Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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Technology lines with improved characteristics compared to conventional technologies. 29 In this article, the basis of metamaterial operation is explained, and the applications of metamaterials are reviewed and discussed. For both photonic crystals and metamaterials, simple, qualitative explanations of the physics underlying the properties of the systems are a focus. Photonic Crystal Stop Bands And The Spatial Manipulation Of Light Flow In photonic crystals, the diffractive effects of the periodic lattice open energy stop bands in the dispersion of light. 1,2 Light at these energies does not propagate in the photonic crystal. This non- propagation can be used to mold the flow of optical energy. Just as the course of water is molded by impenetrable rock channels, the flow of light is molded by the impenetrable stop bands of photonic crystals, which do not allow light at stop band energies into their bulk. A waveguide then is made by introducing a propagation channel through the bulk of an otherwise perfect photonic crystal. The stop bands of the bulk photonic crystal are set to the frequencies of the light to be confined in the channel of the waveguide. Such waveguides are the photonic crystal analogy of optical fibers with the advantage that they allow the bending of the flow of light in space at higher angles with lower radiative losses than are found in traditional fiber-optic technologies. 1 Another approach to limiting the losses in traditional fiber-optics technology is based on putting a photonic crystal cladding around fiber-optic guides (i.e., perpendicular to the fiber axis, the cladding exhibits a periodic dielectric variation with a frequency stop band 11 ). The stop band frequencies of the cladding are adjusted to lower radiative losses from the fiber. An extension of photonic crystal-clad fibers to the design of lasers involves using rare-earth-doped fibers with a photonic crystal cladding. 1,2,11 The cladding again acts as a confining mechanism for the light generated by the laser operation, typically at terahertz frequencies. Consequently, introducing channels and voids in bulk photonic crystals and the development of photonic crystal cladding are two different ways of using photonic crystal technology to enhance traditional waveguide and optical-fiber technologies. Figure 1a shows an example of a two-dimensional photonic crystal formed as a two-dimensional periodic array of parallel axis dielectric cylinders, which are perpendicular to the page. For light propagating within the plane of the page, the optical dispersion displays a series of stop bands. Figure 1b shows the introduction into the system of a waveguide channel made by removing a row of cylinders. The resulting channel acts as a waveguide for light propagating in the plane of the page, with frequencies within the stop band of the bulk photonic crystal in Figure 1a. By removing appropriate sets of cylinder waveguides with bends, off-channel impurities — or intersecting waveguides forming interconnecting circuits of waveguide — can be formed within the bulk of the photonic crystal. 1,2 An oft-studied variant of the two-dimensional system is made from a thin slab of dielectric (i.e., a dielectric slab waveguide) by writing a periodic variation of dielectric within the slab and parallel to the plane of its surfaces (Figure 1c). This forms a photonic crystal slab. Light propagating within the slab can be confined to the slab by the dielectric mismatch at the slab surfaces. (The confinement, as with a dielectric slab waveguide, is by internal reflection.) In addition, the dispersion relation of the confined light is composed of a series of stop bands arising from the periodic dielectric patterning of the slab. Light which is not internally reflected at the slab surfaces, however, escapes the photonic crystal slab and is radiated away from it. This type of photonic crystal slab has been applied in recent studies of Electronic Military & Defense Annual Resource, 6th Edition 25 Figure 1: Schematics of photonic crystals: a) two-dimensional array of dielectric cylinders arrayed in a triangle lattice pattern, b) a waveguide channel introduced into the bulk, c) top view (above) and side view (below) of a two-dimensional photonic crystal slab with a triangle lattice patterning, d) multiplexer in a photonic crystal slab, consisting of a photonic crystal waveguide resonantly interacting with an off-channel site. 1c 1d 1a 1b