Realization of "Trapped Rainbow" in 1D slab waveguide with Surface Dispersion Engineering

TL;DR

This paper demonstrates a dielectric waveguide design that can trap a broad spectrum of visible light in a spatially controlled manner, creating a 'trapped rainbow' effect through surface dispersion engineering.

Contribution

The work introduces a novel 1D dielectric waveguide with engineered surface dispersion enabling broad-band light trapping and frozen modes, using surface grating parameters for tuning.

Findings

Achieved broad visible spectrum trapping in a dielectric waveguide.

Controlled dispersion via surface grating parameters.

Low-loss, planar device with simplified fabrication.

Abstract

We present a design of a one dimensional dielectric waveguide that can trap a broad band light pulse with different frequency component stored at different positions, effectively forming a "trapped rainbow"[1]. The spectrum of the rainbow covers the whole visible range. To do this, we first show that the dispersion of a $\text{SiO}_2$ waveguide with a Si grating placed on top can be engineered by the design parameter of the grating. Specifically, guided modes with zero group velocity(frozen modes) can be realized. Negative Goos-H\"anchen shift along the surface of the grating is responsible for such a dispersion control. The frequency of the frozen mode is tuned by changing the lateral feature parameters (period and duty cycle) of the grating. By tuning the grating feature point by point along the waveguide, a light pulse can be trapped with different frequency components frozen at different positions, so that a "rainbow" is formed. The device is expected to have extremely low ohmic loss because only dielectric materials are used. A planar geometry also promises much reduced fabrication difficulty.