High-resolution photonics-based interference suppression filter with wide passband

A new topology for a photonic signal processor, which overcomes the basic recursive frequency response problem that limits the passband range, is presented. The structure is based on a new multiple-wavelength offset-cavity structure that is cascaded with a series of unbalanced delay line structures. This not only can synthesize a very narrow notch response with good shape factor but also permits a multifold extension of the free spectral range (FSR) and passband width. Results on the interference mitigation filter demonstrate a stopband of 1% of center frequency and a fourfold increase in the FSR and passband width, while also having a very small shape factor, in excellent agreement with predictions.     

Comparative structural and immunochemical properties of leghaemoglobins

Circular dichroism studies on leghaemoglobins from snake bean, lupin, serradella and other plants show that, in common with soybean (reported earlier) they have a similar overall polypeptide chain conformation and haem environment and orientation. Immunochemical studies, on the other hand, suggest that the antigenic determinants on the surface of the leghaemoglobins vary considerably. Thus, firstly the alpha-helix content of the leghaemoglobins as a class is very similar (60-65%) and approaches that of the myoglobins, secondly, the sign, magnitude and shape of their circular dichroism spectra in the near ultraviolet, Soret and visible regions suggest close similarities in the environment and orientation of a structurally important tryptophan residue and of the haem moiety, and thirdly, there is comparatively weak haem-protein interaction. The extent of immuno cross-reactivity was found to be best deomonstrated using the Farr radioimmunoassay procedure. The results were (a) 5 leghaemoglobins from one plant (soybean) crossreacted completely but with varying affinities. (b) The extent of cross reactivity between leghaemoglobins from different plants was compared to that within a single plant; the reaction of antiserum to a soybean leghaemoglobin with a serradella leghaemoglobin was weak, with a snake bean leghaemoglobin still weaker (and incomplete) while lupin leghaemoglobins showed no cross reactivity at all. (c) The "rapid" attenuation of cross reactivity among different plant leghaemoglobins is explicable in terms of the extensive amino acid substitutions which have been demonstrated in the literature and in the present studies. (d) In view of this rapid divergence it is not surprising that sperm whale and horse heart myoglobins showed no cross reactivity with soybean leghaemoglobins. In summary, amino acid substitutions in the leghaemoglobin family are conformationally but not immunochemically conservative.     

Response of the hypothalamic neurons to stimulation of the vestibular nerve and lateral vestibular nucleus in rabbits

Effects of single, double, and rhythmic stimulation upon hypothalamic neurons responding to the 1st excitatory phase of lateral vestibular nucleus stimulation, were studied. The data obtained show that activation of some hypothalamic neurons following stimulation of the lateral vestibular nucleus has a monosynaptic character. The findings suggest that ascending afferents from the lateral vestibular nucleus to the hypothalamus pass via oligo- as well as polysynaptic pathways.     

Optimum design of a 4-Gbit/s GaAs MESFET optical preamplifier

An analysis for determining the optimum MESFET gate width to optimize the sensitivity of a high-speed optical preamplifier is presented. A full MESFET model is employed including correlated gate and drain noise sources. The design of an optimum sensitivity monolithic shunt feedback amplifier, including stability requirements, is investigated. The results show that the optimum gate width for minimizing input equivalent noise is significantly larger than earlier simplfied predictions. A sensitivity improvement of 1.2 dB is demonstrated for a 4-Gbit/s MESFET optical amplifier, and results showing the dependence of optimum FET width on photodetector capacitance are described.     

Linearization processing of a novel short time-delay WDM superposed fiber Bragg grating

A new analytical method for short time-delay profile linearization of wavelength division multiplexing superposed fiber Bragg grating is presented. This can obtain a new index profile for the gratings that results in a highly linear time-delay step profile. An optimum apodization using a cos/sup 4/ function is described for suppressing grating sidelobe interaction. Results demonstrate a highly linear time-delay step profile for a 32-superposed grating, with only a 1.7% standard deviation from linearity, 1-ps delay steps, and more than 99% reflectivity.     

Floating vertical solar still for desalination of marsh water

The performance of a floating conical solar still used for producing drinking water in brackish marsh areas has been investigated. The new proposed still consists of a vertical conical-shaped blackened cotton wick installed inside a floating transparent glass cover of similar shape. The base section of the floating cover was properly designed to allow the bottom of the wick to soak directly in the brackish water. Multiple linear regression equations, relating global solar radiation, ambient air temperature, and wind speed with the productivity of the still, have been developed. The regression analysis showed that the daily global solar radiation can be adopted alone to predict still productivity with acceptable accuracy. Results also showed that there is good competition between the proposed conical still and the conventional basin-type solar still concerning productivity and operation requirements. Recommendations have been made to use this type of still for ensuring fresh drinking water in marsh areas where the natural supply of fresh water is inadequate.     

High capacity optical interconnects for phased array beamformers

Two new concepts for overcoming the optical interconnect losses in highly dense multibeam photonics-based beamforming networks are presented. The first is the use of erbium-doped fiber amplifiers as power boosters at the transmitters, and the second is the use of external modulation techniques at the laser transmitters. Using these concepts, results show that a system noise figure of 3.5 db and a spurious-free dynamic range of 134 dB·Hz^4/5 can be attained for a wideband phased array which can yield around 1000 independent and simultaneous antenna beams     

Optimization of fiber amplifier SCM lightwave video systems usingdirect and external modulation

An analysis of the design factors involved in optimizing laser transmitters for SCM video distribution networks is presented. This includes optimization of the erbium-doped amplifier, linearized external modulation, and laser overmodulation to increase the optical loss budget. A full nonlinear distortion spectral analysis is employed to determine the dependence of the optimum optical modulation index on the allowable postamplifier loss. A general optimization procedure has been developed for the fiber amplifier and modulator to maximize the postamplifier loss for a specified CNR objective. Results are presented showing a comparison between the distribution capacity of direct and externally modulated SCM-EDFA systems for VSB-AM and FM-SCM transmission systems     

Ultra-low-noise and wideband-tuned optical receiver synthesis anddesign

A new general optical receiver design method based on the synthesis of optimum noise-matching networks is presented. It is based on the noise figure concept in conjunction with broadband matching theory. The design is accurate because it directly utilizes the active device noise parameters, such as minimum noise figure, noise resistance, and optimum source impedance, which are readily available at microwave frequencies. The analysis has established the general noise-matching requirements of the tuning network that result in the minimum obtainable equivalent input noise current and the fundamental noise limit in tuned receivers. Synthesis procedures are described that can closely satisfy the general noise-matching requirements, which has led to a new low pass filter-type matching network with ultra-broadband characteristics that also approach the fundamental noise limit. The design principles are verified, with an experimental 10 Gb/s PIN-HEMT optical receiver that demonstrates a bandwidth of 6.3 GHz with a gain flatness of ±0.8 dB over the entire frequency range and a measured average noise current of 5 pA/√(Hz)