Refractive index amplification method, device and medium based on single FFPI vernier effect

Abstract

The present invention provides a refractive index amplification method, device and medium based on single FFPI vernier effect demodulation, wherein the method comprises: reflecting a sensing light source through a FFPI composed of an optical fiber core misalignment pair to obtain a double-beam interference signal, and obtaining the sensing spectrum light intensity in the initial state; performing secondary modulation on the sensing spectrum light intensity in the initial state according to the modulation length to obtain the modulated light intensity, and obtaining the reference spectrum interference light intensity according to the modulated light intensity; adding the sensing spectrum light intensity in the initial state and the reference spectrum interference light intensity and normalizing them to obtain the vernier effect envelope; obtaining the refractive index magnification of the vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and performing refractive index amplification based on the refractive index magnification. Based on the single FFPI signal processing auxiliary vernier effect demodulation, two interferometers are simulated to form a vernier effect in cascade, which solves the problem of the influence of the reference spectrum environment change and provides an adjustable amplification factor.

Description

Technical Field

[0001] This document relates to the field of optical fiber refraction technology, and in particular to a refractive index amplification method, device and medium based on single FFPI vernier effect demodulation. Background Art

[0002] Fiber optic refractive index sensors have attracted considerable attention due to their wide applications in environmental monitoring, biochemical analysis, and medical diagnosis. Among various interferometric fiber optic sensors, the Fabry-Perot interferometer, or FFPI, has the advantages of simple and compact structure, good linearity, and a wide measurement range. There are two types of microcavities in FFPI: one is a closed cavity and the other is an open cavity. In experiments, open-cavity FFPI is usually used to measure the refractive index. Although some methods have been used to improve the performance of the cavity, such as femtosecond laser micromachining, chemical etching, and fiber fusion, the sensitivity of the sensor is only maintained at 10 3 nm / RIU or so.

[0003] Recently, in order to improve the sensitivity of the sensor, the vernier effect is introduced in the FFPI-based sensing system. In this system, two FFPIs are cascaded or connected in series, one FFPI acts as a reference interferometer and the other FFPI acts as a sensing interferometer. By superimposing the spectra of the two FFPIs, a superimposed spectrum with an envelope can be formed. As the external environment changes, the drift of the envelope formed by the vernier effect is much greater than the drift of a single sensing spectrum, so the sensitivity of the system can be amplified by measuring the drift of the envelope. However, the optical path difference of the two FFPIs must be close enough to maximize the sensitivity amplification value. This requires precise manufacturing of FFPIs, but high-precision manufacturing equipment is required and the cost is high. In addition, the reference interferometer in the system is easily affected by the external environment, resulting in measurement errors. Summary of the invention

[0004] The object of the present invention is to provide a refractive index amplification method, device and medium based on single FFPI vernier effect demodulation, aiming to solve the above-mentioned problems in the prior art.

[0005] One or more embodiments of this specification provide a refractive index amplification method based on single FFPI vernier effect demodulation, including:

[0006] S1, obtaining a double-beam interference signal by reflecting the sensing light source through the FFPI composed of the optical fiber core misalignment pair, calculating the total light intensity of the sensing signal of the double-beam interference signal, and obtaining the sensing spectrum light intensity in the initial state according to the total light intensity of the sensing signal of the double-beam interference signal;

[0007] S2, obtaining a first modulation length and a second modulation length according to the modulation length, performing secondary modulation on the sensing spectrum intensity in the initial state according to the modulation function based on the first modulation length and the second modulation length, obtaining the modulated light intensity, and obtaining the reference spectrum interference light intensity according to the modulated light intensity;

[0008] S3, adding the sensing spectrum intensity in the initial state to the reference spectrum interference intensity and normalizing them to obtain the cursor effect envelope;

[0009] S4. Acquire the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope according to the sensing spectrum intensity in the initial state and the vernier effect envelope;

[0010] S5, obtaining the sensitivity and envelope sensitivity of FFPI according to the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope;

[0011] S6. Obtain the refractive index magnification of the vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and perform refractive index amplification based on the refractive index magnification.

