Polymeric photonic crystals

Abstract

Two novel and practical methods for controlling the propagation of light are presented: First. a design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies is derived and used in fabricating an all dielectric omnidirectional reflector consisting of multilayer films. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices. A comprehensive framework2 for creating one, two and three dimensional photonic crystals out of self-assembling block copolymers has been formulated. In order to form useful band gaps in the visible regime, periodic dielectric structures made of typical block copolymers need to be modified to obtain appropriate characteristic distances and dielectric constants. Moreover, the absorption and defect concentration must also be ~ontrolled. This affords the opportunity to tap into the large structural repertoire, the flexibility and intrinsic tunability that these self-assembled block copolymer systems offer. A block copolymer was used to achieve a self assembled photonic band gap in the visible regime. By swelling the diblock copolymer with lower molecular weight constituents control over the location of the stop band across the visible regime is achieved, One and three-dimensional crystals have been formed by changing the volume fraction of the swelling media. Methods for incorporating defects of prescribed dimensions into the self-assembled structures have been explored leading to the construction of a self assembled microcavity light-emitting device.