  Photonic integrated circuits (PICs) play a crucial role in almost every
aspect of modern life, such as data storage, telecommunications, medical
diagnostics, green energy, autonomous driving, agriculture, and
high-performance computing. To fully harness their benefits, an efficient
coupling mechanism is required to successfully launch light into waveguides
from fibers. This study introduces low-loss coupling strategies and their
implementation for a silicon nitride integrated platform. Here we present an
overview of coupling technologies, optimized designs, and a tutorial on
manufacturing techniques for inverted tapers, which enable effective coupling
for both transverse-magnetic and transverse-electric modes. The optimized
coupling losses for the UHNA-7 fiber and the inverted taper Si3N4 coupler
reached -0.81 dB at 1550 nm per connection for single-mode waveguides with
220x1200 nm cross section. The measured coupling losses in the inverted taper
coupler with a standard single-mode fiber were -3.28 dB at 1550 nm per
connection for the same platform.
