Taper Modelling

FIMMPROP allows you to model propagation in z-varying sections, as can be commonly found in tapers, directional couplers, Y-junctions etc. This is done by discretising such sections along the axis of propagation and calculating the local modes along the taper.

FIMMPROP can model tapers of arbitrary length and complexity more efficiently than most simulation tools and it can sweep design parameters very efficiently; for instance scanning the length of a tapered waveguide is quasi-instantaneous.

FIMMPROP includes a unique adaptive taper algorithm, which can refine the discretisation dynamically depending on the variations of the eigenmodes.

For instance in the planar Y-junction shown below, the discretisation needs to be much finer in the region where the waveguide widens than in other parts of the structure, where the width of the waveguide remains constant. Attempting to model this taper with a constant-step taper algorithm would be very inefficient, as to obtain the same accuracy you would need to apply the finest discretisation everywhere.

Photon Design has a well established expertise in the modelling of such structures, and pioneered the development of methods for the modelling of tapers and z-varying structures with EME by publishing articles on the subject as early as 2003 [1].

Many tapered structures include one or two planes of symmetry, and other structures like ring couplers or directional couplers include mirror symmetries. FIMMPROP can take advantage of such symmetries when modelling tapers, reducing calculation time by up to 16x compared with an algorithm that would not account for such symmetries.