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Abstract
We demonstrate a thulium-doped fiber laser that is mode-locked thanks to nonlinear polarization rotation (NPR) in a chalcogenide tapered fiber. The high nonlinearity of the tapered fiber leads to a combined reduction in mode-locking threshold power and cavity length compared to any all-silica NPR based mode-locked lasers. In the continuous wave mode-locking regime, the laser generates stable, tunable solitons pulses. In the Q-switched mode-locked regime, it allows single and multiwavelength pulses, tunable central wavelength and tunable multiwavelength separation.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Mode-locked Thulium-doped fiber lasers (TDFL) are attracting a great deal of attention due to their application in the wavelength range of 2 µm for LIDAR, spectroscopy, sensing and medical applications [1–5]. Techniques that have been developed to passively generate mode-locked pulses in TDFLs include the use of a semiconductor saturable absorber [6], nonlinear amplifying loop mirror [7] and nonlinear polarization rotation (NPR) [8,9]. Among these techniques, NPR is preferred due to its fast saturable absorption that ensures efficient pulse formation and long-term stability [10]. NPR also allows several pulse generation regimes such as continuous wave mode locking (CWML) [11–13], Q-switched mode locking (QML) [14,15] and multi-wavelength multi-pulse [16,17] regime, with each finding technological applications. The QML pulses exhibit higher peak power compared to CWML pulses while retaining ultrashort pulse width and have potential application in micromachining and medical surgery [18]. Multiwavelength lasers find applications in optical fiber sensing [19] and precision spectroscopy [20].
In conventional all-silica TDFLs, tens of meters of silica fibers are paired with several hundred mW of pump power to reach the nonlinearity threshold of silica glass and trigger NPR mode-locking [8,9,21]. A long cavity is usually associated with an increased sensitivity of the laser to environmental fluctuations as well as a relatively low repetition rate. Table 1 summarizes the specifications of NPR based all-silica TDFLs available in the literature, namely the power threshold, cavity length, and nonlinear medium length. Wang et al. demonstrated the lowest mode-locking threshold to this date, a value of 240 mW in a 22 m long fiber cavity, therefore resulting in repetition rate of 9.78 MHz [22]. It can be observed that further reduction of the cavity length requires a significant increase of pump power. However, one method to develop a more compact and stable laser along with a simultaneous reduction in power consumption is to use a medium of increased nonlinearity with respect to silica, to locally trigger NPR.
Table 1. Length and power values of mode-locked TDFL based on NPRa
Chalcogenide (ChG) fibers such as As2S3 are perfect candidates due to their exceptionally high nonlinear refractive index (n2 = 4 × 10−15 cm2/W) that is more than two orders of magnitude beyond silica glass [24]. In addition, the tapering of an As2S3 fiber down into a microwire further enhances the waveguide nonlinearity (γ) by up to four orders of magnitude compared to single mode silica fiber [25–27]. Therefore, to obtain the same amount of nonlinear phase shift (Ф= γPL), the optical power (P) and propagation length (L) can both be reduced with an As2S3 microwire compared to a silica fiber. Additionally, the adjustable chromatic dispersion of the ChG tapered fiber [28–30] allows to balance the net cavity dispersion, a crucial parameter for versatile pulsed operation regimes [31,32]. Four-wave mixing, parametric oscillation and supercontinuum generation are among many pulse generation techniques that have been demonstrated using ChG tapered fibers [33–36]. Al Kadry et al. demonstrated NPR mode-locking from an As2S3 tapered fiber at a wavelength of 1.55 µm [37]. The resulting fiber laser featured soliton and noise-like pulse emission, as well as multi-wavelength emission due to Lyot filtering effect. For this purpose, the cavity and nonlinear medium lengths were 26.5 m and 10 cm, respectively, and the threshold signal power was 11 mW. The operation of this mode-locking technique in the wavelength band of 2 µm as well as the potential improvement in terms of Pth, Lcav and compatibility with multiple laser operation regimes remain to be investigated.
