Optical fiber sensing method and system with opto-electric hybrid oscillation

Abstract

The application provides an optical fiber sensing method and system of photoelectric hybrid oscillation, light frequency combs obtained from a light frequency comb generation device are respectively input into a reference arm and a sensing arm of an interferometer module, a sensing optical fiber on the sensing arm is affected by a to-be-measured quantity to generate an optical fiber delay change, after optical frequency shift, the light frequency combs on the reference arm generate a frequency difference with the light frequency combs on the sensing arm, after coupling, the reference light combs and the sensing light combs are output to an optical filter, two optical spectrum regions are selected according to sensitivity requirements and are respectively transmitted to a photoelectric conversion branch, the sensing light and the reference light of each optical comb line are contained in the optical spectrum regions, an electric signal is obtained after electric amplification and band-pass filtering of a beat frequency electric signal obtained by a photoelectric detector. The phase difference of the electric signals of the two branches is transmitted into a closed loop oscillation cavity module, a target oscillation signal is respectively transmitted to a first frequency mixer and a frequency shift measurement end through a power divider to obtain a frequency shift, and a mapping relationship is established with the optical fiber delay change to reflect the influence of the to-be-measured quantity on the sensing optical fiber.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber sensing, and in particular to an optical fiber sensing method and system based on optical-electric hybrid oscillation. BACKGROUND

[0002] Optical fiber sensing technology has been rapidly developed due to its inherent advantages such as low loss, light weight, large bandwidth, anti-electromagnetic interference, and multi-variable sensitivity. Optical fiber sensors use optical fibers as sensing elements to transmit light from a light source to a receiver through a to-be-measured point. At the to-be-measured point, optical parameters such as amplitude, wavelength, phase, and polarization are modulated as functions related to temperature, strain, displacement, refractive index, and angular velocity and other to-be-measured quantities. Many high-precision measurement tasks use optical phase to transmit sensing information, and a laser interferometer is a typical structure. A single-frequency laser interferometer essentially encodes the optical phase introduced by the sensing element into an interference fringe pattern of the collected spectrum, but is severely affected by laser frequency noise. In some specific applications, the to-be-measured quantity is very small and the weak signal means that the noise source related to the detector readout should be reduced to an extremely low level. Although some digital phase demodulation techniques are widely known, phase measurement still faces great challenges in detection limits due to the limited instrument background noise.

[0003] In the prior art, in a classical opto-electric oscillator, in order to obtain high spectral purity, a low-loss long optical fiber is always used as part of its cavity length, but it is easily affected by environmental disturbances and is difficult to distinguish from the to-be-measured quantity. Although some techniques can achieve high sensing sensitivity, the reconfigurability of the sensitivity is poor and cannot meet various needs. More importantly, random drift of the laser frequency can greatly reduce the sensing accuracy. SUMMARY

[0004] In view of this, the embodiments of the present application provide an optical fiber sensing method and device based on optical fiber hybrid oscillation to eliminate or improve one or more defects in the prior art, and solve the problems of low sensing accuracy and poor reconfigurability of sensitivity in the prior art.

[0005] One aspect of the present application provides an optical fiber sensing system based on optical-electric hybrid oscillation, the system comprising:

[0006] An optical frequency comb generation device, comprising a laser and a phase modulator, the phase modulator modulating a continuous wave generated by the laser by a radio frequency signal and obtaining an optical frequency comb;

[0007] The interferometer module comprises a reference arm deploying a polarization controller and an acousto-optic modulator, a sensing arm deploying a sensing optical fiber, a first coupler and a second coupler, the first coupler receives the optical frequency comb and is divided into a first optical frequency comb and a second optical frequency comb; the first optical frequency comb is input into the sensing arm, the sensing optical fiber is affected by the to-be-measured quantity to generate an optical fiber delay change, causing the first optical frequency comb of the sensing arm to generate a to-be-measured phase and obtain a sensing optical comb, the second optical frequency comb is input into the reference arm, the interference state is adjusted by the polarization controller, and the optical frequency is shifted by the acousto-optic modulator driven by a driving signal to obtain a reference optical comb having a frequency difference with the sensing optical comb; the reference optical comb and the sensing optical comb are coupled by the second coupler to obtain a target optical frequency comb;

[0008] The optical filter receives the target optical frequency comb and selects a first spectral region and a second spectral region from the target optical frequency comb according to the sensitivity requirement, the first spectral region contains a first reference light obtained through the reference arm and a first sensing light through the sensing arm, and the second spectral region contains a second reference light obtained through the reference arm and a second sensing light through the sensing arm;

[0009] The first photoelectric conversion branch comprises a first photodetector, a first electric amplifier and a first band-pass filter, the first photodetector receives the first sensing light and the first reference light having a frequency difference and outputs a first beat frequency electric signal related to the to-be-measured phase, and the first beat frequency electric signal is amplified and band-pass filtered to obtain a first electric signal;

[0010] The second photoelectric conversion branch comprises a second photodetector, a second electric amplifier and a second band-pass filter, the second photodetector receives the second sensing light and the second reference light having a frequency difference and outputs a second beat frequency electric signal related to the to-be-measured phase, and the second beat frequency electric signal is amplified and band-pass filtered to obtain a second electric signal;

[0011] The closed-loop oscillation cavity module comprises a first mixer, a second mixer, a third band-pass filter, a third electric amplifier, a fourth band-pass filter and a power divider, the first electric signal is up-converted by the first mixer and output to the second mixer containing the second electric signal through the third band-pass filter, and the second mixer is down-converted to obtain an oscillation signal carrying the phase difference of the two electric signals, the oscillation signal is amplified and filtered by the third electric amplifier and the fourth band-pass filter to obtain a target oscillation signal, and the target oscillation signal is input into the power divider and transmitted to the first mixer and a target oscillation signal frequency shift measurement end respectively; the target oscillation signal frequency shift measurement end is used for measuring the frequency shift of the target oscillation signal, and the frequency shift of the target oscillation signal establishes a mapping relationship with the optical fiber delay change to reflect the influence of the to-be-measured quantity on the sensing optical fiber.

