Broadband tuning of a long-cavity all-fiber mode-locked thulium-doped fiber laser using an acousto-optic bandpass filter

Abstract

A long-cavity passively mode-locked thulium-doped all-fiber laser is reported incorporating a tapered acousto-optic tunable bandpass filter (AOTBF). The operation of the AOTBF relies on the intermodal coupling between core and cladding modes when a flexural acoustic wave propagates along an 80μm tapered fiber. The filter works in transmission and exhibits a 3dB bandwidth of 9.02nm with an insertion loss of 3.4dB. The laser supports ultrashort pulse generation at a low repetition rate of 784.93kHz. Optical pulses with 2.43nm of optical bandwidth and 2.1ps pulse duration were obtained in a broad tuning range from 1824.77 to 1905.16nm.