Physica B 394 (2007) 289–292 Characterisation of chalcogenide 2D photonic crystal waveguides and nanocavities using silica fibre nanowires C. Smith a,Ã , C. Grillet a , S. Tomljenovic-Hanic a , E.C. Ma¨gi a , D. Moss a , B.J. Eggleton a , D. Freeman b , S. Madden b , B. Luther-Davies b a Centre for Ultrahigh-Bandwidth Devices for Optical Systems (CUDOS)—A28, School of Physics, University of Sydney, Sydney, NSW 2006, Australia b Centre for Ultrahigh-Bandwidth Devices for Optical Systems (CUDOS), The Australian Nation University, Canberra, ACT 0200, Australia Abstract We describe the fabrication of low-loss, highly flexible silica fibre nanowires which are used to characterise chalcogenide two- dimensional photonic crystal waveguide circuits and nanocavities. Localised coupling is achieved in good agreement with theory. Crown Copyright r 2007 Published by Elsevier B.V. All rights reserved. Keywords: Nanowires; Nonlinear; Evanescent; Nanocavities; Waveguides; Chalcogenide 1. Introduction Photonic crystals (PhCs) are a class of optical structure, where the propagation of light is controlled by using a strong periodic modulation of the refractive index [1,2]. Large index contrast in a PhC gives rise to a photonic band-gap, within which light cannot propagate, providing a possible mechanism to trap and manipulate light for photonic circuitry. Using the PhC mechanism, different types of optical circuitry components in these structures have been realised, including waveguides [3,4]: a defect row of holes that act as a conduit for light (see Fig. 1(b)), and nanocavities: compact (wavelength-scale) optical structures with high Q-factors and small mode volumes [5,6] (see Fig. 1(a)). PhC waveguides (PhCWGs) and PhC nanocavities (PhCNCs) have captivated much research interest for the pursuit of all-optical signal processing [7,8]. For the purpose of all-optical signal processing, an interesting glass type to fabricate PhC structures from is chalcogenide. Chalcogenide glasses are transparent in the infrared and posses a high refractive index sufficient for PhC devices (typically 2.4–2.7); they have high third-order nonlinearity (100–1000  that of silica) and exhibit low two-photon absorption, making these materials promising for achieving low-power ultra-fast optical switching and optical logic [9]; and they can be processed using conventional lithographic techniques. Recently, we reported initial results demonstrating highly efficient coupling to chalcogenide PhCWGs [10] (Fig. 2). This was accomplished via the use of evanescent coupling from silica fibre nanowires, made by extreme tapering of a standard single-mode fibre. In this paper we describe the fabrication of highly flexible, low-loss silica nanowires that are used to achieve localised coupling to chalcogenide PhCWGs and PhCNCs. We demonstrate silica nanowires with sub-micron dimen- sions and virtually zero bend loss. We present detailed measurements of chalcogenide PhCWGs and PhCNCs, including coupling dependence upon polarisation and return-reflection differences between waveguides and cav- ities. We also observe a tuning effect on shifting the adjacent holes of a PhCNC. All together, these results promote understanding of the fundamental properties of the PhCWG and PhCNC structures, as well as the system’s evanescent coupling behaviour. 2. Principle The principle of evanescent coupling to PhCWG and PhCNC modes is illustrated in Fig. 2 [11]. The silica ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$ - see front matter Crown Copyright r 2007 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.12.057 Ã Corresponding author. Tel.: +61 2 9351 2543. E-mail address: c.smith@physics.usyd.edu.au (C. Smith).