Many-element coupled-resonator optical waveguides using gapless-coupled microdisk resonators.

We report silicon photonic many-element coupled-resonator optical waveguides (CROWs) using microspiral and double-notch-shaped microdisk resonators. Such microresonators enable gapless inter-cavity coupling via seamlessly jointed sub-micrometer-sized notches. Our experiments reveal CROW transmission spectra using up to 101 gaplessly coupled microdisk resonators. We estimate from the transmission measurements an insertion loss of approximately 0.11-approximately 0.24 dB/disk within the transmission bands. We show high-order filtering performance with maximum 3-dB linewidth of approximately 2.5 nm and measurement-limited side-mode suppression ratio of approximately 30 dB. The demonstrated maximum optical delay from a 101-element 0.4-microm-notch CROW is approximately 70 ps at the transmission band center and approximately 110 ps at the sideband.