Integrated resonance-enhanced variable optical delay lines

A wide-tuning-range optical delay line is demonstrated in high (2%) index contrast waveguides. This device integrates four-stage ring resonator all-pass filters (APFs) with cascaded fixed spiral-type delay waveguides; each fixed delay path varies in length by a factor of two from the previous stage. A 2/spl times/2 switch separates each fixed delay and the tunable parts of the delay line. The APF allows for continuous delay tuning. This device enables coherent switching and continuous tuning ranges up to 2.56 ns.