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New integrated optical all-pass filters are presented that can be used for tunable dispersion compensation, dispersion slope compensation, and as building blocks in tunable bandpass filters. The dispersion slope compensation capability is demonstrated using ring resonators in /spl Delta/=2% Ge-doped silica planar waveguides. In addition, a tunable four-stage filter with free-spectral range (FSR)=25 GHz, a passband width of 14 GHz (0.56/spl times/FSR), and D=1800 ps/nm is reported.
Madsen et al. (Wed,) studied this question.