Highly nonlinear Pb2P2O7-Nb2O5 glasses for optical fiber production
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In this study we present the production and characterization of Pb2P2O7-Nb2O5 glasses and optical fibers. The dependence of Nb2O5 content on thermal, structural and optical properties were investigated by thermal analysis (DSC), Raman spectroscopy, UV-Visible absorption, M-Lines and Z-scan techniques. Glass transition temperature (Tg) increased linearly with Nb2O5 content up to 60 mol%, while thermal stability against crystallization (ΔT) reached a maximum value of 225°C at 40 mol% of Nb2O5. Raman spectra showed a significant structural change by the insertion of NbO6 octahedral units in the glass network. The increase of Nb2O5 concentration shifts the glasses absorption edge to lower energies, and also increases the linear refractive indexes (n0) due to the high polarizability of niobium atoms and formation of non-bridging oxygen. Similarly to n0, an increase in the positive values of nonlinear refractive indexes was observed using Z-Scan technique with increase of Nb2O5 content, based on structural changes caused by the replacement of Pb2P2O7 instead Nb2O5. The average of n2 values at 500-1500 nm raised from 2.2 × 10-19 to 3.8 × 10-19 m2/W, when the Nb2O5 content was increased from 10 to 60 mol%. Lastly, a core-cladding preform was produced by suction method and the optical fiber drawn. The sample containing 40 mol% of Nb2O5 was used for presenting the highest thermal stability against crystallization and n0 values > 2 from green to near-infrared wavelengths. Multimode step index fiber with good core circularity and concentricity was produced and the optical losses were determined by cut-back method at visible and near-infrared ranges.