Complex apodized Bragg grating filters without circulators in silicon-on-insulator.

TLDR: This paper proposes to introduce two identical Bragg gratings in the arms of a Mach-Zehnder interferometer built with multimode interference 2 x 2 couplers to provide a reflective filter without circulator to enable the fabrication of grating based narrowband reflective filters having sharp spectral responses, which represents a major improvement in the filtering capability of the silicon platform.

Abstract: Bragg gratings operating in reflection are versatile filters that are an important building block of photonic circuits but, so far, their use has been limited due to the absence of CMOS compatible integrated circulators. In this paper, we propose to introduce two identical Bragg gratings in the arms of a Mach-Zehnder interferometer built with multimode interference 2 x 2 couplers to provide a reflective filter without circulator. We show that this structure has unique properties that significantly reduce phase noise distortions, avoid the need for thermal phase tuning, and make it compatible with complex apodization functions implemented through superposition apodization. We experimentally demonstrate several Bragg grating filters with high quality reflection spectra. For example, we successfully fabricated a 4 nm dispersion-less square-shaped filter having a sidelobe suppression ratio better than 15 dB and an in-band phase response with a group delay standard deviation of 2.0 ps. This result will enable the fabrication of grating based narrowband reflective filters having sharp spectral responses, which represents a major improvement in the filtering capability of the silicon platform.