All-optical loss modulation with graphene-buried polymer waveguides.

We present an analysis of all-optical loss modulation in a graphene-buried waveguide based on the Pauli blocking effect. We show that, to realize effective loss modulation, both the signal light and the co-propagating control light must be polarized along the direction parallel to graphene's surface, and the loss-modulation efficiency is given by the ratio of the loss coefficients of the signal light and the control light. To demonstrate the principle, we fabricate two polymer waveguide samples, one with a 0.6-mm-long graphene film buried in the center of the waveguide core and the other with a 10.0-mm-long graphene film placed on the top surface of the core. We achieve a loss modulation to 1550-nm signal light from 5.0 dB to 0.4 dB with a 980-nm control power varying from 6.5 dBm to 12. 5 dBm for the first sample, and from 8.0 dB to 0.5 dB with a control power varying from 14.5 dBm to 19.5 dBm for the second sample. The experimental results agree well with the theoretical analysis. A graphene-buried waveguide offers much flexibility as a platform for the realization of all-optical devices, such as optical switches, optical samplers, and optically tunable attenuators.