Open Access
Add to BibSonomyAbstract
Topological insulators have been theoretically predicted as promising candidates for broadband photonics devices due to its large bulk band gap states in association with the spin-momentum-locked mass-less Dirac edge/surface states. Unlike the bulk counterpart, few-layer topological insulators possess some intrinsic optical advantages, such as low optical loss, low saturation intensity and high concentration of surface state. Herein, we use a solvothermal method to prepare few-layer Bi2Te3 flakes. By sandwiching few-layer Bi2Te3 flakes with polymethyl methacrylate (PMMA) polymer, a novel light modulation device had been successfully fabricated with high chemical and thermal stabilities as well as excellent mechanical durability, originating from the contribution of PMMA acting as buffer layers that counteract excessive mechanical bending within the fragile Bi2Te3 flakes. The incorporation of the as-fabricated PMMA-TI-PMMA as saturable absorber, which could bear long-term mechanical loadings, into the fiber laser cavity generated the stable dissipative soliton mode-locking with a 3-dB spectral bandwidth up to 51.62 nm and tunable wavelength range of 22 nm. Our work provides a new way of fabricating PMMA-TI-PMMA sandwiched composite structure as saturable absorber with promising applications for laser operation.
© 2015 Optical Society of America
1. Introduction
In recent years, there has been an intense experimental research activity in exploring roadmaps towards high energy pulses directly out of laser oscillators within passively mode-locked fiber laser technology, and the single-pulse energy available had been increased by several orders of magnitude from the nanojoule to the microjoule level [1–6]. During the course of scaling up the pulse energy, researchers had identified several key strategies/elements that might delimit the pulse energy. In order to avoid the pulse energy limitations imposed by pulse breakup, special cavity designs with normal dispersion and weak bandwidth limitation effect had been employed and the corresponding dissipative soliton fiber lasers had been demonstrated by Wise et al. [7] and Cabasse et al. [8]. After that, dissipative solitons have been experimentally obtained in passively mode-locked fiber laser by nonlinear polarization rotation (NPR) [9], (NOLM) [10], SESAM [11], CNT [12], graphene [13] and graphene oxide [14]. However, the operation wavelengths of NPR and NOLM are limited by the devices in the cavity. Also, the fiber lasers based on SESAMs operate with limited band due to the narrow response spectral width of SESAM itself. Moreover, the response spectral range of CNT is determined by the diameter and chirality, which also restricts its applications. Although graphene and graphene oxide have the innate character of ultra-broadband response, they have a relatively low damage threshold, low saturating intensity, narrow adjustable extent limiting in high pulse energy applications [13–15]. C. Chi el al. has demonstrated a dissipative fiber laser at 1 micron using bulk-structured TI [16]. However, nanosize TI has unusual optical characters and band gap properties differing from those of the bulk materials. When the thickness reaches a magnitude order of several nanometers, besides the changes in band gap, the function of surface states will emerge obviously as well [17].
Topological insulators (TIs) are novel quantum electronic materials that have a bulk band gap like an ordinary insulator but a protected conducting state on their edges or surface [17–20]. These unique properties, originating from the combined effects of spin-orbit interactions and time-reversal symmetry, render TIs with ultra-broadband nonlinear optical response ranging from the visible to the microwave frequency [21]. The saturable absorption property of TIs was experimentally verified based on the Z-scan measurement technology, and the formation of passive mode-locking or Q-switched operation at wavelengths 1064 nm [22], 1550 nm [23–25], 1645 nm [26] and 2 [27] was also demonstrated. Therefore TIs have been considered as the viable substitute materials for traditional saturable absorber (SA), such as semiconductor saturable absorber mirrors (SESAM). Unlike those saturable absorbers, TIs possess one intrinsic advantage that the optical property is more robust against external perturbations. This is because the metallic surface state of TIs, which is a natural result of the strong spin-orbital coupling, can still remain very stable and be able to withstand unexpected impurities or defects. Several methods have been proposed for the synthesis the saturable absorbers of TIs such as mechanical exfoliations [24], chemical exfoliations [28], bulk-structured TIs deposition [29, 30], and so on. However, up to now, lack of uniform TIs film with homogenous morphology and effective transfer technique may delimit further applications of TIs.