[0012] One or more embodiments of the present specification provide a refractive index amplification device based on single FFPI vernier effect demodulation, including:

[0013] A spectrum acquisition module is used to obtain a double-beam interference signal by reflecting the sensing light source through the FFPI composed of an optical fiber core misalignment pair, and calculate the total light intensity of the sensing signal of the double-beam interference signal, and obtain the sensing spectrum light intensity in the initial state according to the total light intensity of the sensing signal of the double-beam interference signal;

[0014] A reference spectrum module is used to obtain a first modulation length and a second modulation length according to the modulation length, perform secondary modulation on the sensing spectrum intensity in the initial state according to the modulation function based on the first modulation length and the second modulation length, obtain the modulated light intensity, and obtain the reference spectrum interference light intensity according to the modulated light intensity;

[0015] The vernier effect envelope module is used to superimpose the sensing spectrum intensity in the initial state with the reference spectrum interference intensity and normalize them to obtain the vernier effect envelope;

[0016] A free spectral range module, used for obtaining the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope according to the sensing spectrum intensity and the vernier effect envelope in the initial state;

[0017] A sensitivity module, used for obtaining the sensitivity and envelope sensitivity of FFPI according to the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope;

[0018] The amplification module is used to obtain the refractive index magnification of the vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and perform refractive index amplification based on the refractive index magnification.

[0019] One or more embodiments of the present specification provide a refractive index magnification device based on single FFPI vernier effect demodulation, characterized in that it includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the steps of the refractive index magnification method based on single FFPI vernier effect demodulation as described above are implemented.

[0020] One or more embodiments of the present specification provide a computer-readable storage medium, characterized in that an implementation program for information transmission is stored on the computer-readable storage medium, and when the program is executed by a processor, the steps of the refractive index amplification method based on single FFPI vernier effect demodulation as described above are implemented.

[0021] By adopting the embodiment of the present invention, the vernier effect demodulation is assisted by the signal processing of a single interferometer, and the vernier effect formed by cascading two interferometers is simulated. The method constructs a reference spectrum by extracting a spectrum from the sensing spectrum, solves the problem of the influence of the reference spectrum environment change, and can provide an adjustable amplification factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate one or more embodiments of this specification 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 recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 It is a flow chart of a refractive index amplification method based on single FFPI vernier effect demodulation according to an embodiment of the present invention;

[0024] Figure 2 FFPI sensing spectrum and the corresponding Fourier transform result in the embodiment of the present invention;

[0025] Figure 2 (a) is the reflection spectrum of FFPI with a cavity length of 500 um in an initial solution with a refractive index of 1.3340;

[0026] Figure 2 (b) is the spatial spectrum of FFPI with a cavity length of 500 um in an initial solution with a refractive index of 1.3340;

[0027] Figure 3The process of constructing a reference spectrum for spatial frequency down-conversion of the sensing spectrum of the embodiment of the present invention;

[0028] Figure 3 (a) is a pair of the embodiments of the present invention Figure 2 (b) Schematic diagram of extracting the corresponding interference component of band1 and normalizing it;

[0029] Figure 3 (b) is a pair of the embodiment of the present invention Figure 3 (a) Schematic diagram of fast Fourier transform;

[0030] Figure 3 (c) is the embodiment of the present invention through the modulation length L m1 = Schematic diagram of modulation by the modulation function of 550 µm;

[0031] Figure 3 (d) is a pair of the embodiment of the present invention Figure 3 (c) Schematic diagram of fast Fourier transform;

[0032] Figure 3 (e) is an embodiment of the present invention Figure 3 (d) The corresponding spectrum;

[0033] Figure 3 (f) is an embodiment of the present invention Figure 3 (d) Schematic diagram of extracting band4;

[0034] Figure 3 (g) is an embodiment of the present invention Figure 3 (f) By modulating the length L m2 = Schematic diagram of secondary modulation with a modulation function of 550 µm;

[0035] Figure 3 (h) is a pair of the embodiment of the present invention Figure 3 (g) Schematic diagram of fast Fourier transform;

[0036] Figure 3 (i) is an embodiment of the present invention Figure 3 (h) Schematic diagram of extracting band5;

[0037] Figure 3 (j) is an embodiment of the present invention Figure 3 (i) Corresponding spectra;

[0038] Figure 4 A schematic diagram of obtaining a vernier effect envelope by superimposing the sensing spectrum intensity with the reference spectrum intensity in an embodiment of the present invention;

[0039] Figure 4(a) is a schematic diagram of the superimposed spectrum and the envelope of the vernier effect according to an embodiment of the present invention;

[0040] Figure 4 (b) is a schematic diagram of a fast Fourier transform of superimposed spectra according to an embodiment of the present invention;

[0041] Figure 5 Schematic diagram of initial refractive index responses of three FFPIs in an embodiment of the present invention;

[0042] Figure 5 (a) is a schematic diagram of the initial refractive index response of FFPI-1 according to an embodiment of the present invention;

