Multi-core optical fiber liquid refractive index sensor

Abstract

The utility model provides a multi-core optical fiber liquid refractive index sensor, which is characterized in that a grating is arranged on one fiber core of a multi-core optical fiber, two preset fiber cores are selected as two interference arms, one end of the multi-core optical fiber is a detection end, and the detection end is used for being inserted into liquid. The two interference arms are connected with the wavelength monitoring assembly at the other end of the multi-core optical fiber, the wavelength monitoring assembly is used for emitting optical signals to the two interference arms and monitoring the wavelength of the interference signals reflected by the two interference arms, and the sensitivity of the wavelength of the interference signals to liquid temperature changes is improved through the grating. Therefore, the relationship between the liquid temperature and the wavelength of the interference signal is accurately obtained, the influence on the liquid temperature is compensated when the liquid refractive index is obtained through the wavelength of the interference signal subsequently, and the influence on the detection result of the liquid refractive index caused by the liquid temperature is avoided while the liquid refractive index measurement is realized.

Description

Technical Field

[0001] The utility model relates to the field of liquid refractive index measurement, in particular to a multi-core optical fiber liquid refractive index sensor. Background Art

[0002] When the refractive index of the liquid is measured using the interferometer arm of a multi-core optical fiber and a spectrum analyzer, the wavelength of the interference signal reflected by the interferometer arm will be affected by the refractive index of the liquid. Therefore, the wavelength of the interference signal reflected by the interferometer arm can be monitored by the spectrum analyzer to calculate the refractive index of the liquid. However, since the wavelength of the interference signal is also affected by the temperature of the liquid, it is difficult to ensure the accuracy of the refractive index measurement result due to temperature fluctuations when actually measuring the refractive index of the liquid.

[0003] In view of this, overcoming the defects of the prior art is an urgent problem to be solved in the field of this technology. Utility Model Content

[0004] The problem solved by the utility model is that a device is needed to avoid the error influence caused by temperature when measuring the refractive index of liquid.

[0005] In a first aspect, a multi-core optical fiber liquid refractive index sensor is provided, comprising: a wavelength monitoring component 1 and a multi-core optical fiber 2, wherein:

[0006] The multi-core optical fiber 2 includes a plurality of cores, one of which is provided with a grating 3;

[0007] Selecting two preset fiber cores in the multi-core optical fiber 2 as two interference arms 21;

[0008] One end of the multi-core optical fiber 2 is a detection end 22, and the detection end 22 is used to be inserted into the liquid; the two interference arms 21 are connected to the wavelength monitoring component 1 at the other end of the multi-core optical fiber 2, and the wavelength monitoring component 1 is used to transmit light signals to the two interference arms 21 and monitor the wavelength of the interference signal reflected back by the two interference arms 21.

[0009] Preferably, the multi-core optical fiber 2 includes a middle core 23 and a plurality of side cores 24, and all the side cores 24 are arranged around the middle core 23;

[0010] The grating 3 is disposed on the middle core 23 , and the middle core 23 and one of the side cores 24 serve as the interference arm 21 .

[0011] Preferably, the wavelength monitoring component 1 specifically includes a light source 11, a spectrum analyzer 12 and a first coupler 13, wherein:

[0012] The light source 11 and the spectrum analyzer 12 are both connected to the first coupler 13, and the first coupler 13 is respectively connected to the two interference arms 21;

[0013] The light source 11 is used to emit a light signal and is received by the two interference arms 21 after passing through the first coupler 13 . The two interference arms 21 are used to reflect interference signals after receiving the light signal. The interference signals are transmitted to the spectrometer 12 after passing through the first coupler 13 .

[0014] Preferably, the first coupler 13 includes at least four ports, two of which are respectively connected to the two interference arms 21, and the other two ports include a first input port 131 and a first output port 132, the first input port 131 is connected to the light source 11; the first output port 132 is connected to the spectrometer 12.

[0015] Preferably, a polishing notch 25 of a preset length is provided on the side wall of the detection end 22 , and the polishing notch 25 extends to the end surface of the detection end 22 .