In this paper, we demonstrate a TDFL that is mode-locked thanks to NPR in a chalcogenide tapered fiber. The high nonlinearity of the tapered fiber results in a reduced mode-locking threshold of 230 mW and a shortened cavity length of 9.45 m, compared to any all-silica based TDFLs [8,9,13,22,23]. The laser can operate in both QML and CWML pulse generation regimes. The QML operation regime generates multiwavelength pulses by the combined effect of QML and intra-cavity optical parametric oscillation (OPO), showing tunable central wavelength, tunable wavelength separation and variable number of laser wavelengths. The CWML operation generates stable solitons with tunable central wavelength from 1.877 µm to 1.945 µm. This demonstration is a major step towards the development of compact and low threshold TDFLs operating in QML and CWML operation regimes.
2. Experimental results and discussion
Figure 1(a) shows a schematic of the proposed fiber laser. It consists of a 20 cm long Thulium-doped silica fiber (Coractive DCF-TM-6/128), core pumped through a wavelength division multiplexer coupler. The pump is amplified spontaneous emission from an Erbium-doped fiber amplifier (Pritel FA-33) in the C-band. An 80/20 fused fiber coupler serves to extract pulses from the laser cavity via the 20% output. The cavity also includes two polarization controllers. A tapered fiber serves as a nonlinear medium that triggers and maintains self-pulsation through NPR. The polarizer-isolator allows a unidirectional operation of the laser and preserves the tapered fiber integrity by blocking the residual pump at 1.55 µm wavelength. The extracted pulses from the laser cavity are characterized with an OSA (Yokogawa- 6375), a photodetector (ET- 300A- 2 GHz), and an oscilloscope (Agilent DSOX3034A- 350 MHz).
Fig. 1. (a) Experimental setup of the proposed mode-locked laser. WDM, wavelength division multiplexer; TDF, Thulium-doped fiber; FC, fiber coupler; Pol-Iso, Polarizer-Isolator; PC, polarization controller; PD, photodiode; OSA, optical spectrum analyzer. (b) Schematic of the ChG tapered fiber.
The ChG tapered fiber is fabricated in multiple steps [29]. In a first step, a hybrid preform is drawn by collapsing a cylinder of bulk As2S3 fiber and a polycarbonate tube together inside a heated funnel. The As2S3 fiber has an initial diameter of 170 µm. In a second step, the preform is stretched into a hybrid fiber of As2S3 core diameter of 14.5 µm, polycarbonate cladding of 750 µm and numerical aperture of 1.84. This design provides modal compatibility with SMF- 28 fiber, therefore minimizing insertion and extraction coupling losses. Finally, the tapered fiber is fabricated from the hybrid fiber using the flame-brush approach and real-time in situ monitoring technique [38,39]. The polycarbonate cladding provides mechanical robustness to the tapered fiber, as well as a wavelength compatibility up to 2.1 µm [29]. A schematic of the tapered fiber is depicted in Fig. 1(b). The device is subdivided into a 10 cm long microwire section where nonlinear process occurs, two 2.5 cm long fiber sections for efficient coupling to silica fiber, and two 3 cm long transition sections that ensure an adiabatic modal conversion in between fiber and microwire sections. The group velocity dispersion (GVD) of the hybrid fiber is given by β2,fiber = 0.33 ps2/m and average <β2,tran>=0.31 ps2/m for the transition sections. The GVD of the microwire section can be engineered into zero, anomalous, or normal dispersion by choosing an appropriate core diameter. In this experiment, the microwire section is designed with a diameter of 2.0 µm, leading to an anomalous dispersion of β2,wire=-0.07 ps2/m at a wavelength of 1.95 µm (Fig. 2(a)). Further reduction in the core diameter reduces the confinement factor of the fundamental mode and results in an increased attenuation due to cladding absorption. To calculate the total chromatic dispersion budget of the cavity, a cumulative length of 9.23 m of SMF-28 is added along with 20 cm long TDF. The GVD of the SMF-28 and the TDF are β2,SMF=- 0.07 ps2/m and β2,TDF=- 0.09 ps2/m, respectively. Therefore, the laser operates with net anomalous dispersion of 0.63 ps2.
