PHOPSHATE OPTICAL FIBERS FOR IR FIBER LASERS

The main aim of this thesis was to design and manufacture double cladding phosphate fibers doped with Yb ions, suitable as short (cm-level) active cavities in pulsed fiber laser systems

Behavioural operations in healthcare : knowledge sharing perspective

Purpose The purpose of this paper is to provide arguments and empirical evidence that different knowledge sharing behaviours – i.e. sharing best practices, sharing mistakes, seeking feedbacks – are promoted and enabled by different types of knowledge assets, and differently affect employees’ innovative work behaviours. Design/methodology/approach The research framework includes four sets of constructs: employees’ innovative work behaviour, knowledge sharing, knowledge assets, psychological safety. The literature-grounded hypotheses were tested collecting data from healthcare professionals from three hospice and palliative care organisations in Italy. In all, 195 questionnaires were analysed using structural equations modelling technique. Findings First, findings show that the linkage between knowledge assets and knowledge sharing is both direct and indirect with psychological safety as relevant mediating construct. The linkage between relational and structural social capital and seeking feedbacks and sharing mistakes is fully mediated by psychological safety. Second, findings show that each dimension of knowledge sharing affects the different dimensions of employees’ innovative work behaviour – i.e. idea generation, idea promotion, idea implementation – in a distinct manner. While sharing of best practices influences all of them, seeking feedbacks affects idea promotion and sharing mistakes influences idea implementation. Practical implications The results provide operations managers with a clearer picture of how to pursue improvements of current operations by leveraging on knowledge sharing among employees through the creation of numerous, high-quality interpersonal relationships among employees, based on rich and cohesive network ties. Originality/value This study, by adopting a micro-level perspective, offers an original perspective on how knowledge assets and knowledge sharing initiatives may contribute to the engagement of innovative work behaviour by employees

Application of neural networks for the retrieval of forest woody volume from SAR multifrequency data at L and C bands.

This work aims at investigating the potential of L (ALOS/PALSAR) and C (ENVISAT/ASAR) band SAR images in forest biomass monitoring and setting up a retrieval algorithm, based on Artificial Neural Networks (ANN), for estimating the Woody Volume (WV, in m3/ha) from combined satellite acquisitions. The investigation was carried out on two test areas in central Italy, where ground WV measurements were available. An innovative retrieval algorithm based on ANN was developed for estimating WV from L and C bands SAR data. The novelty consists of an accurate training of the ANN with several thousands of data, which allowed the implementation of a very robust algorithm. The RMSE values found on San Rossore area were ?40 m3/ha (L band data only), and 25-30 m3/ha (L with C band). On Molise, by using combined data at L and C bands, RMSE<30m3/ha was obtained. Keywords: ANN; backscattering; Woody Volume; LiDAR; ALOS/PALSAR; ENVISAT/ASAR

Yb-doped phosphate double-cladding optical fiber laser for high-power applications

A Yb-doped phosphate glass double cladding optical fiber was prepared using a custom designed glass composition (P2O5 - Al2O3 - Li2O - B2O3 - BaO - PbO - La2O3) for high-power amplifier and laser applications. The preform drawing method was followed, with the preform being fabricated using the rotational casting technique. This technique, previously developed for tellurite, fluoride or chalcogenide glass preforms is reported for the first time using rare earth doped phosphate glasses. The main challenge was to design an adequate numerical aperture between first and second cladding while maintaining similar thermo-mechanical properties in view of the fiber drawing process. The preform used for the fiber drawing was produced by rod-in-tube technique at a rotation speed of 3000 rpm. The rotational casting technique allowed the manufacturing of an optical fiber featuring high quality interfaces between core and internal cladding and between the internal and external cladding, respectively. Loss attenuation was measured using the cut-back method and lasing was demonstrated at 1022 nm by core pumping with a fiber pigtailed laser diode at the wavelength of 976 n

Tuning InP self-assembled quantum structures to telecom wavelength: A versatile original InP(As) nanostructure "workshop"

The influence of hydride exposure on previously unreported self-assembled InP(As) nanostructures is investigated, showing an unexpected morphological variability with growth parameters, and producing a large family of InP(As) nanostructures by metalorganic vapour phase epitaxy, from dome and ring-like structures to double dot in a ring ensembles. Moreover, preliminary microphotoluminescence data are indicating the capped rings system as an interesting candidate for single quantum emitters at telecom wavelengths, potentially becoming a possible alternative to InAs QDs for quantum technology and telecom applications

Comparison of InGaAs and InAlAs sacrificial layers for release of InP-based devices

Heterogeneous integration of InP devices to Si substrates by adhesive-less micro transfer printing requires flat surfaces for optimum attachment and thermal sinking. InGaAs and InAlAs sacrificial layers are compared for the selective undercut of InP coupons by FeCl3:H2O (1:2). InAlAs offers isotropic etches and superior selectivity (> 4,000) to InP when compared with InGaAs. A 500 nm thick InAlAs sacrificial layer allows the release of wide coupons with a surface roughness < 2 nm and a flatness < 20 nm. The InAlAs release technology is applied to the transfer printing of a pre-fabricated InP laser to a Si substrate

Thermal stability and spectroscopic properties of erbium-doped niobic-tungsten-tellurite glasses for laser and amplifier devices

Er3+ doped niobic-tungsten-tellurite glasses doped with concentration of Er3+ ion up to 3 wt% were fabricated. The effect of Er3+ doping concentration on thermal stability and optical properties was investigated in order to obtain the most suitable rare earth content for developing 1.5 micron compact fiber amplifier pumped with a commercial telecom 980 nm laser diode. The maximum doping concentration allowed was found to be around 1.77 x 10^20 ions/cm^3, for which a broad 1.5 micron emission spectra of 65 nm FWHM and a lifetime of 3.4 ms for the 4I13/2 level was measure