In the quest for three-dimensional photonic crystals [1,2] with omnidirectional photonic bandgaps (PBGs), pioneering "topdown" and "bottom-up" approaches have been explored. The former have led to excellent quality photonic crystals; however, fabrication efforts and costs are high. [3][4][5] The latter, using colloidal crystals as templates, provide photonic crystals; however, their crystal structure is limited to face-centered cubic and quality is compromised by defects. [6][7][8] More recent approaches founded on holographic laser lithography [9,10] and direct laser writing in polymer photoresists [11][12][13][14][15][16] have turned out to fulfill most of the necessary requirements [17] for largescale fabrication of three-dimensional (3D) photonic crystals, facilitating straightforward incorporation of functional defects like waveguides and resonators.[18] Unfortunately, a major obstacle must be overcome before the way is clear to photonic bandgap materials; namely, polymer templates have insufficient refractive-index contrast to open a complete photonic bandgap. In this report, we overcome these problems by employing a novel, versatile, scalable, and cost-effective silicon double-inversion method to synthesize the first Si replica of a polymeric photonic crystal. This method can be applied to any photoresist template produced by direct-laser writing (DLW), holographic laser lithography, or combinations thereof. It also incorporates a template-independent step to fine-tune the filling fraction of the high-index material, thereby allowing larger PBGs to be obtained than with the template alone. The procedure exclusively comprises straightforward, inexpensive, industry-compatible steps, perfectly suitable for mass production of complex and functionalized photonic-crystal-based devices.The silicon double inversion is exemplified using the familiar "woodpile" (or log pile) structure to allow direct comparison with "top-down" photonic crystals reported previously. [3][4][5] The Si woodpile, obtained following the steps shown schematically in Figures 1a-f and detailed hereafter, is 24 layers thick and has a calculated PBG of 8.6 %.We begin with a polymer woodpile fabricated in the commercially available negative photoresist EPON SU-8. In brief, 120 fs pulses at 800 nm wavelength, derived from a regeneratively amplified Ti:sapphire laser, are focused into the photoresist using a high numerical aperture (NA= 1.4) oil-immersion microscope objective. Due to the high intensities in the focal volume, two-photon absorption initiates the polymerization process, resulting in exposed ellipsoidal volume elements (voxels) with a minimum lateral diameter down to 150 nm and a ratio of 2.7 between axial and lateral dimensions after development. Such voxels form the basic building blocks for all 3D structures that can be fabricated by sequentially scanning the laser focus through the resist using a computer-controlled 3D piezo scanning stage, synchronized with the laser pulses. Functional defects like resonators and waveguides can...

Q uasicrystals1-4 are a class of lattices characterized by a lack of translational symmetry. Nevertheless, the points of the lattice are deterministically arranged, obeying rotational symmetry. Thus, we expect properties that are different from both crystals and glasses. Indeed, naturally occurring electronic quasicrystals (for example, AlPdMn metal alloys) show peculiar electronic, vibrational and physico-chemical properties. Regarding artificial quasicrystals for electromagnetic waves, three-dimensional (3D) structures have recently been realized at GHz frequencies 5 and 2D structures have been reported for the near-infrared region 6-9 . Here, we report on the first fabrication and characterization of 3D quasicrystals for infrared frequencies. Using direct laser writing 10,11 combined with a silicon inversion procedure 12 , we achieve high-quality silicon inverse icosahedral structures. Both polymeric and silicon quasicrystals are characterized by means of electron microscopy and visible-light Laue diffraction. The diffraction patterns of structures with a local five-fold real-space symmetry axis reveal a ten-fold symmetry as required by theory for 3D structures.Quasicrystals are different from both crystals and glasses: crystals have long-range translational symmetry, whereas glasses show only short-range order. Quasicrystals show long-range order but not in a repeating fashion yielding periodicity [1][2][3][4] : although the local arrangements of atoms are fixed in a regular pattern, each atom has a different atom configuration surrounding it. The Laue diffraction pattern of quasicrystals can, for example, show peaks with a five-or ten-fold symmetry axis, whereas crystals can reveal only two-, three-, four-or six-fold symmetries. Quasicrystals can be viewed as a projection of a six-dimensional (6D) crystal to three dimensions 3,4 . Although nature provides us with 3D quasicrystals for electrons 1 , corresponding structures for light need to be fabricated artificially. Here, the projection procedure is not just a Gedanken experiment, but can rather be The 'central atom' is in the centre of the structure. b, The same as a, but the 'central atom' is outside the structure. c, Oblique-incidence overview of a. d, A focused-ion-beam cut of a structure corresponding to a, but oriented along a local two-fold symmetry axis, revealing an 3D structure.used for the actual fabrication. This was first realized in 2005 at microwave frequencies 5 . The subtle but important difference between real atoms in quasicrystals and the dielectric building blocks, 'photonic atoms' , in photonic quasicrystals is that real atoms can 'float' in vacuum via their binding potential. The