[0012] In some embodiments, the phase modulator modulates the continuous wave generated by the laser by a radio frequency signal and obtains an optical frequency comb, the frequency expression of each optical comb line in the optical frequency comb is:

[0013] f = f0 + kf RF ;

[0014] wherein k represents the serial number of the selected optical comb line in the optical frequency comb, f0 represents the center frequency of the laser light, and f RF represents the center frequency of the radio frequency signal.

[0015] In some embodiments, the first optical frequency comb input into the sensing arm causes the sensing fiber to produce a fiber delay change affected by the to-be-measured quantity, and the expression of the fiber delay difference between the sensing arm and the reference arm is:

[0016] τ = τ0 + τ(t);

[0017] wherein τ0 represents the fixed delay, and τ(t) represents the fiber delay change affected by the to-be-measured quantity.

[0018] In some embodiments, the first optical spectrum region and the second optical spectrum region are converted into the first electrical signal and the second electrical signal through the first photoelectric conversion branch and the second photoelectric conversion branch, and the expression of the obtained first electrical signal and the second electrical signal is:

[0019] V 1,2 (t) ∝ cos [2πf m t + 2π(f0 + kf RF )(τ0 + τ(t))] ;

[0020] After the first electrical signal is up-converted by the first mixer and output to the second mixer containing the second electrical signal through the third band-pass filter and down-converted, an oscillation signal carrying the phase difference between the two electrical signals is obtained, and the expression of the phase difference between the two electrical signals related to the to-be-measured quantity is:

[0021]

[0022] wherein f m represents the center frequency of the driving signal, k represents the serial number of the selected optical comb line in the optical frequency comb, (f0 + kf RF ) represents the frequency of each optical comb line, f0 represents the center frequency of the laser light, f RF represents the center frequency of the radio frequency signal, (τ0 + τ(t)) represents the fiber delay difference between the reference arm and the sensing arm, τ0 represents the fixed delay, τ(t) represents the fiber delay change affected by the to-be-measured quantity, m represents the optical comb line in the first optical spectrum region, and n represents the optical comb line in the second optical spectrum region.

[0023] In some embodiments, the first photoelectric conversion branch further comprises a phase shifter, the power divider forms a closed loop oscillation cavity after transmitting the target oscillation signal to the first mixer, and the phase shifter is used to adjust the oscillation frequency to meet the stable oscillation condition of the closed loop oscillation cavity.

[0024] In some embodiments, in order to meet the stable oscillation condition of the closed loop oscillation cavity, the phase shifter adjusts the oscillation frequency, and the expression is:

[0025]

[0026] Wherein, m represents the optical comb line of the first spectral region, n represents the optical comb line of the second spectral region, τ cavity represents the delay of the closed loop oscillation cavity, N represents the order of the oscillation mode, and φ0 is the phase constant caused by the fixed delay and the phase shifter.

[0027] In some embodiments, the change of the fiber delay on the sensing arm causes the oscillation frequency to move, and the expression is:

[0028]

[0029] Wherein, Δτ represents the change amount of the fiber delay, f RF represents the center frequency of the radio frequency signal, τ cavity represents the delay of the closed loop oscillation cavity, m represents the optical comb line of the first spectral region, and n represents the optical comb line of the second spectral region.

[0030] In some embodiments, the target oscillation signal frequency shift measurement end comprises:

[0031] A frequency counter, the frequency shift of the target oscillation signal is measured by a high-resolution high-speed frequency counter.

[0032] In another aspect, the application also provides a photoelectric hybrid oscillation fiber sensing method, the method comprising:

[0033] The above-mentioned photoelectric hybrid oscillation fiber sensing system is placed in the environment to be measured, and the target oscillation signal frequency shift is output, the target oscillation signal frequency shift and the change of the fiber delay are mapped to reflect the influence of the sensing fiber received by the measured quantity.

[0034] In some embodiments, the method further comprises: the sensing sensitivity can be reconstructed by changing the frequency interval of the first spectral region and the second spectral region or the delay of the closed loop oscillation cavity.

[0035] The beneficial effects of the application are at least:

[0036] The optical fiber sensing method and system of the photoelectric hybrid oscillation disclosed by the application input the obtained optical frequency comb into the reference arm and the sensing arm of the interferometer module respectively, the sensing fiber on the sensing arm produces fiber delay change under the influence of the to-be-measured quantity, the optical frequency comb on the reference arm uses an acousto-optic modulator to produce optical frequency shift and produces frequency difference with the optical frequency comb on the sensing arm, the reference light comb on the reference arm is output, and after being coupled with the sensing light comb output on the sensing arm, is output to an optical filter and selects two optical spectrum regions, the sensing light and the reference light containing each optical comb line in the optical spectrum region are divided into two paths and transmitted to a photoelectric conversion branch, a difference frequency electric signal is obtained through a photoelectric detector, the difference frequency electric signal carries the phase of the to-be-measured quantity, which is not only beneficial to avoiding low-frequency noise but also ensures the bandwidth matching with subsequent electrical devices; the difference frequency electric signals of each branch are electrically amplified to enhance the intensity of the signals, facilitate subsequent processing, and use a band-pass filter to select the required frequency to pass through, reduce noise interference, and improve the quality and stability of the signals. The phase difference of the electric signals of the two branches is transmitted to a third electric amplifier and a fourth band-pass filter through a frequency conversion composed of a first mixer, a second mixer and a third band-pass filter, the target oscillation signal is transmitted to the first mixer and a frequency shift measurement end through a power divider, and after being transmitted to the first mixer, a closed loop oscillation cavity is formed. The phase difference of the electric signals of the two branches is accumulated in a cycle until the gain of the oscillation loop gradually saturates, a stable oscillation signal frequency shift is formed, the detection limit of the optical fiber sensing system is improved, and the output stability of the frequency shift measurement end is further ensured, the frequency shift of the target oscillation signal and the fiber delay change establish a mapping relationship to reflect the influence of the to-be-measured quantity on the sensing fiber.

