Polarization-independent complex bragg grating filters on silicon nitride

Abstract

Integrated optical filters are essential components of on-chip multiplexers, which play a critical role in enhancing data throughput for high-demand networks. Since optical multiplexers are typically connected through fiber-optic links where the polarization state of light fluctuates randomly, polarization insensitivity is an important prerequisite for integrated optical filters. In this work, polarization-insensitive optical filters are demonstrated on the silicon nitride platform operating in the datacom O-band. The filters are based on cladding-modulated Bragg gratings, which offer improved fabrication tolerances and reduced losses compared to conventional sidewall gratings. By judiciously designing grating dimensions, filters are demonstrated with single-band, dual-band, and four-band spectral characteristics. The fabricated filters achieve an insertion loss below 1.0 dB and a band rejection greater than 25 dB for spectral bands that are 3 nm wide and 9 nm apart.