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Based on the open-aperture Z-scan measurement, we firstly uncovered the saturable absorption property of the topological insulator (TI): Bi2Se3. A high absolute modulation depth up to 98% and a saturation intensity of 0.49 GWcm−2 were identified. By incorporating this novel saturable absorber material into an erbium-doped fiber laser, wavelength tunable soliton operation was experimentally demonstrated. Our result indicates that like the atomic layer graphene, the topological insulator Bi2Se3 could also operate as an effective saturable absorber for the passive mode locking of lasers at the telecommunication band.
©2012 Optical Society of America
Corrections
Chujun Zhao, Yanhong Zou, Yu Chen, Zhiteng Wang, Shunbin Lu, Han Zhang, Shuangchun Wen, and Dingyuan Tang, "Wavelength-tunable picosecond soliton fiber laser with Topological Insulator: Bi2Se3 as a mode locker: erratum," Opt. Express 21, 444-444 (2013)https://opg.optica.org/oe/abstract.cfm?uri=oe-21-1-444
1. Introduction
Ultrafast fiber lasers have widespread applications ranging from industrial material processing, medical treatment, to basic researches [1]. In comparison with other types of lasers, fiber lasers are highly efficient, compact, and robust, and always deliver high quality laser beams. To achieve the ultra-short pulses emission of a fiber laser, normally a saturable absorber (SA) whose light absorbance decreases with the increase of the light intensity is incorporated in the cavity [1–3]. Among the various types of SAs, the semiconductor saturable absorber mirrors (SESAMs) [2, 3], single wall carbon nanotubes (SWNTs) [4–8] and graphene [9–21] SAs were extensively investigated. They are all found to be effective laser mode lockers. However, SESAMs require complicated fabrication and packaging technique, and have limited operation bandwidth; SWNTs and graphene SAs demand less stringent fabrication method, have advantages of fast recovery time, low saturation intensity and low cost. Moreover, because graphene has a Dirac-like electronic band structure, it could respond to a wide spectrum of photons, making it applicable as a broadband SA [22, 23] and standing out other types of SA [9, 14]. Very recently, another type of Dirac material, topological insulators (TI), has been widely studied in the condensed-matter physics [24, 25]. Like graphene, TI has also a band structure with Dirac-like linear dispersion in its surface state [26–30]. Several materials, such as Bi2Te3, Bi2Se3 and Sb2Te3, have been experimentally confirmed as the three-dimensional TI with a single Dirac cone in its surface state. Among these TI materials, Bi2Se3 has a relatively larger bulk band gap (0.3 eV), and it is considered as a promising optical material for the room-temperature applications [28]. Despite that many findings on the electronic property of the TI materials had been reported, their optical property, which is equally important as their electronics counterpart, are however less addressed. Very recently, researchers had studied the nonlinear optical property of TI: Bi2Te3, and found that its absorbance could become transparent under strong illumination [31]. Triggered by their finding, we have experimentally investigated the nonlinear absorption of TI: Bi2Se3 by using the open aperture Z-scan technique. We found that, like graphene, TI: Bi2Se3 exhibits saturable absorption, for the first time. By inserting the TI: Bi2Se3 saturable absorber in an erbium-doped fiber laser cavity, we further experimentally demonstrated the passive mode locking of the laser. Stable mode locked solitons with 1.57 ps pulse width at the 1565 nm wavelength were directly generated. Wavelength tuning of the solitons was also achieved by using the intrinsic cavity birefringent filter effect of the fiber ring lasers.
