Raman spectral bandwidths of tellurite glasses are widened by using Raman active components of suitable
concentration in appropriate base glasses. The MoO6 octahedra were found to have high octahedral distortion; therefore,
have high Raman polarizability compared to WO6, NbO6, and TaO6 octahedra and PO4 tetrahedra. This high Raman
polarizability enabled broadening of the spectral width up to ~350 cm-1 while maintaining high Raman scattering
intensities. Although similar bandwidths could be achieved using combined generation of WO6 octahedra and PO4
tetrahedra, the resultant Raman scattering intensity of such glasses is only half of that could be achievable using MoO6.
It is shown that the simplest tellurite glass showing wide spectral broadening is a quaternary system comprising a
network modifier (BaO or Bi2O3) and two Raman oscillators (NbO6 and MoO6 octahedra). Using the newly developed
gain medium gain flattened S+ C+ L ultrabroadband fiber Raman amplifier are designed by solving the inverse
amplifier design problem. The relative gain flatness and the effective bandwidth of new gain medium are better and
larger than those of conventional tellurite fibers.
In this study, we investigated the performance of slow light generation via SBS or SRS in tellurite glass based on characterization of Raman and Brillouin gain coefficients and an evaluation method of slow light generation we developed. The effects of different heavy metal oxides additions on slow light generation via SRS in tellurite glass are also discussed. Our results show that designed tellurite glass is a promising candidate for slow light generation via SBS or SRS due to its high Raman and Brillouin gain coefficients.
A study was initiated to understand requirements to widen and flatten the gain coefficient spectra of tellurite-based
glasses for their application as new gain media for photonic devices. Rationale of broadening was found to be generating
Raman active structural elements such as WO4, MoO4 and PO4 tetrahedra in appropriate concentrations in suitable base
glasses. Suitable base glass with best compromise between glass formations, optical and thermal properties were
determined. Raman active WO4 and PO4 tetrahedra were generated either separately or jointly in a TeO2-Nb2O5-BaO
(TNB) glass system. The Raman spectral response to this addition was studied by exciting the samples at four
wavelengths, 488, 532, 633, and 785 nm. The Raman intensity and bandwidth increased when WO3 and P2O5 were
jointly added in TNB. Pure non-resonant Raman gain coefficient spectra of the new glasses were derived by comparing
with the gain spectrum of fused silica. The bandwidth of the gain spectra of the present tellurite glasses were more than
twice that of a conventional TeO2-Bi2O3-ZnO-Na2O glass and 70% larger than silica glass. However, gain coefficient of
glasses with broader bandwidths was not impressive. This made us to use transition metal oxides as a network modifier
in place of the alkaline earth oxide and use them as base glasses. By doing so, higher gain coefficients and broader
bandwidths were achieved in a single glass.
We systematically doped WO3 (up to 10 mol%) and P2O5 (up to 16 mol%) in TeO2-BaO-SrO-Nb2O5 (TBSN) glass
system and studied thermal and optical properties of the doped glasses. The dependence of the dopant concentration on
glass transition (Tg) and crystallization (Tx) temperatures are presented. The TBSN glass doped with greater-than or equal to 4 mol% WO3
and P2O5 showed high stability against crystallization. The dependence of optical band gap energy due to WO3 and
P2O5 doping, studied using UV-Vis-NIR absorption spectrometry, is presented. The WO3 doping shifted the optical
band gap to longer wavelength side, whereas P2O5 doping shifted that to shorter wavelength side. Structural details of
the doped glasses are studied using Raman spectrometry. New Raman bands due to WO4 and PO4 tetrahedra are
observed in the Raman spectrum of the doped glasses that broadened the Raman spectrum. The Raman gain coefficient
and bandwidth of tellurite glasses has been tailored by systematically adding WO3 and P2O5 in a TeO2-BaO-SrO-Nb2O5
glass system. The Raman gain coefficients of the resultant glasses were obtained from spontaneous Raman scattering
experiments using a 633 nm laser. The glasses here developed showed the widest gain bandwidth so far achieved in
tellurite glasses while maintaining higher gain coefficients. The gain bandwidths of these glasses are more than twice
that of a conventional tellurite-based glass and 70% larger than that of the silica glass. Present glasses developed are
promising candidates for fiber amplifiers in photonic systems.
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