Highly nonlinear Pb2P2O7-Nb2O5 glasses for optical fiber production

Abstract

In this study we present the production and characterization of Pb 2 P 2 O 7 -Nb 2 O 5 glasses and optical fibers. The dependence of Nb 2 O 5 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 temperatures (T g ) increased linearly with Nb 2 O 5 content up to 60 mol %, while thermal stability against crystallization (T) reached a maximum value of 225 o C at 40 mol% of Nb 2 O 5 . Raman spectra showed a significant structural change by the insertion of NbO 6 octahedral units in the glass network. The increase of Nb 2 O 5 concentration shifts the glasses absorption edge to lower energies, and also increase the linear refractive indexes (n 0 ) due to the high polarizability of niobium atoms and formation of non-bridging oxygen. Similarly to n 0 , an increase in the positive values of nonlinear refractive indexes was observed using Z-Scan technique with increase of Nb 2 O 5 content, based on structural changes caused by the replacement of Pb 2 P 2 O 7 instead Nb 2 O 5 . The average of n 2 values at 500 -1500 nm raised from 2.2 × 10 -19 to 3.8 × 10 -19 m 2 /W, when the Nb 2 O 5 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 Nb 2 O 5 was used for presenting the highest thermal stability against crystallization and n 0 values greater than 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.3 IntroductionLead pyrophosphate glasses containing tungsten oxide in the binary system Pb 2 P 2 O 7 -WO 3 have already been investigated and shown interesting thermal and optical properties, resulting chemically stable, extremely high resistance against devitrification and high linear and nonlinear refractive indexes [1,2]. The optical properties were correlated with the specific phosphate glass network containing lead atoms and tungsten octahedrons. At high WO 3 contents the octahedrons WO 6 units linked together through W-O-W bonds to form highly polarizable clusters, which were pointed out to be responsible, in conjunction with lead atoms polarization, for high linear and nonlinear optical properties [2]. Besides the interesting optical properties, lead pyrophosphate glass present high vitrifying ability and unusual capability to dissolve large amounts of others glass formers, modifiers, or intermediate compounds without reduction of glass forming ability [3,4], as observed by the insertion of WO 6 inside the phosphate covalent network that form strong P-O-W bonds which are responsible to enhance the network connectivity [5]. Transparent phosphate glasses containing heavy metal oxides such as Bi 2 O 3 , Sb 2 O 3 , WO 3 , Nb 2 O 5 , and PbO are subject of intense studies and widely exploited as optical compone...

High niobium oxide content in germanate glasses: Thermal, structural, and optical properties

“…The thermal stability further decreases for higher Nb 2 O 5 concentrations. From this content, as previously studied in tantalum germanate glasses, the Nb 2 O 5 solubility in the germanate liquid reaches a limit and a large amount of niobium oxide progressively forms Nb 2 O 5 ‐rich regions with NbO x clusters which behave as nuclei favoring crystallization . For this reason also a more pronounced crystallization peak can be observed for samples 15Nb and 20Nb.…”

“…The decrease in the band gap may be related to the formation of polyhedra NbO 6 which increase the network connectivity and glass overall polarizability. 22 Since valence and conduction bands are formed from filled and empty molecular orbitals, addition of heavy elements in a glass result in more atomic orbitals which combine and also form a larger number of molecular orbitals, in agreement with the bandgap decrease. These values are comparable to those reported in the literature for germanate glasses.…”

“…The formation of Nb–O–Ge and Nb–O–Nb bonds producing a highly connected covalent network can explain the high observed viscosity. Glasses with high thermal stability are interesting for optical fibers fabrication because of their easier manufacturing process for fiber drawing . The thermal stability further decreases for higher Nb 2 O 5 concentrations.…”

“…From this content, as previously studied in tantalum germanate glasses, 11 the Nb 2 O 5 solubility in the germanate liquid reaches a limit and a large amount of niobium oxide progressively forms Nb 2 O 5 -rich regions with NbO x clusters which behave as nuclei favoring crystallization. 22 For this reason also a more pronounced crystallization peak can be observed for samples 15Nb and 20Nb. Two crystallization peaks are observed for these samples at 701°C and 845°C, and 671°C and 848°C, respectively.…”

“…Glasses with high thermal stability are interesting for optical fibers fabrication because of their easier manufacturing process for fiber drawing. 22 The thermal stability further decreases for higher Nb 2 O 5 concentrations. From this content, as previously studied in tantalum germanate glasses, 11 the Nb 2 O 5 solubility in the germanate liquid reaches a limit and a large amount of niobium oxide progressively forms Nb 2 O 5 -rich regions with NbO x clusters which behave as nuclei favoring crystallization.…”