High-Order Mode Mode-Locked Fiber Laser Based on Few-Mode Saturable Absorber

Yi Huang,Longtao Wang,Si Lv,Jiafeng Lu,Jiangtao Xu,Linping Teng,Xianglong Zeng

doi:10.1109/jphot.2021.3077571

Abstract

We presented two kinds of high-order mode (HOM) mode-locked fiber lasers based on few-mode (FM) saturable absorbers for direct HOM oscillation. One is a ring fiber laser based on a carbon nanotube (CNT) saturable absorber (SA), in which the combination of a long period fiber grating (LPFG) and a mode selective coupler (MSC) is used for the cycle of mode conversion between LP 01 and LP 11 modes. The other is a linear-cavity laser using a FM-based SESAM with the HOM oscillation, in which a MSC is used for mode conversion inside the cavity. The presented mode-locked fiber lasers can achieve the saturable absorption of the HOM and the cylindrical vector beams (CVBs). And we also compared the nonlinear saturation absorption characteristics of two SAs operating at LP 01 and LP 11 modes.

Highlights

The mode division multiplexing (MDM) technology based on few-mode fiber (FMF) solves the problem of insufficient capacity of single-mode fiber (SMF) communication system [1,2,3,4]
We proved that mode-locked high-order mode (HOM) in half SMF and half FMF cavities directly oscillate and generate LP11 mode and cylindrical vector beams (CVBs), and LP11 modal light can be saturably absorbed by carbon nanotube (CNT)-saturable absorber (SA) and FM-based SESAM
We experimentally provided two methods of directly generating HOM mode-locking pulses in the hybrid laser cavities, which are a ring cavity composed of a CNT-SA and a linear-cavity composed of a FM-based SESAM

Summary

Introduction

The mode division multiplexing (MDM) technology based on few-mode fiber (FMF) solves the problem of insufficient capacity of single-mode fiber (SMF) communication system [1,2,3,4]. The methods of generating HOM are reported in many ways, such as laterally offset-splicing technique [9], photonic lantern [10], fiber Bragg grating (FBG) [11], LPFG [12,13,14], acoustically induced fiber grating (AIFG) and mode selective coupler (MSC) [15,16,17,18,19,20]. We proved that mode-locked HOMs in half SMF and half FMF cavities directly oscillate and generate LP11 mode and CVBs, and LP11 modal light can be saturably absorbed by CNT-SA and FM-based SESAM

Fabrication and characterization of mode converters

HOM mode-locked laser based on FM saturable absorber

HOM mode-locked laser based on CNT-SA

Findings

Conclusion