Fig. 2. (a) Dispersion and waveguide nonlinearity parameter of As2S3-polycarbonate microwire. (b) Fixed analyzer setup for birefringence measurement; SC, supercontinuum source; POL, polarizer; PC, polarization controller; OSA, optical spectrum analyzer. (c) Wavelength dependent transmission spectrum.
The waveguide nonlinearity parameter of the microwire is γ=3.4 W-1m-1 at a wavelength of 1.95 µm (Fig. 2(a)), which is 9.68 × 103 times higher than that of silica fiber. The input and output facet of the tapered fiber are polished and coupled to SMF-28 using UV epoxy. The total insertion loss of the ChG tapered fiber with two SMF-28 pigtails is 3.4 dB at a wavelength of 1.95 µm. From this loss, 0.5 dB per interface is due to Fresnel reflection and ∼ 0.1 dB per interface is due to mode-mismatch in between ChG fiber and SMF-28, and ∼ 0.4 dB of propagation loss in the tapered fiber.
The tapered fiber possesses linear birefringence due to residual stress applied by the polycarbonate cladding to the As2S3 glass during the fabrication process. The magnitude of this birefringence is controllable over some extent by an adjustment of the fiber drawing temperature and measured using the fixed analyzer method [40]. Figure 2(b) and (c) show the measurement setup and the wavelength dependent transmission through the fixed analyzer structure. Ripples observed in the transmission spectrum results from multimode interference resulting from the large refractive index contrast between the As2S3 core and polycarbonate cladding of the microwire. The main interference peaks are separated in wavelength by 200 nm, resulting in a modal birefringence B=λ2/LΔλ =1.39 × 10−4. From this birefringence, elliptically polarized light from polarization controller (PC2) in Fig. 1(a) splits into two polarization components of unequal intensities along the slow and the fast axis of the microwire. Both components undergo different amount of nonlinear phase shift due to Kerr effect during their propagation inside the microwire section. As a result, there is a power-dependent rotation of the polarization state at the microwire output. Light passes through PC1 and reaches the polarizer-isolator (POL), which only allows a linear polarization to pass though. Therefore, the combination of PC2-fiber taper-PC1-POL acts as a fast saturable absorber for NPR mode-locking.
As the pump power is increased from zero to 120 mW, the cavity starts lasing with continuous wave emission. With the increase in pump power to 170 mW, the cavity switches to a QML regime. QML pulses are produced by adjusting the intracavity pulse energy within the dynamic instability limit, which could be defined as stability criterion, ${({E_{L,sat}}{E_{A,sa}}\Delta R)^{1/2}}$, where ${E_{L,sat}}$ and ${E_{A,sat}}$ are the effective saturation energy of the gain medium and the artificial saturable absorber, respectively and $\Delta R$ is the modulation depth [41,42]. In this regime, mode locked pulses are modulated by long periodic Q-switched envelope [43,44]. This results in an enhanced peak power of the central pulses in the mode-locked train with respect to pulses on the periphery [45]. Figure 3 (a)-(c) show the power profile versus time in the QML regime. It is seen that that the Q-switched envelope repeats periodically every 9.45 µs, leading to a repetition rate of 105.8 kHz (Fig. 3(a)). Figure 3(b) shows a single Q-switched envelope with a FWHM of 4.12 µs. A close-up view of the ML pulses under the Q-switched envelope is shown in Fig. 3 (c). The repetition rate of the ML pulses is 20.9 MHz, corresponding to the cavity round trip time of 47.9 ns, which is consistent with the total optical path length of 9.43 m (46.12 ns) of silica fiber and 21 cm (1.78 ns) of ChG fiber.
Fig. 3. (a) Real-time oscilloscope trace of QML pulses in 50 µs timescale. (b) Envelope of the QML pulses. (c) Mode-locked pulse train under the Q-switched envelope. (d) Measured optical spectrum of the QML pulses at 170 mW pump power. (b) Two lasing wavelengths generated due to combined effect of QML and OPO at 181 mW pump power. (c) Three wavelengths emission with identical pump power, however with different polarization state.