[0037] Further, the application selects two optical spectrum regions meeting the frequency interval requirement according to the sensitivity requirement, and provides the delay of the closed loop oscillation cavity through the fourth band-pass filter, which is beneficial to constructing optical fiber sensing systems with different sensitivities to meet the requirements of different situations, and is beneficial to reducing the influence of the external environment on signal transmission and improving the stability of signal transmission.

[0038] Additional advantages, objects, and features of the application will be set forth in part by the description that follows, and will become apparent to those skilled in the art from the drawings and the following detailed description, or can be learned by practice of the application. The objects and other advantages of the application can be realized and attained by the structure particularly pointed out in the description and the drawings.

[0039] Those skilled in the art will understand that the objects and advantages of the application can be realized and attained by the application, and the above and other objects of the application can be more clearly understood according to the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0040] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0041] Figure 1 Structure diagram of the optical fiber sensing system with opto-electric hybrid oscillation according to an embodiment of the present application.

[0042] Figure 2 Flow diagram of the optical fiber sensing system with opto-electric hybrid oscillation according to an embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments and the accompanying drawings. Herein, the illustrative embodiments of the present application and their descriptions are used to explain the present application, but are not used as limitations to the present application.

[0044] It should be noted that, in order to avoid the present application being obscured by unnecessary details, only the structures and / or processing steps closely related to the solutions according to the present application are shown in the accompanying drawings, and other details not closely related to the present application are omitted.

[0045] It should be emphasized that the terms "comprises / comprising" when used in this specification, specify the presence of stated features, elements, steps or components, but do not preclude the presence or addition of one or more other features, elements, steps or components.

[0046] It should be noted that, if not specifically stated, the term "connected" in this specification can not only mean direct connection, but also mean indirect connection with an intermediate.

[0047] In the following, embodiments of the present application will be described with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0048] In the prior art, in order to obtain high spectral purity, a low-loss long optical fiber is always used as a part of the cavity length of a classical optoelectronic oscillator, but it is easy to be affected by environmental disturbances and difficult to be distinguished from the to-be-measured. Although some technologies can achieve high sensing sensitivity, the reconfigurability of the sensitivity is poor, which cannot meet various requirements. More importantly, random drift of the laser frequency can greatly reduce the sensing accuracy. The present application provides an optoelectronic hybrid oscillation fiber sensing method and system. The optical frequency comb obtained from an optical frequency comb generation device is input into a reference arm and a sensing arm of an interferometer module, respectively. The sensing fiber on the sensing arm is affected by the to-be-measured to generate a fiber delay change. The optical frequency comb on the reference arm uses an acousto-optic modulator to generate optical frequency shift and generate a frequency difference with the optical frequency comb on the sensing arm. The reference light comb on the reference arm is output, coupled with the sensing light comb output from the sensing arm, and then output to an optical filter and select two optical spectrum regions. The optical spectrum region contains the sensing light and the reference light of each optical comb line and is divided into two paths to an optoelectronic conversion branch. The difference frequency electric signal is obtained by an optoelectronic detector. The difference frequency electric signal carries the to-be-measured phase. The difference frequency electric signals of the branches are electrically amplified and band-pass filtered to obtain an electric signal. The phase difference of the electric signals of the two branches is transmitted to a third electric amplifier and a fourth band-pass filter through a first mixer, a second mixer and a third band-pass filter. The target oscillation signal is transmitted to the first mixer and a frequency shift measurement end through a power divider. After being transmitted to the first mixer, a closed loop oscillation cavity is formed. The phase difference of the electric signals of the two branches is accumulated in a cycle until the gain of the oscillation loop gradually saturates, forming a stable oscillation signal frequency shift. The frequency shift measurement end measures the obtained frequency shift and establishes a mapping relationship with the fiber delay change to reflect the influence of the to-be-measured on the sensing fiber.

[0049] Figure 1 The structure diagram of the optoelectronic hybrid oscillation fiber sensing system according to an embodiment of the present application. An aspect of the present application provides an optoelectronic hybrid oscillation fiber sensing system, which comprises:

[0050] An optical frequency comb generation device, which comprises a laser and a phase modulator. The phase modulator modulates the continuous wave generated by the laser by a radio frequency signal and obtains an optical frequency comb. Specifically, the continuous wave generated by the laser has a single frequency but a modulatable phase. A radio frequency signal is used to change the phase of the continuous wave by using a phase modulator, and the radio frequency signal modulates the frequency of the continuous wave to obtain an optical frequency comb. In some embodiments, the phase modulator modulates the continuous wave generated by the laser by a radio frequency signal and obtains an optical frequency comb. The frequency expression of each optical comb line in the optical frequency comb is:

[0051] f = f0 + kf RF ;

[0052] wherein k represents the sequence number of the selected optical comb line in the optical frequency comb, f0 represents the center frequency of the laser light, and f represents the frequency of the selected optical comb line. RF represents the center frequency of the radio frequency signal.

[0053] The interferometer module comprises a reference arm deploying a polarization controller and an acousto-optic modulator, a sensing arm deploying a sensing optical fiber, a first coupler and a second coupler, the first coupler divides the optical frequency comb into a first optical frequency comb and a second optical frequency comb after receiving the optical frequency comb; the sensing optical fiber in the sensing arm is affected by the to-be-measured quantity to generate an optical fiber delay change, causing the first optical frequency comb in the sensing arm to generate a to-be-measured phase and obtaining a sensing optical comb, the second optical frequency comb is input into the reference arm, and the polarization controller adjusts the interference state, and the acousto-optic modulator driven by a driving signal performs optical frequency shift to obtain a reference optical comb having a frequency difference with the sensing optical comb; the reference optical comb and the sensing optical comb are coupled through the second coupler to obtain a target optical frequency comb.

