1.5 mu m tensile-strained single quantum well 20-wavelength distributed feedback laser arrays

Tensile-strained single quantum well 20-wavelength distributed feedback laser arrays have been fabricated with a wide wavelength span of 56 nm in the 1.5 mu m wavelength region. The light output is TM-polarised and the average threshold current is 22.8 mA for an 875 mu m long array. A minimum laser linewidth of 180 kHz is measured by a delay self-heterodyne method.<>     

Enhanced exciton absorption in quantum-confined Stark effect of [110]-oriented InGaAsP quantum wells

A new phenomenon of the quantum-confined Stark effect has been found in InGaAsP quantum wells grown on [110]InP substrates by MOVPE. Enhanced exciton absorption concurrent with the applied voltage is observed for the first time.<>     

Aryl ether-ketone segmented polypyromellitimides

Aromatic ether-ketone segments have been incorporated into polyimide backbone to impart the well-known thermoplastic properties of polyether ketones. For this purpose three aromatic diamines containing ether and ketone connecting groups between aromatic rings have been prepared and polymerized with pyromellitic dianhydride to yield polyimides. The thermal behavior of the polyimide cast films has been investigated.     

Condition monitoring of aircraft by quantitative filter debris analysis

Various condition monitoring techniques are used collectively to monitor the health of aircraft engines and transmission, a concept known as Integrated Health Monitoring (IHM). A well-established quantitative technique is Aircraft Oil Analysis (AOA), in which spectroscopic techniques such as Rotating Disk Electrode Atomic Emission Spectroscopy (RDE-AES) are employed to analyse periodic oil samples for wear debris. Usually, no sample preparation is undertaken, as the oil sample containing both dissolved and suspended metallic wear debris is analysed directly. AOA works well for oil-lubricated systems with relatively coarse filtration that allow circulation of the debris and its subsequent abrasive contact with moving components. To avoid this secondary wear, finer filtration is employed on both new and older aircraft. Less wear debris, and thus information, is available in the oil. A technique that quantitatively analyses the wear debris caught on the filter has been developed and is termed Quantitative Filter Debris Analysis (QFDA). Actual oil filters from CF88 Challenger ALF 502L-2C and Hornet F404 engines were obtained in sequence, when possible, prepared by the developed procedure, and analysed with AOA instrumentation. With sufficient results, both normal and abnormal levels of wear rates emerged, as has been recorded and used for AOA. Moreover, trending of the data for sequential samples has demonstrated the capability of GFDA for condition monitoring.     

Low-threshold and narrow-linewidth 1.5 mu m compressive-strained multiquantum-well distributed-feedback lasers

1.5 mu m compressive-strained multiquantum-well distributed-feedback lasers have been fabricated and characterised. 5.5 mA threshold current, 1 MHz mW linewidth-power product, and 600 kHz minimum linewidth were measured on 500 mu m long devices. Measured threshold current as low as 2.2 mA was also obtained on 150 mu m long devices. Both low threshold and narrow linewidth are attributed to the reduced transparency current and linewidth enhancement factor due to the effect of strain.<>     

Multiwavelength DFB laser array transmitters for ONTCreconfigurable optical network testbed

We discuss the design, fabrication, and performance of experimental multiwavelength laser array transmitters that have been used in the reconfigurable optical network testbed for the Optical Network Technology Consortium (ONTC). The experimental four-node multiwavelength network testbed is SONET/ATM compatible. It has employed multiwavelength DFB laser arrays with 4 nm wavelength spacing for the first time. The testbed has demonstrated that multiwavelength DFB laser arrays are indeed practical and reproducible. For the DFB laser arrays used in such a network the precise wavelength spacing in the array and the absolute wavelength control are the most challenging tasks. We have obtained wavelength accuracy better than ±0.35 nm for all lasers, with some registered to better than ±0.2 nm. We have also studied the array yield of our devices and used wavelength redundancy to improve the array yield. Coupling efficiencies between -2.1 to -4.5 dB for each wavelength channel have been obtained. It is achieved by using specially designed lensed fiber arrays placed on a silicon V-grooved substrate to exactly match the laser spacing. The transmitter consisted of a multichip module containing a DFB laser array, an eight-channel driver array based on GaAs IC's, and associated RF circuitry