Contacts:
Søren Stobbe, DTU Fotonik, ssto@fotonik.dtu.dk
With the recent dramatic progress in nanotechnologies and nanophotonics, state-of-the-art photonic devices build on complex design procedures, often involving inverse design, which results in highly complex geometries and non-intuitive features. As a result, simple models can no longer be used for real-world devices and numerical simulations are necessary. The numerical tools have also undergone rapid developments and finite-element modelling has become extremely powerful and versatile. Even with the most advanced nanofabrication, however, deviations between the input design and resulting physical device are commonplace and even a few nanometers of deviation can lead to large effects and detrimental spectral shifts. For both research and applications, there is therefore a need for accurately measuring the fabricated nanoscale geometries and using this input for numerical modelling. The device geometries can be measured accurately with a scanning electron microscope (SEM) and compared to the simulated model. Today, this is often done by visual inspection and tedious manual work and an automated procedure is therefore highly desirable.
In this project you will develop an image-processing code, which automatically can extract the polygon-outlines of devices from SEM-images and compare them quantitatively to the design by importing the polygons automatically to the finite-element software COMSOL Multiphysics. In particular, you will apply the algorithm to novel types of photonic nanocavities currently researched in our group.
Figure: Left: Scanning electron microscope image of a nanocavity. Middle: Polygon outlines extracted using Matlab. Right: Numerical simulation of the optical mode in the design.
You do not need any prior knowledge of electromagnetism or numerical simulations but familiarity with programming will be advantageous.
Potential further points of investigation depending on your interest:
- Nanofabrication: One application of this code would be automatically correcting design files to iteratively improve the quality of the fabricated devices. Specifically, this would involve linking the script to our electron-beam lithography mask software and understanding our nanofabrication process flow.
- Optical experiments: Since we both simulate, fabricate, and measure devices in our group, you can get access to our optical laboratory and characterize samples experimentally, comparing the results to those of your script.
- Numerical simulations: It is rarely the case that devices are perfect, and thus a more advanced code could look into quantifying feature sharpness and surface roughness.