[0054] Specifically, the Mach-Zehnder interferometer comprising two couplers and two interference arms is adopted, the polarization controller adjusts the interference state to make the optical frequency comb achieve the best interference effect in the interferometer, and the best interference state can make the power of the beat electric signal output by the photodetector maximum; the acousto-optic modulator performs optical frequency shift on the optical frequency comb transmitted to the reference arm through the coupler to make the optical frequency combs on the reference arm and the sensing arm have a frequency difference and be output, the sensing optical fiber is used for sensing the to-be-measured quantity and generating an optical fiber delay change, the to-be-measured quantity includes but is not limited to temperature, strain and vibration, the reference optical comb after the optical frequency shift is coupled with the sensing optical comb in the sensing arm in the coupler at the output end of the interferometer and interference occurs, and the optical fiber delay change generated by the to-be-measured quantity is obtained by comparing the optical fiber delay difference of the reference optical comb and the sensing optical comb.

[0055] Further, the acousto-optic modulator changes the frequency of the optical frequency comb on the reference arm to make the subsequent interference measurement more accurate, and separating the frequencies of the reference optical comb and the sensing optical comb is beneficial to avoid the low-frequency noise of the beat electric signal and ensure the bandwidth matching with the subsequent electrical device.

[0056] In some embodiments, the first optical frequency comb is input into the sensing arm, and the sensing optical fiber is affected by the to-be-measured quantity to generate an optical fiber delay change, and the expression of the optical fiber delay difference between the reference arm is:

[0057] τ = τ0 + τ(t) ;

[0058] wherein τ0 represents a fixed delay, and τ(t) represents the optical fiber delay change generated by the to-be-measured quantity.

[0059] The optical filter receives the target optical frequency comb and selects a first spectral region and a second spectral region from the target optical frequency comb according to a sensitivity requirement, the first spectral region containing a first reference light obtained through a reference arm and a first sensing light through a sensing arm, and the second spectral region containing a second reference light obtained through the reference arm and a second sensing light through the sensing arm.

[0060] The first photoelectric conversion branch includes a first photodetector, a first electrical amplifier and a first band-pass filter, the first photodetector receives the first sensing light and the first reference light with a frequency difference and outputs a first beat frequency electrical signal related to the phase to be measured, and the first beat frequency electrical signal is amplified and band-pass filtered to obtain a first electrical signal.

[0061] The second photoelectric conversion branch includes a second photodetector, a second electrical amplifier and a second band-pass filter, the second photodetector receives the second sensing light and the second reference light with a frequency difference and outputs a second beat frequency electrical signal related to the phase to be measured, and the second beat frequency electrical signal is amplified and band-pass filtered to obtain a second electrical signal.

[0062] Specifically, the target optical frequency comb output by the interferometer module is transmitted to the two photoelectric conversion branches, which is conducive to the measurement of the phase to be measured, and the beat frequency electrical signals on the two photoelectric conversion branches can be independently detected and analyzed. The frequency interval of the selected two spectral regions affects the sensitivity of the fiber sensing system, so it is necessary to select two spectral regions that can meet the requirements according to the actual use requirements of the constructed fiber sensing system. The two spectral regions are transmitted to the first photoelectric conversion branch and the second photoelectric conversion branch respectively, and each branch only needs to retain the reference light and the sensing light of a single spectral region. The acousto-optic modulator performs optical frequency shift on the optical frequency comb on the reference arm to make the optical frequency comb on the reference arm and the sensing arm different in frequency. The sensing light and the reference light of different frequencies are input into the photodetector and output the beat frequency electrical signal, realizing heterodyne interference. The beat frequency electrical signal contains the fiber delay change obtained by the sensing fiber due to the phase to be measured. After the electrical amplifier and the band-pass filter, the electrical signal of each branch is obtained.

[0063] Further, in some embodiments, the method further includes: reconstructing the sensing sensitivity by changing the frequency interval of the first spectral region and the second spectral region or the delay of the closed loop resonant cavity.

[0064] The closed loop oscillation cavity module comprises a first mixer, a second mixer, a third band pass filter, a third electric amplifier, a fourth band pass filter and a power divider, the first electric signal is up-converted by the first mixer and output to the second mixer containing the second electric signal through the third band pass filter, and the oscillation signal carrying the phase difference of the two electric signals is obtained by down-conversion, the oscillation signal is amplified and filtered by the third electric amplifier and the fourth band pass filter to obtain the target oscillation signal, and the target oscillation signal is input into the power divider and transmitted to the first mixer and the target oscillation signal frequency shift measurement end respectively; the target oscillation signal frequency shift measurement end is used for measuring the frequency shift of the target oscillation signal, and the mapping relationship between the target oscillation signal frequency shift and the fiber delay change reflects the influence of the to-be-measured on the sensing optical fiber. Specifically, the to-be-measured includes but is not limited to temperature, strain and vibration.

[0065] In some embodiments, the first spectral region and the second spectral region are converted into the first electric signal and the second electric signal through the first photoelectric conversion branch and the second photoelectric conversion branch, and the expressions of the obtained first electric signal and the second electric signal are:

[0066] V 1,2 ∝cos[2πf m t+2π(f0+kf R0 )(τ0+τ(t))];

[0067] The first electric signal is up-converted by the first mixer and output to the second mixer containing the second electric signal through the third band pass filter, and the oscillation signal carrying the phase difference of the two electric signals is obtained by down-conversion, and the expression of the phase difference of the two electric signals related to the to-be-measured is:

[0068]

[0069] Wherein, f m represents the center frequency of the driving signal, k represents the sequence number of the selected optical comb line in the optical frequency comb, (f0+kf RF ) represents the frequency of each optical comb line, f0 represents the center frequency of the laser light of the laser, f RF represents the center frequency of the radio frequency signal, (τ0+τ(t)) represents the fiber delay difference between the reference arm and the sensing arm, τ0 represents the fixed delay, τ(t) represents the fiber delay change affected by the to-be-measured, m represents the optical comb line of the first spectral region, and n represents the optical comb line of the second spectral region.

