Toward Spectral Engineering of Squeezed Light in High-Gain PDC

TL;DR

This paper explores how dispersion engineering and gain influence the spectral purity of squeezed light generated via parametric down-conversion, revealing conditions for optimal spectral mode control in quantum light sources.

Contribution

It provides a detailed analysis of spectral purity evolution in high-gain PDC, highlighting the role of dispersion engineering and gain in tailoring squeezed-light spectral properties.

Findings

Spectral purity increases monotonically with gain in unapodized waveguides.

Dispersion engineering enables nonmonotonic purity behavior, with initial decrease then recovery.

Group velocity matching conditions lead to rapid spectral purification.

Abstract

We investigated the spectral properties of squeezed light generated via parametric down-conversion in the high-gain regime, considering both unapodized and apodized dispersion-engineered waveguides. The gain-dependent evolution of these states is examined starting from the low-gain regime, which includes both highly correlated and nearly uncorrelated cases. For the unapodized configuration, we observe a monotonic increase in spectral purity with gain, whereas the apodized configuration exhibits a nonmonotonic dependence, initially decreasing and then recovering at higher gain. By combining Schmidt-mode analysis with a group-velocity-based interpretation, we explain why different dispersion conditions exhibit distinct gain-dependent behavior, specifically that rapid purification occurs when the pump group velocity lies between those of the signal and idler. Our study shows that the evolution of spectral purity is governed primarily by the underlying dispersion of the waveguide. These results demonstrate that dispersion engineering and parametric gain can be jointly exploited to tailor the spectral-mode structure of squeezed-light sources, enabling their optimization for a broad range of quantum applications.