Nonlinear Saturable Absorption Research Articles

Metallated Graphynes as a New Class of Photofunctional 2D Organometallic Nanosheets

AbstractTwo‐dimensional (2D) nanomaterials are attracting much attention due to their excellent electronic and optical properties. Here, we report the first experimental preparation of two free‐standing mercurated graphyne nanosheets via the interface‐assisted bottom‐up method, which integrates both the advantages of metal center and graphyne. The continuous large‐area nanosheets derived from the chemical growth show the layered molecular structural arrangement, controllable thickness and enhanced π‐conjugation, which result in their stable and outstanding broadband nonlinear saturable absorption (SA) properties (at both 532 and 1064 nm). The passively Q‐switched (PQS) performances of these two nanosheets as the saturable absorbers are comparable to or higher than those of the state‐of‐the‐art 2D nanomaterials (such as graphene, black phosphorus, MoS2, γ‐graphyne, etc.). Our results illustrate that the two metallated graphynes could act not only as a new class of 2D carbon‐rich materials, but also as inexpensive and easily available optoelectronic materials for device fabrication.

Passive mode-locked Er-doped fiber laser pulse generation based on titanium disulfide saturable absorber

In this study, titanium disulfide (TiS2) polyvinyl alcohol (PVA) film-type saturable absorber (SA) is synthesized with a modulation depth of 5.08% and a saturable intensity of 10.62 MW/cm2 by liquid-phase exfoliation and spin-coating methods. Since TiS2-based SA has a strong nonlinear saturable absorption property, two types of optical soliton were observed in a mode-locked Er-doped fiber laser. When the pump power was raised to 67.3 mW, a conventional mode-locked pulse train with a repetition rate of 1.716 MHz and a pulse width of 6.57 ps was generated, and the output spectrum centered at 1556.98 nm and 0.466 nm spectral width with obvious Kelly sidebands was obtained. Another type of mode-locked pulse train with the maximum output power of 3.92 mW and pulse energy of 2.28 nJ at the pump power of 517.2 mW was achieved when the polarization controllers were adjusted. Since TiS2-based SA has excellent nonlinear saturable absorption characteristics, broad applications in ultrafast photonic are expected.

Ultrafast mode-locking in highly stacked Ti3C2Tx MXenes for 1.9-μm infrared femtosecond pulsed lasers

Abstract Metallic 2D materials can be promising saturable absorbers for ultrashort pulsed laser production in the long wavelength regime. However, preparing and manipulating their 2D structures without layer stacking have been nontrivial. Using a combined experimental and theoretical approach, we demonstrate here that a metallic titanium carbide (Ti3C2Tx), the most popular MXene 2D material, can have excellent nonlinear saturable absorption properties even in a highly stacked state due to its intrinsically existing surface termination, and thus can produce mode-locked femtosecond pulsed lasers in the 1.9-μm infrared range. Density functional theory calculations reveal that the electronic and optical properties of Ti3C2Tx MXene can be well preserved against significant layer stacking. Indeed, it is experimentally shown that 1.914-μm femtosecond pulsed lasers with a duration of 897 fs are readily generated within a fiber cavity using hundreds-of-layer stacked Ti3C2Tx MXene saturable absorbers, not only being much easier to manufacture than mono- or few-layered ones, but also offering character-conserved tightly-assembled 2D materials for advanced performance. This work strongly suggests that as-obtained highly stacked Ti3C2Tx MXenes can serve as superb material platforms for versatile nanophotonic applications, paving the way toward cost-effective, high-performance photonic devices based on MXenes.

Nonlinear saturable absorption in antimonene quantum dots for passively Q‐switching Pr:YLF laser

AbstractAntimonene, a new member of monoelemental two‐dimensional crystals composed of antimony atoms, was predicted to possess high stability, as well as outstanding electrical and optical properties. Here, we report on the experimental results of productive, high‐quality synthesis of antimonene quantum dots (AQDs) via liquid‐phase exfoliation. The obtained AQDs exhibited excellent nonlinear saturable absorption. The modulation depth and the saturable intensity were found to be around 3.9% and 10.02 GW/cm2, respectively. By using the AQDs saturable absorber in the 639 nm Pr:YLF laser, stable Q‐switching pulsed laser was realized. The maximum output power was 83 mW and the corresponding pulse width was 255 ns with a pulse repetition rate of 227 kHz. These results suggest that AQDs are a promising candidate for nonlinear optical applications.

