Non-volatile photorefractive tuning and green light generation in a diamond cavity

TL;DR

This paper demonstrates non-volatile resonance tuning in diamond nanocavities through a photorefractive effect, enabling precise control of optical properties and green light generation, with potential applications in quantum and nonlinear optics.

Contribution

The study reveals a photorefractive effect in diamond nanocavities that allows deterministic, non-volatile tuning of resonances and third-harmonic generation, previously unobserved in diamond.

Findings

Resonance frequency blue-shifted by 20.9 GHz, exceeding cavity linewidth.

Observed refractive index change of -10^{-4}.

Relaxation over several tens of hours.

Abstract

Single-crystal diamond nanocavities have tremendous potential for use in quantum and nonlinear optical technologies. The ability to precisely control their resonant frequencies is essential for many applications, and $\textit{in situ}$ tuning is particularly desirable. In this work, we demonstrate deterministic and non-volatile resonance tuning of a diamond nanocavity. We observed a photorefractive effect in concert with the generation of third-harmonic light within the device. This effect blue-shifted the cavity resonance frequency by $20.9\,\text{GHz}$, exceeding the cavity linewidth. The shift corresponded to a fractional change in refractive index of $-10^{-4}$, and its relaxation occurred over several tens of hours. Although photorefraction is a second-order nonlinear effect and has previously not been observed in diamond owing to its vanishing $\chi^{(2)}$, the observed behaviour is consistent with the generation of non-zero $\chi^{(2)}$ by electric fields from charged crystal defects. This observation could enable the realisation of diamond frequency converters and electro-optical modulators that rely on second-order nonlinearity.