Study On Surface Plasmon Resonance Refractive Index Sensing Based On Few-mode Optical Fiber

The surface plasmon resonance?SPR?sensor uses the fiber core as the carrier instead of the traditional prism structure to excite the SPR effect.It not only has the advantages that SPR technology is very sensitive to the refractive index change of the external environment medium,but also has the unique advantages of small optical fiber volume,electrical insulation,corrosion resistance,strong electromagnetic interference resistance,strong applicability,etc.Therefore,the optical fiber SPR sensor has a broad application prospect in the fields of medical diagnosis,drug development,public safety,environmental monitoring,etc.At present,the optical fiber SPR sensor is usually based on single-mode fiber or multimode fiber.In this paper,a fiber SPR sensor based on few-mode fiber is proposed.The high-order mode and SPP mode in few-mode fiber are resonant to enhance the resonance loss and sensitivity of the sensor.On this basis,a side orthogonal double cut optical fiber structure is proposed to solve the problem of polarization sensitivity of single throw fiber SPR sensor,so that high sensitivity can be realized without polarization control of input light.At the same time,a D-type single hole fiber dual parameter SPR sensor is proposed,which can realize the dual parameter sensing of temperature and magnetic field strength.The relationship between the size,position and other parameters of the metal nanowire and the performance of the sensor is analyzed.The main research contents of this paper include:?1?The development of SPR and the application of SPR technology are introduced.The characteristics and applications of few-mode fiber and side polished fiber are described.The theoretical basis of optical fiber SPR sensor is introduced,including the theory of surface plasmon resonance,the structure of optical fiber SPR sensor,the overview of metal materials and graphene materials.?2?A fiber SPR sensor based on few-mode fiber is proposed.LP₁₁ mode and SPP mode are used to obtain higher resonance loss.On this basis,a novel side orthogonal double cut fiber SPR sensor is proposed,which can realize polarization insensitive sensing,solve the polarization sensitive problem of side polished fiber SPR sensor based on metal mode and nanowire,and effectively reduce the requirements of sensing on light source and optical fiber devices.The sensor consists of side double cut optical fiber,nanowire and dielectric layer.The influence of various parameters on the sensing performance is studied systematically.Finally,it is proposed that graphene layer be plated on the wire to enhance the sensitivity of the sensor.?3?A D-type single hole fiber dual parameter SPR sensor based on few-mode fiber is proposed.A thermal sensitive PDMS film is coated on the polishing surface on the upper side of the D-type single hole fiber core to form channel 1,and magnetic fluid is filled into the air hole on the lower side of the fiber core to form channel 2.Au nanowires and Ag nanowires are used to excite different SPR effects.By coupling them with LP_11b mode of core,two loss peaks are formed at different wavelengths.By measuring the resonance wavelength drift of channel 1 and channel 2 and combining with the two parameter sensitive matrix,the change of the external environment temperature and magnetic field can be detected,the problem of temperature interference in the detection process of the optical fiber SPR magnetic field sensor can be solved,and the two parameter sensing of the magnetic field and temperature can be realized.Finally,an improved scheme is proposed,which adopts the structure of two core and few-mode fiber,so that the fiber core can not transmit LP_11a mode,so as to completely solve the interference problem that may occur when LP_11a mode exists,and improve the stability of the system.