Role of the mirror’s reflectivity in forwardpumped random fiber laser Han Wu,1 Zinan Wang,1,*Mengqiu Fan,1 Li Zhang, 1 Weili Zhang, 1 Yunjiang Rao1,2 1
Key Lab of Optical Fiber Sensing &Communications, University of Electronic Science &Technology of China, Chengdu, Sichuan 611731, China 2
[email protected] *
[email protected]
Abstract: In this paper, we thoroughly analyze the role of the point reflector’s reflectivity in the performance of forward-pumped random fiber laser, in both the long- and short-cavity cases. The results show that the power performance is sensitive to the small reflection added on the pump side of the fiber end, whereas both the power distribution and threshold tend to be stable when the reflectivity reaches a relatively high level (>0.4). Moreover, for the short cavity case (e.g. 500m), the maximum achievable 1st-oder random lasing output can even increase when the reflectivity decreases from 0.9 to 0.01, due to the different lasing power distributions with different reflectivity values. This work reveals a new and unique property of random fiber lasers and provides insights into their design for the applications such as distributed amplification and high power sources. ©2015 Optical Society of America OCIS codes: (140.3510) Lasers, fiber; (140.3550) Lasers, Raman; (290.5870) Scattering, Rayleigh; (290.5910) Scattering, stimulated Raman.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
D. S. Wiersma, “The physics and applications of random lasers,” Nat. Phys. 4(5), 359–367 (2008). S. K. Turitsyn, S. A. Babin, A. E. El-Taher, P. Harper, D. V. Churkin, S. I. Kablukov, J. D. Ania-Castañón, V. Karalekas, and E. V. Podivilov, “Random distributed feedback fiber laser,” Nat. Photonics 4(4), 231–235 (2010). Z. N. Wang, Y. J. Rao, H. Wu, P. Y. Li, Y. Jiang, X. H. Jia, and W. L. Zhang, “Long-distance fiber-optic pointsensing systems based on random fiber lasers,” Opt. Express 20(16), 17695–17700 (2012). I. D. Vatnik, D. V. Churkin, E. V. Podivilov, and S. A. Babin, “High-efficiency generation in a short random fiber laser,” Laser Phys. Lett. 11(7), 075101 (2014). Z. Wang, H. Wu, M. Fan, Y. Rao, I. Vatnik, E. Podivilov, S. Babin, D. Churkin, H. Zhang, P. Zhou, H. Xiao, and X. Wang, “Random fiber laser: simpler and brighter,” Opt. Photon. News 25(December Issue), 30 (2014). S. K. Turitsyn, S. A. Babin, D. V. Churkin, I. D. Vatnik, M. Nikulin, and E. V. Podivilov, “Random distributed feedback fibre lasers,” Phys. Rep. 542(2), 133–193 (2014). A. E. El-Taher, P. Harper, S. A. Babin, D. V. Churkin, E. V. Podivilov, J. D. Ania-Castanon, and S. K. Turitsyn, “Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation,” Opt. Lett. 36(2), 130–132 (2011). A. M. R. Pinto, O. Frazão, J. L. Santos, and M. Lopez-Amo, “Multiwavelength fiber laser based on a photonic crystal fiber loop mirror with cooperative Rayleigh scattering,” Appl. Phys. B 99(3), 391–395 (2010). L. Wang, X. Dong, P. Shum, and H. Su, “Tunable erbium doped fiber laser based on random distributed feedback,” IEEE Photon. J. 6, 1501705 (2014). S. A. Babin, A. E. El-Taher, P. Harper, E. V. Podivilov, and S. K. Turitsyn, “Tunable random fiber laser,” Phys. Rev. A 84(2), 021805 (2011). T. Zhu, X. Bao, and L. Chen, “A self-gain random distributed feedback fiber laser based on stimulated Rayleigh scattering,” Opt. Commun. 285(6), 1371–1374 (2012). S. Sugavanam, N. Tarasov, X. Shu, and D. V. Churkin, “Narrow-band generation in random distributed feedback fiber laser,” Opt. Express 21(14), 16466–16472 (2013). Z. N. Wang, H. Wu, M. Q. 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), 0900506 (2015). H. Zhang, P. Zhou, H. Xiao, and X. Xu, “Efficient Raman fiber laser based on random Rayleigh distributed feedback with record high power,” Laser Phys. Lett. 11(7), 075104 (2014).
