107 research outputs found
Luminescent Ions in Silica-Based Optical Fibers
We present some of our research activities dedicated to doped silica-based
optical fibers, aiming at understanding the spectral properties of luminescent
ions, such as rare-earth and transition metal elements. The influence of the
local environment on dopants is extensively studied: energy transfer mechanisms
between rare-earth ions, control of the valence state of chromium ions, effect
of the local phonon energy on thulium ions emission efficiency, and broadening
of erbium ions emission induced by oxide nanoparticles. Knowledge of these
effects is essential for photonics applications
Improvement of the Tm3+:3H4 level lifetime in silica optical fibres by lowering the local phonon energy
The role of some glass network modifiers on the quantum efficiency of the
near-infrared fluorescence from the 3H4 level of Tm3+ ion in silica-based doped
fibres is studied. Modifications of the core composition affect the
spectroscopic properties of Tm3+ ion. Adding 17.4 mol% of AlO3/2 to the core
glass caused an increase of the 3H4 level lifetime up to 50 s, 3.6 times
higher than in pure silica glass. The quantum efficiency was increased from 2%
to approximately 8%. On the opposite, 8 mol% of PO5/2 in the core glass made
the lifetime decrease downto 9 s. These changes of Tm3+ optical properties
are assigned to the change of the local phonon energy to which they are
submitted by modifiers located in the vicinity of the doping sites. Some
qualitative predictions of the maximum achievable quantum efficiency are
possible using a simple microscopic model to calculate the non-radiative
de-excitation rates
Large mode area leaky optical fiber fabricated by MCVD
Manuscript : 17 pages, 3 figuresInternational audienceA large mode area single-mode optical fiber based on leaky mode filtering has been prepared by modified chemical vapor deposition (MCVD) technique. The fiber has a leaky cladding, which discriminates the fundamental mode from the higher order ones. A preliminary version has 25-µm core diameter and 0.11 numerical aperture. A Gaussian-like mode with 22-µm mode field diameter has been observed after 3-m propagation, in agreement with modeling
Birefringence analysis of multilayer leaky cladding optical fibre
We analyse a multilayer leaky cladding (MLC) fibre using the finite element
method and study the effect of the MLC on the bending loss and birefringence of
two types of structures: (i) a circular core large-mode-area structure and (ii)
an elliptical-small-core structure. In a large-mode-area structure, we verify
that the multilayer leaky cladding strongly discriminates against higher order
modes to achieve single-mode operation, the fibre shows negligible
birefringence, and the bending loss of the fibre is low for bending radii
larger than 10 cm. In the elliptical-small-core structure we show that the MLC
reduces the birefringence of the fibre. This prevents the structure from
becoming birefringent in case of any departures from circular geometry. The
study should be useful in the designs of MLC fibres for various applications
including high power amplifiers, gain flattening of fibre amplifiers and
dispersion compensation.Comment: 18 page
Thulium environment in a silica doped optical fibre
Thulium-doped optical fibre amplifiers (TDFA) are developed to extend the
optical telecommunication wavelength division multiplexing (WDM) bandwidth in
the so-called S-band (1460-1530 nm). The radiative transition at 1.47 lm (3H4
-> 3F4) competes with a non-radiative multi-phonon de-excitation (3H4 -> 3H5).
The quantum efficiency of the transition of interest is then highly affected by
the phonon energy (Ep) of the material. For reliability reasons, oxide glasses
are preferred but suffer from high phonon energy. In the case of silica glass,
Ep is around 1100 cm-1 and quantum efficiency is as low as 2%. To improve it,
phonon energy in the thulium environment must be lowered. For that reason,
aluminium is added and we explore three different core compositions: pure
silica, and silica slightly modified with germanium or phosphorus. The role of
aluminium is studied through fluorescence decay curves, fitted according to the
continuous function decay analysis. From this analysis, modification of the
thulium local environment due to aluminium is evidenced
Spectroscopic signature of phosphate crystallization in Erbium-doped optical fibre preforms
In rare-earth-doped silica optical fibres, the homogeneous distribution of
amplifying ions and part of their spectroscopic properties are usually improved
by adding selected elements, such as phosphorus or aluminum, as structural
modifier. In erbium ion (Er3+) doped fibres, phosphorus preferentially
coordinates to Er3+ ions to form regular cages around it. However, the
crystalline structures described in literature never gave particular
spectroscopic signature. In this article, we report emission and excitation
spectra of Er3+ in a transparent phosphorus-doped silica fibre preform. The
observed line features observed at room and low temperature are attributed to
ErPO4 crystallites
Investigation of the photosensitivity, temperature sustainability and fluorescence characteristics of several Er-doped photosensitive fibers
Three different types of Er doped photosensitive fibers, germanium/erbium
(Ge/Er) fiber, tin/germanium/erbium fiber (Sn/Er) and antimony/germanium/erbium
fiber (Sb/Er) have been manufactured and studied for use in optical sensor
systems. Their characteristics of photosensitivity, the temperature
sustainability of fiber Bragg gratings (FBGs) written into these fibers and the
fluorescence emission from the Er dopant were investigated and compared. It has
been shown in this work that these fibers all show a satisfactory degree of
photosensitivity to enable the fabrication of FBGs and a significant level of
fluorescence emission within the 1550 nm band for sensor use. The high
temperature sustainability of the FBGs written into these fibers was
investigated and seen to be quite significant at temperatures as high as 850
^{\circ}C, in particular for the Sn/Er and Sb/Er fibers. A fiber laser using
the Sb/Er fiber as the gain medium was demonstrated, giving evidence of the
strong fluorescence emission from the Er dopant. These fibers are all suitable
for use in a variety of sensing applications for the simultaneous measurement
of temperature and strain by means of monitoring both the fluorescence
characteristics and the peak wavelength shift of the FBGs formed in fiber laser
sensor application
Design and fabrication of an intrinsically gain flattened Erbium doped fiber amplifier
We report design and subsequent fabrication of an intrinsically gain
flattened Erbium doped fiber amplifier (EDFA) based on a highly asymmetrical
and concentric dual-core fiber, inner core of which was only partially doped.
Phase-resonant optical coupling between the two cores was so tailored through
optimization of its refractive index profile parameters that the longer
wavelengths within the C-band experience relatively higher amplification
compared to the shorter wavelengths thereby reducing the difference in the
well-known tilt in the gains between the shorter and longer wavelength regions.
The fabricated EDFA exhibited a median gain ?28 dB (gain excursion below
2.2 dB within the C-band) when 16 simultaneous standard signal channels
were launched by keeping the I/P level for each at ?20 dBm/ channel. Such EDFAs
should be attractive for deployment in metro networks, where economics is a
premium, because it would cut down the cost on gain flattening filter head
- …