M. Uthman

Design and Characterization of Low-Loss Porous-Core Photonic Crystal Fiber

A rigorous modal solution approach, based on the numerically efficient finite-element method (FEM), has been used to design and characterize a photonic crystal fiber (PCF) with a porous air core, which has the potential for use for low-loss guidance of terahertz (THz) waves. Here, for the first time, it is reported that a large fraction of the power that is also well confined in the waveguide can be guided in the low-loss air holes, thus to reduce the overall modal loss. This novel PCF design can readily be fabricated by use of a range of techniques including stack-and-draw, extrusion, and drilling.

Ultra low bending loss equiangular spiral photonic crystal fibers in the terahertz regime

An Equiangular Spiral Photonic Crystal Fiber (ES-PCF) design in Topas® for use in the Terahertz regime is presented. The design shows ultra low bending loss and very low confinement loss compared to conventional Hexagonal PCF (H-PCF). The ES-PCF has excellent modal confinement properties, together with several parameters to allow the optimization of the performance over a range of important characteristics. A full vector Finite Element simulation has been used to characterize the design which can be fabricated by a range of techniques including extrusion and drilling.

Mode degeneration in bent photonic crystal fiber study by using the finite element method

The development of highly dispersive lower and higher order cladding modes and their degeneration with respect to the fundamental core mode in a bent photonic crystal fiber is rigorously studied by use of the full-vectorial finite element method. It is shown that changes in the bending radius can modify the modal properties of large-area photonic crystal fibers, important for a number of potential practical applications.

Design of bent photonic crystal fiber supporting a single polarization

In this work, it is shown that the differential loss between the TE- and TM-polarized fundamental modes in a highly birefringent photonic crystal fiber (PCF) can be enhanced by bending the fiber. As a result, a design approach for single-mode single-polarization operation has been developed and is discussed. A rigorous full-vectorial H-field-based finite element approach, which includes the conformal transformation and the perfectly matched layer, is used to determine the single-polarization properties of such a highly birefringent PCF by exploiting its differential bending losses.

Stabilized Large Mode Area in Tapered Photonic Crystal Fiber for Stable Coupling

A rigorous modal solution approach based on the numerically efficient finite element method (FEM) has been used to design a tapered photonic crystal fiber with a large mode area that could be efficiently coupled to an optical fiber. Here, for the first time, we report that the expanded mode area can be stabilized against possible fabrication tolerances by introducing a secondary surrounding waveguide with larger air holes in the outer ring. A full-vectorial -field approach is employed to obtain mode field areas along the tapered section, and the Least Squares Boundary Residual (LSBR) method is used to obtain the coupling coefficients to a butt-coupled fiber.

Design and Characterization of Porous Core Polarization Maintaining Photonic Crystal Fiber for THz Guidance

An improved design of Teflon photonic crystal fiber with a porous air-core is presented for low-loss terahertz guidance. Optimization of total power confinement in the air-holes, together both in the cladding and core regions, is carried out for both quasi-TE and quasi-TM polarizations by using a full-vectorial finite element method. To achieve the polarization maintenance, modal birefringence is enhanced by destroying the circular symmetry with the introduction of unequal size air-holes in the first ring.

Emergence of THz technologies and design and optimisation low-loss waveguides and devices

THz is an emerging technology with many important applications in imaging and sensing, but due to lack of suitable low-loss waveguides future progress can be limited. A rigorous full-vectorial modal solution approach based on the computationally efficient finite element method is used to find the propagation properties of THz waveguides. Design approaches are presented to reduce the modal loss of such waveguides. Designs of several THz devices, including quantum cascade lasers, power splitters and narrow-band filters are also presented.

Characterization of low-loss waveguides and devices for terahertz radiation

Abstract. A rigorous full-vectorial modal solution approach based on the finite element method is used to find the propagation properties of terahertz (THz) waveguides, such as photonic crystal fibers, quantum cascaded lasers, plasmonic waveguides, power splitters, and narrow-band filters. Design approaches to reduce the modal loss due to the material and leakage loss in photonic crystal fibers and in metal-coated hollow-glass plasmonic waveguides have also been considered. The plasmonic confinement and gain threshold of quantum cascaded lasers used as THz sources and the chromatic dispersion in plasmonic waveguides are also presented.

Design of low-loss waveguides and devices for the emerging THz technologies

A rigorous full-vectorial modal solution approach based on the computationally efficient finite element method is used to find the propagation properties of THz waveguides. Design approaches are presented to reduce the modal loss of such waveguides. Designs of several THz devices, including quantum cascade lasers, power splitters and narrow-band filters are also presented.

Low-loss waveguides for THz guidance and devices

The terahertz (THz) region occupies a large portion of the electromagnetic spectrum, located between the microwave and optical frequencies and normally is defined as the band ranging from 0.1 to 10 THz. In recent years, this intermediate THz radiation band has attracted considerable interest, because it offers significant scientific and technological potential for applications in many fields, such as sensing [1], imaging [2] and spectroscopy [3]. However, waveguiding in this intermediate spectral region is a major challenge and strong dielectric and conductive losses in the terahertz frequency range have been a major problem for waveguiding. The conventional guiding structures exemplified by microstrips, coplanar striplines and coplanar waveguides [4] are highly lossy and dispersive. However, so far the most promising dielectric waveguides have been the use of photonic crystal fibers at terahertz frequencies [5, 6] and metal coated guides [7] at terahertz frequencies. In this paper, various types of practical dielectric and metal coated waveguides are evaluated and design optimization of Quantum Cascade Lasers, MMI-based power splitters and narrow-band filters are presented, by using full-vectorial finite element method [8].