  In this work we present a detailed analysis of individual loss mechanisms in
silicon nitride partial Euler bends at a wavelength of 850 nm. This structure
optimizes the transmission through small radii optical waveguide bends. The
partial Euler bend geometry balances losses arising from the transition from
the straight to the bend waveguide mode, and radiative losses of the bend
waveguide mode. Numerical analyses are presented for 45-degree bends commonly
employed in S-bend configurations to create lateral offsets, as well as 90- and
180-degree bends. Additionally, 90-degree partial Euler bends were fabricated
on a silicon nitride photonic platform to experimentally complement the
theoretical findings. The optimized waveguide bends allow for a reduced
effective radius without increasing the total bend loss and, thus, enable a
higher component density in photonic integrated circuits.