2. Preparation of the Bi2Se3 nanoplatelets
High quality TI films can be produced by MBE growth [32], vapor-liquid-solid growth [33], and mechanical exfoliation of thin sheets from bulk crystals [34]. Here, the Bi2Se3 nano-platelets (NPs) used were synthesized via a polyol method reported by Ref [35]. All reagents are of analytic purity and used without further purification. The synthesis was conducted as follows: 0.20 g Bi(NO3)3•5H2O, 0.1g sodium selenite, 0.44 g polyvinyl pyrrolidone, and 20 mL ethylene glycol were added into a 50.0 mL two-neck flask containing a Teflon-coated magnetic stirring bar. The flask was connected with a reflux condenser and placed on a heating mantle. The temperature of the solution was increased to 190 °C under constant stirring. After 2 hours, the flask was then removed from the heating mantle. The product was cooled, centrifuged, washed with isopropyl alcohol (IPA) several times. We took out some dispersion and the others were dried at 60 °C. Figure 1(a) shows the representative SEM images of the chemically grown NPs.
It can be seen that most high quality NPs exhibit hexagonal morphologies with planar dimensions that could extend up to several micrometers. The XRD pattern shown in Fig. 1(b) indicates that the product shown in Fig. 1(a) has the rhombohedral phase (JCPDS card No. 33-0214) with good crystalline.
3. Experimental results and discussions
In order to conveniently investigate the linear and nonlinear optical properties of the as-prepared TI: Bi2Se3 and to insert the TI sample into the fiber laser cavity, we firstly dropped the TI dispersion solution onto a 1 mm thick quartz plate. After that, the plate was placed inside a drying oven for evaporation for 8 hours.
The linear absorption spectrum of the sample was measured with a spectrophotometer (Lambda 950) and the result is shown in Fig. 2(a) . It clearly shows that the TI has a smooth transmission curve in the near-infrared wavelength band, suggesting that, like graphene, the TI is a promising broadband optical material. We then experimentally investigated the saturable absorption property of the TI: Bi2Se3 using the open aperture Z-scan technique. The experimental setup used was reported previously [36]. A picosecond pulse laser (pulse duration: 3.8 ps, pulse repetition rate: 100 MHz) was used to excite the nonlinear absorption. The pico-second pulses were generated with a mode locked fiber laser. 5% of the laser beam was split as the reference beam that was monitored with a photo-detector; the residual laser beam was focused by an objective lens (20 times) perpendicularly to the TI sample surface. The TI sample was mounted on a linear translation stage. The relative distance between the objective lens and the TI sample can be continuously varied by the motorized linear translation stage. A second detector was used to measure the entire laser beam intensity passing through the TI sample. By dividing the output power by the reference power, a normalized Z-scan curve was obtained as shown in Fig. 2(b). It clearly shows a very high on-off extinction ratio, i.e. the ratio of the maximum to the minimum optical transmittance, of up to 39. Based on the relation between the laser beam spot size and the normalized transmittance, a nonlinear saturable absorption curve is calculated as shown in Fig. 2(c). By fitting the curve with the following formula
where T is the transmission, A is a normalization constant, ΔT is the absolute modulation depth, I is the intensity and Isat is the saturation intensity, we have obtained the saturation intensity Isat = 0.49 GWcm−2 and the absolute modulation depth ΔT = 98%. The experiment clearly demonstrates that the TI: Bi2Se3 possesses high-modulation-depth (up to 98%) saturable absorption. Researchers experimentally found that a high modulation depth saturable absorber could suppress the wave-breaking effect, which is an intrinsic nonlinear phenomena and can limit the maximum per-pulse energy [37]. Here, the TI: Bi2Se3 with high modulation depth may have promising applications for high power pulse formation.
Fig. 2 (a) The near infrared linear absorption spectra of TI. (b) A typical Z-scan peak curve of TI: Bi2Se3 at 1550 nm. Insert: Z-scan experimental setup. (c) The corresponding nonlinear saturable absorption curve.