The optical spectrum corresponding to the QML signal of Fig. 3(c) is shown in Fig. 3(d). The laser wavelength is centered at 1.919 µm with an optical signal to noise ratio of 57.6 dB, a level that is beneficial for sensitive spectroscopic applications. The anomalous GVD of the microwire also allows satisfying the phase matching condition for parametric side band generation [46]. As pump power increase, the burst of high power QML pulses serve as intra-cavity pump and generates parametric gain. For a pump power of 181 mW, the cavity shows lasing at a wavelength of 1.911 µm due to OPO (Fig. 3 (e)). A wavelength converted signal due to stimulated four-wave mixing (FWM) is also observed at 1.930 µm. Each of these central lasing wavelengths interact to generate cascaded FWM [35] signals at 1.903 µm and 1.895 µm. The emission lines have equidistant spectral separation of 0.7 THz, which is clear indication of cascaded OPO operation. Since parametric gain is polarization dependent, the PCs can be adjusted to properly align the emission line at 1.911 µm axis and generate a third emission line at 1.895 µm wavelength as shown in Fig. 3(f). The emission lines are stable within a power difference of 2.5 dB among the lasing wavelengths. Figure 3(f) also shows that the total cavity loss is less on the shorter wavelength side due to the absorption loss pattern of the polycarbonate cladding [29]. For this reason, the cavity favors OPO mainly on the shorter wavelengths side of the QML pump centered at 1.919 µm wavelength. This result is the first demonstration of multi-wavelength laser operation due to the combined effect of QML and cascaded OPO occurring in an NPR cavity. Take note that in the current cavity, although the PC1-fiber taper-PC2-POL assembly also functions as a Lyot filter as in [13,37,47], it plays no role in the manifestation of multiple wavelengths since birefringence is so low that it would lead to a free spectral range of ∼200 nm (Fig. 1(c)).
Figure 4(a) shows that for two different pump powers of 195 mW and 205 mW, a frequency detuning of 1.3 THz and 2.0 THz are observed between emission lines, respectively. The adjustment of pump power results in the change of the phase matching condition, hence the OPO emission wavelengths [48], as shown in Fig. 4(b). For a fixed pump power, the proper adjustment of the PCs allows the tuning of the wavelength dependent transmittivity function [49], therefore allowing the tuning of emission line central wavelength. Figure 4(c) shows that for a pump power of 205 mW, the QML emission wavelength is tuned from 1.915 µm to 1.907 µm. As a result, the OPO center wavelength shifts from 1.891 µm to 1.883 µm.
Fig. 4. (a) Two wavelength emission measured with different polarization state and at pump powers of 195 mW and 205 mW. (b) Frequency detuning as a function of peak power in the As2S3 microwire (c) Tunable central wavelength measured with different polarization state at pump power of 205 mW.
CWML is obtained from increasing the pump power above the threshold of 230 mW and proper adjustment of the PCs. In CWML, pulses preserve constant properties i.e., peak power, duration, and energy, from one pulse to another. Figure 5(a) shows an oscilloscope trace of the train of solitons while the inset shows the same signal over an extended time window. The pulses are separated by 47.9 ns in the time domain, corresponding to the fundamental cavity repetition rate of 20.9 MHz. Wavelength tunability is obtained mainly by adjusting the polarization dependent loss in the cavity via adjustment of the PCs [13]. Since the cavity loss is also wavelength dependent, the pump power needs to be controlled as well. Figure 5(c) shows that the center wavelength of the soliton can be switched between 1.877 µm to 1.945 µm by adjusting both PCs and pump power between 230 mW to 285 mW. The laser operates with a total anomalous cavity dispersion. Kelly sidebands observed in the spectrum support the soliton behavior of these emission spectra. The soliton centered at a wavelength of 1.877 µm has an average power of 0.41 mW, a 3 dB spectral width of 4.67 nm and measured pulse duration of 2.4 ps. Figure 5(b) shows the output power as a function of input pump power, indicating a slope efficiency of 1.32%. The inset shows the corresponding spectral evolution of the soliton as the pump power increases. The generated pulses are presumably chirped due to residual dispersion in the laser cavity. The laser stability is analyzed by sending the soliton pulses to a radio-frequency (RF) spectrum analyzer. Figure 5(b) shows the RF spectra measured with a resolution bandwidth of 100 Hz. The signal to noise ratio of 61.8 dB is obtained at the fundamental frequency. The inset shows of the same electrical spectrum within a 2 GHz span, measured with a resolution bandwidth of 5 MHz. The graph shows a smooth variation in the total envelope. These results certify a stable mode-locking operation [8,50]. The laser stability is further analyzed by measuring the power fluctuation. Figure 5 (e) shows the measured average power of the laser pulse centered at 1.945 µm wavelength for a duration of one hour at an acquisition rate of 33 mHz. The calculated coefficient of variation (standard deviation/mean) of the power is 7.8%, which indicates a reasonable stability of the system. The slight optical power drift could occur from environmental temperature change.
