Stable Mode-locked Fiber Laser Research Articles

Generation of stable femtosecond pulses using MoS2−xSex as the saturable absorber in Er-doped fiber laser

A new transition-metal dichalcogenide (Janus TMDs), molybdenum selenide sulfide (MoS[Formula: see text][Formula: see text]Se[Formula: see text]), has attracted wide attention due to its unique and highly stable alloy structure, high carrier mobility and the ability to modulate the band gap based on composition. In this work, MoS[Formula: see text][Formula: see text]Se[Formula: see text] nanosheets were prepared through liquid phase exfoliation and further prepared as a saturable absorber (SA). The nonlinear optical response was investigated by the homemade balanced twin-detector measurement system, revealing the potential of MoS[Formula: see text][Formula: see text]Se[Formula: see text]-SA in ultrafast photonics. The SA devices exhibited good saturation absorption characteristics. By applying it to the Er-doped fiber laser, a stable mode-locked fiber laser based on MoS[Formula: see text][Formula: see text]Se[Formula: see text]-SA was successfully achieved. The pulse width was measured to be 509 fs, with a spectral width of 6.33 nm and a maximum output power of 7.44 mW in the mode-locked state. This is the first reported instance of achieving mode-locking operation in the Er-doped fiber laser using MoS[Formula: see text][Formula: see text]Se[Formula: see text]-SA, indicating its great potential for applications in ultrafast photonics.

CsxWO3 nanorods with broadband nonlinear response for Q-switched and mode-locked pulse generation

Nano-CsxWO3 with broadband local surface plasmon resonance is the promising candidate for nonlinear photonics applications. In this work, Q-switched and mode-locked pulses were generated from Er- and Tm- doped fiber lasers by using CsxWO3 nanorods (NRs) as saturable absorbers (SAs). The CsxWO3 NRs were synthesized by a water controlled-release solvothermal process. Then they were mixed with sodium carboxymethylcellulose (NaCMC) solution to fabricate a SA film and deposited onto a d-shaped fiber to fabricate a d-shaped fiber SA. These SAs exhibited excellent nonlinear optical properties at 1.5- μm and 2- μm. A ∼ 1560 nm Q-switched fiber laser with the shortest pulse width of 3.8 µs, the maximum average power of 10 mW, a pulse energy of 0.35 μJ was obtained by using the filmy CsxWO3 SA. A stable soliton mode-locked fiber laser at ∼ 1943 nm was realized based on the d-shape fiber CsxWO3 SA, it had a maximum average output power of ∼ 50 mW, a pulse duration of ∼ 292 fs, and a repetition rate of 25.5 MHz. Our results show that the CsxWO3 NRs are potential nonlinear materials for broadband ultrafast response and Q-switched/mode-locked pulse generation.

Structure and properties of soliton molecules in a single-mode dual core fiber with Kerr nonlinearity

We consider the case where two different frequency optical solitons are incident in a single-mode dual core fiber with Kerr nonlinearity. In this situation, the propagation dynamics of the two optical solitons are controlled by a set of coupled nonlinear Schrödinger equations(CNLSE). In this paper, the one- and two-soliton solutions of the CNLSE are obtained by Horita’s bilinear method, and the differences in constraints between one- and two-soliton solutions are discussed. Subsequently, when analyzing the characteristics of soliton transmission, it is found that the two-solitons will form the soliton molecules under certain conditions. This paper may have implications for the design of the stable mode-locked fiber laser and all-optical switches.

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

We experimentally demonstrate a novel, linear-cavity mode-locked Yb-doped fiber laser based on the graded-index multimode fiber (GIMF) as saturable absorber, and propose the use of varying gain levels by doubling gain fiber length to mitigate the technical difficulty of multimode fiber as a saturable absorber in the length accuracy requirements. It provides a more flexible solution to achieve a highly stable mode-locked fiber laser based on GIMF. By analogy to dispersion management, we refer to this scheme as gain management. By adopting the two mechanisms of flexible GIMF length and gain management simultaneously, a stable mode-locked pulse train with the repetition rate of 10.96 MHz and pulse duration of ∼83.4 ps at 1064.07 nm was generated. Stable pulse bunches with pulse numbers up to 12 in a single bunch were obtained when increasing the pump power. The proposed gain management method opens a promising way for practical highly stable mode-locked technology based on nonlinear multimode interference mechanism.

