White light interferometry detection and multiplexing system and method with fly strain resolution

Abstract

The application discloses a white light interference detection and multiplexing system and method with a flying strain resolution order of magnitude, utilizes the feature that the coherence length of white light is small, adjusts the fiber delay parameter, makes the multiple reflection light in the fiber grating group and the first reflection light perform heterodyne interference, realizes the effect of improving the system phase change and sensitivity, simultaneously adds the interferometer, demodulates the low-order interference light result as the reference of the high-order interference light, reduces the overall noise floor of the system, and finally fully utilizes the advantages of the white light spectrum width and the wavelength selectivity of the fiber grating, realizes the multiplexing, high resolution and low cost large-scale array sensing on one or more optical fibers.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a white light interferometric detection and multiplexing system and method with a strain resolution on the order of flying. Background Technology

[0002] Compared with traditional electronic sensors, fiber optic sensors have advantages such as low transmission loss over long distances, light weight, resistance to electromagnetic interference, and corrosion resistance. They can measure a variety of physical quantities such as temperature, pressure, refractive index, and acceleration, and are therefore widely used in fields such as mineral exploration, power systems, aerospace, and medical biology.

[0003] Fiber optic sensors are mainly classified into several types, including phase modulation, intensity modulation, and wavelength modulation. Phase modulation fiber optic sensors have attracted widespread attention due to their high sensitivity and other advantages. When the photosensitive component is affected by external vibration, the phase of the light wave will change, and the vibration signal can be obtained by detecting the amount of phase change returned.

[0004] Common phase-modulated sensors include Michelson interferometers, Fabry-Perot interferometers, and Sagnac interferometers, which can be used in combination in practical engineering. With the continuous development and improvement of vibration testing technology and the expanding application demands for high-precision and high-sensitivity testing, the development of high-resolution, small-size, and easily networkable vibration sensors has become one of the current and future development trends.

[0005] In the existing technology, sensing and detection systems that achieve strain resolution at the scale of femtospan require expensive narrow-linewidth or even ultra-narrow-linewidth lasers. At the same time, due to the single wavelength characteristic, wavelength division multiplexing (WDM) sensing systems are incompatible with narrow-linewidth lasers, and it is often necessary to increase the number of lasers to achieve sensor multiplexing. Although white light has the advantages of wide spectral range and low cost, the current sensing systems driven by white light are mainly at the scale of pico or nanostrain resolution (Geoffrey A. Cranch, Efficient Fiber Bragg Grating and Fiber Fabry–Pérot Sensor Multiplexing Scheme Using a Broadband Pulsed Mode-Locked Laser[J], Journal of Lightwave Technology, 2005, 23(11), 3798-3807). Some ultra-high resolution white light sensing and detection systems cannot achieve large-scale sensing well due to limitations in sensing units and closed-loop control (Shuting Liu, Ultrahigh-resolution and ultra-simple fiber-optic sensor with resonant Sagnac interferometer[J], Optics Letters, 2023, 48(13), 3543-3546). In addition, in practical applications, phase noise introduced by environmental interference and fiber optic jitter can also increase the background noise level of the system, thereby limiting the detection resolution of the system.

[0006] The applicant has previously developed a high-sensitivity vibration sensing system and method using a broadband light source (see the patent specification with publication number CN117029995A), which can reach the level of skin strain resolution, but its strain resolution still needs to be improved.

[0007] Existing fiber optic vibration sensing systems and methods struggle to simultaneously achieve low cost, high resolution, and wavelength division multiplexing (WDM). Therefore, it is necessary to develop a system and detection method that combines these characteristics to improve the signal detection capabilities of fiber optic sensing systems and arrays. Summary of the Invention

[0008] This invention provides a white light interferometric detection and multiplexing system and method with a strain-scale resolution. Utilizing the short coherence length of white light, by adjusting the fiber delay parameter, heterodyne interference is achieved between the multiple reflected beams and the single reflected beam in the fiber grating array, thereby improving the system's phase change and sensitivity. Simultaneously, an interferometer is added to demodulate the low-order interference light results as a reference for the high-order interference light, reducing the overall system noise floor. Finally, by fully leveraging the advantages of the wide spectrum of white light and the wavelength selectivity of the fiber grating, multiplexable, high-resolution, and low-cost large-scale array sensing is realized on one or more optical fibers.

[0009] A white-light interferometric detection and multiplexing system with speed-to-strain resolution includes:

[0010] White light source module, used to emit broadband light;

[0011] A fiber grating filter for bandwidth filtering of broadband light includes a first circulator and a fiber grating array; the fiber grating array includes one or more fiber gratings with different center wavelengths and the same bandwidth located on the same optical fiber; the first circulator is used to transmit broadband light to the fiber grating array, and the reflected broadband light is output through the first circulator.

