Low loss switchable topological photonic crystal enabled by submicron-scale patterning and phase-change of Sb2Se3

TL;DR

This work tackles the challenge of reconfiguring photonic topological insulators without incurring large optical losses. It introduces submicron Sb2Se3 nanopatterning on a silicon Barik-type 2D PTI to induce a topological phase transition via phase-change, while Sb2Se3 remains ultra-low loss in both amorphous and crystalline states. Simulations show Sb2Se3 patterns yield a selective redshift of the p-mode with preserved high Q ($\sim 10^4$) in both states, and experiments demonstrate an absorption-free topological switch with measured $Q$ around $10^3$, far superior to GST-based devices. The results establish Sb2Se3 as a viable, low-loss PCM platform for practical reconfigurable topological photonic devices and motivate further reversible switching and nonlinear applications in PTIs.

Abstract

Photonic topological insulators (PTIs) offer robust platforms for light manipulation, but reconfigurable control of their topological properties without degrading performance remains a major challenge. While phase-change materials (PCMs) provide large refractive index modulation, widely used materials such as Ge2Sb2Te5 (GST) have been successfully deployed in commercial applications including optical data storage. However, they exhibit significant optical absorption in their crystalline state, which poses a challenge for transmissive photonic devices such as PTIs where high transparency is essential. Here, we overcome this fundamental limitation by integrating the ultra-low-loss PCM antimony triselenide (Sb2Se3) onto a silicon-based 2D PTI. We achieve submicron-scale selective patterning of Sb2Se3 on a photonic crystal for the first time, and demonstrate a topological phase transition induced by the material phase change. Owing to the transparency of Sb2Se3 in both its amorphous and crystalline states, a high Q-factor on the order of 10^3 is preserved-representing nearly an order-of-magnitude improvement over previous GST-based devices. This work resolves the absorption-loss bottleneck in reconfigurable PTIs and paves the way for practical, low-loss, tunable topological photonic devices.

Figures (8)

• Figure 1: (a) Schematic of a Barik-type Si topological photonic crystal slab. (b) Band dispersion curves of the TE-like mode for the photonic crystal with $\Delta R > 0$. (c) Electric-field distributions of the $p$- and $d$-modes at the $\Gamma$ point in the unit cell. The plotted field distributions represent the sum of two eigenmodes of the effective Hamiltonian at the $\Gamma$ point. (d) ${\lvert \boldsymbol{E}_p \rvert }^2 / {\lvert \boldsymbol{E}_d \rvert }^2$ distribution in the unit cell.
• Figure 2: (a) The unit cell of the designed Sb2Se3-loaded PhC structure for numerical simulation. The left side shows the unit cell with a tapered rectangular Sb2Se3 pattern, and the right side defines the structural variables. (b) The geometry of tapered rectangular and cylindrical Sb2Se3 patterns with reduced upper parts.
• Figure 3: (a) Refractive index and extinction coefficient of the 80-nm Sb2Se3 and 30-nm GST films obtained from ellipsometry. (b), (c) Mode frequencies of the $p$- and $d$-modes at the $\Gamma$ point as a function of hole shift $\Delta R$ for (b) GST-loaded PhC and (c) Sb2Se3-loaded PhC. Solid and broken lines represent the $p$- and $d$-modes, respectively. Blue and black lines indicate the amorphous and crystalline states, respectively. (d), (e) Quality factors of the $p$- and $d$-modes at the $\Gamma$ point as a function of $\Delta R$ for (d) GST-loaded PhC and (e) Sb2Se3-loaded PhC. The $d$-mode Q-factors are not shown in (e) because they are theoretically infinite in the absence of material absorption.
• Figure 4: (a) Fabrication process of the Sb2Se3-loaded PTI. (b) The designed Sb2Se3-loaded PhC structure and a SEM image of the fabricated PhC. The lattice constant and slab thickness are $a = 740$ nm and $h = 205$ nm, respectively. (c) AFM image and cross-sectional profile of the deposited Sb2Se3 nanostructure. The height of the Sb2Se3 structure is approximately 50 nm.
• Figure 5: Experimental setup for the reflection measurement.