Optical fiber interference sensor and application method thereof

Abstract

According to the optical fiber interference sensor and the application method thereof, an electro-optical frequency comb is introduced to screen out two comb lines to form a photon-assisted millimeter wave light source, interference is carried out in two frequency spectral regions subsequently, common phase fluctuation is counteracted based on inherent phase coherence, and the strict requirement for the line width index of a laser is avoided. Meanwhile, the two acoustic optical modulators connected in parallel are introduced into the reference arm and the interference arm for frequency shift, the problem of co-frequency crosstalk caused by residual zero-order diffraction of the acoustic optical modulators is solved, and the sensing precision is substantially improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing measurement, and particularly to a fiber optic interferometric sensor and its application method. Background Art

[0002] Fiber optic interferometric sensing technology has been widely applied in many fields such as hydrophones, optical gyroscopes, gravitational wave detection, etc. due to its excellent sensitivity performance. However, the frequency noise of the laser source is difficult to cancel due to the inconsistent propagation delays in the two arms of the interferometer, which directly limits the interferometric sensing accuracy. One strategy is to use a highly stable laser source to fundamentally reduce the noise impact, but this method is often accompanied by high costs, large volumes, and complex locking control mechanisms. Another passive noise suppression technique uses an auxiliary reference interferometer to suppress common-mode noise, but the prerequisite for implementing this technique is that the two interferometers must maintain the same optical path difference, and this strict condition has become the main obstacle to the popularization and application of the technology.

[0003] In heterodyne interferometric sensing, the key component is the optical frequency shifter, typically represented by an acousto-optic modulator (AOM). Existing research generally focuses on the noise of optical and electrical components (such as thermal noise, shot noise, laser noise, etc.), but for the specific noise effects that an acousto-optic modulator may introduce in a heterodyne interferometric sensing system, such as the phase noise of the drive source, intensity noise caused by relative diffraction efficiency fluctuations, etc., although there has been preliminary discussion, it is still lacking. It should be noted that almost all research tends to regard the acousto-optic modulator as an ideal frequency shifting device, ignoring the residual zero-order diffraction caused by non-ideal diffraction conditions, and the specific impact of this potential interference on the system performance has not been comprehensively and deeply evaluated. Therefore, there is an urgent need for a new sensor structure and detection scheme to overcome this problem. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a fiber optic interferometric sensor and its application method to eliminate or improve one or more defects existing in the prior art, and solve the problem that the prior art cannot overcome the frequency noise of the laser source and the noise of the acousto-optic modulator.

[0005] One aspect of the present invention provides a fiber optic interferometric sensor, which includes:

[0006] An electro-optic frequency comb for providing a first comb line and a second comb line with fixed phase coherence, the first comb line having a first frequency and the second comb line having a second frequency;

[0007] A first optical splitter for respectively guiding the first comb line into an interference arm and a reference arm, and guiding the second comb line into the interference arm and the reference arm, and the interference arm introduces a time delay to be measured;

[0008] A first acousto-optic modulator, deployed on the interference arm and operating based on a first electrical driving frequency to obtain corresponding frequency-shifted light;

[0009] A second acousto-optic modulator, deployed on the reference arm and operating based on a second electrical driving frequency to obtain corresponding frequency-shifted light;

[0010] A second optical splitter for combining the output optical signals of the interference arm and the reference arm;

[0011] An optical filter for distinguishing the optical signals according to the first frequency spectral region and the second frequency spectral region;

[0012] A first photodetector, into which the part in the first frequency spectral region introduced by the optical filter undergoes heterodyne interference to obtain a first electrical signal;

[0013] A second photodetector, into which the part in the second frequency spectral region introduced by the optical filter undergoes heterodyne interference to obtain a second electrical signal;

[0014] A phase demodulation unit for extracting a first phase of heterodyne interference in the first frequency spectral region according to the first electrical signal and extracting a second phase of heterodyne interference in the second frequency spectral region according to the second electrical signal;

[0015] A data processing unit for calculating a phase difference according to the first phase and the second phase and mapping to obtain the to-be-measured time delay.

