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Abstract
Black phosphorus (BP), a prosperous two-dimensional optoelectronic material, has been deeply developed for various optoelectronics applications. Here, we demonstrate a sub-hundred nanosecond passively Q-switched Er-doped all-fiber laser with BP as the saturable absorber (SA). The BP-SA is fabricated by a controllable optical deposition technique. To achieve the sub-hundred nanosecond Q-switching output, we deliberately enlarge the modulation depth of the BP-SA by suitably increasing the time and laser power of the optical deposition and shortening the laser cavity length with an integrated multifunctional component. A stable Q-switched pulse train was obtained with a pulse duration as narrow as 91 ns, and the Q-switched lasing characteristics based on the BP-SA have also been investigated and discussed. The experimental results indicate that the BP material can be employed as an effective SA for the nanosecond pulse generation.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
In recent years, high energy nanosecond pulsed fiber lasers have been extensively studied and show significant potential in many applications, such as biomedicine, environmental sensing, material preparation, and micro-machining [1–3]. The passive Q-switching technique based on real saturable absorbers (SAs) can provide an effective approach to yield high energy short pulses owing to the compact structure and low cost. SAs, as one of the crucial optical components in passively Q-switched fiber lasers, must possess excellent nonlinear saturable absorption properties like large modulation-depth, ultrafast recovery time, and high damage threshold, etc. Until now, various SAs have been fabricated and developed as the Q-switcher or mode-locker for some practical applications, such as Semiconductor Saturable Absorption mirror (SESAM) [4,5], Carbon Nano-Tube (CNT) [6–9], Graphene [10–13], Topological Insulator (TI) [14–16], Transition Mental Dichalcogenides (TMDs) [17–20], and various van der Waals heterostructures [21]. However, each SA has its own shortcomings, such as the complex design and high cost for SESAM, the low damage threshold for CNT, the weak light absorption coefficient and low modulation depth for graphene, the gapless surface state for TI, and the large bandgap for TMDs. Researchers have still been seeking more appropriate SAs for pulsed laser applications. Therefore, new desirable and reliable SAs for the Q-switcher are required to be explored. More recently, another single-element two-dimensional (2D) nanomaterial: layered Black Phosphorus (BP), has been rising and developed for some optoelectronics applications, owing to its outstanding physical structure [22–26]. BP has a direct bandgap, which can be conveniently tuned from ∼0.3 (bulk) to ∼2 eV (monolayer) by controlling its number of layers [23]. Combined with the ultra-short relaxation time of 26 fs (shortest among all SAs), BP has been developed into a terrific material for ultrafast optoelectronics operating in different infrared wavelength band [27–34].
On the other hand, despite the emergence of new type of SAs and rapid development of laser technology, it is still struggling to cross the barrier of sub-hundred nanosecond Q-switched pulse generation in an Er-doped all fiber laser because of the relatively long cavity. With regards to an Er-doped all fiber laser, the record shortest Q-switched pulse durations produced using different nanomaterials until now are only 330 ns (CNT) [35], 206 ns (Graphene) [36], 217 ns (TI) [37], 660 ns (MoS2) [38], 154.9 ns (WS2) [39], 742 ns (BP) [40], respectively. For achieving shorter Q-switched pulses, one can work towards optimizing the SA parameters and fiber laser configuration. Regarding the SAs, their recovery time and modulation depth can influence the duration of Q-switched pulses significantly in contrast to other specifications, which was clearly illustrated in previous reports [41–44]. Considering the fast recovery time of above nanomaterials (typical of hundreds or dozens of femtoseconds) in contrast to the relatively long Q-switched pulses, we can expect that the slightly decreasing recovery time can have little impact on the pulse duration [41]. Therefore, the modulation depth of SA would be a critical factor in shortening the Q-switched pulse duration to sub-hundred nanosecond, with the inversely proportional relationship. Besides, concerning the laser cavity design, the cavity length might be another crucial parameter in the pulse compression since the pulse duration is ordinarily proportional to the cavity roundtrip time [44].