Various methods had been demonstrated for the fabrication of TIs films, including spraying [31], inkjet [32], drop casting [23, 33], spin coating [34], optical deposition [35], and polymer composite [36]. Although TIs films have been successfully fabricated through those methods, they normally show uneven thickness distribution and are easy to crack, which together with the process of fabricating or transferring, may seriously degrade the device performance. Self-assembly technique is a simple and useful approach to organize nanosheets into uniform and integral films at the interface between the two immiscible phases [37]. It is very suitable to employ the TIs self-assembly films as saturable absorber to realize the mode-locking operation. But up to now, to the best of our knowledge, the application of TIs self-assembly films in fiber laser has not ever been mentioned or noticed.
In this contribution, we demonstrate the generation of dissipative soliton in fiber laser passively mode-locked by a high quality topological insulator based saturable absorber sandwiched by PMMA polymer. The Bi2Te3 nanosheets generated an ultrathin and uniform film at the interface between the DI water and the air. Since both sides of the Bi2Te3 self-assembly layer covered with PMMA polymer layer in order to protect it from fragmentation, a novel ultrathin saturable absorber had been successfully fabricated. This novel sandwiched PMMA-TI-PMMA structure can both protect Bi2Te3 nanosheets from oxidation, which further increases the durability and long term stability, and lower the scattering loss, allowing for better laser performance. After the incorporation of the saturable absorber device into a normal dispersion laser cavity, very stable wide-spectral dissipative solitons (3-dB bandwidth up to 51.6 nm), whose generation is a natural balance among the intra-cavity gain, loss, optical nonlinearity and dispersion, with central wavelength tunable up to 22 nm, had been generated. These results demonstrate that PMMA-TI-PMMA might be a reliable way in order to deliver enhanced performance.
2. Experiment setup
2.1 Synthesis of Bi2Te3 nanosheets
Bi2Te3 nanosheets were synthesized using a solvothermal method [38]. In a typical synthesis, a stoichiometric ratio of bismuth chloride (BiCl3), and sodium selenide (Na2TeO3) were dissolved in ethylene glycol with vigorous stirring. Then the mixture was transferred into the Teflon-lined stainless-steel autoclave and heated to 200 °C. The autoclave was maintained at the reaction temperature for 36 h and then cooled to room temperature naturally. The black powders were collected by filtering, washed with distilled water and ethanol, and finally dried at 60 °C in vacuum overnight. The as-grown and washed powders were dispersed in an ethanol solution.
2.2 Characterization methods of the samples
Field-emission scanning electron microscopy (FESEM) images were obtained with a JSM-6700F microscope. Transmission electron microscopy (TEM) images were obtained on a JEOL 3010 microscope with an accelerating voltage of 300 kV. Atomic force microscope (AFM) measurements were carried out in a Multimode 8 system. The X-ray diffraction pattern of the products was performed on a D8-Advanee X-ray diffractometer with a Cu-Kα radiation. Raman spectra were obtained by a Labram-010 system.
2.3 Fabrication of sandwiched PMMA-TI-PMMA structure
Figure 1 shows the fabrication of sandwiched PMMA-TI-PMMA structure. The Bi2Te3 nanosheets were centrifuged and redispersed in organic solvent. This dispersion was gently placed on top of the DI water surface. Upon evaporation of organic solvent, the Bi2Te3 nanosheets spontaneously diffused to generate the self-assembled layers. Therefore, the self-assembled films possess high uniformity, as can be seen in the inset 1 of Fig. 1. In the following, PMMA solution of anisole was spin-coated onto a copper foil, which was then dried on the hot plate. We then placed the Bi2Te3 self-assembled layer on the copper foil coated with PMMA so that the original morphology and dispersion of the Bi2Te3 self-assembled layers were still kept on the surface of PMMA. Then another protection layer of PMMA was spin-coated onto the self-assembly layer, which was under the second rounds of drying. After being placed in the ferric chloride solution, the copper layer was completely etched and the PMMA-TI-PMMA structure was finally fabricated after washed several times in DI water. The saturable absorber device based on PMMA-TI-PMMA structure was finally fabricated as shown in the inset 2 of Fig. 1.
Fig. 1 Schematic representation of saturable absorber of Bi2Te3 self-assembly layer nanosheets covered by two PMMA layers. Inset: (1) Bi2Te3 self-assembly layer generated on the DI water surface. (2) Optical image of PMMA-TI-PMMA on the fiber ferrule.
