Huda Tanvir

Characterization of Plasmonic Modes in a Low-Loss Dielectric-Coated Hollow Core Rectangular Waveguide at Terahertz Frequency

In this paper, a low-loss hollow-core rectangular plasmonic waveguide with a dielectric coating of Teflon is analyzed for terahertz (2.5 THz) propagation using a full-vectorial finite-element method (FEM). The modal properties of the waveguide, their effective indices, and power confinements have been calculated with a particular emphasis on the loss characteristics of the different modes. It has been observed that the loss characteristics of the guide are greatly affected by the thickness of the dielectric coating. It has been identified that, in contrast to the fundamental H10x mode, the H12x mode shows interesting modal properties and offers the lowest possible loss for the structure. This mode also tends to yield a near-Gaussian field profile when the dielectric coating thickness is optimized. The optimization of the loss values has been evaluated by comparing the loss characteristics for different dielectric materials, as well as by using different metal claddings.

Impact of “Ghost” Mode Interaction in Terahertz Quantum Cascade Lasers

Mode degeneration caused by the interaction between guided lasing modes and parasitic “ghost” modes in a terahertz (THz) quantum cascade laser (QCL) waveguide has been investigated and is reported here. It is shown that such interactions can degrade the performance of a QCL by causing abrupt rises (by as much as tenfold the normal value) in the gain threshold of the fundamental lasing mode. The impact of such interaction on the performance of a GaSb/AlGaSb THz QCL operating at 3.0 THz is elucidated here through the results of a rigorous numerical simulation. An optimized design is also proposed to suppress such undesirable intermodal interactions and, thus, to enhance the performance of the QCL.

Metal-Coated Defect-Core Photonic Crystal Fiber for THz Propagation

Modal solutions for metal-coated defect-core photonic crystal fiber (PCF) with a central air-hole have been obtained by using a full-vectorial finite element method to model the guidance of THz waves. It has been shown that the surface plasmon modes can couple with the defect-core PCF mode to form supermodes, with potential for sensing applications.

Multimode Interference 3 dB Splitters in Hollow Core Metallic Waveguides for Low-Loss THz Wave Transmission

A multimode interference half-power splitter on hollow core polysterene-coated metallic waveguide is demonstrated in this study. The modal properties, propagation length, optical field evolution, and dispersion of the aforementioned device have been investigated using the full vectorial finite-element-based modal analysis and beam propagation method, as well as the finite-difference time-domain approach.

Evolution of Highly Confined Surface Plasmon Modes in Terahertz Quantum Cascade Laser Waveguides

The evolution of surface plasmon (SP) supermodes through the effective coupling of isolated SP modes in a semiinsulating quantum cascade laser (QCL) waveguide is thoroughly discussed here. The effect of varying the material and geometric parameters of GaSb/AlGaSb QCL operating at 3.0 THz are thoroughly studied using a full-vectorial finite-element method. It was observed that this structure is prone to mode degeneration caused by resonant interaction of the lasing mode with a higher order plasmon mode. An optimized design is also proposed to suppress such adverse affects and highly divergent field profiles arising from the generation of higher order lateral modes.

A Higher Order Lateral Mode Suppression Scheme for Terahertz Quantum Cascade Laser Waveguides

The modal performance of a slot-clad metal-metal waveguide for terahertz quantum cascade lasers (QCLs) is elucidated in this study. Terahertz QCLs, based on metal-metal waveguides having a large ridge width, are susceptible to lase with higher order lateral modes, which may produce poor quality beams and can lead to detrimental consequences for certain applications. By comparing the modal performance of the slot-clad waveguide with previously reported designs, it has been shown that the slot-clad metal-metal waveguide can significantly enhance the degree of suppression of higher order lateral modes.

Study of modal properties in gold nanowire with ZnO cladding by using the finite element method

Zinc oxide is a wide-bandgap semiconductor material, which can be grown as a single crystal and also as a thin film. A gold nanowire with zinc oxide cladding can serve as a waveguide, which can combine the plasmonic features of a metal nanowire with the sensing properties of ZnO. Using an H-field-based fully vectorial finite element method, rigorous modal solutions for the characteristics of a gold nanowire core with zinc oxide cladding are obtained. The modal properties, including the effective index, spot size, confinement factor, and modal hybridness have been analyzed to determine the fundamental plasmonic mode of this waveguide.

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].

Rigorous modal analysis of THz quantum cascade lasers

The evolution of surface plasmon supermodes through the effective coupling of isolated surface plasmon modes in a semi-insulating quantum cascade laser (QCL) waveguide is thoroughly discussed here. The effect of varying the material and geometric parameters of GaSb/AlGaSb QCL operating at 3.0 THz are thoroughly studied using a full-vectorial finite element method.

Design optimization of low-loss waveguides and devices for THz systems

The design of low loss-waveguides, simple power splitters and narrow band filters, suitable for the THz frequency band, along with the optimization of the active region of a quantum cascade laser, are presented here.