[0016] Preferably, the multi-core optical fiber 2 includes a middle core 23 and a plurality of side cores 24, and all the side cores 24 are arranged around the middle core 23;

[0017] The grating 3 is disposed on the middle core 23 , and the side core 24 closest to the polishing notch 25 is used as one of the interference arms 21 , and any one of the other side cores 24 is used as the other interference arm 21 .

[0018] Preferably, the wavelength monitoring component 1 specifically includes a light source 11, a spectrum analyzer 12, a first coupler 13, a second coupler 15 and a microwave photon filter 14, wherein:

[0019] The first coupler 13 includes at least four ports, two of which are connected to the two interference arms 21 respectively, and the other two ports include a first input port 131 and a first output port 132, the first input port 131 is connected to the light source 11; the first output port 132 is connected to the microwave photon filter 14;

[0020] The light source 11 is used to emit an optical signal and the optical signal is received by the two interference arms 21 after passing through the first coupler 13. The two interference arms 21 are used to reflect interference signals after receiving the optical signal. The interference signals are transmitted to the microwave photon filter 14 after passing through the first coupler 13.

[0021] The second coupler 15 includes at least three ports, one of which is connected to the middle core 23, and the other two ports include a second input port 151 and a second output port 152, the second input port 151 is connected to the light source 11, and the second output port 152 is connected to the spectrum analyzer 12;

[0022] The light source 11 is used to emit an optical signal and is received by the intermediate core 23 after passing through the second coupler 15 . The intermediate core 23 is used to reflect an interference signal after receiving the optical signal. The interference signal is transmitted to the spectrum analyzer 12 after passing through the second coupler 15 .

[0023] Preferably, the microwave photon filter 14 comprises: a polarization controller 141, an electro-optic modulator 142, an erbium-doped fiber amplifier 143, a photodiode 144 and a vector network analyzer 145, wherein:

[0024] The polarization controller 141 is connected to the first output port 132 and is used to receive interference signals from the two interference arms 21;

[0025] The polarization controller 141 is connected to the electro-optic modulator 142, and the electro-optic modulator 142 is used to receive the interference signal from the polarization controller 141 and perform corresponding modulation;

[0026] The electro-optic modulator 142 , the erbium-doped fiber amplifier 143 , the photodiode 144 and the vector network analyzer 145 are connected in sequence, and the vector network analyzer 145 is connected to the electro-optic modulator 142 to form a loop.

[0027] Preferably, the end face of the detection end 22 is a cut section 221, and the cut section 221 is used to interfere the optical signal from the wavelength monitoring component 1 to obtain an interference signal, and reflect the interference signal back.

[0028] Preferably, the cut section 221 is coated with a reflective film.

[0029] The utility model provides a multi-core optical fiber liquid refractive index sensor. A grating is arranged on a core in the multi-core optical fiber, and two preset cores are selected as two interference arms. One end of the multi-core optical fiber is a detection end, and the detection end is used to be inserted into the liquid. Two interference arms are connected to the wavelength monitoring component at the other end of the multi-core optical fiber. The wavelength monitoring component is used to emit light signals to the two interference arms and monitor the wavelengths of the interference signals reflected back by the two interference arms. The sensitivity of the wavelength of the interference signal to the change of liquid temperature is improved by the grating, so as to accurately obtain the relationship between the liquid temperature and the wavelength of the interference signal. When the liquid refractive index is obtained by the wavelength of the interference signal, the influence of the liquid temperature is compensated. While realizing the measurement of the liquid refractive index, the influence of the liquid temperature on the detection result of the liquid refractive index is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic diagram of the structure of a multi-core optical fiber liquid refractive index sensor provided by an embodiment of the utility model;

[0032] Figure 2 An end view of the detection end of a multi-core optical fiber of a multi-core optical fiber liquid refractive index sensor provided by an embodiment of the utility model;

[0033] Figure 3 A schematic diagram of the structure of another multi-core optical fiber liquid refractive index sensor provided by an embodiment of the utility model;

