Milan S. Kovačević

Modeling of the loss and mode coupling due to an irregular core–cladding interface in step-index plastic optical fibers

The core-cladding boundary in step-index plastic optical fibers is imperfect. Surface irregularities locked in during the manufacturing process couple the guided modes by reflecting them in directions that deviate unpredictably from the expected directions. This causes an additional loss as the multiple reflections from surface elements with directions randomized around the nominal for the cylinder transfer the power to the radiation modes that are carried away from the core into the cladding. We model such loss and mode coupling by ray tracing. The irregular core-cladding interface is represented by nominally cylindrical surface elements with orientations randomly perturbed around two geometric axes. The results show mode coupling and relative loss per unit fiber length caused by the core-cladding interface irregularities. The loss is high close to the input fiber end where mode coupling is intense. It drops farther along the fiber as mode coupling slows down and stabilizes where the equilibrium mode distribution is reached.

An Analytical Approach and Optimization of Curvature Gauge

The curvature gauge is sensor for the monitoring of deflection of structures under mechanical loading in applications in which strain gauges have traditionally been used. The sensitive zone of the curvature gage is precision machined into the plastic optical fibre on grinding or milling machines. The cut-out produced removes a part of the fibre core and introduces a loss of light propagating along. The extent of such loss is related to the bendradius of the fibre. In this work we present an analytical approach of this sensor. The operation of this curvature gauge is now explained and estimated in order to optimise it and improve its performances. The results are shown that relate the relative light-loss to the fibre curvature for different parameters (its depth, length, number of cuts, bend radius and pitch of cuts). Proposed model allows a quantitative optimization of curvature gauge without the necessity for making of the thousands of sensors with slightly different parameters in order to accomplish a similar objective experimentally.

A Mechanical Analogy for the Photoelectric Effect.

Analogy is a potent tool in the teachers repertoire. It has been particularly well recognized in the teaching of science. However, careful planning is required for its effective application to prevent documented drawbacks when analogies are stretched too far. Befitting the occasion of the World Year of Physics commemorating Albert Einsteins 1905 pioneering contributions to the understanding of the photoelectric effect, a suitable mechanical analogy for introducing this effect to high school students is described in this article. Cost-effectively, it allows students to comprehend the photoelectric effect by relating it to their visual experience from the mechanical world with which they are familiar.

Transients of Modal-Power Distribution in Multimode Solid-Core W-Type Photonic Crystal Fibers

Spatial transients of the modal power distribution are reported for a varied configuration of air holes in the inner cladding of multimode solid-core photonic crystal fibers. Such inner cladding forms an intermediate fiber layer seen in W-type fibers with the layers own effective refractive index due to the distinct size and/or spacing of air holes in it. We show how the modal distribution transients along the fiber depend on the number of rings in the inner cladding containing the distinct arrangement of air holes, and on the size and spacing of such holes in addition to the type of launch condition (excitation).

Plastic optical fiber as a tool for experimenting with simple pendulum

In this paper an experiment with plastic optical fiber to control the motion of a simple pendulum was described. The monitoring system of pendulum position is based on bend loss in plastic optical fiber which depends of bend radius. As a recording device a PC sound card was used. With this measurement technique we are able to visualize theoretical expectation and to extract some of the parameter values from the recorded data as the position, velocity and acceleration of pendulum. The angular displacements, velocity and acceleration are plotted using Mathematica, an available symbolic computer program that allows us to plot easily the obtained dependence as well as their theoretical behavior. Good agreement between measurements and theoretical prediction was observed

Web-based experiment for teaching the electrical characteristics of a solar cell and module

In this paper, an experiment involving a solar module consisting of serially connected solar cells remotely controlled by a web application is presented. The described experiment is fully automated and is accessed and controlled remotely using a web‐based user interface; a new generation of inexpensive SBC (single‐board computer) devices; flat, light LED sources; and some electronic components. Basically, the experiment consists of a solar module illuminated by a flat LED light source and a programmed electronic variable resistor, which enables collecting the solar module current‐voltage (I–V) characteristics. We found that remote access to lab equipment and experiments has many advantages over traditional scheduled supervised access because it provides a safe virtual environment for work and experimentation using real equipment. Promoting interest in solar cells by introducing students at an early stage of their undergraduate curriculum to the basics (fundamentals) of photovoltaic devices is beneficial in many aspects.

Computer sound card as a tool to study of fast changing electromagnetic phenomena

This paper presents an original undergraduate experiment which use capabilities of the PC sound device for observation and data acquisition. We study the rapid changing electromagnetic (EM) phenomena in the undergraduate physics laboratory. These phenomena are often encountered in the standard electro dynamical experiments like as electromagnetic induction and oscillation in LC circuit. The comparison of theoretical study within experimental output shows that the usage of PC sound card as digital oscilloscope is suitable in the undergraduate laboratory. For this purpose, an experiment that analyzes Faradays law of electromagnetic induction using PC sound cards as digital oscilloscope was described. Then we apply the computer sound card to measure damped electromagnetic oscillation in the LC circuit. By using this measurement technique we were able to visualize theoretical expectation and to extract some of the parameter values from the recorded data. Moreover, combining the theoretical description of the problem with an appropriate laboratory experiment and computational procedures gives students a clearer view of the physical problem as a whole.

Investigation of influence of tilt angle on mode dispersion in step-index plastic optical fibers

Effect of numerical aperture on mode dispersion and bandwidth is reported for commercially available step-index plastic optical fibers. For the first time, the functional relationship is given between dispersion and the “tilt-angle” describing the slant of the input/output face for a fiber terminated by a plane not perpendicular to the fiber axis. This tilt of a non-squarely terminated fiber may be intentional as in some biomedical spectroscopic sensors, or otherwise when exploiting the quick-interconnectivity potential of plastic fibers.

Crystallization in a chamber furnace

A model of an air cooler (`cold finger) in a laboratory chamber furnace, for simultaneous regulation of different crystallization rates in a series of Tamman test tubes with the purpose of obtaining crystals, is given.