Open Access
Add to BibSonomy
Abstract
Raman fiber laser (RFL) has been widely adopted in astronomy, optical sensing, imaging, and communication due to its unique advantages of flexible wavelength and broadband gain spectrum. Conventional RFLs are generally based on silica fiber. Here, we demonstrate that the phosphosilicate fiber has a broader Raman gain spectrum as compared to the common silica fiber, making it a better choice for broadband Raman conversion. By using the phosphosilicate fiber as gain medium, we propose and build a tunable RFL, and compare its operation bandwidth with a silica fiber-based RFL. The silica fiber-based RFL can operate within the Raman shift range of 4.9 THz (9.8-14.7 THz), whereas in the phosphosilicate fiber-based RFL, efficient lasing is achieved over the Raman shift range of 13.7 THz (3.5-17.2 THz). The operation bandwidths of the two RFLs are also calculated theoretically. The simulation results agree well with experimental data, where the operation bandwidth of the phosphosilicate fiber-based RFL is more than twice of that of the silica fiber-based RFL. This work reveals the phosphosilicate fiber’s unique advantage in broadband Raman conversion, which has great potential in increasing the reach and capacity of optical communication systems.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Stimulate Raman scattering (SRS) effect, first discovered within a nitrobenzene Kerr cell of a Q-switched ruby laser in 1962 [1], is widely observed in a large number of liquids, gases, and solids [2–5]. Optical fiber, due to its small core size and good transverse confinement characteristics, is an excellent medium for SRS [6]. In the early 1970s, Stolen et al. demonstrated the feasibility of laser generation through SRS effect in optical fiber [7,8]. Compared to optical gain provided by active fibers, the Raman gain based on SRS effect has two fundamental advantages. Firstly, it exists in almost every fiber, thus is much more convenient and cost-effective. Secondly, it is free of the limitation of emission bandwidth. The signal wavelength is determined by the pump wavelength and Raman shift. Provided with appropriate pump laser, Raman fiber laser (RFL) can operate at any wavelength within transparency region of the fiber in principle [9].
In recent decades, RFLs have advanced tremendously in terms of power scaling, spectra manipulation, and wavelength extending [9,10] and have been applied in various aspects, such as astronomy [11,12], biomedical imaging [13,14], environmental sensing [15,16], ultrafast pulse generation [17,18] and most importantly, optical communication [19–21]. Since the early 2000s, Raman amplification has been commercially utilized in optical communication system and has enabled dramatic increases in its reach and capacity [22–24]. Conventional RFLs or Raman amplifiers are generally based on silica fiber. Although the Raman gain spectrum of silica fiber extends over a large frequency shift range of 40 THz, the 3 dB bandwidth of the Raman gain curve is about 6 THz with a peak at 13.2 THz [7]. Previous study has shown that efficient Raman conversion only occurs within the Raman shift range of 10.6 to 15.2 THz [25], which causes difficulties to the design of broadband tunable Raman amplifier and RFLs. The common methods to extend the spectral tuning range of RFLs include using multiple pump wavelength and cascaded Raman conversion [26–29]. Besides, for single order RFL with monochronic pump, exploring fibers with broader Raman gain spectrum is also an effective way [30]. In 2008, Qin et al. demonstrated a widely tunable tellurite fiber Raman laser covering 1495 to 1600 nm region, the corresponding Raman shift range is 2.03 to 15.2 THz [31]. However, the transmission loss of tellurite fiber is much higher than the silica fiber, about 20 dB/km at 1550 nm, and the output power are limited below watt-level [31]. In contrast, the phosphosilicate fiber has broader Raman gain spectrum and similar transmission loss as compared to silica fiber, making it a good choice for broadband Raman conversion. Compared to the common silica fiber with a main Raman peak at around 13.2 THz, the phosphosilicate fiber has two extra Raman peaks. One arises from vibrational modes of the phosphorus-oxygen double bond at a frequency shift of ∼40 THz, and the other one is the boson peak at low frequency shift area [32]. The two extra Raman gain peaks have been adopted for large frequency shift Raman conversion [33,34] and small frequency shift Raman conversion [35,36], respectively. Phosphosilicate fiber-based tunable RFLs have been reported in some papers [26,37], but generally pumped with multiple wavelength, and the broadband Raman gain spectrum of the phosphosilicate fiber hasn’t been fully explored.
