High-speed all-optical differentiator based on a semiconductor optical amplifier and an optical filter.

We demonstrate a novel all-optical differentiator that carries out the first-order temporal derivation of optical intensity variation at high speed. It consists of a semiconductor optical amplifier (SOA) and an optical filter (OF) serving as an optical phase modulator and a frequency discriminator, respectively. A polarity-reversed derivative pair with a certain bias can be obtained by locating the probe wavelength at the positive or negative slope of the OF. Differentiations of super-Gaussian and Gaussian signals are obtained at various data rates. Defined as the mean absolute deviation of the measured result from the ideal result, total average errors of less than 0.12 are observed in all cases. Input power dynamics as well as control wavelength dependence are investigated and show that the cross-gain modulation in the SOA is detrimental to the differentiation performance.