[0012] A sensing element array for reflecting and transmitting light waves carrying reference and sensing signals includes a second circulator. The second circulator is connected to a single optical fiber or multiple optical fibers that are time-division multiplexed via delay fibers, through an optical fiber bundle splitter. Each of these optical fibers is equipped with a fiber grating group, which 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 the same optical fiber are set according to the number of fiber gratings and the center wavelength in the fiber grating array. The bandwidth of the fiber gratings in the fiber grating group is greater than the bandwidth of the fiber gratings in the fiber grating array. The bandwidth-filtered light wave enters from the second circulator, is reflected by the fiber grating group, and the reflected light wave is output through the second circulator.

[0013] The first coupler is used to split the reflected light wave 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. The probe light is composed of light waves reflected multiple times within each fiber Bragg grating group. The reference light is composed of light waves reflected once by the first fiber Bragg grating within each fiber Bragg grating group.

[0014] An acousto-optic frequency shifter is positioned between the first coupler and the reference path beam splitter coupler to shift the frequency of the reference path optical wave and remove zero-frequency noise.

[0015] The reference path beam splitter and the detector path beam splitter are used to split the light waves of the reference path and the detector path into two groups of high-order and low-order light signals, respectively. The low-order light signals of the reference path and the detector path enter the low-order optical interferometer to detect the low-order sensing light signal, and the high-order light signals of the reference path and the detector path enter the high-order optical interferometer to detect the high-order sensing light signal.

[0016] The fiber delay module, located between the reference path beam splitter and the third coupler, includes a first optical path compensation fiber and a first electrically adjustable fiber delay line for a high-order optical interferometer, and a second optical path compensation fiber and a second electrically adjustable fiber delay line for a low-order optical interferometer. The first and second optical path compensation fibers are used to make large-amplitude coarse adjustments to the optical paths of the high-order and low-order optical interferometers, respectively. The first and second electrically adjustable fiber delay lines are used to make small-amplitude precise adjustments to the optical paths of the high-order and low-order optical interferometers, respectively, to match the optical path difference between the reference path and the probe path.

[0017] The third coupler includes a high-order optical interference coupler and a low-order optical interference coupler; the high-order optical interference coupler and the low-order optical interference coupler are used to perform optical path-matched heterodyne interference on the high-order and low-order optical signals, respectively, and output high-order and low-order interference optical signals.

[0018] Multiple photodetectors are used to detect the beat frequency signals of corresponding high-order and low-order interference light at different wavelengths, and to perform photoelectric signal conversion; the number of photodetectors is twice the number of wavelength types at the center of the fiber grating in the fiber grating array.

[0019] The real-time data acquisition and processing module is connected to the photodetector and is used to acquire and process radio frequency signals in real time, demodulate interference signals, obtain the detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and use the low-order interference as a reference for high-order interference for noise reduction.

[0020] In the white light interferometric detection and multiplexing system with a strain-strain resolution of the present invention, the reference optical signal and the sensing optical signal can be reflected and transmitted on the same optical fiber of the sensing element array.

[0021] The aforementioned white light interferometric detection and multiplexing system with a strain resolution on the order of magnitude can use broadband light as either broadband continuous light or broadband pulsed light.

[0022] The white light interferometric detection and multiplexing system with a strain resolution of several orders of magnitude can have a first erbium-doped fiber amplifier configured between the fiber grating filter and the sensor array to amplify and adjust the optical power of the bandwidth-filtered light wave.

[0023] The aforementioned white light interferometric detection and multiplexing system with a strain resolution of several orders of magnitude can be equipped with wavelength division multiplexing devices between the high-order optical interferometric coupler, the low-order optical interferometric coupler, and the photodetector. These devices are used to separate the interferometric light signals of different wavelengths and transmit them to the photodetectors that process the corresponding wavelength signals.

[0024] The aforementioned white light interferometric detection and multiplexing system with a strain-strain resolution scale can have a second erbium-doped fiber amplifier installed between the high-order optical interference coupler, the low-order optical interference coupler, and the wavelength division multiplexing device. This amplifier is used to amplify and adjust the optical power of the high-order and low-order interference optical signals to match the saturated input optical power of the photodetector.

[0025] The white light interferometric detection and multiplexing system with a strain resolution of several orders of magnitude can be driven by a broadband light source module, which can be an SLD, ASE, or LED light source.

[0026] In one embodiment, the white light interferometric detection and multiplexing system with a strain-strain resolution on the order of magnitude has a broadband light bandwidth Δλ. ASE satisfy:

[0027] △λ ASE ≥Δλ FBG1 +…+Δλ FBGn

[0028] Where n is a positive integer, Δλ FBG1 , …, Δλ FBGn These represent the bandwidths of the fiber gratings on the same fiber in the sensor array.

[0029] In one embodiment, the white light interferometric detection and multiplexing system with a strain-to-resolution scale adjusts the optical path so that the optical path difference satisfies δL:

[0030] δL≤λ FBG 2 / Δλ FBG

[0031] Where, λ FBG Δλ represents the center wavelength of the corresponding fiber grating. FBG , where is the bandwidth of any fiber grating in the fiber grating filter or sensor array.