In this paper, we demonstrated the sub-hundred nanosecond Q-switched pulse generation in an Er-doped all-fiber laser. To achieve sub-hundred nanosecond pulse, we firstly enlarged the modulation depth of BP SA as much as possible to 50.94%, through appropriately increasing the time and launched laser power of optical deposition. Then we made great efforts to shorten the cavity length to 44.2 cm by incorporating an integrated multifunctional component. Ultimately, we obtained stable Q-switching operation in a ring cavity with record shortest pulse duration of 91 ns at the maximum pump power. Our results clearly show that BP-SA presents attractive properties like low cost, good fiber compatibility, high power tolerance, as well as the tremendous potential in pulse narrowing.
2. Experimental setup
To make a compact laser cavity, we intended to design an ultrashort all fiber ring laser where the cavity length was greatly reduced, as shown in Fig. 1. One of the crucial optical components from the Q-switched fiber laser is the versatile passive device (WDM + PII + OC) customized in house which integrates a wavelength division multiplexer (WDM), a polarization-independent isolator (PII), and a 10% output coupler (OC) together. In this way, the total cavity length can be significantly reduced by saving the pigtail fibers of different separate passive fiber components. Besides, a 17.8 cm highly Er-doped fiber (EDF, Liekki 110-4/125) was selected as the gain medium to further reduce the cavity length, which was forward-pumped by a 976 nm single-mode laser diode with a maximum output power of 500 mW via the integrated versatile device. The BP-SA was inserted between the EDF and common port of the integrated device. The 10% output port of the integrated device was used as the laser output and the other port was connecting the Er-doped gain fiber. The connecting pigtail fibers between different components were cut as short as possible, resulting in a total cavity length of 44.2 cm. The dispersion parameters of the EDF and the SMF-28 were measured to be −8.92 ps/nm/km and 17.86 ps/nm/km at 1550 nm, respectively, resulting in an extremely small net cavity dispersion of 3.13 fs/nm at 1550 nm. The output pulse characteristics were synchronously monitored by an optical spectrum analyzer (Ando AQ-6317B), a 4 GHz real time oscilloscope (Agilent Technol., DSO9404A), and a radio frequency (RF) spectrum analyzer (Agilent N9322C).
Fig. 1. Experimental setup of the compact Q-switched fiber laser: WDM: wavelength division multiplexer; PII: polarization-independent isolator; OC: output coupler; EDF: Er-doped fiber; and BP-SA: black phosphorus saturable absorber.
3. Preparation and characterization of BP-SA
The adopted BP nano-platelets were prepared by the liquid exfoliation method. The detailed fabrication process is shown in [45,46]. The measured Raman spectrum of the BP nanosheets is illustrated in Fig. 2(a). Three strong Raman peaks were observed at 361 cm-1, 438 cm-1 and 465 cm-1, which correspond to the Ag1, B2g and Ag2 vibrational modes of layered BP, respectively [23]. To characterize the thickness and width of as-prepared BP nanosheets, we also measured the corresponding AFM topography image, as shown in Fig. 2(b). It clearly shows that the BP nanosheets have a relatively uniform distribution with average thickness of about 2-3 nm, namely 4-6 layers [23]. The two curves in the right of Fig. 2(b) refer to the two blue-line-cuts in the left of Fig. 2(b). As can be seen, the average width of BP nanosheets is about 100 nm. Then, the optical deposition process, based on the evanescent field of a tapered fiber made in-house with a waist diameter of ∼20 µm, was performed to manufacture the target SA device. It should be noted that, the modulation depth is proportional to the thickness of samples [47,48], which is then determined by the operation time and launched laser power of the optical deposition method [49,50]. Thus, we deliberately launched a laser beam with a relatively high power of 100 mW into the fiber taper immersed in the solution of BP nanosheets, lasting for 15 minutes. Finally, the BP-SA device was successfully fabricated.
Fig. 2. The measured Raman spectrum (a) and topographic AFM images (b) of the prepared BP nanosheets.
