Revealing the truth about ‘trapped rainbow’ storage of light in metamaterials

Abstract

It was claimed that the incident light can be gradually slowed down and finally trapped in a tapered metamaterial waveguide. Here we show that the energy incident from the input port of the tapered metamaterial waveguide will be totally reflected (instead of being trapped) due to the strong intermodal coupling between the forward and backward modes. The underlying physical mechanism for this strong intermodal-coupling is given. The occurrence of energy reflection is unambiguously proved using several independent methods, (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. The dream of ‘trapped rainbow’ for storage of light might still be possible if this intermodal coupling could be blocked, and our study provides a useful guidance for such an endeavor.

Rainbow Trapping in Hyperbolic Metamaterial Waveguide

“…modes with significantly different optical properties, the HMM waveguide taper constructed by metal and dielectric films can be used to develop practical on-chip optical super absorbers with a tunable absorption band. Compared with previously reported rainbow trapping platforms 6,9,[10][11][12][13][14][15] , the proposed universal HMM waveguide taper design constitute solid state on-chip photonic architectures capable of simultaneous operation over a wide range of wavelengths throughout visible, near-infrared, midinfrared 27 , terahertz (see Section 5 in the supplementary information) and microwave 34 spectral regions, which is not limited by severe theoretical constraints required by previously reported INI, IMI and MIM waveguide tapers 15 . Combined with advanced micro/nanofabrication technologies, this new and robust scheme will make experimental realization of large area on-chip rainbow trapping platforms more achievable, which will pave the way towards on-chip light localization, spectrum splitting 15 and super absorbers 35 , and will impact a broad range of photon-harvesting and energy technologies ranging from photovoltaics 36 , thin-film thermal absorbers/emitters 37 , to plasmon-mediated photocatalysis 38 .…”

“…With the ability to produce highly confined and localized optical fields, it is believed that the conventional rules for light-matter interactions need to be re-examined, and new regimes of optical physics are expected. To develop applications based on this intriguing broadband slow light effect, various architectures have been proposed, including surface graded metallic gratings 9,10 , insulator-negative-index-insulator (INI) 6,11 , insulator-metal-insulator (IMI) 12 and metal-insulator-metal (MIM) waveguide tapers [13][14][15] . However, each proposal has its inherent difficulties resulting in the limited experimental realization of the rainbow trapping structures.…”

LIGHT ABSORBER WITH AN ULTRA-BROAD FLAT BAND BASED ON MULTI-SIZED SLOW-WAVE HYPERBOLIC METAMATERIAL THIN-FILMS (Invited Paper)

“…Therefore, for a waveguide of a certain core width, the slow-wave modes can be excited around a certain wavelength. Though the lossless assumption cannot explain the physics of broadband absorption accurately, the degeneracy points at the dispersion curves of lossless structures can approximately predict the critical width [28,29].…”

Compact broadband slow wave system based on spoof plasmonic THz waveguide with meander grooves

“…By scaling down the feature size of the plasmonic graded metallic grating structures, it has been shown that broadband SPs can be trapped by the plasmonic graded structures in visible frequencies [17]. Up to now, different architectures have been developed for efficiently trapping SPs [18][19][20][21] to facilitate applications of the intriguing slow wave behaviors.…”