Martin Boguslawski

Airy beam induced optical routing

We present an all-optical routing scheme based simultaneously on optically induced photonic structures and the Airy beam family. The presented work utilizes these accelerating beams for the demonstration of an all-optical router with individually addressable output channels. In addition, we are able to activate multiple channels at the same time providing us with an optically induced splitter with configurable outputs. The experimental results are corroborated by corresponding numerical simulations.

Reconfigurable Optically Induced Quasicrystallographic Three‐Dimensional Complex Nonlinear Photonic Lattice Structures

2010 WILEY-VCH Verlag Gm Quasicrystals (QCs) are materials that possess a long-range order with defined diffraction patterns, but lack the characteristic translational periodicity of crystals. From the discovery of the non-crystallographic icosahedral quasiperiodic symmetry found in Al6Mn in 1984, [2] the distinct properties of quasicrystallographic structures attracted a great deal of interest in different realms of science in recent years. Another field of technological interest in the recent past is that of photonic crystals (PCs), the structured materials with a translational periodic modulation of the refractive index. Merging these two fields, a new class of material structures called photonic quasicrystals (PQCs) has drawn the attention of researchers stemming from a cumulative effect from both fields. This is mainly due to the fact that the higher rotational symmetry of QCs leads to more isotropic and complete photonic bandgaps (PBGs) even in materials with a low refractive index contrast. However, as in the case of PCs, the fabrication of 3D PQCs is much more involved in comparison to 2D PQCs and remains a real challenge today. Moreover, many of the conventional methods become technically either unsuitable or extremely complicated for the fabrication of 3D PQCs. Therefore, the fabrication and optimization of higher rotational symmetry 3D PQCs demand an approach that is flexible as well as reconfigurable. The purpose of the present Communication is dual fold. On the one hand, we demonstrate for the first time the generation of well-defined reconfigurable 3D quasi-crystallographic photorefractive nonlinear photonic structures with various rotational symmetries, which are experimentally realized in an externally biased cerium doped strontium barium niobate (SBN:Ce) photorefractive material as the nonlinear optical material of choice. These complex structures are envisaged to form a reconfigurable platform to investigate advanced nonlinear light–matter interaction in higher spatial dimensions with various rotational symmetries. On the other hand, we present a generalized versatile experimental approach for the fabrication of complex 3D axial PQCs with higher order rotational symmetry and variants of complex 3D structures similar to those having icosahedral symmetry, using a real-time reconfigurable holographic technique. It involves a programmable spatial light modulator (SLM)-assisted single step optical induction approach based on computer-engineered optical phase patterns. It is also important to note that the versatility of the experimental approach, we present, is not limited to photorefractive materials alone. It can be easily well adapted to various photosensitive materials as per the application requirement in the diverse fields of material science. Among various photosensitive materials, reconfigurable nonlinear photonic lattices can be easily generated by means of a so-called optical induction technique at very low power levels ( micro watts) in a photorefractive material, exploiting the wavelength sensitivity of these materials. The process of refractive index modulation, which leads to photonic lattice formation in such a medium is caused by a two-step process out of the incident light intensity distribution. Under the influence of an externally applied electric field, the incident light intensity distribution causes a charge carrier redistribution that results in a macroscopic space charge field in the photorefractive material. This, in turn, leads to a space-dependent refractive index modulation via the electro-optic effect thereby representing a nonlinear optical effect of third order that creates the refractive index modulation out of the incident intensity distribution. Apart from the possibility of permanent fixing of the generated structures in a photorefractive crystal, the recorded structure is reconfigurable: it can also be erased by the flush of white light so that new patterns could be again recorded in these materials. Therefore, photorefractive materials are ideal materials for reconfigurable PQC generation either to optimize the required photonic structure on the one hand or to be used as a reconfigurable platform to investigate novel nonlinear wave dynamics. From the optical properties point of view, the photonic lattices formed in SBN:Ce show both polarization as well as orientation anisotropy. In order to obtain refractive index modulated structures that mimic the intensity pattern, o-polarized writing beams are used causing a low modulation due to the appropriate electro-optic coefficient addressed. For the case of using e-polarized writing beams, as the relevant electrooptic coefficient is much higher, a strongly nonlinear refractive index modulation can be obtained for the fabricated lattices. Moreover, as maximum refractive index modulation is induced in the direction parallel to the crystal c axis, there exists also orientation anisotropy in SBN:Ce.

Nonlinear lattice structures based on families of complex nondiffracting beams

We present a new concept for the generation of optical lattice waves. For all four families of nondiffracting beams, we are able to realize corresponding nondiffracting intensity patterns in a single setup. The potential of our approach is shown by demonstrating the optical induction of complex photonic discrete, Bessel, Mathieu and Weber lattices in a nonlinear photorefractive medium. However, our technique itself is very general and can be transferred to optical lattices in other fields such as atom optics or cold gases in order to add such complex optical potentials as a new concept to these areas as well.

