A femtosecond pulse fiber laser at 1935 nm using a bulk-structured Bi2Te3 topological insulator

Self-starting ultrafast fiber lasers mode-locked with alcohol

We report a novel saturable absorber (SA) based on anhydrous alcohol for mode-locked fiber lasers (MLFLs). The SA is an optical ferrule with one alcoholic end-facet sealed by a polyethylene (PE) film. Its modulation depth is measured to be 5.9%. Also, a self-starting MLFL using such an alcohol-SA has been demonstrated to generate 972-fs pulses at 1594.6 nm. The single pulse energy is up to 1.8 nJ with the repetition rate of 20.97 MHz, and the signal-to-noise ratio (SNR) is higher than 50 dB. The MLFL exhibits the performance of self-starting, good stability, and high pulse energy. Such a cost-effective and easily-prepared SA with high damage threshold may find wide applications for ultrafast lasers. Besides, it may arouse wide considerations of the mode-locking function of organic liquids for ultrafast lasers.

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

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.

Dissipative soliton generation in Er-doped fiber laser mode-locked by Sb2Te3 topological insulator

We report on the generation of dissipative solitons in an Er-doped fiber laser mode-locked by antimony telluride (Sb 2 Te 3) topological insulator in the near-zero dispersion regime. Layers of Sb 2 Te 3 were deposited on a side-polished (D-shaped) fiber using a pulsed magnetron sputtering technique. Sub-170-fs pulses with 34-nm full width at half-maximum (FWHM) and 0.21 nJ of pulse energy were obtained from an all-fiber, ring-shaped laser cavity after the compression in a single-mode fiber.

Mechanically exfoliated black phosphorus as a new saturable absorber for both Q-switching and Mode-locking laser operation

Black phosphorus (BP), an emerging narrow direct band-gap two-dimensional (2D) layered material that can fill the gap between the semi-metallic graphene and the wide-bandgap transition metal dichalcogenides (TMDs), had been experimentally found to exhibit the saturation of optical absorption if under strong light illumination. By taking advantage of this saturable absorption property, we could fabricate a new type of optical saturable absorber (SA) based on mechanically exfoliated BPs, and further demonstrate the applications for ultra-fast laser photonics. Based on the balanced synchronous twin-detector measurement method, we have characterized the saturable absorption property of the fabricated BP-SAs at the telecommunication band. By incorporating the BP-based SAs device into the all-fiber Erbium-doped fiber laser cavities, we are able to obtain either the passive Q-switching (with maximum pulse energy of 94.3 nJ) or the passive mode-locking operation (with pulse duration down to 946 fs). Our results show that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.

All-polarization maintaining, graphene-based femtosecond Tm-doped all-fiber laser

We report an all-fiber, all-polarization maintaining (PM) ultrafast Tm-doped fiber laser mode-locked by a multilayer graphene-based saturable absorber (SA). The laser emits 603 fs-short pulses centered at 1876 nm wavelength with 6.6 nm of bandwidth and 41 MHz repetition rate. Graphene used as saturable absorber was obtained via chemical vapor deposition (CVD) on copper substrate and immersed in a poly(methylmethacrylate) (PMMA) support, forming a stable, free-standing foil containing 12 graphene layers, suitable for the use in a fiber laser. The generated 603 fs pulses are the shortest reported pulses achieved from a Tm-doped laser mode-locked by graphene saturable absorber so far. Additionally, this is the first demonstration of an all-PM Tm-doped fiber laser incorporating a graphene-based SA. Such cost-effective, compact and stable fiber lasers might be considered as sources usable in nonlinear frequency conversion, mid-infrared spectroscopy and remote sensing.

Actively mode-locked Tm(3+)-doped silica fiber laser with wavelength-tunable, high average output power

A diode-pumped, actively mode-locked high-power thulium (Tm³⁺)-doped double-clad silica fiber laser is demonstrated, providing an average output power in mode-locked (continuous wave) operation of 53 W (72 W) with a slope efficiency of 34% (38%). Mode-locking in the 6th-harmonic order was obtained by an acousto-optic modulator driven at 66 MHz without dispersion compensation. The shortest measured output pulse width was 200 ps. Owing to a diffraction grating as cavity end mirror, the central wavelength could be tuned from 1.95 to 2.13 μm. The measured beam quality in mode-locked and continuous wave operation has been close to the diffraction limit.