Preparation of tellurium nanowires and its application in ultrafast photonics

As a kind of semiconductors, tellurium has attracted much attention due to its superior optical, electrical, and thermoelectric properties. In particular, a lot of research on low-dimensional tellurium has been performed in recent years, but with relatively few work on its applications in ultrafast photonics. In this work, a femtosecond fiber laser was realized using the prepared tellurium nanowires as the saturable absorber. Tellurium nanowires were synthesized by the hydrothermal method and then deposited on the tapered optical fiber to form the tellurium saturable absorber (Te-SA). The saturable absorption property of Te-SA was tested by the two-arm balance detection method, the saturation intensity and modulation depth were determined to be 8.9 MW/cm2 and 27.0%, respectively. Then, Te-SA was applied in the erbium-doped fiber laser and a stable mode-locked fiber laser with a pulse width of 621 fs was achieved. The results indicate the great potential application of tellurium nanowires in ultrafast photonics.

Stable and high energy ytterbium-doped mode-locked fiber laser based on a franckeite-polymer film modulator

As a novel material with narrow band gap and natural van der Waals heterostructures (vdWH), francketie has potential applications in the field of optoelectronic fields. However, few studies have applied its nonlinear optical absorption properties to ultrafast fiber lasers. Here, we synthesized francketie nanosheets via the liquid-phase exfoliation (LPE) method. By incorporating the polyvinyl alcohol (PVA), a franckeite-PVA saturable absorber (SA) was fabricated to achieve a mode-locked Yb-doped fiber laser (YDFL) for the first time to the best of our knowledge. The saturation intensity and modulation depth of the SA were measured about 75 MW∕cm2 and 7%, respectively. The proposed franckeite-based YDFL demonstrates stable mode-locked operation with the maximum single energy of 5.35 nJ and the pulse duration of 1.57 ns. Our experimental results fully prove that franckeite may have wide potential for designing ultrafast photonics devices with low cost, high stability and excellent performance.

Cerium oxide/polydimethylsiloxane composite tapered fiber saturable absorber for mode-locked pulsed erbium-doped fiber laser

This investigation demonstrates the nonlinear saturable absorption of cerium oxide (CeO2) nanoparticles; a lanthanide allotrope oxide material and its employment as a saturable absorber (SA) for the generation of stable mode-locked pulsed fiber laser. The CeO2 nanoparticles were simply prepared by sonicating its bulk solution and incorporating a polydimethylsiloxane (PDMS) polymer to form a thin film nanocomposite on tapered optical fiber for the fabrication of CeO2/PDMS-SA. The nonlinear intensity-dependent transmission characteristic of this material was confirmed with a modulation depth of 0.66% and saturation intensity of 77 MW/cm2. The SA was integrated into an erbium-doped fiber laser cavity, where mode-locking operation self-started at 35 mW pump power with stable soliton operation up to 250 mW in net anomalous dispersion regime. The pulse laser centered at 1561 nm wavelength with a constant repetition rate of 7.64 MHz, shortest pulse width of 800 fs, and highest signal to noise ratio of 54.2 dB. The highest pulse energy of 0.645 nJ and average power of 4.92 mW were measured at 250 mW pump power. Based on its simple preparation and stable pulse generation, this investigation suggests the viability of CeO2 nanoparticles as a new SA material for ultrashort pulse generation.

Enhanced optical nonlinearity and ultrafast carrier dynamics of TiO2/CuO nanocomposites

Transition metal oxides (TMOs) are drawing multitudinous interest due to their strong thermochemical stability. In the present work, we proposed a facile strategy to fabricate TiO 2 /CuO nanocomposites. By using the conventional open- and closed-aperture Z-scan technology, the eminent nonlinear optical (NLO) properties of the as-prepared TiO 2 /CuO nanocomposites were demonstrated. In order to deeply investigate the NLO enhancement mechanism, we established a theoretical model to study the photogenerated carriers transfer dynamics at the interface with rate equations and the fouth-order Runge-Kutta algorithm. The simulation results indicated that under pumping irradiation, the carriers transferring from CuO to TiO 2 promoted the nonlinear optical absorption of CuO nanosheets and increased the modulation depth. Experimentally, the transient absorption spectroscopy and broadband time-resolved pump-probe measurements were presented to study the role of the carrier dynamics in the broadband near-infrared region. To further confirm the enhanced NLO response in TiO 2 /CuO nanocomposites, a highly stable dissipative soliton mode-locked Yb-doped fiber laser with TiO 2 /CuO saturable absorber was constructed at 1 μm for the first time. Our work manifested the key effects of the interface in TiO 2 /CuO nanocomposites to boost the NLO features which can be applied in ultrafast photonics applications.

