There is considerable research activity in multiresonator optical circuits in silicon photonics, e.g., for higher-order filters, advanced modulation format coding/decoding, or coupled-resonator optical waveguide delay lines. In diagnostics of such structures, it is usually not possible to measure each individual microring resonator without adding separate input and output waveguides to each resonator. We demonstrate a non-invasive diagnostic method of quantitative IR imaging, applied here to a series cascade of rings. The IR images contain information on the otherwise inaccessible individual through ports and the resonators themselves, providing an efficient means to obtain coupling, loss, and intensity-enhancement parameters for the individual rings.
In contrast to recent reports of localization-impaired transport in long slow-light waveguides, we demonstrate light transport in silicon coupled-resonator optical waveguides (CROWs) consisting of up to 235 coupled microrings without localization over frequency bands that are several hundred gigahertz wide. Furthermore, from the unique statistical signatures provided by time-domain propagation delay measurements, we demonstrate the spectrally correlated nature of light propagation in CROWs.
The dispersion of the waveguides that constitute microring resonators can considerably affect the dispersion characteristics of coupled-resonator optical waveguides (CROWs). We derive expressions for CROW dispersion and group delay for silicon-on-insulator microring CROWs, showing both theoretically and experimentally the band-to-band dependence of the bandwidth and group delay on the dispersion properties of the constituent single-mode silicon waveguide.
We demonstrate four-wave mixing in silicon-on-insulator coupled-resonator optical waveguides consisting of 35 and 65 microring resonators, using a cw pump with coupled power below 20 mW and observed parametric conversion across more than 10 THz. The conversion efficiency is enhanced by +16 dB relative to a silicon straight waveguide of equivalent length, due to the slowing factor of the coupled-resonator structure.
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