OPTICAL CIRCUITS FOR EQUALIZING GROUP DELAY DISPERSION OF OPTICAL FIBERS

Optical circuits are synthesized for equalizing the group delay disper sion of single-mode fibers. The transfer function of the equalizing ci rcuits are given by Chebyshev polynomials of the second kind. The vari ous realization methods for the group delay equalizer are shown, inclu ding periodic structures using birefringent crystals, birefringent fib ers, and Mach-Zehnder interferometric planar optical circuits. An opti cal equalizer employing TiO2 birefringent crystals was fabricated and evaluated by using an optical network analyzer, which operates by maki ng modulation-envelope phase and amplitude measurements while scanning the optical carrier frequency. The measured optical equalizer charact eristics show excellent agreement with the simulation analysis. The ef fectiveness of the equalizer for substantial reduction of the dispersi on penalty for a 10 Gb/s signal transmitted over 30 km of normal dispe rsion fiber was demonstrated. The periodicity of the equalizer results in periodic dispersion-free bands, and hence, the equalizer is suitab le for use in future multichannel FDM systems.