Academic literature on the topic 'Sub-wavelength characterisation (loss and dispersion)'

The materials significantly influence the structural, optical and photoelectrical characteristic. Materials such as Arsenic selenide, Tellurite Glass, Silicon carbide, Silicon dioxide and Silicon nitride are investigated through finite element method. The models are established to analyse the structural behaviour of polarization preserving fibre of proposed materials. Photoelectric characteristic determines guided properties of photon particles. Refractive index of the materials influences the properties of photonic crystal fibre. A Polarization Splitter based hexagonal structure is proposed, where inner ring of cladding is in elliptical shape air holes and outer rings are in circular air holes. It provides highly negative dispersion, low confinement loss and high nonlinear coefficient between 1µm to 2µm wide wavelength ranges. The dispersion result shows -2000 db/km-nm at 1.55µm wavelength. Polarization beam splitters photonic crystal fiber characteristics of proposed materials are analysed with same structural parameters.

AbstractAs a combination of fiber optics and nanotechnology, optical microfibers and nanofibers (MNFs) have been emerging as a novel platform for exploring fiber-optic technology on the micro/nanoscale. Typically, MNFs taper drawn from glass optical fibers or bulk glasses show excellent surface smoothness, high homogeneity in diameter and integrity, which bestows these tiny optical fibers with low waveguiding losses and outstanding mechanical properties. Benefitting from their wavelength- or sub-wavelength-scale transverse dimensions, waveguiding MNFs exhibit a number of interesting properties, including tight optical confinement, strong evanescent fields, evident surface field enhancement and large and abnormal waveguide dispersion, which makes them ideal nanowaveguides for coherently manipulating light, and connecting fiber optics with near-field optics, nonlinear optics, plasmonics, quantum optics and optomechanics on the wavelength- or sub-wavelength scale. Based on optical MNFs, a variety of technological applications, ranging from passive micro-couplers and resonators, to active devices such as lasers and optical sensors, have been reported in recent years. This review is intended to provide an up-to-date introduction to the fabrication, characterization and applications of optical MNFs, with emphasis on recent progress in our research group. Starting from a brief introduction of fabrication techniques for physical drawing glass MNFs in Section 2, we summarize MNF optics including waveguiding modes, evanescent coupling, and bending loss of MNFs in Section 3. In Section 4, starting from a “MNF tree” that summarizes the applications of MNFs into 5 categories (waveguide & near field optics, nonlinear optics, plasmonics, quantum & atom optics, optomechanics), we go to details of typical technological applications of MNFs, including optical couplers, interferometers, gratings, resonators, lasers and sensors. Finally in Section 5 we present a brief summary of optical MNFs regarding their current challenges and future opportunities.

Abstract The Dirac point and associated linear dispersion exhibited in the band structure of bound (non-radiative) acoustic surface modes supported on a honeycomb array of holes is explored. An aluminium plate with a honeycomb lattice of periodic sub-wavelength perforations is characterised by local pressure field measurements above the sample surface to obtain the full band-structure of bound modes. The local pressure fields of the bound modes at the K and M symmetry points are imaged, and the losses at frequencies near the Dirac frequency are shown to increase monotonically as the mode travels through the K point at the Dirac frequency on the honeycomb lattice. Results are contrasted with those from a simple hexagonal array of similar holes, and both experimentally obtained dispersion relations are shown to agree well with the predictions of a numerical model.

Metamaterials have recently emerged and shown great potential for noise and vibration reduction in specific frequency ranges, called stop bands. To predict stop bands, their often periodic nature is exploited and dispersion curves are calculated based on a single representative unit cell, typically modeled using the finite element method. Since their sub-wavelength nature and often intricate design can lead to large unit cell models, model reduction methods such as the Generalized Bloch Mode Synthesis have been proposed to greatly accelerate dispersion curve calculations. In order to calculate forced vibro-acoustic responses of finite periodic elastic metamaterial plates composed of an assembly of unit cells, however, full order finite element models rapidly become computationally unaffordable. Therefore, in this work the Generalized Bloch Mode Synthesis is incorporated in a sub-structuring approach, which enables fast forced vibration response calculations of finite elastic metamaterial plates based on a single reduced order unit cell model. The main advantage as compared to a regular Craig-Bampton approach is the additional local reduction of unit cell boundary degrees of freedom, whereby a compatible basis for the identical neighboring unit cells is incorporated. In addition, by combining this Generalized Bloch Mode Synthesis based sub-structuring approach with the Elementary Radiator Approach, efficient sound transmission loss computations of finite periodic metamaterial plates are enabled. The performance of the proposed approach for fast vibro-acoustic response predictions is demonstrated for different cases.

This Thesis reports the development of fibres to guide terahertz (THz) or T-ray radiation. It demonstrates the theoretical studies of THz microwires (air-clad solid core fibres) and a new form of waveguide: the porous fibre. Porous fibre has an arrangement of sub-wavelength featured air-holes in the cross-section, resulting in improved confinementof the propagating mode while retaining the low loss characteristic compared to air-clad sub-wavelength waveguide or microwires. Porous fibres also offer lower frequency dependent loss and dispersion compared to microwires. Furthermore, introducing asymmetrical discontinuity leads to high birefringence, which is comparable to recently achieved high birefringence in photonic crystal fibres. Furthermore, this thesis involves the first successful fabrication of highly porous polymer fibres, with both symmetrical and asymmetrical discontinuities, via an extrusion process. In order to achieve rapid and reproducible waveguide cross-sections three different cleaving techniques—based on the use of a semiconductor dicing saw, focused ion beam milling, and a 193 nm ultraviolet laser—have been investigated for cleaving of polymer porous fibres. Finally, two different techniques have been utilised for characterisation of porous fibres. The first approach leads to the first experimental verification of frequency dependence of effective refractive indices of polymer porous fibres and microwires. The second approach exploits a micromachined photoconductive probe-tip for sampling of the THz pulse along the waveguide, from which the frequency dependent absorption coefficient and refractive index are determined. Moreover, the evanescent field distribution of porous fibres as a function of frequency is measured for the first time.
Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2011

Plasmonics is an emerging and fast-growing branch of science and technology that focuses on the coupling of light to the free electron density in metals, resulting in strong electromagnetic field enhancement due to confinement of light into sub-wavelength dimensions beyond the diffraction limit. The development of novel photonic and optoelectronic devices based on metal-based plasmonics is however plagued by the high loss at optical frequencies, originating partly from inter-band electronic transitions and lack of electrical tunability, practically limiting their potential applications in the terahertz (THz) and mid-IR spectrum range. The recent successful exfoliation of graphene from graphite has rendered a breakthrough in the realm of plasmonics due to its phenomenal properties such as exceptionally tight light confinement, extremely long plasmon lifetime, high carrier mobility leading to a relatively low level of losses, strong optical nonlinearity and electrostatically as well as chemically tunable response. These versatile features of graphene can effectively address the challenges faced by metals, and hence the physics and potential applications of graphene-based plasmonics have triggered increasing attention of industry, academic and research fraternity in recent years. This chapter provides a comprehensive description of the theoretical approaches adopted to investigate the dispersion relation of graphene surface plasmons, types of graphene surface plasmons and their interactions with photons, phonons and electrons, experimental techniques to detect surface plasmons, the behaviour of surface plasmons in graphene nanostructures and the recent applications of graphene-based plasmonics.