Subwavelength nanophotonics: From a new waveguide principle to practical components at telecom wavelengths

We report on a new waveguide principle using subwavelength gratings. It is known that diffraction effects are suppressed for waves propagating in materials structured at the subwavelength scale. Subwavelength gratings can create artificial media engineered using microscopic inhomogeneities to enact effective macroscopic behaviour. For the high-index-contrast waveguides, a subwavelength grating can be created by the combination of high-refractive-index and low-refractive-index materials, for example single crystal silicon and amorphous silica in silicon-on-insulator platform. These periodic structures frustrate diffraction provided they operate outside the Bragg condition and behave like a homogeneous medium. In a subwavelength grating (SWG) waveguide with a core consisting of a periodic arrangement of segments (Fig. 1), light excites a Bloch mode, which can theoretically propagate through the SWG waveguide with minimal scattering losses. Unlike other periodic waveguides such as line-defects in a 2D photonic crystal lattice, a subwavelength grating waveguide confines the light like a conventional index-guided structure and does not exhibit optically resonant behaviour.