Photon upconversion devices for imaging

This paper reviews our research on photon upconversion devices for wavelengths from 1.5 μm to 0.87 μm. The 1.5 μm is chosen for its importance for eye-safe active imaging; whereas 0.87 μm corresponds to the bandgap of GaAs which is the active region of our high efficiency light emitting diode (LED). The basic idea is to integrate a 1.5 μm detector with a 0.87 µm LED, connected in series. The detected photocurrent drives the LED, thereby achieving the upconversion. Various approaches of integration methods and device designs have been tested. The upconversion approach provides an alternative to the standard hybrid integration with readout circuits and may be advantageous for some applications.