Experimental Investigation for Designing Compact Narrow-Linewidth and High-Extinction DBR Filters

An experimental investigation assisted with coupled mode theory for distributed Bragg reflector (DBR) in a single-mode SiN rib waveguide has been carried out in order to obtain narrow-linewidth and high-extinction filters operating in optical C-band (λ ∼ 1550 nm), for silicon photonics applications. A uniform sub-wavelength grating structure with a given periodicity is considered in the cladding region of the rib waveguide structure for the DBR response studies. The upper limit of periodic perturbation strength has been evaluated for designing narrow-linewidth and high extinction DBR filters using coupled mode theory approximation. This study enables photonic integrated circuit design engineers to design a relatively simple and shorter length of DBR device (∼1 mm) exhibiting 3-dB bandwidth as narrow as ∼ 1-nm and rejection as high as > 40-dB, which can be easily integrated for large-scale complex photonic integrated circuit functionalities.