Three Dimensional Invisibility Cloak at Optical Wavelengths
Hidden Under the Carpet Transformation optics, combined with the ability to fabricate structures with complex refractive index profiles, allow materials to be formed with fascinating optical properties, such as cloaks where both the object and the cloak concealing the object are rendered invisible. To date, the cloaks have been restricted to two dimensions, which limits realistic applications. Based on a photonic crystal structure with a polymer filling the empty space, Ergin et al. (p. 337, published online 18 March) have designed, fabricated, and realized a three dimensional cloak operating at optical wavelengths. A structured photonic crystal can be used to cloak an object at optical wavelengths and over a wide viewing angle. We have designed and realized a three dimensional invisibility cloaking structure operating at optical wavelengths based on transformation optics. Our blueprint uses a woodpile photonic crystal with a tailored polymer filling fraction to hide a bump in a gold reflector. We fabricated structures and controls by direct laser writing and characterized them by simultaneous high numerical aperture, far field optical microscopy and spectroscopy. A cloaking operation with a large bandwidth of unpolarized light from 1.4 to 2.7 micrometers in wavelength is demonstrated for viewing angles up to 60deg.
Science