It is well know that free-space laser system performance is limited by atmospheric turbulence. Most theoretical treatments have been described for many years by Kolmogorov's power spectral density model because of its simplicity. Unfortunately, several experiments have been reported recently that show that the Kolmogorov theory is sometimes incomplete to describe atmospheric statistics properly, in particular, in portions of the troposphere and stratosphere. We present a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/ 3, and a generalized amplitude factor instead of constant value 0.033. Using this new spectrum in weak turbulence, we carry out, for a horizontal path, an analysis of long-term beam spread, scintillation index, probability of fade, mean signal-to-noise ratio ͑SNR͒, and mean bit error rate ͑BER͒ as variation of the spectrum exponent. Our theoretical results show that for alpha values lower than ␣ = 11/ 3, but not for alpha close to ␣ = 3, there is a remarkable increase of scintillation and consequently a major penalty on the system performance. However, when alpha assumes a value close to ␣ = 3 or for alpha values higher than ␣ = 11/ 3, scintillation decreases, leading to an improvement on the system performance.

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Several techniques for phase noise PSD measurement of continuous wave (CW) lasers to be used in coherent transmission systems are analyzed. Between them, we evaluate two novel techniques. The first employs a homodyne optical phase-locked loop, while the second uses a signal source analyzer. Experimental results obtained by these two methods are compared with classical linewidth measurement methods like self-heterodyne and Michelson interferometer. Limits and accuracy of each method are discussed. Furthermore, the comparison shows that, for coherent transmission system applications, only a subset of the analyzed methods is useful for laser phase noise characterization.

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In the framework of the EU-funded research project "FABULOUS" we experimentally demonstrate an innovative FDMA-PON architecture whose upstream transmission is based on a reflective Mach-Zehnder modulator. By a careful optimization of electrical spectrum allocation, semiconductor optical amplifier biasing point and modulation index, we upgrade previous results over similar architectures, significantly increasing the achievable optical distribution network loss. We demonstrate an overall upstream capacity of 32 Gbps per wavelength over 37 km of installed fiber and 31 dB loss.