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Received 12 Dec 2014; revised 6 Jan 2015; accepted 12 Jan 2015; published 21 Jan 2015 26 Jan 2015 | Vol. 23, No. 2 | DOI:10.1364/OE.23.001421 | OPTICS EXPRESS 1421
15. Z. N. Wang, H. Wu, M. Q. Fan, Y. J. Rao, X. H. Jia, and W. L. Zhang, “Third-order random lasing via Raman gain and Rayleigh feedback within a half-open cavity,” Opt. Express 21(17), 20090–20095 (2013). 16. X. H. Jia, Y. J. Rao, F. Peng, Z. N. Wang, W. L. Zhang, H. J. Wu, and Y. Jiang, “Random-lasing-based distributed fiber-optic amplification,” Opt. Express 21(5), 6572–6577 (2013). 17. J. Nuño, M. Alcon-Camas, and J. D. Ania-Castañón, “RIN transfer in random distributed feedback fiber lasers,” Opt. Express 20(24), 27376–27381 (2012). 18. X. H. Jia, Y. J. Rao, C. X. Yuan, J. Li, X. D. Yan, Z. N. Wang, W. L. Zhang, H. Wu, Y. Y. Zhu, and F. Peng, “Hybrid distributed Raman amplification combining random fiber laser based 2nd-order and low-noise LD based 1st-order pumping,” Opt. Express 21(21), 24611–24619 (2013). 19. Z. N. Wang, J. J. Zeng, J. Li, M. Q. Fan, H. Wu, F. Peng, L. Zhang, Y. Zhou, and Y. J. Rao, “Ultra-long phasesensitive OTDR with hybrid distributed amplification,” Opt. Lett. 39(20), 5866–5869 (2014). 20. E. G. Turitsyna, S. K. Turitsyn, and V. K. Mezentsev, “Numerical investigation of the impact of reflectors on spectral performance of Raman fibre laser,” Opt. Express 18(5), 4469–4477 (2010). 21. D. V. Churkin, S. A. Babin, A. E. El-Taher, P. Harper, S. I. Kablukov, V. Karalekas, J. D. Ania-Castañón, E. V. Podivilov, and S. K. Turitsyn, “Raman fiber lasers with a random distributed feedback based on Rayleigh scattering,” Phys. Rev. A 82(3), 033828 (2010).
1. Introduction Random laser (RL) refers to a new kind of lasers where the feedback is provided by randomly distributed scattering centers in a gain medium [1]. As an important type of RLs, random fiber laser (RFL) via Raman gain and Rayleigh scattering in fiber as the randomly distributed feedback has been demonstrated in 2010 [2]. RFLs have attracted a lot of attention due to their unique advantages, such as ultra-long-distance cavity, stable output, simplicity and high lasing efficiency, etc [3–6]. Valuable work has been carried out to study RFLs, and various physical features have been reported. RFLs have been tailored to be multiwavelength [7,8], wavelength-tunable [9,10], narrow bandwidth [11,12], high output power [4,5,13,14] and cascaded operation to generate high order Stokes waves [15].The RFL-based distributed fiber-optic amplification could offer low-noise and stable amplification for longdistance transmission [16,17], making it attractive for telecom and sensing applications. Specifically, forward-pumped RFL [6,7,15], which has a point reflector at the pump side of the fiber span, is proposed for the purpose of reducing the threshold first. Furthermore, the random lasing amplification based on the forward-pumped RFL has been utilized to significantly extend the sensing range of BOTDA and Φ-OTDR systems due to its specific power distribution and advantageous noise specification [18,19]. Also, forward-pumped RFL with short fiber length has been demonstrated to have the superb ability to generate high power lasing output, creating a new direction for high-power optical sources [4,5,13]. In previous works, intuitively the preferred reflectors should have high reflectivity [7,15], similar to the cases in conventional Raman fiber lasers. However, different types of the reflectors such as narrow-band FBG, chirped FBG and fiber loop mirror (FLM) etc., are required for diverse demands for laser properties [20], and the reflectivity values vary among