Spectral symmetry of Fano resonances in a waveguide coupled to a microcavity

TL;DR

This paper explores how the symmetry of Fano resonances in a photonic crystal waveguide with a side-coupled cavity can be controlled by adjusting the cavity-block distance, revealing a transition from asymmetric to symmetric spectra.

Contribution

It demonstrates the spectral symmetry behavior of Fano resonances in photonic crystal waveguides and links the parity to the Fabry-Perot roundtrip phase through numerical analysis.

Findings

Spectral symmetry varies with cavity-block distance.

Transmission spectra resemble Fabry-Perot etalon behavior.

Parity correlates with Fabry-Perot roundtrip phase.

Abstract

We investigate the parity of transmission spectra in a photonic crystal (PhC) waveguide with a side-coupled cavity and a partially blocking element. We demonstrate, by means of numerical calculations, that by varying the cavity-block distance the spectra vary from being asymmetric with blue parity, to being symmetric (Lorentzian), to being asymmetric with red parity. For cavity-block distances larger than five PhC lattice constants, we show that the transmission spectrum is accurately described as the transmission spectrum of a Fabry-Perot etalon with a single propagating Bloch mode, and that the parity of the transmission spectrum correlates with the Fabry-Perot roundtrip phase.