There are many advantages to this novel PMMA-TI-PMMA structure. First, the self-assembly layer spontaneously generated at the interface between the DI water and the air can remain very uniform. Second, the self-assembled layer can be effectively protected by double PMMA layers, and the original morphology will be automatically kept while being transferred and installed. Third, the SA device can be effectively protected from oxidation, since it is isolated from air due to the double PMMA sandwich structure.
2.4 Z-scan experimental setup
We measured the nonlinear absorption coefficient of PMMA-TI-PMMA by using the open-aperture Z-scan technique which was used as an effective tool for measuring the saturation absorption parameters. The experimental setup is schematically shown in Fig. 2. We used a pico-second passively mode-locked laser with center wavelength 1562 nm, pulse duration 1.2 ps and repetition rate 20.8 MHz as the illumination source. The average power of the pulse is about 42.89 mW, indicating that the peak pulse power can reach up to 1.72 kW. The laser beam waist was measured to be about 74 µm by using the right-angle knife-edge method and further confirmed by z-scan parameter fitting, corresponding to a peak intensity of 10 MWcm−2. The Bi2Te3 sample and its quartz substrate were perpendicularly oriented towards the beam axis and translated along the axis through the focus with a motorized Precision Translation stage. An open-aperture measurement corresponds to the detection of the entire incident light transmitted through the sample collected by a photo-detector. Therefore, the measurement at the open-aperture regime enables the characterization of the intensity dependent absorption. A typical trace when the sample is translated through the beam focus is shown in Fig. 7. The peak in transmission when the sample passes through the focus is characteristic of saturable absorption.
2.5 Fiber laser experimental setup
The schematic configuration of the experimental setup is shown in Fig. 3. A piece of 14.5 meters erbium-doped fiber (EDF) with a group velocity dispersion (GVD) of −45 ps/nm/km at 1550 nm was used as the gain medium, and a 975 nm laser diode (LD) with maximum of 500 mW provides pump via a 975/1550 nm wavelength division multiplexer (WDM). The total cavity length is about 19 meters including a total length of 4.6 meters standard single mode fiber (SMF-28) from the pigtail of optical components with a GVD parameter of 18 ps/nm/km. The net dispersion of the cavity is 0.725 ps2 at 1550 nm. The unidirectional operation of the ring cavity is ensured by a polarization independent isolator (PII-ISO). The output coupler is placed after EDF by using a 10% port as the output. An intra-cavity polarization controller (PC) was introduced to adjust the cavity birefringence and further optimize the performance of the fiber laser. The TI-SA is incorporated into the fiber laser cavity as a passive mode-locker. And also, before the measurement equipment, we introduce a 1550 nm PII-ISO to remove pump light. An optical spectrum analyzer (AQ-6317B), a commercial autocorrelator (AC) (FR-103XL), a radio-frequency (RF) (Agilent N9322C) analyzer, and a 500 MHz oscilloscope (Tektronix TDS3054B) with a 5 GHz photo-diode detector are used to monitor the outputs simultaneously.
3. Results and discussions
3.1 Characterization of the samples
The morphology and size of the as-prepared Bi2Te3 samples were characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) as shown in Fig. 4. The lower magnification FESEM image (Fig. 4(a)) reveals that a large number of sheet-like structures are uniformly dispersed on the surface of the substrate. The obtained products are predominantly hexagonal-based plates of uniform size and well-defined shape. A higher magnification FESEM image (Fig. 4(b)) shows that the edge length of plates is in the range of 500-800nm, and that the thickness is about 10 nm. The TEM measurement provides further insight into the microstructural details of the Bi2Te3 nanostructures. Figure 4(c) is a typical TEM image of single nanosheets, clearly demonstrating that the nanosheets have perfect hexagonal morphology.
Fig. 4 (a) Low-magnification FESEM image of Bi2Te3nanosheets. (b) High-magnification FESEM image of Bi2Te3nanosheets. (c) TEM image of a single perfect hexagonal nanosheet.
