[show abstract][hide abstract] ABSTRACT: We report on the experimental demonstration of a novel silicon based fully integrated nonlinear Mach Zehnder device. A standard silicon waveguide is used as a nonlinear arm, conversely a large mode SU-8 waveguide acts as a purely linear arm. Given this asymmetry, an intensity dependent phase shift can be introduced between the two interferometric arms. Thanks to a fine tuning of the silicon arm optical properties, a low power, ultrafast, picosecond operation is demonstrated, allowing the use of this device for ultrafast all-optical signal processing in high density communication networks.
[show abstract][hide abstract] ABSTRACT: A new approach to measure the refractive index of a given material, in
its whole transparency window and within a single-shot, is proposed.
This method, which requires the use of only few and common optical
elements, is based on the analysis of the transmission function of a
single etalon fabricated with the material under test, and can be used
also to directly evaluate the sample birefringence with high accuracy.
Method's effectiveness is verified on both isotropic and birefringent
samples with known optical properties in the 0.7-1.65μm
wavelength range. Using the proposed method, the refractive index can be
estimated with accuracy of the order of 10-4.
[show abstract][hide abstract] ABSTRACT: The photorefractive effect induced by 775-nm laser light on doped lithium niobate crystals is investigated by the direct observation in the far field of the transmitted-beam distortion as a function of time. Measurements performed at various Zr-doping concentrations and different light intensities show that the 775-nm light beam induces a steady-state photorefractive effect comparable to that of 532-nm light, but the observed build-up time of the photovoltaic field is longer by three-orders of magnitude. The 775-nm photorefractivity of lithium niobate crystals doped with 3 mol. % ZrO2 or with 5.5 mol. % MgO is found to be negligible.
[show abstract][hide abstract] ABSTRACT: We investigate the applicability of highly reduced lithium niobate samples doped with iron for the use as optoelectronic tweezers. Increasing the reduction degree of Fe-doped lithium niobate is well known to increase the photoconductivity and reduce the writing time of internal space-charge fields. Based on our measurements of the photorefractive properties, we determine the optimal conditions for dielectrophoretic trapping and present the application of Fe-doped lithium niobate as optoelectronic tweezers. For higher reduction degrees, an unexpected decrease in the photovoltaic current density and the saturation space-charge field is reported.
[show abstract][hide abstract] ABSTRACT: In this paper, we determine the optical nonlinear coefficient of hydrogenated amorphous silicon (a-Si:H) waveguides. Up to date, the data reported in the scientific literature for similar structures show a very large variability and the final assessment of their nonlinear performance is still an open issue. We performed a complete and careful characterization of more than 50 waveguides. A nonlinear coefficient of 790 + j20 W-1 m-1 was found, confirming that a-Si:H is a good candidate for nonlinear silicon photonic devices. Nevertheless, free-carrier-dynamics exhibits a recombination time in the nanosecond range, which can hinder their exploitation in ultrafast applications requiring high-power optical beams.
[show abstract][hide abstract] ABSTRACT: Optofluidic microsystems are key components towards lab-on-a-chip devices for manipulation and analysis of biological specimens. In particular, the integration of optical tweezers (OT) in these devices allows stable sample trapping, while making available mechanical, chemical and spectroscopic analyses.
[show abstract][hide abstract] ABSTRACT: We present the characterization of the ultrafast nonlinear dynamics of a CMOS-compatible horizontal-slot waveguide with silicon nanocrystals. Results are compared to strip silicon waveguides, and modeled with nonlinear split-step calculations. The extracted parameters show that the slot waveguide has weaker carrier effects and better nonlinear figure-of-merit than the strip waveguides.
[show abstract][hide abstract] ABSTRACT: The combination of high power laser beams with microfluidic delivery of cells is at the heart of high-throughput, single-cell analysis and disease diagnosis with an optical stretcher. So far, the challenges arising from this combination have been addressed by externally aligning optical fibres with microfluidic glass capillaries, which has a limited potential for integration into lab-on-a-chip environments. Here we demonstrate the successful production and use of a monolithic glass chip for optical stretching of white blood cells, featuring microfluidic channels and optical waveguides directly written into bulk glass by femtosecond laser pulses. The performance of this novel chip is compared to the standard capillary configuration. The robustness, durability and potential for intricate flow patterns provided by this monolithic optical stretcher chip suggest its use for future diagnostic and biotechnological applications.
[show abstract][hide abstract] ABSTRACT: The main trend in optofluidics is currently towards full integration of the devices, thus improving automation, compactness and portability. In this respect femtosecond laser microfabrication is a very powerful technology given its capability of producing both optical waveguides and microfluidic channels. The current challenge in biology is the possibility to perform bioassays at the single cell level to unravel the hidden complexity in nominally homogeneous populations. Here we report on a new device implementing a fully integrated fluorescence-activated cell sorter. This non-invasive device is specifically designed to operate with a limited amount of cells but with a very high selectivity in the sorting process. Characterization of the device with beads and validation with human cells are presented.
Lab on a Chip 08/2012; 12(19):3779-84. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on wavelength conversion through four-wave-mixing in silicon slot-waveguides with embedded silicon nanocrystals. The combination of strong optical confinement and Si:nc nonlinearity provides a huge waveguide nonlinear coefficient gamma 1100 W�^-1 m^-1. Moreover, the improvement in the fabrication procedure allowed a loss reduction with respect to previous reported structures, enabling the achievement of an extreme value for the conversion efficiency which represents the best result ever reported in the scientific literature.
