber grating filter (2). Each fiber of the fiber grating array (7) is provided with multiple fiber gratings with different center wavelengths that correspond one-to-one with the fiber gratings in the fiber grating filter (2); A wavelength division multiplexing device (14) is set between the interference optical power adjustment device and the photodetector to separate signal light of different wavelengths and transmit them to the photodetector that processes the corresponding wavelength signal.

7. The high-sensitivity vibration sensing system using a broadband light source according to claim 5 or 6, characterized in that, Broadband light is pulsed light.

8. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, characterized in that, Bandwidth of broadband light satisfy: Where n is a positive integer, These represent the bandwidth of each fiber grating in the fiber grating array (7).

9. The high-sensitivity vibration sensing system using a broadband light source according to claim 1, characterized in that, The bandwidth of any one of the fiber gratings in the fiber grating filter (2), the fiber Fabry-Perot resonator array (5), and the fiber grating array (7) satisfy: in, The center wavelength of the corresponding fiber grating. The optical path difference between the probe beam and the reference beam is determined by the cavity length matching heterodyne interference.

10. A high-sensitivity vibration sensing method using a broadband light source, characterized in that, The high-sensitivity vibration sensing system using a broadband light source as described in any one of claims 1 to 9 is adopted; The high-sensitivity vibration sensing method using a broadband light source includes: The broadband light source module (1) emits broadband light, which is filtered by the fiber optic grating filter (2) and then splits into two optical signals after passing through the first coupler (4). One optical signal is used as the probe light and passes through the probe path, while the other optical signal is used as the reference light and passes through the reference path. The probe light is transformed into a beam with cavity length matching interference sensing information by the fiber optic Fabry-Perot resonator array (5), and then reflected and transmitted to the second coupler (11) through the first coupler (4). The reference light enters the first port of the second circulator (6), and after being reflected by the fiber grating array (7) at the second port of the second circulator (6) and becoming a beam with cavity length matching interference intrinsic information, it is emitted from the third port of the second circulator (6) and transmitted to the second coupler (11) through the acousto-optic frequency shifter (8) and the fiber delay module. The probe light and the reference light undergo cavity-length matched heterodyne interference, and an interference signal is output. The output interference signal is sequentially processed by the interference optical power adjustment device for power adjustment, the photoelectric detector for photoelectric signal conversion, and the bandpass filter (17) for filtering the frequency shift signal in the electrical signal to extract the radio frequency signal carrying the sensing phase shift information. The real-time data acquisition module (18) and the data processing module (19) acquire and process the radio frequency signal, demodulate the interference signal, and obtain the detection result of the broadband light source high-sensitivity cavity length matched heterodyne interference signal.

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