[0032] The white light interferometric detection and multiplexing system with a strain resolution of several orders of magnitude can use a fiber optic grating that is any one or a combination of phase-shifted fiber optic gratings, uniform fiber Bragg gratings, and apodized fiber optic gratings.

[0033] The present invention relates to a white-light interferometric detection and multiplexing system with a strain-scale resolution. The sensing system can perform time-division multiplexing, wavelength-division multiplexing, or a hybrid time-division and wavelength-division multiplexing demodulation. When the sensing system involves time-division multiplexing, the white light source module uses pulsed light; otherwise, continuous light or pulsed light is used. The pulsed light can be generated by modulating white light using any of the pulse modulation devices such as a semiconductor optical amplifier (SOA), an acousto-optic modulator, or an electro-optic modulator.

[0034] The present invention provides a white light interferometric detection and multiplexing system with a strain-scale resolution. The system comprises a sensor array, a first coupler, an acousto-optic frequency shifter, a second coupler (including a reference path beam splitter and a probe path beam splitter), an optical fiber delay module, and a third coupler, forming an optical path matching interferometer. The optical path matching interferometer can adopt a Michelson-type structure or a Mach-Zehnder-type structure and employs heterodyne interferometry. By adjusting the length of the optical path compensation fiber in the reference path, the optical path of the first reflection of the fiber grating in the reference path is made to be nearly identical to the optical path of the multiple reflections of the fiber grating in the probe path, thereby improving the sensitivity.

[0035] The present invention provides a white light interferometric detection and multiplexing system with a strain resolution of several orders of magnitude. It establishes a low-order interferometer to detect low-order sensing light signals and a high-order interferometer to detect high-order sensing light signals. The low-order interferometric light is used as a reference group for the high-order interferometric light. Based on the periodic difference between random noise and vibration signals, the system eliminates broadband noise with weak correlation between low-order and high-order interferometric light sensing, while retaining vibration signals with strong correlation.

[0036] A white light interferometric detection and multiplexing method with a speed-strain resolution of order of magnitude, employing the aforementioned white light interferometric detection and multiplexing system with a speed-strain resolution of order of magnitude;

[0037] The white-light interferometric detection and multiplexing method with a strain resolution on the order of magnitude includes:

[0038] The white light source module emits broadband light, which is filtered by a fiber optic grating filter and then passes through a sensor array. The light wave enters from the first port of the second circulator and exits from the second port of the second circulator. It is reflected by the fiber optic grating group and exits from the third port of the second circulator. 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.

[0039] The probe light consists of light waves reflected multiple times within each fiber grating group. After passing through the first coupler, it is split into two beams by the probe path beam splitter coupler. One beam participates in low-order optical interference and is transmitted to the low-order optical interference coupler, while the other beam participates in high-order optical interference and is transmitted to the high-order optical interference coupler.

[0040] The reference light consists of light waves reflected once from the first fiber grating in each fiber grating group. It does not carry a sensing signal. After passing through the first coupler, the reference light is first frequency-shifted by an acousto-optic frequency shifter in the reference path. Then, it is split into two beams by the reference path beam splitter. One beam participates in low-order optical interference. After the low-order optical interference is adjusted by the interferometer optical path matching of the second optical path compensation fiber and the second electrically adjustable fiber delay line, it is transmitted to the low-order optical interference coupler. The other beam participates in high-order optical interference. After the high-order optical interference is adjusted by the interferometer optical path matching of the first optical path compensation fiber and the first electrically adjustable fiber delay line, it is transmitted to the high-order optical interference coupler.

[0041] The probe beam and reference beam of high-order and low-order interferometers undergo optical path-matched heterodyne interference, and output interference signals;

[0042] The output interference signal is converted into a photoelectric signal by a photodetector;

[0043] The real-time data acquisition and processing module acquires and processes radio frequency signals in real time, demodulates interference signals, obtains the detection results of corresponding high-order and low-order heterodyne interference signals, and uses the low-order interference as a reference for the high-order interference for noise reduction.

[0044] In one embodiment, the white light interferometric detection and multiplexing method with a strain resolution of several orders of magnitude involves the output interference signal being sequentially amplified and adjusted by a second erbium-doped fiber amplifier, the wavelength division multiplexing device separating signal light of different wavelengths, and the photodetector converting the photoelectric signal.

[0045] This invention provides a white light interferometric detection and multiplexing system and method with a strain-strain resolution scale, which can solve the problems mentioned in the background art above: 1) High-resolution sensing systems rely on expensive narrow-linewidth or even ultra-narrow-linewidth lasers, and narrow-linewidth lasers are not compatible in wavelength division multiplexing sensing systems due to their single wavelength characteristics; 2) White light driven sensing systems have high noise levels, which cannot fully utilize the wavelength division multiplexing potential of white light; 3) It reduces noise problems caused by fiber optic disturbances in practical applications.

