Random Fiber Laser Based On The Short Erbium-doped Fiber And Its Performance Optimization

Random laser(RL)has an obvious feature compared with traditional laser,it has no fixed resonator,thus reducing the requirement of the cavity design.Its characteristic such as better stability,higher reliability,and simpler structure makes it extremely valuable for applications in biological life sciences,earth sciences,and national defense and security.However the high-energy pump power are needed as the result of the high threshold.And RL lacks directional emission.These situations limit its practical application to a certain extent.In recent years,random fiber laser(RFL),a new type of RL,has attract great attention for researchers.Its advantage is that the propagation direction of light is limited by the optical fiber.The structure of RFL is simpler,the design is more flexible,and the reliability is higher.Due to these unique properties,RFL has attracted extensive attention for its practical applications in speckle-free imaging,optical sensing and communications.Single-mode fiber(SMF)is widely used as a gain medium due to its low cost,however,a long distance SMF is needed to accumulate enough gain to overcome the loss,which leads to the high threshold of RFL.Therefore,this paper uses erbium-doped fiber(EDF)as the gain medium to obtain a simple RFL with lower threshold,higher efficiency and better performance,including two different erbium-doped random fiber laser(ERFL).The specific research work is carried out as follows:(1)An erbium-doped random fiber laser with simple structure and convenient operation is proposed.The system is implemented by a highly stable 980 nm laser directly pumped a short EDF that provides both gain and random feedback.Firstly,we analyzed the mechanism of this erbium-doped random fiber laser generation.Then,we investigated the effect of the EDF length on the RFL output emission characteristics by changing the length of EDF.When the EDF length is 11 m,the lowest threshold power of this erbium-doped random fiber laser is only 15.2 m W,and the highest laser efficiency is 16%.Under the pump power of 30 m W,the positions and intensities of random peaks are random.The highest signal-to-noise ratio(SNR)is 28.5 d B.And the number of random peaks increases with the increase of pump power.The linewidth of this erbium-doped random fiber laser is stable at around 300 Hz even though the pump power is different.The proposed ERFL has an important application in the fields of communication,random number generation and sensing.(2)The proposed erbium-doped random fiber laser is optimized by enhancing system feedback.Specifically,A Sagnac-based half-open cavity erbium-doped random fiber laser,a SMF-based erbium-doped random fiber laser and a Sagnac+SMF-based erbium-doped random fiber laser were studied.Finally,it is found that the Sagnac loop-based erbium-doped random fiber laser structure can reduce the system threshold to a minimum of10 m W and increase the laser efficiency to a maximum of 23%.