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Abstract
In this letter, we investigated the Raman scattering characteristics of a series of aTeO2-(90-a)BaF2-10Y2O3 (a = 85, 80, 75, 70, 65, 60, 55 mol%), bTeO2-(95-b)BaF2-5Y2O3 (b = 90, 85, 80, 75, 70, 65, 60, 55, 50 mol%) and cTeO2-(100-c)BaF2 (c = 95, 90, 85, 80, 75, 70, 65, 60 mol%) fluorotellurite glasses. With increasing the concentration of BaF2, the peak Raman gain coefficient at 785 cm−1 increased while the Raman gain bandwidth (full spectral width at half maximum of the Raman peaks around 785 cm−1) decreased, which was attributed to the increasing proportion of non-bridge oxygen bonds in the fluorotellurite glass systems. The same results were also observed for the case of the increasing of the concentration of Y2O3. In these samples, the 50TeO2-40BaF2-10Y2O3 glass has the largest Raman gain coefficient of 29.9 × 10−13 m/W, and the 95TeO2-5BaF2 glass has the widest Raman gain bandwidth of 7.35 THz for the pumping laser at 633 nm. Furthermore, the first-order Raman Stokes light peaked at ∼2373 nm was obtained by using fluorotellurite fiber based on the above glasses as Raman gain medium and a 2000nm picoseconds laser as pump light. Our results provide guidance for further improving the performance of Raman fiber lasers or amplifiers based on fluorotellurite fibers.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Tellurite glasses containing other metal oxides have attracted much attention for a wide range of applications due to their broad transmission window, large linear and nonlinear refractive index, low phonon energies, good thermal and chemical stability. High Raman gain coefficient as well as broad Raman gain bandwidth make tellurite glasses become promising candidates for constructing Raman fiber lasers (RFLs) and amplifiers (RFAs) [1–11]. For tellurite RFLs, Qin et al. demonstrated a widely tunable ring-cavity tellurite RFL covering the S + C + L + U bands [12]. Zhu et al. showed the numerical simulation of a 10-watt-level 3-5 µm tellurite Raman lasers pumped by a continuous-wave (CW) Er-doped fluoride fiber laser operating at 2.8 µm [13]. In the case of RFAs, Masuda et al. demonstrated hybrid tellurite + silica fiber Raman amplifiers with a gain bandwidth of more than 130 nm over S + C + L bands [14]. Qin et al. designed a gain-flattened O, E, and S + C + L ultrabroadband tellurite fiber Raman amplifiers by solving the inverse amplifier design problem [15].
Wide glass-forming range of binary and ternary tellurite glasses allow optimization and tuning of their Raman scattering properties. Generally, tellurite glasses have a peak Raman shift at ∼750 cm−1, which is ascribed to the stretching vibration of the nonbridging oxygen of Te-O− and Te = O bonds in [TeO3 + 1] units (dtbp, distorted trigonal bipyramids) and [TeO3] units (tp, trigonal pyramids), and a second Raman shift at ∼440 cm−1, which is ascribed to the stretching or bending vibration of bridging oxygen of Te-O-Te linkage constructed by [TeO4] units (tbp, trigonal bipyramids). Several studies demonstrated that the Raman gain coefficient and the Raman gain bandwidth could be further improved by the addition of the modifiers such as alkali, alkaline earth and transitional metal oxides or other glass formers [16,17]. However, few of those tellurite glasses could be used for constructing RFLs and RFAs.
Very recently, fluorotellurite fibers based on TeO2-BaF2-Y2O3 (TBY) glasses have been developed by us. By using a 5.38 m fluorotellurite fiber as the Raman gain medium and a 1550 nm nanosecond laser as the pump laser, we observed a third-order cascaded Raman scattering shift with the first-, second-, and third-order Stokes emissions peaked at 1765, 2049, and 2438 nm, respectively [18]. Subsequently, we demonstrated efficient cascaded Raman amplification in all-solid fluorotellurite fibers by using a 1550 nm nanosecond laser as pump light and CW 1765/2049.2 nm lasers as signal source [19]. These results indicated that fluorotellurite fibers can be applied as a gain medium for RFLs and RFAs. However, until now, the effect of BaF2 and Y2O3 on the Raman scattering characteristics of TBY glasses has not been studied yet.
