Mesoscale Engineering of Nanocomposite Nonlinear Optical Materials
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P. Mazzoldi, D. H. Osborne,' J. Solis 2 and R. A. Zuhr 4 'Vanderbilt
2
University, Nashville TN 37235
Instituta de Optica, CSIC, Madrid, Spain
' CNR-INFM, Universitai di Padova, Padova, Italy 4 Oak Ridge National Laboratory, Oak Ridge, TN 37831
Abstract Complex nonlinear optical materials comprising elemental, compound or alloy quantum dots embedded in appropriate dielectric or semiconducting hosts may be suitable for deployment in photonic devices. Ion implantation, ion exchange followed by ion implantation, and pulsed laser deposition have all been used to synthesize these materials. However, the correlation between the parameters of energetic-beam synthesis and the nonlinear optical properties is still very rudimentary when one starts to ask what is happening at nanoscale dimensions. Systems integration of corplex nonlinear optical materials requires that the mesoscale materials science be well understood within the context of device structures. We discuss the effects of beam energy and energy density on quantum-dot size and spatial distribution, thermal conductivity, quantum-dot composition, crystallinity and defects - and, in turn, on the third-order optical susceptibility of the composite material. Examples from recent work in our laboratories are used to illustrate these effects.
Introduction and Motivation Research groups around the world have reported the fabrication of metal quantum-dot composites (MQDCs) by such varied techniques4 as ion implantation,' ion exchange followed by ion 2 implantation, sol-gel synthesisl sputtering and pulsed laser deposition. The motivation cited in these reports has been to synthesize materials suitable for all-optical switching, to take advantage of the short duration and high pulse repetition frequency of optical signals. Invariably cited in all these publications is the large third-order nonlinearity X(3) of these materials, which produces either strong nonlinear absorption 0/o 3mn[yZ(3)] or nonlinear refraction n12 c> 9--(e[()], or both. However, simply having a large value of y," is insufficient to justify deployment of these materials in all-optical switching technology. A much more complex set of problems is associated with optimizing the materials properties of MQDCs to provide an adequate nonlinear optical response within the constraints set by device functionality and operating conditions. In this context, the mesoscale properties of the MQDCs which affect high-frequency performance, such as thermal conductivity and defect properties, are of special concern. Here we address a number of mesoscale materials properties which affect the size of the third-order nonlinearity, such as tunability, relaxation time, and high-fiequcncy operation. Several beam-assisted processing techniques can produce either waveguide or layered structures; the challenge lies in adapting these techniques to produce self-assembling or patterned structures. Coinparisons of the third-order nonlinear optical properties of MQDCs made by ion implantation, ion exchange followed by ion implanta
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