[0016] In some embodiments, the processing unit adopts a field programmable gate array or a graphics processor; the processing unit is provided with a network interface, a file interface, a database interface and a graphical interface interface for externally outputting the detection result of the to-be-measured time delay.

[0017] In some embodiments, the network interface adopts a RESTful API or a GraphQL interface, the file interface is deployed based on the FTP protocol or the SFTP protocol, the database interface is connected to an SQL / NoSQL database, and the graphical interface interface displays the detection result through a web application or a desktop application.

[0018] In some embodiments, the data processing unit further includes: a log interface for forwarding the detection result to a log management platform through a Logstash tool or a Fluentd tool.

[0019] In some embodiments, the fiber optic interferometric sensor further includes: a display module connected to the data processing unit for providing an interactive interface and real-time displaying the detection result.

[0020] In some embodiments, the fiber optic interferometric sensor further includes: a thermoelectric cooling subsystem or a temperature-controlled housing to control the stable operating temperature of the fiber optic interferometric sensor.

[0021] In some embodiments, the fiber optic interferometric sensor is deployed in a vibration isolation table or a shock-absorbing bracket.

[0022] In some embodiments, the fiber optic interferometric sensor further includes: a remote control module, connected to the electro-optic frequency comb, the first acousto-optic modulator, the second acousto-optic modulator, the first photodetector, the second photodetector, the phase demodulation unit, and the data processing unit, for implementing remote operation notification.

[0023] On the other hand, the present invention also provides an application method of a fiber optic interferometric sensor, and the method includes the following steps:

[0024] The comb lines of the first frequency in the optical frequency comb are respectively introduced into the interference arm and the reference arm by a first optical splitter, and the comb lines of the second frequency in the optical frequency comb are respectively introduced into the interference arm and the reference arm;

[0025] Drive the first acousto-optic modulator deployed on the interference arm based on a first electrical driving frequency, drive the second acousto-optic modulator deployed on the reference arm based on a second electrical driving frequency; introduce a time delay to be measured on the interference arm;

[0026] The frequency-shifted light at the ends of the interference arm and the reference arm is combined by a second optical splitter and then introduced into an optical filter to separate a part in the first frequency spectral region and a part in the second frequency spectral region;

[0027] The first photodetector performs heterodyne interference on the part of the optical signal in the first frequency spectral region to obtain a first electrical signal, and performs heterodyne interference on the part of the optical signal in the second frequency spectral region to obtain a second electrical signal;

[0028] The phase demodulation unit processes the first electrical signal to obtain a first phase of heterodyne interference in the first frequency spectral region, and processes the second electrical signal to obtain a second phase of heterodyne interference in the second frequency spectral region;

[0029] The data processing unit calculates a phase difference based on the first phase and the second phase and maps to obtain the time delay to be measured.

[0030] In some embodiments, the method further includes: displaying the detection result of the time delay to be measured to a specified user through a preset graphical interface interface, and submitting the detection result of the time delay to be measured to a database platform through a preset database interface for storage and establishing a log.

[0031] The beneficial effects of the present invention are at least:

[0032] For the fiber optic interferometric sensor and its application method of the present invention, an electro-optic frequency comb is introduced to select two comb lines to form a photon-assisted millimeter-wave light source. Subsequently, interference is carried out in two frequency spectral regions respectively, and the common phase fluctuations are cancelled based on its inherent phase coherence, bypassing the strict requirements for the linewidth index of the laser. At the same time, two acousto-optic modulators connected in parallel are introduced in the reference arm and the interference arm for frequency shifting, solving the problem of crosstalk at the same frequency caused by the residual zero-order diffraction of the acousto-optic modulator, and substantially improving the sensing accuracy.

[0033] The additional advantages, objectives, and features of the present invention will be partially described below, and will become partially apparent to those of ordinary skill in the art after studying the following text, or can be learned from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structure specifically pointed out in the specification and the drawings.