[0043] Figure 5 (b) is an embodiment of the present invention Figure 5 (a) Schematic diagram of the trough drifting with the refractive index;

[0044] Figure 5 (c) is a schematic diagram of the initial refractive index response of FFPI-2 according to an embodiment of the present invention;

[0045] Figure 5 (d) is an embodiment of the present invention Figure 5 (b) Schematic diagram of the trough drifting with the refractive index;

[0046] Figure 5 (e) is a schematic diagram of the initial refractive index response of FFPI-3 according to an embodiment of the present invention;

[0047] Figure 5 (f) is an embodiment of the present invention Figure 5 (c) Schematic diagram of the trough drifting with the refractive index;

[0048] Figure 6 is a demodulation envelope diagram of the vernier effect of a FFPI according to an embodiment of the present invention;

[0049] Figure 6 (a) is a demodulation envelope diagram of the vernier effect of FFPI-1 according to an embodiment of the present invention;

[0050] Figure 6 (b) is a demodulation envelope diagram of the vernier effect of FFPI-2 according to an embodiment of the present invention;

[0051] Figure 6 (c) is a demodulation envelope diagram of the vernier effect of FFPI-3 according to an embodiment of the present invention;

[0052] Figure 6 (d) is an embodiment of the present invention Figure 6 Schematic diagram of the trough drift of the spectrum in (a)-6(c) at 1500 nm;

[0053] Figure 7The vernier effect of the embodiment of the present invention is shown in FIG. m Sensitivity magnification under ;

[0054] Figure 7 (a) is L of the embodiment of the present invention m Schematic diagram of the drift of the envelope of the Vernier effect with the increase of the refractive index when the value is 45 μm;

[0055] Figure 7 (b) is L of the embodiment of the present invention m Schematic diagram of the envelope of the Vernier effect drifting with the increase of refractive index when the value is 25μm;

[0056] Figure 7 (c) is L of the embodiment of the present invention m Schematic diagram of the envelope of the Vernier effect drifting with the increase of refractive index when the value is 12.1μm;

[0057] Figure 7 (d) is L of the embodiment of the present invention m Schematic diagram of the drift of the envelope of the Vernier effect with the increase of the refractive index when the value is 10.6μm;

[0058] Figure 7 (e) is an embodiment of the present invention Figure 7 Schematic diagram of the drift of the trough around 1500 nm in (a)-7(d);

[0059] Figure 8 It is a schematic diagram of a refractive index amplification device based on single FFPI vernier effect demodulation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0060] In order to enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the following will be combined with the drawings in one or more embodiments of this specification to clearly and completely describe the technical solutions in one or more embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this document.

[0061] Method Embodiment

[0062] According to an embodiment of the present invention, a refractive index amplification method based on single FFPI vernier effect demodulation is provided. Figure 1 FIG. 1 is a flow chart of a refractive index amplification method based on single FFPI vernier effect demodulation according to an embodiment of the present invention. Figure 1As shown, the refractive index amplification method based on single FFPI vernier effect demodulation according to an embodiment of the present invention specifically includes:

[0063] Step S101, obtaining a double-beam interference signal by reflecting the sensing light source through the FFPI composed of the optical fiber core misalignment pair, and calculating the total light intensity of the sensing signal of the double-beam interference signal, and obtaining the sensing spectrum light intensity in the initial state according to the total light intensity of the sensing signal of the double-beam interference signal, step S101 specifically includes:

[0064] The sensing light source is reflected through the FFPI composed of the optical fiber core misalignment pair to obtain the reflection spectrum;

[0065] Performing fast Fourier transform on the reflection spectrum to obtain a spatial spectrum;

[0066] Acquire a first parameter and a second parameter according to the frequency band and the peak value of the spatial spectrum, and calculate the sensing spectrum intensity according to the first parameter and the second parameter by using Formula 1;

[0067] Formula 1;

[0068] in, , , and are the light intensities of the two reflecting surfaces, is the refractive index of the FFPI cavity medium, is the wavelength in vacuum, is the FFPI cavity length;

[0069] Obtain the initial state sensing spectrum intensity according to formula 2;

[0070] Formula 2;

[0071] in, , is the wavelength in vacuum, is the refractive index change of the ambient medium, is the FFPI cavity length.

