查看文章

We demonstrate an integrated tunable optical delay line in grating-assisted contradirectional couplers using a CMOS-compatible photonic technology. The input signal is delayed through dispersive Bragg gratings and distributedly coupled to the drop port of the coupler without backreflections. This add–drop design enables monolithic integration of grating-based delay lines without using optical circulators. The gratings are formed by slab perturbations in rib waveguides, with the index chirping realized by linearly tapering the rib widths. Both the pitch and size of the gratings are constant through the entire coupler, for a higher tolerance to fabrication errors. Continuous tuning of the optical group delay of up to 96 ps has been obtained, with a low insertion loss of less than 2 dB and a negative chromatic dispersion of −11  ps/nm that allows for bit rates of up to almost 100  Gb/s at the maximal delay. The device has …