Open Access
Add to BibSonomy
Abstract
Tm3+ doped fluoroaluminate glass fibers are fabricated by using a rod-in-tube method based on AlF3-BaF2-YF3-MgF2-PbF2 glasses. By using a 1400/1570 nm dual-wavelength upconversion pump technique, lasing at ∼2.3 µm is obtained from a 2.3 m long Tm3+ doped fluoroaluminate glass fiber. The measured maximum unsaturated output power is ∼111 mW for a pump power of 1.5/0.14 W at 1400/1570 nm, and the corresponding slope efficiency is ∼11%. The effect of the gain fiber length on lasing at ∼2.3 µm is also investigated. Our results indicate that Tm3+ doped fluoroaluminate glass fibers are promising gain media for constructing ∼2.3 µm fiber lasers.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Tm3+ doped glass fiber lasers operating at ∼2.3 µm are attracting much attention for the requirements in gas sensing and non-invasive blood glucose measurements [1,2]. For Tm3+ doped glass fiber lasers, the ∼2.3 µm lasing is achieved from the stimulated radiative transition between the excited levels 3H4 and 3H5 of Tm3+ ions [3]. Among the fiber materials, fluoride glasses have been considered as the possible gain media of mid-infrared (>2.1∼4 µm) fiber lasers for their relatively low phonon energies, wide transmission window and high solubility for rare earth ions [3–8]. In 1988, L. Esterowitz et al. reported for the first time laser emission at 2.3 µm from a single-mode Tm3+ doped ZrF4 (ZrF4-BaF2-LaF3-AlF3-NaF, ZBLAN) fiber pumped by a pulsed alexandrite laser at 0.786 µm [8]. Soon after, R. Allen et al. demonstrated a diode pumped continuous-wave (CW) ∼2.3 µm Tm3+ ions doped ZBLAN glass fiber laser with an output power of 1 mW and a slope efficiency of ∼ 10% [9]. Since then, efforts were performed on optimizing the parameters of the gain fibers and pump lasers to improve the performance of the ∼2.3 µm fiber lasers [10–13]. Recently, by using a Tm3+ doped double-clad ZBLAN fiber as the gain medium and an upconversion (UC) pumping scheme at ∼1.05 µm, A. Tyazhev et al. obtained 1.24 W lasing at 2269-2282 nm with a slope efficiency of 37% in the quasi-CW regime, whereas, the obtained output power for CW operation was limited to 0.86 W due to the damage of the fiber tip for higher pump powers [13]. In 2020, B. I. Denker et al. reported ∼2.3 µm lasing in tellurite glass fiber, but it was only achieved in pulsed regime [14]. Compared to the ZBLAN glass, fluoroaluminate glasses have relatively high glass transition temperatures(∼380 °C, ∼100 °C higher than that of ZBLAN glass), good water resistance and high laser damage thresholds [15–22]. However, Tm3+ doped fluoroaluminate glass fiber (FAGF) lasers operating at ∼2.3 µm have not been demonstrated.
In this work, we reported lasing at 2298 nm from Tm3+ doped FAGFs by employing a 1400/1570 nm dual-wavelength UC pumping technique. The Tm3+ doped FAGFs were fabricated by using a rod-in-tube method, and the doping concentration of Tm3+ ions was about 4000 ppm. For a pump power of 1.5/0.14 W at 1400/1570 nm, lasing at 2298 nm was obtained from a 2.3 m long Tm3+ doped FAGF. The measured maximum unsaturated output power was ∼111 mW and the corresponding slope efficiency was ∼11%. The influence of the gain fiber length on the performance of lasing at ∼2.3 µm was also investigated.
