# Frequency-multiplexed photon pairs over 1000 modes from a quadratic nonlinear optical waveguide resonator with a singly-resonant configuration

## TL;DR

This paper reports on a novel frequency-multiplexed photon pair source using a quadratic nonlinear waveguide resonator that generates over 1000 modes, enabling high-dimensional quantum photonic applications.

## Contribution

The work introduces a monolithic PPLN waveguide resonator that produces continuous, multi-mode photon pairs over 80 nm without missing modes, surpassing previous multi-resonant sources.

## Key findings

- Generated over 1000 frequency modes in photon pairs
- Achieved continuous photon pair generation over 80 nm range
- Demonstrated comb-like spectral structure with high mode density

## Abstract

We demonstrate a frequency multiplexed photon pair generation based on a quadratic nonlinear optical waveguide inside a cavity which confines only signal photons without confining idler photons and the pump light. We monolithically constructed the photon pair generator by a periodically-poled lithium niobate (PPLN) waveguide with a high reflective coating for the signal photons around 1600 nm and with anti-refrective coatings for the idler photons around 1520 nm and the pump light at 780 nm at the end faces of the PPLN waveguide. We observed a comb-like photon pair generation with a mode spacing of the free spectral range of the cavity. Unlike the conventional multiple resonant photon pair generation experiments, the photon pair generation were incessant within a range of 80 nm without missing teeth due to a mismatch of the energy conservation and the cavity resonance condition of the photons, resulting in over 1000-mode frequency multiplexed photon pairs in this range.