To further confirm the thickness and the width of as-prepared Bi2Te3 nanosheets, the AFM topography images of Bi2Te3 nanosheets are investigated. As shown in Fig. 5, the Bi2Te3 nanosheets have very clean and flat surface with a uniform thickness about 10 nm across the lateral dimensions. The height profiles corresponding to the line-cut in Fig. 5(a) is shown in Fig. 5(b). The two dotted lines in Fig. 5(b) correspond to the two blue points of the line-cut in Fig. 5(a). The average width of the Bi2Te3 nanosheets is about 600 nm, which is represented by the distance between the two dotted lines.
Fig. 5 (a) Topographic AFM images of the Bi2Te3nanosheet. (b) Corresponding height profiles. (c) Corresponding three-dimensional images.
The XRD pattern of the freshly prepared products is shown in Fig. 6(a). All the diffraction peaks can be indexed to rhombohedral Bi2Te3 (space group:) with lattice constants a = b = 0.438 nm, c = 3.05 nm, which are consistent with the literature values (JCPDS No. 15-0863). This result indicates that Bi2Te3 products obtained via our synthetic method consist of a pure phase.
Fig. 6 (a) XRD pattern of the as-prepared Bi2Te3nanosheets. (b) Raman spectra of Bi2Te3 nanosheets at 632nm laser excitation.
The Raman scattering spectrum of the as-prepared Bi2Te3 nanosheets is shown in Fig. 6(b). The Raman spectrum contains four main peaks which correspond to A1g1, Eg2, A1u and A1g2 respectively. The Raman spectrum of bulk polycrystalline Bi2Te3 exhibits three signature optical phonon modes including A1g1, Eg2 and A1g2. The as-prepared Bi2Te3 nanosheets exhibit an extra infrared active phonon mode, A1u mode, which does not exist in the bulk phase. It is possible that the ultrathin structure of our samples breaks the centro-symmetric nature of Bi2Te3 and therefore it allows for the emergence of A1u mode.
We also measured the near-infrared linear absorption spectrum, as shown in Fig. 7(a). It has an almost flat curve, indicating its broadband optical response.
Based on the characterization results, we can conclude that our samples have high quality with small grain size, perfect hexagonal and ultra-thin laminated structure, and uniformity. The uniformity enables the light with arbitrary polarization direction passing through the sample. Otherwise, the light with some special polarization direction cannot experience the sample. Furthermore, the generation of dissipative solitons depends on the balance among different effects including cavity dispersion, optical nonlinearity, laser gain saturation, cavity loss and spectral filtering. We might infer that high uniformity of the sample can benefit the formation of dissipative solitons because of relatively lower transmission loss.
3.2 Z-scan measurements
We use the normalized transmittance in the Z-scan measurement [39]:
Where, is the total absorption coefficient, is the linear absorption coefficient, is the input intensity, is the saturable intensity and is the TPA coefficient, is the sample length. From the fitting curves, we can see that the saturable absorption data fits: the saturable intensityat is 6.48 MW/cm−2 and modulation depth is about 10.39%. The TPAcoefficients at the two bands are negligible.3.3 Fiber laser
Firstly, we measured the insert loss of the whole TI-SA device at 1571 nm, which is 1.11 dB. Thanks to the relatively high quality of the TI-SA, the laser oscillation threshold can reach as low as 40 mW while the self-started mode-locking can be easily achieved just by increasing the pump power above the threshold. The single dissipative soliton operation can maintain up to 152 mW. Figure 8 describes a typical single-pulse mode-locking state at a pump power of 150 mW. Figure 8(a) shows the equally-spaced uniform pulse train, which indicates high stability of the fiber laser. The pulse-to-pulse interval is about 93.37 ns, which corresponds to a repetition rate of 10.71 MHz and matches with the cavity round-trip time. These indicate that the mode locking laser operates in a single-pulse state which can be further confirmed by the measured RF spectrum as shown in Fig. 8(d), where there is no any extra frequency components or side-bands around the central frequency. The insert of Fig. 8(a) shows the pulses train in a large scale, from which, the pulses train still has a uniform peak contribution. The optical spectrum of the mode-locked pulses is shown in Fig. 8(b). It has an extremely steep spectral edge, which is a typical characteristic of dissipative soliton. It has a central wavelength of 1571 nm and a 3 dB spectral bandwidth of 39.95 nm. Also we provide corresponding spectrum in linear scale in the insert. The corresponding autocorrelation trace is shown in Fig. 8(c). It has a full width at half maximum (FWHM) of 6.68 ps. After deconvolution, it gives pulse duration of 4.72 ps. Therefore the time-bandwidth product (TBP) of the pulses is calculated to be 22.9, indicating that the obtained dissipative solitons are strongly chirped. Figure 8(d) is the corresponding RF spectrum of the fiber laser measured with resolution bandwidth (RBW) of 30 Hz, video bandwidth (VBW) of 30 Hz. The central frequency is 10.71 MHz. The signal to noise ratio (SNR) is higher than 72.3 dB, which further confirms the high stability of the mode-locking operation in the current fiber laser cavity. We also measured the RF spectrum in a wider range (up to 1 GHz) shown in the insert of Fig. 8(d). As can be seen, there is no any extra frequency component, which further verifies the high stability of output pulse train. Here, the average output power is about 11 mW, corresponding to single pulse energy of 1.03 nJ. It is worth mentioning that the dissipative soliton mode-locking state can still maintain when the pump power decreased as low as 12 mW. The reason why it can maintain its mode-locking at such a low pump power is because of the low transmission loss from the TI-based saturable absorber device.
