• Photonics Research
  • Vol. 9, Issue 8, 08001592 (2021)
Zhanyuan Zhang1, Feifei Qin1, Yi Xu1、2、*, Songnian Fu2, Yuncai Wang2, and Yuwen Qin2
Author Affiliations
  • 1Department of Electronic Engineering, College of Information Science and Technology, Jinan University, Guangzhou 510632, China
  • 2Advanced Institute of Photonics Technology, School of Information Engineering, and Guangdong Provincial Key Laboratory of Information Photonics Technology, Guangdong University of Technology, Guangzhou 510006, China
  • show less

    Abstract

    Negative refraction might occur at the interface between a two-dimensional photonic crystal (PhC) slab and a homogeneous medium, where the guiding of the electromagnetic wave along the third dimension is governed by total internal reflection. Herein, we report on the observation of negative refraction in the PhC slab where the vertical guiding is enabled by a bound state in the continuum and essentially beyond the light cone. Such abnormal refraction and guiding mechanism are based on the synchronous crafting of spatial dispersion and the radiative lifetime of Bloch modes within the radiative continuum. Microwave experiments are provided to further validate the numerical proposal in an all-dielectric PhC platform. It is envisioned that the negative refraction observed beyond the light cone might facilitate the development of optical devices in integrated optics, such as couplers, multiplexers, and demultiplexers.

    1. INTRODUCTION

    Envisioned by Veselago in the 1960s [1], abnormal refraction has received intense research efforts from the photonics community with long-term quests for new possibility and functionality [218], including but not limited to comprehensive manipulation of spacetime wave packets [2,14], generalized laws of reflection and refraction [12], negative refraction [46,10,11,15], superprism [8,9], self-collimation [13,14], and optical lensing [15]. In particular, the two-dimensional negative refraction in a photonic crystal (PhC) slab provides on-chip solutions for molding the flow of light in an unparalleled manner [5,711,13,14,17]. To date, the guiding mechanism of light along the slab normal for such on-chip negative refraction strictly relies on the effect of total internal reflection, which inevitably imposes a fundamental limitation that such negative refraction can only be achieved below the light cone of surrounding medium.