[0070] Specifically, the first electrical signal and the second electrical signal are electrically amplified and band-pass filtered by a frequency conversion pair composed of a first mixer, a second mixer and a third band-pass filter to obtain an oscillation signal containing a phase difference between the two electrical signals. The core of the closed-loop oscillation cavity module is a positive feedback loop. By introducing an electrical amplifier and a band-pass filter, the closed-loop oscillation cavity module is self-excited and generates a stable target oscillation signal. The target oscillation signal is fed back to the input end of the first mixer to form a closed-loop oscillation cavity. The phase difference is accumulated in the closed-loop oscillation cavity module until the gain of the oscillation loop gradually saturates, and finally converted into a frequency shift of the target oscillation signal. The cyclic accumulation enhancement is the key mechanism to realize stable oscillation, and the closed-loop oscillation cavity can maintain oscillation without external energy input. Since the cyclic accumulation process of the phase difference in the closed-loop oscillation cavity module is very fast, the frequency shift measurement end measures the frequency shift in the stable oscillation state. Further, in the case where there is a closed-loop oscillation cavity module that does not contain the first mixer, the second mixer and the third band-pass filter, the closed-loop oscillation cavity module forms an oscillation due to the superposition of additive noise. The third band-pass filter blocks the image frequency output by the first mixer, thereby avoiding the influence of the same frequency crosstalk. The fourth band-pass filter provides the delay of the closed-loop oscillation cavity and the selection of a single oscillation mode.

[0071] In some embodiments, the first photoelectric conversion branch further comprises a phase shifter, and the power divider transmits the target oscillation signal to the first mixer to form a closed-loop oscillation cavity, and the phase shifter is used to adjust the oscillation frequency to meet the stable oscillation condition of the closed-loop oscillation cavity.

[0072] In some embodiments, in order to meet the stable oscillation condition of the closed-loop oscillation cavity, the phase shifter adjusts the oscillation frequency, and the expression is:

[0073]

[0074] wherein m represents an optical comb line in a first spectral region, n represents an optical comb line in a second spectral region, τ cavity represents the delay of the closed-loop oscillation cavity, N represents the order of the oscillation mode, and φ0 is a constant phase caused by a fixed delay and the phase shifter.

[0075] In some embodiments, the change in the fiber delay on the sensing arm causes the oscillation frequency to move, and the expression is:

[0076]

[0077] wherein Δτ represents the change in the fiber delay, f RF represents the center frequency of the radio frequency signal, τ cavity represents the delay of the closed-loop oscillation cavity, m represents an optical comb line in a first spectral region, and n represents an optical comb line in a second spectral region.

[0078] Specifically, the phase shifter is used to adjust the oscillation frequency so that the closed loop oscillation cavity meets the oscillation condition and performs stable oscillation, the condition of stable oscillation includes that the net gain is approximately 1 and the phase difference of one cycle is an integer multiple of 2π. The phase difference of the first electric signal and the second electric signal is input into the closed loop oscillation cavity through a frequency conversion, and the phase shifter needs to be arranged on an optical-electric conversion branch; according to the expression of the oscillation frequency movement caused by the change of the fiber delay on the sensing arm, when the fiber delay of the sensing arm changes, the oscillation frequency moves in proportion; further, the oscillation mode interval determines the sensing range, and too large delay change will lead to mode jump, affecting the measurement result of the to-be-measured quantity.

[0079] In some embodiments, the target oscillation signal frequency shift measurement end comprises:

[0080] The frequency counter measures the frequency shift of the target oscillation signal through a high-resolution high-speed frequency counter. Specifically, the frequency counter can continuously measure the frequency of the input signal and record its change when measuring the frequency shift, and the frequency shift amount can be calculated by comparing the frequency measurement results at different time points.

[0081] In another aspect, the present application also provides an optical-electric hybrid oscillation fiber sensing method, the method comprising:

[0082] The above-mentioned optical-electric hybrid oscillation fiber sensing system is placed in the environment to be measured and outputs the target oscillation signal frequency shift, and the target oscillation signal frequency shift and the fiber delay change establish a mapping relationship to reflect the influence of the to-be-measured quantity on the sensing fiber.

[0083] The present application will be described below in combination with a specific embodiment:

[0084] Figure 2This is a schematic diagram of the optoelectronic hybrid oscillation fiber optic sensing system according to an embodiment of the present invention. The optoelectronic hybrid oscillation fiber optic sensing system proposed in this invention maps the measurand loaded on the sensing arm of the Mach-Zehnder interferometer module to the frequency shift of the target oscillation signal generated by the closed-loop oscillation cavity module with frequency conversion pairs. Two branch signals, assisting the two frequency conversions, are obtained through heterodyne detection of the interferometer. Their phase includes the measurand, which is proportionally amplified by two optical comb frequencies. The phase difference accumulates and strengthens cyclically in the closed-loop all-electric oscillation cavity, ultimately manifesting as a frequency shift in the oscillation signal. The sensitivity of the fiber optic sensing system can be flexibly constructed by using different optical comb frequency intervals or changing the delay of the closed-loop oscillation cavity, where the delay of the closed-loop oscillation cavity is mainly provided by a narrow-bandwidth bandpass filter. Compared with phase measurement without an oscillation cavity, the detection limit of the present invention can be improved by 42 dB with a frequency shift of 10 Hz and a cavity delay of 1 μs. The sensing accuracy depends on the cavity noise limit and is independent of the instrument and cavity delay. At a frequency interval of 150 gigahertz (GHz), with an average time of approximately 0.2 seconds (s), the minimum Allen deviation reaches 2.7 attoseconds (as).

