Large Dispersion of Silicon Directional Couplers Obtained via Wideband Microring Parametric Characterization

Using the measured transmission spectrum of a waveguide-coupled silicon microring, we develop an algorithm for determining the wavelength dependencies (i.e., the dispersions) of the coupling coefficients and loss of the ring. Our analysis reconstructs the measured spectrum without use of Lorentzian fitting, covers 15 free spectral ranges (FSR), and was performed from~1520to 1570 nm, covering all of and extending past the C-band. We demonstrate that the dispersion of the coupling coefficient of a silicon-waveguide directional coupler considerably exceeds (by a factor of~10) the modal refractive-index dispersions of its constituent waveguides.