[0072] In the embodiment of the present invention, by using a low-precision FFPI composed of a pair of optical fiber core misalignment as a refractive index sensor, the light reflected from the FFPI microcavity can be called double-beam interference. In the sensing experiment, we prepared three pairs of optical fiber core misalignment pairs, named FFPI-1, FFPI-2 and FFPI-3, with a core misalignment of 80um and geometric lengths of Lc = 150 um, Lc = 250 um and Lc = 500 um, respectively. The FFPI was immersed in a diluted glycerol solution of different concentrations, and the refractive index of the solution was measured by the Abel refractive index to be between 1.3340-1.3354. In the experiment, a water bath with an accuracy of 0.05°C was used to control the experimental environment temperature at 30°C.

[0073] like Figure 2 Shown is the sensing spectrum of FFPI in the embodiment of the present invention and the corresponding Fourier transform result;

[0074] Figure 2 (a) is the reflection spectrum of FFPI with a cavity length of 500 um in an initial solution with a refractive index of 1.3340. The absorption of the solution causes the extinction ratio of the sensing spectrum to change with wavelength. At 1500 nm, the free spectral range of the reflection spectrum is 1.70 nm. Figure 2 The fast Fourier transform result of the reflection spectrum in (a), that is, the spatial spectrum is as follows Figure 2 As shown in (b), peaks appear at 0.5882 nm-1 (band 1) and at 0 nm-1, corresponding to the cosine term and constant term in formula 1, respectively.

[0075] Step S102, obtaining a first modulation length and a second modulation length according to the modulation length, performing secondary modulation on the sensing spectrum intensity in the initial state according to the modulation function based on the first modulation length and the second modulation length, obtaining the modulated light intensity, and obtaining the reference spectrum interference light intensity according to the modulated light intensity, step S102 specifically includes:

[0076] Obtain the modulation function according to formula 3;

[0077] Formula 3;

[0078] in, is the wavelength in vacuum, is the modulation length;

[0079] Obtain a first modulation length and a second modulation length according to the modulation length, wherein the first modulation length and the second modulation length satisfy Formula 4;

[0080] L m =L m2 -L m1 Formula 4;

[0081] Among them, L m2 is the first modulation length, L m1 is the second modulation length;

[0082] Modulating the sensing spectrum intensity in the initial state according to the first modulation length by formula 3 to obtain a first modulation result, and extracting an upper sideband frequency band of the first modulation result to obtain a spectrum corresponding to the upper sideband frequency band;

[0083] Modulating the spectrum corresponding to the upper sideband frequency band by the second modulation length using formula 3 to obtain a second modulation result, extracting the lower sideband frequency band of the second modulation result, and obtaining the spectrum corresponding to the lower sideband frequency band as the reference spectrum interference light intensity;

[0084] Wherein, the first modulation result and the second modulation result are obtained by formula 5;

[0085] Formula 5;

[0086] in, is the initial state sensing spectrum intensity, , , and are the light intensities of the two reflecting surfaces, is the FFPI cavity length, , is the wavelength in vacuum, is the refractive index change of the ambient medium, is the refractive index of the FFPI cavity medium;

[0087] The reference spectrum intensity is obtained by modulating the light intensity, which is recorded as ;

[0088] Formula 6.

[0089] Figure 3 The process of constructing a reference spectrum by spatial frequency down-conversion of the measured sensor spectrum is demonstrated, and the specific process of secondary modulation by the modulation function is demonstrated. By using a bandpass finite impulse response Hanning window filter on the sensor spectrum, the interference component corresponding to band 1 is extracted and then normalized, as shown in Figure 3 (a) is shown, and its FFT result is shown in 3 (b). Band 2 is near 0.5882nm-1. Compared with band 1, the spatial position has not changed, but the shape of the band has changed due to the normalization operation. Figure 3 (a) Figure 2 (a) The modulation spectrum of the spectrum. In order to improve the sensing amplification factor, the modulation function should choose a smaller L m, which makes it difficult to directly extract the lower sideband of the modulation spectrum in the subsequent spatial frequency down-conversion operation. To solve this problem, we adopt a two-modulation extraction scheme: Figure 3 (c)- Figure 3 (f) is the first modulation, Figure 3 (g) - Figure 3 (j) is the second modulation. In the first modulation, Figure 3 The spectrum in (a) is the modulation function with a modulation length of Lm1 = 550 µm. The modulation is shown in Figure (c), and its FFT result is shown in 3 (d). Band 3 and Band 4 appear at 0.3431 nm-1 and 0.8333 nm-1, corresponding to the lower and upper sidebands of Band 2, respectively. Since a larger Lm is selected, the two bands are completely separated. The extracted upper sideband Band 4 is shown in Figure 3 (f) shows that the corresponding spectrum is Figure 3 (e) In the second modulation, Figure 3 The spectrum in (e) is modulated again, and the modulation length is Lm2 = 595 µm, as Figure 3 (g) shows that the FFT result is Figure 3 (h) Extraction Figure 3 (h) The lower sideband band 5, such as Figure 3 (j). Its wavelength spectrum is as follows Figure 3 (i) is used as ARS. In this case, the reference spectral intensity can be written as:

