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IMA Workshop 9

Nonlinear Optical Materials

Nonlinear Optical Materials

March 4-8, 1996

The study of nonlinear optics from a fundamental point of view
is concerned with how materials react to the external stimulus
of an incident light field and thereby modify a characteristic
property of the latter. The basic interaction between light
and matter is intrinsically quantum mechanical by nature involving
induced dipoles reradiating their fields back into the incident
optical wave. Loosely speaking, optical interactions with bulk
materials can be classified into two types: resonant and nonresonant.
Resonant interactions involve either a coherent and incoherent
transfer of energy between the optical wave and a material oscillation
whereas nonresonant interactions involve no energy exchange
but instead modify the propagation constant of the electromagnetic
wave. The latter are called induced refractive index changes.
In any event, the strength of the nonlinear interaction and
the effective interaction length play a crucial role in determining
whether a material may prove useful or not for a particular
application. The great technological success of optical fibers
as soliton transmission systems, for example, hinges on very
large interaction lengths available in modern single-mode low-loss
fibers which compensates for the very weak nonlinear refractive
interaction of the glass. Many nonlinear optical applications
require very short interaction lengths (microns) for ultrafast
integrated optical processing of information. In addition to
the processing stage, reliable sources of stable ultrashort
optical pulses are needed. Lasers, through nonlinear resonant
interactions and some form of external modulation, provide such
pulsed sources. Suitable materials for laser operation include
semiconductors, solid state and Erbium doped fibers.

In many instances, the intrinsic nonlinear optical interactions
coefficients are too small to be useful and one has to resort
to novel schemes for enhancement of the effective interaction.
Low dimensional structures grown by Molecular Beam Epithaxy
(MBE), MOCVD and various precision materials growth techniques,
impose geometric enhancements of the effective linear and nonlinear
interaction coefficients. Examples abound in current nonlinear
optica applications involving both laser sources (semiconductor
Quantum-Well, quantum wire, dot structures and Erbium doped
fiber lasers) and optical processing elements (thin-film organic
planar waveguides, nonlinear Bragg grating structures, photonic
bandgap materials). All of these low-dimensional materials benefit
from a localization phenomenon of some sort (either quantum
mechanical or optical) in order to greatly enhance the effective
nonlinear interaction coefficient.

Despite significant advances in materials growth technology,
the potential impact of nonlinear optics in modern technology
is yet to be felt, primarily due to a lack of suitable materials
with large enough interaction coefficients. Typically a large
nonlinear optical interaction coefficient implies a slow response
time, ruling out multi-Gigahertz processing operations. In fact
most functioning nonlinear optics-based switches require some
form of electrical assistance in order to offset such weak interactions.

This workshop will serve to highlight the current state of affairs
with regard to materials for nonlinear optics applications.
An ongoing theme of the period of concentration in nonlinear
optics will be whether there exist scaling laws which would
allow one to a priori design nonlinear optical materials which
compromise between large interaction strengths and fast response
times.

structure of deposited films, and mechanical, electrical and
magnetic properties of films.

The workshop will bring together experts doing experimental
work, materials and mathematical modeling.

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