Research On Tunable Narrow Linewidth Erbium-Doped Fiber Ring Laser

The tunable fiber laser has become an indispensable important laser light source module and core component in contemporary optical communication networks due to its excellent coherence,narrow line width,high power,flexible wavelength range and strong compatibility with optical communication systems.At present,tunable single-frequency fiber lasers for different new structures and bands are one of the hotspots of scholars in the laser field at home and abroad.Its research focus is mainly on the design of new tunable mechanisms and compressed linewidths.A variety of technologies,such as new filter structures,saturable absorbers,new cavity structures,ultra-narrow band filters,and fiber nonlinear effects,are commonly used to achieve narrow linewidth single-frequency fiber lasers with continuously tunable wavelengths and switchable wavelengths.This article focuses on the implementation of tunable narrow linewidth single-frequency fiber lasers.The main contents include:First,the realization methods of narrow linewidth single-frequency fiber laser and tunable fiber laser are analyzed and discussed,and a new type of cavity structure is discussed,which uses a Sagnac fiber ring mirror in the fiber ring laser cavity combined with a section of unpumped erbium-doped fiber.Due to its narrowband filtering effect,it can achieve a single longitudinal mode oscillation output,and use another section of unpumped erbium-doped fiber as a saturated absorber to suppress mode jumps to achieve stable laser output.Secondly,system analysis and Matlab simulations are carried out on the transmission characteristics of various fiber gratings,and the influence of fiber gratings' own parameters on transmission characteristics is studied.In order to optimize the parameters for the selection of phase-shifted fiber grating and uniform fiber grating in this paper.Thirdly,an unpumped erbium-doped fiber Sagnac all-fiber filter is researched,and discussed its filtering characteristics.According to the numerical simulation results,when the difference between the arm length difference of the coupler and erbium-doped fiber length is in the order of centimeters,the filtering characteristics are similar to the characteristics of a uniform fiber grating,but erbium-doped fiber Sagnac all-fiber filters show a very narrow transmission bandwidth;When the value of the arm length difference of the coupler has the same order of magnitude as erbium-doped fiber length,multiple transmission windows appear,causing the original transmission spectrum envelope to split,the transmission window is related to only the arm length difference of the coupler.In both cases,the transmission bandwidth is less than 6.42 MHz.Fourth,a uniform fiber Bragg grating filter based on temperature tuning is discussed,calculations proves that when the temperature change range does not exceed 100 ?,the central wavelength and the temperature change have a good linear relationship,and the wavelength tuning range is about 0.754 nm.Subsequently,discussion on the model and structure of the tunable filter to increase the sensitivity,the numerical simulation shows that the temperature sensitivity is increased by 3.58 times and the tuning range is about 2.7 nm.Fifth,a tunable narrow linewidth fiber laser based on the unpumped erbium-doped fiber Sagnac all-fiber filter and temperature tuned uniform fiber Bragg grating is discussed.The simulation shows that the structure can realize single longitudinal mode oscillation and can obtain the wavelength tunable output in the range of 0.754 nm.