Armando Ricciardi

Optical guided mode resonance filter on a flexible substrate

We demonstrate the operation of a flexible optical filter based on guided mode resonances that operates in the visible regime. The filter is fabricated on a free standing polymeric membrane of 1.3 μm thickness and we show how the geometrical design parameters of the filter determine its optical properties, and how various types of filter can be made with this scheme. To highlight the versatility and robustness of the approach, we mount a filter onto a collimated fibre output and demonstrate successful wavelength filtering.

Surface sensitivity of Rayleigh anomalies in metallic nanogratings

Sensing schemes based on Rayleigh anomalies (RAs) in metal nanogratings exhibit an impressive bulk refractive-index sensitivity determined solely by the grating period. However, the surface sensitivity (which is a key figure of merit for label-free chemical and biological sensing) needs to be carefully investigated to assess the actual applicability of this technological platform. In this paper, we explore the sensitivity of RAs in metal nanogratings when local refractive-index changes are considered. Our studies reveal that the surface sensitivity deteriorates up to two orders of magnitude by comparison with the corresponding bulk value; interestingly, this residual sensitivity is not attributable to the wavelength shift of the RAs, which are completely insensitive to local refractive-index changes, but rather to a strictly connected plasmonic effect. Our analysis for increasing overlay thickness reveals an ultimate surface sensitivity that approaches the RA bulk value, which turns out to be the upper-limit of grating-assisted surface-plasmon-polariton sensitivities.

Lab-on-fiber technology

Multimaterial Fibers.- Monolithic Silicon Photonic Crystal Fiber Tip Sensors.- Electrohydrodinamic Dispenser for Delivering Multiphase Samples at Nanoscale.- Lab-on-Fiber Technology: Towards Multifunctional Optical Nanoprobes.- Functional Metamaterials for Lab-on-a-fiber.- Nanofibers as Valuable Technological Platform for Lab on Fiber.- Lab-on-Fiber by Using the Breath Figures Technique.- Hybrid Nanoimprint-Soft Lithography for Highly Curved Surface with Sub-15 nm Resolution .- Overview of Micro- and Nanostructured Fiber Sensors .- Nanophotonics Within Silica Structured Optical Fibres.- Miniaturized Optical Tweezers Through Fiber-End Microfabrication.- Silicon-on-Insulator Microring Resonator Sensor Integrated on an Optical Fiber Facet.- Optical Fibers as Platforms for Subwavelength Plasmonic Structures..- Fiber-top and Ferrule-top Micromachined Devices: A New Platform of All-optical Sensors and Actuators.- Hydrogen Detection Using a Single Palladium Nano-aperture on a Fiber Tip.- Sensitive and Selective Lab-on-a-Fiber Sensor for Bacteria Detection in Water.- Photonic Crystal Fiber as a Lab-in-Fiber Optofluidic Platform.

Tuning efficiency and sensitivity of guided resonances in photonic crystals and quasi-crystals: a comparative study

In this paper, we present a comparative study of the tuning efficiency and sensitivity of guided resonances (GRs) in photonic crystal (PC) holed slabs based on periodic and aperiodically-ordered unit cells, aimed at assessing the applicability of these important technology platforms to ultra-compact optical sensors and active devices. In particular, with specific reference to square-lattice periodic PCs and aperiodically-ordered Ammann-Beenker photonic quasi-crystals, we study the effects of the hole radius, slab thickness, and refractive index on the GR sensitivity and tunability with respect to variation in the hole refractive index. Finally, we carry out a theoretical and numerical analysis in order to correlate the GR shift with the field distribution of the unperturbed (air holes) structures. Our results indicate that the spatial arrangement of the holes may strongly influence the tuning and sensitivity efficiency, and may provide new degrees of freedom and tools for the design and optimization of novel photonic devices for both sensing and telecommunication applications.

Experimental evidence of guided-resonances in photonic crystals with aperiodically ordered supercells

We report on the first experimental evidence of guided resonances (GRs) in photonic crystal slabs based on aperiodically ordered supercells. Using Ammann-Beenker (quasiperiodic, eightfold symmetric) tiling geometry, we present our study on the fabrication, experimental characterization, and full-wave numerical simulation of two representative structures (with different filling parameters) operating at near-IR wavelengths (1300-1600 nm). Our results show a fairly good agreement between measurements and numerical predictions and pave the way for the development of new strategies (based on, e.g., the lattice symmetry breaking) for GR engineering.

