ABSTRACT
Photonic crystals are articial dielectric structures having periodic refractive index variation in a wavelength scale, which can realize strong light connement (John, 1987; Yablonovitch, 1987). The most extensively studied structure is a so-called photonic crystal slab (Notomi, 2010), which is typically formed by a periodic arrangement of air holes with the diameter of around 400 nm in a semiconductor (Si, GaAs, or InP) membrane of around 200 nm thickness. This structure can be fabricated by a process very similar to making Si-wire photonics since the typical dimension is the same order (note that the typical waveguide cross section for Si-wire photonics is 400 × 200 nm2). In fact, the cross-sectional mode area is almost similar between a conventional Si-wire waveguide and a photonic crystal line-defect waveguide. The waveguide loss is also comparable (Notomi et al., 2007). Then, why do we call for photonic crystals?
