Mahdi Aghadjani

Terahertz Switch Based on Waveguide-Cavity-Waveguide Comprising Cylindrical Spoof Surface Plasmon Polariton

This paper demonstrates a terahertz (THz) switch that comprises a metallic perfect conductor in the form of periodically corrugated cylindrical waveguides surrounding a dielectric medium consisting of GaAs compound semiconductor. The proposed switch deploys a composite waveguide-cavity-waveguide structure. The switch controls its state by dynamically altering the optical properties of an engineered nonlinear material inside the cavity, while the corrugated waveguides on both sides of the cavity are incorporated to limit the propagation of electromagnetic (EM) waves at nearly THz frequencies only. At the resonant frequency, the corrugated waveguide allows strong EM confinement inside the grooves. The cavity has been designed to achieve a high quality factor as well as to trap EM waves for a significant period of time. Small changes in the GaAs refractive index inside the grooves can alter the cavity resonant frequency. Localized doping near the metal conductor inside the cavity is implemented so that by applying a voltage between the metal electrode and the depletion region in the dielectric medium, the switch can be altered from the ON state to the OFF state, and vice versa.

THz Polarizer Controller Based on Cylindrical Spoof Surface Plasmon Polariton (C-SSPP)

Spoof surface plasmon polariton (SSPP) based devices have recently garnered a great deal of attention owing to their ability to propagate THz signal without dispersion and very low signal attenuation. In this paper, a rigorous mathematical model has been proposed by performing full-field analysis on the periodically corrugated cylindrical waveguide. It has been shown that this structure has the capability of propagating localized spoof surface plasmons polariton (SSPP) mode of EM waves. The variation of band diagrams as a function of different groove dimensions has been investigated. Finally, by employing cylindrical SSPP a new polarizer controller has been designed that can be utilized to design THz Boolean gates.

Metamaterial sensor platforms for Terahertz DNA sensing

Three high-sensitivity metamaterial Terahertz DNA sensors based on resonance are proposed to distinguish DNA molecule with different refractive indices. Both numerical electromagnetic method and physical circuit model interpretation are employed to analyze proposed sensor structures. Design guideline based on intuitive physical circuit model is provided and verified through full-wave simulation.

Design and analysis of a terahertz SSPP switch using piezoelectric materials

In this paper, a terahertz switch, consisting of a single-sided corrugated metallic structure, has been designed and analyzed. It demonstrates that it can support spoof surface plasmon polaritons propagation and has multiple band-gaps. We have shown that the band-gap can be altered by changing the grooves height. Piezoelectric material has been implemented to control the grooves height and, as a result, the band-gap of the switch can be controlled. By applying voltage across the piezoelectric layer, the switch can go from conducting (ON) state into blocking (OFF) state.

Dynamic Terahertz switch based on waveguide-cavity-waveguide (WCW) structure

In this brief, a THz switch consisting of GaAs dielectric slab waveguide with periodic perfect conductor patches on its top and bottom is demonstrated. The performance is based on waveguide-cavity-waveguide structure. By pumping optical signal into the slab waveguide and changing the carrier density of semiconductor directly underneath the patches, and modulating the refractive index of GaAs dielectric it switches between on-state and off-state.

Spoof Surface Plasmon Polariton Beam Splitter

Propagation of terahertz (THz) wave utilizing spoof surface plasmon polariton (SSPP) earned a great deal of attention due to the ability of SSPP modes to guide THz waves at very low dispersion. We present an investigation of the SSPP beam splitter, one of the key elements of many optical setups. In contrast with conventional free space implementations, in the case of the SSPP beam splitter, one can no longer disregard scattering of incoming wave back into the input channels. Thus, SSPP implementations must take into consideration both the splitting ratio and the backscattering as important parameters characterizing the beam splitter. Three different designs representing different approaches to solving the problem of the relation between these parameters are investigated. The mathematical formalism to study the dispersion diagrams is proposed. The frequency dependence of splitting ratio, scattering parameters, and backscattering for each beam splitter is investigated. Finally, by employing one of the proposed beam splitter, a controllable filter is designed and analyzed.

Beam splitting using self-collimation phenomenon in photonic crystal

In this paper, we propose an in-plane beam splitter for self-collimated beams in a two-dimensional photonic crystal. An optical filter inserted on the propagation path of the input self-collimated beam divides this beam into two parallel equi-power self-collimated beams. The optical filter has a multistage configuration designed using well-known techniques. The proposed beam splitter has a compact configuration appropriate for integrated optics. Design procedure and the numerical results obtained using the finite-difference time-domain method, as well as a method for extraction of the S parameters of the beam splitter, are presented.

THz analog to digital converter using single sided spoof surface plasmon polariton waveguide

In this paper, an analogue-to-digital convertor (ADC) utilizing the single sided spoof surface plasmon polariton (SS-SSPP) waveguide is presented. The proposed ADC device consists of three stages: first stage is the Mach-Zehnder interferometer (MZI) with two arms which acts as a beam steering device, second is free space propagation stage, and third is the detector arrays to convert analog signal into digital input. The SSPP waveguide includes periodic grooves, which are filled with a thin layer of doped semiconductor. In order to alter the refractive index of the semiconductor the depletion mode has been used. It is demonstrated that the ADC can operate with sampling speed around 47 GS/s.