Passively Q-switched 0.1-mJ fiber laser system at 1.53 mum

Frontier and Hot Topics of Pulsed Fiber Lasers via CiteSpace Scientometric Analysis: Passively Mode-Locked Fiber Lasers with Real Saturable Absorbers Based on Two-Dimensional Materials

Pulsed fiber lasers, with high peak power and narrow pulse widths, have been proven to be an important tool for a variety of fields of application. In this work, frontier and hot topics in pulsed fiber lasers were analyzed with 11,064 articles. Benefitting from the scientometric analysis capabilities of CiteSpace, the analysis found that passively mode-locked fiber lasers with saturable absorbers (SAs) based on two-dimensional (2D) materials have become a hot research topic in the field of pulsed fiber lasers due to the advantages of self-starting operation, high stability, and good compatibility. The excellent nonlinear optical properties exhibited by 2D materials at nanometer-scale thicknesses have become a particularly popular research topic; the research has paved the way for exploring its wider applications. We summarize the performance of several typical 2D materials in ultrafast fiber lasers, such as graphene, topological insulators (TIs), transition metal dichalcogenides (TMDs), and black phosphorus (BP). Meanwhile, we review and analyze the direction of the development of 2D SAs for ultrafast fiber lasers.

Nanosecond Q-switched laser with PEDOT: PSS saturable absorber

We demonstrate deployment of the nonlinear saturable absorption property of the organic material poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) for pulse generation in the near-infrared region. The saturable absorber (SA) film was made using a straightforward process of depositing a layer of the PEDOT: PSS material onto a polyvinyl alcohol (PVA) film. The prepared SA was inserted into an erbium-doped fiber laser cavity as a Q-switcher to produce laser pulses with a maximum pulse rate of 92.75 kHz, minimum pulse duration of 912 ns, and highest pulse energy of 222.83 nJ. Results showed that PEDOT: PSS/PVA SA could become a promising SA for various laser applications. To our knowledge, this is the first time that PEDOT: PSS/PVA has been utilized as a SA to produce a stable Q-switched laser in 1.55 µm.

Wavelength-tunable Q-switched erbium-doped fiber laser based on a digital micromirror device

A wavelength-tunable Q-switched erbium-doped fiber laser based on a digital micromirror device (DMD) is experimentally demonstrated. The Q-switched pulses are generated by incorporating a saturable absorption device made of graphene oxide. Stable Q-switched pulses at 1.5 µm band are obtained at a low threshold of 20 mW, corresponding to the pulse width of 7.1 µs and the repetition rate of 43.3 kHz. The maximum output power and the maximum pulse energy of the Q-switched pulses are 260.1 µW and 3.97 nJ, respectively. By controlling the DMD, the center wavelength of the Q-switched pulses can be tuned from 1528.2 to 1559.3 nm, with a tuning range of about 31 nm. The fine tunable accuracy can reach 0.08 nm by precisely controlling the DMD. Combining the filtering characteristics of the DMD with the saturable absorption characteristics of nanomaterials, the Q-switched laser with tunable wavelength is realized, which, we believe, is reported for the first time and has broad application prospects.

MXenes: synthesis, incorporation, and applications in ultrafast lasers

The rapid expansion of nanotechnology and material science prompts two-dimensional (2D) materials to be extensively used in biomedicine, optoelectronic devices, and ultrafast photonics. Owing to the broadband operation, ultrafast recovery time, and saturable absorption properties, 2D materials become the promising candidates for being saturable absorbers in ultrafast pulsed lasers. In recent years, the novel 2D MXene materials have occupied the forefront due to their superior optical and electronic, as well as mechanical and chemical properties. Herein, we introduce the fabrication methods of MXenes, incorporation methods of combining 2D materials with laser cavities, and applications of ultrafast pulsed lasers based on MXenes. Firstly, top-down and bottom-up approaches are two types of fabrication methods, where top-down way mainly contains acid etching and the chief way of bottom-up method is chemical vapor deposition. In addition to these two typical ones, other methods are also discussed. Then we summarize the advantages and drawbacks of these approaches. Besides, commonly used incorporation methods, such as sandwich structure, optical deposition, as well as coupling with D-shaped, tapered, and photonic crystal fibers are reviewed. We also discuss their merits, defects, and conditions of selecting different methods. Moreover, we introduce the state of the art of ultrafast pulsed lasers based on MXenes at different wavelengths and highlight some excellent output performance. Ultimately, the outlook for improving fabrication methods and applications of MXene-based ultrafast lasers is presented.

