All-optical transversal filter with tap doubling and negative coefficients based on polarization modulation.

A novel all-optical transversal filter with negative coefficients and tap doubling is proposed and experimentally demonstrated. Based on polarization modulation using the anisotropy of the electro-optic coefficient of LiNbO(3) crystals, negative and positive coefficients are simultaneously generated. Tap doubling is also achieved by using wavelength- and polarization-dependent time delays in fiber. Due to the orthogonal polarity between the two coefficients of each wavelength, the proposed filter is free from coherent interference and the synthesis of filter taps is performed in the optical domain. The experimental results demonstrated that stable 6-tap bandpass filter characteristics can be obtained by using only three optical sources.