[0034] Those skilled in the art will understand that the objectives and advantages that can be achieved by the present invention are not limited to the above specifically described, and the above and other objectives that the present invention can achieve will be more clearly understood according to the following detailed description. Description of the Drawings

[0035] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not constitute a limitation to the present invention. In the drawings:

[0036] Figure 1 It is a schematic structural diagram of the fiber optic interferometric sensor according to an embodiment of the present invention.

[0037] Figure 2 It is a flow block diagram of the application method of the fiber optic interferometric sensor according to another embodiment of the present invention.

[0038] Figure 3 It is an example of the sensing results of the parallel AOM, series AOM, and single AOM.

[0039] Figure 4 It is a logic structure diagram of a traditional single AOM fiber optic interferometric sensor with a laser source.

[0040] Reference Numerals:

[0041] 101: electro-optic frequency comb; 102: first optical splitter; 103: first acousto-optic modulator;

[0042] 104: second acousto-optic modulator; 105: second optical splitter; 106: optical filter;

[0043] 107: first photodetector; 108: second photodetector; 109: phase demodulation unit;

[0044] 110: Data processing unit. Detailed implementation manners

[0045] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with the implementation manners and the drawings. Herein, the illustrative implementation manners of the present invention and the descriptions thereof are used to explain the present invention, but do not limit the present invention.

[0046] Herein, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, and other details less related to the present invention are omitted.

[0047] It should be emphasized that the term "comprising / including" when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0048] Herein, it should also be noted that if not specifically stated, the term "connection" herein can not only refer to direct connection, but also represent indirect connection with an intermediate.

[0049] In the following, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0050] As Figure 4 shown, the existing fiber optic interference sensing technology obtains the sensing result by detecting the optical phase change introduced by the time delay to be measured. In order to avoid the confusion of low-frequency noise, an acousto-optic modulator (AOM) is usually placed on the reference arm to generate reference frequency-shifted light, and then it interferes with the sensing light in the photodetector to form a difference-frequency carrier signal. This process is also "heterodyne interference". In order to fundamentally reduce the influence of the laser source frequency noise, a highly stable laser source is required, and the cost is relatively high. In addition, the AOM is not a completely ideal optical frequency shifter, and its residual zero-order diffraction will also interfere with the first-order frequency-shifted light beam, resulting in a decrease in the sensing accuracy.

[0051] The present invention proposes a method for improving the accuracy of heterodyne interference sensing. First, an electro-optic frequency comb is utilized, and two comb lines are selected therefrom to form a photon-assisted millimeter-wave light source. Due to the inherent phase coherence between the comb lines, when a differential detection strategy is adopted, these common phase fluctuations can cancel each other out. Taking the electro-optic frequency comb generated by driving an electro-optic modulator with an RF reference signal as an example, the phase fluctuations introduced by the frequency noise of the laser source among the comb lines of the optical frequency comb are consistent. The frequency stability of this photon-assisted millimeter-wave light source is determined by the RF reference signal, thus bypassing the strict requirements for the laser linewidth index, which is an important technical bottleneck in traditional fiber optic interferometric measurements. Second, a parallel dual acousto-optic modulator is used, that is, an AOM is placed in the reference arm and the interference arm respectively, effectively solving the problem of crosstalk at the same frequency caused by the residual zero-order diffraction of the AOM, and then substantially improving the sensing accuracy.

[0052] In the present invention, the optical frequency comb is injected into the interferometer system. The quantity to be measured applied to the sensing fiber (such as strain, temperature change, etc.) will cause a change in the fiber transmission time delay, and further cause a change in the phase of each comb line in the optical frequency comb. By using a filtering technique to select the frequency spectral regions where any two comb lines of the optical frequency comb are located, enabling them to undergo heterodyne interference on the detector respectively, and based on the phase difference, the information of the quantity to be measured is deduced. The present invention emphasizes the influence of the acousto-optic modulator configuration on the phase difference detection performance. During the interference process, the beat generated by the residual zero-order diffraction and the first-order frequency-shifted light of the AOM has the same frequency as the actual sensing signal, and this crosstalk will affect the detection result and deteriorate the sensing accuracy. Introducing a second AOM, especially in a parallel configuration, can eliminate the influence of the zero-order perturbation. This provides the possibility of optimization for sensing applications where the noise floor has been strictly compressed.

