Performance optimization of RSOA based mm-wave radio-over-fibre access network

In this paper, a Reflective Semiconductor Optical Amplifier based, Radio-over-Fibre access network configuration has been proposed to feed future millimeter-wave radio systems. The system architecture combines several approaches to overcome the challenges of millimeter-wave signal transmission. Reflective semiconductor optical amplifier modulator realizes a colorless and relatively cost-effective Remote Antenna Unit. The same optical carrier is used for both downlink and uplink. Optical single-sideband modulation is used at the downlink, which is robust against chromatic dispersion, but the complex realization of this modulation format is not possible at the Remote Antenna Unit. Optical intermediate frequency transmission is applied at the uplink direction, and the required local oscillator signal originates from the central station. The critical element is the reflective optical amplifier, as it compensates for the optical loss and works as an external intensity modulator. The operation of the reflective optical amplifier is modeled by multisection rate and wave equation-based description. The amplification and modulation behaviors of an available reflective optical amplifier are also measured. The experimental work validated the colorless operation and the quality of the modulation versus bias current and input optical power. Finally, system simulation was realized. The uplink and downlink power budgets were balanced, and optimal values for the optical coupling rate and RSOA bias current have been selected.

Reflective Semiconductor Optical Amplifier Direct Modulation Capability Enhancement Using Birefringent Fiber Loop

The feasibility of employing a birefringent fiber loop to enhance the performance of a directly modulated reflective semiconductor optical amplifier is experimentally demonstrated for the first time. The birefringent fiber loop acts as an optical filter of opposite slope than that of the reflective semiconductor optical amplifier electro-optical response and counteracts the finite reflective semiconductor optical amplifier modulation bandwidth of only 0.89 GHz. By proper adjustment of its detuning, the birefringent fiber loop tailors the spectral components that physically manifest due to the reflective semiconductor optical amplifier dynamic perturbation subject to direct modulation in the saturated gain regime, and suppresses the pattern-dependent distortions in the time domain. In this manner, the birefringent fiber loop manages to significantly improve the quality characteristics of the encoded signal at higher data rates than those enabled by the reflective semiconductor optical amplifier limited modulation capability. Owing to the birefringent fiber loop, the reflective semiconductor optical amplifier modulation range is extended to 4 Gb/s at the raw bit error rate of 1.0×10−9, and to 11 Gb/s at the forward error correction limit of 3.8×10−3. These results, which are unique against the evaluation criterion adopted in the first case, and the modulation speed achieved with post-filtering schemes in the second, highlight the beneficial role that the birefringent fiber loop can play in supporting reflective semiconductor optical amplifier operation for intensity amplification and modulation purposes.