Semi-transparent 3D microelectrodes buried in fused silica for photonics applications.

We report the realization of semi-transparent 3D microelectrodes fully embedded in a fused silica substrate by a combination of femtosecond laser microfabrication and inkjet printing. We also demonstrate the application of such electrodes in a proof-of-concept lab-on-chip device configuration, which acts as a liquid crystal molecular polarization rotator using on-chip electric fields. This work constitutes a first of its kind synergy between two widely used microfabrication techniques, femtosecond laser and inkjet, demonstrating a very efficient integration of optical, electrical and microfluidic components in a unique platform and thus enabling fast prototyping of 3D structured electro-optic lab-on-chips.

Low threshold Fabry-Perot optofluidic resonator fabricated by femtosecond laser micromachining.

We report the realization and characterization of an optofluidic microlaser based on a Fabry-Perot resonator fabricated by exploiting two direct writing fabrication techniques: the femtosecond laser micromachining and the inkjet printing technology. In this way a standard Fabry-Perot cavity has been integrated into an optofluidic chip. When using rhodamine 6G dissolved in ethanol at concentration of 5∙10-3 mol/l, laser emission was detected at a threshold energy density of 1.8 µJ/mm2 at least one order of magnitude lower than state-of-the-art optofluidic lasers. Linewidth below ~0.6 nm was measured under these conditions with a quality factor Q~103. These performances and robustness of the device makes it an excellent candidate for biosensing, security and environment monitoring applications.

Optical trapping induced by reorientational nonlocal effects in nematic liquid crystals.

We report a detailed analysis of optical trapping of low index particles in liquid crystals under experimental conditions that prevent the effect of conventional trapping originated by optical gradient forces. The observation of stable, long-range trapping shows that this phenomenon in liquid crystals is regulated by a completely different mechanism than in isotropic media. In particular, the role of the nonlocality of optical reorientation is highlighted by showing the dependence of the trapping force on the size of the reoriented area. A model based on the actual form of the Gaussian focused beam impinging on the liquid-crystalline medium in the trapping experiment is also reported, with good agreement with experimental data.

Optical and mechanical shrinkage effects in dye-doped photonic bandgap structures based on organic materials.

In this work we study the effects of the optical shrinkage in polymer and liquid crystal (LC) mixtures optimized for their use as active media in compact plastic laser devices. These mixtures are characterized by the presence of the rhodamine 6G as an active dye. Modifications in the reflection properties of the gratings as a function of the active dye concentration have been determined experimentally and a detailed theoretical simulation of the optical transmittance properties of these devices is provided. Moreover, the comparison between two different experimental approaches clarifies the contribution to the optical shrinkage due to the presence of the active dye. In principle this approach allows determining the linear mechanical shrinkage by separating the contribution to optical shrinkage due to photochemical transformations from that due to mechanical effects.

Determination of small anisotropy of holographic phase gratings.

We show the possibility of detecting small anisotropies in holographic polymer dispersed liquid-crystal samples, using a simple experimental setup that allows us to determine the behavior of the diffraction efficiency versus incident angle for two reading polarizations. This analysis is extremely sensitive to small changes in the parameters that define the grating anisotropy, giving us a way to determine with great accuracy the components of the modulated part of the dielectric tensor.