Photonic-crystal-waveguide-based Silicon Mach-Zehnder Modulators

An ultra-compact photonic-crystal silicon Mach-Zehnder modulator is proposed based on the plasma dispersion effects. Transient time response of the device is simulated using semiconductor device simulator MEDICI. An efficient optical modulation has been experimentally demonstrated. ©2006 Optical Society of America OCIS codes: (250.7360) Waveguide modulators; (230.2090) Electro-optical devices Silicon nano-photonics is anticipated to play a critical role in future ultra-compact system integration due to the maturity of silicon complementary metal-oxide-semiconductor (CMOS) technology. Silicon is transparent in the range of optical telecommunication wavelengths, and it has high refractive index that allows for the fabrication of high-index-contrast nano-photonic structures. In photonics, nano-scale structures, particularly photonic crystals [1], hold the promise of achieving the same function in a significantly reduced device size with reduced power consumption. Optical waveguides based on photonic crystal line defects, the so-called photonic crystal waveguides (PCWs), have been demonstrated to provide a few orders of magnitude larger dispersion than conventional waveguides [2]. Such an extraordinary dispersion capability has a profound impact on the phase velocity change over a segment of photonic crystal waveguides [3].For optical intensity modulator, Mach-Zehnder interferometer (MZI) structure that converts a phase modulation into an intensity modulation is widely used. When photonic crystal waveguides are incorporated in a MZI, they lead to a significant enhancement of the phase modulation efficiency, which in turn allow us to reduce the modulator electrode length by several orders of magnitude. Most silicon electro-optic modulators operate based on plasma dispersion effects [4, 5], through which free carrier concentration perturbation results in refractive index change. Carrier injection and capacitive coupling through the metal-oxide-semiconductor (MOS) field effect are two major methods to introduce the free carriers into silicon. In MOS structure based silicon modulator, the overlap between the optical field and carrier perturbation area is usually small because the efficient free-carrier concentration variations only presents within a thin silicon layer beneath the insulated gate region. However, in a p-i-n configuration, overlap between the optical field and electrical field can be maximized since the free carriers will be uniformly injected into a comparative large intrinsic area that covers the