Transmission Performance Investigation of RF Signal in RoF-DAS Over WDM-PON With Bandpass-Sampling and Optical TDM

The radio over fiber (RoF)-distributed antenna system (DAS) over a wavelength division multiplexing-passive optical network (WDM-PON) with multiple input multiple output (MIMO) employing bandpass-sampling and optical time division multiplexing (TDM) techniques has been proposed to realize next generation broadband wireless access with higher throughput and its preliminary feasibility has been confirmed. To investigate the performance of bandpass-sampled and time domain multiplexed optical signals, and enhance the transmission performance in the wireless link of the RoF-DAS over WDM-PON, we perform two-tone signal transmission experiments with 2.4 GHz band radio frequency (RF) signals and analyze the RF carrier power, third-order intermodulation distortion (IMD) power and noise power. The analysis results confirmed that the nonlinearity of the proposed system is mainly caused by a lithium niobate-Mach-Zehnder modulator (LN-MZM) as with the other RoF systems and that the dominant noise components are the signal-spontaneous beat noise arising from the amplified spontaneous emission (ASE) of two erbium doped fiber amplifiers (EDFAs) and the signal-signal beat noise caused by the interference between the optical TDM pulses. The latter is the specific noise component in the proposed system. In addition, we clarify the principle of the signal-signal beat noise generation and report that the signal-spontaneous beat noise can be reduced by the gain optimization of the two EDFAs.