Optical switching by capillary condensation

Photonic materials, which have optical properties that can be modulated by light, are extremely interesting both for their fundamental properties as well as for their potential in the applications of all-optical signal processing and possibly optical computing(1). Earlier studies have been based on nonlinear photonic crystals, and have required relatively high local light intensities to be used(2-5). We propose a completely different strategy based on the interplay between light propagation and capillary condensation of gases in porous photonic structures. We show experimentally that the local light intensity can alter the gas/liquid phase equilibrium inside the pores, which allows the refractive-index distribution inside the material to be optically tuned. As a specific example, we show how this feature can be used to obtain optical bistability in porous superlattices. Our results provide a new approach for achieving optical control in photonic systems.