The Realization And Application Of Long Distance Random Fiber Laser Based On Active Fiber At 1.5?m

The random distributed-feedback fiber laser is a novel light source developed on the basis of random lasers and fiber lasers which is generally called random fiber laser(RFL).Due to the unique feedback mechanism and output characteristics,the RFL has seized lots of attentions since its first present in 2010.Various RFLs with different laser structures and unique features have been demonstrated under continuous exploration and research by researchers within several years.This new type of fiber laser has many significant advantages,such as compact structure,low intensity noise,long-range signal transmission ability and temperature stability,therefore the RFL has a great potential in imaging,high-power lasing,long-distance fiber sensing and etc.In recent years,RFL has been widely studied.Particularly,the use of random lasing amplification for distributed fiber optic sensing has achieved some results.Meanwhile by using the fiber Raman random laser has been achieved long distance(100km)point sensor system,but long-distance point sensor system based on random fiber laser in the structural complexity,sensing distance,transmission optical signal to noise ratio(OSNR)or other sensing performances needs to be further optimized.Referring to the ROPA(Remote Optical Pumping Amplifier)technology in optical fiber communication,this paper introduced the active fiber into RFL,by use the hybrid gain based on the active gain and Raman gain in single mode fiber(SMF),a comprehensive theoretical analysis is used to predict and realize the long-distance RFL at 1.5 ?m which has lower loss based on active fiber.In addition,this paper studied the remote point sensing ability by using temperature sensing as an example.Specifically,based on the classical power balance model and the Giles simplified model of erbium-doped fiber(EDF),the performance of the RFL incorporating active fiber at different EDF positions and different EDF lengths is simulated numerically.The simulation results show that as the scheme has a relatively low power(<0.8W)and high OSNR(>30dB)with the 6m EDF and 100 km SMF,the lasing output with the central wavelength determined by the remote FBG can be obtained.It is worth to note that the location of EDF has a wide range of from 10 to 50 kilometers.The laser power distribution in the fiber can be controlled through the choice of EDF's position,consequently RFL length can be further extended.Then,based on the simulation parameters of RFL,this paper also set up 100 km above RFL to verify the simulation results with two different locations of EDF which is away 25 km and 50 km from the pump side,respectively.Experiments show that the input and output curves at two different EDF positions coincide well with the numerical simulation results.And the OSNRs of these two EDF positions are more than 30 dB,this result is higher 10 dB than the first order RFL based Raman gain with 1455 nm pump in the paper at 2012.Finally,this paper get the linear relationship between the random lasing wavelength and the temperature of FBG with thw help of the temperature-sensitive characteristics of FBG and the rest of the system has the characteristics of temperature stability.It is proved that the RFL based on this structure can be used for remote point sensing,and this system has the wavelength division multiplexing ability,thus making the system has multi-point monitoring capabilities.In this paper,the random fiber lasers based on active fiber provides a simple and easy method for realizing long distance RFL with low threshold and high OSNR.Meanwhile the results show that such a scheme points out a promising direction for sensing system based on random fiber laser.