R. K. Shevgaonkar

Optically Controlled Frequency-Reconfigurable Microstrip Antenna With Low Photoconductivity

In this letter, novel designs for optically switching the resonant frequency of a microstrip patch antenna via photoconductive switches are proposed, and design considerations for maximizing frequency switching ratio with finite photo-conductance are investigated. Furthermore, a configuration to switch the resonant frequency with low switch conductance is proposed for cheap and easy fabrication of a frequency-reconfigurable antenna that can be operated with low optical power. Experimental verification of the low-power configuration is presented.

Dispersion characteristics of an optical fiber having linear chirp refractive index profile

We analyze the dispersion characteristics of an optical fiber having linear chirp type refractive index profile. The chirp type profile is general in nature and by controlling the profile parameters, one can obtain a wide range of profiles from simple step index to complex multiple cladded type. The problem is treated as an optimization problem in the profile parameter space. It is shown that a variety of dispersion characteristics can be realized with proper optimization of the profile parameters. Linear finite element method (LFEM) is employed for computing the modal fields and propagation constants. Tolerance analysis of the fiber dispersion characteristics and bending loss calculation are also carried out.

A fresh look at the Hough transform

In this paper we have taken a fresh look at the process of accumulation in the Hough Transform to show that for certain quantizations of the parameter space, the set of points in an image that accumulate a given accumulator bin belong to a discrete straight line.

Design of subpicosecond dispersion-flattened fibers

Dispersion flattened (DF) fibers are required for wide-band WDM systems. The DF fibers designed in the past have dispersion in the range of 2.0-3.0 ps/km-nm. In this letter, we define a generalized refractive index profile that can be characterized by few controlling parameters. An optimum refractive index profile is obtained by minimizing the maximum dispersion over the wavelength range of 1300-1600 nm with respect to profile parameters. The designed fiber gives dispersion less than 1.0 ps/km-nm over 1350-1590 nm wavelength range. Sensitivity of the dispersion performance to the profile parameters is also discussed.

Beam Steering and Shaping of Smart Cylindrical Antenna

Shape control of parabolic cylindrical antennas and corresponding effect on radiation pattern, using piezoelectric actuators, is investigated. A narrow, 350-mm-long aperture, parabolic cylindrical antenna of Lexan® material is chosen for analysis. Antenna deformation is analyzed using an experimentally validated piezoelectric shell finite element. Radiation pattern is calculated using physical optics. Significant steering and shaping are obtained by deforming the antenna using centrally placed actuators. Using the strategy of making the phase variation at aperture as linear as possible and adjusting the phase difference between the two halves of the antenna to be an integral multiple of 2π, very good quality is achieved for the steered and shaped beams.

Preservation of Topological Properties of a Simple Closed Curve under Digitalization

In many applications of computer vision and image processing, one has to infer the properties of a real scene from its digitalized image. Therefore, preservation of different types of properties under digitalization is of importance. In this paper we have studied the effect of digitalization on the topological properties of simple closed curves, with the aim of determining the conditions under which these properties are preserved. Considering a square digitalizing grid, we have shown that for simple closed curves with a finite number of extrema, there exists an upper bound on the grid spacing for the preservation of the topological properties. Moreover, the properties are preserved for all translations of the grid except for a set of measure zero.

A novel T-shaped optically controlled microwave phase shifter

A novel T-shaped optically controlled microwave phase shifter is presented in this paper. The phase shifter consists of a T-shaped microstrip line with a gap in the shunt arm. The gap is filled with silicon and its conductivity is modulated by photo-excitation. The preliminary design of phase shifter is carried out using the transmission line model. Further Method of Moments is used to accurately model the photo-excited microstrip gap. The phase shifter parameters are optimized to achieve high phase shift with minimal insertion loss and ON-to-OFF amplitude change.

Improved SAC-OCDMA System With Multiple Incoherent Sources

The effect of a nonuniform spectrum on performance of a spectral amplitude coded optical code division multiple access system is investigated. The signal-to-interference ratio (SIR) as a function of nonuniformity of the source spectrum has been computed. Use of multiple sources is proposed to reduce spectral nonuniformity of the source and consequently the SIR.

Optimal steering of a paraboloid antenna using piezoelectric actuators

The use of piezoelectric actuators to modify an antenna radiation pattern has been investigated recently. In this paper, a doubly curved paraboloid antenna of Lexan® material is considered, and the optimal size, location, and field of the piezoelectric actuators are determined, for steering the radiation. The deformation induced by the piezoactuators is determined using a shell element modified for this purpose, and validated using extensive experiments on curved beams and shells with piezopatches. The genetic algorithm is used as the optimization tool. One of the contributions of this paper is a formulation of the optimization problem which reduces the computational effort significantly. A reasonable amount of steering with good beam quality is achieved.

Analysis of diffuse indoor infrared data links

The authors present a simple channel model for diffuse infra-red indoor data communication systems. Based on the model, important trade-offs between the transmitted optical power, the bit-rate, and the receiver parameters are presented for the first time.