Genni Testa

Integrated silicon optofluidic ring resonator

The feasibility of an integrated silicon optofluidic ring resonator is demonstrated. Liquid core antiresonant reflecting optical waveguides are used to realize a rectangular ring resonator with a multimode interference liquid core coupler between the ring and the bus waveguide. In this configuration the same waveguide used to confine the light is able to deliver the liquid sample without the need for any additional microfluidics, resulting in a very compact device with a required liquid volume of about 0.11 nl. Optical characterization shows that ring with a good quality factor (Q ? 800) can be achieved in good agreement with the numerical results.

Integrated optofluidic Mach-Zehnder interferometer based on liquid core waveguides

We report the fabrication and the characterization of an integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides. The light is confined inside a low refractive index liquid core by antiresonant reflecting optical waveguide. Several asymmetric Mach–Zehnder interferometers have been realized with standard silicon technology. An optical characterization of the devices has been carried out by measuring the spectrum of optical transmitted intensity from two different Mach–Zehnder configurations. The results show that interferometers with a good visibility can be achieved in good agreement with the theoretical results.

A hybrid silicon-PDMS optofluidic platform for sensing applications

A hybrid silicon-poly(dimethysiloxane) (PDMS) optofluidic platform for lab-on-a-chip applications is proposed. A liquid-core waveguide with a self-aligned solid-core waveguide and a microfluidic device are integrated with a multilayer approach, resulting in a three-dimensional device assembly. The optofluidic layer was fabricated with a hybrid silicon-polymer technology, whereas the microfluidic layer was fabricated with a soft lithography technique. The combination of different materials and fabrication processes allows a modular approach, enabling both the benefits from the high optical quality achievable with silicon technology and the low cost of polymer processing. The proposed chip has been tested for fluorescence measurements on Cy5 water solutions, demonstrating the possibility to obtain a limit of detection of 2.5 nM.

Perfluorinated Plastic Optical Fiber Tapers for Evanescent Wave Sensing

In this work we describe the fabrication and the characterization of perfluorinated plastic-cladded optical fiber tapers. The heat-and-pull procedure has been used to fabricate symmetric tapers. Devices with different taper ratio have been produced and the repeatability of the process has been verified. The very low refractive indexes of the core-cladding perfluorinated polymers (n = 1.35−1.34) permit a strong enhancement of the evanescent wave power fraction in aqueous environments (n = 1.33), making them very attractive for evanescent wave sensing. The tapers have been characterized carrying out evanescent field absorbance measurements with different concentrations of methylene blue in water and fluorescence collection measurements in an aqueous solution containing Cy5 dye. A good sensitivity, tightly related to the low refractive index of the core-cladding materials and the geometrical profile, has been shown.

Liquid Core ARROW Waveguides by Atomic Layer Deposition

We report on the use of the atomic layer deposition (ALD) process for fabricating liquid core antiresonant reflecting optical waveguides (ARROWs). The ALD permits the deposition of a very conformal sub-100-nm titanium dioxide antiresonant layer. This results in a low loss liquid core ARROW waveguide with a broadband output transmission spectrum. Optical transmitted spectrum from the fabricated structure has been reported, and the measured attenuation losses agree with the theoretical predictions.

High-visibility optofluidic Mach–Zehnder interferometer

A high-visibility integrated optofluidic Mach-Zehnder interferometer based on liquid-core antiresonant reflecting optical waveguides is reported. The devices geometry has been optimized to minimize the intensity imbalance between the two arms for highly unbalanced Mach-Zehnder configurations. This results in a very compact device with a total length of only 2.5 mm and with required liquid volume of about 0.16 nl. High visibility is demonstrated for two interferometers corresponding to different sensing lengths. The devices have been optically characterized, and the measured interference fringes in the transmitted spectra show good agreement with the theoretical ones.

Micro flow cytometer with self-aligned 3D hydrodynamic focusing

A micro flow cytometer with a single step 3D hydrodynamic flow focusing has been developed. The proposed design is capable to create a single-file particle stream that is self-aligned with an integrated optical fiber-based detection system, regardless of the flow rate ratio between the focusing and core liquids. The design approach provides the ability to adjust the stream size while keeping the position of the focused stream centered with respect to the focusing channel. The device has been fabricated by direct micro milling of PMMA sheets. Experimental validation of the hydrodynamic sheath focusing effect has been presented and sample stream with tuneable size from about 18 to 50 μm was measured. Flow cytometry measurements have been performed by using 10-23 μm fluorescent particles. From the analysis of the signals collected at each transit event we can confirm that the device was capable to align and measure microparticles with a good coefficient of variance.

Optofluidic approaches for enhanced microsensor performances.

Optofluidics is a relatively young research field able to create a tight synergy between optics and micro/nano-fluidics. The high level of integration between fluidic and optical elements achievable by means of optofluidic approaches makes it possible to realize an innovative class of sensors, which have been demonstrated to have an improved sensitivity, adaptability and compactness. Many developments in this field have been made in the last years thanks to the availability of a new class of low cost materials and new technologies. This review describes the Italian state of art on optofluidic devices for sensing applications and offers a perspective for further future advances. We introduce the optofluidic concept and describe the advantages of merging photonic and fluidic elements, focusing on sensor developments for both environmental and biomedical monitoring.

High sensitivity UV fluorescence spectroscopy based on an optofluidic jet waveguide.

A novel spectroscopic sensor based on an optofluidic liquid jet waveguide is presented. In this device, a liquid jet waveguide is generated with the solution under analysis. This stream, exploiting total internal reflection, acts as an optical waveguide confining the autofluorescence light produced by chemical or biological samples when opportunely excited. Using a self-aligned configuration, the liquid jet is directly coupled with a multimode optical fiber collecting the fluorescence towards the detection system. Experimental measurements have been performed using an UV excitation source on water solutions containing representative water pollutants as aromatic hydrocarbons or bacteria showing very low limit of detection.

Integrated tunable liquid optical fiber

We present an integrated tunable liquid-core/liquid-cladding (L2) optical fiber, based on a novel three-dimensional hydrodynamic focusing scheme that enables the production of a tunable circular liquid core located in the center of the channel, regardless of the flow-rate ratio of the cladding and core liquids.