We further characterized the nonlinear absorption property of the fabricated BP-SA by the commonly used balanced twin-detector method at the operation wavelength of 1556 nm. The relationship between the transmission ratio versus the input intensity was given in Fig. 3, which indicates an obvious nonlinear absorption property. Additionally, the modulation depth and the saturation intensity of the BP-SA are calculated to be 50.94% and 2.92 MW/cm2, respectively, by fitting the experimental data based on the well-known formula [15]:
where $T$ is the transmission ratio, ${T_{ns}}$ is the non-saturable loss, $\Delta T$ is the modulation depth, and $I$ is the incident laser intensity on the sample while ${I_{{\rm{sat}}}}$ is the saturation intensity.4. Results and discussion
Firstly, we tested the lasing characteristics without inserting the BP-SA into the laser cavity and found that the laser operated in the continuous-wave regime without any random little pulses or modulations no matter how we adjusted the pump power and applied artificial fiber birefringence. We can assume that the self Q-switched operation was completely suppressed in this fiber laser design. In addition, the operating wavelength is located at 1590 nm, indicating that the insertion loss introduced by the integrated device is not significant and acceptable. Then, we incorporated the BP-SA into the laser cavity. Once the pump power was increased over 130 mW, the fiber laser operated in the self-started Q-switching mode and stable Q-switched pulse train can be obtained. Figure 4 shows the evolution characteristics of the Q-switched pulse train with respect to the increasing pump powers (175 mW, 250 mW, 325 mW, 400 mW and 475 mW). As can be seen in Fig. 4(a), the pulse trains exhibit a typical Q-switching evolution feature. As the pump power increases, the pulse intervals decrease gradually instead, which means the repetition rate of the Q-switched pulses grows correspondingly. Moreover, the Q-switched pulses can reoccur faultlessly at each cycle. No obvious modulation on pulse intensity can be observed even at the maximum pump power. It is quite different from any other Q-switched fiber lasers based on 2D materials, where the Q-switched operation will be self-terminated at comparatively high pump powers due to the oversaturation of SAs. This can prove to some extent that our fiber laser possesses good stability and strong high-power tolerance. The corresponding spectra at different pump powers are shown in Fig. 4(b). We can see that, as the pump power increases, the central wavelength remains nearly fixed at around 1563.1 nm with an enhanced intensity only. Besides, the center of the output spectra exhibits slight modulations owing to the multimode oscillation, which is a typical feature of the Q-switched ring fiber laser without intracavity narrowband mode-selection components like fiber gratings or filters [8]. At relatively high pump powers (over 400 mW), one pinnacle appears on the top of the output spectrum, which is the continuous-wave component running out of the Q-switching state, and will become stronger with the increasing pump power.
Fig. 4. The pulse evolution as a function of the increasing pump powers of 175 mW, 250 mW, 325 mW, 400 mW and 475 mW: (a) temporal profiles in the time domain; (b) output spectra.
In contrast to the mode-locking operation, the Q-switched output pulse characteristics can be widely tuned at different pump powers. We investigated the Q-switched lasing characteristics in terms of the repetition rate, the pulse duration, the output power, and the pulse energy as a function of different pump powers, as shown in Fig. 5. In Fig. 5(a), we can see that the repetition rate increases linearly from 15.76 kHz to 295.98 kHz when the pump power varies from 150 to 500 mW. Meanwhile, the pulse duration decreases from 890.7 to 91 ns in the same increasing pump power range. These are typical features of a passively Q-switched fiber laser: as the pump power increases, the time that it takes to reach the threshold number of ions accumulated on the upper laser energy level, corresponding to the opening moment of the Q-switcher, will be decreased. Thus, the time interval between the established adjacent pulses also reduces, corresponding to the increasing repetition rate. It is worth noting that in our experiment, the stable Q-switching state can be maintained at a very broad pump power range, resulting in a broad repetition rate tuning range. Additionally, the rise and fall times of the Q-switched pulses will decrease rapidly when the pump power increases in the initial stage, which makes the pulses shortened significantly. However, once the ions fully occupy the upper laser energy level at sufficiently high pump power levels, the rise and fall times of the Q-switched pulses will keep almost unchanged. Further increasing the pump power can have very little impact on the pulse duration. In our experiment, at lower pump power levels, the pulse duration decreases sharply. Once the pump power increases over 350 mW, the pulse duration remains nearly invariable. Figure 5(b) shows the relationship between the average output power, single pulse energy and the pump power. The average output power increases almost linearly with the pump power. The maximum average output power obtained in our experiment is 4.93 mW. It is worth noting that, the evolution of the pulse energy has no certain regularity, varying between 16.5 to 21.1 nJ.
Fig. 5. Output pulse characteristics as a function of the pump power: (a) repetition rate and pulse duration; (b) average power and pulse energy.
