Squeezed light from a diamond-turned monolithic cavity

TL;DR

This paper demonstrates the fabrication of a monolithic LiNbO3 cavity via diamond turning, achieving vacuum squeezing of 2.6 dB at 1064 nm, with potential for further enhancement.

Contribution

It introduces a novel monolithic, diamond-turned LiNbO3 cavity for optical squeezing, combining precision fabrication with tunable coupling for improved quantum optics applications.

Findings

Achieved 2.6 dB vacuum squeezing at 1064 nm.

Demonstrated high-quality monolithic cavity with low absorption loss.

Showed tunable coupling via birefringent prisms.

Abstract

For some crystalline materials, a regime can be found where continuous ductile cutting is feasible. Using precision diamond turning, such materials can be cut into complex optical components with high surface quality and form accuracy. In this work we use diamond-turning to machine a monolithic, square-shaped, doubly-resonant $LiNbO_3$ cavity with two flat and two convex facets. When additional mild polishing is implemented, the Q-factor of the resonator is found to be limited only by the material absorption loss. We show how our monolithic square resonator may be operated as an optical parametric oscillator that is evanescently coupled to free-space beams via birefringent prisms. The prism arrangement allows for independent and large tuning of the fundamental and second harmonic coupling rates. We measure $2.6\pm0.5$ dB of vacuum squeezing at 1064 nm using our system. Potential improvements to obtain higher degrees of squeezing are discussed.