Silicon inverse woodpile photonic crystals are fabricated for the first time. Our approach, which is based on direct laser writing of polymeric templates and a novel silicon single‐inversion procedure, leads to high‐quality structures with gap/midgap ratios of 14.2 %, centered at a wavelength of 2.5 μm. It is shown that gap/midgap ratios as large as 20.5 %, centered at 1.55 μm, may become possible in the future.

The recent experimental demonstration of polarization stop bands in three-dimensional dielectric circular-spiral photonic crystals is extended in two ways. First, the combination with a one-dimensional set of lamellae on one side allows for "poor-man's optical isolators" or for thin-film polarizers-depending on from which side light impinges onto the device. Second, a chiral three-dimensional photonic crystal sandwiched between two one-dimensional sets of lamellae acts as a thin-film polarizer from both sides. Corresponding polymeric heterostructures are fabricated by means of direct laser writing. Their performance is compared with theory. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2789662͔ Chiral molecules can exhibit circular dichroism and/or optical activity-despite the fact that the molecular dimensions are typically several orders of magnitude smaller than the pitch of the spiral described by the tip of the field vector of circularly polarized light ͑i.e., the wavelength of light͒. In chiral photonic crystals, e.g., in circular-spiral structures, the two spiral pitches can be brought into resonance and polarization stop bands emerge. 1,2 In a polarization stop band, one incident circular polarization of light is transmitted ͑with negligible polarization conversion͒ whereas the other circular polarization is Bragg reflected. 1,2 Clearly, the suppression can be adjusted by the number of lattice constants along the propagation direction, but even less than ten lattice constants and low index contrast can lead to very large effects for appropriate design. Our recent corresponding experimental demonstration based on polymeric three-dimensional circular-spiral photonic crystals allows for normal incidence onto "thin-film" structures located on a substrate. 2 Related chiral structures have, however, also been discussed for waveguide geometries, 3 for optical fibers, 4 for photonic band gap materials, 5-7 for chiral sculptured thin films, 8,9 for layerby-layer chiral photonic crystals, 10,11 as well as in the context of cholesteric liquid crystals. 12 Polarization stop bands can be used as "poor-man's optical isolators" for circularly polarized incident light: If, for example, right-handed polarized light from a laser impinges onto the structure, it is transmitted for a spiral photonic crystal composed of left-handed dielectric spirals. Upon back reflection from a mirror behind the spiral photonic crystal, the backward propagating light has left-handed circular polarization. As the spirals keep their handedness when looked at from the other side, the light is not transmitted, hence, blocked from propagating back into the laser source. This device is only a "poor-man's" isolator because it will fail to isolate if the polarization state of light is messed up behind the device, which is in sharp contrast to true optical isolators based on the Faraday effect.Furthermore, a polarization stop band obviously converts unpolarized incident light into circularly polarized transmitted light, which in itself might ...

With additive manufacturing entering the consumer market and exciting the stock market, “3D printing” has become fashionable in society. Freedom in design as well as easy workflows are positive attributes associated with this umbrella terminology for a variety of fabrication techniques. 3D printing, or additive manufacturing gives designers previously unknown flexibilities and eliminates one of the most cost‐, time‐ and labour‐intensive stages of the product development process in industrial manufacturing, the production of tools. 3D printing is more precise, faster and mostly less expensive than traditional forms of manufacturing, especially in respect of rapid prototyping of individual parts. 3D objects of almost any shape can be printed from a virtual model in a variety of materials.