2. Experiments and results
In the previous works, FAGFs based on the AlF3-BaF2-YF3-MgF2-PbF2 (ABYMP) glasses with a high glass transition temperature of 377 °C (about 100 °C higher than ZBLAN glass), high water resistance, and low hydroxyl (OH-) content have been developed, and lasing at ∼2.9 µm in Ho3+ doped FAGFs has been demonstrated by us [17,18]. Here, Tm3+ doped FAGFs were fabricated based on the ABYMP glass. The core glass had a composition of 30 AlF3-15 BaF2-19.6 YF3-10 MgF2-25 PbF2-0.4 TmF3 (ABYMPT) and the cladding glass had a composition of 35 AlF3-10 BaF2-15 YF3-5 MgF2-20 PbF2-15 CaF2 (ABYMPC). The glass transition temperatures for the core and cladding glasses were 377 and 380 °C, respectively [17]. Figure 1 showed the transmission spectrum of the ABYMPT glass recorded by using a Shimadzu UV3600 spectrometer in the range of 200-2500 nm and a Nicolet 6700 FTIR spectrophotometer in the range of 2500-9000 nm, respectively. Considering a refractive index of about 1.507 at 2.3 µm [17], the transmittance loss caused by the Fresnel reflections is calculated to be about 8%, the other transmittance loss of 1.1% could be attributed the absorption and scattering losses of the ABYMPT glass. In the experiments, all fluoride glasses were prepared by using a conventional melt-quenching method in a glove box filled with dry N2. The detailed process for the fabrication of fluoride glasses could be seen in Ref. [17]. Attributing to the dry atmosphere used in the experiments, no obvious OH- absorption around 3000 nm could be observed, which indicated that there was quite a low content of residual OH- in the ABYMPT glass. This is beneficial to achieve 2.3 µm lasing from the transition 3H4→3H5 of Tm3+ ions. The absorption peaks at 1680 nm, 1212 nm, 790 nm, 684 nm, and 464 nm could be ascribed to the transitions from the ground level 3H6 to the highly excited levels 3F4, 3H5, 3H4, 3F2,3 and 1G4 of Tm3+ ions doped in the ABYMPT glass.
Fig. 1. Transmission spectrum of ABYMPT glass with a thickness of 2.4 mm. Inset: Relative absorption spectrum in the range of 350-2200 nm of ABYMPT glass.
Figure 2 showed the energy level diagram of Tm3+ ions in the ABYMPT glass. Under the excitation of a 793 nm diode laser, intense emissions at ∼1.47, ∼1.9 and ∼2.3 µm were observed from the ABYMPT glass. The stimulated emission cross-section (σemi) was calculated by using the Fuchtbauer-Ladenburg equation [23]:
Fig. 2. Energy level diagram of Tm3+ ions in the ABYMPT glass. MPR: multi-phonon nonradiative relaxation.
Table 1 listed out the parameters used in the calculations, the peak σemi at 2.306 µm was calculated to be about 2.56 × 10−21 cm2, as shown in Fig. 3(a), which was a little larger than that obtained in Tm3+ doped ZBLAN glass (∼2 × 10−21 cm2) [13]. The stimulated absorption cross-sections (σabs) for the transition 3H5 → 3H4 of Tm3+ ions in the ABYPMT glass was obtained by using the McCumber theory [24]:
Fig. 3. (a) Calculated stimulated absorption and emission cross-sections of the transition 3H5↔3H4 of Tm3+ in the ABYMPT glass. (b)Calculated gain cross section of ∼2.3 µm emission in the ABYMPT glass.
Table 1. Parameters used in the calculation of stimulated emission and absorption cross sections
Based on σemi and σabs, the gain cross section G(λ) could be estimated through the following formula [26]:
where the population inversion P was assigned to the concentration ratio of Tm3+ ions in the 3H4 and 3H5 levels. The calculated results were shown in Fig. 3(b). Positive gain could be obtained when P > 0.4. The above results indicated that Tm3+ doped FAGFs had the potential for constructing efficient ∼2.3 µm lasers.By using a similar fiber drawing process mentioned in [17], Tm3+ doped FAGFs with a step-index structure and a core diameter of about 8 µm were fabricated. The fiber drawing temperature used in our experiments was ∼400 °C. The inset of Fig. 4 showed the cross-section of the fabricated the Tm3+ doped FAGFs. By using the refractive indexes of the core (∼1.507 at 2.3 µm) and cladding (∼1.481 at 2.3 µm), the numerical aperture (NA) of the fabricated Tm3+ doped FAGFs was ∼0.28 at ∼2.3 µm. The background loss was measured to be ∼3.7 dB/m at 980 nm by using a cut-back method. In the future, we will try to reduce the fiber loss by using ultra-high purity raw materials, and optimize the fabrication parameters (e.g. glass melting temperature, the glass melting time, the fiber drawing temperature) of fluoride glass fibers for constructing efficient fiber lasers.