[0090]

[0091] Where L m2 – L m1 = L m , which is equivalent to L m =45µm for the down-conversion frequency band of Band 2, Figure 3 In (i), at a wavelength of 1500 nm, the free spectral range of ARS is 1.78 nm. By changing L m With the value of , ARS can obtain different free spectral ranges.

[0092] Step S103, adding the sensing spectrum intensity in the initial state to the reference spectrum interference intensity and normalizing them to obtain the vernier effect envelope; Step S103 specifically includes:

[0093] The reference spectrum contains the dispersion characteristics of the sensing spectrum, which can be used to compensate for the dispersion of the traditional sensing spectrum when constructing the vernier effect later. The measured sensing spectrum intensity is added to the reference spectrum used as the reference interferometer to obtain:

[0094] Formula 7;

[0095] The addition result is normalized by formula 8,

[0096] Formula 8 ；

[0097] The envelope of the cursor effect is obtained as:

[0098] Formula 9;

[0099] in , ≈ ,in, is the FFPI cavity length, is the modulation length, is the wavelength in vacuum, is the refractive index change of the ambient medium. Figure 3 The ARS in the sample is superimposed with the measured sensor spectrum, and the results are as follows: Figure 4 (a) shows that the FFT result is Figure 4 (b) As shown in Figure 4 In (b), band 7 contains two partially overlapping frequency bands corresponding to the sensing spectrum and ARS. Since the sensing spectrum and ARS are in parallel, Figure 4 There is no difference frequency between the two bands in (b), which is the characteristic of the traditional vernier effect formed by the series structure. Figure 4 In (a), the Vernier effect envelope is obtained by fitting the superimposed peaks, and the free spectral range is 50.46 nm.

[0100] Step S104, obtaining the free spectral range of the sensing spectrum and the free spectral range of the vernier effect envelope in the initial state according to the sensing spectrum intensity and the vernier effect envelope in the initial state; Step S104 specifically includes:

[0101] The free spectral range of the sensing spectrum intensity, the reference spectrum intensity and the vernier effect envelope is obtained by using formula 10, formula 11 and formula 12;

[0102] Formula 10;

[0103] Formula 11;

[0104] Formula 12;

[0105] Among them, FSR s 、FSR r and FSR eThey are the sensing spectrum intensity, the reference spectrum intensity and the free spectral range of the vernier effect envelope.

[0106] Step S105, obtaining the sensitivity and envelope sensitivity of FFPI according to the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope, and step S105 specifically includes:

[0107] According to the free spectral range of the sensing spectrum intensity and the free spectral range of the vernier effect envelope, the sensitivity of the sensing spectrum and the sensitivity of the vernier effect envelope are obtained through formula 13 and formula 14;

[0108] Formula 13;

[0109] Formula 14;

[0110] in, is the free spectral range of the sensing spectral intensity, is the free spectral range of the Vernier effect envelope, is the sensitivity of the sensing spectrum, is the sensitivity of the cursor effect envelope, is the refractive index of the FFPI cavity medium, is the modulation length, is the FFPI cavity length, is the wavelength in vacuum, is the refractive index change of the surrounding medium.

[0111] Step S106, obtaining the refractive index magnification of the vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and performing refractive index amplification based on the refractive index magnification. Step S106 specifically includes:

[0112] According to the sensitivity of the sensing spectrum and the sensitivity of the vernier effect envelope, the refractive index magnification of the vernier effect is obtained by formula 15;

[0113] Formula 15;

[0114] in, is the refractive index magnification of the vernier effect, FSR s is the free spectral range of the sensing spectrum, FSR e is the free spectral range of the Vernier effect envelope, is the refractive index of the FFPI cavity medium, is the modulation length, is the FFPI cavity length, is the wavelength in vacuum, is the refractive index change of the surrounding medium.

[0115] It can be intuitively obtained from the free spectral range of the sensing spectrum and the envelope, but it is essentially obtained from the optical path difference and Decide when When set to any small value, theoretically can be very large, however, in actual measurements, It is limited by the limited wavelength range selected by the optical spectrum analyzer (OSA). When the wavelength range is equal to FSRe, there is a minimum , we can get:

[0116] Formula 16;

[0117] Where span is the wavelength range selected during the measurement.

