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Search RSS2015 interdyscyplinarne centrum modelowania matematycznego i komputerowego60Electrostatically Doped DSL Schottky Barrier MOSFET on SOI for Low Power Applications
/resource/bwmeta1.element.ieee-art-000008067464
In this paper, we propose and simulate a novel Schottky barrier MOSFET (SB-MOSFET) with improved performance in comparison to the conventional SB-MOSFET. The proposed device employs charge plasma/electrostatic doping-based dopant segregation layers (DSLs) by using metal extensions (Hafnium) at the source and drain top and bottom edges. The metal hafnium induces charge plasma and hence realizes DSLs adjacent to source and drain regions. These charge plasma DSLs reduce the tunneling width and hence enhances the performance of the proposed device. The proposed electrostatically doped DSL-based SB-MOSFET has all the advantages of the conventional SB-MOSFET and it outperforms the state of the art doped DSL-based MOSFET. A two-dimensional calibrated simulation study has shown that the ON current <inline-formula> <tex-math notation="LaTeX">$(I_{\mathrm{ ON}})$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$I_{\mathrm{ ON}}/I_{\mathrm{ OFF}}$ </tex-math></inline-formula> ratio, subthreshold-swing and cutoff frequency <inline-formula> <tex-math notation="LaTeX">$(f_{T})$ </tex-math></inline-formula> of the proposed device have been increased by ~420 times, ~1000 times, 14.5%, and 290 times in comparison to conventional SB-MOSFET, respectively. The transient analyses have shown that a reduction by 16 times in ON delay and 6 times in OFF delay in the proposed device-based inerter in comparison to the conventional SB-MOSFET-based inverter./resource/bwmeta1.element.ieee-art-000008067464Experimental Investigations of State-of-the-Art 650-V Class Power MOSFETs for Cryogenic Power Conversion at 77K
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With consideration of both the operating properties from cryogenic MOSFETs and refrigerating costs from cryogenic refrigerators, this paper attempts to carry out the experimental tests and performance evaluations of state-of-the-art 650-V class MOSFETs, and thus to explore a possible design guideline for cryogenic power conversions at liquid nitrogen temperature. Three cryogenic operating behaviors of on-state resistances and breakdown voltages of five types of commercial power MOSFETs and on-state voltage across their built-in reverse diodes are tested from 300 K to 77 K. The measured on-state resistances obtained in low-current tests show almost double-exponential functional relations with the operating temperatures, while the other two cryogenic parameters are directly or inversely proportional to the operating temperatures. Moreover, cryogenic on-state resistance behaviors in high-current tests from 20 A to 90 A are also found to have double-exponential functional relations with the operating currents. Based on the experimental results and their fitted temperature-dependent and current-dependent functions, integrated evaluation of overall energy efficiency involved with refrigerating cost is presented to form a feasible design guideline for cryogenic power conversions. Finally, two 40-kW and 4-MW boost choppers are conceptually designed and discussed to verify the proposed design guideline for the use in various MOSFET-based cryogenic power conversions./resource/bwmeta1.element.ieee-art-000008063862UHD AMOLED Driving Scheme of Compensation Pixel and Gate Driver Circuits Achieving High-Speed Operation
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This paper presents a new driving scheme for active-matrix organic light-emitting diode displays. A pixel circuit based on this driving scheme was developed to compensate for the threshold voltage and mobility variations of low-temperature polycrystalline-silicon thin-film transistors (TFTs), eliminate image flickering and current-resistance voltage drops, and suit ultrahigh-definition (UHD) resolution applications. A new gate driver with a concise 6T1C structure is also proposed to realize the driving scheme in practice. Fabricated TFTs and OLEDs were measured to establish models. Simulations using these models demonstrate that the proposed pixel circuit achieves uniform OLED current regardless of undesirable influences at UHD resolution./resource/bwmeta1.element.ieee-art-000008068987A Novel Reconfigurable Sub-0.25-V Digital Logic Family Using the Electron-Hole Bilayer TFET
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We propose and validate a novel design methodology for logic circuits that exploits the conduction mechanism and the presence of two independently biased gates (“n-gate” and “p-gate”) of the electron-hole bilayer tunnel field-effect transistor (EHBTFET). If the device is designed to conduct only under certain conditions, e.g., when <inline-formula> <tex-math notation="LaTeX">$V_{\mathrm {n-gate}} = V_{\mathrm {DD}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$V_{\mathrm {p-gate}} = 0$ </tex-math></inline-formula>, it then shows an “XOR-like” behavior that allows the implementation of certain logic gates with a smaller number of transistors compared to conventional CMOS static logic. This simplifies the design and possibly results in faster operation due to lower node capacitances. We demonstrate the feasibility of the proposed EHBTFET logic for low supply voltage operation using mixed device/circuit simulations including quantum corrections./resource/bwmeta1.element.ieee-art-000008053745Design and Characterization of a Silicon Photomultiplier in 0.35- ${\mu }\text{m}$ CMOS
