Near-infrared waveband based double-peak PCF concentration and magnetic field double-parameter sensing system
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a near-infrared waveband-based double-peak PCF concentration and magnetic field double-parameter sensing system.
Background
Surface Plasmon Resonance (SPR) exists between a metal and a medium (or air), and Surface Plasmon Polaritons (SPP) are excited using a total reflection evanescent wave. The SPR sensing technology has become a multifunctional tool for monitoring the refractive index of an analyte, filtering light of a specific frequency and detecting the formation of a nano-biofilm due to its characteristics of high sensitivity, no background interference, no label on a sample, no need of further purification, real-time rapid detection, etc. In recent years, the concept of SPR sensors based on Photonic Crystal Fibers (PCF) has been proposed. A feature of photonic crystal fibers is their flexibility of design, so that dispersion, birefringence, nonlinearity, etc. can be tailored through different arrangements of air holes. These aspects make photonic crystal fibers particularly attractive in many fields and have wide applications in gas-based nonlinear optics, atom and particle guidance, ultra-high nonlinearity, rare earth-doped lasers, and sensing. The PCF-SPR sensor can realize perfect matching of a plasma mode and a fundamental mode, and has high sensitivity and resolution in refractive index detection because the effective refractive index of the fundamental mode can be designed to be between zero and the refractive index of a core material. The defects of large volume, high transmission loss and low sensitivity of the SPR sensor based on the prism and the traditional optical fiber are overcome. The PCF-SPR sensor has a plurality of structures at present.
H.m. huang et al (a high Magnetic Field Sensitive Photonic Crystal Based on Surface plasma Resonance,2020, sensors (base) 20 (18)) propose a PCF Magnetic Field sensor Based on SPR, using metallic gold as SPR excitation material, with air holes arranged in a square shape, forming two Fiber cores a and B to transmit light; however, the magnetic fluid material is filled with air holes, and the air holes are in the nanometer level, so that great difficulty is brought to manufacturing; a magnetic field sensor based on magnetofluid selectively filled photonic crystal Fiber, which is proposed by W.X.Zhang et al (Analysis of a magnetic field sensor based on photonic crystal Fiber 46: 43-47), consists of three layers of air holes, which are arranged in a regular hexagonal lattice and are also selected to be filled with magnetofluid materials in the air, thereby increasing the manufacturing difficulty; the change of the concentration of the liquid to be detected can cause the change of the refractive index of the liquid to be detected, thereby influencing the shift of the resonance loss spectrum; chen et al (N.Chen, M.Chang, X.L.Lu, J.Zhou and X.D.Zhang, digital Analysis of Midinared D-shaped Photonic-Crystal-Fiber Sensor based on Surface)plasma-Resonance Effect for Environmental Monitoring, Applied Sciences,2020,10(11):3897) proposes a D-type PCF index sensor based on the SPR Effect, operating in the near infrared band (2.9-3.6 μm), for Environmental Monitoring, the analyte being in direct contact with the gold layer and surrounding the whole D-type PCF, instead of just the polished surface, the cladding material being silicon, the three layers of pores in the cladding being arranged in a hexagonal lattice; sakib et al (M.N.Sakib, M.B.Hossain, K.F.Al-tabatabaie, I.M.Mehedi, M.T.Hasan, M.A.Hossain, I.S.Amiri, High Performance Dual Core D-Shape PCF-SPR Sensor Modeling amplifying Gold Coat, Results in physics,2019,15:102788) propose D-type PCF-SPR sensors using Gold coating and solid Dual Core, the refractive index range of the analyte is 1.45-1.48, the two solid fiber cores are symmetrical to the y axis, the energy coupling of the Dual Core and the metal layer is difficult, and the applicable detection range is narrow; s. Singh et al (S.Singh, Y.K. Prajapti, high sensitive passive sensor based on D-shaped PCF with gold-graphene layers on the polarized surface, Applied Physics A,2019,125:437) propose a D-type PCF refractive index sensor coated with gold and graphene layers on the polished surface, place two large air holes in the x direction of the solid fiber core, study the limiting loss spectrum when x direction polarized light is coupled; shentao et al (Shentao, Rongshaofeng, Zhangizian, Liang, Yangyao, Songming and Wang Dongxing, a D-type photonic crystal fiber temperature sensing device and method based on SPR (CN202011302617.0) disclose a D-type PCF sensing device capable of detecting temperature, coating Ag and Ta2O5A thin film, the sensitivity of detection being by wavelength shift.
