Simplified Chromatic Dispersion Model Applied to Ultrawide Optical Spectra for 60 GHz Radio-Over-Fiber Systems

Radio-over-fiber systems can be harnessed to generate millimeter-wave (mm-wave) frequencies, but the optical impairments such as optical noise, chromatic dispersion, and nonlinearity can degrade the quality of the generated heterodyne signals. When optical frequency comb sources are employed, chromatic dispersion has a main importance since it causes a phase shift and phase decorrelation between optical lines. These both effects subsequently induce power fading and also optical noise on the beat note carrier. With utilizing ultrawide optical spectra, higher order dispersion coefficients must be considered during the propagation across optical fiber, which introduces a high level of complexity in the analytic model. In this paper, we present a simple and convenient model to analyze the impact of chromatic dispersion on the power of the mm-wave heterodyne carrier. The proposed model manipulates and integrates the higher order dispersion terms into an equivalent second-order dispersion term. This allows to perform the easiest way to calculate the propagation constant. Simulation and experimental results are conducted for fiber distance up to 30 km in order to validate the suggested model in terms of the carrier power. Through the results obtained, the well-known behavior between the signal power and chromatic dispersion can be modified. Optical phase shift results in a diverse power fading and intensity noise while optical phase de-correlation manifests phase noise. Therefore, data transmission over 25 km fiber is carried out to show the impact of chromatic dispersion on optical noise of the beating carrier. RF power and error vector magnitude reveal that the chromatic dispersion can overcome power fading and increase the tolerance to fiber length with limiting the optical noise in the optical heterodyning system.