In this paper, we reveal the phosphosilicate fiber’s unique advantage in broadband Raman conversion. Firstly, we measure the Raman gain spectra of phosphosilicate fiber and common silica fiber, the 3 dB bandwidth of the Raman gain spectrum of phosphosilicate fiber is more than twice of that of the silica fiber. Then, by using the phosphosilicate fiber and silica fiber as gain medium respectively, we build two tunable RFLs and compare their operation bandwidths. The silica fiber-based RFL can operate within the Raman shift range of 9.8-14.7 THz, whereas in the phosphosilicate fiber-based RFL, efficient lasing is achieved over the Raman shift range of 3.5-17.2 THz under the same condition. Finally, we theoretically calculate the tuning ranges of the two RFLs. The simulation results agree well with the experimental data, which confirms the phosphosilicate fiber’s great advantage in broadband Raman conversion.
2. Experimental principle and setup
The Raman gain spectra of the phosphosilicate fiber and common silica fiber are shown in Fig. 1. The details of Raman spectrum measurement are presented in Supplement 1. For the silica fiber, the 3 dB bandwidth of the Raman gain spectrum is about 6.7 THz. While for the phosphosilicate fiber, the 3 dB bandwidth is about 14.6 THz, more than twice of that of the silica fiber. Here, we attempt to take the advantage of wider gain spectrum of phosphosilicate fiber and build a broadband tunable RFL.
The experimental setup of the phosphosilicate fiber-based broadband tunable Raman laser is depicted in Fig. 2. It employs a ring cavity structure. The pump source is a 1070 nm ytterbium-doped fiber laser, with maximum output power of 30 W and 3 dB linewidth less than 1 nm. The gain medium is a section of 500 m phosphosilicate fiber with core/cladding diameter of 5/125 µm, and the transmission loss is about 1.6 dB/km at 1070 nm. In the ring cavity, the pump light and Raman signal all propagate along the counterclockwise direction. The pump light is first guided into the ring cavity through channel one (port one to port two) of the circulator, and then is reflected back by a 1070 nm high reflectivity fiber Bragg grating (FBG) and coupled into the phosphosilicate fiber through channel two (port two to port three) of the circulator. The 1070 nm high reflectivity FBG has a reflectivity of 99.9%, with 3 dB bandwidth of 2 nm. After the phosphosilicate fiber is a 90:10 coupler. The 90% port is cleaved at an angle of 8° as the laser’s output port. About one tenth of Raman signal is coupled back into the cavity through the 10% port of the coupler. After the 10% port of the circulator, an acoustic optical tunable filter (AOTF) is used to select the signal wavelength. By adjusting the frequency of the electrical signal imposed on the AOTF, the filtering wavelength of the AOTF can be tuned from 1 to 1.3 µm, with 3 dB bandwidth of about 2 nm [38]. The core and cladding diameters of the AOTF’s pigtailed fiber are 9 and 125 µm, respectively, and the NA is 0.14. To be noticed, the power handling capacity of the AOTF is 2 W. For safety’s sake, the inject pump power from the 1070 nm ytterbium-doped fiber laser is limited within 22 W. Between the AOTF and the FBG, an isolator is utilized to prevent the AOTF from un-reflected pump light and ensure counterclockwise oscillation. Like the pump light, the filtered Raman signal is coupled into the phosphosilicate fiber through channel two (port two to port three) of the circulator. Moreover, the pigtail fiber of the pump source, circulator, FBG, isolator, and coupler have the same core/cladding diameter of 10/125 µm. Due to mode area mismatch, there is splicing loss between port 3 of the circulator and the phosphosilicate fiber, about 0.25 dB after splicing optimization.