Taking advantage of the saturable absorption property of the Bi2Se3, we further designed a passively mode locked erbium-doped fiber laser with the Bi2Se3 as a mode locker. The fibre laser setup is schematically shown in Fig. 3 . The laser cavity is made of a piece of 1.1 m heavily doped Erbium-doped fiber (LIEKKI Er80-8/125) with group velocity dispersion (GVD) of ~–20 ps2/km, and 167 m single mode fiber (SMF) with GVD of –23 ps2/km. The net cavity dispersion is estimated as –3.86 ps2. A polarization independent isolator was used to force the unidirectional operation of the ring, and an intracavity polarization controller (PC) was used to adjust the cavity birefringence. A 980/1550 wavelength-division-multiplexer is used to couple the pump light into the cavity, and a 10% fiber coupler is used to output the laser emission. To incorporate the TI saturable absorber into the cavity, a fiber pigtailed bench is inserted in the cavity with a Bi2Se3 coated quartz plate mounted in it. The laser operation is simultaneously monitored with an oscilloscope (Tektronix TDS3054B) and a commercial autocorrelator (FR-103MN). The optical spectrum is measured with an optical spectrum analyzer (Ando AQ-6317B).
Fig. 3 Schematic of the fiber laser. PC: polarization controller. WDM: wavelength division multiplexer. EDF: erbium doped fiber. SMF: single mode fiber.
Self-started mode locking of the laser occurred at an incident pump power of about 65 mW. The mode locking state could be maintained to the maximum available pump power of ~500 mW. Figure 4(a) shows the optical spectrum of the mode locked pulses at a pump power of 130 mW. The output spectrum is centered at 1564.6 nm with a 3 dB bandwidth of 1.79 nm. The Kelly sidebands are clearly visible on the optical spectrum, indicating that the mode-locked operation is in the soliton regime [38]. Figure 4(b) shows a measured autocorrelation trace of the mode locked pulses. It has a FWHW width of 2.42 ps. If a Sech2 pulse profile is assumed, the soliton pulse duration is 1.57 ps. The time-bandwidth product of the pulses is ~0.35, indicating that they are slightly chirped. Figure 4(c) shows the measured oscilloscopes trace in the nanosecond time scale. A pulse is circulating in the cavity at the fundamental cavity repetition rate of 1.21 MHz. Under strong pumping, multiple soliton pulse operation was also observed. In order to evaluate the mode-locking stability, we recorded the optical spectra of the laser every 4-hour over 2-days, as shown in Fig. 4(d). We note that the central spectral peak locations, spectral bandwidth, spectral strength remained reasonably stable over the time period.
Fig. 4 (a) The mode locked soliton spectrum. Its corresponding autocorrelation trace (b) and oscilloscope trace (c). (d) Long term optical spectra measured at a 4-hour interval over 2-days.
It is well-known that large residual cavity birefringence could induce artificial narrow band pass filter effect in a fiber ring laser [39]. Together with the limited bandwidth of the laser gain, this artificial cavity birefringence filter effect could be used to control the central operation wavelength of a laser and achieve tunable mode locked pulses. Making use of the effect of the fiber ring laser we have further designed a wavelength tunable passively mode locked fiber laser with the TI: Bi2Se3 as a saturable absorber. Figure 5 shows the optical spectrum evolution of the solitons as the orientation of an intracavity PC is varied. The wavelength of the solitons could be shifted from 1557 to 1565 nm continuously. To verify whether the mode locking operation is purely contributed by the saturable absorption of the Bi2Se3 nano-platelets, the TI SA was purposely removed out of the laser cavity. In this case no mode locking was observed, despite that the pump power was increased from zero to the maximum available power and the polarization controller was rotated in a full range.
4. Conclusion
In conclusion, we have experimentally studied the saturable absorption property of TI: Bi2Se3 at the telecommunication band using the Z-scan technique. Our result shows that TI: Bi2Se3 has strong saturable absorption with a large absolute modulation depth. Taking advantage of the saturable absorption, we firstly demonstrated the passive mode locking of an erbium-doped fiber laser with the TI: Bi2Se3 as a passive mode locker. Stable soliton pulses with 1.57 ps pulse width at 1564.6 nm were obtained. Continuous wavelength tuning from 1557 to 1565 nm was also achieved in a Bi2Se3 mode locked fiber laser by taking advantage of the intrinsic cavity birefringence filter effect. Our experimental results demonstrated that TI: Bi2Se3 could be a cost-effective saturable absorber for fiber laser mode locking.
