A discussion was held at the Institute of Laser for Postgraduate Studies, University of Baghdad, regarding the doctoral dissertation of student Ali Qadir Bakki, titled “Design and verification of an effective surface polarizer for quantum key distribution.” This dissertation, supervised by Assistant Professor Dr. Shelan Khosro Tawfiq, aimed to investigate two novel structures.
The first structure involved a diffraction grating made of titanium dioxide, designed to serve as a polarizer at four angles (0, 90, 45, -45). This polarizer could be employed in quantum key distribution systems to randomly alter the polarization of photons. The second structure introduced a new concept using vanadium dioxide to create an effective surface acting as a diffraction grating. This material’s behavior is temperature-dependent; a temperature change between 80 and 30 degrees Celsius enables it to function as a polarizer, transmitting photons with polarizations of zero or 90 degrees. The polarization can be randomly controlled by varying the temperature within this range. All these designed structures operate within the visible light spectrum.
Testing was conducted using the COMSOL MULTIPHYSICS 6.0 program and the Monte-Carlo algorithm to determine the optimal dimensions for achieving a high polarization separation coefficient.

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