Bipolar optical modulation and demodulation using dual-mode fiberand a fast diffusion-driven photodetector

A bipolar fiber-optic signal processing and photodetection concept which combines a dual-mode optical fiber with a fast diffusion-driven photodetector is demonstrated. A discussion of the concept is given, and the results of a simple experiment are given. Various permutations of the ideas described can permit different kinds of coherent and incoherent optical-signal processing and optical control of pulsed photodetection     

Uptake and metabolism of nicotine by the isolated perfused rabbit lung

In order to investigate the possibility of pulmonary first-pass metabolism of nicotine inhaled in tobacco smoke, the absorption and disposition of 14C-nicotine were studied in an isolated perfused rabbit lung preparation after nicotine administration directly into the perfusing blood and tobacco smoke administration via in the inspired tracheal air. After administration into the perfusing medium, the rate of nicotine metabolism was first-order and dose-independent at the two doses studies (0.1 and 1.0 mg) but lung metabolic clearance was quite low (3 ml/min) relative to whole body clearance (140 ml/min) measured by administering 14C-nicotine to intact rabbits. Accumulation of nicotine by lung was not extensive (13-23% of the dose administered). After administration of tobacco smoke from 14C-nicotine-spiked cigarettes, absorption of nicotine was rapid but the rate of metabolism was markedly reduced compared to the studies in which drug was administered in the perfusing medium. This reduction in the rate of metabolism was apparently caused by some component of tobacco smoke but was shown to be unrelated to the level of carbon monoxide in the perfusate. The slow clearance of nicotine by rabbit lung (which is further reduced after smoke administration) compared to a high pulmonary blood flow rate makes unlikely the possibility of significant first-pass lung metabolism in smokers.     

Ray-pulse matrices: a rational treatment for dispersive opticalsystems

A new formalism to describe beam propagation in paraxial optical systems with dispersive elements, including both spatial and temporal variations in the propagating signal, is presented. This formalism makes use of 4×4 ray-pulse matrices which take account of dispersive effects up to quadratic phases in both spatial coordinates (as in the usual paraxial ABCD matrix approach) and in the temporal domain. How to use these matrices to write a space-time integral analogous to a generalized Huygens integral is shown, and propagation laws for Gaussian ray pulses which are space- and time-varying analogs of the conventional results for Gaussian beams are derived. The formalism should be useful for analyzing dispersive optical systems such as prism beam expanders, femtosecond pulse compression systems, and dispersive mode-locked laser cavities     

A fast diffusion-driven photodetector: theory and experiment

A high-speed photodetector has been demonstrated. Prototype silicon devices have detection bandwidths of 5 GHz and are limited by neither the saturation-velocity transit time nor the carrier lifetime. These detectors use a combination of the Dember effect and the east of generating fine photocarrier gratings, and scale to bandwidths of several hundred gigahertz