To verify the potential of the Tm3+ doped FAGFs for ∼2.3 µm laser applications, we constructed a Tm3+ doped FAGF laser, as shown in Fig. 4. Note that, as mentioned in Ref. [13], efficient ∼2.3 µm fiber laser with watt level output power was achieved by using a UC pumping at ∼1.05 µm. Compared to the single wavelength pumped UC process, dual-wavelength pumping at 1400 and 1560 nm had the advantage to increase optical efficiency due primarily to its high quantum efficiency and low UC loss, and had been used to improve the performance of S-band Tm3+ doped fiber amplifiers [27,28]. In our previous work, we also realized broadband S-band amplification in Tm3+ doped fluorotellurite glass fibers by using a 1400/1570 nm dual-wavelength pump technique [29]. Here, to realize ∼2.3 µm lasing in the Tm3+ doped FAGFs, we also used the 1400/1570 nm dual-wavelength pump technique in the CW regime. The 1400 nm and 1570 nm pump light were combined into a single-mode optical fiber (SMF-28) by using 1400/1570 nm WDM couplers, and then launched into the Tm3+ doped FAGFs through a mechanical connection method [30]. The coupling efficiency was measured to be ∼71%. The output end of the Tm3+ doped FAGFs was mechanically connected with a fluoride (ZBLAN) fiber cable with a core diameter of 400 µm operating at a wavelength of 0.3-4.5 µm. The output end of the ZBLAN fiber cable was connected directly to an optical spectrum analyzer with a measurement range of 1200-2400 nm (Yokogawa, AQ6375). The output power was measured right behind the Tm3+ doped FAGFs by using a power meter.
In our case, since the Fresnel reflection (∼4% at 2.3 µm) existed on the end of the Tm3+ doped FAGFs, a laser cavity could be formed by using the two straight facets of Tm3+ doped FAGFs, which were cleaved finely perpendicular to the fiber axis only. Therefore, no additional mirrors were necessary for obtaining lasing at ∼2.3 µm. Because the reflectance on the two fiber facets were the same, lasing with the same power would output from both sides of short length Tm3+-doped FAGFs. To avoid the generation of ∼1.9 µm lasers, the pump power of the 1570 nm laser was fixed at a relatively low level of 0.14 W. By increasing the launched pump power to ∼492 mW at 1400 nm, lasing at 2298 nm was obtained in a 2.3 m long Tm3+-doped FAGF. Figure 5(a) showed the output spectrum of the above laser for a launched pump power of 1.5 W at 1400 nm and 0.14W at 1570 nm. The spectral lines at 1400 and 1570 nm were ascribed to the pump lasers. The output spectrum of the ∼2.3 µm laser had two laser lines around 2298 nm, as shown in Fig. 5(b). With increasing the launched pump power to 1.5 W, the obtained unsaturated output power of the 2298 nm laser increased monotonically to ∼111 mW, as shown in Fig. 5(c), the corresponding slope efficiency was 11.1%. We believe that, the output power and slope efficiency of the ∼2.3 µm lasers could be further improved by reducing the fiber loss, optimizing the core diameter and NA of the Tm3+ doped FAGFs, and introducing low loss fiber gratings. Note that, emission at 1.47 µm from the transition Tm3+: 3H4 → 3F4 was also observed in our experiments, and lasing at 1.47 µm could be achieved by optimizing the parameters of the Tm3+ doped FAGF and the pump lasers.
Fig. 5. Output spectrum in the range of (a) 1350-2400 nm and (b) 2290-2310 nm for a launched pump power of 1.5 W at 1400 nm and 0.14 W at 1570 nm. (c) Output power of the 2298 nm laser as a function of the launched pump power at 1400 nm with a fixed 1570 nm pump power of 0.14 W.
In addition, we also investigated the effects of the gain fiber length on the performance of the ∼2.3 µm lasers based on Tm3+ doped FAGFs. It is known that the required gain fiber length should be long enough to make sure that the pump light can be absorbed efficiently by the gain fiber. However, if the gain fiber length is too long, the unpumped part of the gain fiber will degrade the lasing performance. Therefore, there exists an optimal fiber length for obtaining highly efficient lasing. Figure 6 showed the dependence of the lasing threshold power and slope efficiency of the ∼2.3 µm lasers on the length of the Tm3+ doped FAGFs. With increasing the gain fiber length from 0.9 to 2.3 m, the slope efficiency increased from 4% to 11% and the lasing threshold power decreased from 1207 to 492 mW. With further increasing the gain fiber length to 3.7 m, the slope efficiency slightly decreased to ∼5.7%, and the lasing threshold power increased monotonically to 832 mW. Therefore, the optimized fiber length was about 2.3 m for obtaining highly efficient and low threshold ∼2.3 µm lasers under the current conditions. Note that, here the threshold power referred to the pump power at 1400 nm, the pump power at 1570 nm was fixed at 0.14 W.
Fig. 6. Dependence of slope efficiency and threshold power of the ∼2.3 µm fiber lasers on the length of Tm3+ doped FAGFs.