Recent Progress of Two-Dimensional Materials for Ultrafast Photonics

Owing to their extraordinary physical and chemical properties, two-dimensional (2D) materials have aroused extensive attention and have been widely used in photonic and optoelectronic devices, catalytic reactions, and biomedicine. In particular, 2D materials possess a unique bandgap structure and nonlinear optical properties, which can be used as saturable absorbers in ultrafast lasers. Here, we mainly review the top-down and bottom-up methods for preparing 2D materials, such as graphene, topological insulators, transition metal dichalcogenides, black phosphorus, and MXenes. Then, we focus on the ultrafast applications of 2D materials at the typical operating wavelengths of 1, 1.5, 2, and 3 μm. The key parameters and output performance of ultrafast pulsed lasers based on 2D materials are discussed. Furthermore, an outlook regarding the fabrication methods and the development of 2D materials in ultrafast photonics is also presented.

Sub-hundred nanosecond pulse generation from a black phosphorus Q-switched Er-doped fiber laser

Black phosphorus (BP), a prosperous two-dimensional optoelectronic material, has been deeply developed for various optoelectronics applications. Here, we demonstrate a sub-hundred nanosecond passively Q-switched Er-doped all-fiber laser with BP as the saturable absorber (SA). The BP-SA is fabricated by a controllable optical deposition technique. To achieve the sub-hundred nanosecond Q-switching output, we deliberately enlarge the modulation depth of the BP-SA by suitably increasing the time and laser power of the optical deposition and shortening the laser cavity length with an integrated multifunctional component. A stable Q-switched pulse train was obtained with a pulse duration as narrow as 91 ns, and the Q-switched lasing characteristics based on the BP-SA have also been investigated and discussed. The experimental results indicate that the BP material can be employed as an effective SA for the nanosecond pulse generation.

Passively Q-switched fiber lasers based on pure water as the saturable absorber

We propose and demonstrate a passively Q-switched Er-doped fiber laser based on pure water as the saturable absorber (SA). The SA is made of two optical ferrules matched with a cannula, and the gap between the end-facets is filled with pure water. The nonlinear response of this SA has been characterized, and stable Q-switching operation at 1558.03 nm has been achieved. The maximum output power is 21.1 mW with 65.0 kHz repetition rate. The duration is 1.44 μs, and the pulse energy reaches 324.8 nJ. To the best of our knowledge, this is the first demonstration of the passively Q-switched laser with pure water as the SA. It provides further evidence of the possibility of liquid as an effective SA for pulsed lasers.

Ultrashort pulse generation with an erbium-doped fiber laser ring cavity based on a copper oxide saturable absorber

A soliton mode-locked erbium-doped fiber (EDF) laser has been experimentally demonstrated using copper oxide (CuO) thin film as a saturable absorber (SA). The dispersion of the EDF cavity including the CuO-SA was balanced by a suitable length of single-mode fiber (SMF). The fabricated CuO-SA has 3.5% modulation depth and 3.3  MW/cm² saturation intensity. The mode-locked train pulses have 1.7 ps pulse width and 983 kHz repetition rate, while the pulse energy and output power are 1.29 nJ and 1.27 mW, respectively, at maximum pump power of 159 mW. These results indicate that the CuO thin film is a good SA candidate for a fiber laser operating at a low pump power. To the best of our knowledge, this is the first demonstration of a CuO-SA-based mode-locked fiber laser.

Stable passively Q-switched erbium-doped fiber laser incorporating a PbS quantum dots polystyrene composite film based saturable absorber

We demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) using PbS quantum dots in polystyrene films (QDPFs) as saturable absorbers (SAs). Compared to other SAs, PbS QDPFs have advantages of broad absorption range, high quantum yield, low cost, and facile preparation. We have successfully generated stable Q-switched pulses with an average output power of 40.19 mW, a single pulse energy of 586.1 nJ, a repetition rate of 68.04 kHz, a pulse width of 3.9 μs, and a signal-to-noise ratio of 50.5 dB under 660 mW pump power. The output of the EDFL has been monitored for 5 consecutive hours under laboratory conditions to show stable operation of the laser system.

