The ALPINE project is developing innovative fiber lasers for the scribing of new thin film photovoltaic modules with the
aims to push forward the European research and development of fiber laser systems and solar energy exploitation. The
fiber lasers will be based on photonic crystal fibers, which are characterized by unusual and interesting light guiding
properties exploited to deliver high power with excellent beam quality and high resonator stability and efficiency, and
will be applied to substitute mechanical scribing steps in the photovoltaic module production. In addition, new
photovoltaic thin film technologies is applied, which is based on cadmium telluride and copper indium diselenide
materials. With a potential conversion efficiency just below that of crystalline silicon, these new material approaches are
ready to enter the market with low manufacturing costs for immediate economic or environment impact.
The properties of a large mode area Yb-doped double-cladding hybrid photonic crystal fiber, with antisymmetric
high-index inclusions, have been analyzed. Simulations, carried out through a finite-element based modal solver,
and experimental measurements have demonstrated the narrow spectral filtering capability of this fiber, with a
passband of about 80 nm in the Yb gain region. Moreover, high-order mode suppression has been demonstrated
with a proper air-hole size. Finally, the stress-induced birefringence due to the Ge-doped rods used as high-index
insets has been investigated, accounting for the polarization-maintaining behaviour of the manufactured fiber.
The single-mode regime of 19-cell Yb-doped double-cladding photonic crystal fibers, successfully exploited for
high-power applications due to their large mode area, has been studied. The first higher-order mode cut-off
wavelength has been evaluated taking into account the crossing between its dispersion curve, obtained with a
full-vector modal solver based on the finite element method, and the one of the fundamental space-filling mode,
calculated for an infinite cladding. Moreover, the overlap integral on the doped core of the higher-order mode
at cut-off condition has been calculated, in order to investigate its effective suppression in the gain competition
with the fundamental mode, by applying a spatial and spectral amplifier model. 19-cell double-cladding photonic
crystal fibers with different core diameter and refractive index values have been considered. Simulation results
have shown that the approach based on the fundamental space-filling mode effective index is not suitable for the
cut-off analysis of large core fibers with a finite cladding dimension.
The increased concern, emerged in the last few years, on food products safety has stimulated the research on new
techniques for traceability of raw food materials. DNA analysis is one of the most powerful tools for the certification of
food quality, and it is presently performed through the polymerase chain reaction technique. Photonic crystal fibers, due
to the presence of an array of air holes running along their length, can be exploited for performing DNA recognition by
derivatizing hole surfaces and checking hybridization of complementary nucledotide chains in the sample. In this paper
the application of a suspended core photonic crystal fiber in the recognition of DNA sequences is discussed. The fiber is
characterized in terms of electromagnetic properties by means of a full-vector modal solver based on the finite element
method. Then, the performances of the fiber in the recognition of mall synthetic oligonucleotides are discussed, together
with a test of the possibility to extend this recognition to samples of DNA of applicative interest, such as olive leaves.
Yb-doped rod-type photonic crystal fibers are double-cladding
large-mode-area fibers with the outer dimension of
few millimeters. The higher-order mode suppression through gain filtering has been demonstrated in these fibers,
by enlarging the core radius from 30 μm to 40 μm, while keeping fixed the doped-area dimension. Sectioned core
doping, obtained by adding a low refractive index ring in the fiber core, has been taken into account, in order to
design fibers with an effective single-mode behaviour. Moreover, the gain competition among the guided modes
in the enlarged-core rod-type PCFs has been analyzed with a spatial and spectral amplifier model, showing the
positive effect of the gain filtering in improving the fundamental mode amplification, to the detriment of the
higher-order mode one. Comparisons have been made with the properties of rod-type fibers with 30 μm core
radius, both with uniform and sectioned doping, in order to show the effectiveness of the down-doped ring in the
enlarged core for the higher-order mode suppression.
Photonic crystal fibers with kagome lattice are a particular kind of micostructured hollow-core fibers whose
cross-section is characterized by a web of thin silica struts intersecting in a Star-of-David pattern. Such fibers
show unusual properties, such as light confinement in the air-core in absence of a full photonic bandgap. The
primary design parameter for such fibers is the strut thickness, which is responsible for the position and the
width of the transmission bands. In this paper the guiding properties of hollow-core photonic crystal fibers
with kagome lattice are investigated by means of a full-vector modal solver based on the finite element method.
The fundamental mode effective index and confinement loss have been evaluated in a wide wavelength range,
spanning from 300 nm to 1600 nm, accounting for the influence of the silica strut width on the transmission
window. Moreover, the effects of selective alteration of the width and the shape of the silica struts surrounding
the core have been analyzed. Simulation results show that the core-surrounding silica ring has the strongest
effect on the transmission band, the loss level and the resonance wavelength position and, consequently, it should
be carefully controlled during the fiber fabrication.