[0053] Specifically, one aspect of the present invention provides an optical fiber interferometric sensor, as Figure 1 shown, the optical fiber interferometric sensor includes: an electro-optic frequency comb 101, a first optical splitter 102, a first acousto-optic modulator 103, a second acousto-optic modulator 104, a second optical splitter 105, an optical filter 106, a first photodetector 107, a second photodetector 108, a phase demodulation unit 109, and a data processing unit 110.

[0054] The electro-optical frequency comb 101 is used to provide a first comb line and a second comb line with fixed phase coherence. The first comb line has a first frequency, and the second comb line has a second frequency. The electro-optical frequency comb 101 is an optical frequency comb generated by an electro-optic modulator (EOM), usually obtained by modulating a continuous wave (CW) laser with a radio frequency signal. By adjusting the frequency and power of the radio frequency signal, the comb line spacing and quantity are controlled. The comb line spacing is determined by the radio frequency signal frequency (usually in GHz). The present invention requires that the interval between any two comb lines is much larger than the system noise bandwidth to prevent mutual influence. The system noise bandwidth is determined by the response bandwidths of the optical filter, photodetector, and backend electronic circuit.

[0055] The first optical splitter 102 is used to respectively introduce the first comb line into the interference arm and the reference arm, and introduce the second comb line into the interference arm and the reference arm. The interference arm introduces the time delay to be measured. Specifically, the insertion loss of the first optical splitter 102 can be limited to be less than 0.5 dB to reduce the influence of signal loss on the interference accuracy. For example, a high-transparency glass or single-mode fiber optical splitter can be used.

[0056] The first acousto-optic modulator 103 is deployed on the interference arm and operates based on the first electrical driving frequency to obtain the corresponding frequency-shifted light. The first acousto-optic modulator 103 is based on the first electrical driving frequency fm 1 provides a fixed frequency shift for the optical signal passing through the interference arm, and the frequency of the output signal is f 梳线 +fm 1 ,f 梳线 refers to the frequency of the input comb line. The time delay to be measured (such as the optical path change caused by temperature, strain, etc.) is introduced into the interference arm. After frequency shifting by the acousto-optic modulator, the time delay information is encoded into the phase of the frequency-shifted signal. The frequency-shifted optical signal carries the modulation phase of the time delay to be measured.

[0057] The second acousto-optic modulator 104 is deployed on the reference arm and operates based on the second electrical driving frequency to obtain the corresponding frequency-shifted light. The second acousto-optic modulator 104 is based on the second electrical driving frequency fm 2 provides a fixed frequency shift for the optical signal passing through the reference arm, and the frequency of the output signal is f 梳线 +fm 2 ,f 梳线 refers to the frequency of the input comb line. Among them, fm 1 is not equal to fm 2 .

[0058] The second optical splitter 105 is used to combine the output optical signals of the interference arm and the reference arm.

[0059] An optical filter 106 distinguishes optical signals according to a first frequency spectral region and a second frequency spectral region. The central frequency of the optical filter 106 should match the first frequency and the second frequency, and the filtering bandwidth should be narrow enough to exclude interference from adjacent frequencies.

[0060] A first photodetector 107 heterodyne interferes with the portion introduced by the optical filter 106 in the first frequency spectral region to obtain a first electrical signal. This spectral region is generated by the interference of the frequency-shifted optical signals of the first frequency comb line f 1 in the interference arm and the reference arm.