Investigation on the effect of output mirror transmission in WS2-based red-light passively Q-switched Pr:ZBLAN all-fiber lasers

We report the experimental investigation of visible passively Q-switched Pr³⁺-doped all-fiber lasers with tungsten disulfide (WS₂) saturable absorber, where red-light short-pulse generations from different output mirror transmissions are systemically characterized. The proposed simple and compact all-fiber linear cavity was constructed by a fiber-pigtail-based blue laser-diode pump, a Pr³⁺-doped fluorozirconate glass active fiber, and the fiber end-facet mirrors. Integrating a free-standing layered WS₂ film into the laser cavity initiated the Q-switching operation. Stable microsecond-duration output pulses with kilohertz repetition rates are achieved, corresponding to a few mW/nJ average output power and single-pulse energy. The comparisons on red-light Q-switched output parameters for output transmissions of both ∼40% and ∼80% are performed. This work could provide a useful guideline to manipulate the output performance of visible pulsed all-fiber lasers for various practical applications.

Magnesium diboride (MgB2) as a saturable absorber for a ytterbium-doped Q-switched fiber laser

Magnesium diboride (MgB₂) is a well-known superconductor at temperatures below 39 K. At higher temperatures, it behaves as a lossy material. In this paper, we examine the performance of MgB₂ nano-particles as saturable absorber in a ytterbium-doped fiber ring laser at room temperature: we show that the nano-particles can produce pulses between 200 and 1700 ns. The dynamics of the saturable absorber are both examined as a stand-alone saturable absorber and in combination with an acousto-optic modulator. We believe, to the best of our knowledge, that this is the first time that MgB₂ is used as a saturable absorber in a Q-switched laser.

Aluminum oxide nanoparticles as saturable absorber for C-band passively Q-switched fiber laser

We report on aluminum oxide nanoparticles (Al₂O₃ NPs) as a saturable absorber (SA) for passively Q-switched erbium-doped fiber laser (EDFL) operating at a wavelength of 1560.6 nm within the C-band region. A thin film of Al₂O₃-SA was prepared using polyvinyl alcohol (PVA) as a host polymer. Very stable pulses with a 57.8 KHz repetition rate and 5.6 μs pulse width at a threshold pump power of 158 mW were obtained. A 2.8 μs pulse width, 81 kHz pulse repetition rate, with maximum pulse energy of 56.7 nJ at a diode pump power of 330 mW were recorded. To the best of the authors' knowledge, this is the first time that a Al₂O₃-based SA has been used to generate a Q-switched EDFL.

Tunable passively Q-switched thulium-fluoride fiber laser in the S+/S band (1450.0 to 1512.0 nm) region using a single-walled carbon-nanotube-based saturable absorber

A tunable passively Q-switched for S+/S band thulium-fluoride fiber (TFF) laser using single-walled carbon nanotubes as a saturable absorber is proposed and demonstrated. The tunability of the proposed laser covers a wavelength region of 1450.0-1512.0 nm, with a range of 62.0 nm. Stable Q-switched operation can be obtained at a pump power of 115.7-229.9 mW at 1492.0 nm. The resulting pulses have a measured repetition rate and pulse width of 12.0-36.4 kHz and 6.2-3.6 μs, respectively. The maximum pulse energy that was achieved in this experiment is 122.8 nJ. To the author's knowledge, this is the first reported tunable passively Q-switched TFF laser that covers the S+/S region that has been demonstrated.

Stable nanosecond passively Q-switched all-fiber erbium-doped laser with a 45° tilted fiber grating

Nanosecond passive Q-switching generation from an all-fiber erbium-doped laser with a UV inscribed 45° tilted fiber grating (TFG) is systematically demonstrated. The 45° TFG is employed as a polarizer together with two polarization controllers (PCs) to realize nonlinear polarization rotation (NPR). Because of the NPR effect, stable Q-switched pulses with an average output power of 17.5 mW, a single pulse energy of 72.7 nJ, a repetition rate of 241 kHz, a pulse width of 466 ns, and a signal to noise ratio (SNR) of 58.8 dB are obtained with 600 mW pump power. To the best of our knowledge, the SNR is the highest among all-fiber passively Q-switched erbium-doped laser. The stability of this erbium-doped fiber laser (EDFL) is also examined by monitoring the laser consecutively for 5 h under laboratory conditions.