Fig. 2. The experimental setup of the phosphosilicate fiber-based broadband tunable Raman laser. FBG, fiber Bragg grating; AOTF, acoustic optical tunable filter; PF, phosphosilicate fiber.
3. Experimental result and theoretical analysis
3.1 Experimental results
By adjusting the filtering wavelength of the AOTF, the wavelength of the proposed RFL can be flexibly tuned. Figure 3(a) shows the maximum signal power and the corresponding normalized output spectra at different wavelengths. Thanks to the broadband Raman gain spectrum of phosphosilicate fiber, the RFL can deliver more than 10 W signal power over a tuning range of 1084.3-1140.1 nm, the corresponding Raman shift range is 3.5-17.2 THz. In the wavelength range of 1100-1130 nm, due to the relatively high Raman gain coefficient, the output powers are a little higher than those at longer or shorter wavelengths. When the RFL operates at 1128 nm, corresponds to the peak Raman gain at 14.7 THz, the Raman signal power reaches a maximum of 13.8 W. To be noticed, when the RFL operates below 1090 nm, several extra small peaks in the wavelength range of 1110 nm-1130 nm are observed in the output spectra, which could be the result of self-Raman emission pumped by the combination of initial 1070 nm pump light and Raman signal. When the filtering wavelength is further extended to the shorter 1080 nm or the longer 1144 nm, as shown in Fig. 3(b), the corresponding Raman gains are too small to suppress the self-Raman emission at around 1128 nm, thus limiting the further wavelength extending of this tunable RFL.
Fig. 3. (a) The maximum signal power and the corresponding normalized output spectra at different wavelengths. (b) The output spectra of the phosphosilicate fiber-based RFL with filtering wavelength of 1080 nm and 1144 nm.
Figures 4(a) and 4(b) display the detailed output spectra and power evolution properties of the RFL operating at 1128 nm, respectively. While the inset figure in Fig. 4(a) gives the 3 dB linewidth of the Raman signals at different power levels. When the pump power reaches the threshold of 7.1 W, a narrow Raman peak at 1128 nm is generated. As the pump power continues to increase, more of the pump is converted into the Raman signal, the intensity of Raman signal increases while the residual pump drops rapidly, the linewidth of Raman signal is broadened as well. At a maximum pump power of 22 W, the 3 dB linewidth of the Raman signal is increased to 1.12 nm and the signal power reaches a maximum of 13.8 W, corresponding to a conversion efficiency of 62.7%. Another point worth mentioning is that due to the good temporal stability of the pump source, the pump light is almost completely converted into the Raman signal under the maximum pump power [39–41]. As a result, the optical signal to noise ratio reaches 34.6 dB and the spectral purity of the Raman signal is up to 99.95%.
To demonstrate phosphosilicate fiber’s advantage in broadband Raman conversion, we replace the phosphosilicate fiber with a section of common silica fiber and build a tunable RFL based on the same structure and fiber optic components. The silica fiber is the G652D telecom fiber, with core diameter of 8.2 µm and transmission loss of 0.4 dB/km at 1.1 µm. As the peak Raman gain of the phosphosilicate fiber is about 1.5 times of the telecom fiber (see Supplement 1 for Raman gain spectra measurement details) and the phosphosilicate fiber length is 500 m, we used 750 m telecom fiber to ensure similar lasing threshold and Raman conversion efficiency. By adjusting the filtering wavelength of the AOTF, efficient Raman lasing over a tuning range of 1108.7-1129 nm is achieved, corresponding to a Raman shift range of 9.8-14.7 THz. Figure 5(a) displays the maximum signal power and the corresponding normalized spectra at different wavelengths. When the filtering wavelength is further extended to the shorter wavelength of 1104 nm or longer wavelength of 1133 nm, as shown in Fig. 3(b), the corresponding Raman gains are too small to suppress the self-Raman emission at around 1123.4 nm. As a result, the operation bandwidth of the silica fiber based-RFL is 4.9 THz, less than half of the 13.7 THz bandwidth of the phosphosilicate fiber-based RFL.
