Analysis of Intensity Modulation Response of Analog Fiber-Optic Links

We present theoretical analysis of intensity modulation response of analog fiber-optic links with direct intensity modulation and direct detection of the output optical signals. It is shown that the frequency chirp of laser light and the group velocity dispersion of electromagnetic waves in the optical fiber make a significant impact on the signal transmission. The output signals reveal ether power suppression or power revival (and even power enhancement) depending on the modulation frequency. We also examine dispersive harmonic distortions of the signals. It is found that such distortions are not related to optical power of the transmitted signals and occur even at low laser light intensities. We derive 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 be no dispersive harmonic distortions at all. The obtained formulas are useful for the engineering design of fiber-optic links. Experimental results supporting the theoretical calculations are presented.