different reflectors. In this paper, we thoroughly investigate the effect of point reflector’s reflectivity on the characteristics of forward-pumped RFLs with long (e.g. 50km) and short (e.g. 500m) fiber length respectively, and we also discuss the corresponding influences in the applications of distributed amplification and high power generation. The results reveal that with the increase of the reflectivity, the threshold change drastically in the case of relatively low reflectivity (0.4). Also, for the short fiber length (500m), the maximum 1st-oder random lasing output power can even increase (from 41W to 45.7W) when the reflectivity decreases(from 0.9 to 0.01), due to the different lasing power distribution with different reflectivity value. These results also contribute insights into the recently vibrant research on high-power RFLs [5]. 2. Forward-pumped RFL with long fiber length We study the RFL with half-open configuration and unidirectional forward-pumping (forward-pumped RFL) [15,21].Without loss of generality, the pump wavelength is set to
#229437 - $15.00 USD © 2015 OSA
Received 12 Dec 2014; revised 6 Jan 2015; accepted 12 Jan 2015; published 21 Jan 2015 26 Jan 2015 | Vol. 23, No. 2 | DOI:10.1364/OE.23.001421 | OPTICS EXPRESS 1422
1365nm and the corresponding 1st-order Stokes wavelength is 1455nm in SMF.A 50km SMF is performed as both the Raman gain medium and random distributed mirrors. A point reflector is placed at the pump side of the fiber to reflect the 1st-order Stokes light only, and we change the reflectivity of the point reflector in the simulation. Forward-pumped RFL with long fiber length can be used for distributed amplification and the lasing power distribution and the threshold are the main concerns in such systems [18,19]. We apply the steady-state model [15,21] for a detailed analysis of the performance of the laser. The parameters used are summarized in Table 1. Table 1. Parameters for numerical calculation Wavelength(nm) 1365 1455
Loss (dB/Km) 0.32 0.25
Rayleigh backscattering (km−1) 1 × 10−4 6 × 10−5
Raman gain (W−1km−1) 0.5 —
Fig. 1. Calculated power distribution of lasers with different reflectivity of point reflector pumped at 2W.
First, we calculate the power distribution of the 1st-order random lasing with different reflectivity of point-feedback (with 2W pump) (see Fig. 1). Without any point-feedback on the fiber end (R = 0), the majority of lasing power flows toward the pump side of the fiber span. Adding the point reflector at the pump side of the fiber, the power distribution of the 1st-order lasing changes dramatically. Due to the extremely small Rayleigh backscattering coefficient, the integral Rayleigh backscattering coefficient is as weak as ~5 × 10−4. Therefore, even with the point reflector with reflectivity as low as 0.01, most of the lasing power is re-distributed towards the far end of the fiber cavity. With higher reflectivity, the forward power becomes more dominant, and the position of power maximum shifts towards the pump side of the fiber. Moreover, this tendency is more significant in the range of relatively low reflectivity, whereas the power distribution is just slightly changed when the reflectivity is increased to a high level (>0.4).
Fig. 2. The calculated threshold of random lasing as a function of reflectivity of point reflector.
#229437 - $15.00 USD © 2015 OSA
Received 12 Dec 2014; revised 6 Jan 2015; accepted 12 Jan 2015; published 21 Jan 2015 26 Jan 2015 | Vol. 23, No. 2 | DOI:10.1364/OE.23.001421 | OPTICS EXPRESS 1423
Figure 2 shows the calculated generation threshold with different reflectivity. The insert is the enlarged view of the threshold with low reflectivity (