Ytterbium-doped Q-switched fiber laser based upon manganese dioxide (MnO2) saturable absorber

Manganese dioxide (MnO₂) is an abundant material that is widely used in many devices, such as alkaline batteries. At infrared frequencies, MnO₂ is lossy and strongly absorbs light. These characteristics make MnO₂ a potential candidate as a low-cost saturable absorber in Q-switched lasers. In this paper, we examine the performance of MnO₂ as a saturable absorber in an ytterbium-doped Q-switched fiber laser: we show that it can produce pulses with durations ranging from 300 to 1800 ns.

High-damage-resistant tungsten disulfide saturable absorber mirror for passively Q-switched fiber laser

In this paper, we demonstrate a high-damage-resistant tungsten disulfide saturable absorber mirror (WS₂-SAM) fabricated by magnetron sputtering technique. The WS₂-SAM has an all-fiber-integrated configuration and high-damage-resistant merit because the WS₂ layer is protected by gold film so as to avoid being oxidized and destroyed at high pump power. Employing the WS₂-SAM in an Erbium-doped fiber laser (EDFL) with linear cavity, the stable Q-switching operation is achieved at central wavelength of 1560 nm, with the repetition rates ranging from 29.5 kHz to 367.8 kHz and the pulse duration ranging from 1.269 μs to 154.9 ns. For the condition of the maximum pump power of 600 mW, the WS₂-SAM still works stably with an output power of 25.2 mW, pulse energy of 68.5 nJ, and signal-noise-ratio of 42 dB. The proposed WS₂-SAM configuration provides a promising solution for advanced pulsed fiber lasers with the characteristics of high damage resistance, high output energy, and wide tunable frequency.

Tunable Q-switched fiber laser using zinc oxide nanoparticles as a saturable absorber

Nanomaterials have ignited new interest due to their distinctive electronic, mechanical, and optical properties. Zinc oxide nanostructures are fabricated into thin film and then inserted between two fiber ferrules to act as a saturable absorber (SA). The modulation depth and insertion loss of the SA are 5% and 3.5 dB, respectively. When the ZnO-SA is incorporated into the laser cavity, a stable Q-switched pulse tunable from 1536 to 1586 nm (50 nm range) with pulse energy up to 46 nJ was observed. Our result suggests that ZnO is a promising broadband SA to generate passively Q-switched fiber lasers.

Passively Q-switched Er3+-doped fiber lasers using colloidal PbS quantum dot saturable absorber

We report on the demonstration of a passively Q-switched 1.55 µm fiber laser utilizing a colloidal PbS quantum dot (QD) thin film as a saturable absorber. Colloidal PbS QD films have several features that are advantageous in passively Q-switched fiber laser operation, including a large operation wavelength range, cost-effectiveness, and a low saturable absorption intensity. We conducted thorough material and optical studies to verify the advantages of PbS QDs in Q-switched laser operation and successfully generated 801 nJ pulses with a 24.2 kHz repetition rate. To the best of our knowledge, the developed Q-switched fiber laser is the first based on colloidal PbS QDs.

Finite-difference time-domain methods to analyze ytterbium-doped Q-switched fiber lasers

Q-switched lasers are widely used in material processing, laser ranging, medicine, and nonlinear optics--in particular, Q-switched lasers in optical fibers are important since they cannot only generate high peak powers but can also concentrate high peak powers in small areas. In this paper, we present new finite-difference time-domain methods that analyze the dynamics of Q-switched fiber lasers, which are more flexible and robust than previous methods. We extend the method to analyze fiber ring lasers and compare the results with our experiments.

