1.7-$\mu$m Tm/Ho-Codoped All-Fiber Pulsed Laser Based on Intermode-Beating Modulation Technique

Abstract

A 1.7-μm pulsed laser is of tremendous interest for biomedical imaging applications due to its low scattering loss in bio-tissues, but is relatively difficult to generate in a fiber laser. In this paper, we propose and demonstrate a compact 1.7-μm Tm/Ho-codoped fiber pulsed laser based on a novel intermode-beating modulation (IM) technique. A 1211-nm continuous-wave (CW) Raman fiber laser is especially homemade to pump a ~20-cm short-length Tm/Ho fiber for obtaining ~1.7-μm optical gain. A pair of fiber end-facet mirrors with 1.7-1.8-μm reflective band is used to form the all-fiber linear cavity. 1.76- or 1.78-μm lasing is successfully achieved, and surprisingly exhibits stable self-gain-switching operation with ~1-μs pulse duration. Different from the conventional gain-switching requiring pulsed pumping, herein the gain modulation in the 1.7-μm laser is induced by strong intermodebeating of the CW pump source. The pulse repetition rate with an increasing pump power is fixed at 145 kHz, which exactly coincides with the longitudinal-mode beat frequency of the 1211-nm pump laser. Our results may provide a new type of optical modulation (i.e., intermode-beating modulation technique) for a low-cost, compact pulsed laser.