λ-Size ITO and Graphene-Based Electro-Optic Modulators on SOI

One of the key devices that convert electronic signals into high bit-rate photonic data is the electro-optic modulator (EOM). Its on-chip design plays an important role for the integration of electronic and photonic devices for various types of applications including photonic computing and telecommunication. Recently, indium tin oxide (ITO) and graphene have attracted significant attention primarily due to their extraordinary electro-optic properties for the design of ultra-compact EOMs to handle bandwidth and modulation strength trade-off. Here we show design details of a high-performance ITO-EOM in a plasmonic silicon-on-insulator hybrid structure. Results show that ITO is capable of changing its extinction coefficient by a factor of 136 leading to 3 λ-short devices with an extinction ratio of about 1dB/μm. Further numerical device optimizations demonstrate the feasibility for an extinction ratio and on-chip insertion loss of about 6 dB/μm and 0.25 dB, respectively, for a sub-wavelength compact (0.78 λ) EOM design using ITO. Utilizing graphene as an active switching material in a similar ultra-compact plasmonic hybrid EOM design yields enhanced light-matter interaction, in which extinction-ratio is 9 times larger than the insertion-loss for a 0.78 λ short device. Both ITO and graphene EOMs are capable of broadband operations (>500 nm) since no resonator is deployed.