Operation and management signal detection using quadrant photodiode and auxiliary management communication channel for simple and stable free-space optical communication systems

Abstract

Free-space optics (FSO) is key technology for next-generation communication systems and is used for communications with mobile nodes. In an FSO system, both a client signal and a network operation and management (OAM) channel are required to maintain the system. Acquisition of a new radio wave does not occur during transference over an optical signal; however, misalignment tolerances for the laser beam and receiver aperture decrease and the loss of the OAM signal leads to the network control is lost for a while. Although a photodetector with a larger aperture than that of the client signal improves the tolerance, more devices are required. Therefore, we propose receiving the OAM signal with the quadrant photodiode (QPD), which is generally mounted onto FSO equipment for position detection of laser beams. We determined that the allowable displacement expanded to about three times the usual amount without requiring more optical components.