Designing Smarter Directional Couplers with Parametric Models
Learn how to leverage IPKISS to optimize the design of directional couplers and implement advanced parametric modeling.
Introduction
A directional coupler serves as an essential passive component in integrated photonic systems, allowing precise splitting or combining of optical signals between two closely positioned waveguides. Its functionality depends on evanescent field coupling, where the exponentially decaying electromagnetic field of one waveguide interacts with the neighboring waveguide, enabling power exchange across a specified interaction region.
The performance of a directional coupler is governed by several interdependent parameters:
Coupling Length: The longitudinal extent of the parallel waveguide region, which dictates the fraction of optical power transferred, typically modeled as a function of the coupling coefficient (κ) and phase mismatch (Δβ).
Coupling Gap: The lateral separation between waveguide cores - reduced gaps exponentially increase the coupling strength due to enhanced evanescent field overlap.
Material Properties: The refractive indices of the core and cladding, along with material dispersion, determine the modal confinement and effective index of the propagating modes.
Operating Wavelength (λ): The input wavelength affects the coupling efficiency and phase-matching condition, which in turn impact the device’s spectral response.
In this tutorial, we’ll uncover the benefits of creating a parametric model for directional couplers, leveraging the advanced layout and model-building capabilities of IPKISS. The sections below detail the essential steps to build such a model efficiently, optimizing the design to maximize the performance.
Building a Parametric Model for a Smart Directional Coupler: This section demonstrates how to create a regeneration script that runs simulations on a directional coupler PCell using Ansys Lumerical FDTD, and performs polynomial fitting of the simulation data to develop a parametric model for the directional coupler based on two parameters: wavelength and straight length.
Define a Directional Coupler PCell for Simulation: This section explains in detail how to define PCell variations for a directional coupler, and explains the class hierarchy implemented in the SiFab demo PDK.
Let’s look at how to build such a model.