The obtained minimum pulse duration is as narrow as 91 ns at the maximum pump power of 500 mW. The details of the single pulse are shown in Fig. 6(a). Moreover, to investigate the pulse stability, we have measured the radio-frequency (RF) spectrum with a small (45 kHz span, resolution bandwidth (RBW) of 10 Hz) and large frequency scale (5 MHz span, 1 kHz RBW), as shown in Fig. 6(b). Even at the maximum pump power, the RF spectrum exhibits a relatively high signal to noise ratio (SNR) of 43.1 dB. There are no other extra frequency components between the fundamental and harmonic frequencies, further confirming its low timing jitter and high stability.
For comparison, we summarized the relative specifications of previously reported typical passively Q-switched Er-doped fiber lasers based on different low-dimensional materials in Table 1. Considering that actual cavity length should be twice as the physical cavity length in a linear cavity, our well-designed fiber laser has the shortest laser cavity. Benefiting from the short cavity length and large modulation depth of the BP-SA, the Q-switched fiber laser can produce a record shortest pulse with a duration of 91 ns. In addition, it should be noted that at a maximum pump power of 500 mW, the Q-switching state can still maintain with a high stability. We can conclude that narrower Q-switched pulses can be obtained by simply increasing the pump power.
Table 1. Experimental results for narrowest Q-switched fiber lasers with different SAs reported so far
5. Conclusion
In conclusion, we demonstrated the sub-hundred nanosecond Q-switched pulse generation from an Er-doped all-fiber laser. Through optimizing the parameters of optical deposition process, we deliberately increased the modulation depth of the BP-SA to 50.94%. Besides incorporating an integrated device, we cut off the pigtails of each fiber components as short as possible and employed a piece of highly-doped gain fiber, resulting in a significantly shortened cavity length of 44.2 cm. Once the pump power was increased over 130 mW, a stable Q-switching operation can be obtained. When the pump power was gradually increased from 150 mW to 500 mW, the repetition rate increased linearly from 15.76 kHz to 295.98 kHz while the pulse duration decreased from 890.7 to 91 ns. At the maximum pump power, we obtained the record shortest Q-switched pulses in an Er-doped all fiber laser with a high SNR of 43.1 dB. The experimental results can provide a highly effective solution in achieving sub-hundred nanosecond pulses from all-fiber lasers.
Funding
National Natural Science Foundation of China (61805115, 61875132); Natural Science Foundation of Hunan Province (2018JJ3514); Science and Technology Planning Project of Shenzhen Municipality (JCYJ20170302153731930, JCYJ20180305124927623).
Disclosures
The authors declare no conflicts of interest.
References
1. M. E. Fermann and I. Hartl, “Ultrafast fibre lasers,” Nat. Photonics 7(11), 868–874 (2013). [CrossRef]
2. H. L. Offerhaus, N. G. Broderick, D. J. Richardson, R. Sammut, J. Caplen, and L. Dong, “High-energy single-transverse-mode Q-switched fiber laser based on a multimode large-mode-area erbium-doped fiber,” Opt. Lett. 23(21), 1683–1685 (1998). [CrossRef]