Fig. 5. (a) The the maximum signal power and the corresponding normalized output spectra at different wavelengths. (b) The output spectra of the phosphosilicate fiber-based RFL with filtering wavelength of 1104 nm and 1133 nm.
3.2 Theoretical analysis
To further confirm the phosphosilicate fiber’s advantage in broadband Raman conversion, we calculated the power evolution characteristics of the two RFLs based on the modified power balanced model [42–44]. The details of the modified power balanced model and boundary condition are presented in Supplement 1. The simulation results of the two RFLs are shown in Fig. 6. Figure 6(a) gives the calculated the lasing threshold power of the Raman signal and self-Raman emission at different filtering wavelengths. The solid symbol line represents the threshold power of the Raman signal while the dash line represents the threshold power of self-Raman emission at peak Raman gain. In the silica fiber-based RFL, the threshold power of self-Raman emission remains a constant of 15.4 W. When the filtering wavelength of AOTF locates within 1105.4-1132.0 nm, corresponding to a Raman shift range of 9.0-15.3 THz, the threshold power of self-Raman emission is higher than the Raman signal, efficient Raman lasing at filtering wavelength can be achieved. While in the phosphosilicate silica fiber-based RFL, the threshold power of self-Raman emission is 15 W, the lasing threshold of the Raman signal is lower than the self-Raman emission over the wavelength range of 1078.8-1138.7 nm, the corresponding Raman shift range is of 2.3-16.9 THz, more than two times wider of that of the silica fiber-based RFL. Although the simulation results are not completely the same with the experimental results, the slight difference are acceptable considering the random error and imperfection of the simulation model. Figure 6(b) displays the power evolution characteristics of the phosphosilicate fiber-based RFL operates at 1128 nm, corresponding to the peak Raman gain. The green, red and blue line represent the calculated output power of the residual pump, Raman signal and the next order Stokes light. The circle points are the corresponding experimental results. The calculated threshold power and Raman output power at maximum pump of 22 W are in good agreement with the experimental results. Moreover, the simulation results predict that a maximum output power of 15.7 W can be obtained at pump power of 24.8 W, corresponding to a conversion efficiency of 63.3%. And the further power scaling is limited by the generation of next order Stokes light. The above simulation results strongly prove the phosphosilicate fiber’s advantage in broadband Raman conversion, and it could provide some guidance for the further optimization of the proposed RFL.
Fig. 6. (a) The calculated threshold powers of the phosphosilicate fiber-based (blue line) RFL and silica fiber-based RFL (red line) at different filtering wavelengths. The solid symbol line and dash represent the threshold power of the Raman signal and self-Raman emission, respectively. (b) The the power evolution characteristics of the phosphosilicate fiber-based RFL operates at 1128 nm.
4. Conclusion
In conclusion, we propose and demonstrate the phosphosilicate fiber’s great advantage in broadband Raman conversion. The Raman gain spectrum of a phosphosilicate fiber is measured, its 3 dB bandwidth is more than twice of that of the common silica fiber. Efficient lasing over the Raman shift range of 13.7 THz (3.5-17.2 THz) is achieved in the phosphosilicate fiber-based RFL. As a comparison, the operation bandwidth of silica fiber-based RFL is limited within the Raman shift range of 4.9 THz (9.8-14.7 THz). Further simulation results agree well with the experimental data, the calculated operation bandwidth of the phosphosilicate fiber-based RFL is more than twice of that of the silica fiber-based RFL. This work demonstrates the phosphosilicate fiber’s unique advantage in broadband Raman conversion, which has great potential in increasing the reach and capacity of optical communication system.
Funding
National Natural Science Foundation of China (61635005, 61905284); National Postdoctoral Program for Innovative Talents (BX20190063).
