Saturable Absorber Material Research Articles

L-band dual wavelength passively Q-switched erbium-doped fiber laser based on tellurium oxide nanoparticle saturable absorber

We experimentally demonstrate a compact dual wavelength passive Q-switched fiber laser created by an erbium-doped fiber active medium using tellurium oxide nanoparticles (TeO2 NPs) as a new saturable absorber (SA) material. The saturable absorption properties of the prepared TeO2 -PVA thin film were systematically measured, and the modulation depth and saturation intensity were 8% and 90 MW cm−2, respectively. By integrating the proposed SA in an all-fiber ring cavity, a dual wavelength laser with 1568.02 and 1569.09 nm wavelengths was observed without adding spectral filters or polarization maintaining fibers to control the suppression of the mode competition. A frequency difference of 0.13 THz was obtained located in the terahertz waveband. In the meantime, a stable Q-switched regime with a maximal pulse repetition rate of 45.7 kHz, a shortest pulse width of 2.69 µs and maximum pulse energy up to 39.4 nJ was attained at a maximum available pump power of 275 mW. The experimental setup using the TeO2 NP SA represents a step forward in terahertz development and nonlinear optics.

Passively Q-switched erbium-doped fiber laser utilizing tungsten oxide as a saturable absorber.

We demonstrated a passively $Q$Q-switched fiber laser utilizing tungsten oxide (${\rm WO_{3}}$WO3) thin film as a saturable absorber (SA). The ${\rm WO_{3} {\text -} SA}$WO3-SA was sandwiched as a polymer composite film between fiber ferrules in an erbium-doped fiber cavity. ${\rm WO_{3}}$WO3 exhibits high nonlinear optical response characterized by an appropriate modulation depth of 10% and a saturation intensity of ${100}\;{{\rm MW/cm}^2}$100MW/cm2. The fiber cavity starts to generate a stable pulse train whereby as the pump power increases from 45 to 165 mw, the repetition rate increases from 16.75 to 56.3 kHz, while the pulse width decreases from 13.8 to 4.3 µs. The $Q$Q-switched laser generated maximum pulse energy of 6.6 nJ obtained at 165 mW, which was the maximum pump power available by the used laser diode. This is, to the best of our knowledge, the first demonstration of a $Q$Q-switched fiber laser based on the ${\rm WO_{3} {\text -} SA}$WO3-SA, which could contribute as a new potential SA material in the field of pulsed fiber lasers.

Q-switched ytterbium-doped fiber laser based on evanescent field interaction with lutetium oxide.

We demonstrated lutetium oxide (${\textrm{Lu}_2}{\textrm{O}_3}$Lu2O3) deposited onto D-shaped fiber producing Q-switched ytterbium-doped fiber laser (YDFL) with an operating wavelength of 1037 nm. D-shaped fiber ${\textrm{Lu}_2}{\textrm{O}_3}$Lu2O3 as a saturable absorber (SA) was prepared using a polishing-wheel technique by polishing 2 times to establish an excellent evanescent field interaction between material and light on the surface of the polished region. The SA was deployed into a YDFL to generate Q-switching. The proposed D-shaped fiber ${\textrm{Lu}_2}{\textrm{O}_3}$Lu2O3 initiated pulses as short as 3.6 µs, with the highest repetition rate of 65.8 kHz. Stability of the SA is proven, as it produced stable pulses within the pump power of 99 to 133 mW with an SNR of 62.13 dB. Q-switched YDFL generates pulses with an output power of 0.93 to 1.99 mW and pulse energy of 17 to 30 nJ. We obtained a laser cavity with the optical-to-optical efficiency of 3.33%, which was the highest among D-shaped fiber-deposited SA materials in YDFL. Therefore, ${\textrm{Lu}_2}{\textrm{O}_3}$Lu2O3 deposited onto D-shaped fiber can be deployed as an SA in YDFL for a portable Q-switched laser source.