3. A. Ancona, S. Döring, C. Jauregui, F. Röser, J. Limpert, S. Nolte, and A. Tünnermann, “Femtosecond and picosecond laser drilling of metals at high repetition rates and average powers,” Opt. Lett. 34(21), 3304–3306 (2009). [CrossRef]
4. J. Y. Huang, S. C. Huang, H. L. Chang, K. W. Su, Y. F. Chen, and K. F. Huang, “Passive Q switching of Er-Yb fiber laser with semiconductor saturable absorber,” Opt. Express 16(5), 3002–3007 (2008). [CrossRef]
5. R. Paschotta, R. Häring, E. Gini, H. Melchior, U. Keller, H. L. Offerhaus, and D. J. Richardson, “Passively Q-switched 0.1-mJ fiber laser system at 1.53 µm,” Opt. Lett. 24(6), 388–390 (1999). [CrossRef]
6. D. P. Zhou, L. Wei, B. Dong, and W. K. Liu, “Tunable passively Q -switched erbium-doped fiber laser with carbon nanotubes as a saturable absorber,” IEEE Photonics Technol. Lett. 22(1), 9–11 (2010). [CrossRef]
7. B. Dong, C. Y. Liaw, J. Hao, and J. Hu, “Nanotube Q-switched low-threshold linear cavity tunable erbium-doped fiber laser,” Appl. Opt. 49(31), 5989–5992 (2010). [CrossRef]
8. B. Dong, J. Hu, C. Y. Liaw, J. Hao, and C. Yu, “Wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser,” Appl. Opt. 50(10), 1442–1445 (2011). [CrossRef]
9. H. H. Liu, K. K. Chow, S. Yamashita, and S. Y. Set, “Carbon-nanotube-based passively Q-switched fiber laser for high energy pulse generation,” Opt. Laser Technol. 45, 713–716 (2013). [CrossRef]
10. D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, and A. C. Ferrari, “Graphene Q-switched, tunable fiber laser,” Appl. Phys. Lett. 98(7), 073106 (2011). [CrossRef]
11. J. Wang, Z. Luo, M. Zhou, C. Ye, H. Fu, Z. Cai, H. Cheng, H. Xu, and W. Qi, “Evanescent-light deposition of graphene onto tapered fibers for passive Q-switch and mode-locker,” IEEE Photonics J. 4(5), 1295–1305 (2012). [CrossRef]
12. Z. Luo, M. Zhou, J. Weng, G. Huang, H. Xu, C. Ye, and Z. Cai, “Graphene-based passively Q-switched dual-wavelength erbium-doped fiber laser,” Opt. Lett. 35(21), 3709–3711 (2010). [CrossRef]
13. W. J. Cao, H. Y. Wang, A. P. Luo, Z. C. Luo, and W. C. Xu, “Graphene-based, 50 nm wide-band tunable passively Q-switched fiber laser,” Laser Phys. Lett. 9(1), 54–58 (2012). [CrossRef]
14. Z. Yu, Y. Song, J. Tian, Z. Dou, H. Guoyu, K. Li, H. Li, and X. Zhang, “High-repetition-rate Q-switched fiber laser with high quality topological insulator Bi2Se3 film,” Opt. Express 22(10), 11508–11515 (2014). [CrossRef]
15. Y. Chen, C. Zhao, S. Chen, J. Du, P. Tang, G. Jiang, Z. Zhang, S. Wen, and D. Tang, “Large energy, wavelength widely tunable, topological insulator Q-switched erbium-doped fiber laser,” IEEE J. Sel. Top. Quantum Electron. 20(5), 315–322 (2014). [CrossRef]
16. J. Koo, J. Lee, and J. H. Lee, “Integrated fiber-optic device based on a combination of a piezoelectric transducer and a bulk-structured Bi2Te3 topological insulator for Q-Switched mode-locking of a fiber laser,” J. Lightwave Technol. 35(11), 2175–2182 (2017). [CrossRef]
17. J. Chen, G. Deng, S. Yan, C. Li, K. Xi, F. Xu, and Y. Lu, “Microfiber-coupler-assisted control of wavelength tuning for Q-switched fiber laser with few-layer molybdenum disulfide nanoplates,” Opt. Lett. 40(15), 3576–3579 (2015). [CrossRef]
18. H. Xia, H. Li, C. Lan, C. Li, J. Du, S. Zhang, and Y. Liu, “Few-layer MoS2 grown by chemical vapor deposition as a passive Q-switcher for tunable erbium-doped fiber lasers,” Photonics Res. 3(3), A92–A96 (2015). [CrossRef]
