Highly efficient polarization-entangled photon-pair generation in lithium niobate waveguides based on bound states in the continuum

TL;DR

This paper introduces a highly efficient method for generating polarization-entangled photon pairs in lithium niobate waveguides using bound states in the continuum, significantly enhancing efficiency without complex polarization processes.

Contribution

Proposes a simple, BIC-based approach for entangled photon-pair generation in LN waveguides, achieving over five orders of magnitude efficiency improvement with minimal length.

Findings

Generation rate scales linearly with waveguide length

Efficiency is greatly enhanced across a wide spectrum

Method simplifies entangled photon source design

Abstract

Integrated optics provides a platform for the experimental implementation of highly complex and compact circuits for practical applications as well as for advances in the fundamental science of quantum optics. The lithium niobate (LN) waveguide is an important candidate for the construction of integrated optical circuits. Based on the bound state in the continuum (BIC) in a LN waveguide, we propose an efficient way to produce polarization-entangled photon pairs. The implementation of this method is simple and does not require the polarization process needed for periodically poled LN. The generation rate of the entangled photon pairs increases linearly with the length of the waveguide. For visible light, the generation efficiency can be improved by more than five orders of magnitude with waveguides having the length of only a few millimeters, compared with the corresponding case without BICs. The phenomena can appear in a very wide spectrum range from the visible to THz regions. This study is of great significance for the development of active integrated quantum chips in various wavelength ranges.