Mehmet Çiydem

Experimental Conditions for the Excitation of Thin Disk Whispering-Gallery-Mode Resonators

Measurements of mm-wave excitation spectra of highorder whispering gallery modes in free-space cylindrical disk resonators as functions of resonator thickness have been made. Resonators in the form of tight stacks of thin dielectric disks excited via dielectric waveguides have been used in the experiment. Experimental conditions for the excitation of thin-disk resonators have been found. A simple approach for the modeling of resonator spectra and recovery of dielectric parameters has been proposed.

Light-controlled photonics-based mm-wave beam switch.

We present experimental investigation of light-controlled photonics-enhanced quasi-optical mm-wave beam switch operating at a resonant frequency in the mm-wave band of 75 to 110 GHz. The switch is implemented as a Bragg structure with a resonant layer of high-resistivity silicon that creates a narrow transmission peak within the mm-wave propagation gap. The peak amplitude is sensitive to the intensity of light pulses illuminating the structure. When using a silicon wafer of 30 KOhm · cm resistivity and light pulses created by a 400W LED-array light source, we achieved mm-wave transmission peak modulation exceeding 15 dB.

FDTD Algorithm on Wavefront-Ray Grid for Wave Propagation

This paper shows that propagation direction dependence of numerical dispersion can be eliminated by finite-difference time-domain (FDTD) algorithm on wavefront/ray grids. The waves on each ray were found to experience the same type and amount of dispersion due to spatial discretization but not directional dependence

Ray-based finite-difference method for time-domain electromagnetics

In this study, the construction of full time-dependent solution of EM fields in space-time by exploiting discontinuities of fields, Taylor series and geometrical optics (GO) tools is introduced. The solution is establish by first finding the GO field and then improving it with higher order discontinuities on the wavefronts, along the rays in time. The proposed method is implemented on a sample problem of a Hertzian dipole in an isotropic homogeneous medium. Simulation studies, when compared with analytical and FDTD results, show that consistent and accurate results are obtained.

MM-WAVE DIELECTRIC PARAMETERS OF MAGNESIUM FLUORIDE GLASS WAFERS

We measured millimeter-wave dielectric parameters of magnesium fluoride glass wafers at the room temperature in the frequency band of 75–110 GHz by applying the open resonator technique based on the use of Bragg structures and related multi-layer assemblies. Through the comparison of measured and simulated transmission spectra of various structures, the dielectric constant of magnesium fluoride glass is found as ε = 5.50±0.01. The estimate for the loss tangent is found to be tan δ = 0.00005, with a possibility that the actual losses could be smaller than this value.

Elimination of FDTD Numerical Dispersion by using Geometrical Optics

The ray based time domain (RBTD) method for the computation of time-dependent electromagnetic fields is introduced. RBTD deals with discontinuities of field quantities, transports them along the rays and then constructs time-dependent field by using Taylor series with coefficients being discontinuities at the point of interest. The presented theory of RBTD handles propagation, reflection and refraction of finite jump discontinuities but not diffraction. Transport equations are 1D and RBTD implements xutri=nuxutrit along the ray. Hence in effect, RBTD reduces all higher dimensional problems to 1D along the ray. Honoring directional signal propagation and ODE nature of transport equations provide RBTD to eliminate numerical dispersion and superluminal effect of FDTD, which result from discretization of PDEs