Guided resonances in photonic crystals with point-defected aperiodically-ordered supercells

In this paper, we study the excitation of guided resonances (GRs) in photonic-crystal slabs based on point-defected aperiodically-ordered supercells. With specific reference to perforated-slab structures and the Ammann-Beenker octagonal lattice geometry, we carry out full-wave numerical studies of the plane-wave responses and of the underlying modal structures, which illustrate the representative effects induced by the introduction of symmetry-preserving and symmetry-breaking defects. Our results demonstrate that breaking the supercell mirror symmetries via the judicious introduction of point-defects enables for the excitation of otherwise uncoupled GRs, with control on the symmetry properties of their field distributions, thereby constituting an attractive alternative to those GR-engineering approaches based on the asymmetrization of the hole shape. In this framework, aperiodically-ordered supercells seem to be inherently suited, in view of the variety of inequivalent defect sites that they can offer.

Optical Guidance Systems for Epidural Space Identification

Epidurals are the most diffused loco-regional techniques for the relief of operative, postoperative, and chronic pain and are used for about 50% of deliveries. Currently, doctors still identify epidural space relying on subjective perception, by using “blind” manual techniques to which are associated failure rate up to 7%. In the last years, many systems aimed at assisting and guiding the placement of epidural needle have been proposed. In particular, optical systems basically rely on the integration inside the epidural needle lumen of optical fiber probes providing real-time discrimination of differing tissue types during needle penetration. In this study, aside of providing an exhaustive overview on the systems proposed so far, we also report on a novel sensorized medical needle, based on the judicious integration of a fiber Bragg grating sensor inside the epidural needle lumen. Our device, by providing continuous and real-time measurements of the pressure experienced by the needle tip during its advancement, is able to effectively detect the needle passage from one tissue to the other. A pilot study carried out on an epidural training phantom demonstrates the validity of our approach for making the needle placement into the epidural space easier and safer.

Microgel assisted Lab-on-Fiber Optrode

Precision medicine is continuously demanding for novel point of care systems, potentially exploitable also for in-vivo analysis. Biosensing probes based on Lab-On-Fiber Technology have been recently developed to meet these challenges. However, devices exploiting standard label-free approaches (based on ligand/target molecule interaction) suffer from low sensitivity in all cases where the detection of small molecules at low concentrations is needed. Here we report on a platform developed through the combination of Lab-On-Fiber probes with microgels, which are directly integrated onto the resonant plasmonic nanostructure realized on the fiber tip. In response to binding events, the microgel network concentrates the target molecule and amplifies the optical response, leading to remarkable sensitivity enhancement. Moreover, by acting on the microgel degrees of freedom such as concentration and operating temperature, it is possible to control the limit of detection, tune the working range as well as the response time of the probe. These unique characteristics pave the way for advanced label-free biosensing platforms, suitably reconfigurable depending on the specific application.

Simple technique for integrating compact silicon devices within optical fibers

In this work, we present a simple fabrication process enabling the integration of a subwavelength amorphous silicon layer inside optical fibers by means of the arc discharge technique. To assess our method, we have fabricated a compact in-line Fabry-Perot interferometer consisting of a thin (<1  μm) a-Si:H layer completely embedded within a standard single-mode optical fiber. The device exhibits low loss (1.3 dB) and high interference fringe visibility (~80%) both in reflection and transmission, due to the high refractive index contrast between silica and a-Si:H. A high linear temperature sensitivity up to 106  pm/°C is demonstrated in the range 120°C-400°C. The proposed interferometer is attractive for point monitoring applications as well as for ultrahigh-temperature sensing in harsh environments.

Fast and slow light in optical fibers through tilted fiber Bragg gratings

In this paper, slow and fast light in optical fiber through tilted fiber Bragg grating (TFBG) are reported. The experimental results show the capability of TFBGs to enable group velocity control of an optical pulse in optical fiber, due to the anomalous dispersion features induced by the coupling between the propagating core mode and each counter-propagating coupling cladding mode. In particular, superluminal propagation of a pulse train has been observed at optical communication wavelengths with time advancements in the picoseconds time scale in 1cm long TFBG and group velocity as large as about two times the speed of light in optical fiber (approximately 1.3 x c0). Very good agreement has been obtained comparing the measured group delay of the TFBG with the one retrieved from the amplitude response through Hilbert transform. Finally, tunable slow and fast light has also been reported, demonstrating the possibility to control the group velocity at single wavelength through both fluidic and thermal actuation.