[0046] Compared with the prior art, the beneficial effects of this invention are as follows:

[0047] 1. This invention selects a low-cost broadband light source to replace the expensive narrow-linewidth laser for sensing and detection. By precisely controlling the optical path difference of the interferometer, it realizes the detection of high-order interference light signals in the fiber optic grating, thereby improving the sensitivity of the system while reducing the system cost.

[0048] 2. This invention reduces the noise level of the sensing system by using a low-order interferometer to eliminate noise in the detection of high-order interferometer optical signals, thereby improving the system's vibration resolution to the fly-strain level.

[0049] 3. This invention etches multiple fiber grating groups on one or more optical fibers, realizing time-division wavelength-division hybrid multiplexing array detection of multiple sensing units, while eliminating most path interference by using the reference light and sensing light to share the same optical path as much as possible. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the white light interferometric detection and multiplexing system with a strain-resolution scale as described in Example 1.

[0051] Figure 2 This is a comparison chart of strain resolution of the output signals of optical interference of different orders in the sensing system of Example 1;

[0052] Figure 3 The images show the effect of noise reduction before and after using a low-order interferometer in Example 1.

[0053] Figure 4 The strain resolution spectrum of the wavelength division multiplexing system in Example 1;

[0054] Figure 5 This is an optical path structure diagram of time-division and wavelength-division multiplexing in Example 2. Detailed Implementation

[0055] 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.

[0056] Example 1

[0057] See Figure 1 A white light interferometric detection and multiplexing system with fly-strain resolution includes a white light source module 1, a fiber grating filter 2, a first erbium-doped fiber amplifier 3, a sensor array 4, a first coupler 5, an acousto-optic frequency shifter 6, a second coupler 7, a fiber delay module 8, a third coupler 9, a second erbium-doped fiber amplifier 10, a wavelength division multiplexing device 11, a photodetector 12, and a real-time data acquisition and processing module 13. The second coupler 7 includes a reference path beam splitter coupler 701 and a probe path beam splitter coupler 702.

[0058] White light source module 1 is used to emit broadband light. The broadband light can be broadband continuous light or broadband pulsed light.

[0059] The fiber Bragg grating filter 2 is used for bandwidth filtering of broadband light and includes a first circulator 201 and a fiber Bragg grating array. The fiber Bragg grating array includes two fiber Bragg gratings 202 and 203 located on the same optical fiber, with different center wavelengths and the same bandwidth. The first circulator 201 is used to transmit broadband light to the fiber Bragg grating array, and the reflected broadband light is output through the first circulator 201.

[0060] The first erbium-doped fiber amplifier 3 is positioned between the fiber grating filter 2 and the sensor array 4, and is used to amplify and adjust the optical power of the filtered light wave.

[0061] The sensor array 4, used for reflecting and transmitting light waves carrying reference and sensing signals, includes a second circulator 401. The second circulator 401 is connected to an optical fiber, on which two fiber grating groups are mounted. Each fiber grating group consists of a pair of fiber gratings (402 and 403 or 404 and 405) with the same bandwidth and center wavelength. The center wavelength of the fiber grating group corresponds to the center wavelength of the fiber gratings in the fiber grating array, and the bandwidth of the fiber gratings in the fiber grating group is greater than that in the fiber grating array. The bandwidth-filtered light wave enters through the second circulator 401, is reflected by the fiber grating group, and the reflected light wave is output through the second circulator 401.

[0062] The first coupler 5 is used to split the reflected light wave into two optical signals. One optical signal serves as the probe light, passing through the probe path, while the other optical signal serves as the reference light, passing through the reference path. The probe light consists of light waves reflected multiple times within each fiber Bragg grating group. The reference light consists of light waves reflected once from the first fiber Bragg grating within each fiber Bragg grating group.

[0063] The acousto-optic frequency shifter 6 is positioned between the first coupler 5 and the reference path beam splitter 701, and is used to shift the frequency of the reference path optical wave to remove zero-frequency noise.

[0064] The reference path beam splitter coupler 701 and the probe path beam splitter coupler 702 are used to split the reference path and probe path optical waves into two groups of high-order and low-order optical signals, respectively. The low-order optical signals of the reference path and probe path enter the low-order optical interferometer to detect the low-order sensing optical signal, and the high-order optical signals of the reference path and probe path enter the high-order optical interferometer to detect the high-order sensing optical signal.

[0065] The fiber delay module 8 is disposed between the reference path beam splitter coupler 701 and the third coupler 9, and includes a first optical path compensation fiber 801 and a first electrically adjustable fiber delay line 802 for a high-order optical interferometer, and a second optical path compensation fiber 803 and a second electrically adjustable fiber delay line 804 for a low-order optical interferometer. The first optical path compensation fiber 801 and the second optical path compensation fiber 803 are used to perform large-amplitude coarse adjustments to the optical path of the high-order and low-order optical interferometers, respectively. The first electrically adjustable fiber delay line 802 and the second electrically adjustable fiber delay line 804 are used to perform small-amplitude precise adjustments to the optical path of the high-order and low-order optical interferometers, respectively, to match the optical path difference between the reference path and the probe path.

