Bottle microresonator broadband and low repetition rate frequency comb generator

TL;DR

This paper introduces a novel broadband, low repetition rate optical frequency comb generator based on an elongated nanoscale bottle microresonator on an optical fiber surface, enabling efficient comb generation with cw or mode-locked lasers.

Contribution

The authors propose a new microresonator design with a specific spectral structure that facilitates broadband, low repetition rate frequency comb generation, advancing microresonator-based photonic technologies.

Findings

Microresonator exhibits a broadband, equidistant spectrum.

Comb can be generated using cw laser matching a single eigenfrequency.

Alternative pumping with mode-locked laser produces a low repetition rate comb.

Abstract

We propose a new type of broadband and low repetition rate frequency comb generator which has the shape of an elongated and nanoscale-shallow optical bottle microresonator created at the surface of an optical fiber. The free spectral range (FSR) of the broadband azimuthal eigenfrequency series of this resonator is the exact multiple of the FSR of the dense and narrowband axial series. The effective radius variation of the microresonator is close to a parabola with a nanoscale height which is greater or equal to lambda/2pi*n0 (here lambda is the characteristic radiation wavelength and n0 is the refractive index of the microresonator material). Overall, the microresonator possesses a broadband, small FSR, and accurately equidistant spectrum convenient for the generation of a broadband and low repetition rate optical frequency comb. It is shown that this comb can be generated by pumping with a cw laser, which radiation frequency matches a single axial eigenfrequency of the microresonator, or, alternatively, by pumping with a mode-locked laser, which generates a narrowband low repetition rate comb matching a series of equidistant axial eigenfrequencies situated between adjacent azimuthal eigenfrequencies.