[0061] A second photodetector 108 heterodyne interferes with the portion introduced by the optical filter 106 in the second frequency spectral region to obtain a second electrical signal. This spectral region is generated by the interference of the frequency-shifted optical signals of the second frequency comb line f 2 in the interference arm and the reference arm. The unequal frequency shifts of the two acousto-optic modulators shift the frequency of the interference signal into the radio frequency range, avoiding low-frequency noise (such as 1 / f noise) and improving the signal-to-noise ratio of the system. During the interference process, the beat notes generated by the residual zero-order diffraction and any sidebands cannot constitute crosstalk of the same frequency, and only the phase change related to the time delay to be measured is retained.

[0062] A phase demodulation unit 109 is used to extract the first phase of the heterodyne interference in the first frequency spectral region according to the first electrical signal, and extract the second phase of the heterodyne interference in the second frequency spectral region according to the second electrical signal.

[0063] A data processing unit 110 is used to calculate the phase difference according to the first phase and the second phase and map to obtain the time delay to be measured. During the calculation of the phase difference, the common-mode noise of the optical frequency comb (such as the frequency jitter of the laser) is canceled. In some embodiments, the processing unit uses a field-programmable gate array or a graphics processing unit; the processing unit is provided with a network interface, a file interface, a database interface, and a graphical interface interface for externally outputting the detection result of the time delay to be measured. In some embodiments, the network interface uses a RESTful API or a GraphQL interface, the file interface is deployed based on the FTP protocol or the SFTP protocol, the database interface is connected to an SQL / NoSQL database, and the graphical interface interface displays the detection result through a web application or a desktop application. In some embodiments, the data processing unit 110 further includes: a log interface, which forwards the detection result to a log management platform through a Logstash tool or a Fluentd tool.

[0064] In some embodiments, the fiber optic interferometric sensor further includes: a display module, connected to the data processing unit 110 for providing an interactive interface and real-time displaying the detection result.

[0065] In some embodiments, the fiber optic interferometric sensor further includes: a thermoelectric cooling subsystem or a temperature-controlled housing to control the stable operating temperature of the fiber optic interferometric sensor.

[0066] In some embodiments, the fiber optic interferometric sensor is deployed in a vibration isolation table or a shock absorption bracket.

[0067] In some embodiments, the fiber optic interferometric sensor further includes: a remote control module, connected to the electro-optic frequency comb 101, the first acousto-optic modulator 103, the second acousto-optic modulator 104, the first photodetector 107, the second photodetector 108, the phase demodulation unit 109, and the data processing unit 110, for implementing remote operation notification.

[0068] In the present invention, two comb lines of the introduced frequency comb in the fiber optic interferometric sensor are detected using a differential detection strategy, which can cancel out the common phase fluctuations. First, the frequency comb provides two frequency comb lines, namely the first frequency f 1 and the second frequency f 2 . Both of these two comb lines need to be introduced into the interference arm and the reference arm through the first optical splitter 102 for interaction. The interference arm also needs to introduce the time delay τ(t) to be measured. The first acousto-optic modulator 103 provides a fixed frequency shift for the optical signal passing through the interference arm based on the first electrical drive frequency fm 1 , and the second acousto-optic modulator 104 provides a fixed frequency shift for the optical signal passing through the reference arm based on the second electrical drive frequency fm 2 . The four frequency-shifted lights are combined by the second optical splitter 105, and the first frequency spectral region f 1 and the second frequency spectral region f 2 are distinguished through the optical filter 106. The two spectral regions are respectively independently subjected to heterodyne interference. In the first frequency spectral region f 1 , the frequency-shifted light of the interference arm and the frequency-shifted light of the reference arm interfere and beat, and the frequency difference between the frequency shifts of the two arms is detected by the first photodetector 107; in the second frequency spectral region f 2 , the frequency-shifted light of the interference arm and the frequency-shifted light of the reference arm interfere and beat, and the frequency difference between the frequency shifts of the two arms is detected by the second photodetector 108; the phase difference Δφ between the two electrical signals can be calculated as: 2π(f 1 -f 2 )τ(t), where τ(t) represents the time delay to be measured, then the time delay to be measured can be calculated as:

[0069]

[0070] On the other hand, the present invention also provides an application method of a fiber optic interferometric sensor, and the method includes the following steps S101 to S106:

[0071] Step S101: The optical comb lines with the first frequency in the optical frequency comb are respectively introduced into the interference arm and the reference arm by the first optical splitter, and the optical comb lines with the second frequency in the optical frequency comb are respectively introduced into the interference arm and the reference arm.