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Femtosecond harmonic mode-locking of a fiber laser based on a bulk-structured Bi(2)Te(3) topological insulator

We experimentally demonstrate femtosecond harmonic mode-locking of a fiber laser using a bulk-structured Bi(2)Te(3) topological insulator (TI)-deposited on a side-polished fiber as a mode-locker. A bulk-structured Bi(2)Te(3) TI film was prepared at a thickness of ~20 μm using a mechanical exfoliation method. Using the mode-locker in an erbium-doped fiber ring cavity, it was experimentally shown that harmonically mode-locked pulses with temporal widths of 630 ~700 fs could readily be generated upto the 55th harmonics. The pulse repetition rate was shown to be tunable from the fundamental resonance frequency of 14.07 MHz to the harmonic frequency of 773.85 MHz with increasing pump power. The pumping efficiency was measured at ~3.36 MHz/mW. The side mode suppression ratio (SMSR) was observed to be more than 27.3 dB over all harmonic orders, while the corresponding signal-to-noise ratio (SNR) ranged from 46.3 to 63 dB.

A practical topological insulator saturable absorber for mode-locked fiber laser

A novel saturable absorber (SA) was fabricated by coating the topological insulator (TI) film on microfiber using pulsed laser deposition (PLD) method. The TISA device had an insertion loss of ~1.25 dB, a saturable intensity of 26.7 MW/cm², a modulation depth of ~5.7%, and a nonsaturable loss of 20.5%. Upon employing this SA device, we established a passively mode-locked EDFL and achieved nearly free-chirped soliton pulse with 286 fs of pulse duration and >73 dB of signal to noise ratio (SNR). This result clearly evidences that the PLD is an effective scheme for practical SA device fabrication.

Towards low timing phase noise operation in fiber lasers mode locked by graphene oxide and carbon nanotubes at 1.5 µm

We investigate the timing phase noise of fiber lasers mode locked by graphene oxide (GO) and carbon nanotubes (CNTs), respectively, integrated in a linear cavity fiber laser in the reflecting operation. Due to the shorter decay time of the GO and CNTs, weaker slow saturable absorber effects are expected and mode-locked lasers based on these two saturable absorbers exhibit low excess timing phase noise coupled from the laser intensity noise. Compared with a reference laser mode locked by semiconductor saturable absorber mirror (SESAM), GO based laser obtains a timing phase noise reduction of 7 dB at 1 kHz and a timing jitter reduction of 45% experimentally whereas CNTs based laser obtains a timing phase noise reduction of 3 dB and a timing jitter reduction of 29%. This finding suggests that saturable absorbers with short decay time have the potential for achieving mode locking operation with low timing phase noise, which is important for applications including frequency metrology, high-precision optical sampling, clock distribution and optical sensing.

A 2.95 GHz, femtosecond passive harmonic mode-locked fiber laser based on evanescent field interaction with topological insulator film

By utilizing the pulsed laser deposition (PLD) method, we fabricated a kind of microfiber-based topological insulator (TI) saturable absorber (SA) which has inherent merits of effective and robust properties. We also proposed a newly explanation for the impact of nonlinear effect of SA on the harmonic mode-locking (HML) behavior. Upon employing on the SA, we achieved stable fundamental mode-locking (FML) at central wavelength of 1562.4 nm with pulse duration as short as 320 fs. By adjusting the intracavity polarization state at maximum pump power of 395 mW, we obtained stable femtosecond harmonic soliton pulse generation with repetition rate of 2.95 GHz and output power of 45.3 mW. Our results demonstrated that the microfiber-based TI PLD film SA is a promising device for practical multi-GHz ultrashort pulses generation.

Thulium-doped all-fiber mode-locked laser based on NPR and 45°-tilted fiber grating

A nonlinear polarization rotation based all-fiber passively mode-locked Tm³⁺-doped fiber laser is demonstrated by using a 45° tilted fiber grating (TFG) as an in-line polarizer. The 45° TFG centered at 2000 nm with polarization dependent loss (PDL) of >12 dB at 1850 nm~2150 nm range was UV inscribed for the first time in SM28 fiber using a 244 nm Ar⁺ continuous wave laser and a phase mask with 25 mm long uniform pitch and titled period pattern of 33.7° with respect to the fiber axis. Stable soliton pulses centered at 1992.7 nm with 2.02 nm FWHM bandwidth were produced at a repetition rate of 1.902 MHz with pulse duration of 2.2 ps and pulse energy of 74.6 pJ. As increased pump power, the laser also can operate at noise-like regime with 18.1 nm FWHM bandwidth and pulse energy of up to 250.1 nJ. Using the same 45° TFG, both stable soliton and noise-like mode-locking centered at ~1970 nm and ~2050 nm, were also achieved by shortening and extending the length of Tm³⁺-doped fiber, respectively, exhibiting advantages of broadband and low insertion loss at 2 µm band.