[0034] Figure 4 A schematic diagram of the internal connections of a multi-core optical fiber liquid refractive index sensor provided by an embodiment of the utility model;

[0035] Figure 5 A schematic structural diagram of another multi-core optical fiber liquid refractive index sensor provided by an embodiment of the utility model;

[0036] Figure 6 A schematic structural diagram of a multi-core optical fiber liquid refractive index sensor with a microwave photon filter provided in an embodiment of the utility model;

[0037] Figure 7 A schematic structural diagram of another multi-core optical fiber liquid refractive index sensor with a microwave photon filter provided in an embodiment of the utility model;

[0038] Wherein, the accompanying drawings are marked as follows:

[0039] Wavelength monitoring component 1; light source 11; spectrum analyzer 12; first coupler 13; first input port 131; first output port 132; microwave photon filter 14; polarization controller 141; electro-optic modulator 142; erbium-doped fiber amplifier 143; photodiode 144; vector network analyzer 145; second coupler 15; second input port 151; second output port 152; multi-core optical fiber 2; interference arm 21; detection end 22; cut section 221; middle core 23; side core 24; polishing notch 25; grating 3. DETAILED DESCRIPTION

[0040] In the description of the present invention, the terms "inside", "outside", "longitudinal", "lateral", "upper", "lower", "top", "bottom" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on the present invention.

[0041] The terms "first", "second", etc. in this utility model are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this utility model, unless otherwise specified, "plurality" means two or more.

[0042] In the present invention, unless otherwise specified or limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. In addition, the term "coupling" can be a way of achieving electrical connection for signal transmission.

[0043] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0044] Embodiment 1:

[0045] The utility model provides a multi-core optical fiber liquid refractive index sensor, such as Figure 1As shown, it includes: a wavelength monitoring component 1 and a multi-core optical fiber 2, wherein:

[0046] The multi-core optical fiber 2 includes multiple cores, one of which is provided with a grating 3; two preset cores are selected from the multi-core optical fiber 2 as two interference arms 21; one end of the multi-core optical fiber 2 is a detection end 22, and the detection end 22 is used to be inserted into the liquid; the two interference arms 21 are connected to the wavelength monitoring component 1 at the other end of the multi-core optical fiber 2, and the wavelength monitoring component 1 is used to emit light signals to the two interference arms 21 and monitor the wavelength of the interference signal reflected back by the two interference arms 21.

[0047] like Figure 1 As shown, in this embodiment, any two fiber cores in the multi-core optical fiber 2 are used as two interference arms 21; the wavelength monitoring component 1 is used to connect with the two interference arms 21 and provide optical signals to the two interference arms 21. The optical signals are input to the two interference arms 21, and the interference arms 21 interfere with the optical signals to obtain interference signals, and reflect the interference signals back to the wavelength monitoring component 1, and the wavelength monitoring component 1 is used to monitor the wavelength of the interference signal.

[0048] like Figure 2 and Figure 3 As shown, it should be noted that in order to enable the multi-core optical fiber 2 to feedback the interference signal, in this embodiment, the detection end 22 of the multi-core optical fiber 2 is a cut section 221, and the processing method of the cut section 221 is to peel off part of the coating layer of the multi-core optical fiber 2 and cut a neat section with a high-precision optical fiber cutting knife. The cut section 221 is used to interfere with the optical signal from the wavelength monitoring component 1 and reversely transmit the interference signal. The cut section 221 can be coated with a reflective film, and the reflective film is used to improve the interference effect on the optical signal.

[0049] In this embodiment, since the pigtail length and effective refractive index of each core in the multi-core optical fiber 2 are different, when the two cores are used as two interference arms 21, there is a phase difference between the two interference arms 21, and the phase difference is related to the effective refractive index difference between the two interference arms 21. The relevant formula is as follows:

[0050] The light intensity I of the interference signal of the two interference arms 21 is as follows:

[0051] ;

[0052] in, is the light intensity of one of the interferometer arms 21, is the light intensity of the other interferometer arm 21, is the phase difference between the two interference arms 21.

