Light Guiding in Low Index Materials using High-Index-Contrast Waveguides Vilson R. Almeida, Qianfan Xu, Roberto R. Panepucci, Carlos A. Barrios, and Michal Lipson Cornell University, School of Electrical and Computer Engineering, 429 Phillips Hall Ithaca, NY 14853, U.S.A. ABSTRACT We propose a novel high-index-contrast waveguide structure capable of light strong confinement and guiding in low-refractive-index materials. The principle of operation of this structure relies on the electric field (E-field) discontinuity at the interface between high-index- contrast materials. We show that by using such a structure the E-field can be strongly confined in a 50-nm-wide low-index region with normalized average intensity of 20 μm -2 . This intensity is approximately 20 times higher than that can be achieved in SiO 2 with conventional rectangular or photonic crystal waveguides. INTRODUCTION Recent results in integrated optics have shown the ability of efficiently guiding, filtering, bending and splitting light on chips using a variety of waveguide structures [1]. Extremely sharp curves, bends, and splitters have also been demonstrated, allowing a high level of integration [2,3]. Multiplexers and demultiplexers using resonant structures such as ring resonators have been shown [4]. All of these structures are based on total internal reflection (TIR) as the guiding mechanism. This mechanism is commonly thought to prohibit the light to be confined and guided in the lower-index region. In the last few years, guiding light in low-index materials has become increasingly important for applications such as optical sensing, interaction with low index materials, and avoiding nonlinearities in the high-index material. Early attempts to guide light in the low-index material on high-index-contrast platform led to structures that are wavelength dependent and have relatively large transverse dimensions, which limited their optical intensity and ability for integration. The antiresonant reflecting optical waveguide (ARROW) structure uses the external reflection at the high-index-contrast interfaces as a guiding mechanism [5], in contrast to the total internal reflection used in standard waveguides; this structure was recently proposed for sensing applications [6]. Based on similar principles, the OmniGuide fibers and photonic band-gap fibers were investigated [7,8], where 1- D or 2-D periodic structures are used to provide the near-unity reflections for guiding. All aforementioned structures are wavelength dependent, inherently leaky, and present large cross sectional dimensions of at least several micrometers. We propose a waveguide structure that can confine light inside a nanometer-wide area of low-index material with high E-field amplitude and optical intensity. In contrast to the leaky nature of the previously mentioned structures, the guided mode is an eigenmode of our proposed structure; therefore, it is fundamentally lossless. Our proposed structure, hereafter named slot- waveguide, consists of two parallel high-index contrast waveguides separated by a nanometer- sized low-refractive-index slot. Since the slot-waveguide does not rely on resonance principles, the eigenmode is almost wavelength insensitive. Furthermore, it is fully compatible with highly- Mat. Res. Soc. Symp. Proc. Vol. 797 © 2004 Materials Research Society W6.10.1