Investigaton of low power 850nm free space optical link elements

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Fekete Gábor
Department of Broadband Infocommunications and Electromagnetic Theory

Quantum key distribution (QKD) protocols ensure that private encryption keys can be distributed perfectly securely against both classical and quantum attacks. After reviewing the theoretical basics necessary for free-space quantum communications, the thesis introduces the design and investigation of a low power 850 nm free-space optical link using easily obtainable or already available parts and devices. During the investigations, huge emphasis is laid on the measurement of a vertical cavity surface-emitting laser's (VCSEL) properties, such as its laser characteristics, the stability of its output power, its spectrum, the polarization state and the photon statistics of its light. Based on the results of the measurements, the thesis concludes that the particular elements of the optical link, for example the laser, the optical attenuator, the polarizer, the polarization beam splitter or the single-photon detectors are suitable for the realizaton of a future QKD-link using the BB84 protocol.


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