Elsevier

Optics Communications

Volume 479, 15 January 2021, 126441
Optics Communications

Generation of high-order solitons with order continuously adjustable in a fiber laser based on GIMF–SIMF–GIMF saturable absorber

https://doi.org/10.1016/j.optcom.2020.126441Get rights and content

Highlights

  • We fabricated a graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF–SIMF–GIMF) saturable absorber (SA), which has advantages of high damage threshold, easy fabrication and low cost.

  • A fiber soliton laser based on GIMF–SIMF–GIMF SA was designed and proved. Not only fundamental soliton with a duration of 540 fs can be obtained, but 2nd-order to 11th-order solitons can also be achieved through finely controlling the laser operation conditions during experiment.

  • To best of our knowledge, this is the first time to adjust the order of solitons continuously from the first to eleventh in a fiber laser mode-locked by GIMF–SIMF–GIMF SA. One can find that both increasing pump power and adjusting PC can affect the order of high- order solitons. We believe that our work can be served as a guideline to investigate the generation of high-order solitons in passively mode-locked fiber lasers.

Abstract

We report on the generation of high-order solitons with order continuously adjustable in an erbium-doped fiber laser mode-locked by a graded index multimode fiber–step index multimode fiber–graded index multimode fiber (GIMF–SIMF–GIMF) saturable absorber (SA). The SA has advantages of high damage threshold, easy fabrication and low cost. The fundamental soliton to eleventh-order soliton were obtained by adjusting the pump power and PC. It was found that both increasing pump power and adjusting PC can affect the solitons splitting during experiment. The generation of high-order solitons is due to the peak power clamping effect of laser cavity and the pulse shaping effect of GIMF–SIMF–GIMF SA. Last but not least, this is the first time to adjust the order of solitons continuously from the first to eleventh in a fiber laser mode-locked by GIMF–SIMF–GIMF SA.

Introduction

High-order solitons also called bound states of solitons have attracted great attention due to their potential applications in optical communication, high-resolution optics, all-optical data storage, high-modulation information transmission, etc. [1], [2], [3]. Especially, the high-order solitons can be used as data-carrying symbols in the field of high-speed optical communication [4], [5], [6]. The number of solitons in the high-order solitons determines the amount of information that may be carried. Therefore, the study of high-order solitons, which contains more solitons is of great significance for high-speed optical communication. High-order solitons are high-order solitons solution of the nonlinear Schrödinger equation (NLSE), can be obtained in passively mode-locked fiber lasers and formed by the interaction between solitons [7], [8], [9]. When the pump power is increased to a high level, multiple-soliton will be generated in the laser cavity due to the peak power clamping effect and the soliton energy quantization effect [9], then these solitons are bound together through interactions to form high-order solitons [10], [11], [12].

Various passively mode-locked techniques have been utilized to generate bound solitons, such as: nonlinear polarization rotation technology (NPR) [8], [13], [14], figure-eight fiber laser [15] and two-dimensional material SAs mode-locked technology [16], [17], [18], [19], [20], [21]. In 2002, N.H. Seong and Dug Y. Kim used a figure-eight fiber laser to output a fourth-order soliton [15]. In 2013, R. Gomenyuk and O.G. Okhotnikov achieved seven pulses bound state soliton in a fiber laser based on semiconductor saturable absorber mirrors (SESAMs) by adjusting the PC in laser cavity [22]. In 2008, Adil Haboucha et al. reported the bound states of 350 pulses in a fiber laser mode locked by NPR [23]. In 2016, Wang et al. observed a second-order soliton in a 2μm fiber laser mode-locked by nonlinear polarization evolution [13]. In 2017, Li et al. observed second-order soliton and third-order soliton in a fiber laser with a microfiber-based WS2 saturable absorber [10]. In 2109, R. LÜ et al. used a saturable absorber made of MoS2/fluorine mica to generate second-order soliton bound state with a soliton separation of 2.7 ps in a passively mode-locked fiber laser [21]. In recent years, the saturable absorber based on a combination of different optical fibers have become subject to the extensive study of fiber lasers due to their unique optical properties, such as, nonlinear multimode interference (NL-MMI), self-phase modulation, and cross-phase modulation. In 2013, the single mode fiber–graded index multimode fiber–single mode fiber (SMF–GIMF–SMF) structure was demonstrated theoretically it can be used as a SA in mode-locked lasers based on the NL-MMI by E. Nazemosadat and A. Mafi [24]. Recent reports have shown that the SAs based on the NL-MMI can used to generate solitons in fiber lasers. In 2017, Wang et al. designed a hybrid structure of step index multimode fiber–graded index multimode fiber (SIMF–GIMF) as a SA in an erbium-doped fiber laser to output fundamental soliton with duration of 446 fs [25]. In 2018, the same structure was used to generate dissipative soliton in ytterbium-doped fiber lasers [26]. In 2019, the hybrid structure of no-core fiber (NCF) and graded-index multimode fiber (GIMF) was designed as a SA to obtained the tightly bound soliton pairs with separation of 2.07 ps in a fiber laser [27]. Although the high-order solitons have been successfully generated via above techniques or SAs, there are few reports about the generation of high-order solitons with order continuously adjustable. Therefore, it is interesting to generate high-order solitons with order continuously adjustable in passively mode-locked fiber lasers.

