[Paper Review] Multifrequency and multimode topological waveguides in a Stampfli-triangle photonic crystal with large valley Chern numbers

Bei Yan, Yiwei Peng+10 more|Figshare|Apr 29, 2021

Topological Materials and Phenomena4 citations

TL;DR

This paper proposes a multifrequency and multimode topological waveguide in a Stampfli-triangle photonic crystal with large valley Chern numbers, enabling simultaneous transmission of two low-frequency and four high-frequency topological edge states. Using a Z-shaped waveguide with opposite valley Chern number regions, the authors experimentally demonstrate frequency- and position-selective excitation, achieving high-capacity topological transmission and proposing a frequency-dependent multimode beam splitter for integrated photonics.

ABSTRACT

The multifrequency quantum valley Hall effect (QVHE) with a large valley Chern number has been realized to significantly improve the transmission capacity of topological waveguides and increase the mode density of topological waveguides. However, multifrequency and multimode QVHEs have not been realized simultaneously. In this work, using tight-binding model calculations and numerical simulations, a valley photonic crystal (VPC) consisting of a Stampfli-triangle photonic crystal is constructed, and its multiple degeneracies in the low-frequency and high-frequency bands split simultaneously to realize the QVHE with multiple topological edge states (TESs). The multifrequency and multimode topological transmission with two low-frequency modes and four high-frequency modes is realized by means of simulations and experiments through a Z-shaped waveguide constructed using two VPCs with opposite valley Chern numbers to prove the realization of a large valley Chern number in the two frequency bands. The two low-frequency modes are successfully distinguished with position-dependent selective excitations, which experimentally demonstrates the occurrence of a large valley Chern number. A frequency-dependent multimode beam splitter is theoretically proposed for high-performance integrated photonic device applications. These results provide new ideas for high-efficiency and high-capacity optical transmission and communication devices and their integration; furthermore, they broaden the application range of TESs.

Motivation & Objective

• To achieve simultaneous multifrequency and multimode topological edge states in a photonic crystal for enhanced transmission capacity.
• To realize a large valley Chern number in both low- and high-frequency bands using a Stampfli-triangle lattice structure.
• To demonstrate experimentally distinguishable topological edge states via position- and frequency-dependent excitation.
• To propose a frequency-selective multimode beam splitter for high-performance integrated photonic applications.

Proposed method

• Construction of a valley photonic crystal (VPC) based on a Stampfli-triangle lattice with engineered subwavelength dielectric structures.
• Use of tight-binding model calculations to analyze band degeneracies and predict topological properties.
• Numerical simulation of Z-shaped waveguides formed by joining two VPCs with opposite valley Chern numbers to enable topological edge state transmission.
• Implementation of position-dependent selective excitation to distinguish between low-frequency topological edge states.
• Experimental validation of multifrequency and multimode topological transmission in a fabricated waveguide structure.
• Theoretical proposal of a frequency-dependent multimode beam splitter based on the observed topological mode multiplexing.

Experimental results

Research questions

• RQ1 Can a photonic crystal support topological edge states across multiple frequency bands with large valley Chern numbers?
• RQ2 How can multifrequency and multimode topological transmission be experimentally realized in a single waveguide structure?
• RQ3 Can topological edge states at different frequencies and positions be selectively excited and distinguished?
• RQ4 What is the role of valley Chern number in enabling high-capacity topological waveguiding?
• RQ5 How can topological mode multiplexing be leveraged for integrated photonic device design?

Key findings

• Two low-frequency topological edge states were experimentally resolved using position-selective excitation, confirming the presence of a large valley Chern number.
• Four high-frequency topological edge states were simultaneously observed in the waveguide, demonstrating multimode transmission in the high-frequency band.
• The Z-shaped waveguide structure successfully guided both low- and high-frequency modes with topological protection, validated by simulations and experiments.
• The observed topological edge states exhibited robust transmission against structural disorder, confirming their topological nature.
• A theoretical framework for a frequency-dependent multimode beam splitter was proposed based on the multiplexing of topological modes.
• The study demonstrates a significant increase in mode density and transmission capacity through multifrequency topological waveguiding in a single photonic crystal platform.