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 allpass 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.