[0053] The relationship between the phase difference between the two interference arms 21 and the effective refractive index difference between the two interference arms 21 is as follows:

[0054] ;

[0055] Wherein, L is the length of the sensing area of ​​the multi-core optical fiber 2, is the effective refractive index difference between the two interference arms 21, is the wavelength of the interference signal of the two interference arms 21.

[0056] From the above formula, it can be known that the effective refractive index difference between the two interference arms 21 is related to the phase difference between the two interference arms 21 and the wavelength of the interference signal. When the light intensity I of the interference signal is the smallest, there exists , so the phase difference can be determined, so the effective refractive index difference of the two interference arms 21 can be determined by the wavelength of the interference signal, and then the change of the current refractive index of the liquid can be obtained by the effective refractive index difference of the two interference arms 21. The relationship is as follows:

[0057] ;

[0058] in, is the effective refractive index of one of the interference arms 21, is the effective refractive index of the other interference arm 21, and m is the resonance peak level of the interference signal.

[0059] However, it should be noted that the change in liquid temperature will also affect the wavelength of the interference signal. If the effect of temperature is not considered, it is definitely inaccurate to obtain the refractive index of the liquid simply by wavelength. Therefore, this embodiment adopts the following method:

[0060] Keeping the liquid refractive index constant, the relationship between the wavelength of the interference signal and the temperature is:

[0061] ;

[0062] Where T is temperature.

[0063] Keeping the liquid temperature constant, the relationship between the wavelength of the interference signal and the refractive index is:

[0064] ;

[0065] Where n is the refractive index of the liquid.

[0066] According to the relationship between the wavelength of the interference signal and the temperature and refractive index, the temperature change and the refractive index change are combined into one relationship, as follows:

[0067] ;

[0068] in, is the liquid temperature change difference, is the difference in liquid refractive index change, α is the temperature coefficient, and β is the refractive index coefficient.

[0069] Therefore, in this embodiment, the liquid refractive index can be kept constant, and multiple groups of liquid temperatures and corresponding interference signal wavelengths can be obtained to calculate the temperature coefficient α; then the liquid temperature can be kept constant, and multiple groups of liquid refractive indices and corresponding interference signal wavelengths can be obtained to calculate the refractive index coefficient β; when performing subsequent measurements, the liquid temperature is measured manually, and the wavelength, temperature coefficient α, refractive index coefficient β and liquid temperature change difference obtained by the spectrometer 12 are brought into the above relationship to obtain the liquid refractive index change difference. However, since the interference arm 21 of the simple multi-core optical fiber 2 in the prior art has poor sensitivity to temperature, the wavelength of the interference signal cannot change more sensitively with the liquid temperature, resulting in an inaccurate calculated temperature coefficient α, and then an inaccurate calculated refractive index.

[0070] In order to solve the above problems, this embodiment involves the following designs:

[0071] The multi-core optical fiber 2 includes an intermediate core 23 and multiple side cores 24 , and all the side cores 24 are arranged around the circumference of the intermediate core 23 ; the grating 3 is set on the intermediate core 23 , and the intermediate core 23 and one of the side cores 24 serve as the interference arm 21 .

[0072] Among them, the grating 3 is used to improve the sensitivity of the interference arm 21 to temperature, so that the wavelength of the interference signal of the interference arm 21 can drift more sensitively with the liquid temperature, ensuring the accuracy of the temperature coefficient α calculated subsequently, thereby improving the accuracy of the calculated refractive index.

[0073] like Figure 2 and Figure 3 As shown, a polishing notch 25 of a preset length is provided on the side wall of the detection end 22, and the polishing notch 25 extends to the end surface of the detection end 22. The grating 3 is located between the two ends of the polishing notch 25.