[0118] Figure 5 is a corresponding diagram of the initial refractive index of an embodiment of the present invention, Figure 5 (a), 5 (c) and 5 (e) show the reflectance spectra of FFPI-1, FFPI-2 and FFPI-3. Near 1500nm, the free spectral ranges of the three sensor interference spectra are 5.94nm, 3.14nm and 1.70nm, respectively, and the corresponding optical path differences are approximately 378.79µm, 716.56µm and 1323.53µm, respectively. As the refractive index of the medium in the FFPI cavity increases, the optical path difference increases, resulting in a red shift in the spectrum. Figure 5 (b), 5(d) and 5(f) show Figure 5 The troughs of (a), (c) and (e) drift at 1500 nm, and the refractive index sensitivities are 1121.87 nm / RIU, 1134.73 nm / RIU and 1131.52 nm / RIU, respectively. The measured sensitivity values ​​are independent of the length of the FFPI cavity, which is consistent with the conclusion of formula (12). In addition, the determination coefficient (R2) values ​​of the three FFPIs are 0.9914, 0.9941 and 0.9892, respectively, indicating that the sensitivity curves have good linearity.

[0119] The above sensing spectra are demodulated based on the proposed vernier effect scheme. Figure 6 is a demodulation envelope diagram of the vernier effect of a FFPI according to an embodiment of the present invention. m = 45µm, the demodulation envelope diagrams of the cursor effect of the above three FFPIs are as follows: Figure 6 As shown in Figure 2, each envelope is red-shifted as the RI value increases. Figure 6 The trough shifts of the spectra at 1500 nm in (a)-6(c) are shown in Figure 6(d). Due to the vernier effect, the RI sensitivity is amplified to 9320.39 nm / RIU, 17781.21 nm / RIU and 33374.78 nm / RIU. Figure 5 Compared with the sensitivity of the FFPI, the amplification factors are 8.31, 15.67, and 29.50, respectively, which are consistent with the theoretical values ​​of 8.34, 15.54, and 29.28 in formula 15. The results show that lengthening the cavity of FFPI helps to improve the amplification.

[0120] Figure 7 The vernier effect of the embodiment of the present invention is shown in FIG. m The sensitivity magnification under Figure 6 The FFPI-3 has the longest cavity length, so its sensitivity amplification factor is the largest among the three FPPIs mentioned above. Figure 7 It shows that at 30℃, when L m =45μm, 25μm, 12.1μm and 10.6μm, the envelope of the vernier effect drifts with the increase of the refractive index. According to formula 16, L m =12.1μm is close to the theoretical L m The minimum value of . Figure 7 (e) shows Figure 7 The trough in (a)-7(d) drifts around 1500 nm, and the refractive index sensitivities are 33374.78 nm / RIU, 58329.78 nm / RIU, 121168.85 nm / RIU, and 133990.11 nm / RIU, respectively. Figure 7 (e) with Figure 5 (f) Compared with the above, the magnifications are 29.50, 51.55, 107.09 and 118.42, respectively, which are consistent with the theoretical values ​​of 29.28, 51.37, 109 and 119.06. m =10.6 μm, the sensitivity is 133990.11 nm / RIU, the wavelength resolution is selected as 0.02 nm, and the calculated resolution is 1.49×10-7 RIU.

[0121] In summary, we proposed an ultra-sensitive refractive index sensor based on a single FFPI vernier effect demodulation. The ARS extracted from a sensing spectrum acts as a reference interferometer to superimpose with the sensing spectrum to form a vernier effect. By optimizing the cavity length and modulation length L m， The ultra-high refractive index sensitivity of 133990.11 nm / RIU, the amplification factor of 118.42 and the resolution of 1.49 × 10 -7nm / RIU. In the new method, ARS is no longer affected by environmental changes and the sensitivity can be amplified according to actual needs. Most importantly, this scheme provides a universal solution to improve the sensitivity of almost all interferometric sensors.