Acknowledgments
We are grateful to Sen Guo, Bo Ren, Tao Wang, and Cong Zhou for their help on this work.
Disclosures
The authors declare that there are no potential conflicts of financial interest or personal relationships related to this work.
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.
Supplemental document
See Supplement 1 for supporting content.
References
1. E. J. Woodbury and W. K. Ng, “Ruby laser operation in the near IR,” Proc. Inst. Radio Eng. 50(11), 2347–2348 (1962).
2. Q. Chang, Y. Miao, J. Wild, W. Min, and Y. Yang, “Emerging applications of stimulated Raman scattering microscopy in materials science,” Matter 4(5), 1460–1483 (2021). [CrossRef]
3. H. Li, L. Xing, Z. Dou, W. Zhang, W. Fang, C. Sun, and Z. Men, “Generation of dual-supercontinuum coherent radiation in acetone mixed with carbon disulfide by stimulated Raman scattering,” Opt. Lett. 47(18), 4700–4703 (2022). [CrossRef]
4. S. Oh, C. Lee, W. Yang, A. Li, A. Mukherjee, M. Basan, C. Ran, W. Yin, C. J. Tabin, D. Fu, X. S. Xie, and M. W. Kirschner, “Protein and lipid mass concentration measurement in tissues by stimulated Raman scattering microscopy,” Proc. Natl. Acad. Sci. U.S.A. 119(17), e2117938119 (2022). [CrossRef]
5. F. Benabid, J. C. Knight, G. Antonopoulos, and P. S. J. Russell, “Stimulated Raman scattering in hydrogen-filled hollow-core photonic crystal fiber,” Science 298(5592), 399–402 (2002). [CrossRef]
6. G. P. Agrawal, Nonlinear Fiber Optics, 6th ed. (Academic Press, 2019).
7. R. H. Stolen, E. P. Ippen, and A. R. Tynes, “Raman oscillation in glass optical waveguide,” Appl. Phys. Lett. 20(2), 62–64 (1972). [CrossRef]
8. R. H. Stolen and E. P. Ippen, “Raman gain in glass optical waveguides,” Appl. Phys. Lett. 22(6), 276–278 (1973). [CrossRef]
9. V. R. Supradeepa, Y. Feng, and J. W. Nicholson, “Raman fiber lasers,” J. Opt. 19(2), 023001 (2017). [CrossRef]
10. L. Sirleto and M. A. Ferrara, “Fiber amplifiers and fiber lasers based on stimulated Raman scattering: a review,” Micromachines 11(3), 247 (2020). [CrossRef]
11. L. Zhang, H. Jiang, S. Cui, J. Hu, and Y. Feng, “Versatile Raman fiber laser for sodium laser guide star,” Laser Photonics Rev. 8(6), 889–895 (2014). [CrossRef]
12. X. Huo, Y. Qi, Y. Zhang, B. Chen, Z. Bai, J. Ding, Y. Wang, and Z. Lu, “Research development of 589 nm laser for sodium laser guide stars,” Opt. Laser Eng. 134, 106207 (2020). [CrossRef]
13. Z. Hosseinaee, B. Ecclestone, N. Pellegrino, L. Khalili, L. Mukhangaliyeva, P. Fieguth, and P. H. Reza, “Functional photoacoustic remote sensing microscopy using a stabilized temperature-regulated stimulated Raman scattering light source,” Opt. Express 29(19), 29745–29754 (2021). [CrossRef]
14. H. Murakoshi, H. H. Ueda, R. Goto, K. Hamada, Y. Nagasawa, and T. Fuji, “In vivo three- and four-photon fluorescence microscopy using a 1.8 µm femtosecond fiber laser system,” Biomed. Opt. Express 14(1), 326–334 (2023). [CrossRef]
