A dual-channel multiplexed intensity modulated optical fiber sensor system and demodulation method thereof

Abstract

The present invention discloses a dual-channel multiplexed intensity modulated optical fiber sensor system and a demodulation method thereof, belonging to the field of optical fiber sensing technology, comprising a broadband light source, an electro-optical modulator, an optical fiber coupler, a first intensity modulated optical fiber sensor, a second intensity modulated optical fiber sensor, a photodetector and a vector network analyzer connected in sequence; the two intensity modulated optical fiber sensors in the system are respectively located in an optical fiber trunk and an optical fiber ring formed by the optical fiber coupler, and act on the amplitude spectrum intensity and fringe contrast in the frequency response measured by the vector network analyzer, respectively, so as to realize multiplexing demodulation of the two sensors. The dual-channel multiplexed intensity modulated optical fiber sensor based on power self-compensation and its demodulation method proposed by the present invention make full use of frequency response information to realize dual-channel multiplexing, and significantly improve the anti-power fluctuation performance of the intensity modulated optical fiber sensor.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, and in particular to a dual-channel multiplexed intensity modulation optical fiber sensor system and a demodulation method thereof. Background Art

[0002] With the development of optical fiber communication technology and the construction of communication infrastructure, the Internet of Things technology based on optical fiber systems is also developing rapidly. Optical fiber sensors are an important part of the perception layer of the Internet of Things due to their compatibility with existing optical fiber communication systems. They have been widely used in many fields such as civil engineering, electrical engineering, mechanical structure and biochemical detection. According to the way the target parameter to be measured acts on the optical carrier in the optical fiber sensor, it can be divided into intensity modulation, phase modulation, polarization modulation, etc. Among them, the intensity modulated optical fiber sensor has the advantages of simple structure, easy demodulation, high system cost performance, etc., and is the preferred choice in practical engineering applications. A common intensity modulated fiber optic sensor is realized by causing changes in light transmission loss due to micro-bending or macro-bending of the optical fiber. The fiber optic sensor based on micro-bending couples the target parameter to be measured to the mechanical transducer that deforms the optical fiber, thereby indirectly detecting physical quantities such as displacement, pressure, acceleration, force, strain, etc.; while the fiber optic sensor based on macro-bending does not require a mechanical transducer. When an external disturbance occurs, the bending radius or curvature of the optical fiber changes, causing the optical fiber's binding ability to the guided mode and the degree of light leakage to change accordingly. The optical fiber itself directly converts the target parameter to be measured into macro-bending induced transmission loss, resulting in changes in light transmission intensity. However, traditional demodulation methods have difficulty distinguishing the impact of different intensity modulated fiber optic sensors on the total power of the system, and the multiplexing of intensity modulated fiber optic sensors is still an unresolved problem. In addition, the performance of intensity modulated fiber optic sensors is easily affected by the power fluctuation of the light source, and a light source with high power stability will increase the cost. Therefore, improving the ability to resist power fluctuations is an important requirement for intensity modulated fiber optic sensors.

[0003] Microwave photonic technology converts the optical changes in the fiber optic sensor triggered by the target parameter to be measured into changes in the microwave signal. It has the advantages of fast response speed, strong anti-interference ability and high resolution, and has been widely used in fiber optic sensing. Microwave photonic technology can obtain the amplitude, phase, and corresponding time domain information of the system response, thereby providing more sufficient information for the multiplexing of intensity modulated fiber optic sensors in more dimensions. In addition, the fiber ring cavity ring-down system can convert the loss of the intensity modulated fiber optic sensor into the change of the system ring-down time in the time domain, which does not rely on the direct measurement of optical power. It can not only improve the sensing sensitivity, but also eliminate the influence of slight jitter of the light source power to a certain extent. However, the immune effect to larger power fluctuations is still limited. Therefore, it is necessary to combine microwave photonic technology with fiber ring cavity ring-down to further develop a demodulation method that can realize the multiplexing of intensity modulated fiber optic sensors and compensate for power fluctuations. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a dual-channel multiplexed intensity modulated optical fiber sensor system and a demodulation method thereof, so as to realize dual-channel multiplexed demodulation of an intensity modulated optical fiber sensor resistant to power fluctuations.