Acknowledgment
This work is partially supported by the National 973 Program of China (Grant No. 2012CB315701), the National Natural Science Foundation of China (Grant Nos. 61025024 and 61205125), Hunan Provincial Natural Science Foundation of China (Grant No. 12JJ7005). Han Zhang acknowledges the strong support from Program for New Century Excellent Talents in University of China (Grant No. NCET 11-0135), “Thousand Talents Program” for Distinguished Young Scholars and National Natural Science Fund Foundation of China for Excellent Young Scholars (Grant No. 61222505).
References and links
1. U. Keller, “Recent developments in compact ultrafast lasers,” Nature 424(6950), 831–838 (2003). [CrossRef] [PubMed]
2. O. Okhotnikov, A. Grudinin, and M. Pessa, “Ultra-fast fibre laser systems based on SESAM technology: new horizons and applications,” New J. Phys. 6, 177 (2004). [CrossRef]
3. G. Steinmeyer, D. H. Sutter, L. Gallmann, N. Matuschek, and U. Keller, “Frontiers in Ultrashort Pulse Generation: Pushing the Limits in Linear and Nonlinear Optics,” Science 286(5444), 1507–1512 (1999). [CrossRef] [PubMed]
4. S. Y. Set, H. Yamaguchi, Y. Tanaka, M. Jablonski, Y. Sakakibara, A. Rozhin, M. Tokumoto, H. Kataura, Y. Achiba, and K. Kikuchi, “Mode-locked fiber lasers based on a saturable absorber incorporating carbon nanotubes,” in Optical Fiber Communication Conference 2003, Technical Digest (Optical Society of America, 2003), paper PD44.
5. S. Yamashita, Y. Inoue, S. Maruyama, Y. Murakami, H. Yaguchi, M. Jablonski, and S. Y. Set, “Saturable absorbers incorporating carbon nanotubes directly synthesized onto substrates and fibers and their application to mode-locked fiber lasers,” Opt. Lett. 29(14), 1581–1583 (2004). [CrossRef] [PubMed]
6. F. Wang, A. G. Rozhin, V. Scardaci, Z. Sun, F. Hennrich, I. H. White, W. I. Milne, and A. C. Ferrari, “Wideband-tuneable, nanotube mode-locked, fibre laser,” Nat. Nanotechnol. 3(12), 738–742 (2008). [CrossRef] [PubMed]
7. S. Kivistö, T. Hakulinen, A. Kaskela, B. Aitchison, D. P. Brown, A. G. Nasibulin, E. I. Kauppinen, A. Härkönen, and O. G. Okhotnikov, “Carbon nanotube films for ultrafast broadband technology,” Opt. Express 17(4), 2358–2363 (2009). [CrossRef] [PubMed]
8. M. A. Solodyankin, E. D. Obraztsova, A. S. Lobach, A. I. Chernov, A. V. Tausenev, V. I. Konov, and E. M. Dianov, “Mode-locked 1.93 microm thulium fiber laser with a carbon nanotube absorber,” Opt. Lett. 33(12), 1336–1338 (2008). [CrossRef] [PubMed]
9. Q. L. Bao, H. Zhang, Y. Wang, Z. Ni, Y. Yan, Z. X. Shen, K. P. Loh, and D. Y. Tang, “Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers,” Adv. Funct. Mater. 19(19), 3077–3083 (2009). [CrossRef]
10. H. Zhang, D. Y. Tang, L. M. Zhao, Q. L. Bao, and K. P. Loh, “Large energy mode locking of an erbium-doped fiber laser with atomic layer graphene,” Opt. Express 17(20), 17630–17635 (2009). [CrossRef] [PubMed]