Passively mode-locked thulium doped fiber laser based on SnSe nanoparticles as a saturable absorber

In this paper, tin selenide (SnSe) nanoparticles (NPs) are employed as a saturable absorber (SA) in a passively mode-locked thulium (Tm)-doped fiber laser for the first time. The mode-locked pulse has a central wavelength of 1963 nm and a 3-dB bandwidth of 4.3 nm. The repetition rate is 24.59 MHz and the full width at half maximum (FWHM) of the pulse is 1.2 ps. Harmonics from the second order to the eighth order are observed. Our results prove that the SnSe have excellent nonlinear saturable absorption properties and could have wide potential applications on ultrafast photonics in mid-infrared waveband.

Few-layer TaSe2 as a saturable absorber for passively Q-switched erbium-doped fiber lasers

TaSe2 nanosheets are prepared by means of ultrasound-assisted liquid phase exfoliation (LPE) and the nonlinear saturable absorption properties are experimentally investigated. The TaSe2-polyvinyl alcohol (PVA) film is then manufactured and a TaSe2-based saturable absorber (SA) is fabricated for demonstrating a Q-switched erbium-doped fiber laser (EDFL) for the first time. Taking advantage of the saturable absorption properties of the TaSe2-based SA, the obtained shortest Q-switched pulse duration is 1.53 µs with a pulse energy of 65.5 nJ. The results indicate that TaSe2 is a competent candidate for use as SA in promoting stable and flexible ultrafast lasers. The work may pave the way to researches and applications for photonics in the mid-infrared band.

Few-layered W2C nanosheets based on passively mode-locked fiber lasers

Here, few-layered W2C nanosheets and microfiber-based few-layered W2C-SA are fabricated by the magnetron sputtering deposition method. The third-order nonlinear optical responses of the prepared 2D W2C nanosheets are investigated by the Z-scan method with βeff and n2 determined to be −88.2 cm/MW and −1.112×10−13 m2/W, respectively, revealing its excellent nonlinear saturable absorption properties and optical modulation capabilities. In addition, by incorporating microfiber based few-layered W2C-SA into Yb-doped and Er-doped fiber lasers (YDFLs and EDFLs), the passively mode-locked operations at the central wavelength of 1035.1 and 1562 nm are realized, respectively. In addition, multi-soliton bound mode-locked operation in EDFLs with soliton pulses up to 36 is realized. Our results not only demonstrate the capability of few-layered W2C as a wideband optical modulator, but also provide a practical approach to explore soliton dynamics in fiber lasers.

Q-switched fiber laser with tunable wavelength operation utilizing a nonlinear saturable absorption of vanadium pentoxide

Q-switched fiber laser with a tunable wavelength output is experimentally demonstrated utilizing a nonlinear saturable absorption of vanadium pentoxide (V2O5) in conjunction with a tunable bandpass filter (TBF). The V2O5 saturable absorber (SA) was prepared by mixing V2O5 with polyethylene glycol. The SA film exhibits a modulation depth of 7% with a saturation intensity of 90 MW/cm2. By integrating the SA into an erbium-doped fiber laser cavity while controlling the passband wavelength of the TBF, a Q-switched pulsed laser is realized with a tunable wavelength range of 30 nm that extends from 1535 to 1565 nm. At 1565 nm operation, the laser exhibits the highest slope efficiency of 8.31%. The repetition rate varies from 13.32 to 15.25 kHz, while the pulse width shrinks from 21.3 10 12.75 μs when the pump power rises from 14.9 to 37.7 mW. The pulse energy is 102.6 nJ at the maximum pump power of 37.7 mW. This is the first demonstration of a tunable Q-switched fiber laser operating in a 1.5 μm wavelength region utilizing V2O5 SA.

