Integrated Cascaded Bragg Gratings for On-Chip Optical Delay Lines

We have demonstrated on-chip optical delay lines that consist of cascaded Bragg grating segments. Our results show that the band gap and the group index of cascaded gratings are very similar to that of a single grating segment, which means longer time delay can be achieved by cascading more grating segments. In our experiment, a maximum group index of 12.2 and a total time delay of 292 ps was achieved using a 7.2 mm-long delay line on Si chip.