Carriers Generated by Mode-Locked Laser to Increase Serviceable Channels in Radio Over Free Space Optical Systems

Mode-locked optical carriers with applicability for radio over free space optics (RoFSO) systems have been produced via a ring laser cavity incorporating an add/drop filter. This technique of generation allowed for servicing of a greater number of channels in a wavelength-division multiplexing RoFSO system, and the carriers were able to travel in a free space channel with very little dispersion. Sixteen carriers, having a free spectral range (FSR) of 12.5 GHz and full-width at half-maximum (FWHM) of 250 MHz, were created. Eight of these 16 generated carriers were then separately modulated with eight orthogonal frequency-division multiplex signals and subsequently optically multiplexed and transmitted to a free space optic (FSO) channel using an FSO antenna. At the receiver side, the received signal was demultiplexed, and the performance of the system was analyzed via calculating the error vector magnitude and constellation diagram of the entire system.