100 GHz silicon–organic hybrid modulator

Luca Alloatti,Christian Koos,Raluca Dinu,Maryse Fournier,Thomas Zwick,Kai Philipp Pahl,Baoquan Chen,Robert Palmer,Jean-Marc Fedeli,Juerg Leuthold,Wolfgang Freude,Sebastian Diebold

doi:10.1038/lsa.2014.54

Abstract

AbstractElectro-optic modulation at frequencies of 100 GHz and beyond is important for photonic-electronic signal processing at the highest speeds. To date, however, only a small number of devices exist that can operate up to this frequency. In this study, we demonstrate that this frequency range can be addressed by nanophotonic, silicon-based modulators. We exploit the ultrafast Pockels effect by using the silicon–organic hybrid (SOH) platform, which combines highly nonlinear organic molecules with silicon waveguides. Until now, the bandwidth of these devices was limited by the losses of the radiofrequency (RF) signal and the RC (resistor-capacitor) time constant of the silicon structure. The RF losses are overcome by using a device as short as 500 µm, and the RC time constant is decreased by using a highly conductive electron accumulation layer and an improved gate insulator. Using this method, we demonstrate for the first time an integrated silicon modulator with a 3dB bandwidth at an operating frequency beyond 100 GHz. Our results clearly indicate that the RC time constant is not a fundamental speed limitation of SOH devices at these frequencies. Our device has a voltage–length product of only VπL=11 V mm, which compares favorably with the best silicon-photonic modulators available today. Using cladding materials with stronger nonlinearities, the voltage–length product is expected to improve by more than an order of magnitude.

Highlights

High-bandwidth electro-optic modulators are key components for a variety of applications such as photonic transceivers for long-haul and on-chip communications,[1] radio-over-fiber links, low-noise microwave oscillators[2] and optical frequency comb generation.[3]
Our results clearly indicate that the RC time constant is not a fundamental speed limitation of silicon–organic hybrid (SOH) devices at these frequencies
Because unstrained silicon does not possess a x(2)-nonlinearity,[6] state-of-the art silicon photonic modulators mainly rely on free-carrier dispersion in pin or pn junctions.[7,8,9]

Summary

Introduction

High-bandwidth electro-optic modulators are key components for a variety of applications such as photonic transceivers for long-haul and on-chip communications,[1] radio-over-fiber links, low-noise microwave oscillators[2] and optical frequency comb generation.[3]. An alternative approach uses hybrid integration of III–V epitaxy stacks grown on InP substrates, which are subsequently transferred to silicon-on-insulator waveguides to create high-speed electro-absorption modulators.[11] Recently, such a device demonstrated a 3-dB bandwidth greater than 67 GHz, representing the fastest modulator realized on a silicon chip to date. Advanced modulation formats such as quadrature amplitude modulation, require phase modulators with a linear response and a pure phase modulation, rendering the electro-optic effect (Pockels effect12) attractive. Devices with small capacitances are required, and leakage currents as well as driving voltages are to be minimized.[13]

Methods

Results

Conclusion