Study On High-power Superfluorescent Source Based On Distributed Side-coupled Cladding-pumped Fiber

Superfluorescent fiber sources(SFSs)are obtained via the process of amplified spontaneous emission(ASE)in a rare-earth-doped fiber.With the output power scaling,SFSs have been widely applied in a number of fields.Distributed side-coupled cladding-pumped(DSCCP)fiber which realizes distributed pump coupling based on evanescent filed coupling,may get further superfluorescent power promotion.In this paper,we present a SFS based on DSCCP fiber and develop a numerical model.The output property and the limitations of power scaling are analyzed theoretically.By optimizing the design of SFS,high-power superfluorescent output is achieved experimentally.The main contents are as follows:1.Theoretical study on SFS based on DSCCP fiberBased on pump coupling model and rate-equation model,we develop a theoretical model for SFS based on DSCCP fiber.The physical process of pump light coupling and ASE generation can be described clearly by this model.According to the decision principle of parasitic laser oscillation,maximum total gain equal to loss,the parasitic laser oscillation model is developed.By numerical simulation,we study the limitations of power scaling.The following conclusions can be achieved.The optical feedback of fiber end face is a key to the power scaling.In addition,the impact of fiber length on the gain and increasing fiber length will lead to reabsorption of short-wavelength ASE.At the fiber length where the parasitic laser oscillation wavelength shifts from 1045 nm to 1070 nm,the maximum ASE power can be yielded.This fiber length is defined as optimal fiber length which is inversely proportional with dopant concentration.Large core to cladding ratio is beneficial to the power scaling.2.Experimental study on SFS based on DSCCP fiberAn all-fiber SFS based on 30/250-250 ?m fiber is designed.And the output power is 102 W which demonstrates the feasibility of DSCCP fiber in SFSs.By optimizing the angle-cleaved fiber end,4/5 mirror region which proves to be large enough to keep the fiber core region optically smooth,is achieved and the face angle is 7.5 °.ASE power is further promoted to 135 W.The slope efficiency of SFS is up to 79.8%.The bandwidths(FHWM)of forward and backward ASE are 34 nm and 32.8 nm.In addition,a power fluctuation of ±1.4% is measured within 1 min at the maximum output power,which indicates a good power stability of the high-power SFS.Experimental study on the dependence of output power on active fiber length is carried out.It is demonstrated the existence of optimal fiber length.At the fiber length of 7.3 m,SFS yields a maximum ASE power of 186 W.To the best of our knowledge,this is the highest superfluorescent output power from a single-stage configuration.