# Frequency comb generation in SNAP bottle resonators

## TL;DR

This paper presents a theory for generating optical frequency combs in ultra-compact SNAP bottle microresonators, enabling sub-GHz spectral spacing with potential for stable soliton dynamics and dispersion engineering.

## Contribution

It introduces a novel theoretical framework for frequency comb generation in SNAP microresonators, highlighting their advantages over traditional larger resonators.

## Key findings

- SNAP microresonators can produce sub-GHz frequency combs.
- Stable and quasi-periodic comb dynamics are achievable.
- Engineering the radius profile can compensate dispersion effects.

## Abstract

We develop a theory of optical frequency comb generation in ultra-compact Surface Nanoscale Axial Photonic (SNAP) bottle microresonators, employing the nonlinear interaction of whispering gallery modes which are confined along an optical fiber with nanoscale radius variation. We predict that a SNAP microresonator with a few-$\mu$m radius can generate a frequency comb with an ultra-fine sub-GHz spectral spacing, which would require traditional ring resonators of $cm$ radius. We identify regimes of stable or quasi-periodic comb dynamics due to soliton excitation, and also show that special engineering of the SNAP radius profile can be used to compensate nonlinearity induced dispersion.