Scaling the modulation bandwidth and phase efficiency of a silicon optical modulator

• Published in: IEEE journal of selected topics in quantum electronics Vol. 11; no. 2; pp. 367 - 372
• Main Authors: Ansheng Liu, Samara-Rubio, D., Ling Liao, Paniccia, M.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2005; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidth; Capacitors; Devices; Doping; Doping profiles; Metal-oxide-semiconductor (MOS) capacitor; Modulation; Modulators; MOS capacitors; Optical devices; Optical modulation; optical modulator; Optical refraction; Optical variables control; Optical waveguides; Phase modulation; phase shifter; planar lightwave circuits; Semiconductors; Silicon; silicon photonics; silicon-on-insulator (SOI); waveguide; Waveguides
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/JSTQE.2005.845618

We present an optimized design and detailed simulation of an all-silicon optical modulator based on a silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. Based on a fully vectorial Maxwell mode solver, we analyze the modal characteristics of the silicon waveguide. We show that shrinking the waveguide size and reducing gate oxide thickness significantly enhances the phase modulation efficiency because of the optical field enhancement in the voltage induced charge layers of the MOS capacitor, which, in turn, induce refractive index modulation in silicon due to free carrier dispersion effects. We also analyze the device speed by transient semiconductor device modeling. As both optical absorption and modulation bandwidth increase with increasing doping concentration, we show that, with a nonuniform doping profile in the waveguide, balance between the device operation speed and optical loss can be realized. Our simulation suggests that a TE-polarized optical phase modulator with a bandwidth of 10 GHz and an on-chip optical loss less than 2 dB is achievable in silicon.