S. Safavi-Naeini

Photonic-Crystal-Based Polarization Converter for Terahertz Integrated Circuit

In this paper, the fabrication and characterization of newly developed photonic crystal (PC) polarization-controlling devices on a silicon-on-insulator wafer for integrated terahertz applications are presented. The polarization converter is composed of periodic asymmetric loaded PC slab waveguide. Square- and circular-hole PC slab waveguides were studied using a 3-D finite-difference time-domain method. For a square-hole PC-based polarization rotator, polarization rotation efficiency higher than 90% was achieved within the normalized frequency band of a/ λ = 0.258-0.267 . In circular-hole PC polarization converter, the polarization conversion efficiency dropped to 70% for the aforementioned frequency band. Low polarization conversion efficiency of the circular-hole PC-based device is attributed to scattering loss at the top loaded layers. Thus, the square-hole PC structure is a better candidate for integrated terahertz polarization-controlling devices. Planar terahertz integrated circuit technology was developed to implement the proposed device. Characterization setup was designed using rigorous numerical methods to use the newly introduced Agilent Millimeter-wave PNA-X network analyzer (up to 500 GHz) as a source. Scattering parameter characterizations provide a good measure of polarization extinction ratio. For the devices designed for the central frequency of f = 200 GHz, it was observed that, within the frequency band of 198-208 GHz (α/λ = 0.26-0.272), the ratio of S21 to S11 was higher than 15 dB. The bandwidth is in good agreement with our preliminary design presented before.

Polarization and thickness dependent guiding in the photonic crystal slab waveguide

We investigated the impact of the thickness of the twodimensional triangular photonic crystal (PC) on modal propagation along a PC slab waveguide. A single line defect optical waveguide in photonic crystal slab was designed by three-dimensional finite difference time domain method, plane wave expansion and effective index methods. The thickness of the PC slab waveguide was optimized to provide modal propagation for both TE-like and TM-like polarizations within the normalized frequency band of a/lambda=0.26-0.268.

Wide angle phase-corrected Y-junction of dielectric waveguides for low loss applications

An approach to designing very-low-loss, wide-angle Y-junctions for dielectric waveguides is proposed. By introducing two interface planes with properly chosen parameters in the branching region, the conditions for a close (phase) match between the incident field and a desired output distribution suitable for minimal junction scattering are realized. An accurate and numerically efficient method for analysis and design of the proposed structure is described. Numerical results for some sample designs along with a set of simple design criteria are discussed. >

Design and Simulation of Photonic Crystal Based Polarization Converter

A periodic asymmetrically loaded photonic-crystal (PC) based polarization converter has been designed and fabricated. The polarization converter structure consists of a single defect line square hole PC slab waveguide with asymmetrically loaded top layer. The design methodology consists of finding the birefringence induced by geometrical asymmetry through full-wave modal analysis. The proposed design methodology can be extended to arbitrary air hole shape photonic-crystal-based polarization converter. The length and total number of top loaded layers are determined upon full-wave modal analysis. The thickness of the loaded top layer has been optimized to provide wideband and low loss polarization conversion. The optimized thickness of the top loaded layer is 0.2a for which polarization conversion takes place over the propagation distance of 13lambda0. For this distance, the coupling efficiency higher than 90% is achieved within the normalized frequency band of 0.258-0.267 corresponding to 584-604.5 GHz for the design example presented in III.

Design and analysis of novel multimode optical filters in dielectric waveguide

A new multimode filter design for wavelength multiplexing/demultiplexing applications is investigated. An asymmetric bend generates a number of higher-order modes with appropriate amplitudes from a single-mode incident wave containing two wavelengths. These modes, after travelling along a straight section of multimode waveguide, are recombined in the output Y-branch in such a way that the optical signals at two wavelengths are split and redirected toward different output branches. The structure is analyzed by a combination of finite-difference/time-domain (FD/TD) procedure and a recently developed physical optics method. Numerical results on a sample structure are presented and issues related to the accuracy of results are addressed. >

Reduced size electromagnetic band gap (EBG) structures for antenna applications

This paper presents a reduced size planar EBG cell, insensitive to variations in the polarization and/or the angles of incidence of the incident wave. The usefulness of this cell is justified by incorporating it into different antenna systems. Namely, integrating it with an array of 2 patches to minimize the cross coupling between them down till around-40 dB. Also, two multi-band systems implemented with the EBG cells are presented. A main advantage is the simplicity of design and ease of fabrication

A rotating micromirror switching element for 1/spl times/N optical MEMS switch

A new novel design for a rotating micromirror fabricated by MUMPs process is presented. The micromirror is elevated at 45/spl deg/ from the micromotors surface. The electrostatic side drive micromotor is designed to have both stepping and continuous rotation. With rotator diameters of 800/spl mu/m and 1000/spl mu/m, a step motion of either 0.75 or 0.5 degree is achieved with total steps of 480 and 720 for full rotation. The rotating micromirror was used to implement a 1/spl times/N optical MEMS switch with large number of output fibers.

A high resolution and wideband CMOS LO phase shifter

A new active LO phase shifter is introduced and implemented in a 2×2 MIMO receiver using STMicroelectronics 90nm CMOS technology. One of the advantaged of this new phase shifter is its capability of achieving very high resolution phase shifting over a wide range of frequencies which makes it suitable for multi-standard wireless applications. The proposed phase shifter is fully transistor based and it is digitally controlled. Measurement shows that phase shifter is able to change the phase of the output base band signal by 360° when LO is varying from 1.5GHz to 6GHz. the average resolution of the phase shifter is 1.32ps which is equivalent to 0.7 and 2.9 degree at 1.5GHz and 6GHz respectively. The differential I&Q signals are swapped to reduce the phase shift requirement of the phase shifter.

Fast full-wave analysis of conductor-loaded rectangular cavity resonators using surface integral equation and moment method

A recently developed technique for rapid calculation of the Greens functions in a rectangular cavity combined with a surface integral equation formulation and method of moments (SIE-MoM) is applied for full-wave modeling of arbitrarily oriented conducting objects inside a rectangular enclosure. In a multiply coupled resonator structure, each rectangular cavity with apertures of arbitrary shape and orientation on its walls is modeled by a generalized admittance matrix (GAM) obtained through SIE-MoM. Both combline and dual-mode disk resonators with tuning screw are considered for demonstration of the new approach and a remarkable computational efficiency is observed. A commercial EM simulator is used to verify the numerical results with excellent agreement.

An adaptive algorithm for efficient electromagnetic field calculations

The application of the method of moments (MoM) for analyzing large and complex structures is limited by its O(N/sup 2/) memory requirements and solution time, where N is the number of unknowns. An efficient adaptive algorithm is presented which can be used to accelerate the MoM procedure for electromagnetic scattering calculations in large scale and low frequency problems, where the number of unknowns can reach tens of thousands. This algorithm reduces the complexity of the field calculations to O(N).