Q-Switched Fiber Laser at $1.5~\mu$ m Region Using Ti3AlC2 MAX Phase-Based Saturable Absorber

A Ti 3 AlC 2 MAX phase-based saturable absorber (SA) is successfully demonstrated to induce passive Q-switching in an erbium-doped fiber laser (EDFL) at the 1.5 μm region. The Ti 3 AlC 2 -PVA film is fabricated using the solution casting method and incorporated into the laser cavity which uses a 0.89 m long erbium doped fiber as the gain medium. Stable and self-starting Q-switched laser pulses are observed above a threshold pump power of 87.81 mW at a central wavelength of 1567.4 nm. The repetition rate is observed to increase from 24.07 kHz to 46.3 kHz, while the corresponding pulse width decreases from 5.0 μs to 0.99 μs over a pump power range of 108.9 mW to 244.5 mW. At the maximum pump power of 244.5 mW, the highest pulse energy of 102.7 nJ and the maximum output power of 4.75 mW are obtained. These findings demonstrated the feasibility of the Ti 3 AlC 2 MAX phase as an SA material with significant promise for photonic applications. This is also, to the best knowledge of the authors, the first report of a Ti 3 AlC 2 MAX phase-based SA for inducing passive Q-switching in an EDFL.

Zeolite templated carbon nanodots for broadband ultrafast pulsed fiber laser generation

Carbon nanodots (C-dots) with a uniform size of about 2 nm are synthesized via in situ pyrolysis of n-propylamine that is confined in the nanochannels of zeolite Linde Type A (LTA). The as-synthesized C-dots@LTA composite shows nonlinear optical saturable absorption properties in a broad wavelength band and can be used as saturable absorber (SA) to generate ultrafast pulsed fiber lasers. By inserting a zeolite LTA single crystal hosting C-dots into the fiber laser cavity, mode-locked fiber lasers with long-term operation stability at 1.5 μm and 1 μm are achieved. These results show that the C-dots@LTA are a promising SA material for ultrafast pulsed fiber laser generation in a broad wavelength band. To the best of our knowledge, this is the first demonstration of a C-dots@LTA-based mode-locked fiber laser.

Oxidation-Resistant Black Phosphorus Enable Highly Ambient-Stable Ultrafast Pulse Generation at a 2 μm Tm/Ho-Doped Fiber Laser.

Black phosphorus (BP) ranks among the most promising saturable absorber materials for ultrafast pulse generations at 2 μm. However, the easy-to-degrade characteristic of BP seriously limits the long-term operation of ultrafast fiber lasers and hence becomes a bottleneck for its relevant practical applications. In this paper, a modified electrochemical delamination exfoliation process was explored to produce high-performance, large-size, and oxidation-resistant BP nanosheets, where BP nanosheets in high yield with evenly coated tetra-n-butyl-ammonium organics by precisely controlling the intercalation chemistry can be obtained. A mode-locked Tm/Ho co-doped fiber laser with high temporal stability and long-term operation capability was demonstrated based on the innovatively fabricated BP saturable absorber. The self-starting mode-locking operation featuring a high signal-to-noise ratio of 58 dB and long-term stability has been verified for at least 3 weeks, which indicates the successful passivation of the employed synthesis method. These results fully indicated that passivated BP is an efficient candidate in a 2 μm range ultrafast photonic field, which will promote the ultrafast optical application of BP and also other infrared photonic and photoelectronic devices.

Mode-locked pulse generation in erbium-doped fiber laser by evanescent field interaction with reduced graphene oxide-titanium dioxide nanohybrid

In this work, a new nanohybrid saturable absorber (SA) is successfully fabricated from reduced graphene oxide (rGO) nanosheets and titanium dioxide (TiO2) nanoparticles. The nanohybrid material is synthesized using the simple and inexpensive hydrothermal technique. The SA is fabricated by depositing the nanohybrid solution onto a D-shaped fiber in an erbium-doped fiber (EDF) laser cavity. The evanescent wave interaction between the incident light and rGO-TiO2 nanohybrid material induces mode-locking in the EDF laser at the threshold pump power of 100.80 mW. A stable soliton pulse with a center wavelength of 1560.45 nm and 3-dB bandwidth of 2.47 nm is obtained. The generated pulses have a repetition rate and pulse width of 11.19 MHz and 1.05 ps at the highest pump power of 268.10 mW. The proposed rGO-TiO2 nanohybrid of this work is a promising SA material for generating mode-locking in an EDF laser for optical modulation applications.

Large optical nonlinearity of ITO/Ag/ITO sandwiches based on Z-scan measurement.