[0072] Step S102: Drive the first acousto-optic modulator deployed on the interference arm based on the first electric drive frequency, and drive the second acousto-optic modulator deployed on the reference arm based on the second electric drive frequency; introduce the time delay to be measured on the interference arm.

[0073] Step S103: The frequency-shifted light at the ends of the interference arm and the reference arm is combined by the second optical splitter and then introduced into the optical filter to separate the part in the first frequency spectral region and the part in the second frequency spectral region.

[0074] Step S104: The first photodetector performs heterodyne interference on the part of the optical signal in the first frequency spectral region to obtain the first electric signal, and performs heterodyne interference on the part of the optical signal in the second frequency spectral region to obtain the second electric signal.

[0075] Step S105: The phase demodulation unit processes the first electric signal to obtain the first phase of the heterodyne interference in the first frequency spectral region, and processes the second electric signal to obtain the second phase of the heterodyne interference in the second frequency spectral region.

[0076] Step S106: The data processing unit calculates the phase difference according to the first phase and the second phase and maps it to obtain the time delay to be measured.

[0077] In some embodiments, the method further includes: displaying the detection result of the time delay to be measured to the designated user through a preset graphical interface interface, and submitting the detection result of the time delay to be measured to the database platform for storage and establishing a log through a preset database interface.

[0078] Specifically, as Figure 2 shown, the optical frequency comb (including the comb line frequencies f 1 , f 2 …) is injected into the Mach-Zehnder interferometer

[0079] , where the time delay τ(t) to be measured is loaded on the interference arm. The heterodyne interrogation is realized by the parallel acousto-optic modulator 1 and acousto-optic modulator 2, and their electric drive frequencies are f m1 , f m2 respectively, then the heterodyne frequency is f m1 - f m2 . Two spectral regions are separated at the output end of the interferometer. Similar to the traditional laser interferometer, the f 1 and f 2 spectral regions perform independent heterodyne interference respectively to obtain two electric signals carrying the sensing phase. The phase difference between the two branches can be calculated as: 2π(f 1 - f2 ) τ(t), which indicates that the sensitivity of the delay detection is determined by the frequency of the photon-assisted millimeter wave. Assume that the output light of the AOM is expressed as: where η 1 and ε 0 represent the diffraction efficiencies of the first order and the residual zero order respectively. Under this structure, the optoelectronic field of the interference arm can be expressed as: The optoelectronic field of the reference arm is expressed as: where the diffraction efficiencies of the two AOMs are simplified to be the same. Since both arms involve frequency shifting, the residual zero-order diffraction does not constitute crosstalk with the beat frequency of any sideband. Therefore, the two electrical signals are expressed as: V a,b = A a,b cos[(w m2 - w m1 )t + ψ a,b ∝ 2η 1 R PD P in cos[(w m2 - w m1 )t + w 1,2 τ(t)]. Where A a,b ∝ 2η 1 R PD P in , R PD is the responsivity of the detector, P in is the input optical power; ψ a,b = w 1,2 τ(t), and the phase only contains the amplified sensing information. Through the phase difference and sensitivity mapping, we can recover the time delay to be measured without perturbation.

[0080] If there is only a single AOM in the interferometer, then the optoelectronic field of the sensing arm can be expressed as: E s (t) ∝ E in (t)exp[iw 1,2 τ(t)], and at this time the two electrical signals are expressed as: where, when ε 0 << 1, it can be seen that in addition to the phase change introduced by the time delay to be measured weighted by the corresponding optical frequency, there is also an additional phase perturbation caused by the crosstalk of the same frequency due to the residual zero-order diffraction. The detection delay obtained from the phase difference and sensitivity mapping is: Since the phase perturbation cannot be distinguished from the useful phase difference information, the time delay measurement is interfered, resulting in a reduction in the sensing accuracy.