[0085] The continuous wave generated by the laser is modulated by a stable radio frequency signal in a phase modulator to produce an optical frequency comb, the frequency of which can be expressed as f0 + kf. RF Where k is an integer representing the sequence number of the selected optical comb line in the optical frequency comb, f0 and f RF These are the center frequencies of the laser and radio frequency signals, respectively. The optical frequency comb is input into a Mach-Zehnder interferometer consisting of two couplers and two interferometer arms. One arm serves as the reference arm, and the other as the sensing arm, on which a sensing fiber is placed. The fiber delay difference between the two arms is assumed to be τ0 + τ(t), where τ(t) is the fiber delay change caused by the measurement compared to the fixed delay τ0. A polarization controller is used to adjust the interference state to a suitable level, and an acousto-optic modulator is used to achieve heterodyne detection. At the output of the interferometer, an optical filter extracts the two spectral regions of the optical frequency comb and splits them into two paths, which undergo photoelectric conversion including electrical amplification and bandpass filtering, respectively. For each photoelectric conversion branch, the generated electrical signal can be expressed as V. 1,2 ∝cos[2πf m t+2π(f0+kf RF (τ0+τ(t))], where f m This is the center frequency of the drive signal that drives the acousto-optic modulator. It can be seen that its phase includes the product of the fiber delay difference and the corresponding optical comb frequency. When the m-th and n-th combs are selected, the expression related to the measurement in the phase difference between the two branch signals is:

[0086] Two branch signals are injected into two mixers. The oscillation signal is first up-converted, then down-converted after a band-pass filter. The band-pass filter in the middle of the frequency conversion is used to block the image frequency of the mixer output. The signal generated after two frequency conversions is amplified, filtered, and fed back to the up-conversion injection to form a closed-loop oscillation cavity. The delay of the closed-loop oscillation cavity and the selection of a single oscillation mode are provided by the band-pass filter centered at the oscillation frequency. Once the amplitude and phase conditions for oscillation are met, the closed-loop structure allows self-replication. In addition, a phase shifter is inserted in one of the branches to adjust the oscillation frequency as needed. According to the regenerative feedback theory, the oscillation frequency can be given by the formula: where τ cavity is the delay of the closed-loop oscillation cavity, N (= 0, 1, 2,...) is the order of the oscillation mode, and φ0 is the phase constant caused by the fixed delay and the phase shifter. Mathematically, within the range of the oscillation mode spacing, the relationship between the oscillation frequency shift and the fiber delay change is given by the formula: It can be seen that when the fiber delay of the sensing arm changes, the oscillation frequency shift changes proportionally, which can be measured by a high-resolution and high-speed frequency counter. Changing the frequency interval of the two spectral regions or the delay of the closed-loop oscillation cavity can reconstruct the sensing sensitivity. The sensing range is determined by the oscillation mode spacing, because too large a delay change will cause mode jumping, resulting in incorrect measurement. By setting a reasonable frequency interval and cavity delay, a specific fiber sensing system can be constructed to meet the actual needs in different situations.

[0087] The advantages of the present application include:

[0088] 1. Sensitivity reconfigurable. Design experiments to generate two different optical frequency combs using 10 GHz and 25 GHz radio frequency signals, respectively, and obtain frequency intervals of 20 GHz and 150 GHz by setting the parameters of the optical filter; use two narrow-bandwidth bandpass filters for comparative experiments, with a center frequency of about 24 MHz (megahertz), but different bandwidths and group delays. By scanning the sensing fiber, the dynamic characteristics of the sensing system are studied. With the increase of fiber delay change, the frequency shift shows a linear downward trend with a periodic change, and the period is the inverse of the frequency interval, and the frequency shift range is equal to the oscillation mode interval. When the curve is linearly fitted, the slope can be used to represent the sensing sensitivity. Experiments show that when the filter bandwidth is 400 kHz (kilohertz) and the frequency interval is 20 GHz, the sensing sensitivity is 8.3 kHz / ps, and the sensing range is 50 ps (picoseconds); when the frequency interval is 150 GHz, the sensing sensitivity is improved to 62 kHz / ps, and the sensing range is reduced to 6.7 ps; when the filter bandwidth is 2 MHz, the group delay is smaller and the oscillation mode interval is larger, and the sensitivity of the sensor is further improved under the same frequency interval, reaching 22.3 kHz / ps and 162 kHz / ps, respectively; the estimated results are in good agreement with the measured results, and the slight deviation may be the measurement error of the cavity delay.

[0089] 2. Compared with phase measurement without oscillation cavity, for a given instrument resolution, the transfer function between the improvement of detection limit and frequency shift of the present application is calculated as H(f) = -10log 10 (2πfτ cavity ), which shows a great improvement when the frequency shift is low, and decreases at a rate of -10 dB / decade as the frequency shift increases. At a frequency shift of 10 Hz, the introduction of an oscillation cavity with a cavity delay of 1 us can improve the detection limit by 42 dB. For a given detection limit, the present application will greatly reduce the instrument resolution requirement, and shorter cavity delay will have a more significant effect.

[0090] 3. Sensing precision depends on the cavity noise limit, and is independent of the instrument and cavity delay. The present application does not involve long optical fiber, and the insensitivity to environmental disturbance and the stability of the oscillation signal are very prominent. The sensing precision can reach attosecond or even sub-attosecond level. As long as the phase noise is suppressed below the useful phase difference, the sensing result can be considered reliable. Even if the instrument background noise is poor, the target detection limit can be achieved by reducing the cavity delay. The driving signal is divided into two paths by a power divider, replacing the original branch signal injected into the mixer, and the instantaneous oscillation frequency of more than 8s is collected for Allan deviation evaluation. The experiment shows that the Allan deviation decreases first and then increases with the change of the average time, and the overall is better than the existing advanced technology. When the average time is about 0.2s, the minimum value is reached, and when the frequency interval is 150GHz, the value reaches 2.7as. If the frequency interval is widened to more than 1THz, the sensing precision will be further optimized, and can reach the level of sub-attosecond, which is very suitable for sensing applications with high precision requirements but small change range.

