# Fano resonance lineshapes in a waveguide-microring structure enabled by an air-hole

## TL;DR

This paper demonstrates a simple method to induce Fano resonance lineshapes in waveguide-microring structures by inserting an air-hole, enabling enhanced device performance for integrated photonics applications.

## Contribution

The novel approach of inserting an air-hole to achieve Fano lineshapes in waveguide-microring systems is demonstrated and characterized experimentally.

## Key findings

- Fano lineshapes with slope over 400 dB/nm and extinction over 20 dB achieved
- Air-hole position and size control Fano asymmetry parameters
- The structure offers broadband operation and fabrication tolerance

## Abstract

We propose and demonstrate, by simply inserting an air-hole in the waveguide side-coupling with a microring resonator (MRR), the transmission spectrum presents Fano lineshapes at all of the resonant modes. Measured from the fabricated devices, Fano lineshapes with slope rates over 400 dB/nm and extinction ratios over 20 dB are obtained. We ascribe it to the air-hole-induced phase-shift between the discrete resonant modes of the MRR and the continuum propagating mode of the bus-waveguide, which modifies their interference lineshapes from symmetric Lorentzian to asymmetric Fano. From devices with varied locations and diameters of the air-hole, different Fano asymmetric parameters are extracted, verifying the air-hole-induced phase-shifts. This air-hole-assisted waveguide-MRR structure for achieving Fano resonance lineshapes has advantages of simple design, compact footprint, large tolerance of fabrication errors, as well as broadband operation range. It has great potentials to expand and improve performances of on-chip MRR-based devices, including sensors, switchings and filters.