Fig. 5. (a) Oscilloscope trace of CWML pulse train. Inset: Oscilloscope trace in 6 µs timescale. (b) Measured output power as a function of pump power. Inset: Soliton spectrum evolution with increasing pump power. (c) Tunable optical spectrum of the CWML pulses with increasing pump power. (d) RF spectrum in 0.2 MHz range. Inset: RF spectrum in a wide range of 2 GHz. (e) Power stability measurement. Inset: Soliton spectrum at t = 0 and t = 60 minutes.
To understand the impact of ChG tapered fiber in the reduction the mode-locking threshold, the tapered fiber is replaced by a 3 m long silica fiber and increased pump power from C-band amplifiers. Mode-locking was achieved at a significantly high pump power of 1.35 W. Figure 6 shows the soliton spectra centered at 1.910 µm while the inset shows the oscilloscope trace of the soliton train. The replacement of the tapered fiber with a silica fiber increases the pulse separation to 60.1 ns, resulting in a decrease of the cavity repetition rate to 16.6 MHz. This clearly indicates that the use of a ChG tapered fiber simultaneously shortens the nonlinear medium length by a factor of 30 and reduces the mode-locking threshold by a factor of 5.6, compared to an all-silica cavity.
Fig. 6. Optical spectrum of the CWML pulses generated in all-silica cavity. Inset: oscilloscope trace of the pulse train.
3. Conclusion
In conclusion, we have demonstrated the operation of a TDFL mode-locked from NPR in a ChG tapered fiber. The high nonlinearity of the tapered fiber results in a reduced threshold pump power of 230 mW and a shortened cavity length of 9.45 m, compared to the all-silica based mode-locked laser. The laser generates multiwavelength emission with variable number of lasing lines, tunable central wavelength from 1.883 µm to 1.915 µm and tunable frequency separation from 0.7 THz to 2.0 THz. The multiwavelength operation has a threshold pump power of 179 mW and occurs from the combined effect of QLM and intra cavity OPO. The CWML has a threshold pump power of 230 mW and generates stable tunable solitons from 1.887 µm to 1.911 µm.
Funding
Natural Sciences and Engineering Research Council of Canada.
