A novel optical high order quadrature amplitude modulation (QAM) transmission system for high-speed short links is described. Dual-polarization (DP) QAM and twin local lights are generated from one light source in the system, and these lightwaves are simultaneously transmitted via standard single mode fiber. The receiver can be constructed simply because it does not require a coherent light source under wavelength control. The system enables a 3.1 Gbaud DP-16-QAM signal to be successfully demodulated after 80-km transmission without using an optical dispersion compensator. It also achieves high tolerance against phase noise in the signal light source.

Optical coherence tomography using a tunable single-mode laser is investigated to clarify the effects of long coherence length and step-wise frequency changes.

We evaluate the performance of a sub-optimum optical phase estimator obtained using a state variable description of the optical channel and stochastic estimation techniques. We implement the estimator for an urban wireless communications network.

The oscillation characteristics of a 40 GHz, 1-3 ps regeneratively and harmonically mode-locked erbium-doped fiber laser have been investigated in detail with respect to stability, linewidth, and mode hopping. We show that because the Q value of the microwave filter in the feedback loop is limited to around 1000, which is almost the same as that in a 10 GHz laser, the cavity length should not be greatly increased as this would result in as much as a fourfold increase in the number of longitudinal beat signals. We undertook a detailed stability analysis by using three cavity lengths, 60, 80, and 230 m. The 80 m long cavity greatly improved the long-term stability of the laser because the supermode noise was suppressed and there were not too many longitudinal modes. We measured the linewidth of the longitudinal mode of the laser using a heterodyne method, and it was less than 1 kHz. We also point out that there is a longitudinal mode hopping effect with time that is induced by very small changes in temperature.

We propose a frequency stabilization system for laser diodes (LD's), in which the major parameters in the stabilization process can be controlled in respond to the monitored frequency noise characteristics in real-time basis. The performance of this system was also tested through stabilizing a 35 mW visible LD. The center frequency of the LD has been stabilized by negative electrical feedback based on Pound-Drever-Hall technique. The linewidth of the LD has been reduced by adapting optical feedback from resonant confocal Fabry-Perot (CFP) cavity. The controlling parameters, especially gain levels and frequency responses of the negative electrical feedback loop can be manipulated to remove the instantaneous frequency noise by monitoring power spectral density (PSD) of the frequency error signals in the real-time basis. The achieved PSD of frequency noise of a sample LD stabilized by the present system was less than 1105 Hz2/Hz for the Fourier frequency < 10 MHz. The reduced linewidth was estimated to be narrower than 400 kHz. The achieved minimum square root of the Allan variance was 3.910-11 at τ = 0.1 msec.

This paper reports on the use of microelectronic test structures to characterise a novel fabrication technique for thin-film electronic circuit boards. In this technology circuit tracks are formed on paper-like substrates by depositing films of a metal-loaded ink via a standard lithographic printing process. Sheet resistance and linewidth for both horizontal and vertical lines are electrically evaluated and these compared with optical and surface profiling measurements.

Effects of field edge steps on characteristics of MOSFETs with tungsten polycide stacked gate electrodes patterned by KrF excimer laser lithography was studied through an electrical gate length measurement technique. Sheet resistance of the gate electrodes on the field oxide, on the active region and across the field edge steps was determined from the relationship between gate conductance and designed gate linewidth. The sheet resistance of the gate electrode across the field edge steps was larger than that on the flat regions. Effects of field edge steps on gate linewidth variation were evaluated by SEM observations and electrical measurements. Distribution of gate linewidth in a wafer was measured by the MOSFET test structures with the linewidth down to sub-quarter micron. Gate linewidth variation near the field edge steps was found to influence the short channel MOSFET characteristics.

We have investigated the Josephson microwave self-radiation and the linewidth from different types of YBa2Cu3Oy(YBCO) grain boundary junctions: natural grain boundary junctions, step-edge junctions and bicrystal junctions. The Josephson self-rediation was directly observed using a total power radiometer receiver with receiving frequencies fREC=1.7-72 GHz. All junctions exhibited microwave self-radiation peaks with intensity of order of 10-12-10-14 W. For step-edge and bicrystal junction, they appeared at a voltage related to the Josephson frequency-voltage relation, V=n(h/2e)f, while for natural grain boundary junctions, the above relation did not hold, suggesting a Josephson medium property. For all types of junctions the observed Josephson linewidth deviated from the theoretical RSJ values due to the extra noise source in the grain boundary junction. The Josephson linewidth decreased with increasing the receiving frequency for all type of junctions. The reduction of Josephson linewidth at higher frequencies indicates that the critical current fluctuations due to a critical current spread at small bias voltages and a crystalline disorientation at the junction boundary generate an additional noise in grain boundary junctions.

The minimum transferable linewidth by X-ray is derived using waveguide analysis. The minimum width is determined by the refractive index of the absorber and does not depend on the X-ray wavelength. Therefore there is an optimum mask aperture size which provides the minimum linewidth. By using Au as the absorber, 8 nm linewidth is attainable.