Loss and Noise Characteristics of Microwave Direct Modulated Optical Links

Abstract

Loss and noise figure of optical links transmitting microwave signals – e.g. for remote antennas in wireless communications – are dealt with. Conditions are rather general and include arbitrary matching conditions, shot noise, and laser relative intensity noise. Specific and somewhat surprising characteristics are derived. Among others, it is shown, that – like passive, purely microwave systems – noise figure is not proportional to electrical loss and it can be even lower than loss itself. Optical power should be as low as possible – this limit is mainly determined by the required dynamic range of the system. Loss and noise figure were measured in an experimental setup. Results of the measurements proved the theoretical findings rather well. Preliminary results on the transmission of 32TCM signals over the link are briefly presented.