Reducing the optical loss of polysilicon waveguide in bulk CMOS by waveguide geometry engineering

Based on the zero-process-change methodology, we successfully reduce the propagation loss of polysilicon waveguide from 112 dB/cm to only 38 dB/cm by applying subwavelength grating waveguide (SWG) design. Low propagation loss in SWG waveguide is attributed to a significantly reduced optical overlap factor of 0.09 to bulk polysilicon. This achievement can not be made by solely shrinking the waveguide dimension, thus validates a promising design path towards practical photonic-electronic applications in bulk CMOS.