# Dual-Broadband Topological Photonic Crystal Edge State Based on Liquid Crystal Tunability

## TL;DR

This paper introduces a tunable photonic crystal structure using liquid crystals to control terahertz light for advanced optical applications.

## Contribution

A dual-band tunable photonic crystal edge state using liquid crystal for terahertz spectral manipulation is proposed.

## Key findings

- The structure enables excitation of K and K′ valleys in specific terahertz ranges.
- Liquid crystal integration allows continuous tuning of the dual-band spectral range.
- Applications include tunable filters, optical communication, and high-resolution imaging.

## Abstract

The rapid advancements in optical communication and sensing technologies have significantly increased the demand for advanced tunable spectral systems. This study presents a dual-band terahertz transmission and manipulation approach by leveraging the topologically protected properties of valley-topological photonic crystal edge states. The designed structure facilitates the excitation of the K valley within the range of 0.851–0.934 THz and the K′ valley from 1.604 to 1.686 THz, while also demonstrating anomalous refraction and birefringence. The calculated emission angles, derived through momentum matching, enable transitions between single-wave and dual-wave emissions and allow for precise angle control. The introduction of the liquid crystal material NJU-LDn-4 enables continuous tuning of the dual-band spectral range under a varying electric field, broadening the operating frequency bands to the ranges of 0.757–0.996 THz and 1.426–1.798 THz, respectively. These findings suggest promising applications in tunable filter design, optical communication, photonic computing, optical sensing, and high-resolution imaging, particularly in novel optical devices requiring precise control over spectral characteristics and light propagation.