Frozen mode in coupled silicon ridge waveguides for optical true time delay applications
Banaful Paul, Niru K. Nahar, Kubilay Sertel
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>56</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>µ</mml:mtext> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> 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.