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A Study on Entangled Photon Pairs in Graded-Index Optical Fibers
(Izmir Institute of Technology, 2021) Ekici, Çağın; Dinleyici, Mehmet Salih
Quantum optics offer new possibilities, new approaches, and potentially groundbreaking new technologies whose backbone is based on creation, manipulation, and detection of special quantum states of light. The main objective of the thesis is to present a study of spontaneously arisen heralded entangled photon-pairs which play crucial role in emerging quantum enhanced technologies. We have mainly investigated discrete transverse-spatial-mode entangled photon-pairs in waveguide, because it intrinsically offers infinite dimension. Entangled states of higher dimensional systems enable realization of quantum information schemes that can offer higher information density coding and show more error resilience than can be achieved with lower dimensional systems. In this context, we have exploited a graded-index optical fiber as photon-pair-generation platform via nonlinear intermodal-four-wave mixing (FWM), since the fiber may allow different FWM processes to overlap in spectral domain, resulting in an entangled pair of spatial qubits. We have also probed joint spectral properties of the generated photons to show capability of hyperentanglement in frequency and transverse mode. We have discussed spatial Wigner function and its realization to characterize spatial properties of the quantum state. We have shown that entanglement can be verified through a violation of the Clauser - Horne - Shimony - Holt (CHSH) inequality based on spatial Wigner function and coupled-mode theory. This thesis also includes basic analysis of transverse-mode entangled photon-pair distribution in a lossy-dispersive medium. Finally, the ways to follow and the quantities to measure are touched upon. Thus, we have explained the generation and four different detection schemes, relying on a combination of photon-number statistics, joint spectral properties, and spatial entanglement measurements.
Design and Fabrication of a Fiber-Integrated Mode-Selective Photopolymer Grating Coupler
(Izmir Institute of Technology, 2014) Sümer, Can; Dinleyici, Mehmet Salih
The aim of this study is to develop a node for an optical add/drop multiplexer, which is capable of packet switching at very high speeds and is controlled by light. The D-Fiber is employed as the transmission medium and the grating formation and polymerization is implemented on the fiber. The optical multiplexer is constructed by cascading two different photonic structures formed on the planar side of the D-Fiber. Multiplexing is performed by forming a temporary (transient) grating; which is the subject of another project in parallel at our laboratory. Right after this grating, will be the structure that is the subject of this thesis, which is the permanent structure fabricated via photopolymerization. The temporary grating breaks the resonance using nonlinear optical effects, coupling the fiber mode into the higher-order mode and the permanent structure extracts the mode out selectively to another fiber. Due to the very fast response of the nonlinear effects, an optical switch capable of transferring optical packets to other waveguides is formed. Photopolymerization is a method that can be used to fabricate photonic structures such as photonic crystals or permanent gratings, holographically or by direct-writing. The project involves the fabrication of the aforementioned photonic structure via photopolymerization. Even though the main aim of this project is not materials research, extensive effort has been put into optimizing the polymer recipe and characterization of the materials and processing properties.

Phd Degree / Doktora

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