Passively Q-switched erbium-doped fiber laser at C-band region based on WS₂ saturable absorber

We demonstrate a Q-switched erbium-doped fiber laser using tungsten disulfide (WS₂) as a saturable absorber. The WS₂ is deposited onto fiber ferrules using a drop-casting method. Passive Q-switched pulses operating in the C-band region with a central wavelength of 1560.7 nm are successfully generated by a tunable pulse repetition rate ranging from 27.2 to 84.8 kHz when pump power is increased from 40 to 220 mW. At the same time, the pulse width decreases from a maximum value of 3.84 μs to a minimum value of 1.44 μs. The signal-to-noise ratio gives a stable value of 43.7 dB. The modulation depth and saturation intensity are measured to be 0.99% and 36.2  MW/cm², respectively.

Q-switched fiber laser based on transition metal dichalcogenides MoS(2), MoSe(2), WS(2), and WSe(2)

In this paper, we report 4 different saturable absorbers based on 4 transition metal dichalcogenides (MoS(2), MoSe(2), WS(2), WSe(2)) and utilize them to Q-switch a ring-cavity fiber laser with identical cavity configuration. It is found that MoSe(2) exhibits highest modulation depth with similar preparation process among four saturable absorbers. Q-switching operation performance is compared from the aspects of RF spectrum, optical spectrum, repetition rate and pulse duration. WS(2) Q-switched fiber laser generates the most stable pulse trains compared to other 3 fiber lasers. These results demonstrate the feasibility of TMDs to Q-switch fiber laser effectively and provide a meaningful reference for further research in nonlinear fiber optics with these TMDs materials.

High power L-band mode-locked fiber laser based on topological insulator saturable absorber

We demonstrate a passive mode-locked Er:Yb doped double-clad fiber laser using a microfiber-based topological insulator (Bi(2)Se(3)) saturable absorber (TISA). By optimizing the cavity loss and output coupling ratio, the mode-locked fiber laser can operate in L-band with high average output power. With the highest pump power of 5 W, 91st harmonic mode locking of soliton bunches with average output power of 308 mW was obtained. This is the first report that the TISA based erbium-doped fiber laser operating above 1.6 μm and is also the highest output power yet reported in TISA based passive mode-locked fiber laser.

Actively Q-switched ytterbium-doped fiber laser by an all-optical Q-switcher based on graphene saturable absorber

We demonstrate an all-optical Q-switcher based on graphene saturable absorber (GSA). Due to the cross absorption modulation (XAM) effect in graphene, we can change the transmittance of signal light periodically by introducing a train of laser pulses into graphene. This allows controlling the Q-factor of the cavity. This Q-switcher has many advantages such as all-fiber structure, all-optical modulation, broadband applications. With this Q-switcher, we have successfully fabricated an actively Q-switched ytterbium-doped fiber laser. The pulse repetition rate can be tuned from 30.32 kHz to 101.29 kHz. What's more, synchronization of the Q-switched laser pulses and modulation laser pulses can be realized, which has many potential applications such as nonlinear frequency conversion, multi-color pump probe spectroscopy and Raman scattering spectroscopy.

Passive Q-switching of an all-fiber laser induced by the Kerr effect of multimode interference

A novel passively Q-switched all-fiber laser using a single mode-multimode-single mode fiber device as the saturable absorber based on the Kerr effect of multimode interference is reported. Stable Q-switched operation of an Er(3+)/Yb(3+) co-doped fiber laser at 1559.5 nm was obtained at a pump power range of 190-510 mW with the repetition rate varying from 14.1 kHz to 35.2 kHz and the pulse duration ranging from 5.69 μs to 3.86 μs. A maximum pulse energy of 0.8 μJ at an average output power of 27.6 mW was achieved. This demonstrates a new modulation mechanism for realizing Q-switched all-fiber laser sources.

Passively Q-switched nanosecond erbium-doped fiber laser with MoS(2) saturable absorber

Passively Q-switched nanosecond pulsed erbium-doped fiber laser based on MoS(2) saturable absorber (SA) is experimentally demonstrated. The high quality MoS(2) SA deposited on the broadband high-reflectivity mirror with a large modulation depth of 9% was prepared by pulsed laser deposition method. By inserting the MoS(2) SA into an erbium-doped fiber laser, stable Q-switched operation can be achieved with the shortest pulse width of 660 ns, the maximum pulse energy up to 152 nJ and pulse repetition rates varying from 116 to 131 kHz. The experimental results further verify that MoS(2) possesses the potential advantage for stable Q-switched pulse generation at 1.5 μm.

