Sreeramulu Valligatla

High quality factor 1-D Er 3+ -activated dielectric microcavity fabricated by RF-sputtering

Rare earth-activated 1-D photonic crystals were fabricated by RF-sputtering technique. The cavity is constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of ten pairs of SiO2/TiO2 layers. Scanning electron microscopy is employed to put in evidence the quality of the sample, the homogeneities of the layers thickness and the good adhesion among them. Near infrared transmittance and variable angle reflectance spectra confirm the presence of a stop band from 1500 nm to 2000 nm with a cavity resonance centered at 1749 nm at 0° and a quality factor of 890. The influence of the cavity on the ⁴I₁₃/₂ -->⁴I₁₅/₂ emission band of Er3+ ion is also demonstrated.

Optical properties of germanium nanoparticles synthesized by pulsed laser ablation in acetone

Germanium (Ge) nanoparticles (NPs) are synthesized by means of pulsed laser ablation of bulk germanium target immersed in acetone with ns laser pulses at different pulse energies. The fabricated NPs are characterized by employing different techniques such as UV-visible absorption spectroscopy, photoluminescence, micro-Raman spectroscopy, transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mean size of the Ge NPs is found to vary from few nm to 40 nm with the increase in laser pulse energy. Shift in the position of the absorption spectra is observed and also the photoluminescence peak shift is observed due to quantum confinement effects. High resolution TEM combined with micro-Raman spectroscopy confirms the crystalline nature of the generated germanium nanoparticles. The formation of various sizes of germanium NPs at different laser pulse energies is evident from the asymmetry in the Raman spectra and the shift in its peak position towards the lower wavenumber side. The FESEM micrographs confirm the formation of germanium micro/nanostructures at the laser ablated position of the bulk germanium. In particular, the measured NP sizes from the micro-Raman phonon quantum confinement model are found in good agreement with TEM measurements of Ge NPs.

Soda-zinc-aluminosilicate glasses doped with Tb3+, Ce3+, and Sm3+ for frequency conversion and white light generation

Sodium-zinc-aluminosilicate (NaZAS) glasses doped with single or multiple rare earth ions (Ce3+, Tb3+, Sm3+) were synthesized, and their characteristics investigated by m-line spectroscopy, absorption and luminescence spectroscopy, and micro-Raman spectroscopy. Blue-white light, with x = 0.24 and y = 0.24 CIE chromaticity coordinates, was obtained for the Tb3+ singly-doped glass excited at 351 nm. In NaZAS glasses co-doped with Ce3+ and Tb3+ it was possible to observe a non-radiative energy transfer from Ce3+ to Tb3+ ions upon 320 nm excitation; the Ce3+→Tb3+ energy transfer microscopic parameter and efficiency were obtained from the analysis of the cerium emission decay curve. Different concentrations of Ce3+ and Tb3+ ions in the same glass host give rise to blue and blue-green emissions, with different CIE coordinates. Optical waveguides were also produced in the samples by means of Ag+-Na+ ion exchange process, and characterized.

Glass-ceramics for photonics: Laser material processing

Transparent glass-ceramics, activated by luminescent species, present an important class of photonic materials because their specific optical, spectroscopic and structural properties. Several top-down and bottom-up techniques have been developed for transparent glass ceramic fabrication. Among them, laser material processing plays an important role and many significant results have been obtained in the field of waveguide glass ceramics fabrication. Here, after a short description of the state of art regarding laser material processing for glass ceramics, we report on the specific use of CO2 laser for the fabrication of transparent glass ceramic waveguides.

Glass based structures fabricated by rf-sputtering

In this paper we present some results obtained by our consortium regarding rf-sputtered glass-based structures.

