Grating-Assisted On-Chip Optical Dispersive Delay Lines with Suppressed Ripples Based on Disorder-Induced Self-Compensation Effect

Abstract

The grating-assisted optical dispersive delay line has proven to be one of the most effective approaches to providing large dispersions within broad bandwidths. However, when applying conventional apodization technology to mitigating the group delay ripples induced by gratings, major issues arise, including insufficient resolution and random errors in the manufacturing process. Due to the susceptibility of practical responses of apodized Bragg gratings to fabrication variations, a novel solution with large manufacturing tolerance has been proposed and demonstrated by cascading several short grating-assisted contra-directional couplers (GA-CDCs). Thanks to the unique disorder-induced self-compensation effect, this cascade configuration can reliably suppress group delay ripples without apodization technology requiring high-precision manufacture. To predict the performance of cascaded GA-CDCs, a size disorder model has been introduced for the first time, assuming that waveguide width deviation follows a Gaussian distribution. Multiple samples with consistent designs were fabricated and characterized to confirm the robustness of the proposed scheme. Additionally, a 20-stage cascade GA-CDC is demonstrated with a large dispersion, achieving −52.11 ps/nm. Further improvements have been made by adjusting the spacing between adjacent contra-directional couplers to decrease spectral notch depths and side-lobe magnitudes. Moreover, an autonomous compensation system for group delay fluctuations shows great promise through independent thermal tuning of each GA-CDC combined with an automatic control system based on various optimization algorithms.