Generation of wavelength- and OAM-tunable vortex beam at low threshold.

Wavelength-and OAM- tunable laser with large tunable range is the key source for the application in large capacity optical communications. In this paper, we demonstrate a wavelength-and OAM-tunable vortex laser in a 1.2 W single mode fiber coupled LD pumped Yb: phosphate laser. A z-type cavity has been used to precisely control the laser mode diameter. A thin film polarizer (TFP) is inserted to finely control the intra-cavity loss and tune the wavelength. Corresponding laser fundamental mode to pump beam ratio has been optimized to decrease the pump threshold for high order HG mode running. A pair of cylindrical lenses has been used to convert the HG mode to vortex output. The vortex beam with OAM-tunable range from 1h to 14 h with wavelength tuning range of similar to 36.2 nm for LG(0,1) vortex beam, and similar to 14.5 nm for LG(0,14) vortex beam at pump power of only 1.2 W have been realized, which is the largest tuning range of both OAM and wavelength at similar to 1 W pump power range to the best of our knowledge. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.