[0005] To achieve the above effects, the technical solution of the present invention is as follows:

[0006] The present invention provides a dual-channel multiplexed intensity modulated optical fiber sensor system, comprising a broadband light source, a first single-mode optical fiber, an electro-optic modulator, a first optical fiber coupler, a first intensity modulated optical fiber sensor, a second optical fiber coupler, a third optical fiber coupler, a fourth optical fiber coupler, a photoelectric detector, a coaxial cable, and a vector network analyzer, which are connected in sequence; wherein a second intensity modulated optical fiber sensor is connected between the second optical fiber coupler and the third optical fiber coupler; the first optical fiber coupler is connected to the fourth optical fiber coupler;

[0007] When working, the wide-spectrum incoherent light output by the broadband light source is used as the optical carrier; the optical carrier is modulated with the microwave signal output by the vector network analyzer under the action of the electro-optical modulator, and the optical microwave signal is divided into two paths by the first optical fiber coupler; wherein, the first path of optical microwave signal is transmitted to the photoelectric detector via the first optical fiber coupler and the fourth optical fiber coupler to obtain an electrical signal; the second path of optical microwave signal is received by the photoelectric detector after passing through the optical fiber ring composed of the first intensity modulated optical fiber sensor, the second optical fiber coupler and the third optical fiber coupler, and the second intensity modulated optical fiber sensor embedded in the optical fiber ring.

[0008] Furthermore, the first optical fiber coupler, the second optical fiber coupler, the third optical fiber coupler and the fourth optical fiber coupler are all 1×2 optical fiber couplers.

[0009] Furthermore, an antiresonant heterogeneous optical fiber curvature sensor is selected as the first intensity modulated optical fiber sensor, which includes a second input single-mode optical fiber, a hollow-core optical fiber, an output single-mode optical fiber, a first optical fiber fixing fixture, and a second optical fiber fixing fixture connected in sequence.

[0010] Furthermore, the core diameter of the hollow core optical fiber is 50 μm and the length is 1.5 mm.

[0011] Furthermore, an optical fiber coil bending diameter sensor is selected as the second intensity modulated optical fiber sensor, which includes a third single-mode optical fiber, a fixed ring, a first optical fiber fixed displacement stage, a second optical fiber fixed displacement stage, and a displacement guide rail connected in sequence.

[0012] A dual-channel multiplexed intensity modulated optical fiber sensor demodulation method comprises the following steps:

[0013] The wide-spectrum incoherent light output by the broadband light source is used as an optical carrier signal; the optical carrier signal is modulated by the microwave signal output by the vector network analyzer under the action of the electro-optical modulator, and the optical microwave signal is divided into two paths by the first optical fiber coupler; wherein the first optical microwave signal is transmitted to the photoelectric detector via the first optical fiber coupler and the fourth optical fiber coupler to obtain an electrical signal; the second optical microwave signal is received by the photoelectric detector after passing through the optical fiber ring composed of the first intensity modulated optical fiber sensor, the second optical fiber coupler and the third optical fiber coupler, and the second intensity modulated optical fiber sensor embedded in the optical fiber ring;

[0014] The vector network analyzer measures the frequency response of the system based on the electrical signal converted by the photodetector, performs inverse Fourier transform on the frequency response to obtain the time domain response, uses the pulse of the first optical microwave signal in the time domain response as a reference pulse signal for power self-compensation, and compensates the amplitude spectrum of the second optical microwave signal in the frequency response based on the reference pulse signal to resist the influence of power fluctuation on the demodulation result.

