All-fiber active add-drop wavelength router

We describe a fiber Bragg grating Mach-Zehnder interferometer (FBG-MZI) which utilizes active phase control. The active FBG-MZI is operated as a wavelength router, where the grating-selected wavelength channel can be actively routed. We believe this is the first demonstration of an all fibre FBG-MZI wavelength router.     

Structural analysis of iron oxide coated n-silicon heterojunction photoanodes

The iron oxide/n-Si heterojunction electrode was investigated as a possible efficient photoanode with the iron oxide prepared under various conditions. The oxide structure was studied by RBS (Rutherford backscattering spectrometry) and XPS (X-ray photoelectron spectroscopy) techniques and the correlation between photocharacteristics and its oxide structure was discussed. The iron oxide prepared by thermal oxidation and reactive-evaporation methods. The photocurrent in a 0.2 mol dm^?3 KOH solution was found to strongly depend on the preparation of the iron oxide. The reactive-evaporated Fe₂O₃/n-Si electrode showed the most effective characteristics of photoresponse and the 60 min thermally oxidized Fe₂O₃/n-Si electrode gave the best results in the thermally oxidized oxide system. The compositional analysis by RBS indicated that the oxide is formed stoichiometrically as Fe₂O₃ and that small amounts of a heavy-mass and a tungsten impurity are present in the thermally oxidized and the reactive-evaporated oxides, respectively. The XPS analysis of the chemical state of the iron in the oxide showed that the chemical state of the iron oxide formed by thermal oxidation varies as a function of depth and that the iron oxide formed by reactive- evaporation is in a almost constant chemical state throughout the film.     

Optical power equalization for multiwavelength fiber-amplifiercascades using periodic inhomogeneous broadening

Inhomogeneously broadened fiber amplifiers inserted periodically in an amplifier cascade are shown to provide significant interchannel power equalization in wavelength-multiplexed systems. Interchannel power variations in a six-amplifier cascade are reduced from 16 dB in a conventional system to about 5 dB when power equalizers are inserted     

Interferometric noise limitations in fibre-amplifier cascades

Phase-induced intensity noise from weak multiple reflectors is evaluated theoretically and experimentally in amplifier cascades without isolators. Rayleigh backscattering alone significantly limits the number of amplifiers in the span. Theory and experiment agree closely for a six-amplifier cascade.<>     

High-performance amplified optical links without isolators orbandpass filters

Using a simple analysis of saturated amplifier cascades, the authors examine the consequences of removing optical bandpass filters and/or isolators, while still relying on saturation effects to provide automatic power control. The authors find that optical bandpass filters can be removed at only a modest cost in system performance. Moreover, isolators can also be removed or reduced in number, so long as reflection-induced degradations permit. When isolators are removed or reduced in number, backward-traveling spontaneous emission plays a significant role, via saturation effects, in the regulation of optical signal power     

Low residual reflectivity of angled-facet semiconductor laseramplifiers

Ridge-waveguide angled-facet semiconductor laser amplifiers for the 1.5 μm band have been fabricated with facet angles of 7° and 10°. Gain measurements performed with a stable, computer-controlled setup have revealed gain ripples as low as 0.025 dB at 22 dB gain for a 10° device. This corresponds to a residual reflectivity of 1×10^-5. Results demonstrate that the residual reflectivity of angled devices with one-layer antireflection coatings can be as low as that for normal facet devices with highly controlled double-layer antireflection coatings     

Inhomogeneously broadened fiber-amplifier cascade forwavelength-multiplexed systems

The authors observe little or no accumulation of optical-power variations among wavelength-multiplexed signals as they traverse successive stages of a cooled, inhomogeneously broadened, erbium-doped fiber-amplifier cascade. The cascade instead exhibits separate automatic power regulation of each channel, decoupled from other channels, without the use of servo loops     

Performance implications of component crosstalk in transparentlightwave networks

We find both theoretically and experimentally that crosstalk due to small component imperfections in transparent lightwave networks will tend to generate large performance degradations. The most severe degradations, which arise from interference between signal and crosstalk electric fields, are far larger than those predicted from simple power-addition without field interference. Systems corrupted by crosstalk from a single source of optical-field leakage appear to require component crosstalk levels ϵ⩽-20 dB, if conventional receivers are used. Since the degradations are believed to depend on N√ϵ, where N is the number of crosstalk generators, each producing a crosstalk power level of ϵ, the problem is expected to grow rapidly severe with network size     

Rational approach to postoperative transfusion in high-risk patients

An appropriate threshold for transfusion in patients with coronary artery disease has not been defined. Our purpose was to determine: (1) the effects of preoperative volume loading; (2) postoperative function and oxygen delivery (DO2); (3) an appropriate transfusion threshold based on observed DO2 in high-risk patients undergoing abdominal aortic aneurysm (AAA) repair, bypass of aortoiliac disease (AOD), distal bypass, or carotid endarterectomy (CEA). Preoperative volume loading increased cardiac output (CO) in all groups by 15% to 22%. Postoperative CO was unchanged from optimal preoperative values except in the CEA group, in which it decreased. Systemic vascular resistance decreased in the AAA and AOD groups. The decrease in postoperative DO2 in all groups (25% to 31%) was related to a decrease in hemoglobin. Despite marginal (less than 11 mL/kg/min) postoperative DO2 in more than a third of patients, there was no compensatory increase in CO. Thus, after optimization of function by volume loading, red cell transfusion may be the only way to increase DO2. Hemoglobin levels of 10 to 12 g/dL may be required for adequate DO2 when ventricular function is markedly impaired.