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The possibility to design a silicon photomultiplier (SiPM) using standard CMOS processes represents the frontier of current low photon flux detectors. It allows an integrated development of both sensor and intelligent read-out electronics on the same technology line and enables to create intelligent devices with on-chip signal processing. We report the design and characterization of an SiPM composed of <inline-formula> <tex-math notation="LaTeX">$20\times 20$ </tex-math></inline-formula> microcells with size <inline-formula> <tex-math notation="LaTeX">$50\times 50 ~\mu \text{m}^{2}$ </tex-math></inline-formula>. The device exhibits 200-kHz/mm<sup>2</sup> dark rate, 10% cross talk probability, 1.5% afterpulsing probability, and <inline-formula> <tex-math notation="LaTeX">$5.35\times 10^{6}$ </tex-math></inline-formula> intrinsic gain at 29-V operational voltage. It is obtained at a 0.35-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS technology node, which is compatible with the development of integrated electronics. In order to verify the potential application of the device to optical and radiation detection systems, we measure its photon detection efficiency and its response to LED light and scintillation light from an LySO crystal./resource/bwmeta1.element.ieee-art-000008100871Electrical Contacts in SOI MEMS Using Aerosol Jet Printing
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In this paper, an additive method to make electrical contacts in SOI MEMS devices with aerosol jet printing is introduced. Small grooves were etched to the frame of MEMS accelerometer in the same step with the active structure release. Aluminum ink was jetted to the trenches in wafer-level to bridge the device layer to the handle wafer with the minimum amount of material. After subsequent annealing, ohmic contacts between p-type device layer and p-type handle silicon were verified by <italic>I</italic>–<italic>V</italic> measurements. The via resistance less than 4 <inline-formula> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> per via is measured. The method demonstrated in this paper provides simple and low-cost approach for SOI handle contact where additional packaging of wafer process steps can be avoided./resource/bwmeta1.element.ieee-art-000008076900Hysteresis Reduction in Negative Capacitance Ge PFETs Enabled by Modulating Ferroelectric Properties in HfZrO<sub><italic>x</italic></sub>
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We experimentally demonstrate that hysteresis of negative capacitance (NC) Ge pFETs is reduced through modulating the ferroelectric properties in HfZrO<sub><italic>x</italic></sub> (HZO) by changing the post annealing temperature. As annealing temperature varies from 350 °C to 450 °C, HZO exhibits a significant increasing in the ratio of remnant polarization <inline-formula> <tex-math notation="LaTeX">$P_{r}$ </tex-math></inline-formula> to coercive field <inline-formula> <tex-math notation="LaTeX">$E_{c}$ </tex-math></inline-formula>, which results in the improvement of the magnitude of ferroelectric NC <inline-formula> <tex-math notation="LaTeX">$C_\mathrm{FE}$ </tex-math></inline-formula>, therefore contributing to the reduction of hysteresis of the ferroelectric NC Ge transistors. It is also reported that the NC Ge transistor annealed at 450 °C has a small hysteresis of 0.10 V, and achieves the improved SS and <inline-formula> <tex-math notation="LaTeX">$I_\mathrm{DS}$ </tex-math></inline-formula> compared to control device without HZO./resource/bwmeta1.element.ieee-art-000008076871Charge-Based Modeling of Radiation Damage in Symmetric Double-Gate MOSFETs
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In this paper, a comprehensive charge-based predictive model of interface and oxide trapped charges in undoped symmetric long-channel double-gate MOSFETs is developed. The model involves essentially no fitting parameters, but first-principle calculations of both oxide and Si/oxide interface trapping. This charge-based approach represents an essential step toward compact modeling of ionizing dose and aging effects in advanced field effect devices. The soundness of this approach is confirmed by extensive comparisons with numerical TCAD simulations, while the analytical formulation helps understanding the most relevant parameters of the phenomena with respect to a specific technology. The model confirms its validity for all regions of operation, i.e., from deep depletion to strong inversion and from linear to saturation./resource/bwmeta1.element.ieee-art-000008103743Al<sub>2</sub>O<sub>3</sub>-Dielectric In<sub>0.18</sub>Al<sub>0.82</sub>N/AlN/GaN/Si Metal-Oxide-Semiconductor Heterostructure Field-Effect Transistors With Backside Substrate Metal-Trench Structure
