Spatial switching of slow light in periodic photonic structures

Abstract

The speed of light sets the maximum possible rate for transmission of information, in excess of 108 meters per second. Light pulses in optical fibers carry bits of data around the world in sub-second time frame, enabling interactive global communications. There is a constant demand for increasing the network performance in view of steadily growing information flows. It is envisioned that the presently required multiple conversions between optical pulses and electronic signals at network hubs may be eliminated in future when routing and switching of data flows is performed all-optically. This vision can be realized if the speed of light is dynamically controlled, allowing for synchronization and multiplexing of signals. Furthermore, by temporarily making the light slower it becomes possible to compress optical signals and perform their manipulation in compact photonic chips. Additionally, in the regime of slow light the photon-matter interactions are dramatically enhanced, enabling the active control of light and nonlinear transformations of signals. Slowing down the light is a challenging physical problem. In conventional dielectrics, the speed of light can only be reduced by a factor less than four which is limited by the optical refractive index of available materials. The most dramatic slowing down of light to a complete stop was reported in the regime of electromagnetically induced transparency [1]. This phenomenon is based on a resonant interaction of light with an atomic system and accordingly the speed of light is very sensitive to the frequency detuning. This restricts the effect to narrow frequency ranges limiting its applicability to communication networks with demands for data rates in excess of 100Gb per second. In contrast, dielectric photonic structures with a periodic modulation of the optical refractive index at a sub-micrometer scale can be engineered to operate at any frequency range. Periodic modulation results in resonant light scattering, and reduction of pulse speed by more than 100 times was registered experimentally in photonic crystals [2-4]. Ultra-slow light propagation can also be realized based on the coupling between high-Q optical cavities [5-10]. However, in all static structures the maximum usable delay decreases for shorter pulses which have larger bandwidth and exhibit stronger distortions due to the effect of frequency dispersion [11]. It was suggested that the restriction on the delay-bandwidth product, the key parameter characterizing the device capacity to store optical signals [12], can be overcome in dynamically tunable structures, with the exciting possibility to completely stop and then release light pulses all-optically [13, 14]. © 2009 Springer-Verlag Berlin Heidelberg.