Enhanced Q-switching performance of magnetite nanoparticle via compositional engineering with Ti3C2 MXene in the near infrared region

In this work, we reported a new strategy to improve the nonlinear saturable absorption performance of magnetite (Fe3O4) nanoparticles (FONPs) via the compositional engineering with the Ti3C2 MXene in the near-infrared (NIR) region. Based on the DFT simulation, the band structures and work function were significantly modified by the Ti3C2 MXene doping. By using the open-aperture Z-scan technology, the nonlinear optical features of the FONPs@Ti3C2 nanocomposite were significantly improved, showing the great potential as the saturable absorber in the pulsed laser. With the nanocomposite as the saturable absorber, the passively Q-switched Nd:GdVO4 lasers emitted much shorter pulse durations when compared with the pristine FONP saturable absorber. These findings indicated that FONPs@Ti3C2 heterostructure was a promising saturable absorber for the short pulse generation in the NIR region.

Quantum-sized silicon for enhanced photoluminescence and optical nonlinearity

Si quantum dots (SiQDs) with intrinsic characteristics demonstrate significantly enhanced photoluminescence (PL) and nonlinear saturation absorption (NSA) performances.

2.04 µm harmonic noise-like pulses generation from a mode-locked fiber laser based on nonlinear polarization rotation

We report the generation of harmonic noise-like mode-locked pulses in a thulium-doped fiber laser. In this laser, mode-locking can be realized through the nonlinear polarization rotation (NPR) technique. The ring cavity configuration uses 5 m of a Tm-doped dual-cladding fiber, as a gain medium, pumped by a 793 nm diode laser. The cavity uses a couple of polarization controllers (PCs) and polarization-dependent isolator to form a nonlinear polarization-rotating saturable absorber. By carefully adjusting of the PCs, the laser generates noise-like mode-locked pulses at the 2.04 µm band. With the increase of the pump power, the laser generates harmonics of the mode-locking fundamental repetition frequency of 6.88 MHz, from which we can obtain the second harmonic in a controlled mode. The obtained results may be useful for enhancing the understanding of the mechanism and characteristics of noise-like pulse at the 2 µm band.

Passively Q-Switched Erbium-Doped Fiber Laser Based on GeSe Saturable Absorber

GeSe nanosheets were prepared by ultrasonic-assisted liquid phase exfoliation (LPE), and the nonlinear saturated absorption performance was experimentally studied. The modulation depth and saturation intensity of the prepared GeSe saturable absorber (SA) were 15% and 1.44 MW/cm2, respectively. Using the saturated absorption characteristics of GeSe SA, a passively Q-switched erbium-doped fiber laser was systematically demonstrated. As the pump power increases, the pulse repetition frequency increases from 22.8 kHz to 77.59 kHz. The shortest pulse duration is 1.51 μs, and the corresponding pulse energy is 46.14 nJ. Experimental results show that GeSe nanosheets can be used as high-efficiency SA in fiber lasers. Our results will provide a useful reference for demonstrating pulsed fiber lasers based on GeSe equipment.

Saturable absorption behavior of (5,10,15,20-tetraphenylporphyrinato)-silver crystal thin film at wavelength 532 nm

A single crystal of (5,10,15,20-tetraphenylporphyrinato)-silver was obtained and its structure reported. Using direct growth on quartz substrates method, a crystal thin film was obtained and the film’s morphology was investigated by atomic force microscopy. The nonlinear absorption properties of the film were studied using open aperture [Formula: see text]-scan technique by picosecond laser pulses at different fluence at wavelength 532 nm, nonlinear saturable absorption behavior was observed. Time-dependent unrestricted Hartree-Fock with the basis set LanL2DZ was used in computing the linear and non-linear optical properties of (5,10,15,20-tetraphenylporphyrinato)-silver.

