Experimental verification of the "rainbow" trapping effect in plasmonic graded gratings

TL;DR

This paper experimentally demonstrates the 'rainbow' trapping effect in plasmonic graded gratings, confirming theoretical predictions and showing potential for optical storage and delay applications.

Contribution

First experimental verification of trapped rainbow in graded metallic gratings, validating theoretical models and demonstrating wavelength-specific light trapping.

Findings

Observation of reduced group velocities in gratings

Confirmation of plasmonic bandgap formation

Wavelength-dependent light trapping along the grating

Abstract

We report the first experimental observation of trapped rainbow1 in graded metallic gratings2-4, designed to validate theoretical predictions for this new class of plasmonic structures. One-dimensional tapered gratings were fabricated and their surface dispersion properties tailored by varying the grating period and depth, whose dimensions were confirmed by atomic force microscopy. Reduced group velocities and the plasmonic bandgap were observed. Direct measurements on graded grating structures show that light of different wavelengths in the 500-700nm region is "trapped" at different positions along the grating, consistent with computer simulations, thus verifying the "rainbow" trapping effect. The trapped rainbow effect offers exciting pathways for optical information storage and optical delays in photonic circuits at ambient temperature.