Performance Comparison of Grating-Assisted Integrated Photonic Delay Lines

Incorporation of grating waveguides in optical delay lines based on integrated microring resonator structures is proposed. Specifically, transmittive apodized grating waveguides are implemented in two common microring configurations, namely, coupled-resonator optical waveguides (CROWs) and side-coupled integrated spaced sequence of resonators (SCISSORs). The performance of these proposed devices is compared with standard CROWs and SCISSORs (i.e., with no gratings), as well as with grating-assisted waveguides (cascaded complementary apodized grating waveguides). It is shown that, for the same minimum bit rate operation, the proposed grating-assisted SCISSORs exhibit the best performance in terms of delay tunability and delay per footprint. However, the maximum true time delay of grating-assisted waveguides possesses a close to linear dependence on length, while the true delay in mircoresonator-type structures (with or without gratings) do not increase efficiently with the number of rings. Also, it is argued that the grating-assisted waveguides are expected to have the lowest insertion loss per delay time.