# Engineering temporal-mode-selective frequency conversion in off-the-shelf nonlinear optical waveguides: From theory to experiment

## TL;DR

This paper demonstrates high temporal-mode selectivity in quantum frequency conversion using standard nonlinear waveguides, combining theoretical predictions with experimental verification, and paving the way for near-perfect selectivity schemes.

## Contribution

It experimentally verifies model-predicted Schmidt modes for high selectivity in off-the-shelf waveguides, bridging theory and practical implementation in quantum frequency conversion.

## Key findings

- Experimental verification of model-predicted Schmidt modes
- Achieved high temporal-mode selectivity (>80%)
- Potential for near-perfect selectivity with two-stage schemes

## Abstract

Quantum frequency conversion (QFC) in nonlinear optical media is a powerful tool for temporal-mode selective manipulation of light. Recent attempts at achieving high mode selectivities and/or fidelities have had to resort to multi-dimensional optimization schemes to determine the system's natural Schmidt modes. Certain combinations of relative-group velocities between the relevant frequency bands, medium length, and temporal pulse widths have been known to achieve good selectivities (exceeding 80%) for temporal modes that are nearly identical to pump pulse shapes, even for high conversion efficiencies. Working in this parameter regime using an off-the-shelf, second-harmonic generation, MgO:PPLN waveguide, and with pulses on the order of 500 fs at wavelengths around 800 nm, we verify experimentally that model-predicted Schmidt modes provide the high temporal-mode selectivity expected. This paves the way to the implementation of a proposed two-stage QFC scheme that is predicted to reach near-perfect (100%) selectivity.