Tin Telluride Quantum Dots as a Novel Saturable Absorber for Q‐Switching and Mode Locking in Fiber Lasers

AbstractTin telluride (SnTe) quantum dots (QDs) have attracted considerable interest in the optoelectronic field owing to their favorable properties over conventional QDs, such as a relatively large Bohr radius (95 nm) and low toxicity level. However, till date, the nonlinear optical properties and ultrafast photonics applications of SnTe QDs have remained unexplored. In this study, SnTe QDs with an average diameter of 74 nm (smaller than the Bohr radius of SnTe) are fabricated via a liquid‐phase exfoliation method. Consequently, the nonlinear saturable absorption properties of such SnTe QDs are explored by realizing a modulation depth of 2.2% and saturable intensity of 1.67 GW cm−2. The prepared QDs are then used as saturable absorber (SA) in the erbium‐doped fiber laser ring cavity system. Moreover, Q‐switched and mode‐locked laser pulses with a pulse width of 1.81 µs and 691 fs are generated, respectively. Harmonic mode‐locking with a high repetition rate of 62.1 MHz (fifth order) is experimentally realized. This is the first demonstration, to the authors’ knowledge, of using SnTe QDs‐SA for generating ultrafast laser pulses along with high‐repetition‐rate harmonic mode‐locking pulses. Therefore, this study will establish a new research scope for SnTe QDs in ultrafast photonics, nonlinear photonics, frequency combs, and optical communications.

Broadband Fe3O4 nanoparticles saturable absorber for Q-switched fiber lasers

We demonstrated passively Q-switched 1-, 1.5-, and 2-μm fiber lasers by exploiting ferroferric-oxide nanoparticles (FONPs) as a broadband saturable absorber (SA). FONPs were prepared by a method of thermal decomposition, and then were mixed with sodium carboxymethylcelluose (NaCMC) to form a FONPs film. The FONPs film was sandwiched between two fiber ferrules to fabricate the FONPs SA, which had a broadband absorption from 800 to 2000 nm and nonlinear saturable absorption at 1-, 1.5-, and 2-μm. By inserting the same FONPs SA into the ytterbium, erbium and thulium doped fiber laser cavities, the stable passively Q-switching operation at 1039, 1560 and 1982 nm was realized for a threshold pump power of ∼82 mW, ∼62 mW and ∼830 mW, respectively. To the best of our knowledge, it is the first demonstration of the use of a single SA based on FONPs for wide-band Q-switching operation of fiber lasers from 1 to 2 μm.

Titania-carbon nanocomposite as a saturable absorber for generation passively ytterbium-mode locked pulses

Passively pulse dual-wavelength ytterbium-doped fiber laser (YDFL) around 1 μm utilizing titania–carbon nanocomposite (TiO2–C NC) thin film as the optical modulator is experimentally demonstrated. The TiO2–C NC thin-film reveals great nonlinear saturable absorption characteristics with a transmission difference of 24.06% at the lasing emission around the 1 μm region. Stable self-starting mode-locked emission with a pulse of ~8 ns and a repetition rate of 30.7 MHz was achieved at threshold exciting power of about 115 mW. By adapting the polarization controller (PC) together with the pump power, fundamental, third, and sixth harmonic frequencies can be switched to each other. The corresponding pulse durations to the third and sixth harmonic mode-locked were 6.8 and 1.8 ns, respectively. The corresponding maximum output power was 1.8 mW. This work opens up another way to build cost-effective, greatly stable optical modulators, and presents the option to build novel nanocomposite-based photonic devices with TiO2–C NC.

Passively Mode-Locked Operations Induced by Semiconducting Polymer Nanoparticles and a Side-Polished Fiber.

Semiconducting polymer nanoparticles (SPNs) possess many special photophysical and chemical properties. However, little research has been done on the potential of SPNs in laser technology. In this work, we present the ultrafast pulses generation at 1.5 and 2 μm through proposing the deposition of SPNs onto a side-polished fiber (SPF) platform as the nonlinear optical modulator. SPNs are designed and prepared through a combination of density functional theory and nanoreprecipitation method. The prepared SPNs not only exhibit strong linear absorption but also has nonlinear saturable absorption characteristics. Once SPF-SPNs saturable absorber (SA) is integrated into the laser cavity, ultrafast lasers of 1.5 and 2 μm can be achieved with high performance. Our results show that SAs based on the SPNs and SPF are promising nonlinear optical modulators for broadband ultrafast pulse generation.