[0081] If two AOMs are placed in series on the reference arm, the two electrical signals are expressed as: V a,b = A a,b cos[(ω m1 + ω m2 )t + ψ a,b ∝ 2η 1 R PD P in {cos[(ω m1 + ω m2 )t + ω 1,2 τ(t)] + ε 0 cos[(ω m1 + ω m2 )t]}, where, when ε 0 << 1, A a,b ∝ 2η 1 R PD P in ; ψ a,b ≈ ω 1,2 τ(t) - ε 0 sin[ω 1,2 τ(t)]. The actual recovered time delay is: Compared with the structure of a single AOM, the series AOM can square the coefficient of the zero-order perturbation, thus suppressing its influence but not eliminating it.

[0082] As Figure 3 shown are examples of the sensing results of the parallel AOM, the series AOM, and the single AOM. The millimeter-wave frequency is set to 100 GHz, and the sensing sensitivity is 0.2π rad / ps. Assume that ε 0 is 5.6e-2, and a time delay to be measured that linearly changes at a rate of 256 ps / s with time is preset. As can be seen from the figure, within the observation time of 0.1 s, the detected time delay changes by 25.6 ps, but due to the π-phase constraint, the actual detection range is 10 ps. For the single AOM structure, we clearly find that the change is periodic, and the largest contribution of the zero-order perturbation occurs at the half cycle. The enlarged figure shows that the residual zero-order diffraction generates a peak-to-peak jitter of up to 1.5 ps. This is because a small time delay jitter only corresponds to a slight phase change in the sensing millimeter-wave domain but can cause a large change in the optical phase. The jitter can be effectively suppressed by the series AOM, and the peak-to-peak value of the jitter is compressed to 0.3 ps. In contrast, under the structure of the parallel AOM, the detected time delay is completely unaffected by the residual zero-order diffraction and is consistent with the preset time delay to be measured.

[0083] In summary, for the fiber optic interferometric sensor and its application method of the present invention, an electro-optic frequency comb is introduced to select two comb lines to form a photon-assisted millimeter-wave light source. Subsequently, interference is carried out in two frequency spectral regions respectively. Based on its inherent phase coherence, the common phase fluctuations are cancelled, bypassing the strict requirements for the linewidth index of the laser. At the same time, two acousto-optic modulators in parallel are introduced in the reference arm and the interference arm for frequency shifting, solving the problem of crosstalk at the same frequency caused by the residual zero-order diffraction of the acousto-optic modulator and realizing a substantial improvement in the sensing accuracy.

[0084] Those of ordinary skill in the art should understand that the various exemplary components, systems, and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both. Specifically, whether to implement it in hardware or software depends on the specific application and design constraints of the technical solution. A professional technician can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention. When implemented in hardware, it can be, for example, an electronic circuit, an application-specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, and so on. When implemented in software, the elements of the present invention are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium or transmitted via a data signal carried in a carrier wave on a transmission medium or a communication link.

[0085] It should be clear that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, the detailed description of known methods is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order between steps after understanding the spirit of the present invention.

[0086] In the present invention, the features described and / or illustrated for one embodiment can be used in the same or similar manner in one or more other embodiments, and / or combined with the features of other embodiments or replace the features of other embodiments.

