Abstract
A fully numerical method for designing efficient adiabatic mode
evolution structure (AMES) (referred to as NAMES) is introduced, which can
be applied to adiabatic taper, coupler, splitter, mode converter, and a
wide range of AMES based devices. The method can compute efficient
adiabatic waveguiding shapes for these devices, including those with
complex waveguiding geometries involving 2D/3D mode connections. We
introduce two algorithms for the NAMES, referred to as “maximal mode-power
loss at top algorithm” and “mode-power loss at initial slope algorithm”.
Both are based on keeping the mode-connection power exchange constant. We
use the simple case of a waveguide taper to explain the algorithms, and
then apply it to a more complex case of an adiabatic waveguide coupler to
show how it can readily generate a waveguiding shape that can give the
same mode-connection power transfer with a much shorter length than that
based on a linear shape. In the coupler case, we show the device
efficiency is equal to that based on an optimized analytical approach
developed for a simple geometry, but the NAMES can address many different
device types and complex device geometries all with a single numerical
approach that would also enable design automation. The algorithms utilize
Eigenmode Expansion (EME) simulator for field propagation with
functionalities that are particularly efficient for the algorithms. We
cross-checked the EME simulator results using finite-difference
time-domain method. With sufficiently fine division of the structure, the
waveguiding shape generated converges to basically the same shape for both
algorithms and the shape is quite insensitive to the starting parameters.
Thus, the NAMES given is robust, convergent, efficient, and general (not
restricted to a particular device type). The NAMES would have wide
applications to designing AMES based devices with complex geometries for
photonic integrated circuits.
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