Bragg gratings have been produced in germanosilicate optical fibers by exposing the core, through the side of the cladding, to a coherent UV two-beam interference pattern with a wavelength selected to lie in the oxygen-vacancy defect band of germania, near 244 nm. Fractional index perturbations of approximately 3 x 10(-5) have been written in a 4.4-mm length of the core with a 5-min exposure. The Bragg filters formed by this new technique had reflectivities of 50-55% and spectral widths, at half-maximum, of 42 GHz.

Formation of Bragg gratings in optical fibers by a transverse holographic method

The wavelength corresponding to the extinction maximum, λmax, of the localized surface plasmon resonance (LSPR) of silver nanoparticle arrays fabricated by nanosphere lithography (NSL) can be systematically tuned from ∼400 nm to 6000 nm. Such spectral manipulation was achieved by using (1) precise lithographic control of nanoparticle size, height, and shape, and (2) dielectric encapsulation of the nanoparticles in SiOx. These results demonstrate an unprecedented level of wavelength agility in nanoparticle optical response throughout the visible, near-infrared, and mid-infrared regions of the electromagnetic spectrum. It will also be shown that this level of wavelength tunability is accompanied with the preservation of narrow LSPR bandwidths (fwhm), Γ. Additionally, two other surprising LSPR optical properties were discovered:  (1) the extinction maximum shifts by 2−6 nm per 1 nm variation in nanoparticle width or height, and (2) the LSPR oscillator strength is equivalent to that of atomic silver in gas or...

Nanosphere lithography: Tunable localized surface plasmon resonance spectra of silver nanoparticles

The spectroscopic properties, structure and interconversions of optically active oxygen-deficiency-related point defects in vitreous silica are reviewed. These defects, the E′-centers (oxygen vacancies with a trapped hole or 3-fold-coordinated silicons), different variants of diamagnetic `ODCs' (oxygen-deficiency centers), and their Ge-related analogs play a key role in the fiber-optic Bragg grating writing processes. The controversy surrounding the structural models for the Si- and Ge-related ODCs is discussed and the similarity between the bulk and surface point defects in silica is emphasized. The possible interconversion mechanisms between 2-fold-coordinated Si, neutral oxygen vacancies and E′-centers are discussed. The effects of glassy disorder have a profound effect on defect properties and interconversion processes in silica.

Optically active oxygen-deficiency-related centers in amorphous silicon dioxide

We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

Theory of the linear and nonlinear optical properties of semiconductor microcrystallites

/pdf/synthesis-and-optical-properties-of-hybrid-and-alloy-10sge0n27x.pdf

Synthesis and Optical Properties of Hybrid and Alloy Plasmonic Nanoparticles

We describe the picosecond nonlinear optical response of a metal-dielectric composite made by implanting Cu ions in fused silica. The implanted Cu ions aggregate during implantation to form nanometer-diameter clusters in a dense, thin (~150 nm) layer just beneath the surface of the substrate. The third-order susceptibility X((3)) has an electronic component with a magnitude of the order of 10(-8) esu and is enhanced for laser wavelengths near the surface plasmon resonance of the copper colloids.

Picosecond nonlinear optical response of a Cu:silica nanocluster composite

Planar layers of Au clusters with diameters between 5 and 30 nm were synthesized by implanting 2.75‐MeV Au+ ions in fused silica. The metal‐glass composite layer was 0.85 μm below the surface and had a width of 0.5 μm. Thermal annealing enhanced the optical absorption of the annealed samples near 2.4 eV. The third‐order nonlinear optical response time is ≤35 ps; the magnitude of the effective nonlinear susceptibility is 200 times that of similar clusters embedded in ruby‐gold melt glass.

Optical properties of gold nanocluster composites formed by deep ion implantation in silica

Cu clusters of nanometer dimensions were created by implantation of Cu ions into pure fused silica substrates at energies of 160 keV. The sizes and size distributions of the Cu clusters were measured by transmission electron microscopy, and were found to be determined by the ion‐beam current during implantation. Optical‐absorption spectra of these materials show the size‐dependent surface plasmon resonance characteristic of noble‐metal clusters. There are also significant size‐dependent effects in both the nonlinear index of refraction and two‐photon absorption coefficients. The distinctive variations in linear and nonlinear optical properties with Cu nanocluster sizes and size distributions affords potentially interesting possibilities for using these materials in nonlinear optical devices.

Physical and optical properties of Cu nanoclusters fabricated by ion implantation in fused silica

Over a decade ago, it was demonstrated that composites comprising metal clusters embedded in dielectric hosts could be synthesized by ion implantation The optical properties of these metal-cluster composites are dominated by two phenomena which alter the susceptibilities from those of bulk metals: One is a classical field enhancement effect, dielectric confinement, which leads to the characteristic surface plasmon resonance of the metal clusters seen in absorption spectra The other effect is quantum confinement of the conduction-band electrons which enhances the nonlinear susceptibility of the metal clusters for diameters smaller than about 10 nm and makes them behave as quantum dots with electronic properties which approximate those of independent electrons confined in a spherical potential well This paper reviews our studies of the nonlinear optical behavior of quantum-dot composites synthesized by ion implantation We also consider the potential of these quantum-dot composites as materials for nonlinear waveguide devices

Nonlinear optical properties of metal-quantum-dot composites synthesized by ion implantation

Nanometer dimension metal colloids were formed in silica by sequential implantation of Ag and Cu ions. The Ag and Cu were implanted with Ag to Cu ratios of 9:3, 6:6 and 3:9 and total nominal dose 12 × 10 16 ions/cm 2 . The linear optical response was measured from 200 to 900 nm. The non-linear optical properties were measured using the Z-scan technique at a wavelength of 570 nm. The linear and non-linear optical properties were found to be dependent upon the Ag to Cu ratio.

Robert H. Magruder

Papers

Picosecond nonlinear optical response of a Cu:silica nanocluster composite

Optical properties of gold nanocluster composites formed by deep ion implantation in silica

Physical and optical properties of Cu nanoclusters fabricated by ion implantation in fused silica

Nonlinear optical properties of metal-quantum-dot composites synthesized by ion implantation

Non-linear optical properties of nanometer dimension AgCu particles in silica formed by sequential ion implantation