Broadband nonlinear optical modulator enabled by VO2/V2O5 core–shell heterostructures

Abstract Broadband pulsed lasers have become an indispensable part in optical communications, biomedical engineering, materials processing, and national defense. Inspired by the broadband and ultrafast optical components, great efforts from the laser and material community have been paid to explore the emerging nonlinear optical materials. Here, we found that the VO2/V2O5 core–shell heterostructures with type-II staggered band alignment exhibit broadband nonlinear optical response towards mid-infrared spectral range. The nonlinear optical characterizations verify that the heterostructures show the modulation depth and saturation intensity of 27% and 42 GW/cm2 at 1064 nm, 23% and 78 GW/cm2 at 1550 nm, and 16.5% and 63.9 GW/cm2 at 2800 nm, respectively. With the nonlinear optical modulator, stable mode-locked Yb-doped and Er-doped fiber lasers have been realized with pulse output as short as 310 ps and 633 fs, respectively. In addition, the stable Q-switched Er-doped fluoride fiber laser has been demonstrated with a pulse repetition rate of 89 kHz and the shortest pulse width of 680 ns, respectively. The experimental results indicate that VO2/V2O5 core–shell heterostructures can be broadband nonlinear optical modulators from the near-infrared to the mid-infrared spectral range, offering opportunities to develop high-performance photonic devices.

Generation of stable mode-locked fiber laser based MWCNTs in 1.5-µm waveband

Pulses fiber laser had been successfully generated by using multi-wall carbon nanotubes thin film saturable absorber at room temperature. The saturable absorber is incorporated into a ring laser cavity. A stable Kelly sidebands mode-locked pulse spectrum with 1561.3 nm wavelength at the pump power of 86.8 mW. The repetition rate and pulse width of 12.3 MHz and 0.51 picosecond, respectively. A stable operation is observed for an hour at room temperature. These simple and reliable system features offer interesting research study especially in mode-locked pulse generation at 1.5 μm waveband.

Tin telluride quantum dots as a new saturable absorber for a mode-locked Yb+ doped fiber laser

Tin telluride (SnTe), a member of group IV-VI semiconductors, has attracted significant attention due to its super thermoelectricity and ferroelectricity. In addition, SnTe was reported to have a direct bandgap (0.18 eV) and relatively good oxidation resistance, therefore, it has huge application potential in optoelectronics. However, up to now, the study of interaction between light and SnTe is still immature. In this paper, SnTe quantum dots (QDs) were prepared by the ultrasonication assisted liquid-phase exfoliation (UALPE) method and the broadband absorption properties of SnTe QDs were demonstrated. Furthermore, by employing SnTe QDs as a saturable absorber (SA), a stable mode-locked Yb-doped fiber laser (YDFL) with a pulse duration of 265 ps and an output power of 5.68 mW was obtained. Our results demonstrated that SnTe could be a promising candidate in the mode-locked YDFL system and photonic technology application.

Mode-locked thulium doped fiber laser utilizing tungsten trioxide saturable absorber

Stable mode-locked thulium-doped fiber laser (TDFL) is demonstrated using tungsten trioxide (WO3) deposited on a microfiber as a passive saturable absorber. The WO3 composite was prepared and deposited onto the microfiber before being integrated into the laser cavity. Owing to the interaction of WO3 nanoparticles with the evanescent field of the propagating light, a stable soliton mode-locked TDFL at 1955.3 nm with 3 dB bandwidth of 3.22 nm, repetition rate of 10.98 MHz, and pulse width of 1.26 ps was obtained. The pulse energy and peak power were then calculated to be 0.59 nJ and 419 W respectively, with a signal-to-noise ratio of 54.8 dB. The microfiber WO3 saturable absorber showed no sign of deterioration even though the laser cavity was pumped at 1.15 W power. The findings indicate that WO3 could be an excellent candidate as saturable absorber for mode-locking generation at mid-infrared fiber lasers.

