# Complete photonic bandgaps in supercell photonic crystals

## TL;DR

This paper introduces supercell photonic crystals with broken symmetries that support complete photonic bandgaps at visible frequencies in lossless materials, challenging previous assumptions about bandgap behavior.

## Contribution

It presents a novel class of supercell photonic crystals that achieve complete bandgaps at lower index contrasts and in visible frequencies, with findings that contradict prior conjectures.

## Key findings

- Supports complete bandgap at index contrast 2.1
- First 2D photonic crystal with complete bandgap in visible frequencies
- Complete bandgaps do not always increase with index contrast

## Abstract

We develop a class of supercell photonic crystals supporting complete photonic bandgaps based on breaking spatial symmetries of the underlying primitive photonic crystal. One member of this class based on a two-dimensional honeycomb structure supports a complete bandgap for an index-contrast ratio as low as $n_{high}/n_{low} = 2.1$, making this the first such 2D photonic crystal to support a complete bandgap in lossless materials at visible frequencies. The complete bandgaps found in such supercell photonic crystals do not necessarily monotonically increase as the index-contrast in the system is increased, disproving a long-held conjecture of complete bandgaps in photonic crystals.