# Waveguide-based OPO source of entangled photon pairs

## TL;DR

This paper introduces a compact, waveguide-based OPO source of narrow-band, energy-time entangled photon pairs at telecom wavelengths, suitable for long-distance quantum communication, with high coherence and confirmed entanglement quality.

## Contribution

It presents a monolithic doubly resonant PPLN waveguide OPO producing high-quality entangled photon pairs at 1560nm with narrow bandwidth and long coherence time.

## Key findings

- Photon pairs generated at 1560nm with 117MHz bandwidth
- Coherence time of 2.7 ns confirmed by measurements
- High entanglement quality verified by Bell test

## Abstract

In this paper we present a compact source of narrow-band energy-time entangled photon pairs in the telecom regime based on a Ti-indiffused Periodically Poled Lithium Niobate (PPLN) waveguide resonator, i.e. a waveguide with end-face dielectric multi-layer mirrors. This is a monolithic doubly resonant Optical Parametric Oscillator (OPO) far below threshold, which generates photon pairs by Spontaneous Parametric Down Conversion (SPDC) at around 1560nm with a 117MHz (0.91 pm)- bandwidth. A coherence time of 2.7 ns is estimated by a time correlation measurement and a high quality of the entangled states is confirmed by a Bell-type experiment. Since highly coherent energy-time entangled photon pairs in the telecom regime are suitable for long distance transmission and manipulation, this source is well suited to the requirements of quantum communication.