Tunable Three-Wavelength Fiber Laser and Transient Switching between Three-Wavelength Soliton and Q-Switched Mode-Locked States

Zhi-Zeng Si(司志增), Chao-Qing Dai(戴朝卿)$^{\hyperlink{s}{*}}$, and Wei Liu(刘威)$^{\hyperlink{s}{*}}$

doi:10.1088/0256-307X/41/2/020502

⇦Chinese Physics Letters, 2024, Vol. 41, No. 2, Article code 020502⇨ Tunable Three-Wavelength Fiber Laser and Transient Switching between Three-Wavelength Soliton and Q-Switched Mode-Locked States Zhi-Zeng Si (司志增), Chao-Qing Dai (戴朝卿)*, and Wei Liu (刘威)* Affiliations College of Optical, Mechanical and Electrical Engineering, Zhejiang A&F University, Lin'an 311300, China Received 27 November 2023; accepted manuscript online 17 January 2024; published online 4 March 2024 ^*Corresponding authors. Email: dcq424@126.com; liuwei@zafu.edu.cn Citation Text: Si Z Z, Dai C Q, and Liu W 2024 Chin. Phys. Lett. 41 020502 Abstract We report a passive mode-locked fiber laser that can realize single-wavelength tuning and multi-wavelength spacing tuning simultaneously. The tuning range is from 1528 nm–1560 nm, and up to three bands of soliton states can be output at the same time. These results are confirmed by a nonlinear Schrödinger equation model based on the split-step Fourier method. In addition, we reveal a way to transform the multi-wavelength soliton state into the Q-switched mode-locked state, which is period doubling. These results will promote the development of optical communication, optical sensing and multi-signal pulse emission.

DOI:10.1088/0256-307X/41/2/020502 © 2024 Chinese Physics Society Article Text Ultrafast fiber lasers[1-3] have potential applications in optical communication,[4] optical sensing,[5] and nonlinear science.[6] Wavelength-tunable[7-9] fiber lasers and multi-wavelength[10-12] fiber lasers, as the main types of ultrafast fiber lasers, are widely used due to their unique spectral characteristics. Recently, an ultra-wideband (1700 nm–1900 nm) tunable thulium-doped fiber laser[13] achieved dissipative soliton output in the 200 nm range. At the same time, it has also been proved that new layered high-entropy van der Waals material[14] is able to realize traditional soliton output in the 1531 nm–1560 nm band. Furthermore, 1.3/1.4 µm dual-wave band dissipative soliton resonance is realized in passively mode-locked bismuth-doped phosphosilicate fiber laser.[15] In addition, the output of soliton mode with two to five wavelengths can be completed by changing the group delay in the fiber cavity with a programmable pulse shaper.[16] These studies provide an effective scheme for wavelength tuning and multi-wavelength laser output. However, in the wavelength-tuned fiber laser mentioned above, its function is only to tune the spectral range of single wavelength state or to output multi-band soliton state. However, this needs to be realized by complex cavity parameter design,[17] which has severe limitations. With the development of mode-locked fiber laser (MLFL), one of the main difficulties is still to study an efficient fiber laser that integrates multiple spectral tuning functions. In this Letter, an MLFL with a tunable central wavelength is designed, which can realize the simultaneous output of multi-wavelength soliton states. The simulation results of the nonlinear Schrödinger equation (NLSE)[18] verifies the feasibility of this scheme. Finally, the transient switching process between three-wavelength soliton states and the Q-switched mode-locked (QML)[19] state is revealed. These results provide important insight into the design of high-performance fiber lasers, and greatly assists our exploration of multi-wavelength MLFL. Experimental Setup. The experimental setup is shown in Fig. 1. The total cavity length is 65.8 m and the repetition rate is about 3.125 MHz, with net dispersion of $-0.97$ ps$^{2}$, in which the erbium-doped fiber (EDF) dispersion of 9 m is 0.028 ps$^{2}$/m and the single-mode fiber (SMF) dispersion of 56.8 m is 0.0216 ps$^{2}$/m.

