Plasmonic and nanophotonics sensors from visible to terahertz

The global research objective of this thesis is to demonstrate design of novel compact and ultra-sensitive plasmonic sensors operating anywhere from the visible to the THz spectral ranges. The enabling technologies for such sensors are photonic bandgap and microstructured waveguides and fibers containing metallic inclusions. We achieve the stated global objective by systematically addressing several smaller problems. Firstly, this thesis demonstrates plasmonic excitation in metalized microstructured fibers in the context of bio-chemical sensing with enhanced microfluidics for visible and IR ranges. Furthemore, this basic design concept is generalized for the use with photonic bandgap fibers and waveguides; major advantages of using photonic bandgap waveguides in place of Total Internal Reflection (TIR) fibers for plasmonic sensing are discovered.;In the second chapter we show that using microstructured fibers one can solve much easier the problem of phase matching between the surface plasmon wave and fiber core mode, which is common when standard TIR fibers are used. Moreover, the use of microstructured fibers enables integration of the microfluidics and optics during drawing step thus simplifying considerably the sensor fabrication and operation. Furthermore, the different shapes of the metalized surface to enhance the plasmonic excitation were explored with an aim to enhance sensitivity.;In the third chapter, the design of photonic crystal waveguide-based surface plasmon resonance sensor is proposed. By judicious design of a photonic crystal waveguide, the effective refractive index of a core mode can be made considerably smaller than that of the core material, thus enabling efficient phase matching with a plasmon, high sensitivity, and high coupling efficiency from an external Gaussian source, at any wavelength of choice from the visible to near-IR.;In the forth chapter, we propose two designs of effectively single mode porous polymer fibers for low-loss guiding of terahertz radiation. Designing of such a porous fiber, capable of having a low modal effective index, facilitates the phase matching of the fiber core mode and the plasmon waves bordering a low index analyte at Terahertz regime. As a first design we consider a fiber containing an array of subwavelength holes separated by sub-wavelength material veins. As a Second design, we consider a large diameter hollow core photonic bandgap Bragg fiber made of solid film layers suspended in air by a network of circular bridges. Numerical simulations of radiation, absorption and bending losses are presented; strategies for the experimental realization of both fibers are suggested.;In the first chapter, we discuss the theory of surface plasmons, surface plasmon excitation and sensing methodologies.;In the fifth chapter, THz plasmon-like excitation on top of a thin ferroelectric polyvinylidene fluoride (PVDF) layer covering solid-core polymeric Bragg fiber and facing liquid analyte is demonstrated theoretically. Thanks to the refractive index behavior of the ferroelectric PVDF layer we demonstrate new type of plasmonic-like excitations in THz regime which was impossible before while using metal layers in THz regime.;In the sixth chapter, plasmon-like excitation at the interface between fully polymeric fiber sensor and gaseous analyte is demonstrated theoretically in terahertz regime. Such plasmonic excitation occurs on top of a ∼ 30 mum ferroelectric PVDF layer wrapped around a subwavelength porous polymer fiber. The major fraction of power guided in the air inside of the porous fiber alleviates the effects of material absorption and lowers the effective modal index to facilitate the plasmonic phase matching. In a view of designing a fiber-based sensor of analyte refractive index, phase matching of a plasmon-like mode with the fundamental core guided mode of a low loss porous fiber is then demonstrated for the challenging case of a gaseous analyte. We then demonstrate the possibility of designing high sensitivity sensors with amplitude resolution of 3.4 · 10-1 RIU, and spectral resolution of 1.3 · 10 -4 RIU in THz regime. Finally, novel sensing methodology based on detection of changes in the core mode dispersion is proposed.;To summarize, in this thesis we present design methodologies of compact and ultra sensitive sensors of the analyte refractive index using microstructured and photonic crystal fibers. Design methodologies are presented for sensors in spectral ranges from the visible to THz. Performance of such novel plasmonic sensors are contrasted with that of plasmonic sensors based on standard TIR fibers. Major advantages of microstructured and PBG fiber-based sensors are discovered in sensitivity, ease of operation and portability. (Abstract shortened by UMI.)...