15. Y. Qi, S. Lin, J. Zhang, P. Wang, and Z. Wang, “Impact of feedback bandwidth on Raman random fiber laser remote-sensing,” Opt. Express 30(12), 21268–21275 (2022). [CrossRef]
16. S. Lin, Z. Wang, Y. Qi, B. Han, H. Wu, and Y. Rao, “Wideband remote-sensing based on random fiber laser,” J. Lightwave Technol. 40(9), 3104–3110 (2022). [CrossRef]
17. W. Pan, L. Zhang, H. Jiang, X. Yang, S. Cui, and Y. Feng, “Ultrafast Raman fiber laser with random distributed feedback,” Laser Photonics Rev. 12(4), 1700326 (2018). [CrossRef]
18. J. Zhou, W. Pan, W. Qi, X. Cao, Z. Cheng, and Y. Feng, “Ultrafast Raman fiber laser: a review and prospect,” PhotoniX 3(1), 18 (2022). [CrossRef]
19. J. Bromage, “Raman amplification for fiber communications systems,” J. Lightwave Technol. 22(1), 79–93 (2004). [CrossRef]
20. D. V. Churkin, S. Sugavanam, I. D. Vatnik, Z. Wang, E. Podivilov, S. A. Babin, Y. Rao, and S. K. Turitsyn, “Recent advances in fundamentals and applications of random fiber lasers,” Adv. Opt. Photonics 7(3), 516–569 (2015). [CrossRef]
21. B. J. Puttnam, R. S. Luís, G. Rademacher, M. M.-Astudillio, Y. Awaji, and H. Furukawa, “S-, C- and L-band transmission over a 157 nm bandwidth using doped fiber and distributed Raman amplification,” Opt. Express 30(6), 10011–10018 (2022). [CrossRef]
22. M. N. Islam, “Raman amplifiers for telecommunications,” IEEE J. Sel. Top. Quantum Electron. 8(3), 548–559 (2002). [CrossRef]
23. W. S. Pelouch, “Raman Amplification: An Enabling Technology for Long-Haul Coherent Transmission Systems,” J. Lightwave Technol. 34(1), 6–19 (2016). [CrossRef]
24. A. Ghazisaeidi, A. Arnould, M. Ionescu, V. Aref, H. Mardoyan, S. Etienne, M. Duval, C. Bastide, H. Bissessur, and J. Renaudier, “99.35 Tb/s Ultra-wideband unrepeated transmission over 257 km using semiconductor optical amplifiers and distributed Raman amplification,” J. Lightwave Technol. 40(21), 7014–7019 (2022). [CrossRef]
25. J. Song, H. Wu, J. Ye, H. Zhang, J. Xu, P. Zhou, and Z. Liu, “Investigation on extreme frequency shift in silica fiber-based high-power Raman fiber laser,” High Power Laser Sci. Eng. 6, e28 (2018). [CrossRef]
26. S. A. Babin, D. V. Churkin, S. I. Kablukov, M. A. Rybakov, and A. A. Vlasov, “All-fiber widely tunable Raman fiber laser with controlled output spectrum,” Opt. Express 15(13), 8438–8443 (2007). [CrossRef]
27. L. Zhang, H. Jiang, X. Yang, W. Pan, S. Cui, and Y. Feng, “Nearly-octave wavelength tuning of a continuous wave fiber laser,” Sci. Rep. 7(1), 42611 (2017). [CrossRef]
28. U. C. De Moura, M. A. Iqbal, M. Kamalian, L. Krzczanowicz, F. Da Ros, A. M. R. Brusin, A. Carena, W. Forysiak, S. Turitsyn, and D. Zibar, “Multi-band programmable gain Raman amplifier,” J. Lightwave Technol. 39(2), 429–438 (2021). [CrossRef]
29. H. Wu, B. Han, and Y. Liu, “Tunable narrowband cascaded random Raman fiber laser,” Opt. Express 29(14), 21539–21550 (2021). [CrossRef]
30. A. Mori, H. Masuda, K. Shikano, and M. Shimizu, “Ultra-wide-band tellurite-based fiber Raman amplifier,” J. Lightwave Technol. 21(5), 1300–1306 (2003). [CrossRef]
