Strong Light Confinement With Periodicity

Photonic crystals were proposed over two decades ago to realize strong light confinement via their perfect photonic bandgaps, but the expected ultrahigh-Q wavelength-sized cavities were achieved just recently in a slightly different system that has only a partial bandgap, more specifically, a modulated mode-gap cavity in a 2-D photonic crystal. It is now possible to store photons for over a nanosecond in a wavelength-sized volume for this type of cavity, which has not been realized in other systems. The same confinement mechanism has provided various interesting cavities including air-core cavities, index-modulation-induced cavities, and dynamic cavities. We discuss the impact and possible applications of the achieved strong light confinement. First, it has a strong impact on photonic integrated circuits and photonic network-on-chip (NoC) applications because these cavities enable us to realize tiny, low-power-consumption, and integratable photonic devices, which are hard to realize conventionally. It is next shown that an ultrahigh- Q cavity system constitutes an extreme slow-light medium. It is also shown that ultrahigh-Q cavities enable the adiabatic tuning of light, which makes it possible to manipulate optical signals very differently from conventional optics. Finally, other possible systems promising for strong light confinement are investigated, such as 1-D photonic crystals and photonic amorphous structures without any periodicity.