Silicon photonic waveguides for mid- and long-wave infrared region

Silicon photonics is experiencing a dramatic increase in interest due to emerging application areas and several high profile successes in device and technology development (Liu et al Nature 427:615, 2004; Rong et al Nature 433:725, 2005; Almeida et al Nature 431:1081, 2004). Conventional waveguides in silicon photonics are designed for the telecom wavelengths. However, midand long-wave infrared regions are interesting for several application areas including sensing, communications, signal processing, missile detection and imaging (Soref et al J Opt A Pure Appl Opt 8:840, 2006). The most popular waveguide platform in silicon photonics is the Silicon-OnInsulator (SOI) structure, in the form of either a strip or a rib waveguide. This material structure, however, is not suitable for longer wavelengths (except in the 2.9–3.6 lm range) due to the absorption spectra of silicon dioxide (Soref et al J Opt A Pure Appl Opt 8:840, 2006). In this paper, we discuss the design and fabrication of two different waveguide structures, the freestanding (Yang et al Appl Phys Lett 90:241109, 2007) and hollow core waveguides (Stanković et al Proceedings of 51th Conference ETRAN, 2007). The former is suitable for long-wave infrared applications as it has an air cladding, whilst the latter is a candidate for sensing in the mid-wave infrared wavelength region.