Indium tin oxide (ITO)-based sandwich structures with the insertion of silver (ITO/Ag/ITO) show large nonlinear optical enhancement of both nonlinear refraction and saturable absorption. Here optical nonlinearity is measured using a Z-scan experiment with a 1310nm pulsed laser at normal incidence. The nonlinear refractive index (n2=15.43×10-16 m2/W) for an ITO/Ag/ITO sandwich with a 14nm silver interlayer and the nonlinear absorption coefficient (β=-648×10-11 m/W) for an ITO/Ag/ITO sandwich with a 10nm silver interlayer are about 18 and 16 times greater than that of a single-layer ITO, respectively. Meanwhile, a large figure of merit and modulation depth values hinted that ITO/Ag/ITO sandwiches are promising saturable absorber materials to switch continuous laser waves into laser pulses. These novel nonlinear optical properties make ITO/Ag/ITO sandwiches a promising candidate for all-optical modulation devices at optical communication wavelengths.

Versatile Mode-Locked Operations in an Er-Doped Fiber Laser with a Film-Type Indium Tin Oxide Saturable Absorber.

We demonstrate the generation of versatile mode-locked operations in an Er-doped fiber laser with an indium tin oxide (ITO) saturable absorber (SA). As an epsilon-near-zero material, ITO has been only used to fashion a mode-locked fiber laser as an ITO nanoparticle-polyvinyl alcohol SA. However, this type of SA cannot work at high power or ensure that the SA materials can be transmitted by the light. Thus, we covered the end face of a fiber with a uniform ITO film using the radio frequency magnetron sputtering technology to fabricate a novel ITO SA. Using this new type of SA, single-wavelength pulses, dual-wavelength pulses, and triple-wavelength multi-pulses were achieved easily. The pulse durations of these mode-locked operations were 1.67, 6.91, and 1 ns, respectively. At the dual-wavelength mode-locked state, the fiber laser could achieve an output power of 2.91 mW and a pulse energy of 1.48 nJ. This study reveals that such a proposed film-type ITO SA has excellent nonlinear absorption properties, which can promote the application of ITO film for ultrafast photonics.

Fe3O4 nanoparticles as the saturable absorber for a mode-locked fiber laser at 1558 nm

We demonstrated a mode-locked erbium doped fiber laser (EDFL) operating at 1558 nm by exploiting ferroferric-oxide nanoparticles (FONPs) as the saturable absorber (SA) material. FONPs, with an average diameter of ~20 nm, were prepared by a thermal decomposition method, then mixed with sodium carboxymethylcelluose to form an FONP film. The FONP SA was fabricated through a sandwiched FONP film between two fiber connectors. By inserting the FONPs SA into an EDFL cavity pumped by a 980 nm laser diode, stable passive mode-locking was achieved with a threshold pump power of ~120 mW. The obtained mode-locked laser had a central wavelength of ~1558 nm, a spectral bandwidth of ~0.8 nm, a pulse width of ~4.35 ns, and a repetition rate of ~37.32 MHz. Furthermore, a maximum average power of ~17 mW was obtained for a pump power of 340 mW. To the best of our knowledge, this is the first time that it has been demonstrated that FONPs can be used for constructing mode-locked fiber lasers.

Simulation of saturable absorber material length effect on characteristics of Passive Q-switching and Stokes pulses

The effect of saturable absorber material length on characteristics of passive Q-switching and Stokes pulses has been simulated. A software computer program has been based for solving a rate equations model numerically by Rung –Kutta- Fehalberg method. (Nd:GdVO4), (Cr+4:YAG), and Ba(NO3)2 are used as a active medium, saturable absorber material, and Raman medium respectively. The study shows that an decrease in pulse duration for both pulses (passive Q- switching and Stocks) with saturable absorber material length increases. While the energy and the power are increase with saturable absorber material length increases.

MoTe2 Saturable Absorber With High Modulation Depth for Erbium-Doped Fiber Laser

Transition metal dichalcogenides have recently been considered the candidates for saturable absorption materials due to their advantages in both electronic and optoelectronic. Compared with MoS2 and WS2, MoTe2 exhibits smaller bandgap. As a result, MoTe2 owns inherent advantages in the near-infrared applications. In this paper, the MoTe2 saturable absorber (SA) were prepared by the magnetron sputtering deposition method. Owing to the enhanced light-materials interaction between MoTe2 and evanescent field from the microfiber, the modulation depth of the MoTe2 SA was up to 26.97%. By assembling the MoTe2 SA into the erbium-doped fiber laser, the mode-locked fiber laser at 1.5 μm was demonstrated. The pulse duration of 111.9 fs was proved to be the shortest in the fiber lasers based on transition metal dichalcogenides. Moreover, the mode-locked fiber laser maintains the long-term stability. Our results suggest that the proposed MoTe2 SA is promising for the ultrashort pulse generation and stable system operation.

