Controllable Dynamic Single- and Dual-Channel Graphene Q-Switching in a Beam-Splitter-Type Channel Waveguide Laser

Abstract

Direct inscription of structures by femtosecond-laser pulses facilitates the flexible fabrication of diverse optical channel waveguides in dielectric laser gain media. Among them, beam-splitter-type waveguide lasers have been recently studied; however, there is a lack of investigations on the effect of unique characteristics of such waveguides, such as controlled splitting ratios of output powers and selectable excitation of individual channels, for pulsed laser operation. Here, dynamic single- and dual-channel graphene Q-switching of an Yb:YAG waveguide consisting of one input and two output channels is demonstrated by controlling the power-splitting ratio. Single-channel Q-switched operation, exhibiting typical Q-switched pulses, is achieved by interaction between the graphene saturable absorber and the desired one of the two channels. When both channels exceed the Q-switching threshold, dual-channel Q-switching generates a pulse train that simultaneously combines the separately Q-switched pulses induced from each channel under excitation with a single pump source. At a fixed power-splitting ratio, the pulsed mode can be dynamically switched between the single- and dual-channel Q-switched operations by varying the pump power. The beam-splitter-type waveguide laser demonstrated in this study can be further developed for multiple-channel Q-switching, high-repetition-rate mode-locking, and on-chip dual-comb sources advantageous for diverse applications in optical communication, metrology, and sensing.