Design and implementation of micro-structures with refractive index contrast for optical interconnects and sensing applications

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Khan, Muhammad Umar
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University College Cork
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Periodic structures have always been part of our lives. With the development of human understanding it was realised that natural opals, butterfly wings and bird feathers which have been keenly observed for generations are actually naturally occurring photonic crystals (structures with periodic modulation of the refractive index). In this work, I have investigated the scientific use of refractive index contrast and nanometer scale periodicity for applications in optical interconnects and surface plasmon resonance like dielectric optical sensors. One dimensional photonic crystals can be engineered to sustain a surface wave called as Bloch surface wave (BSW). A BSW based label-free sensor is designed and implemented using only a pair of high (Si, 70 nm) and low (SiO2, 676 nm) index materials in contrast to multiple pairs used previously. The demonstrated bulk sensitivity (900 nm/RIU) for a single pair sensor is comparable to the multi-pair sensors using the prism based Kretschmann-Raether configuration.The demonstrated sensor using only a single pair of dielectric layers is the dielectric counterpart of the surface plasmon resonance based sensors using gold on dielectric. A SU8 waveguide is cladded by the above mentioned thicknesses of silicon and silica to demonstrate on-chip sensing using the end-fire coupling for the first time. The demonstrated on-chip sensing platform is simple to fabricate and is believed to lay the foundation of a cheap and sensitive integrated sensing system. Organically Modified Ceramic (ORMOCER) based single-mode waveguides and passive devices for both single and multi-level centimetre sized optical boards using nano-imprint lithography (NIL) are demonstrated with waveguide loss less than 0.2 dB/cm. An ‘optical via’ for vertical coupling of light from one optical plane to another is designed and implemented using NIL. A novel 1 x 4 2D optical port is designed and implemented for the first time to spatially distribute the input light over different optical planes. Polymer waveguides inherently have smaller refractive index contrast between core and cladding requiring a bending radius of atleast 8mm for lossless communication. Sharp in-plane bends are demonstrated for the first time by integrating core-shell colloidal crystals with these polymer waveguides. The demonstrated efficiency for in-plane bends is poor which will improve with optimisation of the colloidal crystal fabrication. Finally, inverted opal photonic crystals are used as under-cladding for the waveguide core to demonstrate effectively an air suspended polymer waveguide that can be used for sensing applications. Component density on optical printed circuit boards can be increased using the demonstrated sharp in-plane bends once better stacking is achieved.
Refractive index , Photonic crystals , Refractive index contrast , Polymer waveguides , Optical sensors , On-chip BSW sensors , Thin films , Periodic structures , Optical PCB , Multilevel optical interconnects , Bloch surface waves , Colloidal crystals , Nano-imprint lithography
Khan, M. U. 2016. Design and implementation of micro-structures with refractive index contrast for optical interconnects and sensing applications. PhD Thesis, University College Cork.