Acknowledgment
We are thankful to Coractive High-Tech for providing the chalcogenide fiber used in the experiments.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. C. Rudy, M. J. F. Digonnet, and R. L. Byer, “Advances in 2-µm Tm-doped mode-locked fiber lasers,” Opt. Fiber Technol. 20(6), 642–649 (2014). [CrossRef]
2. N. J. Scott, C. M. Cilip, and N. M. Fried, “Thulium Fiber Laser Ablation of Urinary Stones Through Small-Core Optical Fibers,” IEEE J. Select. Topics Quantum Electron. 15(2), 435–440 (2009). [CrossRef]
3. M. I. Kayes, N. Abdukerim, A. Rekik, and M. Rochette, “Free-running mode-locked laser based dual-comb spectroscopy,” Opt. Lett. 43(23), 5809–5812 (2018). [CrossRef]
4. J. Liu, J. Xu, K. Liu, F. Tan, and P. Wang, “High average power picosecond pulse and supercontinuum generation from a thulium-doped, all-fiber amplifier,” Opt. Lett. 38(20), 4150–4153 (2013). [CrossRef]
5. N. P. Barnes, B. M. Walsh, D. J. Reichle, and R. J. DeYoung, “Tm:fiber lasers for remote sensing,” Opt. Mater. 31(7), 1061–1064 (2009). [CrossRef]
6. Y. Meng, Y. Li, Y. Xu, and F. Wang, “Carbon Nanotube Mode-Locked Thulium Fiber Laser With 200 nm Tuning Range,” Sci. Rep. 7(1), 45109 (2017). [CrossRef]
7. C. W. Rudy, K. E. Urbanek, M. F. Digonnet, and R. L. Byer, “Amplified 2-µm Thulium-Doped All-Fiber Mode-Locked Figure-Eight Laser,” J. Lightwave Technol. 31(11), 1809–1812 (2013). [CrossRef]
8. C. Gao, Z. Wang, H. Luo, and L. Zhan, “High Energy All-Fiber Tm-Doped Femtosecond Soliton Laser Mode-Locked by Nonlinear Polarization Rotation,” J. Lightwave Technol. 35(14), 2988–2993 (2017). [CrossRef]
9. T. Wang, W. Ma, Q. Jia, Q. Su, P. Liu, and P. Zhang, “Passively Mode-Locked Fiber Lasers Based on Nonlinearity at 2-µm Band,” IEEE J. Select. Topics Quantum Electron. 24(3), 1–11 (2018). [CrossRef]
10. J. Li, Z. Yan, Z. Sun, H. Luo, Y. He, Z. Li, and L. Zhang, “Thulium-doped all-fiber mode-locked laser based on NPR and 45°-tilted fiber grating,” Opt. Express 22(25), 31020–31028 (2014). [CrossRef]
11. C. Li, X. Wei, C. Kong, S. Tan, N. Chen, J. Kang, and K. K. Y. Wong, “Fiber chirped pulse amplification of a short wavelength mode-locked thulium-doped fiber laser,” APL Photonics 2(12), 121302 (2017). [CrossRef]
12. J. Li, Y. Wang, H. Luo, Y. Liu, Z. Yan, Z. Sun, and L. Zhang, “Kelly sideband suppression and wavelength tuning of a conventional soliton in a Tm-doped hybrid mode-locked fiber laser with an all-fiber Lyot filter,” Photonics Res. 7(2), 103–109 (2019). [CrossRef]
13. W. Ma, T. Wang, Y. Zhang, P. Liu, Y. Su, Q. Jia, M. Bi, P. Zhang, and H. Jiang, “Widely tunable 2 µm continuous-wave and mode-locked fiber laser,” Appl. Opt. 56(12), 3342–3346 (2017). [CrossRef]
14. X. Yang and C. X. Yang, “Q-switched mode-locking in an erbium-doped femtosecond fiber laser based on nonlinear polarization rotation,” Laser Phys. 19(11), 2106–2109 (2009). [CrossRef]
15. Y. Gan, W. H. Xiang, and G. Z. Zhang, “Studies on CW and Q-Switched Mode-Locked in Passive Mode-Locked Ytterbium-Doped Fibre Laser,” Laser Phys. 19(3), 445–449 (2009). [CrossRef]
16. X. Wang, Y. Zhu, P. Zhou, X. Wang, H. Xiao, and L. Si, “Tunable, multiwavelength Tm-doped fiber laser based on polarization rotation and four-wave-mixing effect,” Opt. Express 21(22), 25977–25984 (2013). [CrossRef]
17. Y. Wang, J. Li, B. Zhai, Y. Hu, K. Mo, R. Lu, and Y. Liu, “Tunable and switchable dual-wavelength mode-locked Tm3+-doped fiber laser based on a fiber taper,” Opt. Express 24(14), 15299–15306 (2016). [CrossRef]