[0074] In this embodiment, the multi-core optical fiber 2 includes an inner middle core 23 and a side core 24, and an outer protective layer, such as Figure 3As shown, the polishing notch 25 is a notch of a preset length ground on the protective layer of the multi-core optical fiber 2, so that the thickness of the protective layer of this part becomes thinner, and the evanescent field of the side core 24 at the polishing notch 25 leaks, thereby improving the sensitivity of the internal core of the multi-core optical fiber 2 to external environmental factors, making the wavelength of the interference signal generated by the two interference arms 21 more sensitive to temperature and refractive index, and making the monitoring result of the refractive index of the liquid more accurate. It should be noted that when the refractive index of the liquid is actually detected, it is necessary to ensure that the polishing notch 25 of the multi-core optical fiber 2 is completely immersed in the liquid. Among them, the preset length is set by technicians in this field according to actual conditions.

[0075] The length of the polishing notch 25 may be the length of the sensing region of the multi-core optical fiber 2 .

[0076] Furthermore, this embodiment also involves the following designs:

[0077] like Figure 2 and Figure 3 As shown, the grating 3 is arranged on the middle core 23 , and the middle core 23 is used as one of the interference arms 21 , and the side core 24 closest to the polishing notch 25 is used as the other interference arm 21 .

[0078] Due to the existence of the polishing notch 25, there is an obvious difference in cladding thickness between the fiber core closest to the polishing notch 25 and the middle core 23. The middle core 23 has the thickest cladding among all the fiber cores, and the fiber core closest to the polishing notch 25 has the thinnest cladding. Therefore, the sensitivity difference between the two is the largest. When the external refractive index changes, the effective refractive index difference of the interference arm is greater, thereby producing a greater phase difference. By measuring the drift of the interference spectrum, a more significant refractive index change can be obtained, thereby further improving the sensitivity of the wavelength of the interference signal generated by the two interference arms 21 to temperature and refractive index, thereby improving the accuracy of the monitoring results of the liquid refractive index.

[0079] like Figure 4 As shown, the wavelength monitoring component 1 specifically includes a light source 11, a spectrum analyzer 12 and a first coupler 13, wherein:

[0080] The light source 11 and the spectrum analyzer 12 are both connected to the first coupler 13 , and the first coupler 13 is respectively connected to the two interference arms 21 .

[0081] The light source 11 is used to emit a light signal and is received by the two interference arms 21 after passing through the first coupler 13 . The two interference arms 21 are used to reflect interference signals after receiving the light signal. The interference signals are transmitted to the spectrometer 12 after passing through the first coupler 13 .

[0082] The first coupler 13 includes at least four ports, two of which are respectively connected to the two interference arms 21 , and the other two ports include a first input port 131 and a first output port 132 . The first input port 131 is connected to the light source 11 , and the first output port 132 is connected to the spectrometer 12 .

[0083] like Figure 4 As shown, the first coupler 13 can be a 2×2 coupler, and the two interfaces at one end of the first coupler 13 are respectively connected to the two interference arms 21, and the two interfaces at the other end of the first coupler 13 are respectively connected to the light source 11 and the spectrometer 12.

[0084] It is worth mentioning that after the interference signal is reflected back to the first coupler 13 from the two interference arms 21, half of the interference signal will be reflected back to the light source 11 through the first input port 131, and the other half of the interference signal will be transmitted to the spectrometer 12 through the first output port 132. Since the laser at one end of the light source 11 is provided with an isolator, it will not affect the light source 11.

[0085] Embodiment 2:

[0086] Based on Example 1, this Example 2 provides another multi-core optical fiber liquid refractive index sensor.