19. J. Lin, K. Yan, Y. Zhou, L. X. Xu, C. Gu, and Q. W. Zhan, “Tungsten disulphide based all fiber Q-switching cylindrical-vector beam generation,” Appl. Phys. Lett. 107(19), 191108 (2015). [CrossRef]
20. S. H. Kassani, R. Khazaeinezhad, H. Jeong, T. Nazari, D. Yeom, and K. Oh, “All-fiber Er-doped Q-switched laser based on tungsten disulfide saturable absorber,” Opt. Mater. Express 5(2), 373–379 (2015). [CrossRef]
21. H. Mu, Z. Wang, J. Yuan, S. Xiao, C. Chen, Y. Chen, Y. Chen, J. Song, Y. Wang, Y. Xue, H. Zhang, and Q. Bao, “Graphene–Bi2Te3 Heterostructure as Saturable Absorber for Short Pulse Generation,” ACS Photonics 2(7), 832–841 (2015). [CrossRef]
22. L. Li, Y. Yu, G. J. Ye, Q. Ge, X. Ou, H. Wu, D. Feng, X. H. Chen, and Y. Zhang, “Black phosphorus field-effect transistors,” Nat. Nanotechnol. 9(5), 372–377 (2014). [CrossRef]
23. F. Xia, H. Wang, and Y. Jia, “Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics,” Nat. Commun. 5(1), 4458 (2014). [CrossRef]
24. N. Youngblood, C. Chen, S. J. Koester, and M. Li, “Waveguide-integrated black phosphorus photodetector with high responsivity and low dark current,” Nat. Photonics 9(4), 247–252 (2015). [CrossRef]
25. J. Wu, G. K. W. Koon, D. Xiang, C. Han, C. T. Toh, E. S. Kulkarni, I. Verzhbitskiy, A. Carvalho, A. S. Rodin, S. P. Koenig, G. Eda, W. Chen, A. H. C. Neto, and B. Ozyilmaz, “Colossal ultraviolet photoresponsivity of few-layer black phosphorus,” ACS Nano 9(8), 8070–8077 (2015). [CrossRef]
26. M. Engel, M. Steiner, and P. Avouris, “Black phosphorus photodetector for multispectral, high-resolution imaging,” Nano Lett. 14(11), 6414–6417 (2014). [CrossRef]
27. Y. Chen, G. Jiang, S. Chen, Z. Guo, X. Yu, C. Zhao, H. Zhang, Q. Bao, S. Wen, D. Tang, and D. Fan, “Mechanically exfoliated black phosphorus as a new saturable absorber for both Q-switching and mode-locking laser operation,” Opt. Express 23(10), 12823–12833 (2015). [CrossRef]
28. H. Mu, S. Lin, Z. Wang, S. Xiao, P. Li, Y. Chen, H. Zhang, H. Bao, S. P. Lau, C. Pan, D. Fan, and Q. Bao, “Black phosphorus–polymer composites for pulsed lasers,” Adv. Opt. Mater. 3(10), 1447–1453 (2015). [CrossRef]
29. H. Yu, X. Zheng, K. Yin, X. Cheng, and T. Jiang, “Nanosecond passively Q-switched thulium/holmium-doped fiber laser based on black phosphorus nanoplatelets,” Opt. Mater. Express 6(2), 603–609 (2016). [CrossRef]
30. J. Zheng, Z. Yang, C. Si, Z. Liang, X. Chen, R. Cao, Z. Guo, K. Wang, Y. Zhang, J. Ji, M. Zhang, D. Fan, and H. Zhang, “Black Phosphorus Based All-Optical-Signal-Processing: Toward High Performances and Enhanced Stability,” ACS Photonics 4(6), 1466–1476 (2017). [CrossRef]
31. M. Zhang, Q. Wu, F. Zhang, L. Chen, X. Jin, Y. Hu, Z. Zheng, and H. Zhang, “2D Black Phosphorus Saturable Absorbers for Ultrafast Photonics,” Adv. Opt. Mater. 7(1), 1800224 (2019). [CrossRef]
32. K. X. Huang, B. L. Lu, D. Li, X. Y. Qi, H. W. Chen, N. Wang, Z. R. Wen, and J. T. Bai, “Black phosphorus flakes covered microfiber for Q-switched ytterbium-doped fiber laser,” Appl. Opt. 56(23), 6427–6431 (2017). [CrossRef]
33. Z. Wang, R. Zhao, J. He, B. Zhang, J. Ning, Y. Wang, X. Su, J. Hou, F. Lou, K. Yang, Y. Fan, J. Bian, and J. Nie, “Multi-layered black phosphorus as saturable absorber for pulsed Cr: ZnSe laser at 2.4 µm,” Opt. Express 24(2), 1598–1603 (2016). [CrossRef]
