Modeling the Efficiency of an Edge Coupler with a Si3N4-based Taper

The article studies the efficiency of optical radiation input/output between a photonic integrated circuit (PIC) and an edge-coupled tapered silicon nitride waveguide with dimensions 350 nm x 850 nm at a wavelength of 1550 nm. The work determines the losses by radiation for transverse electric and transverse magnetic modes at different taper width and input mode diameter for direct (edge width more than 850 nm) and inverted tapers (edge width less than 850 nm). The results show that the admissible width of the inverted taper edge lies within 150–300 nm with losses by input/output of up to 2 dB and low sensitivity to optical polarization. For the direct taper, the highest input efficiency (losses amounted to 3-6 dB) belongs to the optical fibers with a beam waist diameter of 2–3 μm and taper edge width of 2–3 μm. For both types of edge couplers, the effect of the waist diameter of lensed fiber is more important: the spread should be within 150 nm.