All-Optical Switching and Strong Coupling Using Tunable Whispering-Gallery-Mode Resonators

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All-optical switching is a long-standing goal of photonics. The manipulation of light with light is in general possible via the nonlinear optical response of matter. The effect of this nonlinear light-matter interaction can be amplified be means of optical resonators. This amplification becomes higher the smaller the mode volume V and the higher the Q factor of the resonator are. While a number of resonator concepts exist that offer high values of Q / V, coupling of light into and out of high Q resonators is often inefficient. The situation is different for high-g whispering-gallery-mode resonators, where tapered fiber coupling allows coupling efficiencies exceeding 99 %. We propose the use of the tunable whispering-gallerymode resonators that have been developed during the first funding period of this Research Unit for such all-optical switching applications. The experiments shall on the one hand be carried out using the "bulk" nonlinear response of surface-ads orbed molecules that interact with the evanescent field of the resonator modes. On the other hand, we seek to carry out experiments that exploit the nonlinear response of single atoms in the so-called "strong coupling regime". This approach is motivated by the perspective of realizing a nonlinear interaction at the level of single photons. If such a photon-photon interaction could be realized in the strong coupling regime, this would open the route towards important applications in the framework of quantum communication and quantum information processing.