In this work, a series of aTeO2-(90-a) BaF2-10Y2O3 (a = 85, 80, 75, 70, 65, 60, 55, 50 mol%), bTeO2-(95-b)BaF2-5Y2O3 (b = 90, 85, 80, 75, 70, 65, 60, 55 mol%) and cTeO2-(100-c)BaF2 (c = 95, 90, 85, 80, 75, 70, 65, 60 mol%) fluorotellurite glasses were prepared with a conventional melting quenching method, and the Raman gain spectra of these samples were measured and compared. With increasing the concentration of BaF2, the peak Raman gain coefficient at 785 cm−1 increased while the Raman gain bandwidth decreased, which were attributed to the increasing proportion of non-bridge oxygen bonds in the fluorotellurite glass systems. And the same results were also observed for the case of the increasing of the concentration of Y2O3. In these samples, the 50TeO2-40BaF2-10Y2O3 glass has the largest Raman gain coefficient of 29.9 × 10−13 m/W, and the 95TeO2-5BaF2 glass has the widest Raman gain bandwidth of 7.35 THz at 633 nm. Furthermore, the first-order Raman Stokes light peaked at ∼2373 nm was obtained by using fluorotellurite fiber based on 50TeO2-40BaF2-10Y2O3 glasses as Raman gain medium and a 2000nm picoseconds laser as pump light. Our results provide a guidance for further improving the performance of RFLs or RFAs based on fluorotellurite fibers.
2. Experiments
Fluorotellurite glasses samples were melted by using a conventional melting-quenching method. Table 1 listed out the compositions of the TBY glasses. Crystallization of fluorotellurite glasses would occur outside the above glasses compositional range. High-purity TeO2 (99.999%), BaF2 (99.99%) and Y2O3 (99.999%) were used as the starting chemical materials. The powders of the starting components were precisely weighed and mixed well using a zirconia mortar and pestle. The mixed powders (∼15 g) were melted at ∼950°C for ∼30 min. The melt was then quenched onto a preheated copper plate at ∼400°C and subsequently annealed at this temperature for ∼200 min to eliminate the thermal stress developed during quenching. The glass samples were cut into 20 mm × 20 mm × 2 mm pieces and polished well for subsequent optical measurement.
Table 1. Compositions of TBY glasses
The Raman spectra of the glass samples were measured by a Raman scattering spectrometer (Labram HR Evolution) in the range of 100-1200 cm−1 at room temperature. The glasses samples were excited with a 633 nm laser with an output power of 500 mW. Raman spectrum of the silica glass was also measured at the same conditions as a standard for correcting errors due to reflectivity and angel of data collection. Subsequently, we calculated the Raman gain spectra of selected glass samples from the Raman spectra. To eliminate low wavenumber thermal effects, the spectral intensity should also be divided by the Bose-Einstein correction factor as following equation [20]:
where Icorr is the correct Raman intensity, v is the frequency of the Raman shift relative to the pump, k is the Boltzmann constant (1.381 × 10−23 J K−1), and T is the temperature during the Raman test (298 K for the Raman spectra presented here). Subsequently, the Raman gain coefficient of glasses samples can be calculated by the following equation [20]:3. Results and discussion
We first investigated the effect of BaF2 on the Raman scattering characteristics of the fluorotellurite glasses. Figure 1(a) shows the measured Raman gain coefficient profiles of the TBY0-TBY7 glasses. The TBY glasses have three Raman bands peaked at ∼471, ∼696, and ∼785 cm−1 respectively. Figure 1(b) shows the variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain bandwidth in the TBY0-TBY7 glasses. With increasing the concentration of BaF2, the Raman gain coefficient at 785 cm−1 increased while that at 696 and 471 cm−1 decreased. The Raman gain width decreased with the increasing of the concentration of BaF2. To further explain the mechanism of BaF2 in the TBY glasses, the Raman gain spectra was fitted to multiple Gaussian functions, as