46 research outputs found
On the application of optical forward-scattering to bacterial identification in an automated clinical analysis perspective
The Optical Forward Scattering (OFS) technique can be used to identify pathogens by direct observation of bacteria colonies growing on a culture plate. The identification is based on the acquisition of scattering images from isolated colonies and their subsequent comparison with reference images acquired from known bacteria. The technique has been mainly studied for the identification of pathogens in the food-safety field. This paper focuses on the possibility of extending the applicability of the technique to the field of clinical laboratory automation. This scenario requires that the paradigm of image acquisition at fixed colony-dimension, well established in the food-safety applications, should be substituted by an acquisition at fixed incubation time. As a consequence, the scatterometer must be adjustable in real-time for adapting to the actual features of the bacterial colony. The paper describes an OFS system prototype qualified by the possibility to tune both the laser beam diameter and the acquisition camera field of view. Preliminary experiments on bacteria cultures from pathogens causing infections of the urinary tract show that the proposed approach is promising for the development of an automated bacteria identification station. The new OFS approach also involves an alternative method for building a reference image database for subsequent image analysis
Ge-Doped microstructured multicorefiber for customizable supercontinuum generation
Supercontinuum generation in a multicore fiber in which several uncoupled cores
were doped with dissimilar concentrations of germanium was studied experimentally.
Germanium doping provided control over the separation between the zero-dispersion
wavelength and the 1064-nm wavelength of a Q-switched Nd:YAG pump laser. Supercontinua
generated independently in each core of the same piece of fiber displayed clear
and repeatable differences due to the influence of germanium doping on refractive index and
four-wave mixing. The spectral evolution of the subnanosecond pump pulses injected into
the different cores was accurately reproduced by numerical simulations
Chromatic confocal setup for displacement measurement using a supercontinuum light source
Chromatic confocal microscopy is a technique to measure distances by analyzing the spectrum of the light reflected by a sample. The key element of the confocal setup is a dispersive lens, which focuses
different wavelengths at different distances from the lens. In this paper,a novel setup realized with a
supercontinuum light source and a spatial filter composed by reflective elements is described.The supercontinuum source is implemented by injecting high power pulses from a microchip laser into a
Ge-doped microstructured optical fiber. The usage of metallic parabolic mirrors, for the focusing and
collimation required in the spatial filter, lets the dispersive lens be the only dispersive element of the
confocal setup and improves the efficiency of the spatial filter itself. A silicon-based spectrometer is
used for the acquisition of the spectra, which are normalized and Gaussian-fitted before extracting the
displacement information. A complete calibration is performed, and the set of wavelengths from
500 nm to 900 nm can be mapped into a280 um measuring range. The obtained relativ eaccuracy of
0.36% shows an enhancement of almost one order of magnitude when compared to other supercontinuum-based confocal systems
Nonlinear polarization dynamics of Kerr beam self-cleaning in a GRIN multimode optical fiber
We experimentally study polarization dynamics of Kerr beam self-cleaning in a
graded-index multimode optical fiber. We show that spatial beam cleaning is
accompanied by nonlinear polarization rotation, and a substantial increase of
the degree of linear polarization.Comment: 5 pages, 6 figure
Efficiency of dispersive wave generation in dual concentric core microstructured fiber
We describe the generation of powerful dispersive waves that are observed
when pumping a dual concentric core microstructured fiber by means of a
sub-nanosecond laser emitting at the wavelength of~1064 nm. The presence of
three zeros in the dispersion curve, their spectral separation from the pump
wavelength, and the complex dynamics of solitons originated by the pump pulse
break-up, all contribute to boost the amplitude of the dispersive wave on the
long-wavelength side of the pump. The measured conversion efficiency towards
the dispersive wave at 1548 nm is as high as 50%. Our experimental analysis of
the output spectra is completed by the acquisition of the time delays of the
different spectral components. Numerical simulations and an analytical
perturbative analysis identify the central wavelength of the red-shifted pump
solitons and the dispersion profile of the fiber as the key parameters for
determining the efficiency of the dispersive wave generation process.Comment: 11 pages, 12 figure
Analog signal pre-processing for performance enhancement of a distance meter based on frequency-modulated continuous-wave interferometry
A method for the processing of signal from an absolute distance meter based on a frequency-modulated continuous-wave (FMCW) interferometer is presented. FMCW is implemented using a laser diode driven by a current waveform obtained as the superposition of a triangular signal to a bias current kept well above the diode lasing threshold. The analog signal pre-processing includes a derivative block followed by the time-variant baseline restoration of the photodetector current. A high signal-to-noise ratio is ensured by avoiding the use of a resistive transimpedence preamplifier and subsequent voltage processing. The paper details the scheme of the pre-processing chain as well as the experimental results from an actual prototype of a distance meter
Aiding device for reading a printed text
A novel device developed as a rehabilitation tool for people having difficulties in reading printed text is the object of the patent. The proposed system enables the user to randomly access the words of a printed text by directing a handheld pointer that is similar to a pencil. The application of modern information technologies makes it possible the implementation of a device that combines effectiveness, robustness, and friendliness of use. A micro camera is fixed to the pointer and frames the word the user wants to read. A voice synthesizer reproduces the word just recognized. A suitable measurement of the device motion based on real time image processing allows determining when the user has stopped the pointer thus indicating the wish to hear the pointed word(s)