Dispersive distortions of signals in an analog fiber-optic link with direct intensity modulation

We present experimental results on transmission of signals in an analog fiber-optic link with direct intensity modulation and direct detection of photocurrent at the output of the fiber. It was found that the output electrical signals reveal ether power suppression or power revival (and even power enhancement) depending on the modulation frequency. We also observed nonlinear distortions of the signals. Such distortions are not related to an optical power of the transmitted signals and occur even at low laser light intensities. Theoretical interpretation of the experimental results is presented. It is shown that the frequency chirping of laser radiation and the group velocity dispersion of electromagnetic waves in optical fiber have a critical impact on the signal transmission. We obtained a simple analytical expression for the frequencies of the signals with minimum or maximum power at the output. We also derived a simple analytical expression for the frequencies at which there will he no dispersive harmonic distortions at all. The results are useful for the engineering design of fiber-optic links.