High-speed optical modulation based on carrier depletion in a silicon waveguide

Ansheng Liu,Mario Paniccia,Berkehan Ciftcioglu,Hat Nguyen,Nahum Izhaky,Yoel Chetrit,Ling Liao,Doron Rubin

doi:10.1364/oe.15.000660

Abstract

We present a high-speed and highly scalable silicon optical modulator based on the free carrier plasma dispersion effect. The fast refractive index modulation of the device is due to electric-field-induced carrier depletion in a Silicon-on-Insulator waveguide containing a reverse biased pn junction. To achieve high-speed performance, a travelling-wave design is used to allow co-propagation of electrical and optical signals along the waveguide. We demonstrate high-frequency modulator optical response with 3 dB bandwidth of ~20 GHz and data transmission up to 30 Gb/s. Such high-speed data transmission capability will enable silicon modulators to be one of the key building blocks for integrated silicon photonic chips for next generation communication networks as well as future high performance computing applications.

Highlights

Silicon photonics has recently become a subject of intense interest because it offers an opportunity for low cost optoelectronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects
We have demonstrated high speed operation of the Mach-Zehnder interferometer (MZI) with a 3 dB roll-off frequency of ~20 GHz, the current silicon modulator is by no means optimized for performance
The device can be improved by optimizing the dopant profile and pn junction placement in the waveguide to increase phase efficiency

Summary

Introduction

Silicon photonics has recently become a subject of intense interest because it offers an opportunity for low cost optoelectronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects. Today’s commercially available high-speed optical modulators at >>10 Gb/s are based on electro-optic materials such as lithium niobate [16] and III-V semiconductors [17]. These devices have demonstrated modulation capability as high as 40 Gb/s. Due to the slow carrier generation and/or recombination processes, the modulation speed is usually limited unless the carrier lifetime can be significantly reduced [25] While both MOS capacitor and reverse biased pn junction rely on electric-field induced majority carrier dynamics that can potentially achieve >10 Gb/s operation, one would need to adopt appropriate device design to improve the phase modulation efficiency. It was suggested that the device speed for a reversebiased pn junction is only limited by the RC constant

Device design and fabrication

Device characterization

Discussion and conclusion