Fabrication and testing of nano-optical structures for advanced photonics and quantum information processing applications
Khan, Mughees Mahmood
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Interest in the fabrication of nano-optical structures has increased dramatically in recent years, due to advances in lithographic resolution. In particular, metallic nanostructures are of interest because of their ability to concentrate light to well below the diffraction limit. Such structures have many potential applications, including nanoscale photonics, quantum information processing and single molecule detection/imaging. In the case of quantum computing and quantum communication, plasmon-based metal nanostructures offer the promise of scalable devices. This is because the small optical mode volumes of such structures give the large atom-photon coupling needed to interface solid-state quantum bits (qubits) to photons. The main focus of this dissertation is on fabrication and testing of surface plasmon-based metal nanostructures that can be used as optical wires for effciently collecting and directing an isolated atom or molecule's emission. In this work, Ag waveguides having 100nm?50nm and 50nm?50nm cross sections have been fabricated ranging from 5?m to 16?m in length. Different types of coupling structures have also been fabricated to allow in-coupling and out-coupling of free space light into and out of the nanometric waveguides. The design of waveguides and couplers have been accomplished using a commercial finite difference in time domain (FDTD) software. Different nanofabrication techniques and methods have been investigated leading to robust and reliable process conditions suitable for very high aspect ratio fabrication of metal structures. Detailed testing and characterization of the plasmon based metal waveguides and couplers have also been carried out. Test results have revealed effective surface plasmon propagation range. 0.5dB/?m and 0.07dB/?m transmission losses have been found for 100nm and 50nm wide waveguides respectively, which correspond to 1/e propagation lengths of 9?m and 60?m. Input coupling effciency was found to be 2% and output coupling effciency was found to be 35%. The fabrication and testing results presented provide critical demonstrations to establish the feasibility of nanophotonic integrated circuits, scalable quantum information processing devices, as well as other devices, such as single molecule detectors and imaging systems.