Cicero Martelli

Water-core Fresnel fiber

A water core photonic crystal Fresnel fiber exploiting a hole distribution on zone plates of a cylindrical waveguide was developed and characterized. This fiber has similar guiding properties as the pristine air-hole guiding fiber although a large loss edge ~900nm is observed indicating that the bandgap associated with Fresnel guidance has shifted to longer wavelengths. The absorption bands of the water in the region of the NIR were observed. The application to biosensing is discussed.

Strain and temperature characterization of photonic crystal fiber Bragg gratings.

A Bragg grating in a photonic crystal fiber was written and its dependence with temperature and strain analyzed. The two observed Bragg wavelengths correspond to a fundamental and a higher-order mode in the optical fiber. The temperature and strain calibration curves for both modes are measured and found to be distinct. The general properties of gratings in these fibers, and their implications, are enunciated.

Micromachining structured optical fibers using focused ion beam milling

A focused ion beam is used to mill side holes in air-silica structured fibers. By way of example, side holes are introduced in two types of air-structured fiber, (1) a photonic crystal four-ring fiber and (2) a six-hole single-ring step-index structured fiber.

Hydrostatic Pressure Sensing with High Birefringence Photonic Crystal Fibers

The effect of hydrostatic pressure on the waveguiding properties of high birefringence photonic crystal fibers (HiBi PCF) is evaluated both numerically and experimentally. A fiber design presenting form birefringence induced by two enlarged holes in the innermost ring defining the fiber core is investigated. Numerical results show that modal sensitivity to the applied pressure depends on the diameters of the holes, and can be tailored by independently varying the sizes of the large or small holes. Numerical and experimental results are compared showing excellent agreement. A hydrostatic pressure sensor is proposed and demonstrated using an in-fiber modal interferometer where the two orthogonally polarized modes of a HiBi PCF generate fringes over the optical spectrum of a broad band source. From the analysis of experimental results, it is concluded that, in principle, an operating limit of 92 MPa in pressure could be achieved with 0.0003% of full scale resolution.

Water-soluble porphyrin detection in a pure-silica photonic crystal fiber

Aqueous solutions of the water-soluble porphyrin 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinatomanganese(III) acetate were inserted into the holes of a photonic crystal fiber, and the porphyrin absorption bands were identified. Results were obtained for three concentrations. The porphyrins in water show no surface interactions with the silica walls of the capillary channels. We discuss the implications for future hybrid electronic and photonic fiber devices.

Gratings in Structured Optical Fibres

Grating writing in structured optical fibres and their properties and applications are reviewed. To date, most gratings have been written in a straightforward manner into structured fibres containing a photosensitive germanosilicate step-index core. However, gratings have also been written directly into single material, structured silica fibres and into air-clad cores using two and higher-photon processes with both UV and near IR pulsed (nanosecond-femtosecond) light. Given the intrinsic-added functionality possible within a structured optical fibre, structured fibre gratings offer further capabilities for sensors, diagnostics, lasers, and devices.

Evanescent-Field Spectroscopy using Structured Optical Fibers: Detection of Charge-Transfer at the Porphyrin-Silica Interface

The fabrication of porphyrin thin films derived from dichloro[5,10,15,20-tetra(heptyl)porphyrinato]tin(IV) [Cl-Sn(THP)-Cl] in the holes of photonic crystal fibers over 90 cm in length is described. Evanescent field spectroscopy (EFS) is used to investigate the interfacial properties of the films, with the high surface optical intensity and the long path length combining to produce significant absorption. By comparison with results obtained for similar films formed from Cl-Sn(THP)-Cl inside fused-silica cuvettes and on glass slides, the film is shown to be chemisorbed as a surface Si-O-Sn(THP)-X (X = Cl or OH) species. In addition to the usual porphyrin Q and Soret bands, new absorptions in the in-fiber films are observed by EFS at 445 nm and between 660-930 nm. The 660-930 nm band is interpreted as a porphyrin to silicon charge-transfer transition and postulated to arise following chemisorption at mechanical-strain induced defect sites on the silica surface. Such defect sites are caused by the optical fiber production process and are less prevalent on other glass surfaces. EFS within optical fibers therefore offers new ways for understanding interface phenomena such as surface adsorbates on glass. Such understanding will benefit all devices that exploit interface phenomena, both in optical fibers and other integrated waveguide forms. They may be directly exploited to create ultrasensitive molecular detectors and could yield novel photonic devices.

Bend loss in structured optical fibres

Bend loss characterisation tests are carried out in two air-silica structured fibres: a periodic photonic crystal fibre and a non-periodic fibre. An explanation based on resonant coupling between interstitial zones accounts for the improved confinement of non-periodic structured optical fibres.

White light sources based on multiple precision selective micro-filling of structured optical waveguides

Multiple precision selective micro-filling of a structured optical fibre using three luminescent dyes enables the simultaneous capture of red, blue and green luminescence within the core to generate white light. The technology opens up a new approach to integration and superposition of the properties of multiple materials to create unique composite properties within structured waveguides.

Refractive index measurement within a photonic crystal fibre based on short wavelength diffraction

A new class of refractive index sensors using solid PCF is demonstrated. Refractive indices of water and ice are measured during the ice lh formation inside of the fibre holes.