18. U. Keller, “Recent developments in compact ultrafast lasers,” Nature 424(6950), 831–838 (2003). [CrossRef]
19. L. Talaverano, S. Abad, S. Jarabo, and M. Lopez-Amo, “Multiwavelength fiber laser sources with Bragg-grating sensor multiplexing capability,” J. Lightwave Technol. 19(4), 553–558 (2001). [CrossRef]
20. J. Marshall, G. Stewart, and G. Whitenett, “Design of a tunable L-band multi-wavelength laser system for application to gas spectroscopy,” Meas. Sci. Technol. 17(5), 1023–1031 (2006). [CrossRef]
21. S. Liu, F. Yan, Y. Li, L. Zhang, Z. Bai, H. Zhou, and Y. Hou, “Noise-like pulse generation from a thulium-doped fiber laser using nonlinear polarization rotation with different net anomalous dispersion,” Photonics Res. 4(6), 318–321 (2016). [CrossRef]
22. Q. Wang, T. Chen, B. Zhang, A. P. Heberle, and K. P. Chen, “All-fiber passively mode-locked thulium-doped fiber ring oscillator operated at solitary and noiselike modes,” Opt. Lett. 36(19), 3750–3752 (2011). [CrossRef]
23. Z. Yan, B. Sun, X. Li, J. Luo, P. P. Shum, X. Yu, Y. Zhang, and Q. J. Wang, “Widely tunable Tm-doped mode-locked all-fiber laser,” Sci. Rep. 6(1), 27245 (2016). [CrossRef]
24. A. Zakery and S. R. Elliott, “Optical properties and applications of chalcogenide glasses: a review,” J. Non-Cryst. Solids 330(1-3), 1–12 (2003). [CrossRef]
25. E. C. Mägi, L. B. Fu, H. C. Nguyen, M. R. E. Lamont, D. I. Yeom, and B. J. Eggleton, “Enhanced Kerr nonlinearity in sub-wavelength diameter As2Se3 chalcogenide fiber tapers,” Opt. Express 15(16), 10324–10329 (2007). [CrossRef]
26. C. Baker and M. Rochette, “High nonlinearity and single-mode transmission in tapered multi-mode As2Se3-PMMA fibers,” IEEE Photonics J. 4(3), 960–969 (2012). [CrossRef]
27. C. Baker and M. Rochette, “Highly nonlinear hybrid AsSe-PMMA microtapers,” Opt. Express 18(12), 12391–12398 (2010). [CrossRef]
28. A. Al-Kadry, L. Li, M. E. Amraoui, T. North, Y. Messaddeq, and M. Rochette, “Broadband supercontinuum generation in all-normal dispersion chalcogenide microwires,” Opt. Lett. 40(20), 4687–4690 (2015). [CrossRef]
29. L. Li, A. Al-Kadry, N. Abdukerim, and M. Rochette, “Design, fabrication and characterization of PC, COP and PMMA-cladded As2Se3 microwires,” Opt. Mater. Express 6(3), 912–921 (2016). [CrossRef]
30. L. Li, N. Abdukerim, and M. Rochette, “Chalcogenide optical microwires cladded with fluorine-based CYTOP,” Opt. Express 24(17), 18931–18937 (2016). [CrossRef]
31. S. Kobtsev, S. Smirnob, S. Kukarin, and S. Turitsyn, “Mode-locked fiber lasers with significant variability of generatiown regimes” Opt,” Opt. Fiber Technol. 20(6), 615–620 (2014). [CrossRef]
32. Z. Shao, X. Qiao, Q. Rong, and D. Su, “Observation of the evolution of mode-locked solitons in different dispersion regimes of fiber lasers,” Opt. Commun. 345, 105–110 (2015). [CrossRef]
33. I. Alamgir, F. St-Hilaire, and M. Rochette, “All-fiber nonlinear optical wavelength conversion system from the C-band to the mid-infrared,” Opt. Lett. 45(4), 857–860 (2020). [CrossRef]
34. I. Alamgir, M. H. M. Shamim, W. Correr, Y. Messaddeq, and M. Rochette, “Mid-infrared soliton self-frequency shift in chalcogenide glass,” Opt. Lett. 46(21), 5513–5516 (2021). [CrossRef]
35. I. Alamgir, M. Rezaei, and M. Rochette, “Optical Parametric Oscillator based on All-Chalcogenide Fiber Components,” in OSA Advanced Photonics Congress (AP), paper NpM3E.4 (2020).
