Variable group-delay dispersion equalizer using lattice-formprogrammable optical filter on planar lightwave circuit

The authors report, in detail, an integrated-optic variable group-delay dispersion equalizer based on a lattice-form programmable optical filter. The variable dispersion equalizer consists of an alternating cascade of symmetrical and asymmetrical Mach-Zehnder interferometers. An equalizer with nine symmetrical and eight asymmetrical interferometers is fabricated on a planar lightwave circuit and its dispersion varied step by step from -681 to +786 ps/nm in the operational frequency range of 16.3 GHz. The effectiveness of the equalizer is shown by compensating the dispersion of three different fibers with a single equalizer. The performance of the equalizer is also evaluated and examined by numerical investigations     

Ultraviolet-cured polymer microlens arrays

A method for fabricating microlens arrays that uses the contraction effect of UV-curable photopolymers is presented. Lenses with diameters ranging from 0.2 to 2 mm that were made under different conditions are optically evaluated. The optimum conditions for producing low f-number lenses are discussed.     

Numerical Simulation for Direct Tunneling Current in Poly-Si-Gate MOS Capacitors

We have numerically simulated gate tunneling current in MOS capacitors. Price has demonstrated that the Gamow formulation can be applied to analysis of the escape of electrons from channel into gate in MOSFETs [P.J. Price, Appl. Phys. Lett., 82, 2080 (2003)]. We have integrated the Gamow method into a Schrödinger-Poisson solver for metal-gate and poly-Si-gate n-type MOS capacitors. The numerical results of the tunneling current are then compared with experimental results.     

Effect of magnetic iron impurity on the superconducting properties of an amorphous Nb50Zr35Si15 alloy

The effect of magnetic iron impurity on the superconducting properties of amorphous Nb₅₀Zr_35−x Si₁₅Fe _x (x⩽4 at %) alloys was examined. Doping with an iron impurity resulted in a linear depression ofT _c andH _c2(T) and a decrease in andρ _n after reaching a maximum value at 0.5 to 1.0 at % iron. The observed decrease was about 35% forT _c, 85% forH _c2 at 2.0 K, 16% for and 21% forρ _n. Although the decrease in occurs through the decrease inρ _n as expected from the GLAG theory, the depression inT _c caused by magnetic impurity could not be explained in terms of the GLAG theory which is applicable to Nb-Zr-Si amorphous alloys without magnetic impurity, but was interpreted as arising from the pair-breaking effect in the superconducting nature due to magnetic scattering. However, the pair-breaking effect was found to be smaller by about one-tenth for the present amorphous superconductors than for crystalline superconductors, indicating the high stability of the superconductivity of the Nb-Zr-Si-Fe alloys against the magnetic scattering arising from the magnetic impurity. The reduced magnetic field at which the reduced fluxoid pinning force exhibits a maximum value increased with iron concentration, indicative of an enhancement of fluxoid pinning force. The enhancement in fluxoid pinning force was interpreted as arising from the increase in compositional, electronic and/or magnetic fluctuations by the dope of iron impurity.     

Vertex angle and crossing angle resolution of leveled tree drawings

We study the problem of computing leveled tree drawings, i.e., straight-line drawings of trees where the vertices have distinct preassigned y-coordinates. Our optimization goal is to maximize the crossing angle resolution (i.e., the minimum angle formed by any two crossing edges) and/or the vertex angle resolution (i.e., the minimum angle formed by two edges incident to the same vertex) of the drawing. We provide tight and almost tight worst case bounds for the crossing angle resolution and for the total angle resolution (i.e., the minimum of crossing and vertex angle resolution), respectively.     

230W C-band GaN-FET power amplifier

A C-band high-power amplifier with two GaN-based FET chips exhibits record output powers under continuous-wave (CW) and pulsed operation conditions. At 5.0 GHz, the developed GaN-FET amplifier delivers a CW 208 W output power with 11.9 dB linear gain and 34% power-added efficiency. It also shows a pulsed 232 W output power with 8.3 dB linear gain.