Efficient characterization of harmonic and intermodulation distortion effects in dispersive radio over fiber systems with direct laser modulation

Abstract

results from the Mie series. But for higher values of , the PMCHWT formulation gives incorrect results, while the present formulation still agrees with the Mie series. For ϭ 10 5 S/m, ͉ r ͉ ϭ 1.8 ϫ 10 11 and the skin depth is about 16 mm. The present formulation still works well, even when is as high as 10 8 S/m and the corresponding skin depth is about 0.5 mm. So the present formulation can work with much higher conductivities than the PMCHWT formulation, due to the effective suppression of the error contribution from the internal conductive region.To explore the generality of the present formulation, a highfrequency case using RWG basis is also calculated and the results are illustrated in Figure 4. The frequency here is 10 MHz. For varying from 1 to 1000 S/m, the present formulation provides overall satisfactory performance, while the PMCHWT formulation gives incorrect results when is higher than 10 S/m.For ϭ 10 4 S/m, the new formulation also fails to give correct results, because the skin depth is too small to be accurate enough for the typical seven-point Gaussian quadrature integration, even when the error has already been suppressed. To increase the integration accuracy, we simply divide each triangular patch into four subpatches and apply the seven-point Gaussian quadrature integration to each subpatch, thus effectively increasing the integration points per patch. Note that here the number of basis functions is not increased. Then the new formulation gives a correct result again, as shown in Figure 4(f). Although using subpatches is not the most efficient way to improve the integration accuracy, we illustrate the fact that the number of basis functions does not have to increase with the internal-region wavenumber.The present formulation performs better in the low-frequency band than in the higher frequencies because, for the same skin depth, ͉ r2 ͉ is larger at lower frequencies and thus the internalregion terms are suppressed by a larger factor. Hence, the accuracy of the internal-region terms will be less important for lower frequencies. CONCLUSIONA new SIE formulation has been obtained by tuning the weighting coefficients of the integral equations for the external and internal regions, respectively. Thus, the integration error over the Green's function for the internal conductive region is suppressed and the present formulation provides satisfactory results in a significantly larger range of skin depths than previous SIE formulations. The present formulation can also work in tandem with techniques that improve the integration accuracy for Green's functions in conductive media in order to further enlarge the solvable range of conductivities. INTRODUCTIONThe analysis of harmonic and intermodulation distortion is of great concern in the design of analog or subcarrier multiplexed (SCM) optical systems. These effects may negatively affect the performance of systems that exploit, for example, wavelength conversion via cross gain modulation (XGM) in semiconductor optical amplifiers (SOAs) [1] or systems tha...

Effects of laser frequency chirp on modal noise in short-range radio over multimode fiber links

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Linearity Improvement of VCSELs based Radio over Fiber Systems utilizing Digital Predistortion

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