Emissions properties of glasses in the PbO-Ga2O3-Bi2O3 system doped with a variety of different rare-earth ions were reviewed with particular attention on the applications towards the amplification of the optical signals in the fiber-optic communication systems and for mid-infrared lasers. Due to the low vibrational phonon energy of the glasses, it was possible to realize the efficient emissions for the O-band and S-band amplification by doping Pr3+, Dy3+ or Tm3+. Amplification at these communication bands has not been possible when conventional oxide glasses were used as host materials. Network structure of the glass was made of mixture of GaO4 tetrahedra and PbO3/PbO4 polyhedra as a backbone. They are connected through bridging oxygens and a portion of these oxygen atoms are connected to three cations instead of two. Pb2+ ions also act as charge compensators as evidenced from the large amount of non-bridging oxygens in the glass network. Bi2O3 form BiO6 octahedra.
The possibility of developing 1.6μm band optical amplifiers was investigated using the emission from the Ho3+-doped cholcogenide glasses. Selenide and sulfide glasses with a low vibrational phonon energy were used as host materials. The maximum Ho3+ concentration in the glasses was 0.08mol% due to the cross relaxation process. Tb3+ co-doping reduced the lifetimes of the Ho3+:5I7 level and thereby, provided opportunities for the population inversion.
Emissions at 1.3µm and mid-infrared region from several rare-earths ions doped into PbO-Bi2O3-Ga2O3 glasses were
investigated. Lifetime of the Pr3+:1G4 level was 53µs with a quantum efficiency of 9%. Emission at 2.73µm from Er3+, which
is normally quenched in oxide glass, was evident and the lifetime of the upper emission level was approximately 900µs.
Thermal stability of PbO-Bi2O3-Ga2O3 glass was considerably improved by adding 10 mole % of GeO2. Doping of Tm3+ and
Ho3+ showed potentials for S-band fiber-optic amplification.
A representative of heavy metal oxide glasses, i.e., a PbO- Bi2O3-Ga2O3 glass, was investigated to identify the network structure of the glass and the electronic transition properties of rare-earth ions doped. X-ray absorption spectroscopic analyses showed that gallium forms GaO4 tetrahedral units with an average Ga-O bond length of approximately 1.87 A. Lead forms both PbO3 and PbO4 polyhedra, but the fraction of PbO4 decreases with decreasing PbO content. Bismuth in glasses constructs BiO5 and BiO6 polyhedra, which have a similar coordination scheme of the (alpha) -Bi2O3 crystal. Formation of three-coordinated oxygens is necessary to compensate shortage of oxygens to be two-fold coordinated. These glasses exhibit a relatively good thermal stability as well as the lowest phonon energy among oxide glasses, and thereby enhance numerous fluorescence emissions that are quenched in the conventional oxide glasses. Magnitudes of multiphonon relaxation are the lowest among oxide glasses and comparable to those of fluoride glasses. Fluorescence emission characteristics of Pr3+: 1.3 micrometer and Er3+: 2.7 micrometer were discussed in detail. In addition, influence of OH- on the Nd3+: 1.3 micrometer emission was analyzed. Further research efforts on impurity minimization and fiberization may realize a new oxide-based fiber-optic host.
Chalcogenide and heavy metal oxide (HMO) glasses doped with various rare-earth elements have been studied for the possibility of developing new solid state laser materials to operate in the mid-infrared. This study investigates the synthesis and optical characterization of As2S3 and Bi2O3-PbO-Ga2O3 glasses doped with rare-earth elements Nd, Er, Ho, Dy, Pr and Tm. Absorption and fluorescence spectra of glasses doped with rare- earths confirmed the presence of trivalent rare-earth ions in the amorphous matrix. As2S3 glasses doped with 0.4 wt% Nd showed strong fluorescence at 1.09 and 1.38 micrometers , while glasses doped with 2.0 wt% Dy exhibited fluorescence at 2.98 and 4.40 micrometers . Further, doping of Ho up to approximately 2.0 wt% showed fluorescence at 2.01 and 3.92 micrometers .
Chalcohalide glasses are mixtures of chalcogenides and halides. This paper reviews the properties and structure of various glass-forming chalcohalide systems. These materials possess high transmittance in the infrared, which make them candidates for various applications in the area of infrared fiber optics. In general, the packing density, glass transition temperature (Tg), and refractive indices decrease with the addition of a halogen component into binary chalcogenide glasses. It also seems to be theoretically possible that the attenuation loss of the glasses and fibers, especially at 10.6 μm, decreases at the same time. The observed changes in the properties of glasses are in good agreement with the proposed structural model, suggesting degradation of the network connectivity by the addition of network-terminating halogen atoms.
Tellurium and iodine were added to a base chalcogenide glass composition (Ge33Asl2Se5S) to compare their effects
on physical and optical properties. Iodine decreased the glass transition temperature and increased thermal expansion to a
greater extent than tellurium. However, density was lowered by the presence of iodine and increased by tellurium.
Examination of the multiphonon absorption edge in the 300-900 cm1 range revealed that iodine and tellurium occupy
different structural sites which accounts for their varied effect on physical properties. There appears to be no advantage of
iodine versus tellurium additions with regard to optical fiber applications based on the results obtained.
New IR glasses transmitting from 1 to 20 im and having low loss potentiality in the 8- 12 pm region have
been obtained in the Te-Br-Se and Te-I-Se systems. Single index fibers have been drawn from rods and the
attenuation measuredin normal atmospheric conditions. The influence ofthe band gap absorption mechanism
appears to be very critical as well as the addition ofelements such as Bi which seems to improve the mechnical