Low-cost optical sub-assemblies for metro access applications
The fiber optic communications industry is experiencing significant change as datacom 10 Gb/s Ethernet (10 GbE) networks merge with telecom SONET 10G networks in the drive to reach metro access applications. Lower data rate (1G Ethernet, 1G and 2G fiber channel, and SONET OC-48) applications have already merged to some extent as various versions are available within the SFF or SFP standard transceiver form factors. Traditional 10 Gb/s optical subassemblies (OSAs), developed for SONET OC-192 applications, used variations of the expensive butterfly type package. However, smaller form factor modules (such as the XFP that uses SFF optical connectors and LC duplex optical connectors) require much smaller OSAs. To meet the size limitation of packaging 10G OSAs into the XFP transceiver and also meet the 10 GbE market challenge of providing low-cost solutions, new 10 Gb/s OSA components are needed.
Failure mechanism of avalanche photodiodes in the presence of water vapor
Lower cost optoelectronic modules (transmitters and receivers) could be produced if components could operate reliably in a nonhermetic package. Experiments (operation in humid ambient as a function of temperature, relative humidity (RH), and voltage) were carried out on InP-based avalanche photodiodes (APDs). The objectives were to reveal any moisture-related failure modes, to understand the failure mechanisms, to determine the relevant acceleration factors, and to propose design or material modifications to prevent the failures. Leakage current vs. time was measured for nine cells of 20 devices each. All devices were examined by optical microscopy, and representative samples were studied by scanning electron microscopy. A failure mechanism related to corrosion of the passivating SiN and the underlying semiconductor was identified. Based on the voltage and RH dependence of the degradation rate, a model for the failure process was developed. The mechanism involves RH-dependent transport of charge across the surface of the SiN and Poole-Frenkel current flow through the SiN. This process eventually produces a short circuit.
Venus: Evolution of the Upper Atmospheric Clouds
Abstract The large number of UV photographs taken by different observatories throughout the world are grouped for analysis at the IAU Planetary Photograph Center of Meudon Observatory. Three horizontal V, Y, or psi-shaped dark-hued cloud features are usually aligned along the equator and move 110 m s−1 westward in a planetary-wide rotation. The more intense and distinctly V-Shaped features last several weeks. The smaller scale cloud structures usually show significant changes after each successive rotation in 4 days around the planet. The average UV contrast is 32% but can fluctuate from disappearance to 37%. For periods of several years, the polar areas are sometimes covered by a white cloud. According to a set of photographs taken at Pic-du-Midi, this never occurred between 1962 and 1966 but has happened during 25% of the time for at least one pole since 1967, and only when the planet was in a given half of its orbit. These polar clouds are ephemeral and usually last several weeks or months; they evolve...