Numerical Analysis of Relative Intensity Noise of Distributed-Feedback Fiber Lasers Considering Spatial Mode Profile

The spatial mode profile of distributed feedback (DFB) lasers is a unique characteristic that distinguishes them from lasers based on F-P cavities. It is utilized to achieve single-mode operation and improve relative intensity noise (RIN) performance. The effective cavity length method, as an approximate method for spatial mode profiling, is conveniently used for theoretical analysis. In this paper, the RIN of DFB fiber lasers was analyzed by considering their spatial mode profile without any approximations, and the results were compared with experimental findings. Additionally, numerical simulations of DFB fiber lasers with different structures were conducted to analyze their noise characteristics and the impact of spatial mode profile on the RIN of the lasers was discussed. The spatial mode profile was solved using the shooting method, with boundary conditions provided based on the erbium ion gain model. The spatial mode profile was then substituted into the RIN expression, yielding the RIN of DFB lasers influenced by spatial mode profile. This physical model is widely applicable and can be used to effectively analyze the dynamic characteristics of most DFB fiber laser structures.