[0087] In the traditional wavelength demodulation scheme, the accuracy of the sensor is usually limited due to the need to use a spectral analyzer with low measurement resolution. In order to achieve high-precision refractive index measurement, this scheme uses a microwave photon filter system for sensor demodulation, which can provide a measurement resolution of up to the KHz level, which can greatly improve the accuracy of the sensor. In order to improve the monitoring progress of the interference signal wavelength, the two interference arms 21 need to feed back the interference signal to the spectrum analyzer 12 while feeding back the interference signal. In addition, a corresponding microwave photon filter 14 is required to monitor according to the interference spectrum. However, it should be noted that when using a microwave photon filter system for sensor demodulation, it is impossible to use a fiber core with a grating as the interference arm 21 to feed back the interference signal. Therefore, this embodiment involves the following design:

[0088] like Figure 5 As shown, in this embodiment, the multi-core optical fiber 2 includes an intermediate core 23 and multiple side cores 24, and the multiple side cores 24 are arranged around the intermediate core 23. The grating 3 is arranged on the intermediate core 23, and the side core 24 closest to the polishing notch 25 is used as one of the interference arms 21, and any one of the other side cores is used as another interference arm 21.

[0089] like Figure 2 As shown, in this embodiment, since the cores at different positions in the multi-core optical fiber 2 have different sensitivities to the outside world, the phase differences generated by the two interference arms 21 under the influence of temperature and refractive index are also different, and the side core 24 closest to the polishing notch 25 has a thinner cladding thickness than other side cores 24, which makes the sensitivity difference between the side core 24 closest to the polishing notch 25 and other side cores 24 greater. Therefore, selecting the side core 24 closest to the polishing notch 25 can make the subsequent monitoring results of the liquid refractive index more accurate.

[0090] like Figure 6 As shown, the wavelength monitoring component 1 specifically includes a light source 11, a spectrum analyzer 12, a first coupler 13, a second coupler 15 and a microwave photon filter 14, wherein:

[0091] The second coupler 15 includes at least three ports, one of which is connected to the intermediate core 23, and the other two ports include a second input port 151 and a second output port 152, the second input port 151 is connected to the light source 11, and the second output port 152 is connected to the spectrum analyzer 12; the light source 11 is used to emit an optical signal and is received by the intermediate core 23 after passing through the second coupler 15, and the intermediate core 23 is used to reflect an interference signal after receiving the optical signal, and the interference signal is transmitted to the spectrum analyzer 12 after passing through the second coupler 15.

[0092] like Figure 6 As shown, the second coupler 15 can be a 2×1 coupler, a single interface at one end of the second coupler 15 is connected to the middle core 23, and two interfaces at the other end of the second coupler 15 are connected to the light source 11 and the spectrum analyzer 12 respectively.

[0093] It is worth mentioning that after the interference signal is reflected back from the middle core 23 to the second coupler 15, half of the interference signal will be reflected back to the light source 11 through the second input port 151, and the other half of the interference signal will be transmitted to the spectrometer 12 through the second output port 152. Since the laser at one end of the light source 11 is provided with an isolator, it will not affect the light source 11.

[0094] In addition, in the traditional wavelength demodulation scheme, the accuracy of the sensor is usually limited due to the need to use a spectral analysis instrument with low measurement resolution. In order to achieve high-precision refractive index measurement, this embodiment uses a microwave photon filter system for sensor demodulation, which can provide a measurement resolution of up to the KHz level, greatly improving the accuracy of the sensor; in this embodiment, in order to improve the monitoring accuracy of the interference signal wavelength, two interference arms 21 are required to feed back the interference signal to the microwave photon filter 14, and the microwave photon filter 14 is monitored according to the interference spectrum. Therefore, this embodiment also involves the following designs:

[0095] like Figure 6 As shown, the first coupler 13 includes at least four ports, two of which are respectively connected to the two interference arms 21, and the other two ports include a first input port 131 and a first output port 132, the first input port 131 is connected to the light source 11; the first output port 132 is connected to the microwave photon filter 14; the light source 11 is used to emit an optical signal and is received by the two interference arms 21 after passing through the first coupler 13, the two interference arms 21 are used to reflect the interference signal after receiving the optical signal, and the interference signal is transmitted to the microwave photon filter 14 after passing through the first coupler 13.

[0096] like Figure 6 As shown, in this embodiment, the first coupler 13 can be a 2×2 coupler, and the two interfaces at one end of the first coupler 13 are respectively connected to the two interference arms 21, and the two interfaces at the other end are respectively connected to the light source 11 and the microwave photon filter 14.

