We present some of our results on the femtosecond laser direct writing and characterization of micro-gratings in
Baccarat glass. Gratings were inscribed with amplified 800 nm, ~100 femtosecond pulses at 1 kHz repetition rate. The
change in refractive index of the modified region was estimated from grating efficiency measurements and was found to
be ~10-3. Micro-Raman studies demonstrated an increase in the intensity of the band near 596 cm-1 in the laser irradiated region clearly indicating an increase in the refractive index. Micro-Raman mapping of the grating showed a periodic
variation of the band intensity further confirming the formation of grating. Structures with sub wavelength dimensions
(<800 nm) were achieved with shaping of the input pulses using a rectangular slit. Waveguides were inscribed by optimizing parameters like slit width, focusing conditions, translation speed etc. We shall present our results on the physical, spectroscopic and optical characterization of these structures.
The recent developments of optically confined structures and nanocomposite materials activated by rare earth ions have
opened new possibilities in the field of both basic and applied physics, in a large area covering Information
Communication Technologies, Health and Biology, Structural Engineering, and Environment Monitoring Systems. As
far as optical telecommunications are concerned, Er3+-activated glasses have become one of the key materials because of
their relevance for the development of optical amplifiers. The short-term goal is to develop appropriate material systems
and devices to exploit at the best the luminescence properties of Erbium. Er3+-activated confined structures at different
scales thus offer interesting solutions. The last decade has seen a remarkable increase in the experimental efforts to
control and enhance emission properties of emitters by tailoring the dielectric surrounding of the source. The aim of this
paper is to give a review concerning the advances in glass-based photonic systems, where light confinement or the
presence of nanostructured hosts for the rare-earth induces an enhancement and a control of the optical and/or spectroscopic properties.
Silica-hafnia glass-ceramics waveguides activated by Er3+ ions were fabricated by sol-gel route. X ray diffraction and optical spectroscopy showed that after an adapted heat treatment, the resulting materials showed a crystalline environment. Analysis of the luminescence properties has demonstrated that erbium ions are, at least partially, trapped in a crystalline phase. Losses measurements at different wavelength highlight a very low attenuation coefficient indicating that this nanostructured material is suitable for a single band waveguide amplifier in the C band of telecommunication.
Since the discovery of optical fibers, the possibility to develop optically confined structures has opened new possibilities for making novel optical components. Rare earth-activated confined structures thus offer interesting solutions for this end. A growing activity in this field is aimed at the development of optical amplifiers in planar form based on rare-earthactivated glasses to provide devices such as lossless splitters, which can find applications in the metropolitan and local area networks. A further development to enhance the spectroscopic properties is achieved by rare-earth co-activated nanocomposite materials, also in planar format. The aim of this paper is to give a review concerning the advances in glass-based photonic systems, where light confinement or the presence of nanostructured hosts for the rare-earth induces an enhancement and a control of the optical and/or spectroscopic properties.
We present the details of the Sol-gel processing used to synthesize silica spheres, with particular attention to the conditions that permit to tailor their dimension. We have elaborated a protocol in order to obtain silica micro spheres with low polydispersivity and we have demonstrated that large well-ordered crystals of synthetic opal, that exhibit a photonic stopband, can be produced in few days by vertical deposition and evaporation-assisted sedimentation deposition methods. Scanning electron microscope was employed to characterize the samples reflectance and transmission measurements were used to put in evidence the high quality of the realized opals.
Starting from the silica spheres, core-shell-like Er3+-activated silica spheres were also prepared, where the core is the silica sphere and the shell is an Er2O3-SiO2 coating. Morphologic, structural and spectroscopic properties were investigated by scanning electron microscope and luminescence spectroscopy. The emission of 4I13/2→4I15/2 of Er3+ ion transition with a 27 nm bandwidth was observed upon excitation at 514.5 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime of 12.8 ms.
