Introduction

Guided-wave nonlinear optics has attracted significant interest because of the unique environment that waveguides provide for nonlinear interactions, including tight confinement (high intensity), long interaction lengths (especially for fibres), control of propagation constants, and the possibility to incorporate them with integrated circuits (mainly for planar waveguides) [see (Lin et al., 2007; Knight and Skryabin, 2007; Foster et al., 2008; Afshar and Monro, 2009) and references therein]. Recent and rapid progress in design and manufacturing of complex structured microstructured optical fibres and planar waveguides with subwavelength features (including both subwavelength inclusions and voids) has further extended the opportunities to develop nonlinear devices by enabling extreme nonlinearity to combine with tailorable chromatic dispersion (Lin et al., 2007; Knight and Skryabin, 2007; Foster et al., 2008; Koos et al., 2007).

The nonlinear optical phenomena that occur in waveguides are determined through two main factors; the linear and nonlinear properties of the constituent bulk materials, and the optical properties of the waveguide. Recent advances in the design and fabrication of complex structured waveguides with high contrast linear refractive indices, inhomogeneous cross-sections, and subwavelength features have provided great potential to accelerate the field of guided-wave nonlinear optics. We define a new class of optical waveguides, “emerging waveguides”, as waveguides with a combination of the following features:

1. (i) High index materials

2. (ii) Inhomogeneous and complex structure

3. (iii) Subwavelength features such as voids or material inclusions.