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This paper investigates novel Al<sub>2</sub>O<sub>3</sub>-dielectric In<sub>0.18</sub>Al<sub>0.82</sub>N/AlN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with backside metal-trench structure grown by using a non-vacuum ultrasonic spray pyrolysis deposition technique. 3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> deep metal trenches coated with 150-nm thick Ni were formed on the backside of the Si substrate to improve the heat dissipation efficiency. The present In<sub>0.18</sub>Al<sub>0.82</sub>N/AlN/GaN MOS-HFET (Schottky-gate HFET) has demonstrated improved maximum drain–source current density (<inline-formula> <tex-math notation="LaTeX">$I_{\mathrm{ DS, \max }}$ </tex-math></inline-formula>) of 1.08 (0.86) A/mm at <inline-formula> <tex-math notation="LaTeX">$\textit{V}_{\mathrm{ DS}}=$ </tex-math></inline-formula> 8 V, gate-voltage swing of 4 (2) V, on/off-current ratio (<inline-formula> <tex-math notation="LaTeX">$I_{\mathrm{ on}} /I_{\mathrm{ off}} $ </tex-math></inline-formula>) of <inline-formula> <tex-math notation="LaTeX">$8.9\times 10^{8}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$7.4 \times 10^{4} $ </tex-math></inline-formula>), subthreshold swing of 140 (244) mV/dec, two-terminal off-state gate-drain breakdown voltage (BV<sub>GD</sub>) of −191.1 (−173.8) V, turn-on voltage (<inline-formula> <tex-math notation="LaTeX">$V_{\mathrm{ on}} $ </tex-math></inline-formula>) of 4.2 (1.2) V, and three-terminal on-state drain-source breakdown voltage (BV<inline-formula> <tex-math notation="LaTeX">$_{DS}$ </tex-math></inline-formula>) of 155.9 (98.5) V. Enhanced power performances, including saturated output power (<inline-formula> <tex-math notation="LaTeX">$\textit{P}_{out}$ </tex-math></inline-formula>) of 27.9 (21.5) dBm, power gain (<inline-formula> <tex-math notation="LaTeX">$\textit{G}_{a}$ </tex-math></inline-formula>) of 20.3 (15.5) dB, and power-added efficiency (PAE) of 44.3% (34.8%), are achieved./resource/bwmeta1.element.ieee-art-000008094232Quadruple Gate-Embedded T Structured GaN-Based Metal–Oxide–Semiconductor High-Electron Mobility Transistors
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In this paper, high performance quadruple gate-embedded T structured GaN-based metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) were fabricated using laser interference photolithography method and photoelectrochemical oxidation method, in which polymethylmethacrylate was used as sacrificial layer. The associated drain-source saturation current was improved to 175 mA/mm and the gate leakage current at the gate-source voltage of −80 V was improved to <inline-formula> <tex-math notation="LaTeX">$0.81~\mu \text{A}$ </tex-math></inline-formula> compared with the 125 mA/mm and <inline-formula> <tex-math notation="LaTeX">$7.6~\mu \text{A}$ </tex-math></inline-formula> of the conventional single gate GaN-based MOSHEMTs, respectively. Moreover, the associated maximum extrinsic transconductance of the quadruple gate-embedded T structured GaN-based MOSHEMTs was enhanced from 97.3 mS/mm to 118.4 mS/mm. Besides, the associated unit gain cutoff frequency and the associated maximum oscillation frequency were improved from 7.6 GHz to 10.8 GHz and from 11.4 GHz to 27.4 GHz, respectively. The improved performances of the quadruple gate-embedded T structure GaN-based MOSHEMTs were attributed to the function of the gate length reduction and the gate resistance decrease./resource/bwmeta1.element.ieee-art-000008094224Performance and Power Consumption Trade-Off in UTBB FDSOI Inverters Operated at NTV for IoT Applications
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Power consumption and I<sub>on</sub>/I<sub>off</sub> ratio of an ultra-thin body and buried oxide fully depleted silicon on insulator CMOS inverter circuit has been calculated at near-threshold voltage operation from TCAD simulations. TCAD outputs (current, voltage, and capacitance) were used as parameters to solve the inverter circuit. Besides, a bias operation point (<inline-formula> <tex-math notation="LaTeX">$V_{\mathrm{ OP}}$ </tex-math></inline-formula>) has been proposed, which provides a good trade-off between the I<sub>on</sub>/I<sub>off</sub> ratio and the energy consumption. Variations of this operation point, due to the presence of interface traps, have been also analyzed./resource/bwmeta1.element.ieee-art-000008102997Si<sub>3</sub>N<sub>4</sub>/Al<sub>2</sub>O<sub>3</sub> Stack Layer Passivation for InAlAs/InGaAs InP-Based HEMTs With Good DC and RF Performances
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This paper introduces a novel surface passivation using Si<sub>3</sub>N<sub>4</sub> (20-nm)/Al<sub>2</sub>O<sub>3</sub> (15-nm) stack layers in InAlAs/InGaAs InP-based high-electron-mobility transistors (HEMTs). The new technology gives rise to good dc and RF performances in InP-based HEMTs. Notably different from the conventional Si<sub>3</sub>N<sub>4</sub> approach, an ultrathin layer of Al<sub>2</sub>O<sub>3</sub> (15-nm) grown by atomic layer deposition is incorporated in the surface passivation, which is the main feature of this technology. After passivation, the Si<sub>3</sub>N<sub>4</sub>/Al<sub>2</sub>O<sub>3</sub>-passivated HEMTs exhibit a superior dc performance demonstrating a high drain current up to 800 mA/mm, an increased peak transconductance of 1100 mS/mm at <inline-formula> <tex-math notation="LaTeX">${V} _{\mathrm{ GS}}=-0.2$ </tex-math></inline-formula> V and a slight threshold voltage shift of <inline-formula> <tex-math notation="LaTeX">${\Delta } {V} _{\mathrm{ th}}=+120$ </tex-math></inline-formula> mV. In terms of their RF performance, a maximum oscillation frequency (<inline-formula> <tex-math notation="LaTeX">${f} _{\mathrm{ max}}$ </tex-math></inline-formula>) up to 340 GHz has been obtained, showing an excellent quality of the surface passivation. A physical explanation is addressed over why the good dc and RF performances have been achieved./resource/bwmeta1.element.ieee-art-00000809864475 Years of the Device Research Conference—A History Worth Repeating
