All-fiberized single-frequency silica fiber laser operating above 2 mu m based on SMS fiber devices

摘要

In this paper, a single-frequency thulium-doped silica fiber laser operating above 2 mu m based on cascaded single-mode-multimode-single-mode (SMS) structures incorporating a Sagnac loop was experimentally demonstrated. Based on the analysis of the transmission properties of the SMS fiber structure and the mode selection characteristic of the Sagnac loop, two cascaded SMS fiber devices with the same multimode fiber length of approximately 3.25 cm were used in our laser system, to select the specific lasing wavelength above 2 mu m, as well as enhance the suppression of lasing around 1900 nm. A 6.5-m-long unpumped thulium-doped silica fiber was employed in the Sagnac loop as a saturable absorber to achieve single-longitudinal-mode operation. Single-frequency operation of the fiber laser at 2004.9 nm has been achieved with a maximum output power of 20.9 mW.