Research On Structure And Sensing Characteristics Of Coated Fiber Grating Sensor

Optical fiber sensing technology is a newly developed sensing technology that began in the 1970 s.It is characterized by replacing circuit wires with optical fibers as channels and media for sensing and transmission.Information is transmitted in optical fibers using signal light as a carrier.Changes in physical parameters such as temperature,stress,and refractive index of the outside world will change the parameters of light waves in the optical fiber,and the physical quantities of the outside world can be sensed by detecting changes in the waveform.At present,temperature and stress sensors made of fiber gratings are widely used in industrial production after forming a sensor network,and some sensor applications in refractive index,acceleration,and biology have also been vigorously developed.With the continuous improvement of the requirements of sensor detection accuracy,the sensor sensitivity that traditional fiber Bragg grating(FBG)can provide can no longer meet the demand,so a special structure with higher sensor sensitivity was developed and designed Fiber has become an urgent task.Under this background,long-period fiber grating(LPFG),chirped fiber grating(CFBG),and titled fiber grating(TFBG)Fiber gratings with a coupling mechanism that is completely different from traditional FBG have been introduced since the 1990 s.At the same time,the technology of coating or cladding material to improve the sensitivity of FBG has become a research hotspot.In this paper,the sensitivity of FBG and LPFG to temperature,stress and refractive index is measured,and the effect of material coating on the sensitivity of grating is studied.(1)The temperature sensor of FBG is measured,and the linear relationship between the center wavelength and the temperature is obtained.The temperature measurement of LPFG is compared with FBG,and it is concluded that LPFG is much better than FBG in temperature sensor.The micro bending stress and refractive index of LPFG are measured.The relationship between the center wavelength and the refractive index and stress is obtained,and the sensitivity is calculated.(2)The temperature sensitivity of FBG is measured by metal coating experiment,and the relationship between central wavelength and temperature is analyzed.It is concluded that the temperature sensitivity of FBG is obviously improved by metal coating,but the stability of the sensor is affected by the uneven coating and oxidation.(3)In the experiment of graphene coating on FBG,two coating methods based on evaporation deposition and pulsed laser deposition(PLD)were designed.Firstly,the graphene coated FBG was fabricated by evaporation deposition,and the sensitivity of the FBG was significantly improved by temperature measurement.Secondly,the graphene film was fabricated by laser pulse deposition to improve the uniformity of the coating.