We study the formation of 2D self-trapped beams in nanodisordered potassium-sodium-tantalate-niobate (KNTN) cooled below the dynamic glass transition. Supercooling is shown to accelerate the photorefractive response and enhance steady-state anisotropy. Effects in the excited state are attributed to the anomalous slim-loop polarization curve typical of relaxors dominated by non-interacting polar-nano-regions.

/pdf/photorefractive-light-needles-in-glassy-nanodisordered-kntn-2tj4zq6u28.pdf

Photorefractive light needles in glassy nanodisordered KNTN

We show that self-trapped beams can form in structured monolithic lithium niobate chips. In particular, they are observed to be unaffected when crossing few hundred microns wide gaps. The technique is employed to fabricate an index sensor constituted of a buried circular optical waveguide crossing a fluidic channel in a lithium niobate substrate. Fluidic channels are realized by precision dicing while the optical waveguides are induced by photorefractive beam self-trapping controlled by the pyroelectric effect. The self-aligning property of this latter waveguides provides a simple fabrication technique of an integrated sensor that accurately measures the refractive index of transparent liquids.

/pdf/integrated-optofluidic-index-sensor-based-on-self-trapped-n4cykey755.pdf

Integrated optofluidic index sensor based on self-trapped beams in LiNbO3

In micro-analytical chemistry and biology applications, droplet microfluidic technology holds great promise for
efficient lab-on-chip systems where higher levels of integration of different stages on the same platform is constantly
addressed. The possibility of integration of opto-microfluidic functionalities in lithium niobate (LiNbO 3 ) crystals is
presented. Microfluidic channels were directly engraved in a LiNbO 3 substrate by precision saw cutting, and
illuminated by optical waveguides integrated on the same substrate. The morphological characterization of the
microfluidic channel and the optical response of the coupled optical waveguide were tested. In particular, the results
indicate that the optical properties of the constituents dispersed in the fluid flowing in the microfluidic channel can
be monitored in situ, opening to new compact optical sensor prototypes based on droplets generation and optical
analysis of the relative constituents.

Integrated opto-microfluidics platforms in lithium niobate crystals for sensing applications

Photorefractive spatial solitons supported by pyroelectric effects in strontium barium niobate crystals

Abstract A femtosecond laser at 800 nm was used to create micro-fluidic circuits on lithium niobate (LiNbO3) substrates by means of laser ablation, using different scanning velocities (100-500 μm/s) and laser pulse energies (1-20 μJ). The T-junction geometry was exploited to create on y-cut LiNbO3 crystals a droplet generator, whose microfluidic performance was characterized in a wide range of droplet generation frequencies, from few Hz to about 1 kHz.

T-junction droplet generator realised in lithium niobate crystals by laser ablation

Design, fabrication and test of an optofluidic device are presented It is constituted of a circular waveguide crossing a fluidic channel integrated in a monolithic LiNbO 3 wafer The fluidic channel is realized by precision sawing and the optical waveguide is induced by photorefractive beam self-trapping controlled by the pyroelectric effect The self-aligning property of this latter writing technique allows both, efficient light coupling inside the channel and light collection after channel crossing It is shown that the refractive index of a liquid present in the fluidic channel can be accurately evaluated by simple monitoring of th e light transmitted thro ugh the waveguide Keywords: Optical waveguide, self-trapped beam, ph otorefractive effect, optofluidics, LiNbO 3 , refractive index sensor 1 INTRODUCTION Association of optical waveguides and microfluidic channels has attracted a lot of attention over the past decade Such an association offers rapid chemical or biological tests with use of minimum amount of analyte One important pursued goal is the development of optofluidic lab-on-chip [1-2] Components are based on a variety of substrates and they often involve the combination of different materials For instance, devices have been developed on glasses, silicon, pol ymers or PDMS [3-5] for various applications such as the study of immunoreaction [6], analysis of fluorescence or spectroscopy [7] Standard fabrication techniques (photolithography, etching ) are often employed but the versatility of light inscription also offers great solutions [8] In our work, fluidic channels are combined with waveguides written thanks to unique properties of self-trapped beams This writing technique produces self-aligned waveguides that are perfectly adapted when crossing channels Moreover these light-induced waveguides are buried inside the host material which offers potential for a high density of probing waveguides As an emblematic demonstration we show that self-trapped beam can write waveguides crossing channels engraved in a monolithic ferroelectric LiNbO

/pdf/self-trapped-beams-for-fabrication-of-optofluidic-chips-4on0agom9a.pdf

Self-trapped beams for fabrication of optofluidic chips

Self-trapped beams ability to cross narrow tilted channels is studied. The experiments are performed in photorefractive lithium niobate chips structured with 200 μm wide channels. It reveals that efficient beam self-confinement controlled by the pyroelectric effect can be obtained even when the beam is crossing a channel at large angle of incidence approaching the critical angle. Once formed, self-trapped beams leave place to two perfectly adapted and aligned waveguides on both sides of the channel. This technique with unique self-alignment ability is exploited to demonstrate the fabrication of a guided-wave polarization separator component.

Self-trapped beams crossing tilted channels to induce guided polarization separators

An optical medium whose nonlinearity can be spatially adjusted is considered to study beam reshaping. The concept is applied to perform adiabatic self-focusing of broad beams. Experimental results are obtained in a photorefractive lithium niobate crystal where the self-focusing nonlinearity is controlled over propagation by a temperature gradient. As a demonstration, gradual self-focusing is shown to transform an incoming beam into an output circular spot 10 times smaller over a 2 cm long crystal submitted to a 30 °C temperature gradient. Once formed, the adiabatic self-focused beam has inscribed a funnel waveguide in the crystal.

Luai Al Fares

Papers

Self-trapped beams for fabrication of optofluidic chips

Self-trapped beams crossing tilted channels to induce guided polarization separators

Adiabatic self-focusing in media with spatially variable nonlinearity