Phonon-assisted and phonon-free radiative transitions in sulfur-doped GaAs diffused junctions

In the course of electroluminescence studies of GaAs junctions we investigated the emission spectra of sulfur-doped zinc-diffused diodes. The peaks in the spectra correspond to three main transitions and their associated phonon emission satellites

Mechanochemical reactions of clay minerals with CsCl

Solid state mechanochemical reactions between clay minerals and CsCl during grinding in non-destructive techniques, investigated in our laboratory, are reviewed. Clays were talc, pyrophyllite, sepiolite, palygorskite and minerals from the serpentine-kaolin and smectite groups. No reaction occurred with serpentines, talc, pyrophyllite and palygorskite. Cation-exchange occurred with montmorillonite and saponite. Kaolin-type minerals were delaminated forming disordered aggregates of TO layers with water, Cs cations and Cl anions. XRD did not show any peak but IR spectra proved the presence of H-bonds between water molecules, and inner-surface oxygens or inner-surface hydroxyls. After water thermal evolution CsCl intercalation complexes with a spacing of 1050 pm were identified. Wet-grinding of sepiolite with CsCl resulted in the disappearance of sepiolite XRD peaks indicating a disintegration of the crystal into micro-crystallites with no order in their packing in the particle. Air-grinding of sepiolite with CsCl almost did not change the X-ray pattern of sepiolite

A reduction of interferometric phase-to-intensity conversion noise in fiber links by large index phase modulation of the optical beam

A noise reduction scheme for long haul fiber amplitude modulation (AM) systems is proposed and analyzed. Such systems suffer from intensity noise which results from interference between the (twice) Rayleigh scattered light and the directly transmitted beam. This interference converts the fundamental phase noise of the laser to intensity noise. It is shown that a strong phase modulation of the output of the laser beam causes a large reduction of the detected signal noise in the vicinity of the detected signal component

Optical thresholding and switching using a fiber-coupled phase-conjugate mirror

A fiber-coupled-ring passive phase-conjugate mirror is used to achieve mutual thresholding free of bistability effects and to obtain switching among several mutually incoherent light beams

Fixing of volume holograms in ferroelectric K_(1-y)Li_yTa_(1-x)Nb_xO_3

We report on the fixing of photorefractive volume holograms in potassium lithium tantalate niobate with ionic gratings and also with ferroelectric domain-reversed gratings. A diffraction efficiency of 55% is obtained with domain reversal in a 2-mm-thick ferroelectric phase K1–yLiyTa1–xNbxO3 crystal doped with Co, V, and Ti. We measured the decay rate of the domain gratings and also of the initial electron gratings and ion gratings. The domain grating decay agrees with Vogel–Fulcher fits. The activation energies for ionic and electronic conductivity are 0.76 and 0.12 eV, respectively

Signal-to-noise considerations in fiber links with periodic or distributed optical amplification

The detected signal-to-noise power ratio is evaluated for fiber links with periodic amplification. It is shown that the highest ratio is achieved in the limit of a distributed amplifier (g = α), but that, alternatively, periodic amplification at intervals of α^-1 entails a penalty of less than 2 dB compared with the (ideal) distributed case

Fixing of photorefractive volume holograms in K1-yLiyTa1-xO3

We report the f ixing of photorefractive holographic gratings with high eff iciency in a sample of K1-yLiyTa1-xNbxO3 doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge field by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy

An optimal feedforward design for complete PMD compensation up to the second order

As an extension to a previous paper, this paper describes the optimization of a second-order, feedforward polarization-mode dispersion (PMD) compensation scheme by reducing its degrees of freedom (DOF) by two. The new design is optimal in the sense that the number of DOF used is the same as the minimal number of DOF required. Also derived is a set of constraint equations that govern the choice of various system parameters

The Beginnings of Optoelectronic Integrated Circuits -— A Personal Perspective

The early work (1960s, 1970s) on Integrated Optics at the Bell Telephone Laboratories and at the California Institute of Technology (Caltech), with which the author was involved, is described from a personal perspective