Highly stable and wavelength-switchable single-longitudinal-mode Tm3+-doped fiber laser with a specially-designed tri-coupler dual-ring filter

Dandan Yang, Fengping Yan, Ting Feng, Qi Qin, Ting Li, Chenhao Yu, Xiangdong Wang, Youchao Jiang, Kazuo Kumamoto, Yuping Suo