Dispersion engineering of periodic silicon photonic waveguides for enhanced group delay in the frozen mode

Enhanced group delays around near-infrared wavelengths are achievable via dispersion-engineered silicon photonic waveguides. Using periodic waveguides, we analyze two different geometries designed to have a certain lossless and gainless class of exceptional point degeneracies (EPDs) in their Bloch eigenmodes. These waveguiding geometries support the frozen mode regime (FMR) around the wavelength 1550 nm as calculated in analytic and hybrid full-wave models. From previous work studying the FMR, we expect an increase in the group delay at resonances close to the EPD wavelength. Measurements of photonic chips across various designs agree with theoretical predictions. Our waveguides achieve group delays greater than 750 fs / μ m, with an exponential increase expected when extending the waveguide length due to anomalous scaling of group delay around the FMR. Furthermore, the significant delay around the FMR is expected to amplify incorporated gain media for low-threshold lasing and ultra-fine sensing applications.