[0122] Device Example 1

[0123] According to an embodiment of the present invention, a refractive index amplification device based on single FFPI vernier effect demodulation is provided. Figure 8 Schematic diagram of a refractive index amplification device based on single FFPI vernier effect demodulation according to an embodiment of the present invention. Figure 8 As shown, the refractive index amplification device based on single FFPI vernier effect demodulation according to an embodiment of the present invention specifically includes:

[0124] The spectrum acquisition module 81 is used to obtain a double-beam interference signal by reflecting the sensing light source through the FFPI composed of the optical fiber core misalignment pair, and calculate the total light intensity of the sensing signal of the double-beam interference signal, and obtain the sensing spectrum light intensity in the initial state according to the total light intensity of the sensing signal of the double-beam interference signal;

[0125] A reference spectrum module 82 is used to obtain a first modulation length and a second modulation length according to the modulation length, perform secondary modulation on the sensing spectrum intensity in the initial state according to the modulation function based on the first modulation length and the second modulation length, obtain the modulated light intensity, and obtain the reference spectrum interference light intensity according to the modulated light intensity;

[0126] The vernier effect envelope module 83 is used to superimpose the sensing spectrum intensity in the initial state with the reference spectrum interference intensity and perform normalization to obtain the vernier effect envelope;

[0127] A free spectrum range module 84, used for acquiring the free spectrum range of the sensing spectrum in the initial state and the free spectrum range of the vernier effect envelope according to the sensing spectrum intensity in the initial state and the vernier effect envelope;

[0128] A sensitivity module 85, for obtaining the sensitivity and envelope sensitivity of FFPI according to the free spectral range of the sensing spectrum and the free spectral range of the vernier effect envelope in the initial state;

[0129] The amplification module 86 is used to obtain the refractive index magnification factor of the vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and perform refractive index amplification based on the refractive index magnification factor.

[0130] Device Example 2

[0131] An embodiment of the present invention provides a refractive index magnification device based on single FFPI vernier effect demodulation, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program implements the steps described in the method embodiment when executed by the processor.

[0132] Device Example 3

[0133] An embodiment of the present invention provides a computer-readable storage medium, on which a program for implementing information transmission is stored. When the program is executed by a processor, the steps described in the method embodiment are implemented.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A refractive index amplification method based on single FFPI vernier effect demodulation, characterized in that: include: S1, obtaining a double-beam interference signal by reflecting a sensing light source through an FFPI composed of an optical fiber core misalignment pair, calculating the total light intensity of the sensing signal of the double-beam interference signal, and obtaining the sensing spectrum light intensity in an initial state according to the total light intensity of the sensing signal of the double-beam interference signal; S2, obtaining a first modulation length and a second modulation length according to the modulation length, performing secondary modulation on the sensing spectrum intensity in the initial state according to the modulation function based on the first modulation length and the second modulation length, obtaining the modulated light intensity, and obtaining the reference spectrum interference light intensity according to the modulated light intensity; S3, adding the sensing spectrum intensity in the initial state to the reference spectrum interference intensity and performing normalization to obtain a vernier effect envelope; S4, acquiring the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope according to the sensing spectrum intensity in the initial state and the vernier effect envelope; S5, obtaining the sensitivity and envelope sensitivity of FFPI according to the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope; S6. Obtaining a refractive index magnification factor of a vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and performing refractive index amplification based on the refractive index magnification factor; The step S2 specifically includes: Obtain the modulation function according to formula 3; Formula 3: in, is the wavelength in vacuum, is the modulation length; Obtain a first modulation length and a second modulation length according to the modulation length, wherein the first modulation length and the second modulation length satisfy Formula 4; L m =L m2 -L m1 Formula 4; Among them, L m2 is the first modulation length, L m1 is the second modulation length; Modulating the sensing spectrum intensity in the initial state according to the first modulation length by formula 3 to obtain a first modulation result, and extracting an upper sideband frequency band of the first modulation result to obtain a spectrum corresponding to the upper sideband frequency band; Modulating the spectrum corresponding to the upper sideband frequency band by the second modulation length using formula 3 to obtain a second modulation result, extracting the lower sideband frequency band of the second modulation result, and obtaining the spectrum corresponding to the lower sideband frequency band as the reference spectrum interference light intensity; Wherein, the first modulation result and the second modulation result are obtained by formula 5; Formula 5: in, is the initial state sensing spectrum intensity, , , and are the light intensities of the two reflecting surfaces, is the FFPI cavity length, , is the wavelength in vacuum, is the refractive index change of the ambient medium, is the refractive index of the FFPI cavity medium; The reference spectrum intensity is obtained by modulating the light intensity, which is recorded as ; Formula 6.