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At a time when the scientific community is overrun with conferences, workshops, and congresses to discuss all facets of innovation, much can be learned from considering a meeting that has withstood the test of time: the Device Research Conference (DRC). The DRC has been the launching pad for many game-changing innovations, from early transistors to new electronic materials. While the conference has undergone transformations to adapt to changing times, it remains true to its roots in a way that has enabled 75 years’ worth of successful technical gatherings. Remembering DRC’s past provides inspiration for preserving and, we would argue, repeating the pattern laid by this historic meeting./resource/bwmeta1.element.ieee-art-000008168249AlGaN/GaN MIS-HEMTs With High Quality ALD-Al<sub>2</sub>O<sub>3</sub> Gate Dielectric Using Water and Remote Oxygen Plasma As Oxidants
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We demonstrate the electrical performances of AlGaN/GaN metal–insulator–semiconductorhigh electron mobility transistors (MIS-HEMTs) with high quality Al<sub>2</sub>O<sub>3</sub> gate dielectric deposited by plasma enhanced atomic layer deposition using both H<sub>2</sub>O and remote O<sub>2</sub> plasma as oxygen sources. Excellent gate-dielectric/GaN interface and Al<sub>2</sub>O<sub>3</sub> film quality were obtained, resulting in a very small threshold voltage hysteresis and a low interface trap density. The MIS-HEMT device exhibited high on/off current ratio of <inline-formula> <tex-math notation="LaTeX">$\sim 10^{10}$ </tex-math></inline-formula>, steep subthreshold slope, small gate leakage current, low dynamic on-resistance degradation, and effectively current collapse suppression. These results indicate that incorporating remote O<sub>2</sub> plasma in the ALD-Al<sub>2</sub>O<sub>3</sub> deposition process is an effective and simple way to provide high quality gate dielectric for the GaN MIS-HEMTs production/resource/bwmeta1.element.ieee-art-000008125685Improvement of Charge Injection by Using Separated SiN as Charge Trapping Layer in MONOS Charge Trap Flash Memory
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The charge trapping characteristics in the metal-oxide-nitride-oxide-silicon memory with separated trapping layer were investigated. Charge injection was enhanced for the reduction of effective oxide thickness of the gate dielectric. High program/erase speed as well as large shift of the threshold voltage were obtained. Charges injection was improved according to the constant current stress measurement. The application of separated charge trapping layer can considerably improve the performance of charge trapping memory./resource/bwmeta1.element.ieee-art-000008102992High-Uniformity and High Drain Current Density Enhancement-Mode AlGaN/GaN Gates-Seperating Groove HFET
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In this paper, we report on a novel E-mode AlGaN/GaN gates-seperating groove heterostructure field-effect transistor (GSG HFET). The current turn-on/off is controlled by changing gate voltage to regulate the horizontal energy band between the double gates. A threshold voltage of 0.23 V and a high drain current density of 851 mA/mm are obtained in GSG HFET. Compared with the proposed depletion-mode device, the maximum drain current of the GSG HFET deceases slightly (about 7%). It is noteworthy that the threshold voltage is less sensitive to the etching time. The devices show high-uniformity threshold voltage of 0.23 V within wide etching time range from 5 to 9 min./resource/bwmeta1.element.ieee-art-000008121975Gold-Nanoparticle-Coated Ge MIS Photodiodes
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Ge photodiodes with ultra-high responsivities have been demonstrated with gold nanoparticle assistance. The responsivity can reach a value of 37.7 A/W, which corresponds to a gain of 76. Such a high responsivity originates from the amassment of photo-generated holes in Ge under the boundary of gold nanoparticles, which reduces the barrier for electron tunneling from metal to the hole-amassment Ge ring areas. The depletion layer thinning due to hole amassment is not only proved by band diagram simulation but also confirmed by capacitance measurement./resource/bwmeta1.element.ieee-art-000008119500In–Ga–Zn–O Thin-Film Devices As Synapse Elements in a Neural Network
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We have succeeded in utilizing In–Ga–Zn–O (IGZO) thin-film devices as synapse elements in a neural network. The electrical conductance is regarded as the connection strength, and the continuous change by flowing electrical current is employed as the connection plasticity based on the modified Hebbian learning as a learning rule. We developed a cellular neural network using the IGZO thin-film devices and confirmed that the neural network can learn simple logic functions. These results suggest a possibility to realize 3-D layered structure for brain-type integrated systems./resource/bwmeta1.element.ieee-art-000008119943High-Power Single-Frequency Source in the Mid-Infrared Using a Singly Resonant Optical Parametric Oscillator Pumped by Yb-Fiber Laser