[0091] In summary, the present application provides a kind of optical fiber sensing method and system of photoelectric hybrid oscillation, the optical frequency comb obtained from optical frequency comb generation device is input into the reference arm and sensing arm of interferometer module respectively, the sensing optical fiber on the sensing arm is influenced by the measured quantity and generates optical fiber delay variation, the optical frequency comb on the reference arm generates frequency difference using acousto-optic modulator to generate optical frequency shift and the optical frequency comb on the sensing arm, the reference light comb is output on the reference arm, and after coupling with the sensing light comb output on the sensing arm, it is output to optical filter and selects two optical spectrum regions, the sensing light and reference light containing each optical comb line in the optical spectrum region are divided into two paths and transmitted to photoelectric conversion branch, and the difference frequency electric signal is obtained by photoelectric detector, the difference frequency electric signal carries the phase of the measured quantity, the difference frequency electric signal of each branch is electrically amplified and band-pass filtered to obtain an electric signal, the phase difference of the electric signals of the two branches is transmitted into the third electric amplifier and the fourth band-pass filter by the first mixer, the second mixer and the third band-pass filter, the target oscillation signal is transmitted to the first mixer and the frequency shift measurement end by the power divider, and the closed oscillation cavity is formed after being transmitted to the first mixer. The phase difference of the electric signals of the two branches is accumulated in a loop until the gain of the oscillation loop gradually saturates, forming a stable oscillation signal frequency shift. The mapping relationship between the obtained frequency shift and the optical fiber delay variation reflects the influence of the sensing optical fiber on the measured quantity.

[0092] Further, the present application selects two optical spectrum regions that meet the frequency interval requirement according to the sensitivity requirement, and provides the delay of the closed loop oscillation cavity through the fourth band-pass filter. Setting the frequency interval and the delay of the closed loop oscillation cavity is conducive to constructing different optical fiber sensing systems to meet the needs of different situations, and providing the delay of the closed loop oscillation cavity through the fourth band-pass filter is conducive to reducing the influence of the external environment on signal transmission and improving the stability of signal transmission.

[0093] The computer device can comprise a processor and a memory, wherein the processor and the memory can be connected through a bus or other manners.

[0094] The processor can be a central processing unit (CPU). The processor can also be other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, or a combination thereof.

[0095] The memory, as a non-transitory computer readable storage medium, can be used to store non-transitory software programs, non-transitory computer executable programs and modules, such as program instructions / modules corresponding to the key shielding method of the vehicle display device in the embodiments of the present application. The processor executes various functions and data processing of the processor by running the non-transitory software programs, instructions and modules stored in the memory.

[0096] The memory can comprise a program storage area and a data storage area, wherein the program storage area can store an operating system and at least one application required by a function; and the data storage area can store data created by the processor and the like. In addition, the memory can comprise a high-speed random access memory, and can also comprise a non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state memory device. In some embodiments, the memory can optionally comprise a memory remotely arranged relative to the processor, and these remote memories can be connected to the processor through a network. Examples of the network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0097] The one or more modules are stored in the memory, and when executed by the processor, the method described in the embodiments is performed.

[0098] The embodiment of the present application further provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the steps of the foregoing edge computing server deployment method. The computer readable storage medium can be a tangible storage medium, such as a random access memory (RAM), a memory, a read only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a floppy disk, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0099] Those of ordinary skill in the art will appreciate that the various illustrative components, systems and methods described in connection with the embodiments disclosed herein can be implemented as hardware, software, or a combination thereof. The choice of hardware or software implementation is a matter of design choice and will depend on the particular application and constraints of the design. Those of ordinary skill in the art can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application. When implemented in hardware, the hardware can comprise, for example, an electronic circuit, an application specific integrated circuit (ASIC), a suitably programmed firmware, a plug-in card, a function card, etc. When implemented in software, the elements of the application are the program or code segments to perform the necessary tasks. The program or code segments can be stored in a machine readable medium, or transmitted by carrier waves over a transmission medium or communication link, either optically, acoustically, or electrically.

[0100] It is to be understood that the application is not limited to the particular configurations and processes described herein and shown in the drawings, which are provided by way of example only. Detailed descriptions of known methods are omitted so as not to obscure the description of the present application. In the above embodiments, several specific steps are described and illustrated in order to provide a thorough understanding of the present application. However, the process of the present application is not limited to the specific steps described and illustrated, and the order of the steps can be changed, or other steps can be added, or some steps can be omitted, without departing from the spirit of the present application.

[0101] In the present application, features described and / or illustrated in relation to one embodiment can be used in the same or a similar way in one or more other embodiments, and / or combined with or instead of features on other embodiments.

[0102] The above description is merely illustrative of the application, and is not intended to limit the application. The embodiments of the application can be modified and varied in many ways, and the application is not limited to the embodiments described and illustrated. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the application are intended to be included in the scope of the application.