2. The method according to claim 1, characterized in that The step S1 specifically includes: The sensing light source is reflected through the FFPI composed of the optical fiber core misalignment pair to obtain the reflection spectrum; Performing fast Fourier transform on the reflection spectrum to obtain a spatial spectrum; Acquire a first parameter and a second parameter according to the frequency band and the peak value of the spatial spectrum, and calculate the sensing spectrum intensity according to the first parameter and the second parameter by using Formula 1; Formula 1; in, , , and are the light intensities of the two reflecting surfaces, is the refractive index of the FFPI cavity medium, is the wavelength in vacuum, is the FFPI cavity length; Obtain the initial state sensing spectrum intensity according to formula 2; Formula 2: in, , is the wavelength in vacuum, is the refractive index change of the ambient medium, is the FFPI cavity length.

3. According to the method of claim 2, the S3 specifically comprises: Adding the sensing spectrum intensity to the reference spectrum intensity, Formula 7: The addition result is normalized by formula 8, Formula 8 ； The envelope of the cursor effect is obtained as: Formula 9: in , ≈ ,in, is the FFPI cavity length, is the modulation length, is the wavelength in vacuum, is the refractive index change of the surrounding medium.

4. According to the method of claim 2, the S4 specifically comprises: The free spectral range of the sensing spectrum intensity, the reference spectrum intensity and the vernier effect envelope is obtained by using formula 10, formula 11 and formula 12; Formula 10: Formula 11: Formula 12: Among them, FSR s 、FSR r and FSR e They are the sensing spectrum intensity, the reference spectrum intensity and the free spectral range of the vernier effect envelope.

5. The method according to claim 1, characterized in that The S5 specifically includes: According to the free spectral range of the sensing spectrum intensity and the free spectral range of the vernier effect envelope, the sensitivity of the sensing spectrum and the sensitivity of the vernier effect envelope are obtained by using formula 13 and formula 14; Formula 13: Formula 14: in, is the free spectral range of the sensing spectral intensity, is the free spectral range of the Vernier effect envelope, is the sensitivity of the sensing spectrum, is the sensitivity of the cursor effect envelope, is the refractive index of the FFPI cavity medium, is the modulation length, is the FFPI cavity length, is the wavelength in vacuum, is the refractive index change of the surrounding medium.

6. The method according to claim 1, characterized in that The S6 specifically includes: According to the sensitivity of the sensing spectrum and the sensitivity of the vernier effect envelope, the refractive index magnification of the vernier effect is obtained by formula 15; Formula 15: in, is the refractive index magnification of the vernier effect, FSR s is the free spectral range of the sensing spectrum, FSR e is the free spectral range of the Vernier effect envelope, is the refractive index of the FFPI cavity medium, is the modulation length, is the FFPI cavity length, is the wavelength in vacuum, is the refractive index change of the surrounding medium.

7. A refractive index amplification device based on single FFPI vernier effect demodulation, characterized in that: The refractive index amplification method based on single FFPI vernier effect demodulation according to any one of claims 1 to 6, comprising: A spectrum acquisition module is used to obtain a double-beam interference signal by reflecting a sensing light source through an FFPI composed of an optical fiber core misalignment pair, and calculate the total light intensity of the sensing signal of the double-beam interference signal, and obtain the sensing spectrum intensity in an initial state according to the total light intensity of the sensing signal of the double-beam interference signal; A reference spectrum module, used for obtaining a first modulation length and a second modulation length according to a modulation length, performing secondary modulation on the sensing spectrum light intensity in the initial state according to a modulation function based on the first modulation length and the second modulation length, obtaining the modulated light intensity, and obtaining a reference spectrum interference light intensity according to the modulated light intensity; A vernier effect envelope module, used for superimposing the sensing spectrum intensity in the initial state with the reference spectrum interference intensity and performing normalization to obtain a vernier effect envelope; A free spectrum range module, used for acquiring the free spectrum range of the sensing spectrum in the initial state and the free spectrum range of the vernier effect envelope according to the sensing spectrum intensity in the initial state and the vernier effect envelope; A sensitivity module, used for obtaining the sensitivity and envelope sensitivity of FFPI according to the free spectral range of the sensing spectrum in the initial state and the free spectral range of the vernier effect envelope; The amplification module is used to obtain the refractive index magnification factor of the vernier effect according to the sensitivity and envelope sensitivity of the FFPI, and perform refractive index amplification based on the refractive index magnification factor.

8. A refractive index amplification device based on single FFPI vernier effect demodulation, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the steps of the refractive index amplification method based on single FFPI vernier effect demodulation as claimed in any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores an implementation program for information transmission, and when the program is executed by a processor, the steps of the refractive index amplification method based on single FFPI vernier effect demodulation as described in any one of claims 1 to 6 are implemented.

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