[0015] Furthermore, the intensity of the broadband light source is I The optical carrier of 0 is modulated by the electro-optic modulator and the angular frequency of the output of the vector network analyzer is ω The microwave signal carried by the light is transmitted through the first intensity modulated optical fiber sensor. I 1 is represented by:

[0016] (1)

[0017] In formula (1), η 1 is the transmittance of the first intensity modulated optical fiber sensor, M is the modulation depth, t For time.

[0018] Furthermore, after the optical microwave signal is transmitted to the optical fiber ring and the second intensity modulated optical fiber sensor embedded therein, the relative modulation depth of the output signal is M ′ is expressed as:

[0019] (2)

[0020] In formula (2), n and L are the effective refractive index of the optical fiber and the length of the optical fiber ring, respectively. c is the speed of light in a vacuum; τ is the ring-down time, expressed as:

[0021] (3)

[0022] In formula (3), A 0 and A 1 are the transmission loss in the optical fiber ring and the loss caused by the second intensity modulated optical fiber sensor;

[0023] By scanning the modulation frequency of the microwave signal, the amplitude spectrum of the optical fiber ring and the first intensity modulated optical fiber sensor and the second intensity modulated optical fiber sensor is obtained, and the fringe contrast C f It is expressed as:

[0024] (4)

[0025] The fringe contrast is related to the ring-down time. When the optical fiber ring remains unchanged, the fringe contrast is only related to the loss of the second intensity modulated optical fiber sensor. Independent demodulation of the second intensity modulated optical fiber sensor is achieved based on the fringe contrast.

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0027] 1. Based on the amplitude spectrum intensity and fringe contrast corresponding to the fiber ring, dual-channel multiplexing of the intensity modulated fiber sensor is realized;

[0028] 2. Based on the light source power fluctuation information reflected by the reference pulse signal intensity corresponding to the reference optical fiber line, the amplitude spectrum corresponding to the optical fiber ring is self-compensated for power, thereby improving the ability to resist light source power fluctuations;

[0029] 3. The dual-channel multiplexing and demodulation method is universal and applicable to various intensity modulated optical fiber sensors that apply changes in target parameters to changes in optical carrier intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of a dual-channel multiplexed intensity modulated optical fiber sensor system of the present invention;

[0031] Figure 2 It is a schematic diagram of a first intensity modulated optical fiber sensor based on an anti-resonance heterogeneous optical fiber curvature sensor of the present invention;

[0032] Figure 3 It is a schematic diagram of a second intensity modulated optical fiber sensor based on an optical fiber coil bending diameter sensor of the present invention;

[0033] Figure 4 This is a diagram of the experimental test results of the present invention; Figure 4 a represents the experimental results of the two sensors when different curvatures are applied to the first intensity modulated optical fiber sensor 105, Figure 4 b represents the experimental results of the two sensors when different bending diameters are applied to the second intensity modulated optical fiber sensor 108, Figure 4 c represents the self-compensated and uncompensated experimental results of the first intensity modulated optical fiber sensor 105 when the light source power changes, Figure 4 d represents the self-compensated and uncompensated experimental results of the second intensity modulated optical fiber sensor 108 when the light source power changes.

[0034] In all drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0035] Broadband light source 101, first single-mode optical fiber 102, electro-optic modulator 103, first optical fiber coupler 104, first intensity modulated optical fiber sensor 105, second optical fiber coupler 106, third optical fiber coupler 107, second intensity modulated optical fiber sensor 108, fourth optical fiber coupler 109, photodetector 110, coaxial cable 111, vector network analyzer 112; second input single-mode optical fiber 201, hollow-core optical fiber 202, output single-mode optical fiber 203, first optical fiber fixing fixture 204, second optical fiber fixing fixture 205; third single-mode optical fiber 301, fixing ring 302, first optical fiber fixing displacement stage 303, second optical fiber fixing displacement stage 304, displacement guide rail 305; DETAILED DESCRIPTION

[0036] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0037] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0038] Example