[0066] The third coupler 9 includes a high-order optical interference coupler 901 and a low-order optical interference coupler 902. The high-order optical interference coupler 901 and the low-order optical interference coupler 902 are used to perform optical path-matched heterodyne interference on the high-order and low-order optical signals, respectively, and output high-order and low-order interference optical signals.

[0067] The second erbium-doped fiber amplifier 10 is disposed between the high-order optical interference coupler 901, the low-order optical interference coupler 902 and the wavelength division multiplexing device 11, and is used to amplify and adjust the optical power of the high-order and low-order interference optical signals to match the saturated input optical power of the photodetector 12.

[0068] The wavelength division multiplexing device 11 is disposed between the second erbium-doped fiber amplifier 10 and the photodetector 12 to separate interference light signals of different wavelengths and transmit them to the photodetector 12, which processes the corresponding wavelength signals.

[0069] The number of photodetectors 12 is twice the number of wavelength types at the center of the fiber grating in the fiber grating array. They are used to detect the beat frequency signals of the corresponding high-order and low-order interference light, and to perform photoelectric signal conversion.

[0070] The real-time data acquisition and processing module 13 is connected to the photodetector 12 and is used to acquire and process radio frequency signals in real time, demodulate interference signals, obtain detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and use low-order interference as a reference term for high-order interference for noise reduction processing.

[0071] In the white light interferometric detection and multiplexing system with a strain-strain resolution of the present invention, the reference optical signal and the sensing optical signal can be reflected and transmitted on the same optical fiber of the sensing element array.

[0072] The method for white-light interferometry detection and multiplexing at the speed of fly-strain resolution, using the aforementioned white-light interferometry detection and multiplexing system, includes:

[0073] The white light source module 1 emits broadband light, which is filtered by the fiber optic grating filter 2 and then passes through the sensor array 4. The light wave enters from the first port of the second circulator 401 and exits from the second port of the second circulator 401. It is reflected by the fiber optic grating group and exits from the third port of the second circulator 401. After passing through the first coupler 5, it is split 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.

[0074] The probe light is composed of light waves reflected multiple times inside each fiber grating group. After passing through the first coupler 5, it is split into two beams by the probe path beam splitter coupler 702. One beam participates in low-order optical interference and is transmitted to the low-order optical interference coupler 902, and the other beam participates in high-order optical interference and is transmitted to the high-order optical interference coupler 901.

[0075] The reference light consists of light waves reflected once from the first fiber grating in each fiber grating group. It does not carry a sensing signal. After passing through the first coupler 5, the reference light is first frequency-shifted by the acousto-optic frequency shifter 6 in the reference path. Then, it is split into two beams by the reference path beam splitter coupler 701. One beam participates in low-order optical interference. After the low-order optical interference is adjusted by the interferometer optical path matching of the second optical path compensation fiber 803 and the second electrically adjustable fiber delay line 804, it is transmitted to the low-order optical interference coupler 902. The other beam participates in high-order optical interference. After the high-order optical interference is adjusted by the interferometer optical path matching of the first optical path compensation fiber 801 and the first electrically adjustable fiber delay line 802, it is transmitted to the high-order optical interference coupler 901.

[0076] The probe beam and reference beam of high-order and low-order interferometers undergo optical path-matched heterodyne interference, and output interference signals;

[0077] The output interference signal is sequentially amplified and adjusted by the second erbium-doped fiber amplifier 10, the wavelength division multiplexing device 11 separates the signal light of different wavelengths, and the photodetector 12 converts the photoelectric signal.

[0078] The real-time data acquisition and processing module 13 acquires and processes radio frequency signals in real time, demodulates interference signals, obtains detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and uses low-order interference as a reference for high-order interference for noise reduction processing.

[0079] The white light source module 1 can be driven by a broadband light source, which can be an SLD, ASE, or LED light source.

[0080] The bandwidth Δλ of broadband light ASE satisfy:

[0081] Δλ ASE ≥Δλ FBG1 +…+Δλ FBGn

[0082] Where n is a positive integer, Δλ FBG1 , …, Δλ FBGn These represent the bandwidths of the fiber gratings on the same optical fiber in the sensor array 4.

[0083] Adjust the optical path so that the optical path difference satisfies δL:

[0084] δL≤λ FBG 2 / Δλ FBG

[0085] Where, λ FBG Δλ represents the center wavelength of the corresponding fiber grating. FBG The bandwidth of any fiber grating in fiber grating filter 2 and sensor array 4.