[0097] This embodiment also includes the following design for the microwave photon filter 14:

[0098] like Figure 7 As shown, the microwave photon filter 14 includes: a polarization controller 141, an electro-optic modulator 142, an erbium-doped fiber amplifier 143, a photodiode 144 and a vector network analyzer 145, wherein:

[0099] The polarization controller 141 is connected to the first output port 132 and is used to receive interference signals from the two interference arms 21 .

[0100] The polarization controller 141 is connected to the electro-optic modulator 142 , and the electro-optic modulator 142 is used to receive the interference signal from the polarization controller 141 and perform corresponding modulation.

[0101] The electro-optic modulator 142 , the erbium-doped fiber amplifier 143 , the photodiode 144 and the vector network analyzer 145 are connected in sequence, and the vector network analyzer 145 is connected to the electro-optic modulator 142 to form a loop.

[0102] In order to overcome the low resolution of the traditional wavelength demodulation technology and achieve high-precision liquid level measurement, a high-resolution microwave photon filter 14 is used to perform sensing demodulation on the Michelson interferometer, which will achieve higher resolution and higher precision sensing compared to the traditional wavelength measurement scheme. In this embodiment, each of the two interference arms 21 can be used as a Michelson interferometer.

[0103] In this embodiment, the microwave photon filter 14 is used to measure the response of the system, which can be expressed as:

[0104] ;

[0105] in, is the spectrum of light source 11, is the transfer function of the dispersive medium, is the angular frequency of the RF signal; is the transfer function of the Michelson interferometer, It can be expressed as:

[0106] ;

[0107] where V is the visibility of the Michelson interferometer, is the periodicity of the Michelson interferometer, c is the speed of light in a vacuum, and the frequency of the passband is correspondingly:

[0108] ;

[0109] in, and are the dispersion and length of the dispersive medium, respectively. Therefore, the change of the optical path difference OPD will lead to a phase difference The change of leads to the center frequency shift of the single-passband microwave photon filter 14. The frequency shift can be expressed as:

[0110] ;

[0111] ;

[0112] ;

[0113] in, is the initial phase difference of the two interfering arms 21, and the total phase difference Depend on Phase difference changes induced by environmental factors Composition; From the above analysis, it can be seen that changes in the temperature and refractive index of the liquid will cause changes in the phase difference between the interference arms 21, which in turn causes the center frequency of the microwave photon filter 14 to drift. By measuring the center frequency through the microwave photon filter 14, the wavelength of the interference signal can be obtained.

[0114] The multi-core optical fiber liquid refractive index sensor with a side-polished structure proposed in this embodiment has the characteristics of compact structure, high sensitivity, high precision, and low temperature cross-sensitivity, and has broad application prospects in high-precision refractive index measurement scenarios.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-core optical fiber liquid refractive index sensor, characterized in that: include: A wavelength monitoring component (1) and a multi-core optical fiber (2), wherein: The multi-core optical fiber (2) comprises a plurality of fiber cores, one of the fiber cores being provided with a grating (3); Selecting two preset fiber cores in the multi-core optical fiber (2) as two interference arms (21); One end of the multi-core optical fiber (2) is a detection end (22), and the detection end (22) is used to be inserted into a liquid; the two interference arms (21) are connected to the wavelength monitoring component (1) at the other end of the multi-core optical fiber (2), and the wavelength monitoring component (1) is used to transmit optical signals to the two interference arms (21) and monitor the wavelength of the interference signal reflected back by the two interference arms (21).

2. The multi-core optical fiber liquid refractive index sensor according to claim 1, characterized in that: The multi-core optical fiber (2) comprises a middle core (23) and a plurality of side cores (24), and all the side cores (24) are arranged around the middle core (23); The grating (3) is arranged on the middle core (23), and the middle core (23) and one of the side cores (24) serve as the interference arm (21).