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We present a high-power single-frequency continuously tunable mid-infrared (MIR) singly resonant optical parametric oscillator (SRO) using <inline-formula><tex-math notation="LaTeX">$\text{80-mm}$</tex-math></inline-formula>-long MgO-doped PPLN (MgO:PPLN) crystal pumped by a continuous-wave Yb-fiber laser. The SRO having four-mirror ring-cavity configuration is tunable in the MIR band of <inline-formula><tex-math notation="LaTeX">$\text{3761--3970 nm}$ </tex-math></inline-formula> yielding a maximum power of <inline-formula><tex-math notation="LaTeX">$\text{2W}$ </tex-math></inline-formula> at <inline-formula><tex-math notation="LaTeX">$\text{3895 nm}$</tex-math></inline-formula> when incident pump power is <inline-formula><tex-math notation="LaTeX">$\approx \text{16 W}$</tex-math> </inline-formula>. Due to strong phonon–polariton coupling in MgO:PPLN crystal, the intracavity signal-beam spectrum exhibits multiple peaks depicting stimulated polariton scattering. By replacing one of the cavity mirrors with a <inline-formula><tex-math notation="LaTeX">$\text{5}\%$</tex-math></inline-formula> outcoupler, the stimulated polariton modes are suppressed as a consequence of additional cavity losses. Along with a tunable signal extending from <inline-formula><tex-math notation="LaTeX">$\text{1453}$</tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$\text{1484 nm}$</tex-math></inline-formula>, we obtained the maximum signal power of <inline-formula><tex-math notation="LaTeX">$\approx \text{4W}$</tex-math></inline-formula> at <inline-formula> <tex-math notation="LaTeX">$\text{1464 nm}$</tex-math></inline-formula> at the maximum pump power of <inline-formula> <tex-math notation="LaTeX">$\approx \text{16W}$</tex-math></inline-formula>. In addition, we have measured the frequency and power stability of the outcoupled signal and idler beams over long as well as short durations. The improvement in beam quality of idler was discernible when the intracavity signal was outcoupled, which is essentially a consequence of reduced thermal load on MgO:PPLN crystal./resource/bwmeta1.element.ieee-art-000008063923High Repetition Rate All-Solid-State Pulsed 2 μm Laser Based on Selenide Molybdenum Saturable Absorber
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A kind of saturable absorber (SA) based on layered MoSe<sub>2</sub> nanosheets has been fabricated successfully by an ultrasound-assisted liquid phase exfoliation method. The as-prepared MoSe<sub>2</sub> SA was characterized and employed as Q-switch in a diode-pumped Tm-doped crystalline all-solid-state laser at around 2 <italic>μ</italic>m. A stable passively Q-switched 2 <italic>μ</italic>m laser with a maximum pulse repetition rate of 158 kHz and a minimum pulse width of 520 ns was successfully realized. A maximum average output power of 1.19 W, corresponding to a maximum pulse energy of 12.7 <italic>μ</italic>J and pulse peak power of 21.8 W, has been obtained. It was the first demonstration of MoSe<sub>2</sub> SA in realizing a solid-state 2 <italic>μ</italic>m pulsed laser, to the best of our knowledge. The results confirmed the excellent ability and promising potential of MoSe<sub>2</sub> SA as an optical modulator in generating high repetition rate and short pulsed laser at the midinfrared spectral band./resource/bwmeta1.element.ieee-art-000008078254Passively Q-Switched Nd:GdVO4 1.3 μm Laser with Few-Layered Black Phosphorus Saturable Absorber
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By using a few-layer black phosphorus (BP) as the saturable absorber (SA), a laser-diode end-pumped stable Q-switched Nd:GdVO<sub>4</sub> laser operating at 1.3 μm was realized. A maximum average output power of 452 mW was obtained at 2.22 W absorbed pump power, corresponding to a 34.5% slope efficiency. The shortest pulse width, highest pulse repetition rate, and largest peak power were determined to be 72 ns, 625 kHz, and 10.04 W, respectively. To the best of our knowledge, this pulse duration was the shortest ever reported for passive Q-switched bulk lasers based on two-dimensional materials at 1.3 μm. Results suggested that BP can be used to achieve short laser pulses with high repetition rate at 1.3 μm spectral region./resource/bwmeta1.element.ieee-art-000008093648Expanding Continuous Tuning Range of a CW Single-Frequency Laser by Combining an Intracavity Etalon With a Nonlinear Loss
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Combining intracavity etalon (IE) locked on a laser oscillating mode with a deliberately introduced nonlinear loss, the tuning range of a continuous-wave (CW) single-frequency laser is significantly expanded to transcend the traditional limitation of a free spectral range (FSR) of IE. Due to the action of the nonlinear loss, the frequency of laser oscillating mode can be continuously and smoothly tuned without any mode-hopping in a tuning range much larger than FSR of IE. We theoretically analyze the physical mechanism behind the influence of nonlinear loss on the tuning range expansibility of the laser and experimentally demonstrated the effectiveness of the presented method. By means of this method, the ultrawide continuous frequency scanning range of 222.4 GHz at 532 nm is implemented. The theoretical analysis and the experimental results are in good agreement./resource/bwmeta1.element.ieee-art-000008169032Intrinsic Mechanism for Spectral Evolution in Single-Frequency Raman Fiber Amplifier
