Efficient second-harmonic generation through cascaded optically poled fibers.

We report the experimental demonstration of efficient second-harmonic generation by splicing optically poled fiber segments. A device made from five segments each 20 cm-long exhibits, at a fundamental average power of 4.2 mW, a maximum increase of 5.5 in the conversion efficiency with respect to a single 20 cm poled fiber, corresponding to a conversion efficiency of 5.4%. For any considered fundamental power, the conversion efficiency at the output of a five-segment device is larger than the efficiency of a single poled fiber having the same length.

Nonlinear polarization dynamics of Kerr beam self-cleaning in a graded-index 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 significant increase of the degree of linear polarization.

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.