Optical Fiber Temperature Sensing Based On SPR And Diamond NV Center

As one of the seven basic physical quantities,it is very important to detect temperature accurately.Optical fiber sensor has the advantages of light weight,small volume,remote measurement,corrosion resistance,electromagnetic interference resistance,high sensitivity and so on,becoming an important research direction of new temperature sensor.In this paper,optical fiber temperature sensors based on surface plasmon resonance（SPR）and diamond nitrogen vacancy（NV）color centers are fabricated,and their sensitivity is optimized.The performance of the two sensors is analyzed and compared.The specific work of this paper is summarized as follows:（1）A PDMS/graphene composite temperature sensor based on SPR principle was developed.The sensor consists of a side-polished optical fiber for photoexcitation and readout,a gold layer for SPR excitation,a graphene layer for enhanced SPR effect and accelerated sensing response,and a PDMS layer as a thermo-optic response material.It was found that the PDMS/graphene composite structure improved the temperature sensitivity of the sensor from 0.31 nm·℃^-1 to 1.56 nm·℃^-1.In addition,the graphene layer reduces the sensor’s response time from 65 s to 6 s.It has the characteristics of high sensitivity and fast response.（2）The optical fiber temperature sensing system based on diamond NV color center was built,the system parameters were optimized and the temperature sensing test was completed.This paper introduces the operation and performance of the main components of the system,such as phase-locked amplifier,microwave source,microwave amplifier,helmholtz coil,etc.,and builds the optical fiber temperature sensing system based on this.The system parameters including laser power P_L,microwave power P_M,modulation frequency f_m,modulation depthν_m and phase-locked time constantτ_L were optimized by theoretical calculation of sensitivity.After optimization,the sensitivity of theoretical calculation was increased from 167.5m K·H_Z^-1/2 to 16.0 m K·H_Z^-1/2.Finally,the temperature sensitivity of the sensor is tested by Zeeman splitting principle.（3）The sensitivity of optical fiber temperature sensor system based on diamond NV color center was optimized,and a temperature sensor based on PDMS-magnet structure for magnetic field assisted temperature measurement was proposed and studied.Firstly,the magnetic field sensitivity of the temperature sensor was optimized,and the magnetic field sensitivity was increased from 442 n T·Hz^-1/2 to 40 p T·Hz^-1/2 by 5 orders of magnitude under the support of magnetic collector and tapered fiber.Then the temperature is measured indirectly by high magnetic field sensitivity,and the sensitivity of sensor is characterized by two ways.The results show that the temperature noise spectrum decreases from 5.63 m K·Hz^-1/2 to 4.39 m K·Hz^-1/2,increasing by 21%.The sensitivity was increased by 6 times from 86.0 k Hz·K^-1 to 601.5k Hz·K^-1 by the resonant frequency valley drift scale.The results show that the correlation coefficient between fluorescence intensity and temperature is 80.6℃^-1.The innovations of this paper are as follows:（1）A fiber optic SPR temperature sensor covered with monolayer graphene and PDMS was proposed to improve the sensitivity and response time of temperature sensor simultaneously.（2）A diamond NV color center fiber optic temperature sensor with magnetic-PDMS structure for magnetic field assisted temperature measurement was proposed.The temperature sensitivity can be improved by stimulating the multi-valleys of NV color center.