ABSTRACT Erbium-activated silica-titania and silica-hafnia planar waveguides have been prepared by the sol-gel route. The films were deposited on vitreous silica substrates using a dip-coating technique. The parameters of preparation have been chosen to optimize the waveguides for operation in the near-infrared (NIR) region and to increase the luminescence efficiency of the metastable 4I13/2 state of erbium ions. The waveguides' properties were determined by m-line spectroscopy and loss measurements. Waveguide Raman and luminescence spectroscopy were used to obtain information about the structure of the prepared films and about the dynamical process related to the emission in the C telecom band (1530–1565 nm) of the erbium ions. The results are discussed with the aim of comparing the structural and optical properties of erbium-activated silica-titania and silica-hafnia planar waveguides.
Looking at the literature of the last years is evident that glass-based rare-earth-activated optical structures represent the technological pillar of a huge of photonic applications covering Health and Biology, Structural Engineering, Environment Monitoring Systems and Quantum Technologies. Among different glass-based systems, a strategic place is assigned to transparent glass-ceramics, nanocomposite materials, which offer specific characteristics of capital importance in photonics. These two-phase materials are constituted by nanocrystals or nanoparticles dispersed in a glassy matrix. The respective composition and volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. The key to make the spectroscopic properties of the glass-ceramics very attractive for photonic applications is to activate the nanocrystals by luminescent species as rare earth ions. From a spectroscopic point of view the more appealing feature of glass-ceramic systems is that the presence of the crystalline environment for the rare earth ions allows high absorption and emission cross sections, reduction of the non-radiative relaxation thanks to the lower phonon cut-off energy and tailoring of the ion-ion interaction by the control of the rare earth ion partition. Although the systems have been investigated since several years, chemical and physical effects, mainly related to the synthesis and to the ions interactions, which are detrimental for the efficiency of active devices, are subject of several scientific and technological investigations. Here we focus on fabrication and assessment of glass-ceramic photonic systems based on rare earth activated SiO2-SnO2 glasses produced by sol-gel route.
GeO2 transparent glass ceramic planar waveguides were fabricated by a RF-sputtering technique and then irradiated by a pulsed CO2 laser. Different techniques like m-line, micro-Raman spectroscopy, atomic force microscopy, and positronbannihilation spectroscopy were employed to evaluate the effects of CO2 laser processing on the optical and structuralbproperties of the waveguides. The GeO2 planar waveguide after 2h of CO2 laser irradiation exhibits an increase of 0.04 inbthe refractive index, measured at 1542 nm. Moreover, the technique of laser annealing is demonstrated to significantlybreduce propagation loss in GeO2 planar waveguides due to the reduction of the scattering. Upon irradiation of the surfacebthe roughness decreases from 1.1 to 0.7 nm, as measured by AFM. Attenuation coefficients of 0.7 and 0.5 dB/cm at 1319 and 1542 nm, respectively, were measured after irradiation. Micro-Raman measurements evidence that the system embeds GeO2 nanocrystals and their phase varies with the irradiation time. Moreover, positron annihilation spectroscopy was used to study the depth profiling of the as prepared and laser annealed samples. The obtained results yielded information on the structural changes produced after the irradiation process inside the waveguiding films of approximately 1 μm thickness.
Abstract A reproducible route for the preparation of high‐quality CdSe–ZnS‐doped titania and zirconia waveguides is presented. The optical properties of the resultant composite materials are found to be sensitive to the semiconducting properties of the host matrix. Titania‐based composites are seen to be inherently photounstable because of photoelectron injection into the bulk matrix and subsequent nanocrystal (NC) oxidation. In comparison, zirconia composites are significantly more robust with high photoluminescence (PL) retained for annealing temperatures up to 300 °C. Both titania and zirconia composite waveguides exhibit amplified stimulated emission (ASE); however only zirconia‐based waveguides exhibit long‐term photostability (loss of less than 30 % ASE intensity after more than 40 min continuous excitation). We conclude that the low electron affinity of zirconia and its inherent high refractive index makes it an ideal candidate for NC‐based optical waveguides.
