>>> Polymers in Photonics: Controlling Information by Manipulating Light
In electronic devices, the control of information, with the generation, modulation, transmission, collection and storage of data, is achieved by components that respond to and affect electron flow and charge distribution. The electronic revolution of the past few decades has been made possible by the development of ever smaller and more powerful integrated circuits and of extended networks to exchange data between large numbers of electronic devices. In photonics, the control of information is achieved by light (photons) and it has the potential to overcome some of the limitations of the current generation of electronic devices, in terms of speed and bandwidth attainable. Data transmission already relies heavily on passive optical elements like optical fibers, but optical signals are converted to digital electronic information at the transmitting and receiving ends of the communication system. Data
storage is also accomplished with passive polymeric materials such as those in compact discs, but again, the optical signals are converted to electronic signals.
It is in principle possible to accomplish all the functions of electronic devices with optical equivalents. In these photonic devices, starting
with light from sources like light emitting diodes (LEDs) and lasers, optical information can be encoded and controlled by linear and/ or nonlinear optical filters and switches, androuted/transmitted through optical fibers, waveguides, and/or photonic crystals to collection vessels like photodetectors. Opticalinformation can be transferred over long distances or processed locally on optically integrated circuits. In active configurations, filters and modulators controlled by electric or
magnetic fields, the local thermal environment, or with light itself can be used to dynamically change the direction, amplitude, phase, or
wavelength of optical signals.
Due to the complexity of optically integrated circuits, a combination of materials and fabrication techniques are likely needed to build all the necessary functionalities into a single, small footprint device and to ensure compatibility with existing silicon electronics, where needed. Many practical problems still need to be solved before photonics can fully affect how we process and transmit information, such as miniaturization issues caused by diffraction limitations. Strategies to
circumvent these limitations include, for example, using plasmonics to localize and miniaturize elements. Quantum computing offers an alternate approach to information processing for which light is inherently well suited. Active research areas include the development of new materials and the optimization of their properties, the design of viable optical circuitry and architectures in 2D or 3D, and the identification of common
protocols on which to develop modular building blocks that can be assembled into more complex structures. The final integrated solution will most likely be a combination of organic and inorganic materials, building on the strengths of both types.
In this developing environment, polymers show promise as being instrumental to a variety of the sub-components, both passive
and active. One of the advantages of polymers over other materials classes is that their physical and optical properties can be tailored
to a large extent by controlling the chemical structure and degree of polymerization. Functionalities can be added by incorporating appropriate molecular moieties into the polymer chain or as side pendants. Polymers
can be processed using a variety of methods, including solution and gas-phase deposition, and can be made compatible by suitable surface functionalization with substrate chemistry (including inorganic building
blocks). Polymers also have the potential to be produced on a large scale and at low cost.
This special issue focuses on the study and
applications of polymers in photonics, as we
look towards realizing a future as outlined
above. Sun and Wu review the development of
polymer network liquid crystals for use in
spatial light modulators and the search for
optimized operation conditions of such devices
by varying monomer and liquid crystal host.
Another type of liquid crystal-polymer
composite is discussed in the Perspective by De
Sio and Tabyrian. Here the authors describe the
fabrication and use of layered structures of
liquid crystals and polymers, whose optical
properties can be switched by an electric field,
which could be of interest as switchable
diffractive optical elements with fast response
times in photonics devices.
Priimagi and Shevchenko discuss how
polymers containing azobenzene derivatives,
which undergo photoisomerization under
appropriate illumination conditions and thus
experience large-amplitude molecular
motions, can be used to produce surface relief
gratings with micro- and nano-scale features
for applications in a variety of optical devices.
A different approach to generating periodic
polymeric structures is overviewed by Li,
Smith and Bunning, in which fabrication
techniques, material properties induced by
phase separation, and applications of the
patterned materials are presented.
Lynn, Blanche and Peyghambarian focus on
photorefractive polymers, with emphasis on
their use in holography and on models for the
materials response. Polymer versatility is
evident in tunable distributed feedback lasers,
as discussed in the review by Andrews,
Crescimanno, Singer, and Baer. Ioppolo and
coworkers demonstrate the effect of electric
and magnetic fields on optical resonances of
polymeric microspheres, which can be
exploited as an operating principle for sensors.
Whereas it is not possible to review all the
recent work devoted to the material
development and understanding of
requirements for polymer-based photonics in a
single journal issue, the chosen contributors
provide a wide sampling of the rich and
multidisciplinary research being carried out
across the world in polymer optics. As the control
of data and information becomes increasingly
more reliant on the efficient transport of light,
the need for versatile, inexpensive polymeric
materials continues to grow.
Mariacristina Rumi, Timothy J. Bunning
Air Force Research Laboratory
Materials and Manufacturing Directorate
AFRL/MLPJ
Wright-Patterson Air Force Base,
OH 45433 USA
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