[0039] This embodiment proposes a dual-channel multiplexed intensity modulated optical fiber sensor system. Figure 1 , comprising a broadband light source 101, a first single-mode optical fiber 102, an electro-optical modulator 103, a first optical fiber coupler 104, a first intensity modulated optical fiber sensor 105, a second optical fiber coupler 106, a third optical fiber coupler 107, a fourth optical fiber coupler 109, a photodetector 110, a coaxial cable 111, and a vector network analyzer 112, which are connected in sequence; wherein a second intensity modulated optical fiber sensor 108 is connected between the second optical fiber coupler 106 and the third optical fiber coupler 107; and the first optical fiber coupler 104 is connected to the fourth optical fiber coupler 109;

[0040] When working, the wide-spectrum incoherent light output by the broadband light source 101 is used as an optical carrier to avoid optical interference, and at the same time, the optical carrier power is increased to be suitable for the intensity modulated optical fiber sensor; the optical carrier is modulated with the microwave signal output by the vector network analyzer 112 under the action of the electro-optical modulator 103, and the optical microwave signal is divided into two paths by the first optical fiber coupler 104; wherein, the first path of optical microwave signal is directly transmitted to the photoelectric detector 110 via the first optical fiber coupler 104, the fourth optical fiber coupler 109 and the reference optical fiber line therebetween to obtain an electrical signal; the second path of optical microwave signal is successively transmitted through the optical fiber ring composed of the first intensity modulated optical fiber sensor 105, the second optical fiber coupler 106 and the third optical fiber coupler 107, and the second intensity modulated optical fiber sensor 108 embedded in the optical fiber ring, and then is received by the photoelectric detector 110.

[0041] As a preferred technical solution, in this embodiment, the first fiber coupler 104, the second fiber coupler 106, the third fiber coupler 107 and the fourth fiber coupler 109 are all 1×2 fiber couplers.

[0042] In this embodiment, for ease of implementation, the coupling splitting ratios of the first optical fiber coupler 104 and the fourth optical fiber coupler 109 are both 98%:2% self-coupling:cross coupling, thereby extracting a small portion of the optically-carried microwave signal as a reference signal required for power self-compensation;

[0043] In this embodiment, for ease of implementation, the coupling splitting ratios of the second fiber coupler 106 and the third fiber coupler 107 are both 95%:5% self-coupling:cross coupling, and the cross-coupling ports of the two are connected in pairs to form a fiber ring structure with a fiber ring length of 4.847 m, so that the amplitude spectrum within the observation frequency range of 500-1000 MHz has enough fringes to calculate the fringe contrast.

[0044] As a preferred technical solution, in this embodiment, Figure 2 As shown, an antiresonant heterogeneous optical fiber curvature sensor is selected as the first intensity modulated optical fiber sensor 105, and the first intensity modulated optical fiber sensor 105 includes a second input single-mode optical fiber 201, a hollow-core optical fiber 202, an output single-mode optical fiber 203, a first optical fiber fixing fixture 204, and a second optical fiber fixing fixture 205 connected in sequence.

[0045] In the antiresonant heterogeneous fiber curvature sensor, the second input single-mode fiber 201, the hollow-core fiber 202 and the output single-mode fiber 203 are connected in sequence, the fundamental mode in the input single-mode fiber excites the cladding mode in the hollow-core fiber 202, generates an antiresonance effect in the cladding of the hollow-core fiber 202, and then couples to the output single-mode fiber 203, the first fiber fixing fixture 204 and the second fiber fixing fixture 205 are respectively used to fix the input single-mode fiber and the output single-mode fiber 203, and the curvature of the antiresonant heterogeneous fiber is changed by adjusting the relative positions of the two fiber fixing fixtures. The increase in curvature will aggravate the mode leakage in the antiresonant heterogeneous fiber, resulting in increased loss.

[0046] As a preferred technical solution, in this embodiment, the core diameter of the hollow-core optical fiber 202 is 50 μm and the length is 1.5 mm, so that the fundamental mode of the input single-mode optical fiber can have a sufficient propagation length to couple into the cladding of the hollow-core optical fiber 202, while not introducing excessive propagation losses, thereby ensuring that an optical carrier with sufficient power can be transmitted through the antiresonant heterogeneous optical fiber curvature sensor.