Route to stable dispersion-managed mode-locked Yb-doped fiber lasers with near-zero net cavity dispersion.

We numerically investigate the stability of a dispersion-managed mode-locked Yb-doped fiber laser of near-zero net cavity dispersion. The instability is primarily due to the filtering effect of the chirped fiber Bragg grating. The size of the unstable region is dependent on the modulation depth of the saturable absorbers. At modulation depth higher than 30%, stable mode-locking can operate throughout the dispersion region. Based on the simulation results, stable mode-locking around zero cavity dispersion is experimentally viable by a SESAM with a 34% modulation depth. The fiber laser can generate laser pulses with a 17-nm spectral bandwidth and a 139-fs dechirped pulse duration.

Pulse generation in Yb-doped polarization-maintaining fiber laser by nonlinear polarization evolution**Project supported by the National Natural Science Foundation of China (Grant Nos. 61575011 and 61975003) and the Beijing Natural Science Foundation, China (Grant No. 4192015).

We demonstrate a self-started, long-term stable polarization-maintaining mode-locked fiber laser based on the nonlinear polarization evolution technique. A polarized beam splitter is inserted into the cavity of the linear polarization-maintaining fiber laser to facilitate self-started mode-locking. Pulses with single pulse energy of 26.9 nJ and average output power of 73.9 mW are obtained at the pump power of 600 mW. The transmission characteristics of artificial saturable absorber used in this laser are analyzed theoretically, the influence of the half-wave plate state on mode-locking is discussed, and the mode-locking range is obtained, which is well consistent with the experimental results.

All-Fiber Supercontinuum Source Pumped by Noise-Like Pulse Mode Locked Laser

We demonstrate flat supercontinuum generation in a piece of highly nonlinear fiber pumped with a stable noise-like pulse mode-locked fiber laser. The compact all-fiber laser realizes mode locking based on a nonlinear amplifying loop mirror and emits noise-like mode-locked pulse with high peak power and high average power. The output pulse has a 3-dB bandwidth of ~35.8 nm with the central wavelength of ~1581 nm. Pumping a 102-m highly nonlinear fiber with the noise-like pulse mode-locked fiber laser directly, a flat and weak residual-pump supercontinuum spanning from ~1370 to ~2200 nm is generated. The spectrum within 1865 to 2200 nm contains more than 45% of the whole energy of the supercontinuum.

Nanosecond Pulses Generation with Samarium Oxide Film Saturable Absorber**Supported by the INTI Research Grant Scheme 2018 under Grant No INTI-FITS-01-06-2018.

Nanosecond pulse generation is demonstrated in a mode-locked erbium-doped fiber laser (EDFL) utilizing a samarium oxide (Sm2O3) film. The Sm2O3 film exhibits a modulation depth of 33%, which is suitable for mode-locking operation. The passively pulsed EDFL operates stably at 1569.8 nm within a pumping power from 109 to 146 mW. The train of generated output pulses has a pulse width of 356 nm repeated at a fundamental frequency of 0.97 MHz. The average output power of 3.91 mW is obtained at a pump power of 146 mW, corresponding to 4.0 nJ pulse energy. The experimental result indicates that the proposed Sm2O3 saturable absorber is viable for the construction of a flexible and reliably stable mode-locked pulsed fiber laser operating in the 1.5 μm region.

FIrpic thin film as saturable absorber for passively Q-switched and mode-locked erbium-doped fiber laser

Abstract In this paper, we demonstrate the generation of passive all-fiber Q-switched and mode locked erbium doped fiber lasers (EDFLs) by using Bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato) iridium(III) (FIrpic) as a saturable absorber (SA). The material was prepared by solvent-casting technique and inserted between two fiber ferrules to form an SA. Then it was placed in an EDFL cavity. A stable Q-switched pulse laser operating at 1560.4 nm was achieved at a threshold pump power of 30 mW. The pulse repetition rate increased from 39.22 to 87.4 kHz and the pulse width decreased from 9.5 to 3.4 µs as the pump power was gradually increased from 30 to 208 mW. Meanwhile, a soliton self-starting mode-locking pulses at a wavelength of 1562.57 nm was achieved by adding an additional 52 m SMF to the EDFL cavity. The mode-locked laser had a repetition rate of 3.43 MHz and a pulse width of 120 ns within the pump power of 35–185 mW. The results suggest that FIrpic SA can be used to produce stable Q-switched and mode-locked fiber lasers at a low pump power.

