The Optical Device Prepared In Fiber By Femtosecond Laser And Its Performance Study

Based on optical fiber,more and more attention has been paid to optical components.As a member of the field of optical communication and optical fiber waveguide,the optical components have many advantages,such as the strong limitation to the optical signal,the small size,and the light weight and so on,which have provided the conditions of the wide application of the optical fiber waveguide.According to the preparation of the preform,there are many different types of fiber and they have a different role in many aspects.In recent years,we have prepared different structures about the fiber in the sensing and optical integration fields by modifying the fiber or combining with laser,which have expanded the application background of the optical fiber greatly.In this paper,we have tried to prepare the grating structure in the special fiber,and then we have studied the sensing characteristics about them.By using the femtosecond laser direct writing technology,we have prepared the fiber grating in the panda fiber(the fiber Bragg grating).In addition,we tried to combine the optical structure with the multimode fiber to prepare the optical fiber Fresnel zone plate.After the experiment,it is observed that the structure is stable and the focusing effect is obvious.It is found that there are two aspects in this paper as follows:Firstly,we prepared the PANDA fiber Bragg grating by the femtosecond laser direct writing technology.This method refers to the preparation process of femtosecond laser direct writing in the single-mode fiber Bragg grating.By adjusting the parameters continuously,we have made the fiber Bragg grating in the panda fiber,when the wavelength of femtosecond laser is 800 nm,the repetition rate is100 Hz,and the pulse energy is adjusted to 50 nJ.After observing its reflection spectrum,we have gotten the double-peak reflection spectrum.By researching the special double-peak structure,we can make a difference in the field of sensing.In this paper,we have a simple try in its sensing characteristics,such as the temperature and axial stress.Secondly,we prepared the fiber inscribing Fresnel zone plate in the large core multimode fiber by the femtosecond laser direct writing technique.Firstly,according to the mechanism of the interaction between femtosecond laser and the optical fiber,we have demonstrated the feasibility of laser processing in the large core multimode fiber.Then,we designed the structure reasonably based on the experiment of machining parameters.Lastly,we have gotten the optical fiber Fresnel zone plate,when the wavelength of femtosecond laser is400 nm,the repetition rate is 5kHz,and the pulse energy is adjusted to 48 nJ.To get the parameters of the experiment,we put a frequency doubling crystal through the light path.Then,we observed the structure of the Fresnel zone plate by optical microscope,and it was found that the structure was perfect.We have studied the focusing properties through the observation system,and the focusing effect is obvious.It showed that the functional optical devices were fabricated by femtosecond laser direct writing technique in the large core multimode fiber.