[0047] As a preferred technical solution, in this embodiment, Figure 3 As shown, an optical fiber coil bending diameter sensor is selected as the second intensity modulated optical fiber sensor 108, and the second intensity modulated optical fiber sensor 108 includes a third single-mode optical fiber 301, a fixed ring 302, a first optical fiber fixed displacement stage 303, a second optical fiber fixed displacement stage 304, and a displacement guide rail 305 connected in sequence.

[0048] In the optical fiber coil bending diameter sensor, the single-mode optical fiber is coiled into a coil, and its transmission loss is adjusted by different coil bending diameters. The fixing ring 302 is used to shape the optical fiber coil. The first optical fiber fixing displacement stage 303 and the second optical fiber fixing displacement stage 304 are respectively used to fix the two ends of the single-mode optical fiber coil and are placed on the displacement guide rail 305. The relative positions of the two optical fiber fixing displacement stages are adjusted to change the bending diameter of the optical fiber coil. The reduction of the bending diameter will weaken the binding ability of the single-mode optical fiber to the mode, resulting in increased loss.

[0049] When implementing the dual-parameter sensing of curvature and bending diameter of the dual-path intensity modulated optical fiber sensor, the amplitude spectrum intensity is compensated and corrected based on the fringe contrast of the amplitude spectrum to eliminate the influence of the second intensity modulated optical fiber sensor 108 on the amplitude spectrum intensity; when the curvature of the first intensity modulated optical fiber sensor 105 changes, the curvature size is demodulated according to the amplitude spectrum intensity, and when the bending diameter of the second intensity modulated optical fiber sensor 108 changes, the bending diameter size is demodulated according to the fringe contrast;

[0050] When only the curvature of the first intensity modulated optical fiber sensor 105 is changed, the relationship between the amplitude spectrum intensity and the curvature is as follows: Figure 4 As shown in a;

[0051] When only the bending diameter of the second intensity modulated optical fiber sensor 108 is changed, the relationship between the fringe contrast and the bending diameter is as follows: Figure 4 As shown in b;

[0052] When the light source power changes, the amplitude spectrum demodulation result of the dual-path intensity modulated optical fiber sensor is self-compensated based on the reference pulse signal intensity. The relationship between the amplitude spectrum intensity change and the fringe contrast change and the power change before and after compensation is as follows: Figure 4 As shown in c and d;

[0053] It should be understood that, in order to facilitate the explanation of the principle of the present invention, in this embodiment, the anti-resonance heterogeneous optical fiber curvature sensor and the optical fiber coil bending diameter sensor are taken as examples. In specific applications, any physical quantity that can cause a change in the transmission loss of the two can be used as the target parameter to be measured;

[0054] It should be understood that, in order to facilitate the explanation of the principles of the present invention, in this embodiment, the antiresonant heterogeneous optical fiber curvature sensor and the optical fiber coil bending diameter sensor are taken as the first intensity modulated optical fiber sensor 105 and the second intensity modulated optical fiber sensor 108 as examples respectively, and other types of intensity modulated optical fiber sensors can also be used in specific applications.

[0055] As a preferred technical solution, in this embodiment, a dual-channel multiplexed intensity modulated optical fiber sensor demodulation method includes the following steps:

[0056] When working, the wide-spectrum incoherent light output by the broadband light source 101 is used as an optical carrier to avoid optical interference, and at the same time, the optical carrier power is increased to be suitable for the intensity modulated optical fiber sensor; the optical carrier is modulated with the microwave signal output by the vector network analyzer 112 under the action of the electro-optical modulator 103, and the optical microwave signal is divided into two paths by the first optical fiber coupler 104; wherein, the first path of optical microwave signal is directly transmitted to the photoelectric detector 110 via the first optical fiber coupler 104, the fourth optical fiber coupler 109 and the reference optical fiber line therebetween to obtain an electrical signal; the second path of optical microwave signal is successively transmitted through the optical fiber ring composed of the first intensity modulated optical fiber sensor 105, the second optical fiber coupler 106 and the third optical fiber coupler 107, and the second intensity modulated optical fiber sensor 108 embedded in the optical fiber ring, and then is received by the photoelectric detector 110;