Fs-laser-written thulium waveguide lasers Q-switched by graphene and MoS2.

We report the generation of mid-infrared (~2 µm) high repetition rate (MHz) sub-100 ns pulses in buried thulium-doped monoclinic double tungstate crystalline waveguide lasers using two-dimensional saturable absorber materials, graphene and MoS2. The waveguide (propagation losses of ~1 dB/cm) was micro-fabricated by means of ultrafast femtosecond laser writing. In the continuous-wave regime, the waveguide laser generated 247 mW at 1849.6 nm with a slope efficiency of 48.7%. The laser operated at the fundamental transverse mode with a linearly polarized output. With graphene as a saturable absorber, the pulse characteristics were 88 ns / 18 nJ (duration / energy) at a repetition rate of 1.39 MHz. Even shorter pulses of 66 ns were achieved with MoS2. Graphene and MoS2 are therefore promising for high repetition rate nanosecond Q-switched infrared waveguide lasers.

Nonlinear optical properties of MoS2-WS2 heterostructure in fiber lasers.

As a saturable absorption material, the heterostructure with the van der Waals structure has been paid much attention in material science. In general, the heterogeneous combination is able to neutralize, or even exceed, the individual material's advantages in some aspects. In this paper, which describes the magnetron sputtering deposition method, the tapered fiber is coated by the MoS2-WS2 heterostructure, and the MoS2-WS2 heterostructure saturable absorber (SA) is fabricated. The modulation depth of the prepared MoS2-WS2 heterostructure SA is measured to be 19.12%. Besides, the theoretical calculations for the band gap and carrier mobility of the MoS2-WS2 heterostructure are provided. By employing the prepared SA, a stable and passively erbium-doped fiber laser is implemented. The generated pulse duration of 154 fs is certified to be the shortest among all fiber lasers based on transition mental dichalcogenides. Results in this paper provide the new direction for the fabrication of ultrafast photon modulation devices.

Large aspect ratio gold nanorods (LAR-GNRs) for mid-infrared pulse generation with a tunable wavelength near 3 μm.

We report a tunable passively Q-switched fiber laser at the wavelengths near 3 μm, using large aspect ratio gold nanorods (LAR-GNRs) as a saturable absorber (SA) for the first time. The GNRs with a large average aspect ratio of up to ~20 were prepared using the seed-mediated growth method, which yielded a strong absorption band of 2.2-3 μm with a peak at ~2600 nm, stemming from longitudinal surface plasmon resonance (SPR). The corresponding nonlinear absorption was characterized using 2.87 μm ultrafast pulses, giving the modulation depth of 8.89%, saturation intensity of 14.9 MW/cm2, and nonsaturation loss of 39.9%. When introducing the material into a tunable Ho3+/Pr3+ codoped ZBLAN fiber laser as a SA, stable Q-switched pulses with a tunable wavelength within 2.83-2.88 μm were achieved. The largest output power of 30.8 mW, repetition rate of 78.12 kHz, and narrowest pulse width of 2.18 μs were simultaneously attained when tuned to ~2.865 μm at the pump power of 307.2 mW, while the largest pulse energy of 0.48 μJ was obtained at the longest tuning edge of 2.88 μm. Our work indicates that LAR-GNRs are a type of versatile broadband SA material available for the mid-infrared region.

Compact solid-state waveguide lasers operating in the pulsed regime: a review [Invited

Over the last years, there has been tremendous progress with compact pulsed lasers based on various solid-state gain media, such as crystals and glasses doped with laser-active ions. With the integration of increasingly diverse saturable absorber materials, these small sources are capable of delivering stable pulses with durations as short as femtoseconds and repetition rates exceeding 10 GHz. These promising sources are known as solid-state waveguide lasers, which have become synonymous with miniaturization, integration, and functionality. This article overviews the progress in the development of passively Q-switched and mode-locked solid-state waveguide lasers employing diverse saturable absorbers. The most commonly used laser configurations, state-of-the-art waveguide fabrication techniques, and experimental demonstrations of pulsed waveguide lasers are summarized and reviewed. Selected well-noted topics, which may shape the future directions in this field, are also presented.