shown in Fig. 1(c). The spectra of all compositions were deconvoluted to seven symmetrical Gaussian profiles peaked at ∼140 cm−1, ∼400 cm−1, ∼440 cm−1, ∼610 cm−1, ∼665 cm−1, ∼780 cm−1, and ∼810 cm−1, which were labeled T1 to T7 bands. Each Gaussian profile corresponds to a vibrational mode of a unit composing the glass structure, as listed in Table 2. The T1 and T2 bands are attributed to the symmetrical stretching or bending vibrations of O-Te-O linkages. In addition, vibration of the other O-cation-O linkages can also contribute to the T1 and T2 bands intensities [21,22]. The T3 band is assigned to the bending vibrations of Te-O-Te linkages formed by corner sharing of [TeO4] units, [TeO3 + 1] units and [TeO3] units [17,21]. The T4 and T5 bands are due to the antisymmetric stretching of a continuous network composed of [TeO4] (tbp) and Te-O-Te linkages constructed by two unequal Te-O bonds, respectively [21,23–26]. And T5 band may contain: Te4-eqOax-Te4, Te4-eqO···Te3 + 1, Te4-axOeq-Te3 + 1, Te4-axOeq-Te3, Te3 + 1-eqO···Te3 + 1, and Te3-eqO···Te3 + 1, where the subscript eq and ax refer to the Te-O bond at equal and axial oxygen, respectively [24,27,28]. These linkages are characterized by the connection of a long and a short Te-O bonds [26]. The T6 band is due to stretching modes of Te-O− and Te = O bonds containing NBOs in [TeO3] units and [TeO3 + 1] units [17,28]. The T7 band is due to the distorted [TeO3 + 1] units and stretching vibrations of NBOs atoms and Te in [TeO3] units [23].
Fig. 1. (a) Spontaneous Raman scattering spectra profiles of aTeO2-(90-a) BaF2-10Y2O3 (a = 85, 80, 75, 70, 65, 60, 55 mol%, named as TBY0, TBY1, TBY2, TBY3, TBY4, TBY5, TBY6, TBY7, respectively) glasses. (b) The variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain width in the TBY0-TBY7 glasses. (c) Raman gain coefficient profiles of TBY7 glass fitted to multiple Gaussian functions and moving direction of Raman characteristic peak with the increase of the BaF2 content (d) Dependence of frequency shift trend of Raman characteristic peak on the content of BaF2.
Table 2. Vibrations of the TBY glasses
The Raman band peaked at ∼785 cm−1 is mainly composed of T6 and T7. The Raman band peaked at ∼696 cm−1 is mainly composed of T4 and T5. And the Raman band peaked at ∼471 cm−1 is mainly composed of T2 and T3. The additional Ba2+ replaced the original position of Te6+, and led to the formation of the Ba-O-Te or Ba-O-Ba linkage (corresponding to the vibration of T2), causing the reduction of Te-O-Te linkages (corresponding to the vibration of T2, T3 and T5). The additional F− replaced the position of O2- of Te-axOeq-Te (corresponding to the vibration of T5) [22,26], causing the formation of Te-O− bond (corresponding to the vibration of T6), Te = O bond (corresponding to the vibration of T6), [TeO3] units (corresponding to the vibration of T7), [TeO3 + 1] units (corresponding to the vibration of T7), Te(O,F)3 units and Te(O,F)3 + 1 units [29,30]. The modification of the units in the fluorotellurite glasses caused the variation of the Raman gain coefficient. In addition, with increasing the concentration of BaF2 in the glass system, the peak position of the fitted Gaussian function also moved, as shown in Fig. 1(d). The change of intensity and movement in T1-T7 makes the Raman gain bandwidth decrease with the increasing of the concentration of BaF2.
Furthermore, we investigated Raman scattering characteristics of fluorotellurite glasses as the concentration of Y2O3 was about 5 mol%. Figure 2(a) shows the measured Raman gain coefficient profiles of TBY8-TBY15 glasses. Similar to TBY0-TBY7 glasses, owing to the increasing proportion of NBOs bonds, the Raman gain coefficient at 785 cm−1 increased while that at 696 and 471 cm−1 decreased with the increasing of the concentration of BaF2. And the Raman gain bandwidth decrease with the increasing of the concentration of BaF2, as shown in Fig. 2(b).