[0057] The vector network analyzer 112 measures the frequency response of the system based on the electrical signal converted by the photodetector 110, performs inverse Fourier transform on the frequency response to obtain the time domain response, uses the pulse of the first optical microwave signal in the time domain response as a reference pulse signal for power self-compensation, and compensates the amplitude spectrum of the second optical microwave signal in the frequency response based on the reference pulse signal to resist the influence of power fluctuation on the demodulation result.

[0058] The amplitude spectrum intensity after power self-compensation depends on the loss change of the first intensity modulated optical fiber sensor 105, while the fringe contrast in the frequency response measured by the vector network analyzer is only related to the loss change of the second intensity modulated optical fiber sensor 108. The amplitude spectrum intensity is compensated and corrected based on the change of fringe contrast to eliminate the influence of the second intensity modulated optical fiber sensor 108 on the amplitude spectrum intensity, thereby realizing independent demodulation of the two intensity modulated optical fiber sensors respectively.

[0059] As a preferred technical solution, in this embodiment, the intensity emitted by the broadband light source 101 is I The optical carrier wave of 0 is modulated by the electro-optic modulator 103 and the angular frequency output by the vector network analyzer 112 is ω The microwave signal carried by the light is transmitted through the first intensity modulated optical fiber sensor 105. I 1 is represented by:

[0060] (1)

[0061] In formula (1), η 1 is the transmittance of the first intensity modulated optical fiber sensor 105, M is the modulation depth, t For time.

[0062] As a preferred technical solution, in this embodiment, after the light-carrying microwave signal is transmitted to the optical fiber ring and the second intensity modulated optical fiber sensor 108 embedded therein, the relative modulation depth of the output signal is M ′ is expressed as:

[0063] (2)

[0064] In formula (2), n and L are the effective refractive index of the optical fiber and the length of the optical fiber ring, respectively. c is the speed of light in a vacuum; τ is the ring-down time, expressed as:

[0065] (3)

[0066] In formula (3), A 0 and A 1 are the transmission loss in the optical fiber ring and the loss caused by the second intensity modulated optical fiber sensor 108;

[0067] By scanning the modulation frequency of the microwave signal, the amplitude spectrum of the optical fiber ring and the first intensity modulated optical fiber sensor 105 and the second intensity modulated optical fiber sensor 108 is obtained, and the fringe contrast C f It is expressed as:

[0068] (4)

[0069] The fringe contrast is related to the ring-down time. When the optical fiber ring remains unchanged, the fringe contrast is only related to the loss of the second intensity modulated optical fiber sensor 108. Independent demodulation of the second intensity modulated optical fiber sensor 108 is achieved based on the fringe contrast.

[0070] When the first intensity modulated optical fiber sensor 105 is affected by the target parameter to be measured and the transmission loss changes, the overall intensity of the amplitude spectrum of the output signal changes significantly, while the second intensity modulated optical fiber sensor 108 has little effect on the amplitude spectrum intensity. The change in amplitude spectrum intensity caused by the second intensity modulated optical fiber sensor 108 is compensated and corrected according to the change in fringe contrast, thereby achieving independent demodulation of the first intensity modulated optical fiber sensor 105 based on the amplitude spectrum intensity.

