Comparison of optical properties of 1x128 splitters based on Y-branch and MMI approaches

This paper describes two different designs of 1×128 passive optical splitters for telecommunication applications. The first splitter consists of cascade arranged directional waveguide branches (Y-branch splitter) with a standard waveguide core size (6x6) μm². The second splitter is based on multimode interference occurring in a large MMI coupler, which uses a self-imaging effect for beam propagation, exhibiting the same waveguide core size as a Y-branch splitter. The waveguide channel profile, used in both approaches, is based on a standard silica-on-silicon material platform, with refractive index of core being n_c = 1.456 and a refractive index of cladding n_cl = 1.445. The splitters are designed and simulated at a telecommunication operating wavelength, λ = 1550 nm. Except for the lengths of the used Y-branches and MMI coupler, design parameters such as port pitch between the waveguides and simulation parameters for all splitters are considered fixed. Design, simulation, and optimization of passive optical components are performed by a commercial photonic software tool BeamPROP from Optiwave, which uses the Beam Propagation Method. This work aims to find the minimum physical dimensions of the designed splitters with a satisfactory optical performance. According to the minimum insertion loss and minimum non-uniformity, the optimum length of the splitters is determined. Finally, the optical properties of splitters for both approaches are discussed and compared with each other.