11. G. Sobon, J. Sotor, J. Jagiello, R. Kozinski, M. Zdrojek, M. Holdynski, P. Paletko, J. Boguslawski, L. Lipinska, and K. M. Abramski, “Graphene Oxide vs. Reduced Graphene Oxide as saturable absorbers for Er-doped passively mode-locked fiber laser,” Opt. Express 20(17), 19463–19473 (2012). [CrossRef] [PubMed]
12. Z. Sun, T. Hasan, F. Torrisi, D. Popa, G. Privitera, F. Wang, F. Bonaccorso, D. M. Basko, and A. C. Ferrari, “Graphene Mode-Locked Ultrafast Laser,” ACS Nano 4(2), 803–810 (2010). [CrossRef] [PubMed]
13. K. Kieu and F. W. Wise, “Soliton Thulium-Doped Fiber Laser with Carbon Nanotube Saturable Absorber,” IEEE Photon. Technol. Lett. 21(3), 128–130 (2009). [CrossRef] [PubMed]
14. F. Bonaccorso, Z. Sun, T. Hasan, and A. C. Ferrari, “Graphene photonics and optoelectronics,” Nat. Photonics 4(9), 611–622 (2010). [CrossRef]
15. 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] [PubMed]
16. Y. W. Song, S. Y. Jang, W. S. Han, and M. K. Bae, “Graphene mode-lockers for fiber lasers functioned with evanescent field interaction,” Appl. Phys. Lett. 96(5), 051122 (2010). [CrossRef]
17. J. Sotor, G. Sobon, and K. M. Abramski, “Scalar soliton generation in all-polarization-maintaining, graphene mode-locked fiber laser,” Opt. Lett. 37(11), 2166–2168 (2012). [CrossRef] [PubMed]
18. 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] [PubMed]
19. J. Liu, S. Wu, Q. H. Yang, and P. Wang, “Stable nanosecond pulse generation from a graphene-based passively Q-switched Yb-doped fiber laser,” Opt. Lett. 36(20), 4008–4010 (2011). [CrossRef] [PubMed]
20. J. L. Xu, X. L. Li, Y. Z. Wu, X. P. Hao, J. L. He, and K. J. Yang, “Graphene saturable absorber mirror for ultra-fast-pulse solid-state laser,” Opt. Lett. 36(10), 1948–1950 (2011). [CrossRef] [PubMed]
21. Z. Wang, Y. Chen, C. Zhao, H. Zhang, and S. Wen, “Switchable Dual-Wavelength Synchronously Q-Switched Erbium-Doped Fiber Laser Based on Graphene Saturable Absorber,” IEEE Photon. J. 4(3), 869–876 (2012). [CrossRef]
22. Z. Zheng, C. Zhao, S. Lu, Y. Chen, Y. Li, H. Zhang, and S. Wen, “Microwave and optical saturable absorption in graphene,” Opt. Express 20(21), 23201–23214 (2012). [CrossRef]
23. A. K. Geim and K. S. Novoselov, “The rise of graphene,” Nat. Mater. 6(3), 183–191 (2007). [CrossRef] [PubMed]
24. M. Z. Hasan and C. L. Kane, “Colloquium: Topological insulators,” Rev. Mod. Phys. 82(4), 3045–3067 (2010). [CrossRef]
25. X. L. Qi and S. C. Zhang, “Topological insulators and superconductors,” Rev. Mod. Phys. 83(4), 1057–1110 (2011). [CrossRef]
26. D. Hsieh, D. Qian, L. Wray, Y. Xia, Y. S. Hor, R. J. Cava, and M. Z. Hasan, “A topological Dirac insulator in a quantum spin Hall phase,” Nature 452(7190), 970–974 (2008). [CrossRef] [PubMed]
27. J. E. Moore, “The birth of topological insulators,” Nature 464(7286), 194–198 (2010). [CrossRef] [PubMed]
