Research On Optical Fiber Sensing Characteristics Based On Flexible Optical Materials

In the past few decades,as one of the branches of photonic technology,optical fiber sensors have received widespread attention in the fields of national defense science and technology,medical monitoring,and geological exploration by virtue of their high sensitivity,small size,strong anti-electromagnetic interference ability and fast response speed.Because the material of optical fiber is Si O₂,the material is single,usually in some sensing applications such as heat,magnetism,electricity and other aspects need to combine some specific substances,in order to be competent in some complex test environments.In this paper,a flexible optical material polydimethylsiloxane（PDMS）,a magnetic field and temperature sensing based on Fabry-Pérot（F-P）interferometer structure（PDMS-doped magnetic manganese tetroxide nanoparticle end cap cavity）were carried out,based on PDMS thin film encapsulation U-shaped micro-nanofiber（MNF）bending and temperature sensing and PDMS-based fiber preparation and optical properties of the study.The main research content of this article is as follows:Firstly,magnetic field and temperature dual parameter fiber optic sensors with dual F-P structure were studied.The ferromagnetic material（Mn₃O₄ nanocrystalline material）is mixed into the PDMS,transferred to the end face of the optical fiber by impregnation,cured at high temperature,and formed into an F-P cavity cap,and at the same time cascaded a section of air cavity to form a cascaded F-P cavity interferometer.When a magnetic field is applied,a magnetic force acts on its surface,causing a change in cavity length that modulates the interference spectrum.Experimental results show that the maximum linear sensitivity of the sensor at 1310 nm wavelength is-563.2 pm/m T in the range of linear magnetic field strength of 0～14 m T.In addition,in the temperature range of 30～70°C,the temperature sensitivity of the sensor near the wavelength of 1550 nm is-1160 pm/°C,and the magnetic field can be sensed simultaneously with temperature according to the matrix algorithm.Secondly,the bending and temperature sensing characteristics of U-type MNF in PDMS-based thin-film packages were studied.In order to solve the problem of fragile and easy to break the MNF structure,the MNF is encapsulated into a PDMS film,and the film thickness（d）experiment can be made intoμm magnitude.The prepared sensor is closely attached to the bending device,and the static bending and dynamic bending of the sensor are tested by recording the output optical power,respectively.Experimental results show that under static bending,the output optical power of the sensor increases with the increase of bending curvature.At the same time,the smaller the d,the greater the bending sensitivity of the sensor,where the bending sensitivity is up to 15.46 m W/m^-1（d=650μm）.Under dynamic bending,the sensor shows excellent bending motion response,for example,in the human finger bending test,the bending signal caused by the fast and slow jitter of the finger can be clearly captured.In addition,the sensor exhibits a lower temperature response,with a temperature sensitivity of only 0.037 d B/°C near a wavelength of 1550 nm.At the same time,the three-dimensional surface sensing structure based on U-type MNF and the three-dimensional curve surface reconstruction theory based on curve curvature are proposed,and the reconstruction of three-dimensional curved surface is realized by MATLAB.Thirdly,the fiber preparation and sensing characteristics based on PDMS material were studied.PDMS was injected into PTFE Teflon tubes of different diameters,and PDMS core structures of different diameters were prepared,which were in theμm range and the refractive index was about1.424.In order to achieve the best light transmission efficiency,the PDMS optical fiber structure with cladding was prepared by lifting method and homogenization method,in which the diameter difference between the cladding and the core is about 64μm,and the refractive index is about 1.417.By building a spatial optocoupler lens system,the transmission spectrum of the PDMS fiber was tested and the transmission loss of the PDMS fiber was calculated.The optimal transmission band is about 650 nm and the transmission loss is about 0.8 d B/cm.The PDMS fiber exhibits excellent flexibility and robustness,can be easily wound,knotted and stretched without any mechanical fracture,and has great application prospects in wearable devices and flexible sensing fields.