Study Of Refractive Index And Temperature Sensor Device Fiber Grating Based On The Femtosecond Laser Micro-hole Technique

Optical fiber microfluidic sensors are widely used in pharmaceutical,biochemical sensing and environmental pollution detection due to their small size,high sensitivity,small sample capacity,and real-time detection.On the other hand,fiber optic devices have the advantages of light in weight,high integration,and easy reuse,"fiber on line" photonic devices have gained more and more applications.Therefore,how to make fiber microfluidic sensors has attracted people's research interest.In the past,people often used existing micro-structured optical fibers to construct optical microfluidic sensors,which have the advantages of convenient use and low optical transmission loss.However,the optical fiber structure is relatively fixed,and since the optical wave transmission channel and the microfluidic channel overlap or are close to each other,it is difficult to system integration.In recent years,with the vigorous development and wide application of femtosecond laser writing technology,people began to prepare microfluidic sensors by drilling or slotting on the optical fiber.This technology is flexible in operation,and the femtosecond laser has the advantages of small thermal damage area and high processing precision,which has been favored by researchers.The main works of this paper are:(1)Aiming at the problem of temperature cross-sensitivity of fiber optic sensors,a temperature compensated fiber optic microfluidic sensor based on femtosecond laser drilling technique is realized in this paper.Using femtosecond laser induced-water breakdown method,one uniform-sized microfluidic channel is written between the fiber Bragg grating(FBG)and the fiber gold plated end face.By performing Fourier analysis on the single reflection spectrum of the device,the spectral information of the FBG and Fabry-Perot(FP)resonators can be obtained simultaneously.Experiments show that the FBG and FP spectrum have different response characteristics to the ambient temperature and refractive index: the temperature change information can be obtained by detecting the FBG spectrum,and the temperature change part can be subtracted from the FP spectrum,so that the temperature compensated microfluidic refraction index change information can be obtained.The sensor proposed in this paper has the advantages of simple structure,high integration,good stability,etc.It has a good application prospect in the field of biochemistry,medicine and other sensing fields.(2)A phase-shifted fiber grating based on micro-hole filling is realized,that is,the femtosecond laser micromachining method is used to introduce a micro-hole channel in the middle of the Bragg grating,by filling different substances,such as solid ultraviolet glue,etc.A transmission window with a narrow line width is opened in the transmission spectrum of the grating with a bandwidth of 0.06513 nm.Different spectral properties are achieved by changing the filled material.We analyzed its temperature characteristics and found that the temperature stability of the device is improved by filling material compared to the bare grating.The device has the advantages of simple structure and good stability,and has potential application value in the fields of fiber narrow-band laser,erbium-doped fiber amplifier gain flatness and wavelength division multiplexing.