Publications on Intenational Jounals
J1. Farnesi D, Chiavaioli F, Righini GC, Soria S, Trono C, Jorge P, Nunzi Conti G (2014). “Long period grating-based fiber coupler to whispering gallery mode resonators”. Optics Letters, vol. 39 (22), p. 6525-6528.
Abstract: We present a new method for coupling light to high-Q silica whispering gallery mode resonators (WGMs) that is based on long period fiber gratings (LPGs) written in silica fibers. An LPG allows selective excitation of high-order azimuthally symmetric cladding modes in a fiber. Coupling of these cladding modes to WGMs in silica resonators is possible when partial tapering of the fiber is also implemented in order to reduce the optical field size and increase its external evanescent portion. Importantly, the taper size is about one order of magnitude larger than that of a standard fiber taper coupler. The suggested approach is therefore much more robust and useful especially for practical applications. We demonstrate coupling to high-Q silica microspheres and microbubbles detecting the transmission dip at the fiber output when crossing a resonance. An additional feature of this approach is that by cascading LPGs with different periods, a wavelength selective addressing of different resonators along the same fiber is also possible.
J2. Chiavaioli F, Biswas P, Trono C, Bandyopadhyay S, Giannetti A, Tombelli S, Basumallick N, Dasgupta K, Baldini F (2014). “Towards sensitive label-free immunosensing by means of turn-around point long period fiber gratings”. Biosensors and Bioelectronics, vol. 60, p. 305-310.
Abstract. Long period fiber gratings have been effectively used in the field of biochemical sensing since a few years. Compared to other well-known label-free optical approaches, long period gratings (LPGs) take advantage of the typical peculiarity of optical fibers. Coupling the propagating core mode with a high-order cladding mode near its turn-around point (TAP) was the strategy adopted to achieve good performances without additional coatings, except for the sensing and selective bio-layer deposited on the fiber. Both the modeling and manufacturing of TAP LPGs were discussed. After the functionalization of the fiber surface with the deposition of a Eudragit L100 copolymer layer followed by immunoglobulin G (IgG) covalent immobilization, an IgG/anti-IgG bioassay was implemented along the grating region and the kinetics of antibody/antigen interaction was analyzed. A quantitative comparison between a TAP LPG and a non-TAP LPG was carried out to highlight the improvement of the proposed immunosensor. The real effectiveness and feasibility of an LPG-based biosensor were demonstrated by using a complex matrix consisting of human serum, which also confirmed the specificity of the assay, and a limit of detection of 70 μg L–1 (460 pM) was achieved.
J3. Chiavaioli F, Trono C, Giannetti A, Brenci M, Baldini F (2014). “Characterisation of a label-free biosensor based on long period grating”. J. Biophotonics, vol. 7(5), p. 312-322.
Abstract. Optical fibre gratings, especially long period gratings, have been recently proposed as optical devices for biochemical sensing. A biochemical interaction along the grating portion induces a refractive index change and hence a change in the fiber transmission spectrum. This provides an alternative methodology with respect to other label-free optical approaches, such as surface plasmon resonance, interferometric configurations and optical resonators. The fibre bio-functionalization has been carried out by means of a novel chemistry using Eudragit L100 copolymer as opposed to the commonly used silanization procedure. Antigen-antibody interaction has been analysed by means of an IgG/anti-IgG bioassay. The biosensor was fully characterised, monitoring the kinetics during the antibody immobilization and the antigen interaction and achieving the calibration curve of the assay. A comparison of the biosensor performance was made by using two different long period gratings with distinct periods.
J4. Chiavaioli F, Trono C, Baldini F (2013). “Specially designed long period grating with internal geometric bending for enhanced refractive index sensitivity”. Applied Physics Letters, vol. 102(23), p. 231109(4pp).
Abstract. We propose a long period grating (LPG) characterized by specially designed refractive index (RI) profile in which each grating plane is tilted at increasing angles, as moving away from the center of symmetry of the structure towards its both edges. This internally manufactured geometric structure, which basically simulates the bending of an optical fiber, increases the RI sensitivity of an LPG to the external medium. We experimentally demonstrate a three-fold improvement in the RI sensitivity, thus providing the basis for another step forward in the field of RI sensors based on optical fiber gratings.
J5. Pilla P, Trono C, Baldini F, Chiavaioli F, Giordano M, Cusano A (2012). “Giant sensitivity of long period gratings in transition mode near the dispersion turning point: an integrated design approach”. Optics Letters, vol. 37 (19), p. 4152-4154.
Abstract. We report an original design approach based on the modal dispersion curves for the development of long period gratings in transition mode near the dispersion turning point exhibiting ultrahigh refractive index sensitivity. The theoretical model predicting a giant sensitivity of 9900 nm per refractive index unit in a watery environment was experimentally validated with a result of approximately 9100 nm per refractive index unit around an ambient index of 1.3469. This result places thin film coated LPGs as an alternative to other fiber-based technologies for high-performance chemical and biological sensing applications.