31. G. Qin, M. Liao, T. Suzuki, A. Mori, and Y. Ohishi, “Widely tunable ring-cavity tellurite fiber Raman laser,” Opt. Lett. 33(17), 2014–2016 (2008). [CrossRef]
32. Y. Zhang, J. Xu, J. Ye, J. Song, T. Yao, and P. Zhou, “Ultralow-quantum-defect Raman laser based on the boson peak in phosphosilicate fiber,” Photonics Res. 8(7), 1155–1160 (2020). [CrossRef]
33. I. A. Lobach, S. I. Kablukov, and S. A. Babin, “Linearly polarized cascaded Raman fiber laser with random distributed feedback operating beyond 1.5 µm,” Opt. Lett. 42(18), 3526–3529 (2017). [CrossRef]
34. E. I. Dontsova, S. I. Kablukov, I. D. Vatnik, and S. A. Babin, “Frequency doubling of Raman fiber lasers with random distributed feedback,” Opt. Lett. 41(7), 1439–1442 (2016). [CrossRef]
35. X. Ma, J. Xu, J. Ye, Y. Zhang, L. Huang, T. Yao, J. Leng, Z. Pan, and P. Zhou, “Cladding-pumped Raman fiber laser with 0.78% quantum defect enabled by phosphorus-doped fiber,” High Power Laser Sci. Eng. 10, e8 (2022). [CrossRef]
36. Y. Zhang, S. Li, J. Ye, X. Ma, J. Xu, T. Yao, and P. Zhou, “Low quantum defect random Raman fiber laser,” Opt. Lett. 47(5), 1109–1112 (2022). [CrossRef]
37. H. Wu, W. Wang, B. Hu, Y. Li, K. Tian, R. Ma, C. Li, J. Liu, J. Yao, and H. Liang, “Widely tunable continuous-wave visible and mid-infrared light generation based on a dual-wavelength switchable and tunable random Raman fiber laser,” Photonics Res. 11(5), 808–816 (2023). [CrossRef]
38. S. Li, J. Xu, J. Liang, J. Ye, Y. Zhang, X. Ma, J. Leng, and P. Zhou, “Multi-wavelength random fiber laser with a spectral-flexible characteristic,” Photonics Res. 11(2), 159–164 (2023). [CrossRef]
39. J. Dong, L. Zhang, H. Jiang, X. Yang, W. Pan, S. Cui, X. Gu, and Y. Feng, “High order cascaded Raman random fiber laser with high spectral purity,” Opt. Express 26(5), 5275–5280 (2018). [CrossRef]
40. Y. Zhang, J. Song, J. Ye, J. Xu, T. Yao, and P. Zhou, “Tunable random Raman fiber laser at 1.7 µm region with high spectral purity,” Opt. Express 27(20), 28800–28807 (2019). [CrossRef]
41. V. Balaswamy, S. Ramachandran, and V. R. Supradeepa, “High-power, cascaded random Raman fiber laser with near complete conversion over wide wavelength and power tuning,” Opt. Express 27(7), 9725–9732 (2019). [CrossRef]
42. S. K. Turitsyn, S. A. Babin, A. E. El-Taher, P. Harper, D. V. Churkin, S. I. Kablukov, and E. V. Podivilov, “Random distributed feedback fibre laser,” Nat. Photonics 4(4), 231–235 (2010). [CrossRef]
43. Z. Wang, H. Wu, M. Fan, L. Zhang, Y. J. Rao, W. L. Zhang, and X. H. Jia, “High power random fiber laser with short cavity length: theoretical and experimental investigations,” IEEE J. Sel. Top. Quantum Electron. 21(1), 10–15 (2015). [CrossRef]
44. J. Ye, X. Ma, Y. Zhang, J. Xu, H. Zhang, T. Yao, J. Leng, and P. Zhou, “Revealing the dynamics of intensity fluctuation transfer in a random Raman fiber laser,” Photonics Res. 10(3), 618–627 (2022). [CrossRef]
