Recently, disordered photonic media and random textured surfaces have attracted increasing attention as strong light diffusers with broadband and wide-angle properties. We report the experimental realization of an isotropic complete photonic band gap (PBG) in a 2D disordered dielectric structure. This structure is designed by a constrained optimization method, which combines advantages of both isotropy due to disorder and controlled scattering properties due to low-density fluctuations (hyperuniformity) and uniform local topology. Our experiments use a modular design composed of Al 2 O 3 walls and cylinders arranged in a hyperuniform disordered network. We observe a complete PBG in the microwave region, in good agreement with theoretical simulations, and show that the intrinsic isotropy of this unique class of PBG materials enables remarkable design freedom, including the realization of waveguides with arbitrary bending angles impossible in photonic crystals. This experimental verification of a complete PBG and realization of functional defects in this unique class of materials demonstrate their potential as building blocks for precise manipulation of photons in planar optical microcircuits and has implications for disordered acoustic and electronic band gap materials. The first examples of synthetic materials with complete photonic band gaps (PBGs) (1, 2) were photonic crystals using Bragg interference to block light over a finite range of frequencies. Because of their crystallinity, the PBGs are highly anisotropic, a potential drawback for many applications. The idea that a complete PBG (blocking all directions and all polarizations) can exist in isotropic disordered systems is striking, because it contradicts the longstanding intuition that periodic translational order is necessary to form PBGs. The paradigm for PBG formation is Bloch's theorem (3): a periodic modulation of the dielectric constant mixes degenerate waves propagating in opposite directions and leads to standing waves with high electric field intensity in the low dielectric region for states just above the gap and in the high dielectric region for states just below the gap. Long-range periodic order, as evidenced by Bragg peaks, is necessary for this picture to hold. The intrinsic anisotropy associated with periodicity may limit the scope of PBG applications greatly and places a major constraint on device design. For example, although 3D photonic crystals with complete PBGs have been fabricated for two decades (4), 3D waveguiding continues to be a challenge. Very recently, Noda and coworkers reported the first successful demonstration of 3D waveguiding (5). However, they found that because of the mismatch of the propagation modes in line defects along various symmetry orientations, vertical-trending waveguides must follow one particular major symmetry direction to effectively guide waves out of the horizontal symmetry plane in a 3D woodpile photonic crystal (5).Recently, disordered photonic media and random textured surfaces have attracted incr...

Using microwave and macroscopic samples of dielectric solid to study the photonic properties of disordered photonic bandgap materials

Abstract:We report the first experimental demonstration of guiding, bending, filtering, and splitting of EM wave in 2D disordered PBG materials, along arbitrarily curved paths, around sharp bends of arbitrary angles, and through Y shape junctions.©2012 Optical Society of America OCIS codes: 130.5296, 130.7408, 160.5293, 160.5298 Line defects in photonic band gap (PBG) materials can confine and guide light through narrow channels and around sharp corners, which is important for large scale all-optical circuit applications [1]. An enormous range of technological developments in telecommunication industry, laser engineering, optical computing, spectroscopy, and radiation, have been suggested, when light with selected frequencies can be directed along chosen paths or be confined within a specific volume in PBG materials [2]. Conventional PBG materials are periodic structures, in which only limited numbers of rotational symmetries are allowed. Angular differences make it difficult to form a complete PBG in periodic structures without a large dielectric contrast. The orientations of channels cut in photonic crystals for light guiding are also restricted by the crystal symmetries, limiting potential applications.Contradicting the long standing intuition that periodicity or long-range translational order is required in photonic band gap formation, a new class of disordered hyperuniform (HPU) materials was predicted to possess sizeable and isotropic photonic band gaps [3]. Recently, we have experimentally observed isotropic PBG in these disordered materials [4]. In these isotropic disordered structures there are no preferential symmetry directions; hence it becomes possible to construct wave-guiding and filtering channels with arbitrary bending angles in them.In this paper, we report the first experimental demonstrations of guiding, bending, filtering, and splitting of electromagnetic wave in 2D isotropic disordered PBG materials, along straight or arbitrarily curved paths, around sharp bends of arbitrary angles, and through Y shape junctions. We demonstrate broad band pass through channels of various shapes, as well as versatile and flexible defect tuning abilities for narrow band filtering, in these disordered PBG materials. In our study, nearly 100 percent transmission of electromagnetic waves around sharp corners of arbitrary angles with bending radii smaller than one wavelength is observed experimentally.The 2D isotropic HPU disordered PBG material constructed for this study consists of a network of Al 2 O 3 cylinders and thin sheets.. Each cylinder has three nearest neighbors to which it is connected by sheets. The cylinders are particularly important for forming PBG for the TM polarization, while the connected sheets are important for the TE polarization. There is neither Bragg scattering nor long range order in this structure. It was argued that hyperuniformity, combined with uniform local topology and short-range geometric order can explain the origin of PBGs in these disordered materials [3]. The PBGs are as...

Abstract:We introduce novel architecture for cavity design in an isotropic disordered photonic band gap material. We demonstrate that point-like defects can support localized modes with different symmetries and multiple resonant frequencies, useful for various applications. ©2012 Optical Society of America OCIS codes: 130.5296, 130.7408, 160.5293, 160.5298 Since photonic band gap (PBG) materials were first introduced, optical cavities (point defects in PBG materials) have attracted extensive attention due to their ability to trap light of certain frequencies within extremely small mode volume. Better understanding and control of frequency, location, and symmetry order of cavity modes inside the PBG will have an important impact on designing of novel sensors, filters, lasers, optical switches, and optical circuits [1].Recently, it has been predicted and observed that hyperuniform disordered dielectric structures, which do not possess long-range translational order like crystals do, can also have complete PBGs [2][3][4]. More importantly the structures and PBGs are isotropic, not limited to crystalline rotational symmetry, hence allowing novel and flexible architecture of cavity (point defects) and wave-guide (line defects) design.According to recent simulation studies by Florescu et al, introducing a point defect by removing a single dielectric cylinder from a 2D hyperuniform PBG structure, results in a localized cavity mode with monopole symmetry [5]. The electric field oscillation pattern was predicted to extend 1-2 cell widths into the surrounding structure ( Figure 1). When a defect dielectric cylinder of increasing radius is used to replace a regular one, the electric field of the localized cavity modes would oscillate with changing symmetries. For every symmetry order, such as monopole, dipole, quadrupole, hexapole and octopole, it was observed that an increase in defect cylinder radius will introduce higher resonant frequencies inside the PBG region.Our experimental structure is assembled using Al 2 O 3 cylindrical rods (r = 2.5mm, h = 10cm), inserted into a platform of a hyperuniform disordered pattern with 1cm deep slots. The average cell size (spacing between rods) is a = 13.3 mm. The structure has a TM polarization PBG from 9.2 to 10.7 GHz. Cavities are easily generated and changed in this structure by removing rods to create voids and placing bundled clusters of rods into the voids. We use horn antennas attached to a microwave vector network

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