In this paper, we fabricated a GIMF–SIMF–GIMF SA with a high damage threshold. In the experiment, the SA was inserted into an erbium-doped fiber laser cavity with a negative net dispersion. Not only fundamental soliton with duration of 540 fs can be obtained, but second-order to eleventh-order soliton can also be achieved by adjusting the pump power and PC. It is worth noting that both increasing pump power and adjusting PC can affect the order of the high-order solitons. We explain that the generation of high-order solitons with order continuously adjustable is due to the pulse shaping effect of GIMF–SIMF–GIMF SA and the pulse peak power clamping effect.

Section snippets

Experimental setup

The GIMF–SIMF–GIMF SA has been proven to be used in mode-locked fiber lasers according to previous report of our research group [28]. Fig. 1(a) shows the schematic diagram of the GIMF–SIMF–GIMF SA, it consists a piece of GIMF (Yangtze Optical Fiber, length 20 cm, core/cladding 62.5/125μm), a piece of SIMF (Yangtze Optical Fiber, length 395μm, core/cladding 105/125μm) and a piece of GIMF (Yangtze Optical Fiber, length 20 cm, core/cladding 50/125μm). Fig. 1(b) shows the microscope image of

Fundamental soliton

A fundamental soliton was obtained by adjusting the PC when the pump power was increased to 110 mW. Fig. 3 shows the spectrum, soliton train, autocorrelation trace, and RF signal of the fundamental soliton. In Fig. 3(a), the Kelly sidebands in the spectrum indicate that the fiber laser output optical soliton. Kelly sidebands are caused by constructive interference between the solitons and dispersive waves, which is an inherent characteristic of soliton fiber lasers with net anomalous dispersion 

Conclusions

In this work, we report on the generation of high-order solitons with order continuously adjustable in an erbium-doped fiber laser mode-locked by a GIMF–SIMF–GIMF SA. Not only fundamental soliton with a duration of 540 fs can be obtained, but 2nd-order to 11th-order soliton can also be achieved by adjusting the pump power and PC. The GIMF–SIMF–GIMF structure based on NL-MMI was fabricated and used as a SA to generate high-order solitons, it has advantages of high damage threshold, easy

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work was supported by the Science and Technology Planning Project of Shenzhen Municipality, China (JCYJ20180306171923592, JSGG20190819175801678).

References (34)

  • TangD.Y. et al.

    Observation of bound states of solitons in a passively mode-locked fiber laser

    Phys. Rev. A

    (2001)
  • TangD.Y. et al.

    Mechanism of multisoliton formation and soliton energy quantization in passively mode-locked fiber lasers

    Phys. Rev. A

    (2005)
  • LiX. et al.

    Bound states of solitons in a fiber laser with a microfiber-based WS2saturable absorber

    IEEE Photonics Technol. Lett.

    (2017)
  • XiangY. et al.

    Observation of wavelength tuning and bound states in fiber lasers

    Sci. Rep.

    (2018)
  • ZhaoL.M. et al.

    Bound states of dispersion-managed solitons in a fiber laser at near zero dispersion

    Appl. Opt.

    (2007)
  • WangP. et al.

    Generation of wavelength-tunable soliton molecules in a 2-μm ultrafast all-fiber laser based on nonlinear polarization evolution

    Opt. Lett.

    (2016)
  • PengJ. et al.

    Generation of soliton molecules in a normal-dispersion fiber laser

    IEEE Photon. Technol. Lett.

    (2013)
  • Cited by (16)

    • Mode-locked Yb-doped fiber laser with graded-index multimode fiber as saturable absorber with gain management

      2023, Optik
      Citation Excerpt :

      It has attracted a great deal of attention because of their advantages such as low cost, small sensitivity to environmental perturbations, long-term reliability, and high damage threshold [17]. Lots of research have been done by many groups [18–20], and these works are focused on spectral regions such as 1 µm [21,22], 1.5 µm [23–25] and 2 µm [26]. Referring to the peak power clamping effect [27] and multiple-soliton distribution dynamic theory [28], several groups have demonstrated harmonic mode-locked operation and the observation of soliton bound states based on GIMF-based SA [29–31].

    • Wavelength-switchable noise-like square pulsed fiber laser based on nonlinear effects

      2022, Optical Fiber Technology
      Citation Excerpt :

      Passively mode-locked fiber lasers with high-energy pulses have become a focus of research in the field of ultrafast photonics. Due to the soliton area theory [8], the pulse energy of conventional solitons and bound solitons are usually less than 0.1 nJ [9,10]. Compared with the above solitons, square pulses have higher energies, typically on the order of nJ.

    • Recent research progress of nonlinear multimode interference mode-locking technology based on multimode fibers

      2022, Infrared Physics and Technology
      Citation Excerpt :

      The latest research of Er-doped fiber laser based on NL-MMI mode-locked technology was proposed by Gan et al. in 2021. Here, high-order solitons with order continuously adjustable were generated in the Er-doped fiber laser mode-locked by a GIMF-SIMF-GIMF for the first time [89]. The structure of this SA is the same as that used in Ref [88].

    View all citing articles on Scopus
    1

    Yaping Gan and Qianchao Wu contributed equally to this work.

    View full text