2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

Solitons are stable localized wave packets that can propagate long distance in dispersive media without changing their shapes. As particle-like nonlinear localized waves, solitons have been investigated in different physical systems. Owing to potential applications in optical communication and optical signal processing systems, optical solitons have attracted intense interest in the past three decades. To experimentally study the formation and dynamics of temporal optical solitons, fiber lasers are considered as a wonderful nonlinear system. During the last decade, several kinds of theoretically predicted solitons were observed experimentally in fiber lasers. In this review, we present a detailed overview of the experimentally verified optical solitons in fiber lasers, including bright solitons, dark solitons, vector solitons, dissipative solitons, dispersion-managed solitons, polarization domain wall solitons, and so on. An outlook for the development on the solitons in fiber lasers is also provided and discussed.

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Recent progress of study on optical solitons in fiber lasers

We demonstrate the usage of a new saturable absorber material – antimony telluride (Sb2Te3) for efficient mode-locking of an Erbium-doped fiber laser. The Sb2Te3 layers were obtained by mechanical exfoliation and transferred onto the fiber connector tip. The all-fiber laser was capable of generating optical solitons with the full width at half maximum of 1.8 nm centered at 1558.6 nm, with 4.75 MHz repetition rate. The pulse energy of the generated 1.8 ps pulses was at the level of 105 pJ.

Mode-locking in Er-doped fiber laser based on mechanically exfoliated Sb_2Te_3 saturable absorber

Graphene and other two-dimensional (2d) crystals are promising materials for photonic and optoelectronic applications. A key requirement for these applications is the development of industrial-scale, reliable, inexpensive production processes, while providing a balance between ease of fabrication and final material quality with on-demand properties. Solution-processing offers a simple and cost-effective pathway to fabricate various 2d crystal based photonic devices, presenting huge integration flexibility compared to conventional methods. Here we present an overview of graphene and other 2d crystals based ultrafast photonics, from solution processing of the raw bulk materials, the fabrication of saturable absorbers, to their applications in ultrafast lasers.

Solution processing of graphene, topological insulators and other 2d crystals for ultrafast photonics

We demonstrate the use of an all-fiberized, mode-locked 1.94 μm laser with a saturable absorption device based on a tungsten disulfide (WS2)-deposited side-polished fiber. The WS2 particles were prepared via liquid phase exfoliation (LPE) without centrifugation. A series of measurements including Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the prepared particles had thick nanostructures of more than 5 layers. The prepared saturable absorption device used the evanescent field interaction mechanism between the oscillating beam and WS2 particles and its modulation depth was measured to be ~10.9% at a wavelength of 1925 nm. Incorporating the WS2-based saturable absorption device into a thulium-holmium co-doped fiber ring cavity, stable mode-locked pulses with a temporal width of ~1.3 ps at a repetition rate of 34.8 MHz were readily obtained at a wavelength of 1941 nm. The results of this experiment confirm that WS2 can be used as an effective broadband saturable absorption material that is suitable to passively generate pulses at 2 μm wavelengths.

Mode-locked, 1.94-μm, all-fiberized laser using WS₂ based evanescent field interaction.

we report three types of pulse generation in Yb-doped nonlinear polarization rotation mode-locked fiber lasers in all-normal-dispersion regime through simulation, including dissipative soliton, dissipative soliton resonance and noise-like pulse. We distinguish the different conditions of generating such different pulses by analyzing the transmission curve of saturable absorber, which plays a key role in pulse shaping.

Simulation of generation of dissipative soliton, dissipative soliton resonance and noise-like pulse in Yb-doped mode-locked fiber lasers

We observed dissipative soliton resonance phenomenon in a graphene oxide mode-locked Yb-doped fiber laser, which delivered square-shaped pulse of 0.52 ns~60.8 ns and single pulse energy of 159.4 nJ at 1064.9 nm. The 3 dB-bandwidth of Lorentz-shaped spectrum was 0.19 nm. We pointed out that the reverse saturable absorption played a big role in generating square-shaped or flat-top pulses, which verified by additional simulation work.

Dissipative soliton resonance and reverse saturable absorption in graphene oxide mode-locked all-normal-dispersion Yb-doped fiber laser.

We demonstrated dissipative soliton obtained from a graphene oxide mode-locked Er-doped fiber laser, which operated in normal dispersion cavity by employing the dispersion compensation fiber. The highly chirped pulses at the repetition rate of 19.5 MHz can be compressed from 11 ps to 542 fs by using single mode fiber. Numerical simulations were in good agreement with the experimental results. The hydrophilic graphene oxide with easier fabrication shows great potential to be a novel low-cost saturable absorber in reliable and compact mode-locked fiber laser system.

Dissipative soliton generation from a graphene oxide mode-locked Er-doped fiber laser

Different pulse-shaping mechanisms were investigated experimentally and numerically in passively mode-locked thulium-doped fiber lasers. Conventional solitons were demonstrated in a passively semiconductor saturable absorber mirror mode-locked anomalous dispersion thulium-doped fiber laser. With normal dispersion fiber and spectral filter added in cavity, pulse-shaping processes were theoretically analyzed in the presence of dispersion map and dissipation in thulium-doped fiber lasers. The existence of parabolic pulse as nonlinear attraction was proved and distinct pulse intensity profiles evolution from Gaussian shape to parabolic shape was proposed in dissipative dispersion-managed thulium-doped fiber lasers.

Pulse-shaping mechanisms in passively mode-locked thulium-doped fiber lasers

We report on an ultraviolet-enhanced supercontinuum generation in a uniform photonic crystal fiber pumped by a giant-chirped mode-locked Yb-doped fiber laser. We find theoretically and experimentally that the initial pluses with giant chirp leads more initial energy transferred to the dispersive waves in visible and ultraviolet wavelength. An extremely wide optical spectrum spanning from 370 nm to beyond 2400 nm with a broad 3 dB spectral bandwidth of 367 nm (from 431 nm to 798 nm) is obtained. Over 36% (350 mW) of the total output power locates in the visible and ultraviolet regime between 370 nm and 850 nm with a maximum spectral power density of 1.6 mW/nm at 550 nm.

Huihui Li

Papers

Simulation of generation of dissipative soliton, dissipative soliton resonance and noise-like pulse in Yb-doped mode-locked fiber lasers

Dissipative soliton resonance and reverse saturable absorption in graphene oxide mode-locked all-normal-dispersion Yb-doped fiber laser.

Dissipative soliton generation from a graphene oxide mode-locked Er-doped fiber laser

Pulse-shaping mechanisms in passively mode-locked thulium-doped fiber lasers

Ultraviolet-enhanced supercontinuum generation in uniform photonic crystal fiber pumped by a giant-chirped fiber laser