36. D. D. Hudson, S. Antipov, L. Li, I. Alamgir, T. Hu, M. El Amraoui, Y. Messaddeq, M. Rochette, S. D. Jackson, and A. Fuerbach, “Toward all-fiber supercontinuum spanning the mid-infrared,” Optica 4(10), 1163–1166 (2017). [CrossRef]
37. A. Al-Kadry, M. E. Amraoui, Y. Messaddeq, and M. Rochette, “Mode-locked fiber laser based on chalcogenide microwires,” Opt. Lett. 40(18), 4309–4312 (2015). [CrossRef]
38. I. Alamgir, N. Abdukerim, and M. Rochette, “In situ fabrication of far-detuned optical fiber wavelength converters,” Opt. Lett. 44(18), 4467–4470 (2019). [CrossRef]
39. C. Baker and M. Rochette, “A generalized heat-brush approach for precise control of the waist profile in fiber tapers,” Opt. Mater. Express 1(6), 1065–1076 (2011). [CrossRef]
40. D. Derickson, Fiber Optic Test and Measurement (Prentice Hall, 1998).
41. C. Honninger, R. Paschotta, F. Morier-Genoud, M. Moser, and U. Keller, “Q-switching stability limits of continuous-wave passive mode locking,” J. Opt. Soc. Am. B 16(1), 46–56 (1999). [CrossRef]
42. M. Jiang, G. Sucha, M. E. Fermann, J. Jimenez, D. Harter, M. Dagenais, S. Fox, and Y. Hu, “Nonlinearly limited saturable-absorber mode locking of an erbium fiber laser,” Opt. Lett. 24(15), 1074–1076 (1999). [CrossRef]
43. C. Cuadrado-Laborde, A. Díez, J. L. Cruz, and M. V. Andrés, “Doubly active Q switching and mode locking of an all-fiber laser,” Opt. Lett. 34(18), 2709–2711 (2009). [CrossRef]
44. L. C. Kong, G. Q. Xie, P. Yuan, L. J. Qian, S. X. Wang, H. H. Yu, and H. J. Zhang, “Passive Q-switching and Q-switched mode-locking operations of 2 µm Tm:CLNGG laser with MoS2 saturable absorber mirror,” Photon. Research 3(2), A47–A50 (2015). [CrossRef]
45. J. Lin, H. Chen, H. Hsu, M. Wei, K. Lin, and W. Hsieh, “Stable Q-switched mode-locked Nd3+:LuVO4 laser by Cr4+:YAG crystal,” Opt. Express 16(21), 16538–16545 (2008). [CrossRef]
46. N. Abdukerim, L. Li, and M. Rochette, “Chalcogenide-based optical parametric oscillator at 2 µm,” Opt. Lett. 41(18), 4364–4367 (2016). [CrossRef]
47. S. Liu, F. Yan, F. Ting, L. Zhang, Z. Bai, W. Han, and H. Zhou, “Multi-wavelength thulium doped fiber laser using a fiber-based Lyot filter,” IEEE Photon. Technol. Lett. 28(8), 864–867 (2016). [CrossRef]
48. G. P. Agrawal, Nonlinear Fiber Optics, 5th ed. (Academic, 2013).
49. X. Feng, Hwa-y. Tam, and P. K. A. Wai, “Stable and uniform multiwavelength erbium-doped fiber laser using nonlinear polarization rotation,” Opt. Express 14(18), 8205–8210 (2006). [CrossRef]
50. Z. Wang, K. Qian, X. Fang, C. Gao, H. Luo, and L. Zhan, “Sub-90 fs dissipative-soliton Erbium-doped fiber lasers operating at 1.6 µm band,” Opt. Express 24(10), 10841–10846 (2016). [CrossRef]