Systematic approach to complex periodic vortex and helix lattices.

We present a general comprehensive framework for the description of symmetries of complex light fields, facilitating the construction of sophisticated periodic structures carrying phase dislocations. In particular, we demonstrate the derivation of all three fundamental two-dimensional vortex lattices based on vortices of triangular, quadratic, and hexagonal shape, respectively. We show that these patterns represent the foundation of complex three-dimensional lattices with outstanding helical intensity distributions which suggest valuable applications in holographic lithography. This systematic approach is substantiated by a comparative study of corresponding numerically calculated and experimentally realized complex intensity and phase distributions.

Increasing the structural variety of discrete nondiffracting wave fields

We investigate discrete nondiffracting beams (DNBs) being the foundation of periodic and quasiperiodic intensity distributions. Besides the number of interfering plane waves, the phase relation among these waves is decisive to form a particular intensity lattice. In this manner, we systematize different classes of DNBs and present similarities as well as differences. As one prominent instance, we introduce the class of sixfold nondiffracting beams, offering four entirely different transverse intensity distributions: in detail, the hexagonal, kagome, and honeycomb pattern, as well as a hexagonal vortex beam. We further extend our considerations to quasiperiodic structures and show the changeover to Bessel beams. In addition, we introduce a highly flexible implementation of the experimental analog of DNBs, namely discrete pseudo-nondiffracting beams, and present locally resolved intensity and phase measurements, which underline the nondiffracting character of the generated wave fields.

Nondiffracting kagome lattice

We introduce a generalized approach to generate an elementary nondiffracting beam, whose transverse intensity is distributed corresponding to a two-dimensional kagome structure. Furthermore, we present an effective experimental implementation via a computer controlled phase controlling spatial light modulator in combination with a specific Fourier filter system. Intensity and phase analysis of the kagome lattice beam accounts for an experimental wave field implementation. Altogether, the examined wave field may be a fundament for the fabrication of large two-dimensional photonic crystals or photonic lattices in kagome symmetry using miscellaneous holographic matter structuring techniques.

Embedding defect sites into hexagonal nondiffracting wave fields

We present a highly purposive technique to optically induce periodic photonic lattices enriched with a negative defect site by using a properly designed nondiffracting (ND) beam. As the interference of two or more ND beams with adequate mutual spatial frequency relations in turn reproduces an ND beam, we adeptly superpose a hexagonal and a Bessel beam to create the ND defect beam of demand. The presented wavelength-independent technique is of utmost universality in terms of structural scalability and does not make any specific requirements to the photosensitive medium. In addition, the technique is easily transferable to all pattern-forming holographic methods in general and its application is highly appropriate, e.g., in the fields of particle as well as atom trapping.

Analysis of transverse Anderson localization in refractive index structures with customized random potential

We present a method to demonstrate Anderson localization in an optically induced randomized potential. By usage of computer controlled spatial light modulators, we are able to implement fully randomized nondiffracting beams of variable structural size in order to control the modulation length (photonic grain size) as well as the depth (disorder strength) of a random potential induced in a photorefractive crystal. In particular, we quantitatively analyze the localization length of light depending on these two parameters and find that they are crucial influencing factors on the propagation behavior leading to variably strong localization. Thus, we corroborate that transverse light localization in a random refractive index landscape strongly depends on the character of the potential, allowing for a flexible regulation of the localization strength by adapting the optical induction configuration.

Multiplexing complex two-dimensional photonic superlattices

We introduce a universal method to optically induce multiperiodic photonic complex superstructures bearing two-dimensional (2D) refractive index modulations over several centimeters of elongation. These superstructures result from the accomplished superposition of 2D fundamental periodic structures. To find the specific sets of fundamentals, we combine particular spatial frequencies of the respective Fourier series expansions, which enables us to use nondiffracting beams in the experiment showing periodic 2D intensity modulation in order to successively develop the desired multiperiodic structures. We present the generation of 2D photonic staircase, hexagonal wire mesh and ratchet structures, whose succeeded generation is confirmed by phase resolving methods using digital-holographic techniques to detect the induced refractive index pattern.

Photonic ratchet superlattices by optical multiplexing

We present a method based on incremental holographic multiplexing to create a refractive index ratchet distribution into a photorefractive crystal as an example for the generation principle of such complex multiperiodic lattices. The implemented technique follows a finite optical series expansion of the desired index modulation. To analyze the induced lattice, we determine the phase retardation of a probe beam at the back face of the crystal by digital holography analysis. Our result depicts a first example to optically explore the fascinating phenomena of ratchet resembling systems.