FIMMWAVE

Bend Modes & Bend Losses of Optical Waveguides

Simulation with FIMMWAVE software

FIMMWAVE supports no less than three different bend mode solvers, allowing you to calculate the bend modes of curved waveguides of arbitrary geometries with great accuracy. FIMMWAVE can calculate bend losses accurately.

Bend modes of a Planar SOI Waveguide
Whispering Cavity Modes of a Microdisk Resonator
Bend modes of a Photonic Crystal Fibre

Bend Modes of a Planar SOI Waveguide

FIMMWAVE can calculate the bend modes of a planar SOI waveguide in a rigorous way. The FMM Solver used as a bend mode solver relies on fully cylindrical coordinates. Bend losses were calculated with true transparent boundary conditions, which provide more stable and accurate results than PMLs (Perfectly Matching Layers).

A low bending loss SOI waveguide was simulated with FIMMWAVE (see details of structure here). The low bending loss was achieved using a large etch depth (r=0.2). For a bend radius of 10um, FIMMWAVE calculated bend losses of 0.00017cm-1 for the fundamental TM-like mode and 6.55cm-1 for the fundamental TE-like mode. The mode profiles below clearly show the field profile distortion associated with the curvature.

Mode profiles for (left) the fundamental TM-like mode (Ey field profile)
(right) the fundamental TE-like mode (intensity profile) with a bend radius of 10um, W=1.4um, H=1.5um, r=0.2 at 1.55um

The evolution of mode loss with radius of curvature can be generated automatically with a WG Scanner. The resulting curve for the TE-like mode is shown below.

Evolution of bend loss (cm-1) with radius of curvature (um)
for the fundamental TE-like mode at 1.55um

Whispering Cavity Modes of a Microdisk Resonator

Here the FDM Bend Solver was used to calculate the fundamental and high-order bend modes of a silicon mesa disk buried in a silica substrate. The whispering cavity modes were found very easily even for a disk radius as small as 1.49um.

Cross-section of the mesa disk (outer section). The radius of the disk is 1.49um
and the radius of the central section 0.59um, the thickness of the outer
edge is 0.72um and the thickness of the central section 2.34um.

Mode profiles calculated for a wavelength of 1.55um:
(first row) Ex field profiles of the TE-like modes (second row) Ey field profiles of the TM-like modes
(first column) fundamental modes (second column) vertical first order modes (third column) horizontal first order modes

Bend Modes of a Photonic Crystal Fibre

The FEM Solver was used as a bend solver to find the bend modes of the same photonic crystal fibre for a radius of curvature of 100um (see the details of the structure here). Bend loss was calculated using PMLs (Perfectly Matching Layers). 

The contour plots of the fundamental TE-like mode for the straight and the bent PCFs are shown below. You can observe the horizontal asymmetry of the bend mode profile.

Contour plot of the Ex-field profiles for the fundamental TE-like mode at 500nm
with no curvature (left) and a radius of curvature of 100um (right)

More publications 

Click here to find publications that include FIMMWAVE simulations of bends on Google Scholar.