Abstract
The modulational instability of quasi-plane-wave optical beams in biased photorefractive media is investigated under steady-state conditions. The spatial. growth rate of the sideband perturbations is obtained by globally treating the space-charge field. Our analysis indicates that the growth rates depend on the strength of the externally applied electric field and, moreover, on the ratio of the optical beam's intensity to that of the dark irradiance. Our results are then compared to previous local treatments of the space-charge field equation. The two approaches are found to be in good agreement in the low spatial-frequency regime provided that the external bias field is sufficiently high. Conversely, in the high spatial-frequency region notable differences may exist. Relevant examples are provided.

Abstract
The so-called screening solitons that occur in steady state when an external bias voltage is appropriately applied to a PR crystal are known to occur when the drift term dominates in the expression of the space charge field. In a recent study, the effects arising from first-order diffusion terms have also been investigated. It was found that the PR soliton can experience adiabatically self-deflection that varies linearly with the applied electric field. However, recent experiments suggest that this self-deflection can exceed that predicted by theory, especially in the regime of quite high bias fields. To account for this discrepancy, this paper investigates the effects of other higher-order electric field terms on the evolution of bright steady-state solitons in PR media.

Abstract
It is shown that a new type of incoherently coupled soliton pairs is possible under steady-state conditions provided that their carrier beams share the same polarization and wavelength and are mutually incoherent. They can be readily realized in a simple experimental setup where the optical beams co-propagate collinearly in a biased photorefractive crystal, in which case they experience equal electro-optic coefficients. The two optical beams can be also slightly misaligned at the input so as to differentiate them at the output plane.

Abstract
Power supply current monitoring is a promising technique for the development of new test methodologies for analogue and mixed-signal circuits, following the success attained in the digital domain. This paper shows that improved test efficiency and confidence is obtained when both functional output voltage and power supply current signals are observed. Results obtained from simulation of a number of circuits are presented comparing Fault Coverage, Normalised Deviation, and the Coefficient of Variation of faulty responses deviation amplitudes. Also, different test stimuli are compared to evaluate their suitability for testing.

Abstract
Vector quantization of images raises problems of complexity in codebook search and subjective quality of images. The family of image vector quantieation algorithms proposed in this paper addresses both of those problems. The Fuzzy Classified Vector Quantizer (FCVQ) is based on fuzzy set theory and consists basically in a method of extracting a subcodebook from the original codebook, biased by the features of the block to be coded. The incidence of each feature on the blocks is represented by a fuzzy set that captures its (possibly subjective) nature. Unlike the Classified Vector Quantizer (CVQ), in the FCVQ a specific subcodebook is extracted for each block to be coded, allowing a better adaptation to the block. The CVQ may be regarded as a special case of the FCVQ. In order to explore the possible correlation between blocks, an estimator for the degree of incidence of features on the block to be coded is included. The estimate is based on previously coded blocks and is obtained by maximizing a possibility; a distribution that intends to represent the subjective knowledge on the feature's possibility of occurrence conditioned to the coded blocks is used. Some examples of the application of a FCVQ coder to two test images are presented. A slight improvement on the subjective quality of the coded images is obtained, together with a significant reduction on the codebook search complexity and, when applying the estimator, a reduction of the bit rate.

Abstract
This work uses Volterra kernels to model the distortion of complex optical systems using both frequency and intensity modulation of a DFB laser and an optical discriminator. The laser's IM and FM complex responses and also the laser's intrinsic FM distortion are shown to be crucial to model accurately the system's third-order intermodulation product (IMP3) performance. The results show that it is possible to achieve a large reduction of the third-order IMP3 in some frequency ranges by off-setting the bias of the discriminator from the point of maximum slope. Furthermore, at high frequencies the system's IMP3 performance can be better than in the case of a purely intensity modulated laser without a discriminator.