O.V. Minin

Terajets produced by dielectric cuboids

The capability of generating terajets using three-dimensional (3D) dielectric cuboids working at terahertz (THZ) frequencies (as analogues of nanojets in the infrared band) is introduced and studied numerically. The focusing performance of the terajets is evaluated in terms of the transversal full width at half maximum (FWHM) along x- and y-directions using different refractive indices for a 3D dielectric cuboid with a fixed geometry, obtaining a quasi-symmetric terajet with a subwavelength resolution of ∼0.46λ0 when the refractive index is n = 1.41. Moreover, the backscattering enhancement produced when metal particles are introduced in the terajet region is demonstrated for a 3D dielectric cuboid and compared with its two-dimensional (2D) counterpart. The results of the jet generated for the 3D case are experimentally validated at sub-THZ waves, demonstrating the ability to produce terajets using 3D cuboids.

All-dielectric periodic terajet waveguide using an array of coupled cuboids

In this paper, the recently proposed technique to produce photonic jets (terajets at terahertz (THz) frequencies) using 3D dielectric cuboids is applied in the design of a mesoscale cuboid-chain waveguide. The chains are basically designed with several dielectric cubes with side λ0 placed periodically along the axial z-axis and separated by an air-gap. Based on this, a systematic study of the focusing properties and wave guiding of this chain is performed when the air-gap between the dielectric cubes is changed from 0.25λ0 to 3λ0 with the best performance achieved at 2.5λ0. An analysis when losses are included in the cubes is also done, demonstrating a robust performance. Finally, the wave guiding is experimentally demonstrated at sub-THz frequencies with a good agreement with numerical results. The simulation results of focusing and transport properties are carried out using Finite Integration Technique. The results here presented may be scaled to any frequency ranges such as millimeter, sub-millimeter, ...

Subwavelength Diffractive Photonic Crystal Lens

We applied the principles of photonic crystal devices to the millimeter wave portion of the electromagnetic spectrum. For the lens, we have observed their collimation and imaging ability both shown in the amplitude and phase. The results described in the report shown that the diffractive photon crystal lens is a perspective candidate to subwavelength focus lens in different area of applications, including microscopy, lens array element, etc.

Flat and conformal zone plate antennas with new capabilities

We call attention to the existence of a free parameter in the design of Fresnel zone plates. Historically, zone plates have been designed with a specific choice for this parameter, which can be taken as a type of phase reference. We present two methods of interpreting the parameter, either in terms of a reference radius or equivalently a reference phase. Importantly, the parameter can be chosen to have non-standard values which are shown to improve important aspects of antenna performance and to add new functionality to zone plate antennas

Zoned Fishnet Lens Antenna With Reference Phase for Side-Lobe Reduction

Reduction of first side-lobe level (SLL) and nulls in artificial fishnet metalenses is accomplished here by applying the reference phase concept along with the zoning technique. Higher focusing efficiency is achieved for a specific reference phase when comparing numerically and experimentally four different designs. For such best design, an improvement of the first SLL (~2.4 dB), first null (~13 dB), and gain (~1.77 dB) is achieved experimentally compared to the design without reference phase.

Variable Reference Phase in Diffractive Antennas: Review, Applications, New Results

We review a free parameter in the design of Fresnel-zone-plate antennas. Historically, zone-plate antennas have been designed with a specific choice for this parameter. Two methods of interpreting the parameter have been identified, either in terms of a reference radius or, equivalently, a reference phase. For simplicity, here we treat this variable parameter as a reference phase. Importantly, the reference phase can be chosen to have non-standard values, which have been shown to improve important aspects of antenna performance and to add a new functionality to zone-plate antennas. In particular, a nearly linear one-to-one relationship between reference phase and the phase of the main-lobe beam exists, which is not present in the phase of sidelobes. This difference in phase response between main lobe and sidelobes is present independently of phase in feed circuitry: a zone-plate phase shift is fundamentally different from a feed phase shift. Frequency modulation of the reference phase thus appears as strong modulation of the main-lobe signal, but not of the signals through the sidelobes. This difference in frequency and phase response allows sidelobe signals to be discriminated against, making new applications possible. We review applications that exploit these features, including multipath-fading reduction, radar sidelobe-clutter reduction, and enhanced security in communications.

New technique to combat multipath fading in wireless networks

Mobile wireless networks of the future will be expected to function in highly diverse environments from dense foliage to dense urban settings. Under these conditions, the phenomenon of multipath fading will be a problem Here we describe a new technique to eliminate multipath fading in such wireless networks. Our technique is based on a free parameter in the design of Fresnel zone plate antennas, a type of reference phase. The technique exploits our ability to control relative phase between desired signals arriving in the antenna beam and of undesired multipath signals coming from outside of the beam direction. By control over relative phase, we can reduce the degree of fading to arbitrarily small values.

Elimination of Multipath Fading in Point-to-Point Communication

We describe a technique to eliminate multipath fading in point to point communications. The technique exploits our ability to control relative phase between desired signals arriving in the antenna beam and of undesired multipath signals coming from outside of the beam direction. Using out ability to control relative phase, we can in principle reduce the destructive interference know as multipath fading to arbitrarily small values.

NEW TECHNIQUE TO SUPPRESS SIDELOBE CLUTTER IN PERIMETER SECURITY SYSTEMS

False echoes degrade the operation of radar and imaging antennas. The false returns or clutter arise from antenna sidelobes and raise the threshold of detection in perimeter security systems. Accordingly there is great interest in reducing the sidelobes in present day millimeter wave and future terahertz antennas. Here we describe a new technique to suppress antenna sidelobe returns. The technique exploits our ability to distinguish between the phase of desired signals arriving in the antenna main beam and the phase of undesired clutter signals coming from the sidelobes. We demonstrate that through modulation of phase and taking the Fourier transform of the received signal, we can preferentially suppress the clutter return relative to the desired main beam signal. Suppression of average clutter return of over 25 dB is found.

FDTD Analysis of a Flat Diffractive Optics with Sub-Reyleigh Limit Resolution in MM/THz Waveband

The focusing properties of phase correcting Fresnel lenses with small values of focal length-to-diameter (FID) and with focal lengths of two wavelengths or less are investigated. For these lenses, the paraxial approximation for the Rayleigh resolution criterion is no longer valid. For Fresnel lenses designed with F/D < 0.2 and F les lambda, spatial resolutions of less than 0.5lambda are possible, which is finer than what can typically be achieved for conventional (paraxial) designs. The spot beams in these cases are not quite axially symmetrical due to the presence of anti-symmetric field components, which vanish for larger values of F/D.