Subband all-pass filter architectures with applications to dispersion and dispersion-slope compensation and continuously variable delay lines

A new optical filter architecture is proposed that employs optical subband and all-pass filters but circumvents the typical tradeoff between passband width and peak delay inherent to all-pass filters. A filter design for a dispersion compensator with a tuning range of ±1000 ps/nm and 95-GHz passband width on a 100-GHz grid is presented. Compared with a cascade architecture, a lower core-to-cladding index contrast for planar waveguide ring resonator implementations can be used, and lower filter losses are achieved, since the signal propagates through fewer all-pass filter stages for the same dispersion. A continuously variable delay line is designed with more than 90% bandwidth utilization. For a ten-stage all-pass filter with 25-GHz free spectral range (FSR) in a double-pass configuration, a 1000-ps continuous tuning range can be achieved. Finally, a dispersion-slope compensator design is presented with a change in dispersion of 700 ps/nm over a wavelength range determined by the filter FSR-to-channel-spacing ratio.