Random Fiber Laser Based On Specialty Optical Fibers

Random fiber lasers are also an important branch of both random lasers and fiber lasers.Their operating mechanism of them is resemble to these traditional 2-dimentional and 3-dimentional random lasers,and the feedback is originated from random scattering.Random fiber laser consists of optical fiber components and can be regard as a one-dimensional version of a random laser.Its controllability and directionality are significantly better than traditional random lasers.In 2010,the research team from Aston University in the UK first realized the random fiber laser in which the feedback is based on Rayleigh scattering and the gain is provided by stimulated Raman scattering.This work is of great significance for the development of random fiber lasers.Since then,random fiber lasers have become one of focus of researchers at home and abroad,ushered in its era of great development.Although random fiber lasers have developed rapidly in recent years,their physical mechanisms and performance are still imperfect due to their short development history.As an important branch of random fiber lasers,the research of random fiber lasers based on specialty optical fibers needs to be supplemented as well.Then,we also statistically analyze the output power fluctuation of the random fiber laser based on specialty fiber.In addition,we process the fiber through radiation to try to realize the Rayleigh enhanced fiber.In the design part of the new random fiber laser based on specialty fiber,we propose a new random fiber laser structure with low threshold and high lasing efficiency.In this thesis,a novel random fiber laser based on double-clad ytterbiumdoped fiber is constructed with core pumping.The theoretical simulation results show that core pumping can well combine the ytterbium-doped gain and the stimulated Raman gain.Thus,a random fiber laser with a milliwatt-level lasing threshold and a lasing efficiency of up to 81.5% is achieved.More importantly,we present a new random laser lasing mechanism based on a new type of specialty fiber in this section,where a piece of active fiber provides both distributed active gain and distributed random Rayleigh feedback simultaneously.According to the new idea,we take the low pump power conditions and high pump power conditions in consideration in turn,and then build and gradually optimize the theoretical model.Furthermore,a novel random fiber laser is theoretically implement based on a novel double-clad weakly erbium-doped fiber through simulation.According to the theoretical results,the proposed random fiber laser can realize a milliwatt-level lasing threshold and a random laser output of more than 200 W.random fiber lasers based on specialty optical fibers,especially active fibers,show significant advantages in terms of low threshold,high power,and linear output,and are considered to be preferred for light sources.However,like other random lasers,its output spectrum and power show strong fluctuations near the threshold.Therefore,the analysis of the output fluctuation of random fiber lasers based on specialty optical fibers is of great significance.In this thesis,we build a 1090 nm random fiber laser based on a 10 m ytterbium-doped fiber and a 10 km single-mode fiber.Then,based on Lévy-?-stable distribution function,the spectral intensity probability density functions are fitted and the statistical types of random lasers are identified at different pump powers.The results show that the statistical characteristics of the random fiber laser evolves from Lévy distribution to Gaussian behavior with the increase of pump energy.The evolution of this statistical distribution is consistent with the statistical evolution of other random lasers with strong scattering feedback,which implies The evolution of the statistical distribution of Lévy to Gaussian commonly exists in random laser systems.In the field of random fiber laser,the Rayleigh scattering coefficient occupies a critical position.According to the previous researches,Rayleigh-enhanced fiber can improve the power performance of random fiber laser.In this thesis,we conduct an exploratory study on the implementation of Rayleigh enhanced fiber,and for the first time quantify the impact of irradiation on fiber.By analyzing the backscattering power,the attenuation coefficient and Rayleigh scattering coefficient of the sample fibers are obtained in turn.The results show that both of the two types of radiation have an enhancement effect on fiber attenuation and Rayleigh scattering.However,the enhancement trend of the same fiber parameter present differences under different irradiations.