Up-conversion of eye-safe beams carrying 2D-spatially-modulated information for detection with Si-FPA cameras in FSO applications

In this paper we propose an optical frequency up-conversion system for detection of spatially encoded 2D information by using silicon focal plane arrayed sensors (Si-FP A), like those mounted in standard CCD or CMOS cameras, for applications in free-space optical (FSO) communications operating at 1550 nm. In this way, transmission of data in 2D-matrix formats by spatially intensity-modulated laser beams at 1550 nm would benefit from low atmospheric attenuation and eye-safe radiation allowing high power levels in long-range and secure communication links. The experimental setup consists of a Nd3+:YVO4 solid state laser inside which the 2D-data modulated beam is mixed with the 1064 nm laser oscillation in a KTP nonlinear crystal. As a result, the infrared information is transferred to the visible spectrum (631 nm) by sum-frequency mixing (SFM) for subsequent detection by a standard CMOS device. As a proof of concept, the upconverted information is collected by the CMOS camera of a conventional smartphone before being decoded and displayed successfully. The data rate per frame is determined by the resolution and field of view provided by the proposed system and the availability of compact devices is ensured by the potential integration capability of the underlying technology.