Terahertz Hollow Core Antiresonant Fibre

Research on fibres operating in the terahertz frequency range is rapidly growing with numerous potential applications such as in spectroscopy, imaging, security, and transmission. However, designing a terahertz fibre with controllable and desirable transmission characteristics is challenging due to the complex cladding structure. In this thesis, we study hollow core antiresonant photonic crystal fibre (HC-ARPCF) for electromagnetic transmission and refractometric sensing in the terahertz regime. The HC-ARPCF consists of an air-core surrounded by a structured polymer cladding, which confines most of the power within the air-core region. The idea behind hollow-core antiresonant fibres is that light is guided in the hollow air core, thus drastically reducing the transmission loss. Guidance of light is achieved via reflection provided by thin membranes of the antiresonant tubes that surround the core, behaving effectively as a Fabry-P´erot cavity. At antiresonant frequencies, the thin membranes reflect the light towards the core because of the higher refractive index of the membranes. The guidance mechanism of the HC-ARPCF can also be explained due to the inhibited coupling mechanism (coupling between core and cladding mode is forbidden in guidance), where the cladding mode maintains a lower density of states (ηeff) than the fundamental core mode. Inhibited coupling guidance in HC-ARPCF offers broad bandwidth. At resonance frequencies, the light couples to the thin membranes and the core mode becomes more lossy, which can assist in gas sensing. The idea for the terahertz HC-ARPCF is inspired by those in the well-developed infrared and mid-infrared range. The effect of cladding pattern, cladding material, and cladding sector angle are analysed to investigate and tune the transmission loss, bending loss, and modal properties. The detailed simulations of several designs give a new understanding of the effect of the cladding elements on the leakage loss. The HCARPCFs are considered as a suitable candidate for low loss and broadband terahertz transmission. In addition, we model and simulate a simple hollow-core antiresonant terahertz waveguide, show the linear properties and explore the mechanism of achieving nonlinearity. First, the linear properties of HC-ARPCF are discussed, and then the nonlinear properties of the same structure are demonstrated, considering a gas-filled core in the terahertz regime. Furthermore, this thesis describes two different fabrication techniques for terahertz HC-ARPCF, using Zeonex and UV-resin as the bulk materials via a 3D printing process. The Zeonex filaments are made by using a Filabot EX2 Filament Extruder designed for filament production. To measure the effective material loss of the Zeonex, a circular disc with an uneven thickness of 0.65±0.05mmand a diameter of 24mmis printed.We demonstrate the first successful fabrication of Zeonex and UV resin fibre using Fused Decomposition modelling (FDM) and Steriolithography Apparatus (SLA) methods, respectively, to investigate the surface quality and thickness variations of the printed structure. These printing approaches have potential to replace conventional costly terahertz fibre drawing process. The fabricated fibres are then experimentally investigated for terahertz transmission. Fibres fabricated using the FDM and SLA methods are also investigated numerically and the results are compared against the experimental results. The detailed simulations suggest their attenuation can be improved by orders of magnitude with improvements in the quality of the fabrication process. We also discuss the possible post-processing techniques that can be useful for improving fibre quality and consistency in future work.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Electronic Engineering, 202

Dual-polarized highly sensitive plasmonic sensor in the visible to near-IR spectrum

We propose and numerically characterize the optical characteristics of a novel photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor in the visible to near infrared (500–2000 nm) region for refractive index (RI) sensing. The finite element method (FEM) is used to design and study the influence of different geometric parameters on the sensing performance of the sensor. The chemically stable plasmonic material gold (Au) is used to produce excitation between the core and plasmonic mode. On a pure silica (SiO2) substrate, a rectangular structured core is used to facilitate the coupling strength between the core and the surface plasmon polariton (SPP) mode and thus improves the sensing performance. By tuning the geometric parameters, simulation results show a maximum wavelength sensitivity of 58000 nm/RIU (Refractive Index Unit) for the x polarization and 62000 nm/RIU for the y polarization for analyte refractive indices ranging from 1.33 to 1.43. Moreover, we characterize the amplitude sensitivity of the sensor that shows a maximum sensitivity of 1415 RIU−1 and 1293 RIU−1 for the x and y polarizations, respectively. To our knowledge, this is the highest sensitivity for an SPR in published literature, and facilitates future development of sensors for accurate and precise analyte measurement. The sensor also attains a maximum figure of merit (FOM) of 1140 and fine RI resolution of 1.6 × 10−6. Owing to strong coupling strength, high sensitivity, high FOM and improved sensing resolution, the proposed sensor is suited for real-time, inexpensive and accurate detection of biomedical and biological analytes, biomolecules, and organic chemicals.This work is supported by Australian Research Council (grant no. DP170104984). We gratefully acknowledge their support

Ultra Low-Loss Hybrid Core Porous Fiber For Broadband Applications

Research Article published by Optical Society of America Vol.56,(No 4)In this paper, we present the design and analysis of a novel hybrid porous core octagonal lattice photonic crystal fiber for terahertz (THz) wave guidance. The numerical analysis is performed using a full-vector finite element method (FEM) that shows that 80% of bulk absorption material loss of cyclic olefin copolymer (COC), commercially known as TOPAS can be reduced at a core diameter of 350 μm. The obtained effective material loss (EML) is as low as 0.04 cm−1 at an operating frequency of 1 THz with a core porosity of 81%. Moreover, the proposed photonic crystal fiber also exhibits comparatively higher core power fraction, lower confinement loss, higher effective mode area, and an ultra-flattened dispersion profile with single mode propagation. This fiber can be readily fabricated using capillary stacking and sol-gel techniques, and it can be used for broadband terahertz applications. © 2017 Optical Society of Americ

Extremely low material loss and dispersion flattened TOPAS based circular porous fiber for long distance terahertz wave transmission

Research Article published by ElsevierIn this paper, we present a porous-core circular photonic crystal fiber (PC-CPCF) with ultra-low material loss for efficient terahertz wave transmission. The full vector finite element method with an ideally matched layer boundary condition is used to characterize the wave guiding properties of the proposed fiber. At an operating frequency of 1 THz, simulated results exhibit an extremely low effective material loss of 0.043 cm 1, higher core power fraction of 47% and ultra-flattened dispersion variation of 0.09 ps/THz/cm. The effects of important design properties such as single mode operation, confinement loss and effective area of the fiber are investigated in the terahertz regime. Moreover, the proposed fiber can be fabricated using the capillary stacking or sol-gel technique and be useful for long distance transmission of terahertz waves

Terahertz Sensing in a Hollow Core Photonic Crystal Fiber

A terahertz sensor based on a hollow core photonic crystal fiber has been proposed in this paper for chemical analyte detection in the terahertz frequency range. The Zeonex-based asymmetrical hollow core is filled with an analyte and surrounded by a number of asymmetrical rectangular air holes bounded by a perfectly matched layer with absorbing boundary conditions. The performance of the proposed sensor is numerically investigated by using finite element method-based COMSOL software. It is found that a hollow core provides a high relative sensitivity as well as low transmission loss. Moreover, simplicity in design facilitates manufacturability, making it practical for a number of different biological and industrial applications

Terahertz Hollow Core Antiresonant Fiber with Metamaterial Cladding

A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation results show that broadband terahertz radiation can be guided with six times lower loss in such hollow core fibers with metallic inclusions, compared to tube lattice fiber, covering a single mode bandwidth (BW) of 700 GHz