34. Z. Qin, G. Xie, H. Zhang, C. Zhao, P. Yuan, S. Wen, and L. Qian, “Black phosphorus as saturable absorber for the Q-switched Er: ZBLAN fiber laser at 2.8 µm,” Opt. Express 23(19), 24713–24718 (2015). [CrossRef]
35. B. Dong, J. Hao, J. Hu, and C. Y. Liaw, “Wide pulse-repetition-rate range tunable nanotube Q-switched low threshold erbium-doped fiber laser,” IEEE Photonics Technol. Lett. 22(24), 1853–1855 (2010). [CrossRef]
36. L. Wei, D. P. Zhou, H. Y. Fan, and W. K. Liu, “Graphene-based Q-switched erbium-doped fiber laser with wide pulse-repetition-rate range,” IEEE Photonics Technol. Lett. 24(4), 309–311 (2012). [CrossRef]
37. M. Wu, Y. Chen, H. Zhang, and S. Wen, “Nanosecond Q-switched Erbium-doped fiber laser with wide pulse-repetition-rate range based on topological insulator,” IEEE J. Quantum Electron. 50(6), 393–396 (2014). [CrossRef]
38. J. Ren, S. Wang, Z. Cheng, H. Yu, H. Zhang, Y. Chen, L. Mei, and P. Wang, “Passively Q-switched nanosecond erbium-doped fiber laser with MoS2 saturable absorber,” Opt. Express 23(5), 5607–5613 (2015). [CrossRef]
39. H. Chen, Y. S. Chen, J. Yin, X. Zhang, T. Guo, and P. Yan, “High-damage-resistant tungsten disulfide saturable absorber mirror for passively Q-switched fiber laser,” Opt. Express 24(15), 16287–16296 (2016). [CrossRef]
40. Y. Cai, Y. He, X. Zhang, R. Jiang, C. Su, and Y. Li, “Submicrosecond Q-switching Er-doped all-fiber ring laser based on black phosphorus,” Adv. Condens. Matter Phys. 2017, 1–4 (2017). [CrossRef]
41. P. Roy and D. Pagnoux, “Analysis and optimization of a Q-switched erbium doped fiber laser working with a short rise time modulator,” Opt. Fiber Technol. 2(3), 235–240 (1996). [CrossRef]
42. O. A. Louchev, Y. Urata, and S. Wada, “Numerical simulation and optimization of Q-switched 2 µm Tm, Ho: YLF laser,” Opt. Express 15(7), 3940–3947 (2007). [CrossRef]
43. J. J. Degnan, “Optimization of passively Q-switched lasers,” IEEE J. Quantum Electron. 31(11), 1890–1901 (1995). [CrossRef]
44. T. Hakulinen and O. G. Okhotnikov, “8 ns fiber laser Q switched by the resonant saturable absorber mirror,” Opt. Lett. 32(18), 2677–2679 (2007). [CrossRef]
45. S. B. Lu, L. L. Miao, Z. N. Guo, X. Qi, C. J. Zhao, H. Zhang, S. C. Wen, D. Y. Tang, and D. Y. Fan, “Broadband nonlinear optical response in multi-layer black phosphorus: an emerging infrared and mid-infrared optical material,” Opt. Express 23(9), 11183–11194 (2015). [CrossRef]
46. S. Chen, Y. Chen, M. Wu, Y. Li, C. J. Zhao, and S. C. Wen, “Stable Q-switched erbium-doped fiber laser based on topological insulator covered microfiber,” IEEE Photonics Technol. Lett. 26(10), 987–990 (2014). [CrossRef]
47. G. Sobon, A. Duzynska, and M. Świniarski, “CNT-based saturable absorbers with scalable modulation depth for Thulium-doped fiber lasers operating at 1.9 µm,” Sci. Rep. 7(1), 45491 (2017). [CrossRef]
48. J. Zhang, T. Jiang, X. Zheng, C. Shen, and X. Cheng, “Thickness-dependent nonlinear optical properties of CsPbBr3 perovskite nanosheets,” Opt. Lett. 42(17), 3371–3374 (2017). [CrossRef]
49. A. Martinez, K. Fuse, B. Xu, and S. Yamashita, “Optical deposition of graphene and carbon nanotubes in a fiber ferrule for passive mode-locked lasing,” Opt. Express 18(22), 23054–23061 (2010). [CrossRef]
50. K. Kashiwagi, S. Yamashita, and S. Y. Set, “In-situ monitoring of optical deposition of carbon nanotubes onto fiber end,” Opt. Express 17(7), 5711–5715 (2009). [CrossRef]
