# Frequency doubling of temporally incoherent light from a superluminescent diode in a periodically poled lithium niobate waveguide crystal

## TL;DR

This paper demonstrates highly efficient frequency doubling of incoherent superluminescent diode light using a waveguide in periodically poled lithium niobate, enabling access to new wavelengths for applications and quantum optics.

## Contribution

It reports the first high-efficiency frequency doubling of temporally incoherent superluminescent diode light in a waveguide with quasi phase matching.

## Key findings

- Achieved six orders of magnitude higher conversion efficiency than previous methods.
- Successfully frequency doubled incoherent light in a single spatial mode.
- Demonstrated potential for accessing new wavelengths in quantum optics.

## Abstract

The amplified spontaneous emission from a superluminescent diode was frequency doubled in a periodically poled lithium niobate waveguide crystal. The temporally incoherent radiation of such a superluminescent diode is characterized by a relatively broad spectral bandwidth and thermal-like photon statistics, as the measured degree of second order coherence, g$^{(2)}$(0)=1.9$\pm$0.1, indicates. Despite the non-optimized scenario in the spectral domain, we achieve six orders of magnitude higher conversion efficiency than previously reported with truly incoherent light. This is possible by using single spatial mode radiation and quasi phase matched material with a waveguide architecture. This work is a principle step towards efficient frequency conversion of temporally incoherent radiation in one spatial mode to access wavelengths where no radiation from superluminescent diodes is available, especially with tailored quasi phase matched crystals. The frequency doubled light might find use in applications and quantum optics experiments.