Design and Simulation of Fiber to Chip Butt Coupler for SiN Integrated Photonics

SiN is a suitable material for fabricating of photonic integrated circuits with middle refractive index contrast for the visible and near infrared spectral region with ultra-low propagation losses. The paper deals with the design and simulation of fiber to SiN chip butt coupler with single step fabrication process without thickness tapering. Coupler is designed for 850 nm band for coupling between strip 0.25 μm × 1.00 μm waveguide and Nufern's 780-OCT single mode optical fiber with core diameter 4.4 μm. The coupling losses simulation results of the two simulation methods finite-difference beam propagation techniques and eigenmode expansion method are compared.