Ing. Jan Šístek, Ph.D.

We have developed a data transparent optical packet switch, working at optical powers conventional in telecommunications. Polarization sensitivity of only 0.6 dB was achieved. The optical packet switch exploited wavelength conversion based on four-wave mixing. To achieve higher switching efficiencies, Ge-doped silica suspended-core and chalcogenide arsenic-selenide singlemode fibers were employed and compared to conventional highly-nonlinear fibers. Improved connectorization technology has been developed for both fibers to reduce overall component insertion loss, where we achieved connection losses of 0.9 dB. For the arsenic-selenide fiber we present the lowest attenuation up-to-date of 0.58 dB/m. Pump power limits for optical packet switching were set to 23 dBm, as limited by most thin-film components. Conversion efficiency of -16 dB was obtained for the highly-nonlinear fiber utilizing pump peak powers of 16 dBm. Arsenic-selenide fiber of 26 m length was evaluated, providing conversion efficiency lower than -38 dB with component insertion loss of -16.5 dB, thus further optimization was carried out according to simulated results. Conversion efficiency of -20 dB was observed with arsenic-selenide fiber length reduced to one meter.

The log-periodic principle of antennas can be applied to circuits with guided waves as well. It promises wideband performance with almost unlimited bandwidth. Although described in literature more than 40 years ago such circuits did not find wide use. This article aims to demonstrate practical design and properties of a circuit based on log-periodic principle. The authors selected a balun consisting of a wideband equal power divider (Wilkinson type) and a 180-degree differential phase shifter. The shifter, based on log-periodic principle, consists of cells containing asymmetric striplines interconnected by offset broadside-coupled striplines. The resulting circuit covers two octaves centered at 1 GHz.

Multistate reflectometers represent an alternative to expensive network analyzers. This paper describes two particular instruments developed at the FEE CTU in Prague. One extends the classic scalar network analyzer by means of a special designed Perturbation Two-Port (PTP) while the second suggests a completely new circuitry for the detector as well as the linear variable part.

This paper presents a novel multistate reflectometer for automated reflection measurements. Along with theoretical considerations and details concerning design of the instrument, practical results are given. Based in a resistive bridge in conjunction with a 45-degree phase shifter, the instrument seems promising for wide-band measurements.

The paper focuses on vector measurements exploiting multistate reflectometers. Since one of the most cricital components is the phase shifter, it suggest a technique that requires differential shift of only 45 degrees to achieve optimum location of the q-points. Preliminary experimental results given in the paper confirm our theoretical investigation.