Diode-Pumped Solid-State Q-Switched Laser with Rhenium Diselenide as Saturable Absorber

We report a solid-state passively Q-switched Nd:YVO4 laser adopting rhenium diselenide (ReSe2) as saturable absorber (SA) materials. ReSe2 belongs to a type of transition metal dichalcogenides (TMDs) materials and it has the weak-layered dependent feature beneficial for the preparation of few-layer materials. The few-layer ReSe2 was prepared by ultrasonic exfoliation method. Using a power-dependent transmission experiment, its modulation depth and saturation intensity were measured to be 1.89% and 6.37 MW/cm2. Pumped by diode laser and based on few-layer ReSe2 SA, the Q-switched Nd:YVO4 laser obtained the shortest Q-switched pulse width of 682 ns with the highest repetition rate of 84.16 kHz. The maximum average output power was 125 mW with the slope efficiency of 17.27%. Our experiment, to the best of our knowledge, is the first demonstration that used ReSe2 as SA materials in an all-solid-state laser. The results show that the few-layer ReSe2 owns the nonlinear saturable absorption properties and it has the capacity to act as SA in an all-solid-state laser.

Femtosecond Tm–Ho co-doped fiber laser using a bulk-structured Bi2Se3 topological insulator**Project supported by the National Research Foundation of Korea (NRF) Grant Funded by the Korea Government (MSIT), Republic of Korea (Grant No. NRF-2018R1A2B6001641), Ministry of Science and ICT (MSIT) under the Information Technology Research Center (ITRC) Support Program (Grant No. IITP-2018-2015-0-00385), and supervised by the Institute for Information and Communications

We experimentally demonstrate a femtosecond mode-locked thulium–holmium (Tm–Ho) co-doped fiber laser incorporating a saturable absorber (SA) based on a bulk-structured bismuth selenide (Bi2Se3) topological insulator (TI). The SA was prepared by depositing a mechanically exfoliated Bi2Se3 TI layer onto a side-polished optical fiber platform. Unlike high-quality nano-structured Bi2Se3 TI-based SA, bulk-structured Bi2Se3 with non-negligible oxidation was used as a saturable absorption material for this experimental demonstration due to its easy fabrication process. The saturation power and modulation depth of the prepared SA were measured to be ∼28.6 W and ∼13.4%, respectively. By incorporating the prepared SA into a Tm–Ho co-doped fiber ring cavity, stable soliton pulses with a temporal width of ∼853 fs could be generated at 1912.12 nm. The 3-dB bandwidth of the mode-locked pulse was measured to be ∼4.87 nm. This experimental demonstration reaffirms that Bi2Se3 is a superb base material for mid-infrared passive mode-locking even under oxidation.

Antimonene: a long-term stable two-dimensional saturable absorption material under ambient conditions for the mid-infrared spectral region

We experimentally demonstrate a long-term stable two-dimensional saturable absorption material under ambient conditions—multi-layer antimonene feasible for the mid-infrared spectral region—for the first time to our knowledge. The multi-layer antimonene material prepared using a liquid-phase exfoliation method was coated on a quartz/CaF2 for characterizations and an Au mirror as a reflection-type saturable absorber (SA) device. It has a modulation depth of 10.5%, a saturation peak intensity of 0.26 GW/cm2, and a non-saturation loss of 19.1% measured at 2868.0 nm using the typical power-dependent method. By introducing the SA device into a linear-cavity Ho3+/Pr3+-codoped fluoride fiber laser at 2865.0 nm, stable Q-switched pulses were obtained. It generated a maximum output power of 112.3 mW and pulse energy of 0.72 μJ, while the shortest pulse duration and largest repetition rate were 1.74 μs and 156.2 kHz, respectively. The long-term stability of the SA device was also checked using the same laser setup within 28 days. The results indicate that multi-layer antimonene is a type of promising long-term stable SA material under ambient conditions that can be applied in the mid-infrared spectral region.

Mechanism of dissipative-soliton-resonance generation in fiber laser mode-locked by real saturable absorber.

Generation of dissipative soliton resonance (DSR) is numerically investigated in an all-normal-dispersion Yb-doped fiber laser mode-locked by a real saturable absorber (SA). In the simulation model, the SA includes both the saturable absorption and reverse saturable absorption (RSA) effects. It is found that the RSA effect induced by the SA material itself plays a dominant role in generating the DSR pulses. We also systematically analyze the influence of key SA parameters on the evolution of DSR pulses in the cavity. Our simulation results not only offer insight into the underlying mechanism of DSR generation in mode-locked fiber lasers by means of real SAs, but also provide a guideline for engineering SA parameters to generate optical pulses with the highest possible energy.