Photonic crystals, the photonic analog of traditional semiconductors, are currently the subject of intense investigation for applications in integrated optics. Such crystals is exhibit a photonic bandgap (analogous to the electronic bandgap of semiconductors) that determines which photon wavelengths can propagate through the crystal. By introducing specific defects into the crystal's bandgap structure, the flow of photons inside the crystal can be manipulated and a variety of micrometer-scale optical devices fabricated.
In particular, it is postulated that a three-dimensional (3-D) photonic crystal with appropriate line defects will act as a low-loss waveguide device, enabling light to be turned through a 90-degree bend without significant scattering losses. Such a device would be potentially useful in increasing the density of components on an optical chip and in chip-to-back plane applications. Other potential device applications include use in optical interconnects, optical switches, couplers, isolators, multiplexers, tunable filters, and low-threshold emitters.
In particular, it is postulated that a three-dimensional (3-D) photonic crystal with appropriate line defects will act as a low-loss waveguide device, enabling light to be turned through a 90-degree bend without significant scattering losses. Such a device would be potentially useful in increasing the density of components on an optical chip and in chip-to-back plane applications. Other potential device applications include use in optical interconnects, optical switches, couplers, isolators, multiplexers, tunable filters, and low-threshold emitters.
3M Innovative Properties Company (St. Paul, MN) earned U.S. Patent 7,655,376 for a process to produce photonic crystals and control defects to produce lightwave circuits and optical devices for a variety of applications.
According to inventors Mark T. Anderson, Catherine A. Leatherdale and D. Scott Thompson, unlike conventional multibeam interference (MBI) processes that use organic materials, the 3M process utilizes a substantially inorganic photoreactive composition to produce thermally stable, robust, highly ordered periodic dielectric structures that can withstand temperatures up to about 600 to 1300 degree. C.
The refractive index contrast of the structures can therefore be enhanced, for example, through semiconductor CVD, optionally followed by removal of the structure (by, for example, hydrogen fluoride etching) to produce air voids. The use of cationically reactive species can enable multiple exposures without a significant change in refractive index, and the use of precondensed, inorganic nanoparticles can provide surprisingly reduced shrinkage (relative to corresponding compositions comprising uncondensed metal oxide precursors).
Thus, the 3M process not only meets the need for a process that can provide high refractive index contrast periodic dielectric structures containing controlled or engineered defects to selectively route and control light propagation through the structure, but also facilitates optimization of the optical properties of the structure. The resulting defect-containing structures can be used, for example, in planar lightwave circuits.
Thus, the 3M process not only meets the need for a process that can provide high refractive index contrast periodic dielectric structures containing controlled or engineered defects to selectively route and control light propagation through the structure, but also facilitates optimization of the optical properties of the structure. The resulting defect-containing structures can be used, for example, in planar lightwave circuits.
(a) providing a substantially inorganic photoreactive composition comprising (1) at least one cationically reactive species, (2) a multi-photon photoinitiator system, and (3) a plurality of precondensed, inorganic nanoparticles.
(b) exposing, using a multibeam interference technique involving at least three beams, at least a portion of the photoreactive composition to radiation of appropriate wavelength, spatial distribution, and intensity to produce a two-dimensional or three-dimensional periodic pattern of reacted and non-reacted portions of the photoreactive composition;
(c) exposing at least a portion of the non-reacted portion of the photoreactive composition to radiation of appropriate wavelength and intensity to cause multi-photon absorption and photoreaction to form additional reacted portion;
(d) removing the non-reacted portion or the reacted portion of the photoreactive composition to form interstitial void space; and
(e) at least partially filling the interstitial void space with at least one material having a refractive index that is different from the refractive index of the remaining portion.
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