Monolithic integration on InP of a Wannier Stark modulator with astrained MQW DFB 1.55-μm laser

We present the technical approach and the preliminary device results on the first integration of a Wannier Stark (WS) electroabsorption (EA) modulator with a DFB laser on InP. The WS modulator active layer consists of a lattice matched InGaAs-InAlAs superlattice (SL) grown by solid source MBE. It is butt-coupled to a laser grown by AP-MOVPE whose active layer includes a strained InGaAsP-InGaAsP MQW stack. Device results cover static performances of integrated lasers and modulators, and measurements of high frequency characteristics (small signal bandwidth and 10 Gb/s eye diagram)     

Bisphenol-A polycarbonate–poly(butylene terephthalate) transesterification. III. Study of model reactions

Exchange reactions in molten bisphenol-A polycarbonate–poly(butylene terephthalate) mixtures are investigated by means of model reactions. Transesterification can result either from direct ester-ester interchange or via alcoholysis or acidolysis. Among the various reactions investigated, only the PBTP alcoholysis by phenol is not found to occur. Taking into account that bisphenol-A terephthalate units (A₂B₁) and butylene carbonate units (A₁B₂) are formed in equimolecular amounts, it is concluded that direct ester-ester interchange is the most likely mechanism for PC-PBTP transesterification.     

Adiabatic self-focusing in media with spatially variable nonlinearity

An optical medium whose nonlinearity can be spatially adjusted is considered to study beam reshaping. The concept is applied to perform adiabatic self-focusing of broad beams. Experimental results are obtained in a photorefractive lithium niobate crystal where the self-focusing nonlinearity is controlled over propagation by a temperature gradient. As a demonstration, gradual self-focusing is shown to transform an incoming beam into an output circular spot 10 times smaller over a 2 cm long crystal submitted to a 30 °C temperature gradient. Once formed, the adiabatic self-focused beam has inscribed a funnel waveguide in the crystal.     

NMR study of ester-interchange reactions during melt mixing of poly(ethylene terephthalate)/poly(butylene terephthalate) blends

The occurrence of ester-interchange reactions during PET/PBT blend processing has been confirmed by ¹³C-NMR measurements. The limitations of the method for precise quantification of the extent of reaction between high molecular weight polyester blends have also been pointed out. Titanium alkoxide has been confirmed as an efficient catalyst, and, within experimental precision, the stabilizing effect of triphenyl phosphite addition has been demonstrated. © 1996 John Wiley & Sons, Inc.     

Molten bisphenol-A polycarbonate-poly(ethylene terephthalate) blends. I. Identification of the reactions

This paper is devoted to the study of the reactions taking place in molten bisphenol-A polycarbonate-poly(ethylene terephthalate) mixtures. The analysis of the reaction products by infrared, proton and nuclear magnetic resonance spectroscopy, and by thermogravimetric analysis shows that the main reaction is an exchange reaction identical to that occurring in bisphenol-A polycarbonate-poly(butylene terephthalate) mixtures. However, some other reactions consecutive to this exchange reaction also take place, probably resulting from the instability of the ethylene carbonates produced by transesterification.     

An investigation of the structural aspects of the tomato fruit by means of quantitative nuclear magnetic resonance imaging

In this study, magnetic resonance imaging (MRI) was applied to study the structural aspects of the tomato fruit. The main study was performed on tomatoes (cv. Tradiro) using a 0.2-T electromagnet scanner. Spin-echo images were acquired to visualize the tomato macrostructure. The air bubble content in tissues was evaluated by exploiting susceptibility effects using multiple gradient echo images. The microstructure was further studied by measuring spin–spin (T₂) and spin–lattice (T₁) relaxation time distributions. Nuclear magnetic resonance relaxometry, macro vision imaging and chemical analysis were used as complementary and independent experimental methods in order to emphasize the MRI results. MRI images showed that the air bubble content varied between tissues. The presence of gas was attested by macro vision images. Quantitative imaging showed that T₂ and T₁ maps obtained by MRI reflected the structural differences between tomato tissues and made it possible to distinguish between them. The results indicated that cell size and chemical composition contribute to the relaxation mechanism.     

Reaction between polyesters and phosphorus compounds in the molten state

The reactions occurring between polyesters and phosphorus compounds in the molten state are investigated. A large molecular weight increase is observed in blends of Poly(ethylene terephtalate) and Poly(butylene terephtalate) after triphenyl phosphite addition. The formation of links containing phosphorus atoms between the polyester chain ends has been established. The weakness of this bond makes the observations difficult. An effect of phosphite on promoting the direct esterification between chain ends is suggested but not definitely proved yet.