ACS Photonics, Just Accepted Manuscript
DOI: 10.1021/acsphotonics.6b00751
Publication Date (Web): January 5, 2017
Copyright © 2017 American Chemical Society
One of the major difficulties in the development of optoelectronic THz modulators is finding an active material that allows for large modulation depth. Graphene is a promising candidate because in the terahertz regime it behaves as a Drude metal with conductivity that can be electrostatically tuned through the application of a gate voltage. However, the maximum absorption incurred when a terahertz signal passes through a monolayer of graphene is still only of order 10-20%, even for the highest practically achievable carrier concentrations. We demonstrate here a THz modulator that overcomes this fundamental limitation by incorporating a graphene sheet on the surface of a passive silicon dielectric waveguide, in which the evanescent field penetrates the graphene sheet. By applying a gate voltage to the graphene sheet, a modulation depth of up to 50% was achieved. The performance of the modulator is confirmed through electromagnetic simulations, which give further insights into the spatial structure of the guided mode and polarization-dependence of the modulation. We show, both theoretically and experimentally that the modulation depth can be increased to over 90% by integrating the graphene sheet at the center of the waveguide.