1.06 μm Q-switched ytterbium-doped fiber laser using few-layer topological insulator Bi₂Se₃ as a saturable absorber

Passive Q-switching of an ytterbium-doped fiber (YDF) laser with few-layer topological insulator (TI) is, to the best of our knowledge, experimentally demonstrated for the first time. The few-layer TI: Bi₂Se₃ (2-4 layer thickness) is firstly fabricated by the liquid-phase exfoliation method, and has a low saturable optical intensity of 53 MW/cm² measured by the Z-scan technique. The optical deposition technique is used to induce the few-layer TI in the solution onto a fiber ferrule for successfully constructing the fiber-integrated TI-based saturable absorber (SA). By inserting this SA into the YDF laser cavity, stable Q-switching operation at 1.06 μm is achieved. The Q-switched pulses have the shortest pulse duration of 1.95 μs, the maximum pulse energy of 17.9 nJ and a tunable pulse-repetition-rate from 8.3 to 29.1 kHz. Our results indicate that the TI as a SA is also available at 1 μm waveband, revealing its potential as another broadband SA (like graphene).

Stable passively Q-switched and gain-switched Yb-doped all-fiber laser based on a dual-cavity with fiber Bragg gratings

We demonstrate a stable passively Q-switched and gain-switched Yb-doped all-fiber laser cladding-pumped by a continuous fiber-coupled 976 nm laser diode. By use of an all-fiber dual-cavity, the efficient elements of the laser mainly include the fiber Bragg gratings and rare-earth doped fiber, allowing the oscillator to be integrated in a compact size with reliable and stable output. In this scheme, an efficient laser output with 45 ns pulse width, 62 μJ pulse energy, and 1.4 kW peak power operating at 1081 nm was obtained. To the best of our knowledge, this is the minimum pulse width in this similar kind of all-fiber configuration at present. Sequential nanosecond pulses were obtained at the repetition rate of several to tens of kHz with the variation of the diode pumping power. Effects of laser parameters such as pump power, cavity length, external-cavity wavelength, and FBG reflectivity on laser performance were also presented and discussed.

Passively Q-switched microchip Er, Yb:YAl3(BO3)4 diode-pumped laser

We report, for the first time to our knowledge, a diode-pumped cw and passively Q-switched microchip Er, Yb:YAl(3)(BO(3))(4) laser. A maximal output power of 800 mW at 1602 nm in the cw regime was obtained at an absorbed pump power of 7.7 W. By using Co(2+):MgAl(2)O(4) as a saturable absorber, a TEM(00)-mode Q-switched average output power of 315 mW was demonstrated at 1522 nm, with pulse duration of 5 ns and pulse energy of 5.25 μJ at a repetition rate of 60 kHz.

Q-switched fiber lasers with carbon nanotubes hosted in ceramics

Q-switched fiber ring lasers operated by single-walled carbon nanotubes (SWNTs) hosted in SiO(2) matrix are demonstrated by highlighting their stable operation and dramatically improved thermal damage threshold. Employing aerosol deposition process, SWNTs are incorporated into the ceramic host at room-temperature without solubility limitation. After experiencing the intracavity optical power higher than 15.3 dBm, the hosted SWNTs survive to provide Q-switching operation. The continuous repetition rate tuning is achieved in the range of 11.1-32.2 kHz with the pulse-duration of 7.1-15.8 μs at 1558.5 nm.

Active Q-switching in an erbium-doped fiber laser using an ultrafast silicon-based variable optical attenuator

Presented herein is the use of an ultrafast Si-based variable optical attenuator (VOA) as a Q-switch for rare earth-doped fiber lasers. The ultrafast VOA is based on a forward-biased p-i-n diode integrated with a ridge waveguide, which was originally designed and optimized for WDM channel power equalization in optical communication systems. By incorporating a Si-based VOA with a transient time of ~410 ns into an erbium-doped fiber-based Fabry-Perot cavity it has been shown that stable Q-switched pulses possessing a temporal width of less than ~86 ns can be readily obtained at a repetition rate of up to ~1 MHz. The laser's peak power of ~38 W is shown to be obtainable at 20 kHz with a slope efficiency of ~21%.