Fig. 8 Single dissipative soliton operation of the laser at pump power of 150 mW: (a) Pulse train. (b) Optical spectra measured. (c) Pulse profile. (d) Oscilloscope trace of pulse train.
By continuously increasing the pump power, its 3 dB spectral bandwidth also continues to increase and becomes as broad as 51.6 nm at a pump power of 500 mW (shown in Fig. 8(b), red). The emergence of broad spectral bandwidth is also contributed by the broadband saturable absorption of TI. If we compare the spectral bandwidth with the other work, we could find that the spectral bandwidth is much wider than other mode-locking technology in Er-doped dissipative solitons, such as NPR of 30.3 nm [40], SESAM of 11.8 nm [41], CNT of 35 nm [42], graphene of 7.8 nm [43], graphene oxide of 6.5 nm [14].
To further investigate the long-term stability, we also record the output optical spectra every 2 hours over 14 hours with fixed laser cavity operations, as shown in Fig. 9(a) by using the auto recording function of optical spectrum analyzer. During the entire measurement process, neither the central wavelength drifting nor new wavelength components were observed, revealing that the dissipative soliton laser shows reasonably long-term stability. Most importantly, we found that even if we turn on the pump again after 4 months, the mode-locking can be still obtained, indicating that the PMMA-TI-PMMA structure can well protect the device from oxidation.
Fig. 9 (a) Long-term stability: optical spectra measured at a 2 h interval over 14 h. (b) Multi-pulse state with two pulses. (c) Multi-pulse state with three pulses. (d) Output average power versus pump power.
Once the pump power was slightly increased beyond 152 mW (shown in Fig. 9(d)), the occurrence of two-photo absorption effect in the TI-SA might lead to the peak limiting and soliton quantization effect on pulses. The pulses start to break up and laser operating transforms to multi-pulse operation regime. Figures 9(b) and 9(c) respectively shows typical uniform intensity ordered multi-pulse state output with two and three pulses coexisting in the cavity. Figure 9(d) shows the relationship between output average power versus pump power, from which, it keeps almost linear. The evolution of pulse durations and 3 dB spectrum widths with pump power increasing is shown in Fig. 10. As the pump power increases from 60 mW to 500 mW, the spectral intensities increase and the 3 dB spectrum widths gradually broaden from 35.95 nm to 51.62 nm. Also, the pulse duration exhibits analogous variation tendency but with relatively minor change. The pulse duration increases slightly from 4.5 ps to 6.2 ps with the increasing of the pump power. The calculated TBPs increase from 19.68 to 38.93. Noting that the maximum pulse spectral width (51.62 nm) is limited by the maximum available power of pump LD and the gain bandwidth the EDF, we can conclude that TI-SA is an effective broad band operation saturable absorber for dissipative soliton generation.
Fig. 10 The evolution of dissipative solitons pulse spectra (a) and profiles (b) with the increasing of the pump power. (c) The relation of the spectral bandwidth, pulse duration and the time-bandwidth product with respect to different pump powers.