The detection methods of PCF-SPR disclosed above are all based on some kind of coupling mode, and the resonance wavelength of single loss peak and its drift change are detected. However, the PCF-SPR sensor has a plurality of couplings simultaneously, and it is difficult and unstable to detect the peak value of only one coupling mode. Because there is a problem that the resonance wavelength fluctuation of the constraint loss peak and the constraint loss peak corresponding to a specific coupling mode cannot be distinguished in practical use, which results in the undetected state, Ying Guo et al propose (Ying Guo, Jianshe Li, Xinyu Wang, Shuhuan Zhang, Yundong Liu, Jie Wang, Shun Wang, Xiaojian Meng, Rui Hao, shukuang Li, high purity sensitive sensor based on D-shaped photonic crystal fiber core, Optics and Laser Technology 123(2020)105922) a bimodal detection photonic crystal fiber sensor, which detects the wavelength shift amount of two peaks respectively and has two sensitivities at the same time, but has no difference from the above unimodal photonic crystal fiber sensor in the detection method. Gongli Xiao et al propose (Gongli Xiao, Zetao Ou, Hongyan Yang, Yanping Xu, Jianyun Chen, Haiou Li, Qi Li, Lizhen Zeng, Yanron Den and Jianqing Li, An Integrated Detection base on a Multi-Parameter plasma Optical Fiber Sensor, Sensors 2021,21,803) double-peak Detection dual-Parameter photonic crystal Fiber Sensors, which detect two parameters simultaneously by loss peaks in two coupling modes, and also judge the refractive index and sensitivity of the test object according to the shift amount of the single-peak resonance wavelength and the resonance wavelength, and have low stability. The PCF-SPR sensor is essentially different from the method for judging the state of an analyte and calculating the sensitivity of the PCF-SPR sensor, and the high-sensitivity sensor proposed at present is also limited by the performance of a spectrometer, so most of PCF-SPR sensors only exist in a simulation theory at present, and the actual manufacturing effect is poor. Therefore, it is very important to provide a new practical PCF structure and detection method operating in the near infrared band.
Disclosure of Invention
Aiming at the problems, the technical problem to be solved by the invention is to provide a near-infrared band double-peak PCF concentration and magnetic field double-parameter sensing system, and a novel analyte state (comprising refractive index, magnetic field or concentration) judgment method and a stable sensitivity calculation method.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the technical scheme is as follows: based on near-infrared wave band bimodal PCF concentration and two parameter sensing systems in magnetic field, its characterized in that: the device comprises a light source (1), a single-mode optical fiber (2), a sensing unit (3), a sensing unit (4), a spectrum analyzer (5), a photoelectric converter (6), a signal processing module (7) and a computer (8);
further, the sensing unit (3) is a photonic crystal fiber (3-1); the device is composed of a cladding (3-2), a silver film (3-6) and an analysis liquid (3-7), wherein the cladding (3-2) comprises 10 circular air holes (3-3), 12 circular air holes (3-4) and 3 circular air holes (3-5); the method is characterized in that: the air holes (3-3) are symmetrically arranged about the y axis of the optical fiber; the air holes (3-4) are positioned between the air holes (3-3) and the air holes (3-5); the air holes (3-5) are positioned at the innermost layer of the cladding (3-2) and are arranged in a triangular shape; the silver film (3-6) is arranged at the boundary of the cladding (3-2) and the analysis liquid (3-7);
further, the sensing unit (3) is characterized in that: the distance Lambda between the air holes in the cladding (3-2) is 2 micrometers, the diameter of the cladding (3-2) is 15 micrometers, the diameter of the air holes (3-3) is 1.5 micrometers, the diameter of the air holes (3-4) is 0.6 micrometers, and the diameter of the air holes (3-5) is 2 micrometers; the thickness of the silver film (3-6) is 40 nm;
further, the sensing unit (4) is a photonic crystal fiber (4-1); the device is composed of a cladding (3-2), a silver film (4-5), a graphene layer (4-6) and an analysis solution (4-4); wherein the cladding (3-2) consists of 8 circular air holes (4-2) and 7 circular air holes (4-3); the method is characterized in that: the photonic crystal fiber (4-1) is symmetrical about the y axis; the air holes (4-2) are arranged in a semi-hexagonal shape at the outermost layer of the optical fiber, the air holes (4-3) at the inner layer are arranged in a hexagonal shape, and the middle part of the air holes is the core part of the optical fiber;
further, the sensing unit (4) is characterized in that: the air hole pitch Lambda of the photonic crystal fiber (4-1) is 1.5 micrometers, the diameter of the photonic crystal fiber (4-1) is 6 micrometers, the diameter of the air hole (4-2) is 0.9 micrometers, the diameter of the air hole (4-3) is 0.8 micrometers, the thickness of the silver film (4-5) is 30nm, the thickness of the graphene layer (4-6) is 1.0nm, and the number of layers is 3; the substrate material of the photonic crystal fiber (4-1) is fused silica, and the refractive index of the fused silica is defined by a Sellmeier formula:
