Optical-to-electrical wavelength demultiplexing detector: design,fabrication, and analysis

An optical-to-electrical wavelength demultiplexing detector has been fabricated using a short length of twin-core optical fiber and an integrated bi-cell detector. The twin-core fiber splits 1325 and 1535 nm input signals onto different output cores, thus directing each demultiplexed channel onto the spatially separated active areas of the bi-cell. We discuss the design, fabrication, and post-tuning techniques used to successfully demonstrate the wavelength demultiplexing functionality of the device and present some preliminary results from an assembled laboratory prototype     

Fading in lightwave systems due to polarization-mode dispersion

System fading caused by polarization-mode dispersion is investigated at 1.7 Gb/s using highly-birefringent, dispersion-shifted fiber at 1.55 μm. The observed fading, which is manifested by random fluctuations of the bit error rate for a fixed receiver power, is observed to depend on the environmental conditions of the fiber, with the time constant for fading varying from minutes to hours depending on the rate of change of the ambient temperature. The mean dispersion penalty inferred from the observed fluctuations in the bit error rate is consistent with a square-law dependence on the polarization-mode dispersion for small penalties     

Subharmonic injection locking phenomena in synchronous oscillators

Subharmonic locking behaviour of a synchronous oscillator has been demonstrated. It is shown that the oscillator can be locked using all subharmonics down to the tenth. Locking behaviour is similar to that observed for IMPATT diode and Gunn microwave injection locked oscillators.<>     

Carrier Dynamics of Quantum-Dot, Quantum-Dash, and Quantum-Well Semiconductor Optical Amplifiers Operating at 1.55 μm

We assess the influence of the degree of quantum confinement on the carrier recovery times in semiconductor optical amplifiers (SOAs) through an experimental comparative study of three amplifiers, one InAs-InGaAsP-InP quantum dot (0-D), one InAs-InAlGaAs-InP quantum dash (1-D), and one InGaAsP-In-GaAsP-InP quantum well (2-D), all of which operate near 1.55-mum wavelengths. The short-lived (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the three devices are characterized via heterodyne pump-probe measurements. The quantum-dot device is found to have the shortest long-lived gain recovery (~80 ps) as well as gain and phase changes indicative of a smaller linewidth enhancement factor, making it the most promising for high-bit-rate applications. The quantum-dot amplifier is also found to have reduced ultrafast transients, due to a lower carrier density in the dots. The quantum-dot gain saturation characteristics and temporal dynamics also provide insight into the nature of the dot energy-level occupancy and the interactions of the dot states with the wetting layer.     

Fundamental device design considerations in the development of disruptive nanoelectronics

In the last quarter of a century silicon-based integrated circuits (ICs) have played a major role in the growth of the economy throughout the world. A number of new technologies, such as quantum computing, molecular computing, DNA molecules for computing, etc., are currently being explored to create a product to replace semiconductor transistor technology. We have examined all of the currently explored options and found that none of these options are suitable as silicon IC's replacements. In this paper we provide fundamental device criteria that must be satisfied for the successful operation of a manufacturable, not yet invented, device. The two fundamental limits are the removal of heat and reliability. The switching speed of any practical man-made computing device will be in the range of 10(-15) to 10(-3) s. Heisenberg's uncertainty principle and the computer architecture set the heat generation limit. The thermal conductivity of the materials used in the fabrication of a nanodimensional device sets the heat removal limit. In current electronic products, redundancy plays a significant part in improving the reliability of parts with macroscopic defects. In the future, microscopic and even nanoscopic defects will play a critical role in the reliability of disruptive nanoelectronics. The lattice vibrations will set the intrinsic reliability of future computing systems. The two critical limits discussed in this paper provide criteria for the selection of materials used in the fabrication of future devices. Our work shows that diamond contains the clue to providing computing devices that will surpass the performance of silicon-based nanoelectronics.     

Simulated silica

We review how molecular dynamics computer simulations are providing a comprehensive picture of the behaviour of silica, as modelled by the van Beest-Kramer-van Santen (BKS) potential. We have recently evaluated a number of key properties of this model system: the phase diagram, including melting lines of three crystal phases; the equation of state and free energy of the liquid phase; the dynamical equation of state; the average energy of inherent structures, and configurational entropy, associated with the potential energy landscape of the liquid; and a characterization of the local coordination environments in the supercooled liquid. The results reveal the interplay among a number of phenomena, in particular, the relationship between the energy landscape and the fragile-to-strong crossover of the liquid dynamics; and the relation of both of these to the possibility of a liquid-liquid phase transition in the supercooled liquid.     

Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

Choice of Filtration Methods for Monitoring the Dissolution of Frusemide

Although the British Pharmacopoeia indicates the need for filtration during the removal of samples in the course of dissolution tests, there is little guidance as to the type of filters that should be used to clarify fluids during their removal. On the basis of results obtained using frusemide as a model drug, the following recommendations are made regarding the use of filters in dissolution testing.

[1] If membrane filters are to be used to clarify dissolution fluids, filters with the smallest diameter and the highest pore size as practically permissible should be utilized to minimise drug loss into the filters.

[2] Whatman Paper filters, or equivalent, are probably to be preferred to membrane filters since they do not seem susceptible to drug sorption.

[3] The membrane type should be varied to the pH of the dissolution fluid. At pH 5.8, cellulose acetate filters sorbed less frusemide than cellulose nitrate filters but with 0.1M HC1 more sorption occurred into the cellulose acetate filters.