This paper presents the application of a new erbium-doped fiber ring laser configuration for the multiplexing
of intensity sensors. The proposed scheme exploits two separated branches to generate simultaneous emission
at four different wavelengths. Fiber Bragg gratings are used to select the operating wavelengths within the
erbium-doped fiber ring. The first branch presents a serial configuration to generate the reference lasers. The
second branch exploits a tree configuration and includes the optical intensity temperature sensors. A comparison
between both branches of the same setup is carried out, and their temperature and time stability is shown by
varying the erbium doped fiber.
This paper shows a long-distance remote sensing system using a multiwavelength Raman laser. The sensor network is
based on a 50 km of standard single-mode fiber (SMF) and is composed by a simple cavity based on a loop mirror and
four Fiber Bragg Gratings (FBGs) arranged in a star configuration. FBGs are used for both the sensing function and the
selection of the lasing wavelengths. The system is designed to be inherently resilient to fiber failures. The
multiwavelength laser has been characterized for temperature measurements showing a good stability performance.
KEYWORDS: Fermium, Frequency modulation, Refractive index, Doping, Photonic crystal fibers, Amplifiers, Optical fibers, Cladding, Finite element methods, High power lasers
Rod-type photonic crystal fibers are large mode area double-cladding fibers with an outer diameter of few
millimeters which can provide important advantages for high-power lasers and amplifiers. Numerical studies
have recently demonstrated the guidance of higher-order modes in these fibers, which can worsen the output
beam quality of lasers and amplifiers. In the present analysis a sectioned core doping has been proposed for Ybdoped
rod-type photonic crystal fibers, with the aim to improve the
higher-order mode suppression. A full-vector
modal solver based on the finite element method has been applied to properly design the low refractive index
ring in the fiber core, which can provide an increase of the differential overlap between the fundamental and the
higher-order mode. Then, the gain competition among the guided modes along the Yb-doped rod-type fibers has
been investigated with a spatial and spectral amplifier model. Simulation results have shown the effectiveness
of the sectioned core doping in worsening the higher-order mode overlap on the doped area, thus providing an
effective single-mode behavior of the Yb-doped rod-type photonic crystal fibers.
The paper presents a theoretical analysis of the dynamic characteristics of an ytterbium-doped high power fiber
laser. The proposed analysis focuses on the last stage of amplification, characterized by a photonic crystal
fiber. For the intrinsic characteristics of this stage, an ytterbium-doped large mode area fiber is necessary to
obtain great efficiency. Photonic crystal fibers present one of the most useful option due to the good thermal
properties, large mode area, high damage threshold and a high threshold for the nonlinear effect such as Raman
and Brillouin scattering. The dynamic behaviour of an Ytterbium-doped rodlike photonic crystal fiber for pulsed
laser is numerically investigated through a "Reservoir" model. Theoretical results demonstrate the effect of the
pulse duration and the frequency repetition rate on the amplifier characteristics. Through the numerical model,
the optimum length and pump power have been obtained in order to achieve high output peak power. Moreover,
an analysis on the temporal evolution and shape of the signal pulses at the amplifier output is carried out by
exploiting the dynamic model.
Microstructured optical fibers have the potential to provide improved performance relative to more traditional
spectroscopic fiber sensors. In fact the manipulation of the geometry of the fiber cross section can allow to
maximize the interaction of light and sample. Recently, solid air-suspended core fibers have been appointed as
the most promising design for evanescent field sensing. In this kind of device, sensing is carried out through the
interaction between evanescent tails of index-guided modes and sample, which fills cladding holes. Suspended
core fibers are made by three silica webs joining in the fiber center and forming the core. This design can
provide an evanescent field power fraction greater than any other structure previously proposed, together with
a wide transmission band. In this paper, the electromagnetic field behaviour of the guided modes of a range
of suspended-core fibers is investigated, using a full-vectorial finite element based modal solver. The impact of
different design parameters and materials on guidance, the amount of power in the cladding and the possibility
of obtaining effective single-mode guidance are also investigated.
We developed a new hierarchical joint segmentation technique, which provides an effective fusion of a sequence of
multitemporal single-channel SAR images of a given area with a multispectral optical image over the same target area.
The proposed segmentation method is totally unsupervised, and it allows identifying regions that are homogeneous with
respect to the whole data set (both optical and multitemporal SAR images). This is accomplished, first, by modeling the
statistic of the joint distribution of SAR and optical data, then treating the multi-channel input images as a single entity,
and performing the segmentation using information from all channels simultaneously. To this purpose, we consider two
different statistical models: 1) multivariate Gaussian model for the multiband optical images and gamma distribution for
the SAR images, 2) again multivariate Gaussian model for the multiband optical images and multivariate log-normal
distribution for the SAR images.
The proposed segmentation algorithm is based on a fast multi-scale iterated weighted aggregation method and
generalized to multispectral remote sensing data in. A quantitative analysis of the proposed joint segmentation
technique for the fusion of multitemporal SAR and multispectral optical images is carried out using real images. To this
purpose, any desired classification schema can be applied after the segmentation step on the identified homogeneous
regions, which allows the full exploitation of the spatial-temporal information available in the multitemporal and
multisource data. Results show that the proposed joint segmentation technique, combined with even simple
classification methods, greatly improves the discrimination capability of the classifier.
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