Nonlinear Optical Properties of Ag Nanoplates Plasmon Resonance and Applications in Ultrafast Photonics

Metal nanomaterials have attracted increasing attention due to their outstanding nonlinear optical and photonic properties, making them as potential saturable absorber (SA) candidates for realizing ultrafast photonic devices. In this article, we demonstrate the generation of mode-locked dual-wavelength pulse trains in an Ag nanoplates (AgNPTs)-based Yb-doped all-fiber laser for the first time to the best of our knowledge. The AgNPTs are synthesized by seed-mediated growth and then integrated into a fiber ferrule by optical deposition, which serve as SA in the ring laser cavity. The plasmonic properties of such nanoplates are measured by absorption spectrophotometry and their nonlinear optical properties are characterized by Z-scan. The measured nonlinear saturable absorption of the AgNPTs-based SA is 6.4%. In our laser, the dual-wavelength synchronous mode-locking is achieved at the center wavelengths of 1031.92 and 1033.24 nm with 3-dB spectral bandwidth of 0.52 and 0.46 nm, respectively, where 293-ps pulse trains with a repetition rate of 11.43 MHz are obtained at the pump power of 350 mW. The results demonstrate that the solution-processed AgNPTs are promising SA candidates for achieving stable and low-cost pulsed laser sources which could be used for spectroscopy and ultrafast photonics.

Nonlinear saturated absorption properties of Ag-MoSe2 films by co-sputtering

In this paper, the Ag-MoSe2 films were prepared on quartz substrates by magnetron sputtering, and the influence of Ag doping on their morphology, optical band gap and nonlinear optical properties was studied. The SEM images show images show the relative low content of silver, and the Se precipitation. The nonlinear absorption properties were measured by Z-scan technique, indicating the saturable absorption behavior. Under different DC sputtering power, the nonlinear absorption coefficient decreased and then increased. The significant nonlinear absorption is demonstrated with the coefficient of ~ 10-4 cm/W. The proposed Ag-MoSe2 film is a promising candidate for the application in optoelectronic devices.

Ultrathin amorphous Ge film enabling stabilized femtosecond fiber laser pulsation

Ultrathin amorphous Ge (α-Ge) film is synthesized as nonlinear saturable absorber to enable the femtosecond pulsation of erbium-doped fiber laser, which self-starts the fiber laser pulsation with nearly 700-fs pulsewidth at threshold pumping condition. Under high-gain condition, the α-Ge film with thickness of 17 nm exhibits the largest self-amplitude modulation coefficient of 8.9 × 10−4 to further compress the fiber laser pulsewidth to 305 fs. To compare, other Si-doped Ge films are also synthesized by linearly decreasing the Ge/(Ge + Si) composition ratio during plasma enhanced chemical vapor deposition, which reveal ultrahigh Ge/Si composition ratios with bandgap energy tunable from 1.05 to 0.87 eV. All recipes perform relatively comparable mode-locking force for pulsating the fiber laser with corresponding self-amplitude modulation coefficient degraded only by 6 × 10−6 as compared to the pure α-Ge film. Decreasing the Ge/(Ge + Si) composition ratio by 5% only broadens the fiber laser pulsewidth by 8.2% to 330 fs and slightly increases the peak amplitude fluctuation of the pulse-train to 1.81%. These results corroborate the pulsating stability of fiber laser under high pumping condition via the ultrathin α-Ge even with residual Si dopants, indicating that the pure α-Ge can serve as the optimized group-IV semiconductor nonlinear saturable absorption to provide sufficiently large nonlinear saturable absorbance as well as self-amplitude modulation, particularly suitable for stabilization the pulsed fiber laser no matter in the initial mode-locking or in the soliton compression regime.