Search

PART ONE: The "Lab on Fiber" concept envisions novel and highly functionalized technological platforms completely integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems to be incorporated in modern optical systems for communication and sensing applications. The realization of integrated optical fiber devices requires that several structures and materials at nano and micro scale are constructed, embedded and connected all together to provide the necessary physical connections and light-matter interactions. This paper reviews the strategies, the main achievements and related devices in the "Lab on Fiber" roadmap discussing perspectives and challenges that lie ahead. PART TWO: After having reviewed, in the previous part, the main results achieved in the "Lab o Fiber" roadmap through the development of several wavelength-scale devices and components based on the lab on fiber concept, here we focus the attention on new trends involving innovative nano-fabrication strategies enabling to exploit further intriguing photonic and/or plasmonic phenomena at the forefront of optical research. Novel complex fabrication techniques of "Lab-on-fiber" device at the nanoscale are here presented and discussed, from advanced multi material stacks and drawing technique up to the use of nanotechnologies, including standard lithographic tools as well as new nano-imprinting approaches. In particular, for the first time, we report some preliminary results obtained by our multidisciplinary research group concerning the design and fabrication of a 2D hybrid metallo-dielectric photonic crystal (PC) nanostructure, directly realized by innovatively applying the electron beam lithography technique on the cleaved end of standard single mode optical fibers.

Here, we report on recent experimental results obtained with Fiber Bragg Grating (FBG) hydrophones for underwater sound pressure detection. Investigated optical hydrophones consist of FBGs coated with ring shaped polymers of different size. Coating material has been selected to provide mechanical amplification through a low elastic modulus combined with acoustic impedance matching. Underwater acoustic measurements carried out in the range 4-35KHz reveal a resonant behaviour depending on the coating size. This behaviour is consistent with numerical analysis performed using finite element method and presented in part I. In addition, good linearity was observed versus local sound pressure demonstrating a minimum detectable sound pressure of few Pascal.

A novel interrogation scheme for Tilted Fiber Bragg Gratings (TFBGs) sensors is here proposed based on single wavelength time delay measurements. To this aim, the group delay of a weakly tilted TFBG has been characterized by direct time domain measurement. The experimental characterization shows the capability of TFBGs to enable superluminal and subluminal propagation of an optical pulse in optical fibers. The sharp group delay features of the TFBGs are exploited for refractometric applications to detect the SRI variations by single wavelength time delay measurements. The obtained preliminary results demonstrate the possibility to detect SRI changes by means of single wavelength time delay measurements with a sensitivity enhanced in the range 1.33-1.40 with respect to previously reported interrogation techniques.

We report on recent results obtained with a fiber optic hydrophone based on the intensity modulation of the laser light in a FBG (Fiber Bragg Grating) under the influence of the sound pressure. In order to control the behavior of the hydrophone in terms of sensitivity and bandwidth, FBGs have been coated with proper materials, characterized by different elastic modulus and shapes. In particular, new experiments have been carried out using a cylindrical geometry with two different coating, showing that the sensitivity is not influenced by the shape but by the transversal dimension and the material characteristics of the coating.

In the last decade there has been an increasing interest for terahertz technology. The reasons of this increasing interest is mainly due to its potential use in security applications with particular reference to drug and explosive detection. In this framework, the appropriate integration of metamaterials with nanotechnologies looks very promising for the construction of new compact low cost devices. Following this line of argument, we are exploring the possibility to combine the use of nanocathodes as sources of electron beams with engineered metamaterial layers in order to deliver coherent tunable terahertz radiation. More exactly, starting from a revised design of microwave sources, we discuss the issues related to manufacture miniaturized planar devices taking advantage of some appropriate integration of post silicon technologies.

In this work, the possibility to detect ppm ammonia concentrations in water environment, at room temperature, by means of Standard Optical Fibers (SOFs) sensors coated by Metal Oxides (MOXs) films has been demonstrated. Electro-spray pyrolisis technique has been used to deposit SnO2 films onto the distal end of single-mode optical fibers. This deposition technique allows the possibility to tailor the fabricated films properties by varying the deposition parameters, such as the metal chloride concentrations, the solution volume and the substrate temperature. The sensor operating principle relies on the measurement of the light intensity reflected by the fiber-sensitive layer interface: the pollutant molecules adsorption within the MOX film causes a change in its complex dielectric function and thus in the fiber-film reflectance. Spectral characterization of the obtained sensing probes has been carried out in the range 400-1750nm. Single wavelength reflectance measurements have been carried out to test the sensor performances for ppm ammonia detection. High sensitivity to the target analyte, response times of approximately 10-20 minutes and a Limit Of Detection as low as sub-ppm has been observed.