Through over-bending the optical fibers looped in the PCs, an artificial birefringence filter can be introduced with the central wavelength widely tunable by controlling the intra-cavity PCs. By fixing the pump power at 140 mW and just adjusting the orientation of the intra-cavity PCs, the central wavelength of the dissipative solitons can be largely tuned. Figure 11 shows the optical spectral evolution of dissipative solitons with the orientation variation of the PCs. As can be seen, the central wavelength of the dissipative solitons can be continuously tuned from 1548.2 nm to 1570.1 nm. A further wider tuning range is also feasible but mostly limited by the gain bandwidth of the EDF. It is important to note that the trailing edge of dissipative soliton pulse is already close to the edge of the EDF gain bandwidth. We can conclude that the tunable range is limited by the gain bandwidth other than the operation wavelength of the TI-SA.
4. Conclusions
In conclusion, we have demonstrated a wide spectral and wavelength-tunable dissipative soliton fiber laser by using high quality topological insulator Bi2Te3 covered by the upper and down PMMA polymer layers. Through sandwiching Bi2Te3 layer with PMMA polymer which is self-assembled at the interface of the DI water and the air, a novel ultrathin PMMA-TI-PMMA saturable absorber has been successfully fabricated. This special structure can guard the sample against damage during transfer and oxidation. From characterization results of samples, the TI has high quality with small grain size, perfect hexagonal and laminated structure, and uniformity, which generates a stable low threshold, wide-spectrum (up to 51.62 nm), wavelength tunable (22 nm), dissipative soliton output. Our studies clearly show that TI could be a promising saturable absorber for high energy and tunable dissipative solitons and this wide spectrum is very attractive to wavelength division multiplexing applications. We also experimentally found that the as-fabricated PMMA-TI-PMMA saturable absorber can successfully operate as an effective passive mode-locker without degrading the performance for several months, indicating the functionality of PMMA protection layer. This work suggests that the PMMA protection layer might not only just be suitable for TI, but also widely applicable for other 2-dimensional layer materials.
Acknowledgments
This work is partially supported by the MOE grant (Grant No. NCET 11-0135), National Natural Science Fund (Grant No. 61222505, 61435010), and Project supported by Hunan Provincial Natural Science Foundation of China (Grant No. 13JJ1012).
References and links
1. V. L. Kalashnikov, E. Podivilov, A. Chernykh, S. Naumov, A. Fernandez, R. Graf, and A. Apolonski, “Approaching the microjoule frontier with femtosecond laser oscillators: theory and comparison with experiment,” New J. Phys. 7, 217 (2005). [CrossRef]
2. T. Schreiber, C. K. Nielsen, B. Ortac, J. Limpert, and A. Tünnermann, “Microjoule-level all-polarization-maintaining femtosecond fiber source,” Opt. Lett. 31(5), 574–576 (2006). [CrossRef] [PubMed]
3. A. Chong, W. H. Renninger, and F. W. Wise, “All-normal-dispersion femtosecond fiber laser with pulse energy above 20 nJ,” Opt. Lett. 32(16), 2408–2410 (2007). [CrossRef] [PubMed]
4. S. Kobtsev, S. Kukarin, and Y. Fedotov, “Ultra-low repetition rate mode-locked fiber laser with high-energy pulses,” Opt. Express 16(26), 21936–21941 (2008). [CrossRef] [PubMed]
5. C. Lecaplain, B. Ortaç, and A. Hideur, “High-energy femtosecond pulses from a dissipative soliton fiber laser,” Opt. Lett. 34(23), 3731–3733 (2009). [CrossRef] [PubMed]
6. S. Lefrançois, K. Kieu, Y. J. Deng, J. D. Kafka, and F. W. Wise, “Scaling of dissipative soliton fiber lasers to megawatt peak powers by use of large-area photonic crystal fiber,” Opt. Lett. 35(10), 1569–1571 (2010). [CrossRef] [PubMed]
7. W. Renninger, A. Chong, and F. W. Wise, “Dissipative solitons in normal-dispersion fiber lasers,” Phys. Rev. A 77(2), 023814 (2008). [CrossRef]