[show abstract][hide abstract] ABSTRACT: Numerical tools for the evaluation of optical forces exerted by non-focused Gaussian beams are becoming increasingly important for the design of integrated devices dedicated to cell manipulation without physical contact. Here we consider two methods for the evaluation of optical forces based on a ray-optics approach and we compare them with experimental results. We show that optical forces can be calculated with good accuracy also within the Rayleigh range of the Gaussian beam and for a wide range of particle sizes.
Journal of optics 06/2011; 13(7):075712. · 1.99 Impact Factor
[show abstract][hide abstract] ABSTRACT: Measurements of refractive indices, electro-optic coefficients and photorefractivity are performed for a set of Zirconium-doped congruent lithium niobate (Zr:LN) crystals as functions of the dopant concentration in the range 0.0-3.0 mol%. The photorefractive properties are studied by measuring the green-light induced birefringence change and by direct observation of the transmitted-beam distortion. The index of refraction data show that the threshold concentration, above which there is a change in the Zr incorporation mechanism, is about 2.0 mol%, but photorefractivity results suggest that the concentration of ZrO(2) required to strongly reduce the photorefractive effect is somewhat larger than the 2.0 mol% "threshold" concentration derived from index-of-refraction data. The electro-optic coefficients are little influenced by Zr-doping. All the reported results confirm that Zr:LN is a very promising candidate for the realization of efficient electro-optic and all-optical nonlinear devices working at room temperature.
[show abstract][hide abstract] ABSTRACT: The objective of this study was to examine the in vitro effect of a single or a multiple doses of low-level laser irradiation (LLLI) on proliferation of the human osteosarcoma cell line, SAOS-2. SAOS-2 cells were divided in five groups and exposed to LLLI (659 nm diode laser; 11 mW power output): group I as a control (dark), group II exposed to a single laser dose of 1 J/cm2, group III irradiated with a single dose of 3 J/cm2, and group IV and V exposed for three consecutive days to 1 or 3 J/cmÂ², respectively. Cellular proliferation was assessed daily up to 7 days of culturing. The obtained results showed an increase in proliferative capacity of SAOS-2 cells during the first 96 h of culturing time in once-irradiated cells, as compared to control cells. Furthermore, a significantly higher proliferation in the group IV and V was detected if compared to a single dose or to control group after 96 h and 7 days. In conclusion, the effect of the single dose on cell proliferation was transitory and repeated irradiations were necessary to observe a strong enhancement of SAOS-2 growth. As a future perspective, we would like to determine the potential of LLLI as a new approach for promoting bone regeneration onto biomaterials.
[show abstract][hide abstract] ABSTRACT: .¢" ... . .. . , ¢ � The experimental data show that the minimum dopant concentration required to strongly reduce the photorefractive effect is close to 2% (in accordance with ), and that the presence of Zr in the crystal lattice doesn't reduce the electro-optical properties of the crystal. The impact of the dopant concentration on the ordinary and extraordinary refractive indices was also evaluated. The obtained results indicate that Zr:LN can be a very good candidate for the design of efficient nonlinear all-optical devices.
[show abstract][hide abstract] ABSTRACT: We report on characterisation of Four-Wave-Mixing efficiency and bandwidth in slot waveguides with embedded silicon nanocrystals (Si-nc). Extreme nonlinear properties are measured (γTM=1100W-1m-1) that can be ascribed to interplay of high confinement and Si-nc nonlinearity.
[show abstract][hide abstract] ABSTRACT: We present an optofluidic monolithic chip for the study of mechanical properties of single cells by means of optical forces. The chip is fabricated by femtosecond laser micromachining in a fused-silica substrate.
[show abstract][hide abstract] ABSTRACT: We present successful trapping and manipulation of red blood cells by miniaturized optical tweezers based on optical fibers. Tweezers are obtained by fabricating micro-beam deflectors on a fiber-bundle output facet by two photon lithography
[show abstract][hide abstract] ABSTRACT: In this work we study the photorefractive and electro-optical properties of Zirconium-doped congruent lithium niobate (LN) crystals. In order to set the ground for the utilization of these crystals in nonlinear wavelengthconversion devices, we investigate the dependence of the photorefractive properties of the crystals on dopant concentration and incident power. In our experiments the birefringence variations induced by a 532-nm laser beam are measured by using the Sénarmont method, in the ZrO2 concentration range 0-3mol% and intensity range 155- 1800 W/cm2. In order to investigate photorefractivity at high intensities, we have also utilized the direct observation of the distortion of the light spot transmitted by the crystal. In presence of photorefractivity, the transmitted light spot becomes smeared and elongated along the c-axis. Our data show that the threshold ZrO2 concentration can be in the range 2.5-3mol%. Considering that the growth of large homogeneous Zr:LN crystals should be easier than for Mg:LN, and that electrical poling of these crystals has already been demonstrated, Zr-doped LN could represent a more convenient choice than Mg:LN for the realization of room-temperature wavelength converters.
[show abstract][hide abstract] ABSTRACT: A frequency shifting device is fabricated and tested in a ferroelectric waveguide in a low-photorefractivity crystal. Periodic poling for quasi-phase-matching and channels for operation in the near-infrared C-band were obtained in congruent lithium tantalate, demonstrating for the first time both wave confinement and two-stage parametric conversion in such waveguides.