SWIR upconversion quad-detector using an array of PPLN waveguides and SNSPDs

Quad-detectors are a tried and tested technology used in applications ranging from maintaining CD/DVD data track alignment to solar tracking and LiDAR. The development of SPAD arrays has enabled the creation of single-photon quad detectors for single-photon LiDAR at 1030 nm, capable of tracking a target's velocity and distance at kilometres away [1]. There are many advantages to expanding this technology to longer wavelengths beyond Si or even InGaAs SPADs, including access to preferable atmospheric windows and chemical detection. Yao et al. showed that sum frequency generation (SFG) in PPLN waveguides can realise 40% system efficiency for conversion of 1550 to 863 nm for quantum key distribution [2], and recently zinc-indiffused MgO-doped PPLN waveguides have demonstrated efficient SFG from longer SWIR wavelengths (2-3.5 μm) to short NIR [3].