Fig. 1. Schematic of the multi-wavelength fiber laser in this experiment.

This indicates that the fiber laser works in the negative dispersion state. A 976 nm pump enters the ring cavity through a 980/1550 nm wavelength division multiplexer (WDM). For a saturable absorber (SA),[20-22] we use CNT-SA with stable performance and low cost. A polarization-dependent isolator (PD-ISO) makes the pulse more sensitive to changes in polarization state and prevents the pulse from returning. An output coupler (OC) with a ratio of $7\!:\!3$ is used to observe the ML state under different energy distributions in the cavity. A polarization controller (PC) is inserted into the cavity to optimize the polarization state and adjust the output characteristics. Experimental Results. To realize the simultaneous output of multiple wavelengths in the same gain medium, it is necessary to add an effective wavelength selection mechanism and to weaken the wavelength competition mechanism in the resonator. Based on the above conditions, a $\sim$ 9 m EDF with wide working band and high gain makes it possible to produce ultrafast pulse output in the band of 1528–1560 nm in Fig. 2(a). At the same time, the PD-ISO excites one or several band pulses and suppresses the others, so that it can achieve output of single-wavelength and multi-wavelength soliton states. Figure 2(b) describes the spectrum tuning phenomenon with CNT-SA. In Fig. 2(c), the experimental result is consistent with the simulation through the split-step Fourier method (SSFM) based on the NLSE: \begin{align*} \frac{\partial\psi}{\partial z}=\frac{g}{2}\psi+\Big(\frac{g}{2\varOmega_{\rm g}^{2}}-i\frac{\beta_{2}}{2}\Big)\frac{\partial^{2}\psi}{\partial t^{2}}+i\gamma|\psi|^{2}\psi, \end{align*} where $\psi$, $\beta_{2}$, $\gamma$, and $\varOmega_{\rm g}$ are the pulse envelope, second-order dispersion, Kerr nonlinearity coefficient, and bandwidth of the gain, respectively. The gain coefficient $g$ is given as follows: $g=g_{0}\exp(-\frac{E}{E_{\rm sat}})$, where $g_{0}$, $E$, and $E_{\rm sat}$ are the small-signal gain, pulse energy, and saturation energy, respectively. For EDF, $L_{\rm EDF}=9$ m, $\varOmega_{\rm g}=30$ nm, $\beta_{2}=0.028$ ps$^{2}$/m, $\gamma =2\times 10^{-3}$ W$^{-1}$, $g_{0}=3$ m$^{-1}$, and $E_{\rm sat}$ is 10 pJ for Figs. 2 and 3 and 36 pJ for Fig. 4. For SMF, $L_{\rm SMF}=56.8$ m, $\beta_{2}=-0.0216$ ps$^{2}$/m, and $\gamma =2\times 10^{-3}$ W$^{-1}$. The simulation parameters are consistent with the experimental values.

Fig. 2. Spectral tuning of multi-wavelength solitons. (a) Output spectrum from 1528 nm–1560 nm without CNT. [(b), (c)] Central wavelength tuning in experiments and simulations, respectively.

ML is available in the cavity. Later, the output of multi-wavelength soliton states with different wavelength combinations is realized. The central wavelength combinations of the double-wavelength soliton states are 1546/1560 nm, 1529/1538 nm, and 1542/1557 nm, respectively, while the central wavelength combinations of the three-wavelength soliton states are 1532/1541/1555 nm. At the same time, based on the multi-peak gain spectrum model,[23] when the system parameters are consistent, the double-wavelength and three-wavelength soliton states of each wavelength combination are simulated and realized experimentally. This confirms the influence of gain competition in the cavity on the output of multi-wavelength soliton states. The stability of fiber laser is shown in Fig. S1 of the Supplementary Material, which proves the long-term stability of laser output.

Fig. 3. Double-wavelength soliton spectrum by experiment and simulation.

Fig. 4. Three-wavelength soliton spectrum by experiment and simulation.