Fig. 2. (a) Spontaneous Raman scattering spectra profiles of bTeO2-(95-b)BaF2-5Y2O3 (b = 90, 85, 80, 75, 70, 65, 60, 55 mol%, named as TBY8, TBY9, TBY10, TBY11, TBY12, TBY13, TBY14, TBY15, respectively) glasses. (b) The variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain width in the TBY8-TBY15 glasses.
For binary glass components of TeO2-BaF2, the measured Raman gain coefficient profiles were shown in Fig. 3(a). They have a smaller Raman gain coefficient and a wider Raman gain bandwidth than that of ternary glass system of TeO2-BaF2-Y2O3. The variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain bandwidth with the concentration of BaF2 were shown in Fig. 3(b). Also due to the increasing proportion of NBOs bonds in the TBY16-TBY23 glasses, the Raman gain coefficient at 785 cm−1 increased while that at 696 cm−1 and 471 cm−1 decreased with the increasing of the concentration of BaF2. And the Raman gain bandwidth decreased with the increasing of the concentration of BaF2.
Fig. 3. (a) Spontaneous Raman scattering spectra profiles of cTeO2-(100-c)BaF2 (c = 95, 90, 85, 80, 75, 70, 65, 60 mol%, named as TBY16, TBY17, TBY18, TBY19, TBY20, TBY21, TBY22, TBY23, respectively) glasses. (b) The variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain width in the TBY16-TBY23 glasses.
The effect of Y2O3 on the Raman scattering characteristics of the fluorotellurite glasses was also investigated, and the measured Raman gain coefficient profiles of TBY0, TBY8 and TBY16 glasses were shown in Fig. 4(a). Figure 4(b) shows the variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain bandwidth with the concentration of Y2O3. With increasing the concentration of Y2O3, the Raman gain coefficient at 785 and 696 cm−1 increased while that at 471 cm−1 decreased. The additional Y3+ replaced the Te6+ and led to the formation of a hexahedron structure and Te-O-Y linkages, causing the reduction of bridging oxygen of Te-O-Te linkage (corresponding to the vibration of T2 and T3), Te-eqOax-Te linkage (corresponding to the vibration of T5). And the NBOs of Te-eqO− and Te-axO− bonds (corresponding to the vibration of T6) could be formed.
Fig. 4. (a) Spontaneous Raman scattering spectra profiles of TBY0, TBY8, TBY16 glasses. (b) The variations of Raman gain coefficient at 785, 696, 471 cm−1 and the Raman gain width in the TBY0, TBY8 and TBY16 glasses.
Table 3 summarized the Raman gain coefficient and Raman gain bandwidth of TBY0-TBY23 glasses for the pumping laser at 633 nm. The TBY7 (50TeO2-40BaF2-10Y2O3) glass has the maximum Raman gain coefficient of ∼29.9 × 10−13 m/W, and the TBY16 (95TeO2-5BaF2) glass has the widest Raman gain bandwidth of ∼7.35 THz. Table 4 compared the Raman gain coefficients and gain bandwidths of different tellurite/fluorotellurite glasses. The Raman gain coefficients and gain bandwidths obtained in our work were comparable with that of other fluorotellurite glasses and tellurite glasses. These results provide a reference guidance for further improving the performance of RFLs or RFAs based on fluorotellurite fibers.