1-D Photonic Crystals Fabricated by RF Sputtering Towards Photonic Applications

A great technological and scientific challenge is related to the fabrication of confined structures where the light is confined in systems with characteristic dimensions scale from micro to nanometers. The nanotechnology, that allows the study of innovative functional materials and gives advances in the miniaturization, has opened the way to the manufacturing of such structures and focalize the attention of new features of light-matter interaction (Ristic D et. al, Proc ICTON Tu. B 5.2:1–5, 2013). An example concerns planar microcavities, or one-dimensional (1-D) photonic crystals, which are the simplest photonic band – gap (PBG) devices exploitable to manage the spectroscopic properties of luminescent species such as rare earth ions (Valligatla S, Chiasera A, Varas S, Bazzanella N, Narayana Rao D, Righini GC, Ferrari M, Opt Express 20:21214, 2012) and quantum dots (Jasieniak J, Sada C, Chiasera A, Ferrari M, Martucci A, Mulvaney P, Adv Funct Mater 18:3772, 2008). The fundamental optical principle for the photonic crystals is, “localization of light” (John S, Phys Rev Lett 58:2486, 1987) so that combination of photonic crystals and nonlinear optics leads us towards new nonlinear optical devices (Ma GH, Shen J, Rajiv K, Tamg SH, Zhang ZJ, Hua ZY, Appl Phys B 80:359, 2005; Valligatla S, Chiasera A, Krishna MBM, Varas S, Narayana Rao D, Ferrari M, Righini GC, Int Conf Fiber Opt Photon 2012:W1C.2).

RF-sputtering derived phosphosilicate planar waveguides activated by Er 3+ ions

SiO₂-P₂O₅-HfO₂-Al₂O₃-Na₂O planar waveguide was fabricated by rf-sputtering technique. The optical, structural and morphological parameters were measured by various techniques such as m-line spectroscopy, Energy Dispersive X-ray Spectroscopy and Atomic Force Microscopy. The waveguide exhibits a single propagation mode at 1319 and 1542 nm with an attenuation coefficient of 0.2 dB/cm in the infrared. The emission of ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ion, with a 28.5 nm bandwidth was observed upon TE0 mode excitation at 514.5 nm. The optical and spectroscopic features of the Er³⁺-activated parent P₂O₅-SiO₂-Al₂O₃-Na₂O glass were also investigated.

RF-sputtering derived dielectric 1-D photonic crystal activated with Er3+ ions

Rare earth activated 1-D photonic crystals were fabricated by rf sputtering technique. Near infrared transmittance spectra confirm the presence of a stop band with a cavity resonance centred at 1749 nm 0° with quality factor of 890.

Glass-Based Photonic Crystals: From Fabrication to Applications

We report on the fabrication and on the assessment of the properties of two glass-based photonic crystals (PhCs) obtained using alternative approaches such as rf-sputtering and sol-gel techniques. (i) By means of rf-sputtering a one-dimensional dielectric photonic crystal constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of 10 pairs of SiO2∕TiO2 layers has been realized. Near infrared transmittance spectra evidenced the presence of a stop band from 1500 to 2000 nm with a cavity resonance centered at 1749 nm. Intensity enhancement and narrowing of the emission band of Er3+ ions, due to the cavity effect have been observed and a cavity quality factor of 890 has been achieved. (ii) Through chemical route a 3D colloidal crystal based on polystyrene (PS) nanoparticles (NPs) embedded in elastomeric matrix has been realized. In the specific has been shown that the structure can produce a variation of its color applying different organic solvents that can be also easily observed by the naked eye. Optical measurements have evidenced a red shift of the diffraction peak as a function of the solvents applied. This feature has been exploited in order to create a sensitive material showing high sensitivity and reversibility of the signal change.

High quality factor dielectric multilayer structures fabricated by rf-sputtering

Rare earth activated 1-D photonic crystals were fabricated by rf-sputtering technique. The cavity is constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of ten pairs of SiO2/TiO2 layers. SEM microscopy is employed to put in evidence the quality of the sample, the homogeneities of the layers thicknes and the good adhesion. NIR transmittance and variable angle reflectance spectra confirm that the presence of a stop-band from 1500 nm to 2000 nm with a cavity resonance centered at 1749 nm at 0° with a quality factor Q is about 890. The influence of the cavity on the 4I13/2 → 4I15/2 emission band of Er3+ ion is also demonstrated.