Dynamic Switching between ML and QML. Figure 5 describes the switching process between QML and ML at the same pump power. Figure 5(a) shows that the three-wavelength soliton state still contains solitons with different group velocity[24] before it is converted into QML. Due to the cross-phase modulation effect and the sudden change of polarization state in the cavity, the interaction occurs when the solitons collide with each other. The transition from ML to QML experiences the continuous amplitude oscillation of pulse, and the period is doubled until it reaches a steady state. Further adjusting the polarization state, we capture the coexistence of ML and QML, as shown in Fig. 5(b). Because the nonlinearity and dispersion of the cavity reach a delicate balance, the ML pulse with the weak energy coexists with the QML pulse with the strong energy and its modulation period of about 310 µs, which corresponds to the coexistence of the double-wavelength Q-switched spectrum at 1530/1540 nm and the ML spectrum with obvious Kelly sideband at 1560 nm in Fig. 5(d). Figures 5(c) and 5(e) show the three-wavelength soliton state with relatively uniform spectral intensity and three-wavelength Q-switched state with a smooth spectral profile before and after the state in Fig. 5(d), respectively.

Fig. 5. Switching between QML and ML, and loss characteristics of three-wavelength solitons. (a) Three-wavelength soliton state and QML switching process after DFT processing, (b) coexistence state of QML and ML after DFT processing, (c) three-wavelength soliton state, (d) coexistence state of QML and ML, (e) spectrum of three-wavelength QML state.

In summary, we design an MLFL that can realize single-wavelength tuning and multi-wavelength spacing tuning at the same time. The tuning range is 1528–1560 nm. The realization of three-wavelength soliton states proves that there is strong gain competition around 1530 nm, 1540 nm, and 1550 nm, which is confirmed by the NLSE model based on SSFM. In addition, the dynamic switching process from multi-wavelength soliton state to QML is revealed, which is period doubling. The evolution mechanism of coexistence of QML and mode-locking behavior is found. These results promote the development of laser source field and deepen the understanding of the QML and multi-wavelength conversion mechanism in nonlinear science. Acknowledgments. This work was supported by the Zhejiang Provincial Natural Science Foundation of China (Grant No. LR20A050001), the National Natural Science Foundation of China (Grant Nos. 12261131495 and 12275240), and the Scientific Research and Developed Fund of Zhejiang A&F University (Grant No. 2021FR0009). References Femtosecond Fiber Laser Based on BiSbTeSe₂ Quaternary Material Saturable AbsorberPreparation of Bi₂ Te₃ Based on Saturable Absorption System and Its Application in Fiber LasersDeep neural network for modeling soliton dynamics in the mode-locked laserPhotonic Lanterns, 3-D Waveguides, Multiplane Light Conversion, and Other Components That Enable Space-Division MultiplexingRotation Active Sensors Based on Ultrafast Fibre LasersChirped Bright and Kink Solitons in Nonlinear Optical Fibers with Weak Nonlocality and Cubic-Quantic-Septic Nonlinearity60 nm Span Wavelength-Tunable Vortex Fiber Laser with Intracavity Plasmon MetasurfacesWidely wavelength tunable Dy³⁺ /Er³⁺ co-doped ZBLAN fiber lasersBroadband, tunable wavelength conversion using tapered silicon fibers extending up to 2.4 μ mHarmonic dual-wavelength and multi-soliton pattern fiber laser based on GO-Sb2Se3 saturable absorbersMulti-wavelength random fiber laser with a spectral-flexible characteristicSynchronous multi-wavelength mode-locked laser at 2-μm based on Mamyshev cavityTunable dissipative soliton Tm-doped fiber laser operating from 1700 nm to 1900 nmTunable Dual-Wavelength Fiber Laser in a Novel High Entropy van der Waals Material1.3/1.4 µm dual-wave band dissipative soliton resonance in a passively mode-locked Bi-doped phosphosilicate fiber laserSynchronized multi-wavelength soliton fiber laser via intracavity group delay modulationTunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMFOrigin of spectral rogue waves in incoherent optical wave packetsNanosecond-Pulsed Passively Q-Switched Fiber Laser by Using Photothermal Dynamics in a Dielectric MicrocavityTernary Transition Metal Dichalcogenides for High Power Vector Dissipative Soliton Ultrafast Fiber LaserGaSb Film is a Saturable Absorber for Dissipative Soliton Generation in a Fiber LaserChromium oxide film for Q-switched and mode-locked pulse generationSwitchable property of dissipative soliton and dispersion-management soliton in fiber laser“Periodic” soliton explosions in a dual-wavelength mode-locked Yb-doped fiber laser

