Silicon nitride chirped spiral Bragg grating with large group delay
Zhenmin Du, Chao Xiang, Tingzhao Fu, Minghua Chen, Sigang Yang, John E. Bowers, Hongwei Chen
Abstract
As one of the most important optical filtering devices, Bragg gratings have been extensively used in various systems. A long Bragg grating is desired for many applications including frequency selection in semiconductor lasers and dispersion control for ultra-short pulses. As a prominent example, integrated spiral Bragg grating waveguides (SBGWs) have drawn much attention in the years. However, until now, the length of an integrated grating is still limited to a few milli-meters due to total waveguide loss. In this work, we propose and demonstrate a novel long chirped SBGW with waveguide loss as low as 0.05 dB/cm on a silicon nitride (Si3N4) platform. A 13.8 cm SBGW is fabricated, which is the longest on-chip waveguide grating reported so far. The SBGW’s reflection bandwidth is 9.2 nm from 1556.3 nm to 1565.5 nm, and it provides a total of 1440 ps group delay, that is, −156.5 ps/nm of dispersion. The group delay response shows great linearity and temperature stability. This integrated device holds great potential for various applications including in-line dispersion compensation, optical true delay phase array, and microwave photonics.