Jolly Xavier

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.

Three-dimensional optically induced reconfigurable photorefractive nonlinear photonic lattices.

We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear photonic lattices in an externally biased cerium doped strontium barium niobate photorefractive crystal by a spatial light modulator-assisted versatile simplified single step optical induction approach. The analysis of the generated 3D nonlinear photonic lattices by plane wave guiding, momentum space spectroscopy, and far field diffraction pattern imaging is presented, which points to the embedded potential of these 3D structures as reconfigurable platform to investigate advanced nonlinear light-matter interaction in periodic structures.

Tunable complex photonic chiral lattices by reconfigurable optical phase engineering

We present a novel single-step fabrication approach, based on optical phase engineering, for tunable complex photonic chiral lattices of diverse geometries in a large area. By means of engineered reconfigurable phase patterns, we computationally simulate as well as experimentally investigate these complex structures. We show the generation of both periodic right- and left-handed chiral structures as well as photonic transversely quasi-crystallographic chiral structures. These complex chiral lattices are also demonstrated in a photorefractive material, and the lattice formation is analyzed by plane-wave-guided imaging as well as diffraction pattern imaging. Furthermore, complex photonic chiral structures with engineered tunable relative phase shifts between adjacent spiral units realizable in a single step are explored and analyzed.

Three dimensional optical twisters-driven helically stacked multi-layered microrotors

We demonstrate tunable helically stacked multi-layered microrotors realized in vortex-embedded three dimensional (3D) optical twister patterns. Intensity-tunable annular irradiance profiles with higher order vortex are generated as well as simultaneously unfolded by phase-engineered multiple plane wave interference. In the individually tunable 3D helical bright arms of these unfolded vortex structures, 2 μm silica beads are optically trapped as spiraling multilayered handles of multi-armed microrotors. Further, multiple rows of such microrotors are parallelly actuated with controllable sense of rotation. We also present our observation on helical 3D stacking of micro-particles in these longitudinally gyrating multi-armed rotor traps.

Formation of all fourteen Bravais lattices of three-dimensional photonic crystal structures by a dual beam multiple-exposure holographic technique.

We make use of a dual beam multiple-exposure (DBME) holographic technique for the formation of all 14 Bravais lattices of three-dimensional photonic crystal microstructures. For simplicity of experimental implementation, the DBME method has been modified such that, prior to each exposure, once the proper angle between the wave vectors of the interfering beams is chosen, a single axis rotation of the recording medium gives the desired results. The parameters required for the generation of the lattice structures have been derived by appropriate modification of interference of four noncoplanar beams (IFNB) analysis for corresponding implementation in the DBME technique, and the results have been verified by computer simulations. After giving a comparative study of the results with the IFNB method, recording geometries for the DBME approach are also proposed in order to realize all 14 Bravais lattices experimentally.

Tailored complex 3D vortex lattice structures by perturbed multiples of three-plane waves

As three-plane waves are the minimum number required for the formation of vortex-embedded lattice structures by plane wave interference, we present our experimental investigation on the formation of complex 3D photonic vortex lattice structures by a designed superposition of multiples of phase-engineered three-plane waves. The unfolding of the generated complex photonic lattice structures with higher order helical phase is realized by perturbing the superposition of a relatively phase-encoded, axially equidistant multiple of three noncoplanar plane waves. Through a programmable spatial light modulator assisted single step fabrication approach, the unfolded 3D vortex lattice structures are experimentally realized, well matched to our computer simulations. The formation of higher order intertwined helices embedded in these 3D spiraling vortex lattice structures by the superposition of the multiples of phase-engineered three-plane waves interference is also studied.

Sculptured 3D twister superlattices embedded with tunable vortex spirals

We present diverse reconfigurable complex 3D twister vortex superlattice structures in a large area embedded with tunable vortex spirals as well as dark rings, threaded by vortex helices. We demonstrate these tunable complex chiral vortex superlattices by the superposition of relatively phase engineered plane waves. The generated complex 3D twister lattice vortex structures are computationally as well as experimentally analyzed using various tools to verify the presence of phase singularities. Our observation indicates the application-specific flexibility of our approach to tailor the transverse superlattice spatial irradiance profile of these longitudinally whirling vortex-cluster units and dark rings.

Complex photonic lattices embedded with tailored intrinsic defects by a dynamically reconfigurable single step interferometric approach

We report sculptured diverse photonic lattices simultaneously embedded with intrinsic defects of tunable type, number, shape as well as position by a single-step dynamically reconfigurable fabrication approach based on a programmable phase spatial light modulator-assisted interference lithography. The presented results on controlled formation of intrinsic defects in periodic as well as transversely quasicrystallographic lattices, irrespective and independent of their designed lattice geometry, portray the flexibility and versatility of the approach. The defect-formation in photonic lattices is also experimentally analyzed. Further, we also demonstrate the feasibility of fabrication of such defects-embedded photonic lattices in a photoresist, aiming concrete integrated photonic applications.

Complex 3D Vortex Lattice Formation by Phase-Engineered Multiple Beam Interference

We present the computational results on the formation of diverse complex 3D vortex lattices by a designed superposition of multiple plane waves. Special combinations of multiples of three noncoplanar plane waves with a designed relative phase shift between one another are perturbed by a nonsingular beam to generate various complex 3D vortex lattice structures. The formation of complex gyrating lattice structures carrying designed vortices by means of relatively phase-engineered plane waves is also computationally investigated. The generated structures are configured with both periodic as well as transversely quasicrystallographic basis, while these whirling complex lattices possess a long-range order of designed symmetry in a given plane. Various computational analytical tools are used to verify the presence of engineered geometry of vortices in these complex 3D vortex lattices.

Controlled formation and manipulation of colloidal lattices by dynamically reconfigurable three dimensional interferometric optical traps

We present real-time controlled manipulation of microparticles optically trapped in three dimensional (3D)-trap array lattices generated by dynamically reconfigurable n + 1 non-coplanar multiple plane wave interference in an umbrella-like configuration. Through a programmable spatial light modulator-assisted approach, reconfigurable stable 3D interferometric optical traps belonging to diverse transverse rotational symmetry are realized and used to trap micro beads in multi-layers. Dynamically controlled translation as well as rotation of trapped array of particles are also demonstrated using presented approach. Further, the optical stacking of microparticles in an array of 3D single-stranded chiral traps portrays the versatility in tailoring axially tunable trap arrays.