# Efficient parametric frequency conversions in lithium niobate nanophotonic chips

## TL;DR

This paper demonstrates highly efficient, chip-integrated lithium niobate nanowaveguides for nonlinear optical processes, enabling advanced classical and quantum photonic applications with high conversion efficiencies and broadband capabilities.

## Contribution

Introduction of an optimally mode-matched, periodically poled lithium niobate nanowaveguide achieving record efficiencies in frequency conversion on chip.

## Key findings

- Second harmonic generation efficiency over 2200% W^{-1}cm^{-2}
- Broadband difference frequency generation over 4.5 THz
- High coincidence to accidental ratio of 600 in photon pair generation

## Abstract

Chip-integrated nonlinear photonics holds the key for advanced optical information processing with superior performance and novel functionalities. Here, we present an optimally mode-matched, periodically poled lithium niobate nanowaveguide for efficient parametric frequency conversions on chip. Using a 4-mm nanowaveguide with subwavelength mode confinement, we demonstrate second harmonic generation with efficiency over $2200\%~W^{-1}cm^{-2}$, and broadband difference frequency generation with similar efficiency over a 4.5-THz spectral span. These allow us to generate correlated photon pairs over multiple frequency channels via spontaneous parametric down conversion, all in their fundamental spatial modes, with a coincidence to accidental ratio as high as 600. The high efficiency and dense integrability of the present chip devices may pave a viable route to scalable nonlinear applications in both classical and quantum domains.