High-speed silicon electrooptic Modulator design

An electrically driven Mach-Zehnder waveguide modulator based on high-index contrast silicon split-ridge waveguide technology and electronic carrier injection is proposed. The excellent optical and carrier confinement possible in high-index contrast waveguide devices, together with good thermal heat sinking and forward biased operation, enables high-speed modulation with small signal modulation bandwidths beyond 20 GHz, a V/sub /spl pi// times length figure of merit of V/sub /spl pi//L=0.5 V/spl middot/cm and an insertion loss of about 4 dB. The modulator can be fabricated in a complementary metal-oxide-semiconductor compatible way.

I. Introduction

The DEVELOPMENT of future electronic–photonic integrated circuits based on silicon (Si) technology critically depends on the availability of complementary metal–oxide–semiconductor (CMOS)-compatible high-speed modulators that enable the interaction of electronic and optical signals. Fig. 1. (a) Externally biased MZ modulator with coplanar RF feeder. (b) Split-ridge waveguide pin-phase modulator with single-mode intensity profile. Si-based phase modulators using the plasma dispersion effect in a -structure have been proposed for Si-based optoelectronic phase and amplitude modulators [1]. Switching speeds up to 10 MHz [2] have been demonstrated and up to 1 GHz are predicted [3]. The speed of the response in these devices is limited by carrier recombination. Very recently a modulator based on an MOS structure has been proposed [4] operating at 1-GHz speed. However, this device needs an applied voltage of 10 V for achieving a phase shift within 1-cm length and showed 6.7-dB loss due to the doped polysilicon rib-waveguide. Much lower drive voltage in the order of 1–5 V is needed, when fed by CMOS circuitry. The same is true for top contacted rib-waveguides of previously proposed pin-structures [1].