An optical thin film Bessel filter for 40Gbit/sec -100GHz spacingD-WDM system

It is difficult to employ conventional Butterworth filters in 40Gbit/sec applications with 100GHz-spacing due to their strong group delay dispersions. This paper shows design, fabrication and measurements of a thin film Bessel filter applicable for 40Gbit/sec VSB signals, and compares the results to a typical Butterworth filter. This Bessel filter has very low dispersion because of its flattened group delay, and in turn, this allows VSB signal filtering with minimal linear distortions.