28. H. Zhang, C. X. Liu, X. L. Qi, X. Dai, Z. Fang, and S. C. Zhang, “Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface,” Nat. Phys. 5(6), 438–442 (2009). [CrossRef]
29. Y. Xia, D. Qian, D. Hsieh, L. Wray, A. Pal, H. Lin, A. Bansil, D. Grauer, Y. S. Hor, R. J. Cava, and M. Z. Hasan, “Observation of a large-gap topological-insulator class with a single Dirac cone on the surface,” Nat. Phys. 5(6), 398–402 (2009). [CrossRef]
30. D. Hsieh, Y. Xia, D. Qian, L. Wray, J. H. Dil, F. Meier, J. Osterwalder, L. Patthey, J. G. Checkelsky, N. P. Ong, A. V. Fedorov, H. Lin, A. Bansil, D. Grauer, Y. S. Hor, R. J. Cava, and M. Z. Hasan, “A tunable topological insulator in the spin helical Dirac transport regime,” Nature 460(7259), 1101–1105 (2009). [CrossRef] [PubMed]
31. F. Bernard, H. Zhang, S. P. Gorza, and P. Emplit, “Towards mode-locked fiber laser using topological insulators,” in Nonlinear Photonics, OSA Technical Digest (online) (Optical Society of America, 2012), paper NTh1A.5.
32. Y. Zhang, K. He, C. Z. Chang, C. L. Song, L. L. Wang, X. Chen, J. F. Jia, Z. Fang, X. Dai, W. Y. Shan, S. Q. Shen, Q. Niu, X. L. Qi, S. C. Zhang, X. C. Ma, and Q. K. Xue, “Crossover of the three-dimensional topological insulator Bi2Se3 to the two-dimensional limit,” Nat. Phys. 6(9), 584–588 (2010). [CrossRef]
33. H. Peng, K. Lai, D. Kong, S. Meister, Y. Chen, X. L. Qi, S. C. Zhang, Z. X. Shen, and Y. Cui, “Aharonov-Bohm interference in topological insulator nanoribbons,” Nat. Mater. 9(3), 225–229 (2010). [PubMed]
34. S. Y. F. Zhao, C. Beekman, L. J. Sandilands, J. E. J. Bashucky, D. Kwok, N. Lee, A. D. LaForge, S. W. Cheong, and K. S. Burch, “Fabrication and characterization of topological insulator Bi2Se3 nanocrystals,” Appl. Phys. Lett. 98(14), 141911 (2011). [CrossRef]
35. J. Zhang, Z. P. Peng, A. Soni, Y. Y. Zhao, Y. Xiong, B. Peng, J. B. Wang, M. S. Dresselhaus, and Q. H. Xiong, “Raman spectroscopy of Few-Quintuple Layer Topological insulator Bi2Se3 nanoplatelets,” Nano Lett. 11(6), 2407–2414 (2011). [CrossRef] [PubMed]
36. H. Zhang, S. Virally, Q. L. Bao, L. K. Ping, S. Massar, N. Godbout, and P. Kockaert, “Z-scan measurement of the nonlinear refractive index of graphene,” Opt. Lett. 37(11), 1856–1858 (2012). [CrossRef] [PubMed]
37. A. Cabasse, G. Martel, A. Hideur, and J. Oudar, “High modulation depth SESAM for high power dissipative soliton in an Erbium-doped fiber laser,” in CLEO/Europe and EQEC 2009 Conference Digest, (Optical Society of America, 2009), paper CJ10_5.
38. S. M. Kelly, “Characteristic sideband instability of periodically amplified average soliton,” Electron. Lett. 28(8), 806–807 (1992). [CrossRef]
39. H. Zhang, D. Y. Tang, L. M. Zhao, Q. L. Bao, K. P. Loh, and R. J. Knize, “Graphene mode locked, wavelength-tunable, dissipative soliton fiber laser,” Appl. Phys. Lett. 96(11), 111112 (2010). [CrossRef]
