Photonic nanostructures for controlling light

Tanabe Photonic Structure Group, Keio University

A high-Q microcavity is a tiny container that can cage photons for a long time.   It enable strong interaction between light and matter even when the input light is very weak.  As a result, optical nonlinearities occurs that allow us to demonstrate all-optical switches, memories, and other active components.

When electrons are used for signal processing, the resistance of electrical wiring causes Joule heating, and this means energy is lost.  But with photons, this energy loss can be avoided, and so signal processing with high energy efficiency can be achieved.  Optical microcavities are considered as a strong candidate for the basic element of all-optical logic gates.

In our group, we are particularly interested in the fundamentals and applications using whispering gallery mode (WGM) microcavities and photonic crystal (PhC) nanocavities.  Both cavities have the highest Q/V, where Q is the quality factor and V the mode volume (size of the cavity).  WGM microcavities made of silica and crystalline materials are attractive due to the ultrahigh Q and the wide bandgap of the material.  These properties allow us to use third-order nonlinearities, such as optical Kerr effect and four-wave-mixing (FWM).  One of the interesting application is the Kerr comb generation in such WGM microcavities.  On the other hand, a PhC nanocavity is a candidate as a basic element for constituting all-optical logic gates, because of the small size and the integration properties.   It paves the way to the realization of all-optical signal processing at the lowest possible energy.

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