Table 3. The Raman gain coefficient and Raman gain bandwidth of TBY0-TBY23 glasses for the pumping laser of 633 nm
Table 4. Comparison of Raman gain coefficients and gain bandwidths of different tellurite/fluorotellurite glasses
Furthermore, to verify the potential of the above fluorotellurite glasses for constructing mid-infrared RFLs and RFAs, we performed experiments on stimulated Raman scattering in a 10 m fluorotellurite glass fiber. The fluorotellurite fibers based on TBY7 (50TeO2-40BaF2-10Y2O3) glasses were fabricated by using a rod-in-tube method, in which a suction method is used to make the fiber preforms. The inset of Fig. 5(a) shows the scanning electron microscope image of the cross-section of the fluorotellurite fiber. The fiber has a step-index structure and a core diameter of 5.5 µm. The numerical aperture of the fiber was about 0.28 at 2 µm and the nonlinear coefficient of the fiber was calculated to be ∼47.38 km−1 W−1 at 2 µm by using a nonlinear refractive index of 3.5 × 10−19 m2 W−1 for TBY glasses. And the transmission loss of the fluorotellurite fiber was measured to be ∼0.093 dB/m at 2 µm by using a cut-back method. A 2000nm picosecond fiber laser with a pulse width of 3 ps and a repetition of 50 MHz was used as the pump laser source. The pump light was mechanically coupled into the fluorotellurite glass fiber, as mentioned in Ref. [35]. The output signal from the fluorotellurite fiber was recorded by using a power meter and two optical spectrum analyzers with a measurement range of 1200-2400 nm (Yokogawa, AQ6375) and 1900-5500 nm (Yokogawa, AQ6377), respectively. Figure 5(a) shows the first-order Raman shift spectra of the fluorotellurite fiber. When the pump power was 0.94 W, the spontaneous Raman Stokes light peaked at ∼2373 nm was obtained, corresponding to the main Raman shift of ∼785 cm−1 of TBY glass in Fig. 1(a). As the pump power was increased to 1.62W, another Raman Stokes light was observed peaked at ∼2193 nm, which could be attributed to the first Raman gain band (around 470 cm−1) of the TBY glass. With the increase of pump power, the spontaneous Raman emission was amplified by the stimulated Raman scattering. Since the operating wavelengths of pump and Stokes lights were located in the anomalous dispersion region of the fluorotellurite fiber, large spectral broadening was observed for the further increase of the pump power, which might be caused by other nonlinear optical effects (e.g., soliton fission) in the fluorotellurite fiber [36]. Figure 5(b) shows the dependence of the average output power on the launched pump power of the 2000nm picosecond laser. With increasing the launched average pump power to 2.213 W, the total output power linearly increased to 1.595 W, and the first-order Stokes light was exponentially grown to 0.31 W, corresponding an optical-optical convention efficiency of 14%, which could be improved by managing the dispersion of the fluorotellurite glass fiber and using long-pulse/CW pump lasers. We believe that, efficient mid-infrared Raman fiber lasers will be achieved by optimizing the parameters of the fluorotellurite glass fibers and developing appropriate fiber Bragg gratings (FBGs).
Fig. 5. (a) Dependence of the measured first-order Raman shift spectra from the fluorotellurite glass fiber pumped by a 2000nm quasi-continuous laser. Inset: scanning electron micrograph of the fiber cross-section. (b) Dependence of the average output power on the launched pump power of the 2000nm quasi-continuous laser.
4. Conclusions
The Raman scattering properties of TeO2-BaF2-Y2O3 glass samples were studied. The TBY glasses have three Raman bands peaked at ∼471, ∼696, and ∼785 cm−1 respectively. The effects of BaF2 and Y2O3 on the glass structure were also systematically studied by analyzing the changes in Raman gain spectra. The results showed that, with increasing the concentration of BaF2, the Raman gain coefficient at 785 cm−1 increased while that at 696 and 471 cm−1 decreased. With increasing the concentration of Y2O3, the Raman gain coefficient at 785 and 696 cm−1 increased while that at 471 cm−1 decreased. These changes were attributed to the increasing proportion of non-bridge oxygen bonds in the fluorotellurite glass systems. In these samples, the 50TeO2-40BaF2-10Y2O3 glass has the largest Raman gain coefficient of 29.9 × 10−13 m/W at ∼785 cm−1 and the 95TeO2-5BaF2 glass has the widest Raman gain bandwidth of 7.35 THz for the pumping laser at 633 nm. Furthermore, by using fluorotellurite fiber based on 50TeO2-40BaF2-10Y2O3 glass as Raman gain medium and a 2000nm laser as pump light, first-order Raman Stokes lights peaked at ∼2193 and ∼2373 nm were obtained. Our results provide a guidance for further improving the performance of RFLs or RFAs based on fluorotellurite fibers.
Funding
National Natural Science Foundation of China (62090063, 62075082, U20A20210, 61827821, U22A2085, 62235014, 62205121); the Opened Fund of the State Key Laboratory of Integrated Optoelectronics.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. G. P. Agrawal, Nonlinear Fiber Optics. (Springer, 2000).