where λ is the wavelength of the light wave, parameter a1=0.6961663,a2=0.4079426,a3=0.8974794,b1=0.0684043um,b2=0.1162414um,b39.896161um, so the dispersion of the PCF transmission mode can be calculated;
further, a photonic crystal fiber (3-1) and a photonic crystal fiber (4-1) are prepared by adopting a stacking-drawing technology, the lengths of the photonic crystal fiber (3-1) and the photonic crystal fiber (4-1) are 20mm, and the silver film (3-6) can be obtained by utilizing a radio frequency magnetron sputtering method;
the stacking-wire drawing technology comprises the following steps: firstly, pretreating a quartz sleeve, drawing a capillary tube according to parameters in an ultra-clean environment at the drawing temperature of 1900-2000 ℃, then carrying out tapering and hole sealing on two ends of the capillary tube by using oxyhydrogen flame, stacking the capillary tube in the quartz sleeve according to design requirements to form a required structure, filling a gap by using a pure quartz rod, sintering the quartz sleeve and the capillary tube together by using oxyacetylene flame, and preparing the photonic crystal fiber on a wire drawing tower by using a twice wire drawing technology;
further, the analysis liquid (3-7) is a liquid to be detected, the change of the concentration of the liquid to be detected can change the refractive index of the liquid to be detected, the analysis liquid (4-4) is Magnetic Fluid (MFs), and the type of the used magnetic fluid is water-based Fe3O4The magnetofluid is prepared by a dispergation method, wherein the magnetofluid is prepared by the chemical action of ferric salt or ferrous salt to generate Fe3O4Or Fe2O3Then adding a dispersing agent and a carrier, stirring to enable magnetic particles to be adsorbed in the dispersing agent and the carrier, finally heating and separating the colloid from the solution to obtain a magnetic fluid, wherein the change of the magnetic field intensity (H) can change the refractive index (MFs), and further the purpose of double-parameter measurement is achieved; the refractive index of MFs obeys the Langevin function:
wherein n ismIs the maximum refractive index value that can be reached by water-based ferroferric oxide Magnetofluid (MFs), ni is the original refractive index of the external magnetic field, Hc,nIs the critical magnetic field strength, alphaMFSetting parameters, wherein n represents a value that the refractive index of the water-based ferroferric oxide Magnetic Fluid (MFs) changes along with the change of the external magnetic field intensity, H is the magnetic field intensity, and T is the temperature; changes in magnetic field alter water-based ferroferric oxide Magnetofluids (MFs)) Refractive index of (a);
further, the near-infrared band based double-peak PCF concentration and magnetic field double-parameter sensing system is characterized in that: light signals emitted by a light source (1) are transmitted to a sensing unit (3) and a sensing unit (4) through a single-mode optical fiber (2), the sensing unit (3) and the sensing unit (4) are output to a spectrum analyzer (5) and a photoelectric converter (6), the photoelectric converter (6) converts the light signals into electric signals and outputs the electric signals to a signal processing module (7), and the electric signals are finally displayed in a computer (8);
further, the light source (1) outputs an optical signal in a wavelength band of 750-2000 nm;
further, the optical signal is transmitted to the sensing unit (3) and the sensing unit (4) through the single mode fiber (2), and the optical fiber is characterized in that: the wave vectors of the plasma waves excited on the surfaces of the silver films (3-6) and (4-5) and the wave vectors of the incident light field reach phase matching in a specific wavelength range, and are coupled twice to generate two resonance loss peaks; surface Plasmon Resonance (SPR) is very sensitive to medium environment, the change of the refractive index RI of the analysis liquid (3-7) or the analysis liquid (4-4) can change the resonance condition, so that two resonance loss peaks are obviously changed, and high-sensitivity and real-time detection can be realized;
further, the near-infrared band based double-peak PCF concentration and magnetic field double-parameter sensing system is characterized in that: an optical signal is emitted by a light source (1) and transmitted to a sensing unit (3) and a sensing unit (4) through a single-mode optical fiber (2), when the refractive index of an analysis liquid (3-7) or an analysis liquid (4-4) is changed, the condition of the plasma resonance phenomenon of a photonic crystal optical fiber (3-1) or a photonic crystal optical fiber (4-1) is changed, two coupling modes are changed, and the distance delta lambda between two peaks displayed in a spectrum analyzer (5) is changedpeakA significant change occurs in that the distance between the two peaks decreases when the refractive index of the analysis liquid (3-7) or the analysis liquid (4-4) increases, and the distance between the two peaks increases when the refractive index of the analysis liquid (3-7) or the analysis liquid (4-4) decreases. The sensitivity was calculated via a bimodal sensitivity formula.