[1]	Xiao Y J, Xing X W, Cui W W, Chen Y Q, and Liu W J 2023 Chin. Phys. Lett. 40 054201
[2]	Wang H Y, Xiao Y J, Liu Q, Yang H J, and Liu W J 2023 Chin. Phys. Lett. 40 114204
[3]	Fang Y, Han H B, Bo W B, Liu W, Wang Y Y, and Dai C Q 2023 Opt. Lett. 48 779
[4]	Fontaine N K, Carpenter J, Gross S, Leon-Saval S, Richardson D J, and Amezcua-Correa R 2022 Proc. IEEE 110 1821
[5]	Kudelin I, Sugavanam S, and Chernysheva M 2021 Sensors 21 3530
[6]	Zhou Q, Zhong Y, Houria T, Sun Y Z, Liu W J, and Anjan B 2022 Chin. Phys. Lett. 39 044202
[7]	Gui L L, Wang C S, Ding F, Chen H, Xiao X S, Zhang X G, and Xu K 2023 ACS Photonics 10 623
[8]	Wang J F, Norwood R A, and Peyghambarian N 2021 Opt. Express 29 38646
[9]	Wu D, Saini T S, Sun S Y, Huang M, Fu Q, Ballato J, and Peacock A C 2023 APL Photonics 8 106105
[10]	Wang B H, Yu L J, Han H B, Tian Z S, and Wang Y Y 2022 Opt. Laser Technol. 146 107590
[11]	Li S C, Xu J M, Liang J R, Ye J, Zhang Y, Leng J Y, and Zhou P 2023 Photonics Res. 11 159
[12]	Gong R, Pei L, and Wei H 2023 Front. Phys. 11 1273027
[13]	Liu X Y, Sahu J K, and Gumenyuk R 2023 Opt. Lett. 48 612
[14]	Cui W W, Xing X W, Chen Y Q, Ye H, and Liu W J 2023 Chin. Phys. Lett. 40 024201
[15]	Wang H, Yang Y, Hong J, Zhou X, Ruan Q, Dong Z, Melkumov M, Lobanov A, and Luo Z 2023 Opt. Lett. 48 299
[16]	Mao D, Wang H, Zhang H, Zeng C, Du Y, Sun Z, and Zhao J 2021 Nat. Commun. 12 6712
[17]	Yu Q X, Liu M Y, Qi Y Y, Luan N N, Bai Z X, Ding J, Wang Y Z, and Lu Z W 2023 IEEE Photonics Technol. Lett. 35 1043
[18]	Du Y Q, He Z W, Zhang H Z, Gao Q, Mao D, and Zhao J L 2022 Phys. Rev. A 106 053509
[19]	Wang W Y, Xiao B W, Zhao P, Ren L H, Shi L, and Zhang X L 2023 ACS Photonics 10 3656
[20]	Li L, Pang L, Wang R, Zhang X, Hui Z, Zhao F, and Liu W 2022 Laser & Photonics Rev. 16 2100255
[21]	Pang L H, Zhao M, Zhao Q Y, Li L, Wang R F, Lv Y, and Liu W J 2022 ACS Appl. Mater. & Interfaces 14 55971
[22]	Li L, Cheng J, Zhao Q, Zhang J, Yang H, Zhang Y, Zhao F, and Liu W 2023 Opt. Express 31 16872
[23]	Zhang Y S, Dai K, and Chen D R 2023 Opt. Laser Technol. 158 108790
[24]	Liu M, Li T J, Xu W C, and Luo Z C 2020 Photonics Res. 8 246