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In this paper, the spectral evolution properties in single-frequency Raman fiber amplifier (RFA) based on different pump schemes are analyzed theoretically for the first time based on the gain dynamics. It reveals that the walk-off effect in counter-pumped scheme acts as a natural low-pass filter for single-frequency RFA. When multilongitudinal mode rare-earth-doped fiber laser is used as the pump source for RFA, strong temporal fluctuations of the pump source would lead to spectral broadening in copumped scheme, while single-frequency operation could be maintained in the countered-pumped case because of the natural low-pass filter./resource/bwmeta1.element.ieee-art-000008214208Watt-Level Continuous-Wave and Black Phosphorus Passive Q-Switching Operation of Ho3+,Pr 3+:LiLuF4 Bulk Laser at 2.95 μm
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Efficient continuous wave (CW) and passively Q-switched Ho<sup>3+</sup>,Pr<sup>3+</sup>:LiLuF <sub>4</sub> (Ho,Pr:LLF) laser operating at 2.95 <italic>μ</italic>m were realized using a 1150-nm Raman fiber laser as the pump source. A CW output power as high as 1.15 W, which we believe to be the highest one ever achieved from Ho <sup>3+</sup>-doped bulk laser emission around 3 <italic>μ</italic>m, corresponds to an optical-to-optical conversion efficiency of 14.5% and a slope efficiency of 15.5%, respectively. A high-quality saturable absorber (SA) based on multilayered black phosphorus (BP) nanosheet film deposited on a CaF<sub>2</sub> substrate was successfully fabricated and employed. Under the absorbed pump power of 7.36 W, the shortest pulse width of 194.3 ns was obtained, which is the shortest among the two-dimensional materials as SA around 3 <italic>μ</italic>m. The results not only indicated that Ho,Pr:LLF crystal would be a promising mid-infrared (MIR) gain medium for obtaining high power output, but verified that the multilayered BP is a promising optical modulator for generating short pulses in MIR spectral range./resource/bwmeta1.element.ieee-art-000008016559High-Energy Single-Frequency Millisecond 1336.630-nm Nd:LGGG Amplifier (April 2017)
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We demonstrate a high-energy, single-frequency, and millisecond (ms) 1336.630-nm amplifier with high beam quality and narrow-linewidth simultaneously based on the Nd<sup>3+</sup>:(Lu<sub>x</sub>Gd<sub>1-x</sub>)<sub>3</sub>Ga <sub>5</sub>O<sub>12</sub> (Nd:LGGG) disordered crystal for the first time. The amplifier system consists of a polarized single-frequency 1336.630-nm LD oscillator, two-stage Raman fiber preamplifier, and four-stage Nd:LGGG main amplifier. The seed laser pulse energy is amplified up to a record high pulse energy of 2.05 J at a repetition rate of 5 Hz and a pulse duration of 1 ms with linewidth as narrower as 0.5 pm. The beam quality factor is <inline-formula><tex-math notation="LaTeX">${\rm{M}}^{2}\,= \,1.46$</tex-math></inline-formula>. The wavelength of the single-frequency amplifier can be tuned from 1336.600 to 1336.660 nm. All results indicate that the Nd:LGGG is high performance 1.3-μm laser amplification medium, especially for generating the specific wavelength at 1336.630 nm. Moreover, such laser source with the specific wavelength at 1336.630 nm is promising for the development of a high accuracy <sup>27</sup>Al<sup>+</sup> ion optical clock./resource/bwmeta1.element.ieee-art-000008013695Investigation of Geomagnetic Orientation Preserved in a Stain Containing Iron Compounds Using a Vector-Type SQUID Magnetometer
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We investigate the orientation of the magnetic field preserved in a stain containing iron compounds, such as ink pigment or blood, using a superconducting quantum interference device (SQUID) magnetometer system. The magnetization of a cloth or paper sample is observed by applying a vector-type SQUID gradiometer, which detects three orthogonal components of the magnetic field, and mechanical modulation, which converts dc magnetic signals to time-varying signals detectable by SQUIDs. Numerical experiments indicate that the orientation of the magnetization could be identified by the vector-type SQUID magnetometer when the sample was moved linearly under the probe. This paper describes in detail the instrumentation of the measurement system and a proof-of-principle experiment to confirm the system's effectiveness. The obtained results suggest that the magnetization of iron-compound-containing stains preserved the orientation of the magnetic field in which they were produced, as we hypothesized./resource/bwmeta1.element.ieee-art-000008226861Influences of Tape Thickness on the Properties of Ag-Sheathed Sr1-xKxFe2 As2 Superconducting Tapes
/resource/bwmeta1.element.ieee-art-000008141936