3. Conclusions
In conclusion, we fabricated Tm3+ doped FAGFs by using a rod-in-tube method based on the ABYMP glasses. By using a 2.3 m long Tm3+ doped FAGF as the gain medium, lasing at 2298 nm was achieved for a pump power of 0.492/0.14 W at 1400/1570 nm. The obtained maximum unsaturated output power was about 111 mW and the corresponding slope efficiency was 11%. Our results indicated that Tm3+ doped FAGFs could be used for constructing ∼2.3 µm fiber lasers.
Funding
National Key Research and Development Program of China (2020YFB1805800); National Natural Science Foundation of China (62090063, 62075082, U20A20210, 61827821, 11774132); the Open Fund State Key Laboratory on Integrated Optoelectronics.
Disclosures
The authors declare that there are no conflicts of interest related to this article
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. F. J. McAleavey, J. O’Gorman, J. F. Donegan, B. D. MacCraith, J. Hegarty, and G. Mazé, “Narrow linewidth, tunable Tm3+-doped fluoride fiber laser for optical-based hydrocarbon gas sensing,” IEEE J. Select. Topics Quantum Electron. 3(4), 1103–1111 (1997). [CrossRef]
2. S. T. Fard, W. Hofmann, P. T. Fard, G. Bohm, M. Ortsiefer, E. Kwok, M. C. Amann, and L. Chrostowski, “Optical absorption glucose measurements using 2.3-µm vertical-cavity semiconductor lasers,” IEEE Photon. Technol. Lett. 20(11), 930–932 (2008). [CrossRef]
3. S. D. Jackson, “Towards high-power mid-infrared emission from a fibre laser,” Nat. Photonics 6(7), 423–431 (2012). [CrossRef]
4. J.-L. Adam, “Fluoride glass research in France: fundamentals and applications,” J. Fluorine Chem. 107(2), 265–270 (2001). [CrossRef]
5. B. Srubuvasan, E. Poppe, J. Tafoya, and R. K. Jain, “High-power (400 mW) diode-pumped 2.7 µm Er: ZBLAN fibre lasers using enhanced Er-Er cross-relaxation processes,” Electron. Lett. 35(16), 1338–1340 (1999). [CrossRef]
6. S. Duval, M. Bernier, V. Fortin, J. Genest, M. Piché, and R. Vallée, “Femtosecond fiber lasers reach the mid-infrared,” Optica 2(7), 623–626 (2015). [CrossRef]
7. F. Maes, V. Fortin, S. Poulain, M. Poulain, J.-Y. Carrée, M. Bernier, and R. Vallée, “Room-temperature fiber laser at 3.92 µm,” Optica 5(7), 761–764 (2018). [CrossRef]
8. L. Esterowitz, R. Allen, and I. Agarwal, “Pulsed laser emission at 2.3 µm in a thulium-doped fluorozirconate fibre,” Electron. Lett. 24(17), 1104 (1988). [CrossRef]
9. R. Allen and L. Esterowitz, “cw diode pumped 2.3 µm fiber laser,” Appl. Phys. Lett. 55(8), 721–722 (1989). [CrossRef]
10. R. G. Smart, J. N. Carter, A. C. Tropper, and D. C. Hanna, “Continuous-wave oscillation of Tm3+-doped fluorozirconate fibre lasers at around 1.47 µm, 1.9 µm and 2.3 µm when pumped at 790 nm,” Opt. Commun. 82(5-6), 563–570 (1991). [CrossRef]
11. R. M. El-Agmy and N. M. Al-Hosiny, “2.31 µm laser under up-conversion pumping at 1.064 µm in Tm3+: ZBLAN fibre lasers,” Electron. Lett. 46(13), 936–937 (2010). [CrossRef]
12. L. Guillemot, P. Loiko, R. Soulard, A. Braud, J.-L. Doualan, A. Hideur, R. Moncorgé, and P. Camy, “Thulium laser at ∼2.3 µm based on upconversion pumping,” Opt. Lett. 44(16), 4071–4074 (2019). [CrossRef]
13. A. Tyazhev, F. Starecki, S. Cozic, P. Loiko, L. Guillemot, A. Braud, F. Joulain, M. Tang, T. Godin, A. Hideur, and P. Camy, “Watt-level efficient 2.3 µm thulium fluoride fiber laser,” Opt. Lett. 45(20), 5788–5791 (2020). [CrossRef]