Mode-locked ytterbium-doped fiber laser based on topological insulator: Bi₂Se₃

We demonstrated an all-normal-dispersion Yb-doped mode-locked fiber laser based on Bi₂Se₃ topological insulator (TI). Different from previous TI-mode-locked fiber lasers in which TIs were mixed with film-forming agent, we used a special way to paste a well-proportioned pure TI on a fiber end-facet. In this way, the effect of the film-forming agent could be removed, thus the heat deposition was relieved and damage threshold could be improved. The modulation depth of the Bi₂Se₃ film was measured to be 5.2%. When we used the Bi₂Se₃ film in the Yb-doped fiber laser, the mode locked pulses with pulse energy of 0.756 nJ, pulse width of 46 ps and the repetition rate of 44.6 MHz were obtained. The maximum average output power was 33.7 mW. When the pump power exceeded 270 mW, the laser can operate in multiple pulse state that six-pulse regime can be realized. This contribution indicates that Bi₂Se₃ has an attractive optoelectronic property at 1μm waveband.

Ytterbium-doped fiber laser passively mode locked by few-layer Molybdenum Disulfide (MoS2) saturable absorber functioned with evanescent field interaction

By coupling few-layer Molybdenum Disulfide (MoS₂) with fiber-taper evanescent light field, a new type of MoS₂ based nonlinear optical modulating element had been successfully fabricated as a two-dimensional layered saturable absorber with strong light-matter interaction. This MoS₂-taper-fiber device is not only capable of passively mode-locking an all-normal-dispersion ytterbium-doped fiber laser and enduring high power laser excitation (up to 1 W), but also functions as a polarization sensitive optical modulating component (that is, different polarized light can induce different nonlinear optical response). Thanks to the combined advantages from the strong nonlinear optical response in MoS₂ together with the sufficiently-long-range interaction between light and MoS₂, this device allows for the generation of high power stable dissipative solitons at 1042.6 nm with pulse duration of 656 ps and a repetition rate of 6.74 MHz at a pump power of 210 mW. Our work may also constitute the first example of MoS₂-enabled wave-guiding photonic device, and potentially give some new insights into two-dimensional layered materials related photonics.

Ultrafast erbium-doped fiber laser mode-locked by a CVD-grown molybdenum disulfide (MoS2) saturable absorber

We demonstrate an erbium-doped fiber laser passively mode-locked by a multilayer molybdenum disulfide (MoS(2)) saturable absorber (SA). The multilayer MoS(2) is prepared by the chemical vapor deposition (CVD) method and transferred onto the end-face of a fiber connector. Taking advantage of the excellent saturable absorption of the fabricated MoS(2)-based SA, stable mode locking is obtained at a pump threshold of 31 mW. Resultant output soliton pulses have central wavelength, spectral width, pulse duration, and repetition rate of 1568.9 nm, 2.6 nm, 1.28 ps, and 8.288 MHz, respectively. The experimental results show that multilayer MoS(2) is a promising material for ultrafast laser systems.

Sub-130 fs mode-locked Er-doped fiber laser based on topological insulator

In this work we present for the first time, to the best of our knowledge, a stretched-pulse mode-locked fiber laser based on topological insulator. As a saturable absorber (SA) a ~0.5 mm thick lump of antimony telluride (Sb2Te3) deposited on a side-polished fiber was used. Such a SA introduced 6% modulation depth with 43% of non-saturable losses, which is sufficient for supporting stretched-pulse mode-locking. The ring laser resonator based on Er-doped active fiber with managed intracavity dispersion was capable of generating ultrashort optical pulses with full width at half maximum (FWHM) of 30 nm centered at 1565 nm. The pulses with duration of 128 fs were repeated with a frequency of 22.32 MHz.