For three-dimensional photonic crystals, made either by top-down microfabrication or by bottom-up self-assembly approaches, to comply with the stringent requirements of optical telecommunication applications, their degree of structural perfection and optical quality must meet an exceptionally high standard. Only with such superior quality photonic crystals can their unique optical properties be harnessed in optical devices and circuits constructed from micrometer-sized optical components. In this paper, we present a new strategy for making silica colloidal crystal films with a sufficiently high level of structural perfection and optical quality to make it competitive as a practical route to photonic crystal optical components. The attainment of this goal takes due cognizance of three key synergistic factors in the film formation process. The first recognizes the necessity to prepare high-quality silica spheres, which are highly monodisperse, with a polydispersity index significantly better than 2%, and the second recognizes that the population of spheres must be devoid of even the smallest fraction of substantially smaller or larger spheres or sphere doublets. The latter turns out to have a minimal effect on the polydispersity index, and yet a major detrimental effect on the overall structural order of the film. The third concerns the film-forming method itself, which necessitated the development of a novel process founded upon isothermal heating evaporation-induced self-assembly (IHEISA) of spheres on a planar substrate. This new method has several advantages over previously reported ones. It is able to deposit very high-quality silica colloidal crystal film rapidly over large areas, with a controlled thickness and without any restrictions on sphere sizes.

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The concept of three-dimensional (3D) photonic crystals (PCs) and photonic bandgap materials [1,2] was introduced nearly twenty years ago. However, the fabrication of highquality 3D structures for the optical regime still remains a challenge. Three techniques have been discussed: i) direct semiconductor fabrication by using a layer-by-layer (LbL) method, combining high-precision alignment and wafer-fusion techniques; [3][4][5][6] ii) templating by means of self-assembly of low-refractive-index colloidal microspheres; [7,8] and iii) holographic laser lithography [9,10] and direct laser writing (DLW) [11,12] to fabricate large-area, defect-free polymer templates. The latter two approaches require subsequent inversion [13][14][15] or double inversion [16,17] steps with high-refractiveindex materials. Here we present a novel approach, namely DLW in all-inorganic, high-refractive-index chalcogenide glasses. This approach combines the flexibility of DLW with the benefits of a direct fabrication method, hence eliminating the need for subsequent inversion. The fabrication of woodpile structures [18] with a complete gap of 3.5 % takes less than two hours. There are two stringent requirements for materials to be suitable for the fabrication of 3D PCs with an omni-directional photonic bandgap (PBG): i) the material has to be transparent over the wavelength region in which the PC is operated, and ii) the index of refraction should allow for an index contrast of at least 1.9 in the final structure to open the PBG.[18] Unfortunately, most of the materials that fulfill requirement (i) do not comply with requirement (ii). This is especially awkward as most of the materials suitable for fabrication by using lithographic techniques like holographic laser lithography [9,10] and direct laser writing [11,12] belong to this group (i.e., all-organic photoresists). Prominent materials such as silicon or gallium arsenide, which fulfill both requirements, are however not suitable for 3D lithographic techniques. Therefore, these materials are usually incorporated by means of chemical vapor deposition (CVD) techniques into suitable templates, which are then removed at a later stage. [14,17] Direct fabrication of 3D PCs in high-index materials seems preferable, but requires fabrication in a LbL assembly. [19] Each layer has to be fabricated with a whole set of lithography and etching steps. [3][4][5][6] Furthermore, ultra-precise alignment and wafer fusion for each additional layer is required at the cost of fabrication speed. Therefore, a technique combining both direct fabrication into a high-index material with the high flexibility, speed, and accuracy of direct laser writing is highly desirable.Here, we present for the first time direct laser written 3D PCs with a PBG made from As 2 S 3 chalcogenide glasses. These materials are amorphous semiconductors with high transparency throughout the near-infrared and infrared spectral region. The index of refraction lies between 2.45 and 2.53, [20] sufficient to open a PBG. In As 2 S 3 the positi...

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