[0086] Fiber Bragg gratings can be any one or a combination of phase-shifted fiber Bragg gratings, uniform fiber Bragg gratings, and apodized fiber Bragg gratings.

[0087] The process and principle of the high-resolution white light interferometry detection and multiplexing method used in this embodiment are as follows:

[0088] The sensor array 4, the first coupler 5, the acousto-optic frequency shifter 6, the second coupler 7, the first optical path compensation fiber 801, the first electrically adjustable fiber delay line 802, and the high-order optical interference coupler 901 constitute an optical path matching high-order optical sensing interferometer.

[0089] The sensor array 4, the first coupler 5, the acousto-optic frequency shifter 6, the second coupler 7, the second optical path compensation fiber 803, the second electrically adjustable fiber delay line 804, and the low-order optical interference coupler 902 constitute an optical path matching low-order optical reference interferometer.

[0090] In this embodiment, the optical path matching interferometer is pre-designed, and the interferometer is selected from either a Michelson type structure or a Mach-Zehnder type structure, using heterodyne interferometry.

[0091] After passing through fiber optic grating filter 2, the bandwidth of broadband light becomes narrower. When the light wave passes through sensor array 4, it is divided into two types of light waves.

[0092] The light wave that is reflected only once by the first fiber grating in the same group and does not carry a sensing signal is the reference light wave. After passing through the first coupler 5, the reference light wave passes through the reference path, is first frequency-shifted by the acousto-optic frequency shifter 6, and then splits into two beams by the reference path beam splitter coupler 701. One beam participates in low-order optical interference, and after being adjusted by the second optical path compensation fiber 803 and the second electrically adjustable fiber delay line 804 for low-order optical interferometer path matching, it is transmitted to the low-order optical interference coupler 902. The other beam participates in high-order optical interference, and after being adjusted by the first optical path compensation fiber 801 and the first electrically adjustable fiber delay line 802 for high-order optical interferometer path matching, it is transmitted to the high-order optical interference coupler 901. The reference light signal is represented as E = A. ′ e j[ 2π[(f+Δf)]+φ(t)], where A ′ The amplitude corresponding to the reference optical signal is Δf, which is the frequency shift amount of the acousto-optic frequency shifter 6, j represents the imaginary unit, f is the center frequency of fiber optic gratings 202 and 203, and φ(t) is the initial phase.

[0093] The other light wave is the probe light wave, which is reflected multiple times between the fiber gratings in the same group. After passing through the first coupler 5, it is split into two beams by the probe path beam splitter coupler 702. One beam participates in low-order optical interference and is transmitted to the low-order optical interference coupler 902, while the other beam participates in high-order optical interference and is transmitted to the high-order optical interference coupler 901. According to the phase change formula... ε represents the strain applied to the sensing fiber, n represents the refractive index of the fiber, N is the interference order (i.e., the sensitization factor), l is the length between fiber gratings, and λ is the center wavelength of fiber gratings 202 and 203. The sensing optical signal is represented as follows: Where A″ is the amplitude corresponding to the probe optical signal, j represents the imaginary unit, f is the center frequency of fiber gratings 202 and 203, and φ(t) is the initial phase. This is for sensing phase changes.

[0094] In this embodiment, the fiber length of the reference path is precisely adjusted by adjusting the fiber delay module 8 in the reference path. Optical path matching interferometry requires that interfering light will not interfere; interference will only occur when the optical path difference between the reference path and the probe path is nearly equal, i.e., it must satisfy: ΔL < <L FBG ΔL is the optical path difference between the reference path and the probe path. Figure 1 The system sensitivity can be improved by adjusting the fiber delay module.

[0095] The final interference optical signal can be represented as: Where Δf is the frequency shift amount of the acousto-optic frequency shifter 6, t is the time-domain independent variable, and φ(t) is the initial phase. To sense phase changes, since the same sensing element is arranged on a single grating, and the reference and probe beams follow the same fiber path except for the demodulation interferometer section, most transmission path noise can be eliminated. Furthermore, by using low-order interference light as a reference group for high-order interference light, the weakly correlated broadband noise between the low-order and high-order interference light sensing is eliminated based on the periodic differences between random noise and vibration signals, while retaining the strongly correlated vibration signals. After passing through the photodetector 12 and the real-time data acquisition and processing module, the electrical signal can be represented... B represents the amplitude of the AC term, and vibration signal information is obtained based on this electrical signal.

[0096] The spectrum comparison diagram of the output signals of optical interference of different orders in this embodiment is shown below. Figure 2 As shown, when the applied signal magnitude remains constant and the amplitude of the uniform sensing signal is maintained, the equivalent resolution of the interference involving fifth-order reflected light is better. The experimental results demonstrate that this invention can significantly improve the equivalent resolution and sensitivity of the system, further illustrating the feasibility of the system and method of this invention.

