Jakub Haberko
AGH University of Science and Technology, Faculty of Physics and Applied Computer Science
Jakub Haberko graduated in physics from AGH University of Science and Technology in Cracow, Poland. He also obtained his PhD there, studying thin films containing conjugated polymers for use in organic electronics. A post-doc position at the University of Fribourg, Switzerland, opened a new research field of optical metamaterials for him, including photonic crystals and non-periodic structures with a photonic bandgap. His current interests include the design, computer simulations and fabrication of novel optical metamaterials as well as studies of organic materials using surface-sensitive techniques, mainly X-ray photoemission spectroscopy.
IntroductionControlling the polarization state of light is of utmost importance in many scientific and industrial applications, such as stereoscopic vision, polarization microscopy or non-linear light frequency conversion.... [ view full abstract ]
Introduction
Controlling the polarization state of light is of utmost importance in many scientific and industrial applications, such as stereoscopic vision, polarization microscopy or non-linear light frequency conversion. Typically, to achieve this goal dichroism, birefringence or optical activity are utilized. However, new ideas are also investigated, involving plasmonic metasurfaces or designer metamaterials. On one hand novel nano/microfabrication techniques, such as two-photon laser nanolithography, have recently allowed these ideas to become reality. On the other hand computer simulation techniques facilitate the search for innovative metamaterial designs. I will present two different concepts: i) a successfully designed and fabricated array of twisted bands [1] and ii) a metasurface consisting of quasi-random metallic pixels, designed with a stochastic search algorithm, acting as a waveplate in the near- to mid-infrared range [2].
Methods
The twisted band array (i) was first manufactured by two-photon laser nanolithography in a polymer photoresist and was consecutively sputter-coated with a 50 nm layer of gold. The polarization of light reflected off the array was measured with a Fourier transform infrared spectrometer. Polarization properties of the structure were simulated using the Finite Difference Time Domain technique (FDTD). The optimal geometry of the metasurface (ii) was determined using the FDTD method combined with a custom-designed stochastic search algorithm.
Results and discussion
We have been able to design and manufacture a twisted band array transforming linearly-polarized light into circularly-polarized wave for a specific wavelength and into elliptically polarized light with ellipticity above 0.9 in a considerable frequency range. Computer simulations are in good qualitative agreement with experimental results, but also show sensitivity of the design to geometric parameters. We have also proposed a simple stochastic search algorithm which, provided a suitable fitness function, successfully optimizes a metallic metasurface geometry to act as a broadband quarter- or half-waveplate, working in reflection in a wavenumber range of 3000-4500 cm-1. Similar methodology can be utilized to design other classes of optical devices, such as polarization rotators. Both designs presented here are scalable and can be tuned to a different frequency range.
Literature
[1] Appl. Phys. B (2017) 123:285
[2] Opt. Comm. 410 (2018) 740-743