[0071] Implementing the embodiments of the present invention has the following beneficial effects:

[0072] The basic principle of the dual-channel multiplexed intensity modulated optical fiber sensor and its demodulation method described in the present invention is: intensity modulated optical fiber sensors are embedded in the input optical fiber trunk and the optical fiber ring outside the optical fiber ring formed by two optical fiber couplers to form dual-channel multiplexing; a reference optical fiber line is introduced in front of the first intensity modulated optical fiber sensor 105 embedded in the optical fiber trunk to monitor the signal power that has not passed through the sensor in real time, so as to compensate for the sensor demodulation result; after the optical carrier emitted by the broadband light source 101 is modulated with a microwave signal by the electro-optical modulator 103, the generated optical carrier microwave signal is transmitted through the reference optical fiber line, the optical fiber ring and the two intensity modulated optical fiber sensors inside and outside it, and then the vector network analyzer 112 is used to measure the total frequency response of the system, thereby realizing the multiplexing of the dual-channel intensity modulated optical fiber sensor based on the amplitude spectrum intensity and the fringe contrast. During operation, the frequency response is frequency-time transformed to obtain a time domain pulse signal response, including a reference pulse corresponding to the reference optical fiber line and a ring-down pulse sequence corresponding to the optical fiber ring; the optical microwave signal is affected by the target parameter to be measured when it is transmitted through the first intensity modulated optical fiber sensor 105, and the attenuation of the optical carrier is reflected in the weakening of the microwave signal intensity, thereby reducing the overall intensity of the amplitude spectrum in the frequency response; then the optical microwave signal is coupled into the optical fiber ring through the optical fiber coupler, and except for the first half of the circle directly coupled out from the optical fiber ring, it will pass through the second intensity modulated optical fiber sensor in the ring-down process of each subsequent circle. The modulated optical fiber sensor 108, the target parameter to be measured will act on the other pulse signals except the first pulse. At this time, the attenuation of the optical carrier will be reflected in the change of the decay time, which is manifested as a faster decay of the time domain pulse signal and a decrease in the contrast of the amplitude spectrum fringe; when the power of the light source fluctuates, the reference pulse will change accordingly, and the amplitude spectrum corresponding to the decay pulse sequence will be compensated based on its intensity change; according to the amplitude spectrum intensity and fringe contrast corresponding to the optical fiber ring, and the intensity fluctuation of the reference pulse signal, the multiplexing and demodulation of the dual-path intensity modulated optical fiber sensor with self-power compensation is realized.

[0073] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A dual-channel multiplexed intensity modulated optical fiber sensor system, characterized in that: The invention comprises a broadband light source (101), a first single-mode optical fiber (102), an electro-optic modulator (103), a first optical fiber coupler (104), a first intensity modulated optical fiber sensor (105), a second optical fiber coupler (106), a third optical fiber coupler (107), a fourth optical fiber coupler (109), a photoelectric detector (110), a coaxial cable (111), and a vector network analyzer (112) which are connected in sequence; wherein a second intensity modulated optical fiber sensor (108) is connected between the second optical fiber coupler (106) and the third optical fiber coupler (107); and the first optical fiber coupler (104) is connected to the fourth optical fiber coupler (109); When working, the wide-spectrum incoherent light output by the broadband light source (101) is used as an optical carrier; the optical carrier is modulated with a microwave signal output by a vector network analyzer (112) under the action of an electro-optical modulator (103), and the optical microwave signal is divided into two paths by a first optical fiber coupler (104); wherein the first path of optical microwave signal is transmitted to a photoelectric detector (110) via the first optical fiber coupler (104) and a fourth optical fiber coupler (109) to obtain an electrical signal; and the second path of optical microwave signal is received by the photoelectric detector (110) after passing through an optical fiber ring formed by a first intensity modulated optical fiber sensor (105), a second optical fiber coupler (106) and a third optical fiber coupler (107), and a second intensity modulated optical fiber sensor (108) embedded in the optical fiber ring.

2. A dual-channel multiplexed intensity modulated optical fiber sensor system according to claim 1, characterized in that: The first optical fiber coupler (104), the second optical fiber coupler (106), the third optical fiber coupler (107) and the fourth optical fiber coupler (109) are all 1×2 optical fiber couplers.

