Frozen mode in coupled silicon ridge waveguides for optical true time delay applications

We propose a simple photonic waveguide structure that exhibits light propagation modes with vanishing group velocity via mode degeneracy. This enables stationary inflection point dispersion leading to the frozen mode and a true time delay device suitable for ultra-wide-band beamforming for millimeter wave (mmWave) phased arrays. The structure consists of three silicon ridge waveguides in proximity with periodic gaps introduced in the outer waveguides to create a band gap. The structure is complementary metal–oxide–semiconductor compatible with a very small footprint of only about 56µm2 and more resilient to fabrication uncertainties as compared to the previously studied structures. Simulation results show transmission of 70% of the incident wave for the frozen mode at the 1.55 µm (193.6 THz) wavelength through the waveguide. It also enables a delay-bandwidth product of 6.75 along with unprecedented frequency independent bandwidth of about 0.5 THz for RF-mmWave–terahertz beamforming.