Spectroscopic properties of Ag/Er co-doped thin plates of silicate and phosphate glass were investigated with the aim of assessing the effective role of silver as a sensitizer for erbium. Additive heat treatments in air at different temperatures were performed on both a silver-exchanged and a silver-free plate in order to promote the formation of silver nanoparticles in the former and to refer to the later in the spectroscopic characterization. Absorption as well as photoluminescence measurements in the region of the 4I13/2 -> 4I15/2 transition of the Er3+ ion were performed; excitation wavelengths in the range from 360 to 750 nm were used. For the silicate glasses enhancement of the Er3+ luminescence at 1.53 mm was observed when the excitation wavelength was in the blue region. This spectral range typically coincides with the excitation energy of the surface plasmon resonance of nanometer-sized spherical silver particles.
Several modified silicate glass samples activated with erbium ions at two different doping rates, namely 0.2 and 0.5 mol%, exhibit at room temperature a fine-structured emission band around 1.5 mm. The decay of luminescence from the Er3+4I13/2 metastable level is found to evolve according to a single-exponential law and a lifetime as long as 14.2 ms is measured from the glass with the lower erbium concentration. An estimation of the corresponding radiative lifetime, τrad, is achieved on the basis of various theoretical models. Internal gain curves resulting from absorption and stimulated emission cross sections are also shown. A 75% quantum efficiency is deduced for the less Er3+ concentrated glass, which is nearly the highest one obtained from silica based doped-glasses.
In this work we report on spectroscopic properties of Er3+-doped and Er3+/Ce3+-codoped tungsten-tellurite glasses of molar composition 45 TeO2: 39 WO3: 15 Na2O: 1 Er2O3 and 43 TeO2: 39 WO3: 15 Na2O: 1 Er2O3: 2 CeO2, respectively.
Vibrational properties were investigated by Raman spectroscopy. The measured absorption spectra were analyzed by McCumber theory, in order to obtain radiative transition rates and stimulated emission cross sections. The study of de-excitation dynamics of the 4I11/2 and 4I13/2 Er3+ states upon pulsed excitation at 532 nm shows that Ce3+ codoping is highly effective in favoring the population feeding of the 4I13/2 Er3+ level.
Recent results obtained for SiO2-HfO2: Er3+ and SiO2-TiO2: Er3+-Yb3+ waveguides are presented. (100-x)SiO2-xHfO2 (x = 10, 20, 30, 40 mol) planar waveguides, doped with 0.01 and 0.3 mol % Er3+ ions were prepared by sol-gel route, using dip-coating deposition on v-SiO2 substrates. The waveguides were characterized by m-line, Raman and photoluminescence spectroscopy. The spectral shape of the band assigned to the 4I13/2->4I15/2 transition does not change practically with the hafnium and erbium content. The 4I13/2 level decay curves present a single-exponential profile, with a lifetime between 5.5 and 7.1 ms, for the 0.3 mol% doped samples, and between 8.5 and 6.6 ms for the 0.01 mol% doped samples. The SiO2-TiO2: Er3+-Yb3+ waveguides were prepared by rf-sputtering technique. All waveguides were single-mode at 1550 nm. The losses, for the TE0 mode, were evaluated at 632.8 and 1300 nm and an attenuation coefficient equal or lower than 0.2 dB/cm was measured both at 632.8 nm and 1300 nm. The emission of 4I13/2->4I15/2 of Er3+ ion transition was observed upon excitation in the TE0 mode at 981 and 514.5 nm. Back energy transfer from Er3+ to Yb3+ was demonstrated by measurement of Yb3+ emission upon Er3+ excitation at 514.5 nm. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb3+ ions.
Erbium activated SiO2-HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-gel method. The films were deposited on v-SiO2 and silica-on-silicon substrates using dip-coating technique. The waveguides show high densification degree, effective intermingling of the two film components, and uniform surface morphology. The waveguide deposited on silica-on-silicon substrates shows one single propagation mode at 1.5μm, with a confinement coefficient of 0.81 and an attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuous-wave excitation at 980 nm or 514.5 nm. The shape of the emission band corresponding to the 4I13/2→4I15/2 transition is found to be almost independent both on erbium content and excitation wavelength, with a FWHM between 44 and 48 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1-6.6 ms, depending on the erbium concentration. Infrared to visible upconversion luminescence upon continuous-wave excitation at 980 nm was observed for all the samples. Channel waveguide in rib configuration was obtained by etching the active film in order to have a well confined mode at 1.5 μm.