Research On Environmental Sensing Characteristics Of Long Period Fiber Bragg Grating

Fiber gratings can be divided into long-period fiber gratings and Bragg fiber gratings according to the length of the period.Long-period fiber gratings?LPFG?have a series of advantages such as small volume,low additional loss,good wavelength selectivity and low cost.Long-period fiber gratings have a wide range of applications in the field of environmental sensing.By using a high-frequency CO₂ laser pulse,a long-period fiber gratings with a period of 600?m were written into a conventional single-mode fiber grating and a fine-core micro-nano fiber of a diameter of 11?m.This paper mainly studied the environmental sensing characteristics of long-period fiber gratings,such as temperature,refractive index,and the concentration of pollutants in the air.The main research contents and results are as follows:?1?The relationship between the resonant wavelength of the fiber grating transmission spectrum and the ambient temperature was studied.When the ordinary single-mode fiber was used for temperature sensing,the center wavelength of the resonant peak shifts toward the long-wave direction with increasing temperature,and its temperature sensitivity is 0.038 nm/°C.When the grating prepared by micro-nano fiber was used,the temperature rise presents an opposite trend,that is,the temperature rises and its center wavelength shifts into the short-wave direction,with a higher average temperature sensitivity of 0.140 nm/°C.?2?The refractive index sensing experiment of the fiber grating on the liquid was carried out.The experimental results showed that the center wavelength of the resonance peak changed linearly with the refractive index.The larger the refractive index resulted in a larger central wavelength.The long-period micro/nano fiber grating has a refractive index sensitivity of 512 nm/RIU.?3?The sol-gel film layer was coated on the surface of the long-period micro-nano fiber grating by the pulling method.The center wavelength of the resonant peak of the micro/nano fiber changes quadratically with the change of the concentration of polution molecules.The average sensitivity is about 8.78 nm/?g/m³?.In this thesis,long-period fiber gratings were prepared by CO₂ laser pulse direct writing.Micro-nano fiber gratings have higher ambient temperature sensing sensitivity than the ordinary fiber gratings.Micro-nano fiber gratings also have considerable sensitivity,stability,and desorption capacity of pollutants in terms of liquid refractive index and environmental pollutant concentration measurement.This thesis provides a certain reference value for expanding the application of micro-nano fiber gratings in sensors.