Hollow-core Bragg Fiber And Its Application In Dual-wavelength Erbium-doped Fiber Laser

High performance multi-wavelength fiber laser has wide application prospect in optical communication system and optical sensor fields.In order to achieve multi-wavelength erbium-doped fiber lasers with good performance,high stability,easy fabrication at room temperature,it is necessary to find an effective method to suppress the mode competition caused by the homogeneous gain broadening effect exists in erbium-doped fiber.Hollow core Bragg fiber,which guides light by the bandgap effect caused by the periodic structure of cladding,has many advantages such as low loss,controllable dispersion,tunable nonlinear coefficient and so on,which makes it have a broad application prospect in optical fiber communication,dispersion compensation and in the field of high power laser transmission.This paper takes hollow core Bragg fiber as a breakthrough,to carry out its theoretical and experimental researches,and based on the actual newly hollow core Bragg fiber,this paper proposed and achieved a switchable and tunable erbium-doped fiber laser at room temperature.The main results obtained are as follows:1.The bandgap characteristics of hollow core Bragg fiber were studied using the transfer matrix method.The relationship between the bandgap characteristics of hollow core Bragg fiber and cladding parameters was studied,including the number of periodical layers,thickness of high and low refractive index layer,refractive index contrast,which has an important guiding significance on the design of hollow core Bragg fiber and the actual production.2.Considering the actual production process of hollow core Bragg fiber and to expand the application fields of the hollow core Bragg fiber,a low refractive index contrast Ge-doped hollow core Bragg fiber with a large air core was designed.The theoretical results show that the band gap of the hollow core Bragg fiber is located in the 1550nm band with a minimum loss of 4.5dB/m,and the band gap spectrum has broadband comb spectrum output,which can be used as the fiber filter to modulate the lasing output.3.A hollow core Bragg fiber with ultra wide bandwidth and low loss was proposed and designed.By increasing the fiber size,the band gap can be covered to 4000nm,and the loss of band gap is 10-8 dB/m.Based on the existing fabrication process and material,the design realizes long distance transmission with a low loss on common transmission window,which will have important application prospects in optical communication system.4.The low refractive index contrast Ge-doped hollow core Bragg fiber with a large air core was successfully prepared using the chemical vaporous deposition method.Simulation results show that the band gap position of the actual optical fiber moved to the short wavelength direction with a 5nm shift,and the loss increased by 1dB/m,which was consistent with the designed structure.5.A switchable and tunable Erbium-doped fiber lasers using a homemade hollow core Bragg fiber was proposed.To the best of our knowledge,it is the first time that hollow core Bragg fiber is used as a comb filter in the EDFL.With the introduction of hollow core Bragg fiber,strong mode competition in EDFL is suppressed and a switchable and stable dual-wavelength EDFL with a SMSR as high as 50 dB is achieved.By adjusting the polarization controllers(PCs),the output lasing can be switched between single and dual-wavelength lasing at room temperature.Moreover,the wavelength shift and peak power fluctuation are monitored to be less than 0.1 nm and 2 dB at a 3-min interval over half an hour.Contrast experiments have also been carried out,which confirms the superiority of hollow core Bragg fiber in enhancing the stability and SMSR in EDFL.