14. B. I. Denker, V. V. Dorofeev, B. I. Galagan, V. V. Koltashev, S. E. Motorin, V. G. Plotnichenko, and S. E. Sverchkov, “A 200 mW, 2.3 µm Tm3+ -doped tellurite glass fiber laser,” Laser Phys. Lett. 17(9), 095101 (2020). [CrossRef]
15. Y. Fujimoto, J. Nakanishi, T. Yamada, O. Ishii, and M. Yamazaki, “Visible fiber lasers excited by GaN laser diodes,” Prog. Quantum Electron. 37(4), 185–214 (2013). [CrossRef]
16. F. Huang, Y. Ma, W. Li, X. Liu, L. Hu, and D. Chen, “2.7 µm emission of high thermally and chemically durable glasses based on AlF3,” Sci. Rep. 4(1), 3607 (2014). [CrossRef]
17. S. J. Jia, Z. X. Jia, C. F. Yao, S. B. Wang, H. W. Jiang, L. Zhang, Y. Feng, G. S. Qin, Y. Ohishi, and W. P. Qin, “Ho3+ doped fluoroaluminate glass fibers for 2.9 µm lasing,” Laser Phys. 28(1), 015802 (2018). [CrossRef]
18. H. He, Z. Jia, S. Jia, Q. Hu, Y. Ohishi, W. Qin, and G. Qin, “Ho3+/Pr3+ co-doped AlF3 based glass fibers for efficient ∼2.9 µm lasers,” IEEE Photon. Technol. Lett. 32(23), 1489–1492 (2020). [CrossRef]
19. Y. Fujimoto, M. Nakahara, P. Binun, S. Motokoshi, O. Ishii, M. Watanabe, M. Yamazaki, T. Shinozaki, T. Sato, and Y. Yanomori, “2 W single-mode visible laser oscillation in Pr-doped double-clad structured waterproof fluoro-aluminate glass fiber,” in 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) (2019), pp. 1.
20. S. Wang, J. Zhang, N. Xu, S. Jia, G. Brambilla, and P. Wang, “2.9 µm lasing from a Ho3+/Pr3+ co-doped AlF3-based glass fiber pumped by a 1150 nm laser,” Opt. Lett. 45(5), 1216–1219 (2020). [CrossRef]
21. M. Liu, J. Zhang, N. Xu, X. Tian, S. Jia, S. Wang, G. Brambilla, and P. Wang, “Room-temperature watt-level and tunable ∼3 µm lasers in Ho3+/Pr3+ co-doped AlF3-based glass fiber,” Opt. Lett. 46(10), 2417–2420 (2021). [CrossRef]
22. N. Xu, Z. Yang, J. Zhang, N. Lv, M. Liu, R. Wang, Z. Li, S. Jia, G. Brambilla, S. Wang, and P. Wang, “Direct femtosecond laser inscription of Bragg gratings in Ho3+/Pr3+ co-doped AlF3-based glass fibers for a 2.86 µm laser,” Opt. Lett. 47(3), 597–600 (2022). [CrossRef]
23. B. F. Aull and H. P. Jenssen, “Vibronic interactions in Nd:YAG resulting in nonreciprocity of absorption and stimulated emission cross sections,” IEEE J. Quantum Electron. 18(5), 925–930 (1982). [CrossRef]
24. D. E. McCumber, “Theory of phonon-terminated optical masers,” Phys. Rev. 134(2A), A299–A306 (1964). [CrossRef]
25. W. J. Miniscalco and R. S. Quimby, “General procedure for the analysis of Er3+ cross sections,” Opt. Lett. 16(4), 258–260 (1991). [CrossRef]
26. K. Ohta, H. Saito, and M. Obara, “Spectroscopic characterization of Tm3+: YVO4 crystal as an efficient diode pumped laser source near 2000nm,” J. Appl. Phys. (Melville, NY, U. S.) 73(7), 3149–3152 (1993). [CrossRef]
27. T. Kasamatsu, Y. Yano, and T. Ono, “Laser-diode-pumped highly efficient gain-shifted thulium-doped fiber amplifier operating in the 1480-1510-nm band,” IEEE Photon. Technol. Lett. 13(5), 433–435 (2001). [CrossRef]
28. T. Kasamatsu, Y. Yano, and T. Ono, “1.49-µm-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems,” J. Lightwave Technol. 20(10), 1826–1838 (2002). [CrossRef]
29. J. Wang, Z. Jia, C. Zhang, Y. Sun, Y. Ohishi, W. Qin, and G. Qin, “Thulium-doped fluorotellurite glass fibers for broadband S-band amplifiers,” Opt. Lett. 47(8), 1964–1967 (2022). [CrossRef]
30. Z. Li, Z. Jia, C. Yao, Z. Zhao, N. Li, M. Hu, Y. Ohishi, W. Qin, and G. Qin, “22.7 W mid-infrared supercontinuum generation in fluorotellurite fibers,” Opt. Lett. 45(7), 1882–1885 (2020). [CrossRef]
