125 research outputs found
Nonlinear optical polymers for electro-optic signal processing
Photonics is an emerging technology, slated for rapid growth in communications systems, sensors, imagers, and computers. Its growth is driven by the need for speed, reliability, and low cost. New nonlinear polymeric materials will be a key technology in the new wave of photonics devices. Electron-conjubated polymeric materials offer large electro-optic figures of merit, ease of processing into films and fibers, ruggedness, low cost, and a plethora of design options. Several new broad classes of second-order nonlinear optical polymers were developed at the Navy's Michelson Laboratory at China Lake, California. Polar alignment in thin film waveguides was achieved by electric-field poling and Langmuir-Blodgett processing. Our polymers have high softening temperatures and good aging properties. While most of the films can be photobleached with ultraviolet (UV) light, some have excellent stability in the 500-1600 nm range, and UV stability in the 290-310 nm range. The optical nonlinear response of these polymers is subpicosecond. Electro-optic switches, frequency doublers, light modulators, and optical data storage media are some of the device applications anticipated for these polymers
Raman scattering study of the a-GeTe structure and possible mechanism for the amorphous-to-crystal transition
We report on an inelastic (Raman) light scattering study of the local
structure of amorphous GeTe films. A detailed analysis of the
temperature-reduced Raman spectra has shown that appreciable structural changes
occur as a function of temperature. These changes involve modifications of
atomic arrangements such as to facilitate the rapid amorphous-to-crystal
transformation, which is the major advantage of phase-change materials used in
optical data storage media. A particular structural model, supported by
polarization analysis, is proposed being compatible with the experimental data
as regards both the structure of a-GeTe and the crystallization transition. The
remarkable difference between the Raman spectrum of the crystal and the glass
can thus naturally be accounted for.Comment: Published in: J. Phys. Condens. Matter. 18, 965-979 (2006
Ultralong-term high-density data storage with atomic defects in SiC
There is an urgent need to increase the global data storage capacity, as
current approaches lag behind the exponential growth of data generation driven
by the Internet, social media and cloud technologies. In addition to increasing
storage density, new solutions should provide long-term data archiving that
goes far beyond traditional magnetic memory, optical disks and solid-state
drives. Here, we propose a concept of energy-efficient, ultralong, high-density
data archiving based on optically active atomic-size defects in a radiation
resistance material, silicon carbide (SiC). The information is written in these
defects by focused ion beams and read using photoluminescence or
cathodoluminescence. The temperature-dependent deactivation of these defects
suggests a retention time minimum over a few generations under ambient
conditions. With near-infrared laser excitation, grayscale encoding and
multi-layer data storage, the areal density corresponds to that of Blu-ray
discs. Furthermore, we demonstrate that the areal density limitation of
conventional optical data storage media due to the light diffraction can be
overcome by focused electron-beam excitation.Comment: 8 pages, 4 figure
Ultrafast optical manipulation of atomic arrangements in chalcogenide alloy memory materials
A class of chalcogenide alloy materials that shows significant changes in
optical properties upon an amorphous-to-crystalline phase transition has lead
to development of large data capacities in modern optical data storage. Among
chalcogenide phase-change materials, Ge2Sb2Te5 (GST) is most widely used
because of its reliability. We use a pair of femtosecond light pulses to
demonstrate the ultrafast optical manipulation of atomic arrangements from
tetrahedral (amorphous) to octahedral (crystalline) Ge-coordination in GST
superlattices. Depending on the parameters of the second pump-pulse, ultrafast
nonthermal phase-change occurred within only few-cycles (~ 1 ps) of the
coherent motion corresponding to a GeTe4 local vibration. Using the ultrafast
switch in chalcogenide alloy memory could lead to a major paradigm shift in
memory devices beyond the current generation of silicon-based flash-memory.Comment: 11 pages, 7 figures, accepted for publication in Optics Expres
Mixed-Mode Electro Optical Properties of Ge2Sb2Te5
This is the author accepted manuscript.In this paper we present ongoing work on a novel alternative mode of operation of phase change materials, specifically Ge2Sb2Te5: mixed-mode electro-optical operation, which offers a new set of potential applications for this material
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