Performance Evaluation of Optical Reflection Tolerance and Its Improvement Techniques in Various Optical Analog Transmitters

Analog radio-over-fiber (RoF) technologies have been studied as a suitable solution for mobile applications such as mobile fronthaul and accommodation of distributed antennas. On the other hand, multiple reflections are known to cause significant degradation in the transmission signal quality of analog RoF systems. In this paper, the influence of multiple reflections and the effectiveness of its mitigation scheme, high-frequency phase dithering and polarization randomization, are experimentally studied for different types of optical transmitters based on directly modulated laser (DML), electro-absorption modulator laser (EML), and lithium niobate Mach-Zehnder modulator (LN-MZM). The noise induced by multiple reflections and its mitigation effect are quantitatively evaluated in various conditions for the multiple reflections and the mitigation techniques. Additionally, transmission qualities of intermediate frequency over fiber (IFoF) signals under multiple reflections conditions are clarified. The operational conditions for achieving an error vector magnitude (EVM) criterion of 64-QAM OFDM signal are also presented.