Fast linear electro-optic effect in a centrosymmetric semiconductor

Mathias Berciano,Diego Pérez Galacho,Eric Cassan,Laurent Vivien,Delphine Marris-Morini,Pedro Damas,Paul Crozat,Carlos Alonso Ramos,Daniel Benedikovic,Xavier Le Roux,Guillaume Marcaud

doi:10.1038/s42005-018-0064-x

Abstract

Silicon photonics, considered as a major photonic platform for optical communications in data centers, is today also developed for others applications including quantum photonics and sensing. Advanced silicon functionalities based on optical nonlinearities are then required. As the presence of inversion symmetry in the Si crystal structure prevents the exploitation of second-order optical nonlinearities, the generation of strain gradients in Si by a stressed material can be considered. However, due to the semiconductor nature of silicon with the presence of carriers, no clear evidence of second-order nonlinearities have been reported yet. Here we report an experimental demonstration of high-speed Pockels effect in silicon waveguides at 1550 nm. Additionally, a theoretical model is developed to describe its frequency behavior. A second-order nonlinear susceptibility chi _{xxy}^{(2)} of −1.8 ± 0.2 pm V−1 is then experimentally determined. These results pave the way for the development of fast linear electro-optic effect for advanced silicon photonics devices.

Highlights

Silicon photonics, considered as a major photonic platform for optical communications in data centers, is today developed for others applications including quantum photonics and sensing
A set of 10 asymmetric Mach–Zehnder interferometers (MZI), of length Larm = 2 mm and a delay ΔL = 60 μm between the two arms, with different orientation angles φ ranging between 0° and 45° according to the wafer orientation notch along the [01̄1] axis, was fabricated (Fig. 1)
The sample was covered by a silicon nitride (SiN) stressed thin film, with a level of internal stress σi = −1.3 GPa to induce strain gradients in silicon waveguides

Summary

Introduction

Silicon photonics, considered as a major photonic platform for optical communications in data centers, is today developed for others applications including quantum photonics and sensing. A second-order nonlinear susceptibility χxð2xÞy of −1.8 ± 0.2 pm V−1 is experimentally determined These results pave the way for the development of fast linear electro-optic effect for advanced silicon photonics devices. It has been reported that the linear electro-optic effect detected in strained silicon waveguides was induced by charging centers in the SiN stress overlayer, which moves the silicon waveguide directly into an inversion regime, where the electron concentration grows linearly with the voltage[22,23,24] This result has deep consequences for the interpretation of the electro-optic effect in strained silicon waveguides, in the conclusion that there are two main electro-optic (EO) effects that jointly contribute to the total change in effective mode index (Δneff) in a strained silicon waveguide. The overall electrooptic effect may be written as follows: Δneff 1⁄4 Δneffc þ ΔneffP : ð1Þ

Methods

Results

Conclusion