[0087] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the embodiments of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fiber optic interferometer sensor, characterized in that: The optical fiber interferometer sensor comprises: An electro-optical frequency comb, used to provide a first comb line and a second comb line with fixed phase coherence, wherein the first comb line is a first frequency and the second comb line is a second frequency; A first optical splitter, used to introduce the first comb line into an interference arm and a reference arm respectively, and introduce the second comb line into the interference arm and the reference arm respectively, and the interference arm introduces a time delay to be measured; A first acousto-optic modulator is disposed on the interferometer arm and operates based on a first electrical driving frequency to obtain corresponding frequency-shifted light; a second acousto-optic modulator, disposed on the reference arm and operated based on a second electrical driving frequency to obtain a corresponding frequency-shifted light; A second optical splitter, used for combining the output optical signals of the interference arm and the reference arm; an optical filter, which distinguishes the optical signal according to the first frequency spectrum region and the second frequency spectrum region; A first photodetector, which obtains a first electrical signal by heterodyne interference of the portion of the first frequency spectrum region introduced by the optical filter; A second photoelectric detector, which obtains a second electrical signal by heterodyne interference of the portion of the second frequency spectrum region introduced by the optical filter; a phase demodulation unit, configured to extract a first phase of heterodyne interference in the first frequency spectrum region according to the first electrical signal, and to extract a second phase of heterodyne interference in the second frequency spectrum region according to the second electrical signal; A data processing unit is used to calculate a phase difference according to the first phase and the second phase and map it to obtain the delay to be measured.

2. The optical fiber interferometer sensor according to claim 1, characterized in that: The processing unit adopts a field programmable gate array or a graphics processor; the processing unit is provided with a network interface, a file interface, a database interface and a graphical interface for externally outputting the detection result of the delay to be measured.

3. The optical fiber interferometer sensor according to claim 2, characterized in that: The network interface adopts RESTful API or GraphQL interface, the file interface is deployed based on FTP protocol or SFTP protocol, the database interface is connected to SQL / NoSQL database, and the graphical interface displays the detection results through web application or desktop application.

4. The optical fiber interferometer sensor according to claim 3, characterized in that: The data processing unit also includes: a log interface, which forwards the detection result to a log management platform through a Logstash tool or a Fluentd tool.

5. The optical fiber interferometer sensor according to claim 1, characterized in that: The fiber optic interference sensor also includes: a display module connected to the data processing unit for providing an interactive interface and displaying the detection results in real time.

6. The optical fiber interferometer sensor according to claim 1, characterized in that: The fiber optic interferometer sensor further comprises: a thermoelectric cooling subsystem or a temperature control housing to control the working temperature of the fiber optic interferometer sensor to be stable.

7. The optical fiber interferometer sensor according to claim 1, characterized in that: The optical fiber interference sensor is deployed in a vibration isolation table or a shock absorbing bracket.

8. The optical fiber interferometer sensor according to claim 1, characterized in that: The fiber optic interferometer sensor also includes: a remote control module, which is connected to the electro-optic frequency comb, the first acousto-optic modulator, the second acousto-optic modulator, the first photodetector, the second photodetector, the phase demodulation unit and the data processing unit, and is used to realize remote operation notification.

9. An application method of the fiber optic interferometer sensor according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: The first optical splitter introduces the comb line of the first frequency in the optical frequency comb into the interference arm and the reference arm respectively, and introduces the comb line of the second frequency in the optical frequency comb into the interference arm and the reference arm respectively; driving a first acousto-optic modulator disposed on the interference arm based on a first electrical driving frequency, and driving a second acousto-optic modulator disposed on the reference arm based on a second electrical driving frequency; Introducing a time delay to be measured on the interferometer arm; The frequency-shifted light at the end of the interference arm and the reference arm is combined by a second beam splitter and then introduced into an optical filter to separate a part in the first frequency spectrum region and a part in the second frequency spectrum region; A first photodetector performs heterodyne interference on a portion of the optical signal in the first frequency spectrum region to obtain a first electrical signal, and performs heterodyne interference on a portion of the optical signal in the second frequency spectrum region to obtain a second electrical signal; The phase demodulation unit processes the first electrical signal to obtain a first phase of heterodyne interference in the first frequency spectrum region, and processes the second electrical signal to obtain a second phase of heterodyne interference in the second frequency spectrum region; A data processing unit calculates a phase difference according to the first phase and the second phase and maps the phase difference to obtain the time delay to be measured.

10. The application method of the optical fiber interferometer sensor according to claim 9, characterized in that: The method further includes: displaying the detection result of the delay to be measured to a designated user through a preset graphical interface, and delivering the detection result of the delay to be measured to a database platform through a preset database interface for storage and establishing a log.

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