The influence of carrier-injecting layers on the built-in potential of polymer light-emitting diodes (PLEDs) is analysed by means of electroabsorption spectroscopy. Two promising materials on which research has recently focused are: first, poly(ethylene-dioxythiophene)/poly(styrene sulphonic acid) (PEDOT:PSS), a doped conducting polymer employed as hole injector; and secondly, lithium fluoride (LiF), which has been shown to enhance electron injection of Al-based cathodes. In the first samples LEDs with an indium tin oxide (ITO) anode were compared to those incorporating a PEDOT:PSS layer (in an ITO/PEDOT:PSS bilayer anode). In the second set of samples the comparison was between LEDs with an aluminium cathode and those incorporating a LiF layer (in an Al/LiF bilayer cathode) as a function of LiF thickness. Electroabsorption spectroscopy results supported by work function measurements clearly prove that both PEDOT:PSS and LiF introduce a large reduction in the barrier height at the anode and cathode interfaces, respectively. The ensuing enhancement in carrier injection is considered to be responsible for the marked improvement in device performance (lower operating voltages, higher luminous efficiencies and longer lifetimes).

A method is demonstrated for the determination of quaternary compositions using a single X-ray measurement. By comparing the integrated intensity of a reflection with theoretical calculations and combining this with the mismatch of the layer, a solution for the composition can be determined. For the quaternary, InAlAsSb, the intensity of the (002) reflection is shown to depend strongly on composition and allow determination of In∶Al and As∶Sb ratios. Since the bandgap/composition relationship is not well known for this system, the accuracy of the technique is assessed by measuring InAsSb layers using peak intensities and comparing the calculated composition with that determined using the layer mismatch in the usual way. The values calculated by the two techniques are in good agreement and therefore provide confidence in the quaternary compositions measured.

Through semi-analytical simulation, the feasibility of an application of the dispersion-supported transmission (DST) technique in the normal propagation regime is investigated and its performance compared with that in the anomalous propagation regime. It is shown that, in the normal propagation regime, the DST technique operating at 20 Gbit/s can improve the maximum system sensitivity by about 7 dB relative to the anomalous propagation regime. However, a reduction of the maximum transmission distance and a greater dispersion dependence of system sensitivity around its maximum value are observed. The influence of laser adiabatic and transient chirps on the DST performance in both propagation regimes is investigated. It is shown that in the normal propagation regime, the presence of laser transient chirp can be beneficial, improving the system performance by opening the eye diagram at system output. Contrarily, in the anomalous propagation regime, its presence can strongly degrade the system performance, by closing the eye diagram at system output.

Previous publications have addressed the impact of bursty, self-similar traffic on erbium-doped fibre amplifiers (EDFA). Several gain control techniques have been suggested to combat the gain fluctuations of EDFA with this type of traffic. The effectiveness of two such methods are investigated, namely highly inverted amplifiers and all-optical gain clamping, while varying the parameters characterising the burstiness of the sources. While previous publications have focused on the effect of the average load or activity factor, the paper further investigate the dependence on the relative variability of the packet burst lengths (ON times), and lengths of the interburst idle times (OFF times). Both gain control methods reduce the output power and signal-to-noise ratio excursions with respect to a standard amplifier chain. The authors find that, for an eight channel WDM system and a cascade of six EDFAs, all-optical gain clamping can reduce the variations by a factor of five, provided adequate power is present in the clamping laser, while highly inverted amplifiers have variations reduced by a factor of two. The authors find that, in a clamped chain, the source activity factor does not uniquely determine the required level of lasing power. The authors also deduce that information on the relative variability of ON and OFF times is essential.

Progress in technology, theory and applications of high-frequency mode-locked diode lasers is reviewed. We present a systematic overview of a wealth of experimental and theoretical results and approaches reported recently in the field of physics, technology and applications of monolithic mode-locked laser diodes.

The bit error rate performance of IrDA links when influenced by physical layer and channel asymmetries are examined. Physical layer asymmetries are possible due to component variations, ambient noise variations, and third party interference. It is shown how such asymmetries cause differential link bit error rates, which in turn result in throughput degradation at the link and higher layers. A model is developed for the asymmetries incorporating PHY layer and LINK layer parameters. The condition for symmetry in optical wireless links is derived. It is demonstrated that link layer throughput asymmetries are possible as a result of physical layer parameter asymmetries. The magnitude of such throughput asymmetries is calculated. Examples are analysed based on some typical user model environments where asymmetries may take place. Results based on a model of the IrDA protocol stack are given.

Using a rigorous numerical approach, it is shown that the modal birefringence of semiconductor optical waveguides can be eliminated by optimising the waveguide parameters, to achieve polarisation independent performances.

The growth and characterisation of GaInAsSb alloys, lattice-matched to GaSb substrates, are reported, with a particular focus on these alloys for thermophotovoltaic (TPV) devices. Using a unique combination of organometallic precursors, high-quality metastable GaInAsSb epitaxial layers with energy gaps as low as 0.5 eV have been grown by organometallic vapour-phase epitaxy. The GaInAsSb material quality is significantly improved for growth at a lower growth temperature of 525°C compared with 575°C, and at a higher growth rate of 5 μm/h compared with 1.2 μm/h. 4 K photoluminescence full width at half maximum values are as low as 4.3 meV for 0.59 eV GaInAsSb and 9.5 meV for 0.5 eV GaInAsSb. The importance of the surface-step structure and growth kinetics on these metastable alloys is discussed. Uncoated TPV devices incorporating metastable GaInAsSb, with energy gaps in the range 0.495–0.549 eV, and a GaSb window layer exhibit an external quantum efficiency (QE) of nearly 60%, which corresponds to an internal QE of 90%. The open-circuit voltage is 313 mV for the 0.549 eV device, and decreases to 239 mV for the 0.495 eV device.

Hybrid integration of GaAs/AlGaAs multiple quantum well self electro-optic effect device (SEED) arrays are demonstrated flip-chip bonded directly onto 1 mu m silicon CMOS circuits. The GaAs/AlGaAs MQW devices are designed for 850 nm operation. Some devices are used as input light detectors and others serve as output light modulators. The measurement results under applied biases show good optoelectronic characteristics of elements in SEED arrays. Nearly the same reflection spectrum is obtained for the different devices at an array and the contrast ratio is more than 1.2:1 after flip-chip bonding and packaging. The transimpedance receiver-transmitter circuit can be operated at a frequency of 300 MHz.