Home/Technical Information/Design and Analysis Guides
Design and Analysis Guides
How to design coupling from an optical fibre into a photonic chip using a microlens and an edge coupler: fibre mode analysis in Lumerical MODE, alignment evaluation with POP in OpticStudio, and analysis of the coupling region with FDTD and EME.
This article sets out in detail how to couple light from an optical fibre into a photonic chip using a microlens and an edge coupler. The approach uses Ansys LumericalandAnsys Zemax OpticStudio, combining FDTD (finite-difference time-domain) and POP (physical optics propagation) so that coupling efficiency and power loss under misalignment can be quantified, supporting an efficient design with low insertion loss.
In photonics, fibre-to-chip coupling is extremely sensitive: a small offset or alignment error has a large effect on the whole system. A workflow that links Lumerical and OpticStudio is effective for optimising this process, and evaluating coupling performance under a range of conditions reduces development cost while achieving efficient coupling.
The first step is to use the Lumerical MODE FDE (finite-difference eigenmode) solver to analyse the fibre modes and export the field in ZBF format. This also handles single-mode fibres that are not Gaussian (SMF-28, for example), and lets you set parameters such as core radius and cladding index.
Next, model the microlens using POP analysis in OpticStudio and simulate field propagation from the fibre to the chip facet. Set horizontal and vertical translation and rotational offsets to evaluate coupling performance under complex alignment conditions. The resulting fields and parameters are then exported for use in the next stage of analysis.
Next, import the field exported from OpticStudio into Lumerical FDTD and set it as a custom source. This allows electromagnetic propagation from free space into the waveguide to be simulated accurately, and lets you verify the loss and coupling performance of the final input field.
Finally, use the EME solver in Lumerical MODE (eigenmode expansion) to carry out mode conversion in the spot-size converter of the edge coupler and calculate the final coupled power. This method suits SSC device simulation in particular, which is computationally demanding, and evaluates coupling performance efficiently and accurately.
Importing and exporting the electric field as ZBF data is central to this workflow. Export from Lumerical requires uniform spatial sampling, and the OpticStudio settings add a guard band on resampling to prevent diffraction artefacts.
Accounting for the relative position and rotational offset between the fibre and the microlens improves the robustness of the coupling. Considering tilt misalignment about the X and Y axes as well adds further accuracy.
Setting an optimised number of modes, transverse mesh resolution and cell count keeps the simulation accurate while remaining computationally efficient. Adjusting the coefficients of the forward-propagating modes improves coupling performance further.
For more advanced analysis or automation, this workflow can be integrated with Ansys optiSLang to handle complex design scenarios. Linking the OpticStudio and Lumerical modules provides a comprehensive design environment covering parametric analysis, alignment tolerance settings and yield analysis.
As photonic chip integration advances, co-packaging optical components in 3D integrated circuits is becoming increasingly important. This workflow is expected to deliver efficient design, cost reduction and improved system reliability, making it an essential tool in modern photonic system design.
Using a microlens and an edge coupler optimises coupling performance between fibre and photonic chip, and is expected to form the basis of advanced photonics applications.
Our engineers can advise on building a design flow for your application, and on validating an analysis model, from practical experience.