Optical Sciences

Biomolecules and nanostructures

The Optical Sciences group studies the interaction of light and matter at the nanoscale. We do this by exploring ways to shape light and its environment. It's what we call active and passive control. Our current focus is on the interaction of light with biomolecules and nanostructures. We are part of Twente University's Department of Science and Technology and member of the MESA+ institute.
We participate in the EU-COST actions MP1102: Coherent Raman microscopy (MicroCor) and CM1202: Supramolecular photocatalytic water splitting (PERSPECT-H2O)

 

Vacancies


  • MSc project on: Dielectric parameters of water-salt solutions

  • MSc project on: Focusing long-wavelength fields

  • BSc project: building an OCT-based setup for 3D structural imaging

  • date: Jan 23, 2017

    Introduction


    Figure 1. Stucture of the KY(WO4)2 during polishing. The KY(WO4)2 is located in a trench in a SiO2 substrate, glued to it with a polymer glue.

    To fabricate optical waveguide structures in the crystalline material KY(WO4)2, thin layers of this material have to be produced, with a thickness in the order of a few micrometer. This is done by taking a thick layer of the material (1 mm) and polish it down to the desired thickness [1]. Monitoring the thickness and surface quality of the thin layer is essential to get thin layers that can be used to fabricate optical waveguides. None of the currently used monitoring methods can measure both thickness and surface quality, and most require transfer of the polished sample to the cleanroom, which takes a lot of time.




    Figure 2. Example of an OCT setup. In this setup a photodiode is used for light collection, but alternatively a camera can be used to get a laterally resolved image. [source:Wikipedia]

    As a solution, a setup based on optical coherence tomography (OCT) could be used. OCT is a method that is widely used to measure structures in human tissue, by looking at the interference of the backscattered reflections of (partly) transparent material. Its basis is a Michelson interferometer, with a broadband light source (typically near-infrared, ~100 nm full width half max) to get a very short coherence length [2]. The sample under investigation is put in one of the arms of the interferometer, a reference mirror is put in the other. The reference mirror can additionally be scanned to change the optical path length difference, so the setup can scan at different depths of the sample. This method is able to completely visualize the structure of a sample, which means that both thickness of the KY(WO4)2 layer and surface quality can be measured at the same time. This method is potentially very fast, has a high lateral and depth resolution, and can be used without too much effort.

    Project and goals

    During the assignment, an OCT setup will be built which can scan a sample both in depth and laterally (parallel to the top-surface), with a resolution in the order of 1-2 μm. This work includes modifying an existing Michelson interferometer setup, writing control software for the setup in LabVIEW and development of more extensive code for measurement analysis in Matlab. A set of tests should also be designed and performed to calibrate the setup and determine the limits in terms of resolution, scanning range and interference pattern intensity.

    The final goal is to have a setup able to provide a quick depth scan of a sample with micrometer resolution withing a few minutes, while lateral scans or even full structure scans may take much longer.

    Contact

    Do you want more information about the project, are you interested in doing this project, or are you looking for a bachelor assignment, but just not this one? Don't hesitate, and drop by the office! You can either contact Raimond Frentrop (CR4.542, r.n.frentrop@utwente.nl) or Sonia García-Blanco (CR4.617, s.m.garciablanco@utwente.nl).

    References

    [1]   Mustafa Akin Sefunc, Frans Segerink, Sonia M. Garcia-Blanco, "High index contrast potassium double tungstate waveguides towards efficient rare-earth ion amplification on-chip", Proc. SPIE 9365, Integrated Optics: Devices, Materials, and Technologies XIX, 93650P feb. 27, 2015
    [2]   Pedrotti, "Introduction to Optics", 3rd edition, Pearson International Edition.



    Apart from the listed projects, we invite students to suggest projects of their own.
    Printable version