Claims

1. An opto-electric hybrid oscillating fiber optic sensing system, characterized by, The system comprises: An optical frequency comb generation device comprising a laser and a phase modulator, the phase modulator modulating a continuous wave generated by the laser by a radio frequency signal and obtaining an optical frequency comb; An interferometer module comprising a reference arm deploying a polarization controller and an acousto-optic modulator, a sensing arm deploying a sensing optical fiber, a first coupler and a second coupler, the first coupler being divided into a first optical frequency comb and a second optical frequency comb after receiving the optical frequency comb; the first optical frequency comb inputting the sensing arm, the sensing optical fiber being affected by a to-be-measured quantity to generate an optical fiber delay change, causing the first optical frequency comb of the sensing arm to generate a to-be-measured phase and obtaining a sensing optical comb, the second optical frequency comb inputting the reference arm, the polarization controller adjusting the interference state, and the acousto-optic modulator driven by a driving signal performing optical frequency shift to obtain a reference optical comb having a frequency difference with the sensing optical comb; the reference optical comb and the sensing optical comb being coupled by the second coupler to obtain a target optical frequency comb; An optical filter receiving the target optical frequency comb and selecting a first spectral region and a second spectral region from the target optical frequency comb according to sensitivity requirements, the first spectral region containing a first reference light obtained through the reference arm and a first sensing light through the sensing arm, and the second spectral region containing a second reference light obtained through the reference arm and a second sensing light through the sensing arm; A first photoelectric conversion branch containing a first photodetector, a first electric amplifier and a first band-pass filter, the first photodetector receiving the first sensing light and the first reference light having a frequency difference and outputting a first beat frequency electric signal related to the to-be-measured phase, the first beat frequency electric signal being amplified and band-pass filtered to obtain a first electric signal; A second photoelectric conversion branch containing a second photodetector, a second electric amplifier and a second band-pass filter, the second photodetector receiving the second sensing light and the second reference light having a frequency difference and outputting a second beat frequency electric signal related to the to-be-measured phase, the second beat frequency electric signal being amplified and band-pass filtered to obtain a second electric signal; A closed-loop oscillation cavity module comprising a first mixer, a second mixer, a third band-pass filter, a third electric amplifier, a fourth band-pass filter and a power divider, the first electric signal being up-converted by the first mixer and output to the second mixer containing the second electric signal through the third band-pass filter and being down-converted to obtain an oscillation signal carrying a phase difference of the two electric signals, the oscillation signal being amplified and filtered by the third electric amplifier and the fourth band-pass filter to obtain a target oscillation signal, the target oscillation signal being input to the power divider and transmitted to the first mixer and a target oscillation signal frequency shift measurement end respectively; the target oscillation signal frequency shift measurement end is used for measuring the frequency shift of the target oscillation signal, and the target oscillation signal frequency shift and the optical fiber delay change establish a mapping relationship to reflect the influence of the to-be-measured quantity on the sensing optical fiber.

2. The opto-electrically hybridly oscillating fiber optic sensing system of claim 1, wherein, The phase modulator modulates a continuous wave generated by the laser by a radio frequency signal and obtains an optical frequency comb, and the frequency expression of each optical comb line in the optical frequency comb is: ； wherein represents the sequence number of the selected optical comb line in the optical frequency comb, represents the center frequency of the laser light, represents the center frequency of the radio frequency signal.

3. The opto-electrically hybridly oscillating fiber optic sensing system of claim 1, wherein, The first optical frequency comb input sensing arm after the sensing fiber is affected by the to-be-measured quantity to produce a fiber delay change, and a difference between a fiber delay of the sensing arm and a fiber delay of the reference arm is expressed as: ； wherein, represents a fixed delay, represents a change in the fiber delay due to the influence of the measured quantity.

4. The opto-electrically hybridly oscillating fiber optic sensing system of claim 1, wherein, The first optical spectrum region and the second optical spectrum region are converted into the first electrical signal and the second electrical signal through the first photoelectric conversion branch and the second photoelectric conversion branch, and the first electrical signal and the second electrical signal obtained are expressed as: ； The first electrical signal is up-converted through the first frequency mixer, output to the second frequency mixer containing the second electrical signal through the third band-pass filter, and down-converted to obtain an oscillation signal carrying a phase difference between two electrical signals, and an expression of the phase difference between two electrical signals related to the to-be-measured quantity is: ； wherein denotes the center frequency of the driving signal, denotes the sequence number of the selected optical comb line in the optical frequency comb, denotes the frequency of each optical comb line, denotes the center frequency of the laser light, denotes the center frequency of the radio frequency signal, denotes the fiber delay difference between the reference arm and the sensing arm, denotes the fixed delay, denotes the fiber delay change induced by the measurand, denotes the optical comb lines of the first spectral region, denotes the optical comb lines of the second spectral region.

5. The opto-electrically hybridly oscillating fiber optic sensing system of claim 1, wherein, The first photoelectric conversion branch further comprises a phase shifter, and the power divider transmits the target oscillation signal to the first frequency mixer to form a closed-loop oscillation cavity, and the phase shifter is used to adjust the oscillation frequency to meet a stable oscillation condition of the closed-loop oscillation cavity.

6. The opto-electrically hybridly oscillating fiber optic sensing system of claim 5, wherein, In order to meet the stable oscillation condition of the closed-loop oscillation cavity, the phase shifter adjusts the oscillation frequency, and an expression is: ； wherein represents an optical comb line of the first spectral region, represents an optical comb line of the second spectral region, represents a delay of the closed loop optical cavity, represents an order of the oscillation mode, is a phase constant of the fixed delay and the phase shifter, represents a center frequency of the radio frequency signal, represents a change in the fiber delay resulting from the influence of the quantity to be measured.

7. The opto-electrically hybridly oscillating fiber optic sensing system of claim 6, wherein, The fiber delay change on the sensing arm causes the oscillation frequency to move, and an expression is: ； wherein denotes the amount of change in the optical fiber delay, denotes the center frequency of the radio frequency signal, denotes the delay of the closed loop optical cavity, denotes the optical comb lines of the first spectral region, denotes the optical comb lines of the second spectral region.

8. The opto-electrically hybridly oscillating fiber optic sensing system of claim 1, wherein, The target oscillation signal frequency shift measurement end comprises: A frequency counter, and the frequency shift of the target oscillation signal is measured through a high-resolution high-speed frequency counter.

9. A hybrid opto-electric oscillation fiber sensing method, characterized by, The method comprises: Placing the optoelectronic hybrid oscillation fiber sensing system as claimed in any one of claims 1 to 8 in an environment to be measured and outputting a target oscillation signal frequency shift, the target oscillation signal frequency shift and the fiber delay change establishing a mapping relationship to reflect the influence of the to-be-measured quantity on the sensing fiber.

10. The opto-electric hybrid oscillating fiber sensing method of claim 9, wherein, The method further comprises: reconstructing the sensing sensitivity by changing a frequency interval of the first optical spectrum region and the second optical spectrum region or a delay of the closed-loop oscillation cavity.

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