A self-tuning optical resonator

TL;DR

This paper presents a monolithic nonlinear optical resonator that passively maintains resonance with input light through intensity-dependent refractive index effects, enabling stable second-harmonic generation without active feedback.

Contribution

It introduces a self-tuning optical resonator leveraging a strong nonlinear effect for passive resonance stabilization in a monolithic cavity.

Findings

Achieved stable second-harmonic generation without active feedback.

Demonstrated the resonator's ability to self-tune across FSR-scale laser frequency excursions.

Identified a previously unreported strong optical nonlinearity supporting the self-tuning.

Abstract

We demonstrate a nonlinear optical resonator that tunes itself onto resonance with an input beam. In a monolithic Fabry-Perot cavity implemented in rubidium-doped periodically-poled potassium titanyl phosphate, an intensity-dependent refractive index produces line-pulling by multiple free-spectral ranges (FSRs). In this condition, the cavity passively maintains optical resonance in the face of FSR-scale excursions of the drive laser frequency: when one resonant operating-point becomes unstable, the resonator rapidly transitions to another resonant operating point. We demonstrate stable second-harmonic generation with no active feedback to laser or cavity. The self-tuning effect appears to be supported by a very strong, previously unreported optical nonlinearity.