Fig. 1: Construction of one topological interface mode (TIM) and its tunability.
From: Realization of photonic charge-2 Dirac point by engineering super-modes in topological superlattices
a The proposed structure for a single TIM. The upper panel shows the unit cell of both photonic crystals (p-type and q-type unit cell) and the configuration of the defective unit. All of them are made up of alternating layers of two dielectric materials, denoted as M1 (white) and M2 (gray). The thickness notations are indicated on each layer. b Scanning electron microscope (SEM) picture of Sample II. The orange arrowhead shows the direction of incident light. Here, we employ HfO2 as M1 (bright region) and SiO2 as M2 (dark region). The refractive indices of HfO2 and SiO2 are 2 and 1.46, respectively. c Measured transmission spectra of Sample II under normal incidence, oblique incidence of transverse-magnetic (TM) waves, and oblique incidence of transverse-electric (TE) waves are shown by black, red, and blue circles, respectively. The oblique incident angle is 30°. The magenta circles show measured transmission spectrum of Sample III under normal incidence. d The calculated electric field profile of the TIM for Sample II under normal incidence is plotted by the solid red line. The gray line shows the corresponding refractive index profile. e d-dependent resonance frequency of the TIM with kx = 0 μm−1. f The in-plane dispersion relation of the TIM for the TM (red line) and TE (blue line) polarizations excited in sample II. In both e and f, solid lines are calculated by the simulation software COMSOL, and open markers are obtained directly from experimental data. The corresponding experimental transmission spectra of the black, red, blue, and magenta arrowheads in e and f are shown in c. The ranges of ±standard deviation of measured data are shown by the error bars.
