Quantum correlations and fluctuations in the pulsed light produced by a synchronously pumped optical parametric oscillator below its oscillation threshold

TL;DR

This paper develops a quantum theory for pulsed light from a synchronously pumped optical parametric oscillator below threshold, revealing unique temporal correlations and conditions for perfect squeezing in the pulsed regime.

Contribution

It provides a simplified quantum model for SPOPOs, clarifying which quantum effects are similar to continuous-wave cases and which are specific to pulsed operation.

Findings

Quantum fluctuations within the same pulse are uncorrelated.

Correlations exist between nearby pulses at similar relative times.

Perfect squeezing occurs at multiples of the pulse repetition frequency near threshold.

Abstract

We present a simple quantum theory for the pulsed light generated by a synchronously pumped optical parametric oscillator (SPOPO) in the degenerate case where the signal and idler trains of pulses coincide, below threshold and neglecting all dispersion effects. Our main goal is to precise in the obtained quantum effects, which ones are identical to the c.w. case and which ones are specific to the SPOPO. We demonstrate in particular that the temporal correlations have interesting peculiarities: the quantum fluctuations at different times within the same pulse turn out to be totally not correlated, whereas they are correlated between nearby pulses at times that are placed in the same position relative to the centre of the pulses. The number of significantly correlated pulses is of the order of cavity finesse. We show also that there is perfect squeezing at noise frequencies multiple of the pulse repetition frequency when one approaches the threshold from below on the signal field quadrature measured by a balanced homodyne detection with a local oscillator of very short duration compared to the SPOPO pulse length.