2. J. M. Dudley and J. R. Taylor, Supercontinuum Generation in Optical Fibers (Cambridge University Press, 2010).
3. A Mori, “Tellurite-based fibers and their applications to optical communication networks,” J. Ceram. Soc. Jpn. 116(1358), 1040–1051 (2008). [CrossRef]
4. I D Aggarwal and J S Sanghera, “Development and applications of chalcogenide glass optical fibers at NRL,” J. Optoelectron. Adv. Mater. 4(3), 665–678 (2002).
5. M D O’donnell, K Richardson, and R Stolen, “Tellurite and fluorotellurite glasses for fiberoptic Raman amplifiers: glass characterization, optical properties, Raman gain, preliminary fiberization, and fiber characterization,” J. Am. Ceram. Soc. 90(5), 1448–1457 (2007). [CrossRef]
6. X. Li, M. An, G. Li, et al., “MOF-Derived Porous Dodecahedron rGO-Co3O4 for Robust Pulse Generation,” Adv. Mater. Interfaces 9(5), 2101933 (2022). [CrossRef]
7. C. Zhang, J. Liu, Y. Gao, et al., “Porous nickel oxide micron polyhedral particles for high-performance ultrafast photonics,” Opt. Laser Technol. 146, 107546 (2022). [CrossRef]
8. X. Li, J. Feng, W. Mao, et al., “Emerging uniform Cu2O nanocubes for 251st harmonic ultrashort pulse generation,” J. Mater. Chem. C 8(41), 14386–14392 (2020). [CrossRef]
9. X. Li, W. Xu, Y. Wang, et al., “Optical-intensity modulators with PbTe thermoelectric nanopowders for ultrafast photonics,” Applied Materials Today 28, 101546 (2022). [CrossRef]
10. Y. Zhao, W. Wang, X. Li, et al., “Functional porous MOF-derived CuO octahedra for harmonic soliton molecule pulses generation,” ACS Photonics 7(9), 2440–2447 (2020). [CrossRef]
11. C. Zhang, X. Li, E. Chen, et al., “Hydrazone organics with third-order nonlinear optical effect for femtosecond pulse generation and control in the L-band,” Opt. Laser Technol. 151, 108016 (2022). [CrossRef]
12. G. Qin, M. Liao, T. Suzuki, et al., “Widely tunable ring-cavity tellurite fiber Raman laser,” Opt. Lett. 33(17), 2014–2016 (2008). [CrossRef]
13. G. Zhu, L. Geng, X. Zhu, et al., “Towards ten-watt-level 3-5 µm Raman lasers using tellurite fiber,” Opt. Express 23(6), 7559–7573 (2015). [CrossRef]
14. H. Masuda, A. Mori, K. Shikano, et al., “Design and spectral characteristics of gain-flattened tellurite-based fiber Raman amplifiers,” J. Lightwave Technol. 24(1), 504–515 (2006). [CrossRef]
15. G. Qin, R. Jose, and Y. Ohishi, “Design of ultimate gain-flattened O-, E-, and S+ C+ L ultrabroadband fiber amplifiers using a new fiber Raman gain medium,” J. Lightwave Technol. 25(9), 2727–2738 (2007). [CrossRef]
16. . V. Rajendran, N. Palanivelu, B. K. Chaudhuri, et al., “Characterisation of semiconducting V2O5-Bi2O3-TeO2 glasses through ultrasonic measurements,” J. Non-Cryst. Solids 320(1-3), 195–209 (2003). [CrossRef]
17. N. Manikandan, A. Ryasnyanskiy, and J. Toulouse, “Thermal and optical properties of TeO2-ZnO-BaO glasses,” J. Non-Cryst. Solids 358(5), 947–951 (2012). [CrossRef]
18. Y. Jiao, Z. Jia, X. Guo, et al., “Third-order cascaded Raman shift in all-solid fluorotellurite fiber pumped at 1550 nm,” Opt. Lett. 47(3), 690–693 (2022). [CrossRef]
