Numerical validation of low-coherence interferometers using low-group-velocity and low-dispersion photonic crystal waveguides for ultra-compact OCT applications

Abstract In this study, an ultra-compact optical coherence tomography (OCT) system based on integrated photonic crystal waveguides (PhC-WGs) was proposed and validated numerically. A low-velocity and low-dispersion (LVLD) PhC-WG is employed in the reference arm, enabling significant reduction in its length because of the high group index achieved with a broadband light source. Optical delays in the reference arm were found to increase with the designed group index of the LVLD-PhC-WG, confirming the low-coherence interference. Additionally, similar findings were observed in a PhC-WG-based OCT (PhC-OCT) model integrating a directional coupler and the LVLD-PhC-WG. The PhC-OCT with a considerably small footprint, e.g. 20 × 100 μm 2 , for the interferometer including the reference arm indicated interferometric signals with an axial resolution of approximately 40 μm. These results demonstrate the feasibility of an ultra-compact OCT system using PhC-WGs.