In this paper, the relationships between transport <inline-formula><tex-math notation="LaTeX">$J_{{\rm{c}}}$ </tex-math></inline-formula>, the core density and texture are systematically studied by fabricating silver sheathed Sr <sub>1-x</sub>K<sub>x</sub>Fe<sub>2</sub>As<sub>2</sub> superconducting tapes with different thickness. The cores densities increase when the tape thickness decreases to 0.5 mm. But the core density of 0.4 mm tapes is the same with that of the 0.5 mm ones as the core density has been saturated in such rolling deformation. However, there is a positive correlation between the transport <inline-formula><tex-math notation="LaTeX">$J_{{\rm{c}}}$ </tex-math></inline-formula> and texture of superconducting tapes. We conclude that the core density and the texture have a combined influence on the final performance of tapes and the <inline-formula><tex-math notation="LaTeX"> $J_{{\rm{c}}}$</tex-math></inline-formula> of iron-based superconducting tapes can be further improved by increasing the texture degree when the core density saturated within the experimental conditions./resource/bwmeta1.element.ieee-art-000008141936Concave Gold Bipyramid Saturable Absorber Based 1018 nm Passively Q-Switched Fiber Laser
/resource/bwmeta1.element.ieee-art-000008070935
Concave gold bipyramids (CAuBPs) exhibit enhanced saturable absorption characteristics due to their large electromagnetic-field enhancement, large third order nonlinearity and fast recovery time. In this paper, the CAuBPs are synthetized through a seed-mediated wet-chemical growth method, and a 1018 nm passively Q-switched fiber laser exploiting CAuBPs saturable absorber (SA) is demonstrated in a ring cavity. The maximum average output power of 9.61 mW is obtained under the pump power of 270 mW in Q-switched regime. The minimum pulse width is 1.83 <italic>μ</italic>s at the pulse repetition rate of 97.47 kHz. The results prove that CAuBP is a promising SA with potential for important applications in the field of pulsed lasers./resource/bwmeta1.element.ieee-art-0000080709353.1–5.2 μm Coherent MIR Frequency Comb Based on Yb-Doped Fiber Laser
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An offset-free, wavelength-tunable, and midinfrared frequency comb working at 184 MHz based on difference frequency generation (DFG) in a PPMgSLT crystal was demonstrated. A coherent Raman soliton pulse and Yb-fiber laser output were used as the seed pulses of DFG, and wavelength tunability in the range 3.1–5.2 <italic>μ </italic>m was realized. A quantum cascade laser stabilized by the absorption line of N<sub>2</sub>O was used to measure the beat signal with an MIR comb. The MIR comb had a good spatial beam profile, and a high signal-to-noise ratio (SNR) of 70 dB at a wavelength of 4.52 <italic>μ</italic>m was confirmed. A stable and sharp beat signal was observed in the MIR region with a linewidth of 160 kHz, and the SNR was larger than 20 dB./resource/bwmeta1.element.ieee-art-000008063968Titanium Selenide Saturable Absorber Mirror for Passive Q-Switched Er-Doped Fiber Laser
/resource/bwmeta1.element.ieee-art-000008059832
Titanium selenide saturable absorber mirror (TiSe<sub>2</sub>-SAM) is fabricated by a combination of magnetron sputtering method and chemical vapor deposition method. With the optical circulator, the TiSe<sub>2</sub>-SAM is flexibly injected in the experimental cavity as the saturated absorber, and a steady Q-switched Er-doped fiber (EDF) laser is established. The modulation depth of TiSe<sub>2</sub>-SAM is measured to be 25.92%. Through appropriately adjusting the polarization states and changing the pump power, the shortest pulse duration and maximum output power of the passive Q-switched EDF laser are 1.126 <italic>μ</italic>s and 11.54 mW, respectively. The adjustable range of the repetition rate is 70–154 kHz, and the signal to noise ratio is greater than 62 dB. To our best knowledge, there is no report on Q-switched EDF lasers based on TiSe<sub>2</sub> up to now, and our new attempt on TiSe<sub>2</sub>-based Q-switched EDF laser proves that TiSe<sub>2</sub> as a powerful candidate is promising in ultrafast optical generation for the characteristics of high modulation depth and high stability./resource/bwmeta1.element.ieee-art-000008059832Ultrafast Thulium-Doped Fiber Laser Mode Locked by Monolayer WSe<sub>2</sub>
/resource/bwmeta1.element.ieee-art-000008053759
We report the usage of chemical vapor deposition-grown monolayer WSe<sub>2</sub> as a saturable absorber (SA) for a mode-locked thulium-doped fiber laser. The monolayer WSe<sub>2</sub> was transferred onto a microfiber and then incorporated into a typical all-fiber-integrated ring cavity configuration. Stable soliton pulses emitting at 1863.96 nm were obtained with pulse duration of 1.16 ps, repetition rate of 11.36 MHz, and an average power of 32.5 mW. This is, to the best of our knowledge, the first demonstration of WSe<sub>2</sub>-based SA in fiber lasers at 2 <italic>μ</italic>m regime./resource/bwmeta1.element.ieee-art-000008053759WS2-Clad Microfiber Saturable Absorber for High-Energy Rectangular Pulse Fiber Laser
/resource/bwmeta1.element.ieee-art-000008053748
