Compact intracavity mid-infrared upconversion detector – a systematic study

Mid-IR light detection based on intracavity upconversion using a compact structure has been studied experimentally and theoretically. The mid-IR detector consists of a 47.5 mm MgO doped periodically poled lithium niobate crystal placed in a resonant cavity of a 1064 nm diode-pumped Nd:YVO 4 laser to enhance efficiency. The generated 1064 nm light is mixed with a mid-infrared source emitting at 3469 nm using an intracavity dichroic mirror. This produces short wave infrared 814.2 nm light via sum frequency generation (SFG). The upconverted light overlaps with the high responsivity for commercial off-the-shelf silicon photodetectors, enabling high speed and high sensitivity detection, surpassing direct mid-infrared detection. The lowest power detected was 150 nW, and the theoretical noise equivalent power for state-of-the-art Si detectors is 1.7⋅ f W/Hz. The free-running cavity requires no active stabilization, and the total packaged prototype size is 3.75 × 3.0 × 8.0 cm, which is relatively compact. An experimental power conversion efficiency of up to 36.0% is observed, which agrees well with theoretical simulations. A systematic theoretical study is performed to investigate the potential for further device optimization.