[0097] The effect diagrams before and after noise reduction using low-order interference light in this embodiment are shown below. Figure 3 As shown in the experimental results, the present invention can effectively eliminate random noise in the system and has almost no impact on the magnitude of the detection signal, further demonstrating the feasibility of the system and method of the present invention.

[0098] In this embodiment, the system uses a wavelength division multiplexing device 11 to separate sensing signals of different wavelengths and transmits them to different photodetectors 12 for photoelectric detection. A vibration signal is applied to the sensitive fiber between fiber grating groups 402 and 403 of the wavelength 1 sensing element, while no vibration signal is applied to the sensitive fiber between fiber grating groups 404 and 405 of the wavelength 2 sensing element. Simultaneously, the vibration sensing signals of both wavelengths and their crosstalk are detected. Figure 4 As shown in the experimental results, the present invention can detect sensing signals of multiple wavelengths simultaneously, and the detection result of wavelength 2 is not affected by wavelength 1, further demonstrating the feasibility of the system and method of the present invention.

[0099] Example 2

[0100] refer to Figure 5 The white-light interferometric detection and multiplexing system with a fly-strain resolution in this embodiment is a hybrid multiplexing link using wavelength division and time division multiplexing. This system is similar to that in Embodiment 1 and... Figure 1 Similar devices and connections will not be described again here. Furthermore, the working principle of the optical path structure in this embodiment is the same as in Embodiment 1, and will not be described in detail here either.

[0101] It should be specifically noted that, unlike Embodiment 1, the white light source module 1 in this embodiment adopts a pulsed form. The sensor array 4 in this embodiment includes a second circulator 401, an optical fiber beam splitter 406, and multiple optical fibers connected to the optical fiber beam splitter 406. Each optical fiber of the sensor array 4 is independently provided with multiple sets of fiber gratings identical to those in Embodiment 1. The multiple optical fibers of the sensor array 4 are time-division multiplexed through delay optical fibers 406.

[0102] 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 white-light interferometric detection and multiplexing system with a strain-resolution scale, characterized in that, include: White light source module (1), used to emit broadband light; A fiber grating filter (2) for bandwidth filtering of broadband light includes a first circulator (201) and a fiber grating array; the fiber grating array includes one or more fiber gratings with different center wavelengths and the same bandwidth located on the same fiber; the first circulator (201) is used to transmit broadband light to the fiber grating array, and the broadband light reflected back is output through the first circulator (201). The sensing element array (4) used for reflecting and transmitting light waves carrying reference and sensing signals includes a second circulator (401); the second circulator (401) is connected to an optical fiber or to multiple optical fibers that are time-division multiplexed through delay optical fibers (407) via an optical fiber bundle splitter (406). Each of these optical fibers is provided with a fiber grating group. The fiber grating group 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 the same optical fiber are set according to the number of fiber gratings and the center wavelength in the fiber grating array. The bandwidth of the fiber grating in the fiber grating group is greater than the bandwidth of the fiber grating in the fiber grating array. The light wave after bandwidth filtering enters from the second circulator (401), is reflected by the fiber grating group, and the reflected light wave is output through the second circulator (401). The first coupler (5) is used to split the reflected light wave 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 probe light is composed of light waves reflected multiple times inside each fiber grating group. The reference light is composed of light waves reflected once by the first fiber grating in each fiber grating group. An acousto-optic frequency shifter (6) is disposed between the first coupler (5) and the reference path beam splitter (701) for frequency shifting of the reference path optical wave to remove zero-frequency noise; The reference path beam splitter coupler (701) and the detector path beam splitter coupler (702) are used to split the reference path and detector path light waves into two groups of high-order and low-order light signals, respectively. The low-order light signals of the reference path and the detector path enter the low-order optical interferometer to detect the low-order sensing light signal, and the high-order light signals of the reference path and the detector path enter the high-order optical interferometer to detect the high-order sensing light signal. The fiber delay module (8) is located between the reference path beam splitter coupler (701) and the third coupler (9). It includes a first optical path compensation fiber (801) and a first electrically adjustable fiber delay line (802) for a high-order optical interferometer, and a second optical path compensation fiber (803) and a second electrically adjustable fiber delay line (804) for a low-order optical interferometer. The first optical path compensation fiber (801) and the second optical path compensation fiber (803) are used to make large-amplitude coarse adjustments to the optical path of the high-order and low-order optical interferometers, respectively. The first electrically adjustable fiber delay line (802) and the second electrically adjustable fiber delay line (804) are used to make small-amplitude precise adjustments to the optical path of the high-order and low-order optical interferometers, respectively, to match the optical path difference between the reference path and the probe path. The third coupler (9) includes a high-order optical interference coupler (901) and a low-order optical interference coupler (902); the high-order optical interference coupler (901) and the low-order optical interference coupler (902) are used to perform optical path matching heterodyne interference on the high-order and low-order optical signals, respectively, and output high-order and low-order interference optical signals. Multiple photodetectors (12) are used to detect the beat frequency signals of corresponding high-order and low-order interference light at corresponding wavelengths and to perform photoelectric signal conversion; the number of photodetectors (12) is twice the number of wavelength types at the center of the fiber grating in the fiber grating array; The real-time data acquisition and processing module (13) is connected to the photodetector (12) and is used to acquire and process radio frequency signals in real time, demodulate interference signals, obtain the detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and use the low-order interference as a reference term for high-order interference for noise reduction processing.

