In this work, a novel type of optical waveguide, namely two-step undercut-etching Si waveguide (TSUESW), fabricated in Si-substrate is proposed and demonstrated. All this waveguide processing is based on two step of SF6-based dry etching method. In the first step, an anisotropic etching by Reactive Ion Etching (RIE) is used to define the waveguide core. After that, an undercut etching through an isotropic etching processing Electron Cyclotron Resonance (ECR) is then utilized to decouple the optical light of the waveguide core from Si substrate. In the measurement setup, an optical propagation loss coefficient of 2.89dB/cm is obtained by extracting from Fabry-Perot oscillation, suggesting the confined optical mode in TSUESW can be realized. A tapered optical waveguide is also designed and fabricated, where the core of tapered structure is defined as widths of from 20£gm to 6£gm for optical fiber coupler. A 4.13dB/cm of loss from 700£gm long waveguide is found in such tapered waveguide. Through the nonlinear properties of Si material, a Four-Wave Mixing (FWM) behavior is observed in tapered waveguide, further confirming the optical power can be highly confined in small core of TSUESW. It also should be noted that the waveguide technology template can be processed in a Si-substrate to realize CMOS-compatible processing, avoiding high-cost Silicon-On-Insulator (SOI) technology.

Abstract In this thesis, we propose a new geometrical structure of waveguide for the application of traveling-wave electroabsorption modulator (TWEAM). As approaching to high-speed performance in TWEAM, low parasitic capacitance in the waveguide is necessary to get good microwave propagation properties. In this work, a novel processing called two-step undercut-etching the active region (UEAR) is developed to reduce the parasitic capacitance. First of all, Beam Propagation Method (BPM) is used to calculate this 2-D structure optical modes ensuring the guiding capability in such kind of waveguides. Based on an equivalent circuit model, the microwave propagation on different structures of waveguide is then investigated to decide the UEAR waveguide structure. By the selectively etching solution on InP/InGaAsP, the processing by two-step UEAR is developed to reduce the parasitic capacitance in the waveguide core. H3PO4:HCl is used to selectively etch P-InP layer on the top of InGaAsP M.Q.W. (multiple quantum wells, active region). H3PO4:H2O2:H2O is subsequently and selectively remove InGaAsP M.Q.W.s to define the waveguide core. This processing has been successfully developed. The electrical transmission measurement on this kind of TWEAM shows low reflection S11 of < -17.5dB and a low insertion loss S21 of < ¡V2.7dB from D.C. to 40GHz, indicating high microwave performance on such two-step UEAR waveguide can be achieved due to the low parasitic capacitance.