On-Chip Circulator-Free Chirped Spiral Multimode Waveguide Grating for Dispersion Management

Abstract

Waveguide gratings are one of the key optical dispersion handling devices and are highly desired for many on-chip photonic systems. However, most of the previously reported waveguide gratings require optical circulators to separate input and reflected signals. Here, a circulator-free chirped spiral multimode waveguide grating (SMWG) composed of an asymmetric chirped multimode waveguide grating and a mode (de)multiplexer is first proposed and demonstrated for dispersion management on a silicon-on-insulator (SOI) platform. The chirped SMWG reflects the TE0 mode into the TE1 mode so that input and reflected signals can be separated with the assistance of a mode (de)multiplexer instead of a circulator. The spiral waveguide with a continuously varying radius enables a large amount of dispersion within a compact footprint. Group delay ripples are suppressed by superposition modulation on lateral corrugations. The fabricated 5 mm chirped SMWG realizes a maximum group delay of 150 ps and dispersion of 6.49 ps/nm within a bandwidth of 22 nm. The proposed circulator-free chirped SMWG will find many applications such as optical communication, microwave photonics, and pulse compression.