2. The white-light interferometric detection and multiplexing system with a strain-resolution scale according to claim 1, characterized in that, The broadband light is broadband continuous light or broadband pulsed light.

3. The white-light interferometric detection and multiplexing system with a strain-resolution scale according to claim 1, characterized in that, A first erbium-doped fiber amplifier (3) is provided between the fiber grating filter (2) and the sensor array (4) for amplifying and adjusting the optical power of the filtered light wave.

4. The white-light interferometric detection and multiplexing system with a strain-level resolution according to claim 1, characterized in that, A wavelength division multiplexing device (11) is set between the high-order optical interference coupler (901), the low-order optical interference coupler (902) and the photodetector (12) to separate interference optical signals of different wavelengths and transmit them to the photodetector (12) that processes the corresponding wavelength signals.

5. The white-light interferometric detection and multiplexing system with a strain-resolution scale according to claim 4, characterized in that, A second erbium-doped fiber amplifier (10) is provided between the high-order optical interference coupler (901), the low-order optical interference coupler (902) and the wavelength division multiplexing device (11) to amplify and adjust the optical power of the high-order and low-order interference optical signals to match the saturated input optical power of the photodetector (12).

6. The white-light interferometric detection and multiplexing system with a strain-resolution scale according to claim 1, characterized in that, The white light source module (1) is driven by a broadband light source, wherein the broadband light source is an SLD, ASE or LED light source; The bandwidth Δλ of broadband light ASE satisfy: Dl ASE ≥Dl FBG1 +…+Dl FBGn Where n is a positive integer, Δλ FBG1 , …, Δλ FBGn These represent the bandwidths of each fiber grating on the same fiber in the sensor array (4).

7. The white-light interferometric detection and multiplexing system with a strain-resolution scale according to claim 1, characterized in that, Adjust the optical path so that the optical path difference satisfies δL: δL≤λ FBG 2 / Dl FBG Where, λ FBG Δλ represents the center wavelength of the corresponding fiber grating. FBG The bandwidth of any fiber grating in the fiber grating filter (2) and the sensor array (4) is denoted as .

8. The white-light interferometric detection and multiplexing system with a strain-resolution scale according to claim 1, characterized in that, A fiber optic grating is any one or a combination of phase-shifted fiber optic gratings, uniform fiber Bragg gratings, and apodized fiber optic gratings.

9. A white-light interferometric detection and multiplexing method with a strain resolution on the order of magnitude, characterized in that, The white light interferometric detection and multiplexing system with a speed-strain resolution of any one of claims 1 to 8 is adopted; The white-light interferometric detection and multiplexing method with a strain resolution on the order of magnitude includes: The white light source module (1) emits broadband light, which is filtered by the fiber optic grating filter (2) and then passes through the sensor array (4). The light wave enters from the first port of the second circulator (401) and exits from the second port of the second circulator (401). It is reflected by the fiber optic grating group and exits from the third port of the second circulator (401). After passing through the first coupler (5), it is split 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 probe light is composed of light waves reflected multiple times inside each fiber grating group. After passing through the first coupler (5), it is split into two beams by the probe path beam splitter coupler (702). One beam participates in low-order optical interference and is transmitted to the low-order optical interference coupler (902), and the other beam participates in high-order optical interference and is transmitted to the high-order optical interference coupler (901). The reference light consists of light waves reflected once by the first fiber grating in each fiber grating group. It does not carry sensing signals. After the reference light passes through the first coupler (5), it is first frequency-shifted by the acousto-optic frequency shifter (6) in the reference path. Then it is split into two beams by the reference path beam splitter (701). One beam participates in low-order optical interference. After the low-order optical interference is adjusted by the interferometer optical path matching of the second optical path compensation fiber (803) and the second electrically adjustable fiber delay line (804), it is transmitted to the low-order optical interference coupler (902). The other beam participates in high-order optical interference. After the high-order optical interference is adjusted by the interferometer optical path matching of the first optical path compensation fiber (801) and the first electrically adjustable fiber delay line (802), it is transmitted to the high-order optical interference coupler (901). The probe beam and reference beam of high-order and low-order interferometers undergo optical path-matched heterodyne interference, and output interference signals; The output interference signal is converted into a photoelectric signal by the photodetector (12); The real-time data acquisition and processing module (13) acquires and processes radio frequency signals in real time, demodulates interference signals, obtains the detection results of corresponding wavelength high-order and low-order heterodyne interference signals, and uses low-order interference as a reference for high-order interference for noise reduction processing.

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