One-dimensional photonic crystal slot waveguide for silicon-organic hybrid electro-optic modulators.

In an on-chip silicon-organic hybrid electro-optic (EO) modulator, the mode overlap with EO materials, in-device effective r₃₃, and propagation loss are among the most critical factors that determine the performance of the modulator. Various waveguide structures have been proposed to optimize these factors, yet there is a lack of comprehensive consideration on all of them. In this Letter, a one-dimensional (1D) photonic crystal (PC) slot waveguide structure is proposed that takes all these factors into consideration. The proposed structure takes advantage of the strong mode confinement within a low-index region in a conventional slot waveguide and the slow-light enhancement from the 1D PC structure. Its simple geometry makes it robust to resist fabrication imperfections and helps reduce the propagation loss. Using it as a phase shifter in a Mach-Zehnder interferometer structure, an integrated silicon-organic hybrid EO modulator was experimentally demonstrated. The observed effective EO coefficient is as high as 490 pm/V. The measured half-wave voltage and length product is less than 1  V·cm and can be further improved. A potential bandwidth of 61 GHz can be achieved and further improved by tailoring the doping profile. The proposed structure offers a competitive novel phase-shifter design, which is simple, highly efficient, and with low optical loss, for on-chip silicon-organic hybrid EO modulators.