The bimodal sensitivity formula is:
s=(Δλpeak2-Δλpeak1)/Δna (3)
in the formula, delta lambdapeakIs the difference in wavelength of two loss peaks, Δ n, at the same refractive indexaAs a change in concentration/magnetic field, Δ λpeak2-Δλpeak1Is the difference in wavelength distance of two peaks at two different concentrations and magnetic field states, and s is the sensitivity of the double peak. Wherein Δ λpeakThe size of the magnetic field corresponds to the concentration and the magnetic field state of the sensing unit (3) or the sensing unit (4); the sensing unit (3) or the sensing unit (4) will carry delta lambdapeakThe optical signal of the numerical value is transmitted to a photoelectric converter (6), the photoelectric converter (6) converts the optical signal into an electric signal and outputs the electric signal to a signal processing module (7), and finally information of the analysis liquid (3-7) or the analysis liquid (4-4) is displayed in a computer (8);
further, the near-infrared band based double-peak PCF concentration and magnetic field double-parameter sensing system is characterized in that: when the magnetic field and the concentration are measured simultaneously, the following formula is needed to be used for calculation:
in the formula (4) < delta > < lambda >1Is the variation of the distance between two peaks after concentration change, Delta lambda2Is the amount of change in the distance between two peaks after concentration change, SnAnd SBSensitivity of concentration and magnetic field, respectively, Delta lambdapeak2-Δλpeak1The difference between the wavelength distances of two peaks at two different concentrations and in the magnetic field state is represented by Δ n and Δ B, which are the variation of the concentration and the magnetic field, respectively, and the variation of the concentration and the magnetic field can be obtained from the formula (5).
The invention has the structure that: based on near-infrared waveband bimodal PCF concentration and magnetic field dual-parameter sensing system.
Compared with the prior art, the invention has the beneficial effects that:
1. the near-infrared waveband double-peak PCF concentration and magnetic field based double-parameter sensing system disclosed by the invention is special in structure, greatly increases the birefringence characteristic and the dispersion characteristic, is beneficial to maintaining the polarization state, and can be widely applied to the fields of polarization control, precise optical fiber sensing and the like.
2. The near-infrared waveband double-peak PCF concentration and magnetic field based double-parameter sensing system provided by the invention has two constraint loss peaks, and the problems of poor sensitivity measurement precision and poor actual test effect of the traditional PCF-SPR sensor are solved through calculation of the double-peak sensitivity formula provided by the invention, so that the stability of the measuring system is improved.
3. The working wavelength of the near-infrared band-based double-peak PCF concentration and magnetic field dual-parameter sensing system is positioned in the near-infrared band, and the interference of external environment light to the sensor can be ignored.
4. The near-infrared band double-peak PCF concentration and magnetic field double-parameter sensing system disclosed by the invention adopts silver as an SPR excitation material and adopts the liquid to be detected and Magnetic Fluid (MFs) as analysis liquid, so that the concentration and magnetic field double-parameter measurement can be realized, the maximum sensitivity is 1.5nm/oe, and the system can be widely applied to the fields of sample detection, such as life science research, biochemistry, environmental monitoring and the like.
Drawings
FIG. 1 is a diagram of an apparatus for providing a near-infrared band based dual-peak PCF concentration and magnetic field dual-parameter sensing system.
Fig. 2 and fig. 3 are cross-sectional views of sensing units of a near-infrared band-based dual-peak PCF concentration and magnetic field dual-parameter sensing system provided by the invention.
