Design and demonstration of a flexibly cascaded N-ring-cavity ultrafast soliton all-fiber laser based on circulators

Abstract

We propose and demonstrate a flexibly cascaded N-ring-cavity (N is an integer, N = 1, 2, 3, …, n) femtosecond soliton fiber laser based on optical circulators. Utilizing the optical circulators, the single ring cavity fiber laser as the basic cascaded unit is cascaded together to form the N-ring-cavity femtosecond soliton fiber laser. Moreover, the cascaded N-ring-cavity ultrafast fiber laser can be designed as a three-dimensional cylindrical structure in space. Based on the nonlinear multimode interference effect, the graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) structure is designed as the saturable absorber for N-ring-cavity ultrafast fiber laser. In order to prove the feasibility of the cascaded N-ring-cavity fiber laser, the case that N = 2, that is a cascaded dual-ring-cavity fiber laser is designed and studied as an example. The experimental results show that each cascaded single ring cavity can operate independently, and the pulse widths of cavity 1 and cavity 2 output solitons are 358.6 fs and 458.4 fs, respectively. The research results show that cascaded N-ring-cavity ultrafast fiber laser has many advantages such as compact structure, multi-channel output, independent operation, etc. This work is of great significance to the miniaturization, integration, modularization, and multi-functionalization of ultrafast fiber lasers.