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

Abstract

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.

Periodic waveguide structures for on-chip modulation and sensing

“…The waveguide length is also chosen to be 300 µm. The simulated group index is 3.79 53) at 1550 nm. Inverse tapers with polymer overlay are used to interface single mode fibers.…”

“…The details of the fabrication can be found in Ref. 53. Figure 4(a) shows the transmission spectrum of the fabricated Mach-Zehnder interferometer (MZI) with one arm loaded with the 1D SPCW.…”

“…1. 52,53) This novel structure is referred as slow light 1D slot PCW (SPCW), which exploits both the strong mode confinement in the low-index region of a conventional slot waveguide and the slow light enhancement from the 1D PCW. Its simple geometry makes it robust to fabrication imperfections and helps suppress the scattering loss.…”

High‐Speed Modulator Based on Electro‐Optic Polymer Infiltrated Subwavelength Grating Waveguide Ring Resonator

“…Modulators with bandwidth over 100 GHz have been demonstrated, but their millimeter long device length defeats the purpose of chip‐scale integration . Structural slow light, such as slot photonic crystals and plasmonic devices, can effectively shrink the phase shifter size but at the price of significantly increased insertion loss . Inspired by the success of silicon microring resonators, a few attempts have been made to replicate microrings on SOH platform through several waveguiding structures .…”

Efficient coupling into slow-light one-dimensional fishbone waveguide by mode converter method

“…[5][6][7] The one-dimensional (1D) silicon fishbone waveguide possesses a reasonable scattering loss and is easily fabricated at a low cost. 8,9) However, the engineering implementation of the 1D silicon fishbone waveguide is limited by the inadequate dispersion of the group index and the low coupling efficiency of light in and out of the 1D silicon fishbone waveguide. [10][11][12][13][14] Note that the slow light in the 1D silicon fishbone waveguide can be designed at the band edge, while the curvature of the band edge will determine the group index dispersion.…”