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Photonic crystals are periodic optical structures that can control the flow of light. Multiple reflections from surfaces separated by a distance similar to the wavelength prevent an optical beam from propagating through the crystal. Photonic crystal devices can therefore force light around sharp bands or even trap it entirely.
Photonic crystals occur in nature in the form of structural coloration and animal reflectors, and, in different forms, promise to be useful in a range of applications. The colors on the wings of a butterfly, for instance, are not due to just pigments. Although there might be some pigments on their wings, most of their primary colors come from the periodic nanostructures on the scales on the wings. These periodic nanostructures have repeating units which are close to the wavelength of light and can interact with light in very interesting ways, reflecting certain wavelengths and more, as we will see below. Simply put, these structures which show color not due to pigments, but due to periodic nanostructures on the surface are photonic crystals!
Photonic crystals can be fabricated for one, two, or three dimensions. One-dimensional photonic crystals can be made of layers deposited or stuck together. Two-dimensional ones can be made by photolithography, or by drilling holes in a suitable substrate. Fabrication methods for three-dimensional ones include drilling under different angles, stacking multiple 2-D layers on top of each other, direct laser writing, or, for example, instigating self-assembly of spheres in a matrix and dissolving the spheres.
1D photonic crystals are the simplest structure in photonic crystal family. Interestingly, 1D photonic crystals still possess many exciting properties such as adjustable dispersion and birefringence, acting as homogeneous materials. Compared with 2D or 3D photonic crystals, the simple structure of 1D photonic crystals makes them easy to be integrated with the existing photonic devices without changing fabrication procedures. Consequently, many high-performance silicon-based devices have been proposed and demonstrated by exploiting those exciting properties of 1D photonic crystals.
Photonic crystals can, in principle, find uses wherever light must be manipulated. Existing applications include thin-film optics with coatings for lenses. Two-dimensional photonic-crystal fibers are used in nonlinear devices and to guide exotic wavelengths. Three-dimensional crystals may one day be used in optical computers. Three-dimensional photonic crystals could lead to more efficient photovoltaic cells as a source of power for electronics, thus cutting down the need for an electrical input for power.
Discovery in bird feathers has the potential to make fiber optics, solar cells, and fuel cells more efficient
A team of scientists from Yale-NUS College, ETH Zurich, and Yale University have discovered how leafbirds make complex color-producing crystals with highly desirable optical and electronic properties. These crystals may serve as inspiration for multifunctional applications and have the potential to make fiber optics, solar cells, and fuel cells more efficient, according to the newly published research.
The international team of collaborators, led by Vinodkumar Saranathan from Yale-NUS College, includes Eric R. Dufresne from ETH Zurich, Richard O. Prum from Yale University, and Suresh Narayanan and Alec Sandy from the Argonne National Laboratory, a U.S. Department of Energy multidisciplinary science and engineering research center. Published in Proceedings of the National Academy of Sciences of the United States of America (PNAS), this study is particularly relevant as the search for renewable sources of energy and sustainable manufacturing has taken on a fresh urgency.
The research breakthrough came from the team’s investigation of the feather colors of leafbirds, an enigmatic group of perching birds endemic to South and Southeast Asia (including Singapore). In the plumage of one species of this bird, the blue-winged leafbird, the scientists discovered a complex, three-dimensional crystal called the single gyroid that has evolved to produce vivid, saturated structural colors.
According to Saranathan, “Knowing how leafbirds manufacture these exotic structures can spur novel biomimetic eco-friendly self-assembly strategies for large-scale materials synthesis at these highly challenging optical length-scales, given the urgent ecological need for such materials.”
By comparing the color-producing nanostructures present in close relatives, the team reported that this species is able to directly synthesise single gyroid photonic crystals, which have highly desirable optical and electronic properties that make them ideal for use in photovoltaic cells to generate solar energy. Use of this crystal – a “crowning achievement” in material science engineering which thus far has been manufactured only with great difficulty – has the potential not only to improve photovoltaic cells, meaning they can be produced more easily and cheaply, but also for use in other industrial applications like catalysis in fuel cells and fiber optics.
Military Applications
Generating Electricity from Spectral & Directional Control of IR Radiation: The increasing power demands of portable electronics and micro robotics has driven recent interest in millimeter-scale microgenerators. Many technologies (fuel cells, Stirling, thermoelectric, etc.) that potentially enable a portable hydrocarbon microgenerator are under active investigation.
Thermophotovoltaics (TPV) converts the radiant energy of a thermal source into electrical energy using photovoltaic cells. TPV has a number of attractive features, including fuel versatility (nuclear, fossil, solar, etc.), quiet operation, low maintenance, low emissions, light weight, high power density, modularity, and possibility for cogeneration of heat and electricity. Some of these features are highly attractive for military applications (Navy and Army). Photonic crystals have been used to substantially improve the radiative efficiency in TPV
Controlling Thermal Radiation for IR Camouflage
Pumping Laser Weapons with Thermal Radiation from PBG Materials
PBG Thermal radiation control
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