Tuning of near‐ and far‐field properties of all‐dielectric dimer nanoantennas via ultrafast electron‐hole plasma photoexcitation

All‐optical ultrafast signal modulation and routing by low‐loss nanodevices is a crucial step towards an ultracompact optical chip with high performance. Here, we propose a specifically designed silicon dimer nanoantenna, which is tunable via photoexcitation of dense electron‐hole plasma with ultrafast relaxation rate. On the basis of this concept, we demonstrate the effect of beam steering by up to 20 degrees through simple variation of the intensity of incident light. The effect, which is suitable for ultrafast light routing in an optical chip, is demonstrated both in the visible and near‐IR spectral regions for silicon‐ and germanium‐based nanoantennas. We also reveal the effect of electron‐hole plasma photoexcitation on the local density of states (LDOS) in the dimer gap and find that the orientation averaged LDOS can be altered by 50%, whereas modification of the projected LDOS can be even more dramatic, almost five‐fold for transverse dipole orientation. Moreover, our analytical model sheds light on the transient dynamics of the studied nonlinear nanoantennas, yielding all temporal characteristics of the suggested ultrafast nanodevice. The proposed concept paves the way to the creation of low‐loss, ultrafast, and compact devices for optical signal modulation and routing.

     

Modification of spontaneous emission rate in planar dielectric microcavities – seen as superradiance and subradiance

The modification of the spontaneous emission rate of an atom in a cavity can be seen as superradiance/subradiance induced by virtual image dipoles. This result is used to gain physical insight why the spontaneous emission is enhanced or suppressed in various cavity geometries. A general model for spontaneous emission engineering, which simultaneously handles dispersive and lossy cavities, is derived.