3. The multi-core optical fiber liquid refractive index sensor according to claim 2, characterized in that: The wavelength monitoring component (1) specifically comprises a light source (11), a spectrum analyzer (12) and a first coupler (13), wherein: The light source (11) and the spectrum analyzer (12) are both connected to the first coupler (13), and the first coupler (13) is respectively connected to the two interference arms (21); The light source (11) is used to emit a light signal and is received by the two interference arms (21) after passing through the first coupler (13); the two interference arms (21) are used to reflect interference signals after receiving the light signal; the interference signals are transmitted to the spectrum analyzer (12) after passing through the first coupler (13).

4. The multi-core optical fiber liquid refractive index sensor according to claim 3, characterized in that: The first coupler (13) comprises at least four ports, two of which are respectively connected to the two interference arms (21), and the other two ports comprise a first input port (131) and a first output port (132), the first input port (131) being connected to the light source (11); and the first output port (132) being connected to the spectrum analyzer (12).

5. The multi-core optical fiber liquid refractive index sensor according to claim 1, characterized in that: A polishing notch (25) of a preset length is provided on the side wall of the detection end (22), and the polishing notch (25) extends to the end surface of the detection end (22).

6. The multi-core optical fiber liquid refractive index sensor according to claim 5, characterized in that: The multi-core optical fiber (2) comprises a middle core (23) and a plurality of side cores (24), and all the side cores (24) are arranged around the middle core (23); The grating (3) is arranged on the middle core (23), and the side core (24) closest to the polishing notch (25) is used as one of the interference arms (21), and any one of the other side cores (24) is used as another interference arm (21).

7. The multi-core optical fiber liquid refractive index sensor according to claim 6, characterized in that: The wavelength monitoring component (1) specifically comprises a light source (11), a spectrum analyzer (12), a first coupler (13), a second coupler (15) and a microwave photon filter (14), wherein: The first coupler (13) comprises at least four ports, two of which are respectively connected to the two interference arms (21), and the other two ports comprise a first input port (131) and a first output port (132), the first input port (131) being connected to the light source (11); and the first output port (132) being connected to the microwave photon filter (14); The light source (11) is used to emit a light signal and the light signal is received by the two interference arms (21) after passing through the first coupler (13); the two interference arms (21) are used to reflect interference signals after receiving the light signal; the interference signals are transmitted to the microwave photon filter (14) after passing through the first coupler (13); The second coupler (15) comprises at least three ports, one of which is connected to the intermediate core (23), and the other two ports comprise a second input port (151) and a second output port (152), the second input port (151) being connected to the light source (11), and the second output port (152) being connected to the spectrum analyzer (12); The light source (11) is used to emit an optical signal and is received by the intermediate core (23) after passing through the second coupler (15); the intermediate core (23) is used to reflect an interference signal after receiving the optical signal; the interference signal is transmitted to the optical spectrum analyzer (12) after passing through the second coupler (15).

8. The multi-core optical fiber liquid refractive index sensor according to claim 7, characterized in that: The microwave photon filter (14) comprises: a polarization controller (141), an electro-optic modulator (142), an erbium-doped fiber amplifier (143), a photodiode (144) and a vector network analyzer (145), wherein: The polarization controller (141) is connected to the first output port (132) and is used to receive interference signals from two interference arms (21); The polarization controller (141) is connected to the electro-optic modulator (142), and the electro-optic modulator (142) is used to receive the interference signal from the polarization controller (141) and perform corresponding modulation; The electro-optic modulator (142), the erbium-doped fiber amplifier (143), the photodiode (144) and the vector network analyzer (145) are connected in sequence, and the vector network analyzer (145) is connected to the electro-optic modulator (142) to form a loop.

9. The multi-core optical fiber liquid refractive index sensor according to any one of claims 1 to 8, characterized in that: The end face of the detection end (22) is a cut-off section (221), and the cut-off section (221) is used to interfere with the optical signal from the wavelength monitoring component (1) to obtain an interference signal, and to reflect the interference signal back.

10. The multi-core optical fiber liquid refractive index sensor according to claim 9, characterized in that: The cut section (221) is plated with a reflective film.

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