3. A dual-channel multiplexed intensity modulated optical fiber sensor system according to claim 1, characterized in that: An anti-resonance heterogeneous optical fiber curvature sensor is selected as a first intensity modulated optical fiber sensor (105), wherein the first intensity modulated optical fiber sensor (105) comprises a second input single-mode optical fiber (201), a hollow-core optical fiber (202), an output single-mode optical fiber (203), a first optical fiber fixing fixture (204), and a second optical fiber fixing fixture (205) which are connected in sequence.

4. A dual-channel multiplexed intensity modulated optical fiber sensor system according to claim 3, characterized in that: The core diameter of the hollow core optical fiber (202) is 50 μm and the length is 1.5 mm.

5. A dual-channel multiplexed intensity modulated optical fiber sensor system according to claim 1, characterized in that: An optical fiber coil bending diameter sensor is selected as the second intensity modulated optical fiber sensor (108), and the second intensity modulated optical fiber sensor (108) comprises a third single-mode optical fiber (301), a fixed ring (302), a first optical fiber fixed displacement stage (303), a second optical fiber fixed displacement stage (304), and a displacement guide rail (305) which are connected in sequence.

6. A dual-channel multiplexed intensity modulated optical fiber sensor demodulation method, applied to a dual-channel multiplexed intensity modulated optical fiber sensor system as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Using the wide-spectrum incoherent light output by the broadband light source (101) as an optical carrier; The optical carrier is modulated by the electro-optic modulator (103) to obtain a microwave signal output by the vector network analyzer (112), and the optical microwave signal is divided into two paths by the first optical fiber coupler (104); wherein the first path of the optical microwave signal is transmitted to the photoelectric detector (110) via the first optical fiber coupler (104) and the fourth optical fiber coupler (109) to obtain an electrical signal; and the second path of the optical microwave signal is received by the photoelectric detector (110) after passing through the optical fiber ring composed of the first intensity modulated optical fiber sensor (105), the second optical fiber coupler (106) and the third optical fiber coupler (107), and the second intensity modulated optical fiber sensor (108) embedded in the optical fiber ring; The vector network analyzer (112) measures the frequency response of the system based on the electrical signal converted by the photodetector (110), performs inverse Fourier transform on the frequency response to obtain a time domain response, uses the pulse of the first optical microwave signal in the time domain response as a reference pulse signal for power self-compensation, and compensates the amplitude spectrum of the second optical microwave signal in the frequency response based on the reference pulse signal to resist the influence of power fluctuation on the demodulation result.

7. The method according to claim 6, characterized in that The optical carrier with an intensity of I0 emitted by the broadband light source (101) is modulated by the electro-optic modulator (103) onto a microwave signal with an angular frequency of ω output by the vector network analyzer (112). The intensity I1 of the optical carrier microwave signal after being transmitted through the first intensity modulated optical fiber sensor (105) is expressed as: I1=η1I0[1+Msin(ωt)] (1) In formula (1), η1 is the transmittance of the first intensity modulated optical fiber sensor (105), M is the modulation depth, and t is time.

8. The method according to claim 7, characterized in that After the light-carrying microwave signal is transmitted to the optical fiber ring and the second intensity modulated optical fiber sensor (108) embedded therein, the relative modulation depth M′ of the output signal is expressed as: In formula (2), n and L are the effective refractive index of the optical fiber and the length of the optical fiber ring, respectively; c is the speed of light in vacuum; and τ is the ring-down time, which is expressed as: In formula (3), A0 and A2 are the transmission loss in the optical fiber ring and the loss caused by the second intensity modulated optical fiber sensor (108), respectively; By scanning the modulation frequency of the microwave signal, the amplitude spectra of the optical fiber ring and the first intensity modulated optical fiber sensor (105) and the second intensity modulated optical fiber sensor (108) are obtained, and the fringe contrast C f It is expressed as: The fringe contrast is related to the ring-down time. When the optical fiber ring remains unchanged, the fringe contrast is only related to the loss of the second intensity modulated optical fiber sensor (108). Independent demodulation of the second intensity modulated optical fiber sensor (108) is achieved based on the fringe contrast.

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