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Published online: 20 February 2008 | Corrected online: 27 February 2008 | doi:10.1038/nchina.2008.39

Optical switches: A new low

Felix Cheung

Introduction

© (2008) Nature Photonics

Nonlinear photonic crystals guide the propagation of 'signal' photons in different directions in response to 'pump' photons — photons at different frequencies that activate the crystal's nonlinear properties. Such crystals are promising materials for making optical switches, which can be used to route information in optical-fibre networks with a better capacity and reliability than conventional electronic switches. Qihuang Gong and co-workers at the Peking University in Beijing¹ have devised a strategy for making ultrafast photonic-crystal-based optical switches that can operate under low-power pump light.

Most photonic crystals require high pump powers to operate because they have low nonlinearity — that is, there is little interaction between the pump light and the crystal. For crystals with high nonlinearity, the response time of optical switching can become problematically slow.

The researchers formed a rectangular photonic crystal (pictured top) by connecting 20 slabs together. Each slab, etched with periodic patterns of submicrometre holes, is made from a blend of polymer and organic chromophore, which have absorption bands that overlap each other. A line defect (pictured bottom) was allocated at the centre of the crystal to create a 'microcavity', or quantum confinement well, which enhances the interaction between the pump light and the crystal.

When pump light at a frequency within the absorption band was used to excite the crystal, the nonlinearity properties were enhanced by two orders of magnitude as a result of the microcavity. A pump power of 110 kW cm^-2 is needed for the crystal to perform optical switching — about four orders of magnitude less than that of previous reports. The response time need not be compromised because the interelectron transfer between the polymer and the chromophore is fast, enabling response times of 1.2 picoseconds.

The authors of this work are from:
State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing, China.

Reference

1. Hu, X., Jiang, P., Ding, C., Yang, H. & Gong, Q. Picosecond and low-power all-optical switching based on an organic photonic-bandgap microcavity. Nature Photon. doi: 10.1038/nphoton.2007.299 (2008). | Article |