220 μJ monolithic single-frequency Q-switched fiber laser at 2 μm by using highly Tm-doped germanate fibers

We report a unique all fiber-based single-frequency Q-switched laser in a monolithic master oscillator power amplifier configuration at ~1920 nm by using highly Tm-doped germanate fibers for the first time. The actively Q-switched fiber laser seed was achieved by using a piezo to press the fiber in the fiber Bragg grating cavity and modulate the fiber birefringence, enabling Q-switching with pulse width and repetition rate tunability. A single-mode polarization maintaining large core 25 μm highly Tm-doped germanate fiber was used in the power amplifier stage. For 80 ns pulses with 20 kHz repetition rate, we achieved 220 μJ pulse energy, which corresponds to a peak power of 2.75 kW with transform-limited linewidth.

1 kW peak power passively Q-switched Nd(3+)-doped glass integrated waveguide laser

Embedded optical sensors always require more compact, stable, and powerful laser sources. In this Letter, we present a fully integrated passively Q-switched laser, which has been realized by a Ag(+)/Na(+) ion exchange on a Nd(3+)-doped phosphate glass. A BDN-doped cellulose acetate thick film is deposited on the waveguide, acting as an upper cladding and providing a distributed saturable absorption. At λ=1054 nm, the device emits pulses of 1.3 ns FWHM with a repetition rate of 28 kHz. These performances, coupled with the 1 kW peak power, are promising for applications such as supercontinuum generation.

Actively Q-switched all-fiber laser with an electrically controlled microstructured fiber

Actively Q-switching of an all-fiber laser system is demonstrated. The active element is a polarization switch with nanosecond risetime based on a microstructured fiber with electrically driven internal electrodes. Optical feedback between two 100% reflectors is inhibited until a nanosecond current pulse Q-switches the laser. After a short optical pulse develops several roundtrips later, the fiber switch is turned off, removing the short optical pulse from the cavity through a polarization splitter. Pulses of 50 W peak power and approximately 12 ns duration are obtained with 400 mW pump power at 100 Hz.

Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers

We demonstrate all-fiber passively Q-switched erbium lasers at 1570 nm using Tm(3+)-doped saturable-absorber fibers. The absorption cross section of a Tm(3+)-doped fiber at 1570 nm was measured in a bleaching experiment to be about 1.44 x 10(-20) cm(2). With a thulium-doped fiber, sequential pulses with a pulse energy of 9 microJ and a pulse duration of about 420 ns were stably produced at repetition rates in the range 0.1 to 2 kHz. The maximum pulse repetition rate was 6 kHz, limited by the maximum pump power of a 980-nm laser diode, about 230 mW.

A self-Q-switched all-fiber erbium laser at 1530 nm using an auxiliary 1570-nm erbium laser

We demonstrate a self-Q-switched, all-fiber, tunable, erbium laser at 1530 nm with high pulse repetition rates of 0.9-10 kHz. Through the use of an auxiliary 10-mW, 1570 nm laser that shortened the relaxation time of erbium, sequentially Q-switched pulses with pulse energies between 4 and 6 microJ and pulse widths of 40 ns were steadily achieved. A peak pulse power of 165 W was obtained.

All-fiber passively Q-switched erbium laser using mismatch of mode field areas and a saturable-amplifier pump switch

We propose and demonstrate an all-fiber self-Q-switched erbium laser system that is saturable-absorber Q switched by the mismatch of the mode-field areas in the resonator and stabilized with a saturable-amplifier pump switch. Sequential pulses with a pulse energy of 8-6 microJ and a pulse duration of 80-320 ns, corresponding to a pulse repetition rate of 0.25-1 kHz, were obtained using a cw 980 nm laser-diode pump. A peak pulse power of near 100 W was achieved.

A saturable absorber Q-switched all-fiber ring laser

We propose a simple design of a saturable absorber Q-switched all-fiber ring laser. By locating a saturable absorber fiber in the intensity-enhanced section of a ring resonator, the laser is passively Q-switched. A set of location-dependent rate equations is established for Q-switching modeling. The design has been numerically and experimentally demonstrated using Er(3+)-doped fiber at the emission wavelength of 1550 nm. A single-mode Q-switched pulse with pulse energy of 0.37 microJ and pulse duration of 218 ns was achieved with 980-nm pump power near 7 mW.