Improved optical damage threshold graphene Oxide/SiO2 absorber fabricated by sol-gel technique for mode-locked erbium-doped fiber lasers

In this study, a mode-locked erbium-doped fiber (EDF) laser based on solid-state graphene oxide (GO)-doped sol-gel glass saturable absorber (SA) was designed and tested. The GO-based SA was fabricated for the first time using low-temperature sol-gel technique. Compared to traditional ways of fabricating SAs, the SAs-doped sol-gel glass showed outstanding advantages in terms of high optical damage threshold. The optical damage threshold of SAs-doped sol-gel glass reached as high as 50.69 GW/cm2. X-ray diffractometry (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and annex-energy spectrometry (EDS) identified the main component of prepared sol-gel glass as compact amorphous silicon dioxide. The application of GO-doped sol-gel glass to EDF laser yielded stable mode-locked fiber laser operation. The pulse duration, maximum output power and peak power were recorded as 582 fs, 17.58 mW and 1.30 kW, respectively. Overall, these data indicated that the proposed sol-gel method is promising for fabricating practical SAs for mode-locked fiber lasers.

Reduced graphene oxide as saturable absorbers for erbium-doped passively mode-locked fiber laser**Project supported by the Central University Special Fund for Basic Research and Operating Expenses, China (Grant No. GK201702005), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2017JM6091), the National Natural Science Foundation of China (Grant No. 61705183), and the Fundamental Research Funds for the Central Universities (Grant

We demonstrate a nanosecond mode-locked erbium-doped fiber laser (EDFL) based on a reduced graphene oxide (RGO) saturable absorber (SA). The RGO SA is prepared by depositing the graphene oxide (GO) on fluorine mica through thermal reduction of GO. A scanning electron microscope (SEM), Raman spectrometer, and x-ray photoelectron spectroscopy (XPS) are adopted to analyze the RGO characteristics. The results show that the reduction degree of graphene oxide is very high. By embedding the RGO SA into the EDFL cavity, a stable mode-locked fiber laser is achieved with a central wavelength of 1567.29 nm and repetition rate of 12.66 MHz. The maximum output power and the minimum pulse duration are measured to be 18.22 mW and 1.38 ns respectively. As far as we know, the maximum output power of 18.22 mW is higher than those of other nanosecond mode-locked oscillators reported. Such a nanosecond pulse duration and megahertz repetition rate make this mode-locked erbium-doped fiber laser a suitable seed oscillator for high-power applications and chirped pulse amplifications.

Highly stable mode-locked fiber laser with graphene oxide-coated side-polished D-shaped fiber saturable absorber

A highly stable mode-lock fiber laser with a thin film coating of graphene oxide (GO) nanoparticles on a D-shaped fiber is proposed and demonstrated. The GO-coated D-shaped fiber, which serves as the cavity's saturable absorber (SA), is fabricated by drop-casting GO nanoparticles on the smooth and consistently polished area of the D-shaped fiber made using a disk-polishing machine. Mode-locking is induced through the interaction of the evanescent field from the D-shaped fiber and GO nanoparticle layer. The cavity has a length of 12.5 m with a fundamental frequency of 16.5 MHz and operates in the anomalous dispersion regime. Stable soliton modelocking is obtained above a pump power of 76.6 mW, with a central lasing wavelength of 1555.7 nm and welldefined Kelly's sidebands. The generated pulses have a repetition rate of 16.5 MHz and pulse duration of 1.18 ps over a pump power range of 76.6 to 280.5 mW, with only minor fluctuations observed. A signal-to-noise ratio of 58.3 dB is computed, indicating a highly stable output. The proposed SA fabrication technique provides a simple, cost-effective, and consistent method of generating mode-locked pulses in fiber lasers. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).