All-optical mode switching with a graphene-buried polymer waveguide directional coupler

We demonstrate all-optical mode switching with a graphene-buried polymer waveguide asymmetric directional coupler (DC) by using the photothermal effect of graphene, where TE-polarized pump light and TM-polarized signal light are employed to maximize pump absorption and minimize graphene-induced signal loss. Our experimental device, which uses a graphene length of 6.2 mm, shows a pump absorption of 3.4 dB (at 980 nm) and a graphene-induced signal loss of 0.1 dB. The device can spatially switch between the fundamental mode and the higher-order mode with extinction ratios larger than 10 dB (at 1580 nm) and switching times slightly shorter than 1 ms at a pump power of 36.6 mW. Graphene-buried polymer waveguides offer many new possibilities for the realization of low-power all-optical control devices.