Modulator integrated DFB lasers with more than 600-km transmission capability at 2.5 Gb/s

The modulator integrated DFB laser diodes with more than 600-km transmission capability over normal fiber at 2.5 Gb/s, have been reproducibly achieved. The longest transmission length obtained in the experiment is as long as 800 km.     

S-band erbium-doped silica fibre amplifier with flattened-gain ofover 21 dB

A gain-flattened erbium-doped silica fibre amplifier (EDSFA) has been developed for amplifying WDM signals in the S-band. The EDSFA exhibits a signal gain of over 21 dB, a gain excursion of less than 1.9 dB, and a noise figure of less than 6.7 dB in the 1491-1518 nm wavelength range     

Control scheme for optimizing the interferometer phase bias in a symmetric-Mach-Zehnder-type all-optical switch

A control scheme for accurately optimizing (and also automatically stabilizing) the interferometer phase bias of symmetric-Mach-Zehnder (SMZ)-type ultrafast all-optical switches is proposed. In this control scheme, weak continuous-wave light is used as supervisory input light and its spectral power ratio at the switch output is used as a bipolar error signal. Our experimental results for 168-Gb/s 16:1 demultiplexing with a hybrid-integrated SMZ switch indicate the feasibility and the sensitivity of this control scheme.     

Gain-shifted TDFA employing high concentration doping techniquewith high internal power conversion efficiency of 70%

The amplification characteristics of a high Tm³⁺ concentration gain-shifted Tm-doped fluoride fibre amplifier (GS-TDFA) have been determined with a high input signal power. This GS-TDFA achieved the highest reported internal power conversion efficiency of 70% with a double pass configuration     

Millimeter-Wave Beam Multiplexing Method Using Subarray Type Hybrid Beamforming of Interleaved Configuration with Inter-subarray Coding

A millimeter-wave beam multiplexing method using a subarray type interleaved configuration hybrid beamforming with inter-subarray coding is proposed. By multiplexing of adequate directional beams, the proposed method can reduce inter-beam interference and create multiple beams of a theoretical maximum gain that an array antenna can generate. As results of performance comparison in subarray type beamforming with the feasibility, it is shown that channel capacity of the interleaved configuration with inter-subarray coding is larger than that of the localized configuration. Particularly, in user dense environments, the interleaved configuration is effective. Therefore, we think that the interleaved configuration is suitable for millimeter-wave beam multiplexing.     

Boroxine Nanotubes: Moisture‐Sensitive Morphological Transformation and Guest Release

Boroxines, (R‐BO)₃, which can be easily synthesized via a dehydration reaction of boronic acids, R–B(OH)₂, selectively self‐assemble in toluene into nanofibers, nanorods, nanotapes, and nanotubes, depending on the aromatic substituent (R). Spectroscopic measurements show that the nanotube consists of a J‐aggregate of the boroxine. Humidification converts the morphology from the nanotube to a sheet as a result of the hydrolysis of the boroxine components and subsequent molecular‐packing rearrangement from the J‐aggregate to an H‐aggregate. Such a transformation leads to the compulsive release of guest molecules encapsulated in the hollow cylinder of the nanotube. The hydrolysis and the molecular‐packing rearrangement described above are suppressed by coordination of pyridine to the boron atom, with the resulting moiety acting as a Lewis acid of the boroxine component. The pyridine‐coordinated nanotube is transformed into a helical coil by humidification. Guest release during the nanotube‐to‐helical‐coil transformation is much slower than during the nanotube‐to‐sheet transformation, but faster than from a nanotube that did not undergo morphological transformation. The storage and release of guest molecules from the boroxine nanotubes can be precisely controlled by adjusting the moisture level and the concentration of Lewis bases, such as amines.     

Occurrence of multiple ethyl 4-chloro-3-oxobutanoate-reducing enzymes in Candida magnoliae

Multiple ethyl 4-chloro-3-oxobutanoate (COBE)-reducing enzymes were isolated from a cell-free extract of Candida magnoliae. A NADPH-dependent COBE-reducing enzyme, distinct from the carbonyl reductase and aldehyde reductase previously reported, was purified to homogeneity using five steps, including polyethylene glycol treatment. The relative molecular mass of the enzyme was estimated to be 86,000 on high performance gel-permeation chromatography and 29,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme catalyzed the reduction of COBE to the corresponding (S)-alcohol with a 51% enantiomeric excess. The substrate specificity of the enzyme was different from those of the other COBE-reducing enzymes of the same strain. The partial amino acid sequences of the enzyme showed that it belongs to the short chain alcohol dehydrogenase/reductase (SDR) family. This is the first report of multiple COBE-reducing enzymes with various stereoselectivities occurring in the same strain but belonging to different (super)families.     

Equal-gain loci and stability of a microwave GaAs MESFET gate mixer

The performance of a microwave GaAs MESFET gate mixer is theoretically investigated to clarify the existence of a conditionally stable RF frequency range as well as an unconditionally stable frequency range in which maximum available conversion gain (MACG) can be defined. For the unconditionally stable range, the MACG and load and source impedances are calculated as functions of RF frequency. For the conditionally stable range, the stability circle and equal gain loci are shown for source RF and load IF impedances. The conditionally stable region of the GaAs MESFET mixer appears around F_T of the MESFET. Higher conversion gain is easily obtained by choosing a MESFET for which the F_T is close to the RF frequency     

40 Gbit/s electroabsorption modulators with impedance-controlled electrodes

A novel travelling-wave electroabsorption optical modulator, electrically matched for 50 /spl Omega/ loads of driving circuit drivers, was developed. The scattering parameter of electric reflection (S/sub 11/) from this modulator is less than -20 dB at 20 GHz. It can thus enable a 40 Gbit/s, 2 km SMF transmission with a 0.3 dB penalty at a 1.3 /spl mu/m wavelength.