Highly reliable spot-size converter integrated laser diodes over a wide temperature range for access network systems

In this paper, we present highly reliable high-temperature spot-size converter integrated laser diodes (LDs) fabricated using a full-wafer process with dry etching and MOVPE. The lasers lase at 150°C and operate stably for 10,000 h at 85°C and 10 mW. The median lifetime is estimated to be over 10⁵ h. We also demonstrate a novel screening test procedure for a bar configuration of LDs, which can greatly reduce optical module cost.     

Recent R&D on Drying Technology in Japan

This article presents the outlook of the energy situation in Japan and reviews the recent R&D on innovative drying technologies performed in Japan. The overview of drying includes fundamentals as well as industrial technologies. The topics considered are drying characteristics of several materials, drying of hard-to-handle powders, drying of coatings, drying-induced strain-stress problems, drying modeling, and drying of agricultural wastes for functional recycling and noble dryers. An appropriate combination of heating methods and dryer type can result in significant enhancement of efficiency, drying rate, and/or material quality. The final goal of this article to contribute to providing an idea for development and evaluation of precise drying systems with a high performance and an effect of energy saving in drying.     

Deformation Behavior of Ceramic Slabs by Nonuniform Drying

ABSTRACT

The presenr paper is to study the transient deformation characteristics of molded ceramics undergoing nonunifom drying. The linear viscoelasticity was assumed for the strain-stress analysis. Three dimensional equations of the strain-stress as well as heat and moisture transfer werc solved numerically by the Galerkln finlle element melhod using isoparametric parameters of twenty-nodes so to allow easily the application to any feature of ceramics. Both the analysis and experiments were carried out to be compared on the behavior of drying and deformation for a slab clay in preheating and constant drying rare periods. When the bottom surface of the slab uras shielded to model the nonuniform drying. a warp phenomrnon to the opposite side of the shielded surface was observed experimentally as drying by hot air heating proceeds. The behavior could be successively simulaled by the present theoretical model. The degree of warp became rcmarkabel with a rise in air temperature or nonuniformity of drying. The surface area exposed to the atmosphere was subjected to a comparatively large tensional stress through drying. The tensile sltresses on the top surface were significantly larger than on the bottom surface.     

A Numerical Study of Transient Deformation and Stress Behavior of a Clay Slab During Drying

A transient three-dimensional analysis was carried out on internal strain-stress as well as heat and the moisture transfer in a ceramic slab during drying. A model was developed to analyze viscoelastic behavior, heat conduction and moisture diffusion. The basic equations were solved by the finite element method. The effects of several dimensionless parameters are discussed to find an optimum drying process and a precise design of molds in ceramic production. The stress and the gradient of moisture content were influenced significantly by the Biot or Lewis number. When the moisture diffusion is enhanced or the drying is controlled well so as to form only gentle gradients of moisture content in the slab, the maximum tensile stress can be reduced. Nonuniform drying results in the develoment of warp and increase in the maximum tensile stress. The drying characteristics were not appreciably influenced by shrinkage.     

Laser diodes integrated with butt-jointed spotsize converterfabricated on 2-in wafer

Laser diodes integrated with spotsize converters by butt-joint technology combined with selective area metal organic vapor phase epitaxial (MOVPE) growth have been successfully fabricated. Satisfactory uniformity, reproducibility (>99%) and tolerance for low threshold current, a narrow emitted beam, and low optical coupling loss to fiber (<-2.4 dB) are obtained by using 2-in full wafer fabrication technology in the experimental fabrication. To investigate the tolerance in fabrication, the characteristic dependence on the variation of the wet etching time just before the butt-joint MOVPE growth and also on the mesa stripe width are investigated. A wide tolerance for these fabrication parameters is confirmed. The results indicate that the butt-joint technology is a useful and reliable process for realizing spotsize converters of the present type and also suggest that the technology is widely applicable to various photonic integrated circuits     

110-GHz, 50%-efficiency mushroom-mesa waveguide p-i-n photodiodefor a 1.55-μm wavelength

A mushroom-mesa structure is proposed to reduce the CR-time constant which originates from the waveguide photodiode structure. Experimental results at a 1.55-μm wavelength show that the multimode waveguide p-i-n photodiode with mushroom-mesa structure has an electrical 3-dB bandwidth of more than 75 GHz in the frequency domain and an electrical 3-dB bandwidth of 110 GHz in the time domain. The external quantum efficiency is 50% or 0.63 A/W, which leads to a record bandwidth-efficiency product of 55 GHz for long wavelength p-i-n photodetectors     

Deformation Behavior of Ceramic Slabs by Nonuniform Drying

The presenr paper is to study the transient deformation characteristics of molded ceramics undergoing nonunifom drying. The linear viscoelasticity was assumed for the strain-stress analysis. Three dimensional equations of the strain-stress as well as heat and moisture transfer werc solved numerically by the Galerkln finlle element melhod using isoparametric parameters of twenty-nodes so to allow easily the application to any feature of ceramics. Both the analysis and experiments were carried out to be compared on the behavior of drying and deformation for a slab clay in preheating and constant drying rare periods. When the bottom surface of the slab uras shielded to model the nonuniform drying. a warp phenomrnon to the opposite side of the shielded surface was observed experimentally as drying by hot air heating proceeds. The behavior could be successively simulaled by the present theoretical model. The degree of warp became rcmarkabel with a rise in air temperature or nonuniformity of drying. The surface area exposed to the atmosphere was subjected to a comparatively large tensional stress through drying. The tensile sltresses on the top surface were significantly larger than on the bottom surface.     

Electric-field-induced orientation control of organic semiconductor rubrene crystals

The electric field-induced orientation of rubrene single crystals was observed in a nonpolar solvent. Rubrene single microcrystals responded to an AC electric field beyond a crystal-size dependent threshold. The longitudinal axis, i.e., b-axis, of rubrene single crystals on a SiO₂/Si substrate was aligned almost parallel to the direction of the applied electric field. Field-effect transistors with these orientated crystals exhibited low variability of the carrier mobility.     

636 nm room temperature CW operation by heterobarrier blocking structure InGaAlP laser diodes

636 nm room temperature CW operation has been achieved by heterobarrier blocking structure InGaAlP laser diodes with a quaternary active layer. This structure was fabricated by two-step metal-organic chemical vapour deposition. The threshold current was 102 mA at 20 degrees C and CW operation of 3 mW was attained at up to 48 degrees C.<>     

Influence of the Ionization Potential and of the Interfacial Electric Field on Photoinduced Hole Transfer Processes in Langmuir-Blodgett Films

The presence of a monolayer of ω-(2-anthryl)-alkanoic acid on an anthracene or perylene single crystal modifies the kinetics of photosensitized hole injection. An increase in the chain length of the ω-(2-anthryl)-alkanoic acid leads to a decrease in the quantum yield of the sensitized hole current (SHC). This effect becomes more important when the ionization potential of the dye is decreased. This argument supports the hypothesis that electron transfer is assisted by an interaction between the HOMO of the dye and that of the alkyl chain. The permanent electric field existing at the interface between the monolayer of ω-(2-anthryl)-alkanoic acid and the monolayer containing the dye is also expected to influence the free energy gain associated with this electron transfer process. When the dye is diluted by tripalmitine instead of arachidic acid, the change in the electrical potential difference at the interface with the monolayer of ω-(2-anthryl)-alkanoic acid leads to a tenfold decrease in the quantum yield of the SHC.