Coupling between Forward and Backward Modes and the Truth about 'Trapped Rainbow' Storage of Light in Metamaterials

Abstract

[evdate 2012-10-03] Croucher Advanced Study Institute on New Materials and New Concepts for Controlling Light and Waves. Talk no.8 Host: HKUST Institute for Advanced Study.

Sponsor: The Croucher Foundation.

Abstract: It has been predicted that a metamaterial slab waveguide can slow down light propagation significantly (even to zero velocity) as the thickness of the core layer approaches a critical thickness. Tsakmakidis et al. claimed in [Nature 450, 397-401, 2007] that a tapered metamaterial waveguide could lead to a complete standstill of light at the critical core thickness, and such a 'trapped rainbow' waveguide could be used for storage of light. Their theoretical conclusion was based on the application of the adiabatic approximation method, which, in fact, is not applicable near the critical thickness, where degenerated forward and backward modes coexist. Here we show that coupling between the forward and backward modes becomes significant near the critical thickness and consequently, even if the metamaterial is lossless the energy incident from the input port of such a tapered metamaterial waveguide will be totally reflected (instead of being trapped at the position of critical thickness). We explain the underlying physical mechanism for this strong intermodal-coupling, and prove the energy reflection using several independent methods, namely, (1) the semi-analytical mode matching technique, (2) the numerical finite element simulation, (3) the requirement of energy and momentum conservation, and (4) an experimental verification at microwave frequency.

Duration: 39 min.