8. A. Cabasse, B. Ortaç, G. Martel, A. Hideur, and J. Limpert, “Dissipative solitons in a passively mode-locked Er-doped fiber with strong normal dispersion,” Opt. Express 16(23), 19322–19329 (2008). [CrossRef] [PubMed]
9. L. R. Wang, X. M. Liu, Y. K. Gong, D. Mao, and L. N. Duan, “Observations of four types of pulses in a fiber laser with large net-normal dispersion,” Opt. Express 19(8), 7616–7624 (2011). [PubMed]
10. L. Yun, X. Liu, and D. Mao, “Observation of dual-wavelength dissipative solitons in a figure-eight erbium-doped fiber laser,” Opt. Express 20(19), 20992–20997 (2012). [CrossRef] [PubMed]
11. H. Zhang, D. Y. Tang, L. M. Zhao, X. Wu, and H. Y. Tam, “Dissipative vector solitons in a dispersionmanaged cavity fiber laser with net positive cavity dispersion,” Opt. Express 17(2), 455–460 (2009). [CrossRef] [PubMed]
12. J. H. Im, S. Y. Choi, F. Rotermund, and D. I. Yeom, “All-fiber Er-doped dissipative soliton laser based on evanescent field interaction with carbon nanotube saturable absorber,” Opt. Express 18(21), 22141–22146 (2010). [CrossRef] [PubMed]
13. H. Zhang, D. Y. Tang, R. J. Knize, L. M. Zhao, Q. L. Bao, and K. P. Loh, “Graphene mode locked, wavelength-tunable, dissipative soliton fiber laser,” Appl. Phys. Lett. 96(11), 111112 (2010). [CrossRef]
14. J. Xu, S. Wu, H. Li, J. Liu, R. Sun, F. Tan, Q. H. Yang, and P. Wang, “Dissipative soliton generation from a graphene oxide mode-locked Er-doped fiber laser,” Opt. Express 20(21), 23653–23658 (2012). [CrossRef] [PubMed]
15. 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] [PubMed]
16. C. Chi, J. Lee, J. Koo, and J. H. Lee, “All-normal-dispersion dissipative-soliton fiber laser at 1.06 µm using a bulk-structured Bi2Te3 topological insulator-deposited side-polished fiber,” Laser Phys. 24(10), 105106 (2014). [CrossRef]
17. H. J. 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]
18. J. E. Moore, “The birth of topological insulators,” Nature 464(7286), 194–198 (2010). [CrossRef] [PubMed]
19. 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]
20. 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]
21. S. Chen, C. Zhao, Y. Li, H. Huang, S. Lu, H. Zhang, and S. Wen, “Broadband optical and microwave nonlinear response in topological insulator,” Opt. Mater. Express 4(4), 587–596 (2014).
22. Z. Q. Luo, Y. Z. Huang, J. Weng, H. H. Cheng, Z. Q. Lin, B. Xu, Z. P. Cai, and H. Y. Xu, “1.06 μm Q-switched ytterbium-doped fiber laser using few-layer topological insulator Bi₂Se₃ as a saturable absorber,” Opt. Express 21(24), 29516–29522 (2013). [CrossRef] [PubMed]
23. Y. Chen, C. J. Zhao, H. H. Huang, S. Q. Chen, P. H. Tang, Z. T. Wang, S. B. Lu, H. Zhang, S. C. Wen, and D. Y. Tang, “Self-assembled topological insulator: Bi2Se3 membrane as a passive Q-switcher in an erbium-doped fiber laser,” J. Lightwave Technol. 31(17), 2857–2863 (2013). [CrossRef]
24. J. Sotor, G. Sobon, W. Macherzynski, P. Paletko, K. Grodecki, and K. M. Abramski, “Mode-locking in Er-doped fiber laser based on mechanically exfoliated Sb2Te3 saturable absorber,” Opt. Mater. Express 4(1), 1–6 (2014). [CrossRef]
25. Z. C. Luo, M. Liu, H. Liu, X. W. Zheng, A. P. Luo, C. J. Zhao, H. Zhang, S. C. Wen, and W. C. Xu, “2 GHz passively harmonic mode-locked fiber laser by a microfiber-based topological insulator saturable absorber,” Opt. Lett. 38(24), 5212–5215 (2013). [CrossRef] [PubMed]
26. P. H. Tang, X. Q. Zhang, C. J. Zhao, Y. Wang, H. Zhang, D. Y. Shen, S. C. Wen, D. Y. Tang, and D. Y. Fan, “Topological insulator: Bi2Te3 saturable absorber for the passive Q-switching operation of an in-band pumped 1645-nm Er:YAG ceramic laser,” IEEE Photon. J. 5(2), 1500707 (2013). [CrossRef]
27. Z. Luo, Y. Z. Huang, J. Weng, H. H. Cheng, Z. Q. Lin, B. Xu, Z. P. Cai, and H. Y. Xu, “Topological-insulator passively Q-switched double-clad fiber laser at 2 μm wavelength,” IEEE J. Sel. Top. Quantum Electron. 20(5), 0902708 (2014).