Analytical model for optimizing the parameters of an external passive Q-switch in a fiber laser

An analytical model is developed for optimizing two key parameters of an external passive Q-switch in a fiber laser from the criterion of the minimum average mode area inside the saturable absorber. One parameter is the optimum focal position that is analytically derived to be a function of the thickness and initial transmission of the saturable absorber. The other parameter is the optimum magnification of the reimaging optics that is analytically derived to be in terms of the numerical aperture and core radius of the laser fiber as well as the thickness and initial transmission of the saturable absorber. To demonstrate the utilization of the present model, an experiment on the subject of the passively Q-switched fiber laser is performed and optimized.

Compact, single-frequency all-fiber Q-switched laser at 1 microm

We demonstrate a unique, all-fiber, actively Q-switched laser operating in the 1 microm region. The laser is compact, single mode, single frequency, highly polarized, and exhibits high peak power. The laser cavity is constructed without external coupling, utilizing fiber Bragg gratings that permit feedback at only a single polarization. By using a piezoelectric to press the fiber and modulate the fiber birefringence, the cavity is switched between high and low loss states, permitting Q-switching. We demonstrate this Q-switching at repetition rates up to 700 KHz.

High power passively Q-switched ytterbium fiber laser with Cr(4+):YAG as a saturable absorber

We report an efficient high-peak-power and high-average-power passively Q-switched ytterbium fiber laser with a Cr(4+):YAG crystal as a saturable absorber in an external-resonator configuration. At an incident pump power of 17.5 W, the passively Q-switched fiber laser produces an average power greater than 6.2 W with a pulse repetition rate of 48 kHz. The output pulses noticeably display a mode-locking phenomenon that leads to the maximum peak power to be higher than 20 kW.

Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser

Efficient repetitive passive Q switching of a cladding-pumped Er-Yb fiber laser has been demonstrated by use of an external-cavity configuration containing a Co(2+): ZnS crystal as a saturable absorber. Energies of as much as 60muJ in pulses of durations as short as 3.5 ns (FWHM), corresponding to a peak power of >10kW, have been generated, and the maximum slope efficiency with respect to the absorbed pump power was 13%. Using a bulk diffraction grating in the Littrow configuration to provide wavelength-selective feedback, we tuned the passively Q -switched fiber laser over 31 nm from 1532 to 1563 nm. The prospects for further improvement in performance are discussed.

Sequence lasing in a gain-switched Yb3+,Er(3+)-doped silica double-clad fiber laser

Experimental results relating to the gain-switched operation of a double-clad Yb3+,Er(3+)-doped silica fiber laser that is pulse pumped with the output from a flash-lamp-pumped Ti:sapphire laser are presented. For all the configurations of the fiber laser that we studied, the 2F5/2-->2F7/2 laser transition of the Yb3+ ion lased prior to laser emission from the 4I13/2-->4I15/2 transition of the Er3+ ion. To the best of our knowledge, this is the first reported operation of sequence lasing in the Yb3+,Er(3+)-codoped system. This succession of laser pulses deduced from the measurements of this investigation is a consequence of both the short intense pump pulse and the short 900-nm wavelength of the pump that does not overlap with any important excited-state absorption transitions. We believe that the predominant interionic interaction during the course of the pump pulse is the double-energy transfer to the Er3+ ion acting twice from the 2F5/2 energy level of the Yb3+ donor ion. A maximum total output of 1.65 mJ is obtained (1.38 mJ from the 2F5/2-->2F7/2 transition of Yb3+ and 0.27 mJ from the 4I13/2-->4I15/2 transition of Er3+) from a nonoptimized configuration of the fiber laser. The wavelength of the output from the fiber laser was measured to vary approximately linearly with fiber length from 1040 to 1046 nm for the Yb(3+)-based laser and 1535 to 1541 nm for the Er(3+)-based laser.

All-fiber passively Q-switched low-threshold erbium laser

A novel all-fiber passively Q-switched erbium laser with a Co(2+):ZnSe crystal as a saturable absorber is demonstrated experimentally. A pump power threshold of 20.5 mW, which the authors believe is the lowest to date, has been measured. Giant pulses with energy of 3.6 nJ and peak power of 0.7 mW have been obtained.