FIG. 4 is a coupling diagram of a near-infrared band based dual-peak PCF concentration and magnetic field dual-parameter sensing system provided by the invention.
FIG. 5 is a graph of loss peaks for a near-infrared band based dual-peak PCF concentration and magnetic field dual-parameter sensing system.
Detailed Description
The following describes a specific embodiment of a near-infrared band based dual-peak PCF concentration and magnetic field based dual-parameter sensing system according to the present invention with reference to the accompanying drawings.
As shown in figure 1, the invention provides a device diagram based on a near-infrared band double-coupling photonic crystal fiber refractive index sensing method, a light signal emitted by a light source (1) is transmitted to a sensing unit (3) and a sensing unit (4) through a single mode fiber (2), when light is transmitted to a silver film (3-6) or a silver film (4-5), surface plasmon elementary phenomena occur on the silver film (3-6) or the silver film (4-5) due to inconsistent refractive index of an analysis liquid (3-7) or the analysis liquid (4-4), and two confinement loss peaks appear. The sensing unit (3) or the sensing unit (4) outputs to the spectrum analyzer (5) and the photoelectric converter (6), the photoelectric converter (6) converts an optical signal into an electric signal and outputs the electric signal to the signal processing module (7), and the electric signal is finally displayed in the computer (8);
as shown in fig. 2, for the cross-sectional view of the sensing unit provided by the method for sensing the refractive index of the near-infrared band double-coupled photonic crystal fiber, the sensing unit (3) is a photonic crystal fiber (3-1); the device is composed of a cladding (3-2), a silver film (3-6) and an analysis liquid (3-7), wherein the cladding (3-2) comprises 10 circular air holes (3-3), 12 circular air holes (3-4) and 3 circular air holes (3-5); the method is characterized in that: the air holes (3-3) are symmetrically arranged about the y axis of the optical fiber; the air holes (3-4) are positioned between the air holes (3-3) and the air holes (3-5); the air holes (3-5) are positioned at the innermost layer of the cladding (3-2) and are arranged in a triangular shape; the air holes influence the mode property, light can be controlled in the fiber core, the silver film (3-6) is arranged at the junction of the cladding (3-2) and the analysis liquid (3-7), and when an optical signal is transmitted to the photonic crystal fiber (3-1), the surface plasmon resonance phenomenon is caused by the existence of the silver film (3-6), so that high-sensitivity detection is realized;
as shown in fig. 3, for the cross-sectional view of the sensing unit provided by the method for sensing the refractive index of the near-infrared band double-coupled photonic crystal fiber, the sensing unit (4) is a photonic crystal fiber (4-1); the device is composed of a cladding (3-2), a silver film (4-5), a graphene layer (4-6) and an analysis solution (4-4); wherein the cladding (3-2) consists of 8 circular air holes (4-2) and 7 circular air holes (4-3); the method is characterized in that: the photonic crystal fiber (4-1) is symmetrical about the y axis; the air holes (4-3) are positioned at the innermost layer of the photonic crystal fiber (4-1) and are arranged in a hexagon shape; the air holes influence the mode property, light can be controlled in the fiber core, and the sensitivity of the sensor can be improved by using the graphene layers (4-6), so that high-sensitivity detection is realized;
as shown in FIG. 4, the present invention provides a double-coupling photonic crystal fiber double-coupling diagram, when the operating wavelength is 1200-2000nm, the sensing system can detect two confinement loss peaks, and the coupling between the fiber core and the silver film (3-6) or the silver film (4-5) occurs twice.
As shown in fig. 5, for the loss peak chart of different analyte concentrations and different magnetic field strengths provided by the present invention, when the operating wavelength is 1100nm-2000nm, the different magnetic field strengths and different analyte concentration changes will cause the strength and matching phase of the resonance coupling, thereby achieving the purpose of dual-parameter measurement.
The specific implementation method comprises the following steps:
detecting the concentration and the magnetic field of seawater by using a near-infrared band double-coupling photonic crystal fiber refractive index sensing method and a measuring system; the sensing unit is placed in seawater, the concentration of the seawater and the magnetic field influence the refractive index of an analysis liquid of the sensing unit, based on the surface plasma resonance principle, the device can generate two resonance loss peaks, and the distance delta lambda between the two loss peakspeakAnd the magnetic field and the concentration of the seawater can be calculated by the formulas (3), (4) and (5), and are finally displayed on a computer.