Being a key enabling technology, optofluidics allows precise light-based manipulation of liquids and solid particles on micrometer scales in fluidic environments and covers high potential to fabricate efficient integrated lab-on-a-chip devices. In many of these devices, the ability to control and to manipulate particles by light is of utmost importance. This comprises an all-optical treatment of particles, viable cells, or droplets to be moved or trapped for analytical purposes. Such an all-optical control can be realized either by direct exposure in optical tweezers or indirectly by activating electric, thermal or mechanical properties by nonlinear light-matter interaction. Beneath particle manipulation, we demonstrate control of cells by holographic optical tweezers as well as droplet manipulation based on dielectrophoretic optical tweezers.Σ

We introduce a versatile concept to optically induce photonic structures of local refractive index modulations as well as photonic lattices holding single defect sites. For a given structure, we develop a set of nondiffracting beams obtained by fractionalizing the corresponding spatial spectrum. By combining this set in a multiplexing procedure, we achieve an incoherent combination of all individual structures of the set resulting in a locally addressable refractive index manipulation. We exemplarily present experimental results for apodized, meaning locally confined index changes in a photorefractive crystal resembling a sixfold and a circular symmetric structure. By an additional multiplexing step, we furthermore create periodic photonic lattices featuring embedded defects. (C) 2014 AIP Publishing LLC.

We introduce an experimental approach to realize aperiodic photonic lattices based on multiplexing of nondiffracting Bessel beams. This holographic optical induction scheme takes advantage of the well localized Bessel beam as a basis to assemble two-dimensional photonic lattices. We present the realization of an optically induced two-dimensional golden-angle Vogel spiral lattice, which belongs to the family of deterministic aperiodic structures. With our technique, a very broad class of photonic refractive index landscapes now becomes accessible to optical induction, which could not be realized with established distributed holographic techniques.

We experimentally demonstrate all-optical vortex switching in nonlinear coupled waveguide arrays optically induced in photorefractive media. Our technique is based on multiplexing of nondiffracting Bessel beams to induce various types of waveguide configurations. Using double- and quadruple-well potentials, we demonstrate precise control over the coupling strength between waveguides, the linear and nonlinear dynamics and symmetry-breaking bifurcations of guided light, and a power-controlled optical vortex switch.

We present the first experimental observation of spatial solitons in a photorefractive photonic curvilinear Weber lattice. The existence as well as the propagation dynamics of the soliton is shown experimentally as well as numerically.

We introduce a new induction approach based on liquid crystal spatial light modulators that allows generation of arbitrary lattice structures. In this context, we demonstrate formation of complex nondiffracting photonic lattices, structures and superlattices. Our technique additionally enables an intuitive way of randomization, offering the necessary conditions for Anderson localization. We further use the high nonlinear response of these systems to experimentally demonstrate soliton oscillations in a parabolic potential landscape.

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.

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.

Spatiotemporal nonlinear effects caused by the interplay between transverse modulation and nonlinearity open the rich field of research on wave propagation in nonlinear structures. In optics, the induction of two-dimensional refractive index structures in photorefractive materials has been utilized to demonstrate for instance discrete solitons, Bloch oscillations and Zener tunneling, as well as discrete vortex solitons. The unique properties of photorefractive crystals like strontium barium niobate (SBN) facilitate highly nonlinear and reconfigurable refractive index patterns even at low power levels.

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.

In photonics, the investigation of structured nonlinear systems is an active and vivid research area. Their ability to control the dispersion and diffraction properties of light allows tailoring light in its spectral, temporal, and spatial features. Manipulating the spatial features, i.e., overcoming diffraction, is an actual and challenging issue that is of utmost importance for further information processing tasks. With this contribution, we highlight some of the most recent publications in this field. Among others, we discuss the progress in complex photonic lattice generation as well as the guiding and control of discrete spatial solitons-entities that no longer spread during propagation. We also emphasize the importance of photonic lattices as optical analogies to quantum mechanical systems and review current results on Anderson localization of light.

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.

In this contribution, we present a highly flexible multiplexing method to optically induce multiperiodic photonic structures. We demonstrate this technique via introducing the representative induction of a photonic ratchet. To determine the excited refractive index landscape we implement digital holography methods, enabling us to locally analyze two-dimensional refractive index changes.

We present the light-induced manipulation of absorbing liquid droplets in air. Ink droplets from a printer cartridge are used to demonstrate that absorbing liquids—just like their solid counterparts—can interact with regions of high light intensity due to the photophoretic force. It is shown that droplets follow a quasi-ballistic trajectory after bouncing off a high intensity light sheet. We estimate the intensities necessary for this rebound of airborne droplets and change the droplet trajectories through a variation of the manipulating light field.

Ubiquitous miniaturization requires an everchanging tool set for handling, controlling and manipulating on the micro- and nanoscale. Light-based technologies like optical tweezers provide the contactless high-precision treatment needed for work done at these scales. Holographic optical tweezers (HOT) are used in hundreds of interdisciplinary applications, allowing researchers to move many dielectric particles and biological specimens in 3-D.

We present a convolution approach for the generation of optical bottle beams that combines established techniques of holographic optical trapping with hollow intensity distributions in order to manipulate absorbing particles. The versatility of our method is demonstrated by the simultaneous stable trapping of multiple particles at defined positions. Furthermore, the presented phase shaping technique allows for the dynamic manipulation of absorbing particles along arbitrary paths.

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.

We report on the first experimental observation of an oscillating spatial soliton in parabolic Weber photonic lattices imprinted in photorefractive nonlinear media. The existence and propagation of the soliton is shown numerically and experimentally.

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.