28. J. Boguslawski, J. Sotor, G. Sobon, J. Tarka, J. Jagiello, W. Macherzynski, L. Lipinska, and K. M. Abramski, “Mode-locked Er-doped fiber laser based on liquid phase exfoliated Sb2Te3 topological insulator,” Laser Phys. 24(10), 105111 (2014). [CrossRef]
29. J. Sotor, G. Sobon, and K. M. Abramski, “Sub-130 fs mode-locked Er-doped fiber laser based on topological insulator,” Opt. Express 22(11), 13244–13249 (2014). [PubMed]
30. J. Lee, J. Koo, Y. M. Jhon, and J. H. Lee, “A femtosecond pulse erbium fiber laser incorporating a saturable absorber based on bulk-structured Bi2Te3 topological insulator,” Opt. Express 22(5), 6165–6173 (2014). [CrossRef] [PubMed]
31. C. Torres-Torres, B. A. Can-Uc, R. Rangel-Rojo, L. Castañeda, R. Torres-Martínez, C. I. García-Gil, and A. V. Khomenko, “Optical Kerr phase shift in a nanostructured nickel-doped zinc oxide thin solid film,” Opt. Express 21(18), 21357–21364 (2013). [CrossRef] [PubMed]
32. B. S. Y. Ung, B. Weng, D. Abbott, S. T. Cundiff, and C. Fumeaux, “Inkjet printed conductive polymer-based beam-splitters for terahertz applications,” Opt. Mater. Express 3(9), 1242–1249 (2013). [CrossRef]
33. C. J. Zhao, H. Zhang, X. Qi, Y. Chen, Z. T. Wang, S. C. Wen, and D. Y. Tang, “Ultra-short pulse generation by a topological insulator based saturable absorber,” Appl. Phys. Lett. 101(21), 211106 (2012). [CrossRef]
34. T. R. Schibli, K. Minoshima, H. Kataura, E. Itoga, N. Minami, S. Kazaoui, K. Miyashita, M. Tokumoto, and Y. Sakakibara, “Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes,” Opt. Express 13(20), 8025–8031 (2005). [CrossRef] [PubMed]
35. M. Wu, Y. Chen, H. Zhang, and S. C. 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]
36. H. Zhang, Q. L. Bao, D. Y. Tang, L. M. Zhao, and K. Loh, “Large energy soliton erbium-doped fiber laser with a graphene-polymer composite mode locker,” Appl. Phys. Lett. 95(14), 141103 (2009). [CrossRef]
37. Y. J. Li, W. J. Huang, and S. G. Sun, “A universal approach for the self-assembly of hydrophilic nanoparticles into ordered monolayer films at a toluene/water interface,” Angew. Chem. Int. Ed. Engl. 45(16), 2537–2539 (2006). [CrossRef] [PubMed]
38. E. E. Foos, R. M. Stroud, and A. D. Berry, “Synthesis and characterization of nanocrystalline bismuth telluride,” Nano Lett. 1(12), 693–695 (2001). [CrossRef]
39. 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]
40. L. X. Xu, G. L. Chen, C. Gu, A. T. Wang, H. Ming, and P. K. A. Wai, “Square shape spectrum in 1550 nm and 1060 nm bands in passive mode-locked fiber laser,” in Proceedings of 14th OptoEectronics and Communications Conference, 2009, pp. 3–4.
41. A. Cabasse, G. Martel, A. Hideur, and J.-L. Oudar, “High modulation depth SESAM for high power dissipative soliton in an Erbium-doped fiber laser,” in Proceedings of Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference, 2009, pp. 1. [CrossRef]
42. L. Yun and D. D. Han, “Bound state of dissipative solitons in a nanotube-mode-locked fiber laser,” Opt. Commun. 313, 70–73 (2014). [CrossRef]
43. Y. D. Cui and X. M. Liu, “Graphene and nanotube mode-locked fiber laser emitting dissipative and conventional solitons,” Opt. Express 21(16), 18969–18974 (2013). [CrossRef] [PubMed]