19. Y. Jiao, F. Meng, Z. Jia, et al., “Cascaded Raman amplifiers based on fluorotellurite fibers,” Opt. Mater. Express 12(6), 2309–2317 (2022). [CrossRef]
20. M.D. O’Donnell, K. Richardson, R. Stolen, et al., “Raman gain of selected tellurite glasses for IR fibre lasers calculated from spontaneous scattering spectra,” Opt. Mater. 30(6), 946–951 (2008). [CrossRef]
21. G. Qin, R. Jose, and Y. Ohishi, “Stimulated Raman scattering in tellurite glasses as a potential system for slow light generation,” J. Appl. Phys. 101(9), 093109 (2007). [CrossRef]
22. G.S. Murugan and Y. Ohishi, “Raman spectroscopic studies of TeO2-BaO-SrO-Nb2O5 glasses: Structure-property correlations,” J. Appl. Phys. 96(5), 2437–2442 (2004). [CrossRef]
23. T. Sekiya, N. Mochida, A. Ohtsuka, et al., “Raman spectra of MO1/2-TeO2 (M = Li, Na, K, Rb, Cs and Tl) glasses,” J. Non-Cryst. Solids 144, 128–144 (1992). [CrossRef]
24. T. Sekiya, N. Mochida, and A. Ohtsuka, “Raman spectra of MO-TeO2 (M = Mg, Sr, Ba and Zn) glasses,” J. Non-Cryst. Solids 168(1-2), 106–114 (1994). [CrossRef]
25. V. Kamalaker, G. Upender, C. Ramesh, et al., “Raman spectroscopy, thermal and optical properties of TeO2-ZnO-Nb2O5-Nd2O3 glasses,” Spectrochim. Acta, Part A 89, 149 (2012). [CrossRef]
26. J. Hrabovsky, F. Desevedavy, L. Strizik, et al., “Glass formation and properties of the TeO2-ZnO-BaO tellurite optical glasses,” J. Non-Cryst. Solids 582, 121445 (2022). [CrossRef]
27. T. Sekiya, N. Mochida, and A. Soejima, “Raman spectra of binary tellurite glasses containing tri- or tetra-valent cations,” J. Non-Cryst. Solids 191(1-2), 115–123 (1995). [CrossRef]
28. T. Sekiya, N. Mochida, A. Ohtsuka, et al., “Raman spectra of BO3/2-TeO2 glasses,” J. Non-Cryst. Solids 151(3), 222–228 (1992). [CrossRef]
29. E.F. El Agammy, H. Doweidar, K. El-Egili, et al., “Structure of NaF–TeO2 glasses and glass-ceramics,” Ceram. Int. 46(11), 18551–18561 (2020). [CrossRef]
30. E.F. El Agammy, H. Doweidar, K. El-Egili, et al., “PbF2-TeO2 glasses and glass-ceramics: a study of physical and optical properties,” Appl. Phys. A 127(12), 962 (2021). [CrossRef]
31. R. Jose, G. Qin, Y. Arai, et al., “Tailoring of Raman gain bandwidth of tellurite glasses for designing gain-flattened fiber Raman amplifiers,” J. Opt. Soc. Am. B 25(3), 373–381 (2008). [CrossRef]
32. R. Stegeman, L. Jankovic, H. Kim, et al., “Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica,” Opt. Lett. 28(13), 1126–1128 (2003). [CrossRef]
33. R. Jose and Y. Ohishi, “Enhanced Raman gain coefficients and bandwidths in P2O5 and WO3 added tellurite glasses for Raman gain media,” Appl. Phys. Lett. 89(12), 121122 (2006). [CrossRef]
34. A. Lin, A. Pyasnyanskiy, and J. Toulouse, “Fabrication and characterization of a water-free mid-infrared fluorotellurite glass,” Opt. Lett. 36(5), 740–742 (2011). [CrossRef]
35. Z. Li, Z. Jia, C. Yao, et al., “22.7 W mid-infrared supercontinuum generation in fluorotellurite fibers,” Opt. Lett. 45(7), 1882–1885 (2020). [CrossRef]
36. C. Yao, Z. Jia, Z. Li, et al., “High-power mid-infrared supercontinuum laser source using fluorotellurite fiber,” Optica 5(10), 1264–1270 (2018). [CrossRef]
