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 60 degrees.

We miniaturize all features in a previously introduced polarization-independent three-dimensional carpet invisibility cloak by more than a factor of 2. This leads to operation wavelengths in the visible. The structures are characterized by electron and optical microscopy. In contrast to our previous work at IR wavelengths, we can directly measure two-dimensional images at visible frequencies, perform control experiments from the backside, and compare the images with theory. We find excellent agreement. Furthermore, we study the wavelength dependence in the range from 900 nm down to 500 nm. Cloaking action deteriorates as the woodpile stop band at around 575 nm is approached. © 2011 Optical Society of America OCIS codes: 230.3205, 160.3918, 080.2710, 160.1245 Transformation optics can be viewed as a powerful tool for designing optical systems. The strength of this tool is emphasized by invisibility cloaking [1][2][3], which was long believed to be impossible. In particular, the carpet-cloak concept [4] has inspired experiments by several groups [5][6][7][8][9][10][11][12][13]. In brief, by tailoring a refractive-index profile, the carpet cloak makes a bump in a metal mirror (the carpet) appear flat. This allows for hiding objects underneath this carpet. However, the "Holy Grail" of a macroscopic three-dimensional (3D) cloak for unpolarized visible light has not been accomplished so far. Our 2010 work [9] demonstrated a microscopic 3D carpet cloak for unpolarized light down to wavelengths of about 1:5 μm. More recent work [12,13] by other groups has demonstrated macroscopic carpet cloaks at visible frequencies, however, only for one linear polarization of light (due to the birefringent calcite used) and in an effectively twodimensional configuration. In this Letter, we miniaturize our 2010 structure by more than a factor of 2, leading to what we believe to be the first 3D carpet cloak for unpolarized visible light. This also allows for refined characterization via optical microscopy. Comparison with ray-tracing calculations shows that the cloaking performance is close to the theoretical expectation.The polymer structures in this work are fabricated by stimulated-emission-depletion (STED)-inspired direct laser writing, closely following along the lines of our Ref.[14], with two modifications. First, we employ a different photoinitiator in a similar monomer, i.e., 0.25 wt. % 7-diethylamino-3-thenoylcoumarin in pentaerythritol tetraacrylate. This ketocoumarin offers a better ratio between depletion efficiency and undesired absorption of the 532 nm cw depletion laser (which limits resolution). Second, we not only improve the lateral but also the axial resolution by using a suitable phase mask known from STED microscopy [15]. After exposure, the photoresist structures are developed in 2-propanol and dried supercritically with CO 2 (Leica EM CPD030).As in previous work [9], the refractive-index profile of the carpet cloak calculated from the quasi-conformal mapping [4] is mimicked by adjusting the local volume filling ...

Transformation optics is a design tool that connects the geometry of space and propagation of light. Invisibility cloaking is a corresponding benchmark example. Recent experiments at optical frequencies have demonstrated cloaking for the light amplitude only. In this Letter, we demonstrate far-field cloaking of the light phase by interferometric microscope-imaging experiments on the previously introduced three-dimensional carpet cloak at 700 nm wavelength and for arbitrary polarization of light.

We study the all-optical switching behavior of one-dimensional metal-dielectric photonic crystals due to the nonlinearity of the free metal electrons. A polychromatic pump-probe setup is used to determine the wavelength and pump intensity dependence of the ultrafast transmission suppression as well as the dynamics of the process on a subpicosecond timescale. We find ultrafast (subpicosecond) as well as a slow (millisecond) behavior. We present a model of the ultrafast dynamics and nonlinear response which can fit the measured data well and allows us to separate the thermal and the electronic response of the system. PACS numbers: I. arXiv:0903.2115v1 [cond-mat.other]