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We present a simple and practical strategy that allows to design high-efficiency grating couplers. The technique is based on the simultaneous apodization of two structural parameters: the grating period and the fill-factor, along with the optimization of the grating coupler etching depth. Considering a 260 nm Si-thick Silicon-on-insulator platform, we numerically demonstrated a coupling efficiency of −0.8 dB (83%), well matching the experimental value of −0.9 dB (81%). Thanks to the optimized design, these results represent the best performance ever reported in the literature for SOI structures without the use of any back-reflector.

Silicon nitride has become increasingly prominent in the integrated photonics research community during the last two decades, with an ever-growing number of demonstrations reported for different applications. In particular, thin-film silicon nitride platforms are attracting increasing interest thanks to the possibility of achieving ultra-low propagation loss due to their weak mode-field confinement. However, the realization of efficient grating couplers in the thin-film silicon nitride platforms is extremely challenging due to the poor grating scattering strength. In this work, we propose and experimentally demonstrate a grating coupler for perfectly-vertical fiber-to-chip efficient coupling to thin-film silicon nitride waveguides. The device consists of a silicon-rich silicon nitride apodized grating on top of a 150 nm-thick silicon nitride waveguide. Unlike most previously demonstrated bi-layer grating couplers, which typically employ an amorphous silicon layer to enhance the grating efficiency, the use of a top silicon-rich silicon nitride grating offers improved fabrication tolerances and gives an additional degree of freedom in the design of efficient grating couplers. A record coupling efficiency of -1.78 dB at 1550 nm was experimentally measured without employing any back-reflector or index-matching fluid, demonstrating the device’s potential for efficient and fabrication-tolerant fiber-to-chip coupling on thin-film silicon nitride platforms.

We propose and demonstrate an on-chip optofluidic device allowing active oscillatory microrheological measurements with sub- μ L sample volume, low cost and high flexibility. Thanks to the use of this optofluidic microrheometer it is possible to measure the viscoelastic properties of complex fluids in the frequency range 0.01–10 Hz at different temperatures. The system is based on the optical forces exerted on a microbead by two counterpropagating infrared laser beams. The core elements of the optical part, integrated waveguides and an optical modulator, are fabricated by fs-laser writing on a glass substrate. The system performance is validated by measuring viscoelastic solutions of aqueous worm-like micelles composed by Cetylpyridinium Chloride (CPyCl) and Sodium Salicylate (NaSal).

Nonlinear integrated photonics, which takes advantage of the strong field enhancement in integrated waveguides to boost the efficiency of nonlinear effects, has paved the way for the demonstration of cutting-edge applications. These achievements have also been made possible by the impressive progress in material engineering and fabrication processes, which have enabled a remarkable control of the nonlinear dynamics in the waveguides. While researchers initially focused their attention on single-mode devices, in recent years, the exploitation of nonlinear effects in integrated multimode waveguides has attracted significant interest. Indeed, the simultaneous use of different spatial modes of the same multimode waveguide has opened new avenues in the realization of integrated nonlinear processors, thanks to the ability to tune the dispersion profiles of the different modes. In this review, we discuss the most recent advances in nonlinear multimode photonics on-chip. In the first part, we review the use of intermodal nonlinear effects for frequency generation. The use of intermodal nonlinear effects has been extensively reported, for example, for wavelength conversion for telecom applications, generation of photon pair sources for quantum optics and mid-infrared frequency generation. Then, we discuss several demonstrations of nonlinear multimode waveguides used to perform simultaneous multi-channel and multi-functional optical signal processing, such as nonlinear switching and logic operations. Next, supercontinuum generation in nonlinear multimode waveguides will be discussed. Finally, we report the use of high-quality-factor micro-resonators based on multimode waveguides for the realization of compact and widely-tunable integrated Raman lasers and optical frequency comb sources with record-low threshold power.

Optoelectronic tweezers (OET) are a promising technique for the realization of reconfigurable systems suitable to trap and manipulate microparticles. In particular, dielectrophoretic (DEP) forces produced by OET represent a valid alternative to micro-fabricated metal electrodes, as strong and spatially reconfigurable electrical fields can be induced in a photoconductive layer by means of light-driven phenomena. In this paper we report, and compare with the experimental data, the results obtained by analyzing the spatial configurations of the DEP-forces produced by a 532 nm laser beam, with Gaussian intensity distribution, impinging on a Fe-doped Lithium Niobate substrate. Furthermore, we also present a promising preliminary result for water-droplets trapping, which could open the way to the application of this technique to biological samples manipulation.

In this work, we show the design of a silicon photonic-based polarization converting device based on the integration of semiconduction InP nanowires on the silicon photonic platform. We present a comprehensive numerical analysis showing that full polarization conversion (from quasi-TE modes to quasi-TM modes, and vice versa) can be achieved in devices exhibiting small footprints (total device lengths below 20 µm) with minimal power loss (<2 dB). The approach described in this work can pave the way to the realization of complex and re-configurable photonic processors based on the manipulation of the state of polarization of guided light beams.

NRC publication: Yes

In the present work, an integrated optofluidic chip for fluid viscosity measurements in the range from 1 mPa·s to 100 mPa·s is proposed. The device allows the use of small sample volumes (<1 µL) and the measurement of viscosity as a function of temperature. Thanks to the precise control of the force exerted on dielectric spheres by optical beams, the viscosity of fluids is assessed by comparing the experimentally observed movement of dielectric beads produced by the optical forces with that expected by numerical calculations. The chip and the developed technique are validated by analyzing several fluids, such as Milli-Q water, ethanol and water–glycerol mixtures. The results show a good agreement between the experimental values and those reported in the literature. The extremely reduced volume of the sample required and the high flexibility of this technique make it a good candidate for measuring a wide range of viscosity values as well as for the analysis of nonlinear viscosity in complex fluids.

Optical tweezers represent a powerful tool for a variety of applications both in biology and in physics. Standard optical tweezers make use of a freely propagating laser beam that is tightly focused near the sample by means of a high-numerical-aperture microscope objective. Most of the limitations associated with the microscope's bulky structure could be overcome by exploiting optical fibres for the delivery of the trapping radiation, provided that proper beam-shaping is performed. Here we present the design and the realization of a miniaturized single-fibre optical tweezer that is able to create a purely optical three-dimensional trap. The tweezer uses engineered fibre structures with microstructured end surfaces, and its effectiveness is demonstrated by trapping 10-µm-diameter polystyrene beads. The optical tweezer is able to provide optical manipulation and analysis of microscale specimens and could be the fundamental building block in future integrated fibre-based devices.

In this work we fabricate and validate two optofludic devices for the manipulation and analysis of single cells. The chips are fabricated by femtosecond laser micromachining exploiting the 3D capabilities of the technique and the inherent perfect alignment between microfluidic channels and optical networks. Both devices have been validated by probing the mechanical properties of different cancer cell lines, which are expected to show different elasticity because of their different metastatic potential.