Polymeric photonic band gap materials

Details Polymeric photonic band gap materials Polymeric photonic band gap materials

2000-01-10

2002-08-13

Lester, Evelyn A. (Department: 2873)

Optical: systems and elements

Light interference

Produced by coating or lamina

C359S589000, C359S241000

Reexamination Certificate

active

06433931

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to polymeric materials that display periodic ordering, and more particularly to a polymeric article defining an optical band gap material.
BACKGROUND OF THE INVENTION
Photonic band gap materials, that is, materials that can control the propagation of electromagnetic radiation by creating periodic dielectric structures, have been the subject of vigorous research in recent years. A photonic band gap material is one that prohibits the propagation of electromagnetic radiation within a specified frequency range (band) in certain directions. That is, band gap materials prevent light from propagating in certain directions with specified energies. This phenomenon can be thought of as the complete reflection of electromagnetic radiation of a particular frequency directed at the material in at least one direction because of the particular structural arrangement of separate domains of the material, and refractive indices of those domains. The structural arrangement and refractive indices of separate domains that make up these materials form photonic band gaps that inhibit the propagation of light centered around a particular frequency. (Joannopoulos, et al., “Photonic Crystals, Molding the Flow of Light”, Princeton University Press, Princeton, N.J., 1995). One-dimensional photonic band gap materials include structural and refractive periodicity in one direction, two-dimensional photonic band gap materials include periodicity in two directions, and three-dimensional photonic band gap materials include periodicity in three directions.
Ho, et al., “Existence of Photonic Gaps in Periodic Dielectric Structures”,
Phys. Rev. Lett
., 65, 3152 (1990) correctly predicted that a properly-arranged, three-dimensional photonic band gap material would include a complete band gap, that is, that the material would reflect light of any polarization incident at any angle at a particular frequency. If one or more defects are created in such a material, the material can serve a variety of useful purposes. Point defects could define low loss optical resonance cavities, planar defects could define narrow-band filters, and pathways within three-dimensional photonic band gap materials could define lossless waveguides capable of guiding light around sharp corners, crucial to the creation of proposed optical computers. Totally-reflective UV or laser shields, and countless other commercial applications-would benefit from relatively simple and reliable techniques for forming these materials.
Fan, et al., (“Design of Three-Dimensional Photonic Crystals at Submicron Lengthscales”,
Appl. Phys. Lett
., 65, 11, 09/12/94) describe a class of periodic, three-dimensional dielectric photonic crystal structures amenable to submicron-scale fabrication. Fabrication involves creating a layered structure of materials alternating in dielectric constant, and etching (drilling) holes through the article normal to the layered structure. Specifically, the layered structure is created by depositing a layer of silicon on a substrate, etching grooves into the resulting silicon layer, and filling the grooves with silicon dioxide. Another layer of silicon is deposited on the first layer, grooves offset from those of the first set of grooves are etched, and those grooves filled with silicon dioxide. The process is repeated to create the multi-layered structure, through which the holes are etched. Assuming dielectric constants of 12.096 for silicon and 2.084 for silicon dioxide, (both at wavelength=1.53 microns), the band gap was computed to extend from wavelength=1.43 microns to 1.64 microns.
Joannopoulos, et al. (referenced above) provides an overview of photonic band gap materials, and their theoretical treatment. Experimental results are reported, including construction of a two-dimensional crystal lattice that reflects essentially all in-plane light within a specified frequency band. Specifically, construction involved etching a triangular lattice of air columns in a crystal via electron-beam lithography (see Wendt, et al., “Nanofabrication of Photonic Lattice Structures in GaAs/AlGaAs”,
J. Vac. Sci. & Tech. B
. 11, 2637 (1993)). The columns of air were fabricated having a radius of 122.5 nm, the lattice constant was 295 nm, and the columns were about 600 nm tall.
International Patent Application WO 97/01440 to 3M, entitled “Multilayer Polymer Film with Additional Coatings or Layers” ('440) describes a multilayer polymeric film including a plurality of alternating polymer layers that may act as a mirror or polarizer. The multilayer polymer films described in '440 include alternating layers of at least two materials where at least one of the materials has the property of stress induced birefringence, such that the index of refraction of the material is affected by mechanical stretching. By stretching the multilayer stack either uniaxially or biaxially, an optical film may be created with a range of reflectivities for differently oriented plain-polarized incident light. Desired refractive index contrast can be obtained by stretching the polymer films during or after film formation.
Chen, et al., “Theoretical Prediction of the Optical Waveguiding Properties of Self-Assembled Block Copolymer Films”,
Macromolecules
, 17, (1995) describe a lamellar-forming block copolymeric waveguide, and computer calculations of propagation constants and optical field intensity distributions of selected diblock and triblock copolymeric thin-film waveguides. It is reported that by choosing the chemical composition of each block, the refractive index of each layer can be precisely controlled. Where the refractive index of a guiding layer is greater than the refractive indices of the substrate and superstrate layers, a waveguide can result. Chen, et al. report that the domain size of individual lamellae can be varied from tens of angstroms to thousands of angstroms.
U.S. Pat. No. 5,281,370 ('370) to Asher et al. entitled “Method of Making Solid Crystalline Narrow Band Radiation Filter” describes a method for making a solid polymeric optical filter material which filters a predetermined wavelength band from a broader spectrum of radiation. The method includes creating a colloidal suspension composed of polymeric particles dispersed within a medium, arranging the particles, for example by electrophoresis, to form an ordered array, and fixing the structure, for example by fusing the particles together, to yield a solid three-dimensional array having a periodic lattice spacing.
Three-dimensional periodicity in block-copolymeric, self-assembled structures are known. (Thomas, et al., “Phase Morphology in Block Copolymer Systems”,
Phil. Trans. R. Soc. Lond A
., 348, 149-166). Lamellar, cylindrical, spherical, and ordered bicontinuous double diamond morphologies in block copolymeric systems have been identified (see, for example, Helfand, et al.,
Developments in Block Copolymers
. 1; Goodman, I., Ed.; Applied Science Publishers: London, 1982; vol. 1, pp. 99-126; Herman, et al.,
Macromolecules
, 20, 2940-2942, (1987). Researchers have been successful in incorporation of metallic species, including clusters, selectively in a first but not a second domain of a two-domain species resulting from thermodynamic phase separation of block copolymeric species Sankaran, et al., “Synthesis of Zinc Sulfide Clusters and Zinc Particles Within Microphase-Separated Domains of Organometallic Block Copolymers”,
Chem. Mater
., 5, 1133-1142 (1993); Sohn, et al., “Processable Optically Transparent Block Copolymer Films Containing Superparamagnetic Iron Oxide Nanoclusters”,
Chem. Mater
., 9, 1, 264-269 (1997). Sankaran, et al. and Sohn, et al. pursued goals of creating monodisperse metal/semiconductor clusters in an organized array for the purpose of growing metal clusters in a controlled fashion for electrical, optical, magnetic, and catalytic applications. These and other techniques have shown some promise with respect to several diverse goals. However, there is a need in the art for inexp

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