Tungsten disulfide (WS<sub>2</sub>), which possesses broadband nonlinear saturable absorption property, displays promising applications in passively mode-locked lasers. Recent research works have demonstrated that WS<sub>2</sub> shows much higher thermal conductivity than other transition metal dichalcogenides, which can withstand higher optical intensity and exhibit a higher damage threshold. However, the WS<sub>2</sub>-based high-energy fiber lasers have not been extensively studied. Here, a WS<sub>2</sub>-clad microfiber (WCM) saturable absorber (SA) is exploited by an effective transferring approach, which is precisely accomplished under optical microscope. The evanescent field interaction scheme has ability to further raise the optical damage threshold, as well as take full advantage of the nonlinear effect of WS<sub>2</sub>. Based on the WCM SA, high-energy rectangular pulses are achieved in an Er-doped fiber laser whose pulse duration and energy almost increase linearly with the enhancement of pump power. The maximum energy of single pulse in the cavity can reach 810 nJ under pump power of 800 mW. The experimental results open up venues to create new high-energy laser systems with rich functionalities and novel physical effects./resource/bwmeta1.element.ieee-art-000008053748Optimization of Phase Modulation Formats for Suppression of Stimulated Brillouin Scattering in Optical Fibers
/resource/bwmeta1.element.ieee-art-000008038774
We theoretically investigate nonlinear optimization of periodic phase modulation for suppression of stimulated Brillouin scattering (SBS) in single-mode optical fibers. We use nonlinear multiparameter Pareto optimization to find modulations that represent the best tradeoff between SBS and optical linewidth, as measured by its rms value. The optimization uses a temporal-amplitude-domain finite-difference Brillouin solver with noise initiation to find the best phase modulation patterns in the presence of coherent so-called cross-interactions. These can be important in short fibers, when the period is large enough to make the frequency-domain separation of the modulated signal comparable to, or smaller than, the Brillouin gain linewidth. We calculate the SBS threshold for the optimized modulation patterns and find that smaller spectral line spacing improves the SBS threshold for the same linewidth. By contrast, whereas the maximum modulation depth and modulation frequency influence the range of accessible linewidths, they do not significantly alter the threshold for a given linewidth. We investigate the dependence on fiber length and find that while shorter fibers have a higher threshold, the increase is smaller than the often-assumed inverse dependence on length. Furthermore, we find that optimized formats are superior in terms of SBS threshold as well as in terms of linewidth control, compared to random modulation./resource/bwmeta1.element.ieee-art-000008038774Ultrafast Green-Light Swept-Source Imaging Through Advanced Fiber-Optic Technologies
/resource/bwmeta1.element.ieee-art-000008063314
A green-light time-stretch confocal microscopy is demonstrated on a fiber-based platform. On the basis of large dispersion provided by a newly designed dispersive fiber for 1-<italic>μ</italic>m wavelength, this platform enables high-resolution time-stretch imaging merely at a sampling rate of 1 GS/s, which is almost 80 times slower than similar systems demonstrated previously. Both forward- and epi-detection time-stretch imaging at 6 MHz are realized in the same imaging system at a micron-level resolution. To the best of our knowledge, this is the first time that MHz microscopy at 1 GS/s has been demonstrated in green color that exhibits a <italic> μ</italic>m-resolution. It is believed that this low data-stream time-stretch system can enable ultrafast <italic> in-situ</italic> imaging in a biofavorable window through practical and affordable hardware configurations./resource/bwmeta1.element.ieee-art-000008063314High Energy (100 mJ) and High Peak Power (8 MW) Nanosecond Pulses Delivered by Fiber Lasers and Self-Focusing Analysis Based on a Novel Mode Decomposition Method
/resource/bwmeta1.element.ieee-art-000008070379
Nanosecond (∼10 ns) laser pulses with high peak power of 8 MW and high energy of 100 mJ are reported, which are generated by a cascaded pulsed Yb-doped fiber amplifier system working at a repetition frequency of 10 Hz. The peak power that is higher than the self-focusing threshold for Gaussian beams is achieved for the first time in the fiber lasers. To analyze the self-focusing threshold for multimode lasers in fibers, a novel mode decomposition based on the beam quality measurements is introduced. Based on the mode decomposition and nonlinear laser propagation simulations, the threshold of self-focusing for our case is estimated./resource/bwmeta1.element.ieee-art-000008070379Wavelength Conversion and Supercontinuum Generation in Silicon Optical Fibers
/resource/bwmeta1.element.ieee-art-000008068187
This paper describes the state of the art in wavelength conversion and supercontinuum generation using glass-clad silicon core optical fibers. Such semiconductor fibers have enjoyed considerable attention due to their intrinsically high third-order nonlinearities, which are markedly higher than in conventional infrared glasses. Results to date from small core silicon fibers fabricated using both the high-pressure chemical vapor deposition technique and the molten core drawing method are presented. Also discussed are directions for continued study and development, including engineering the dispersion and nonlinear properties as well as improved interconnection./resource/bwmeta1.element.ieee-art-000008068187An Ultrafast Wideband Discretely Swept Fiber Laser
/resource/bwmeta1.element.ieee-art-000008038771
The wavelength sweeping technology has gained its popularity in various research areas for the high resolution and high throughput capabilities. Illuminating with continuously wavelength-swept spectra, traditional spectrally encoded optical systems show low detection sensitivities in either time or spectral domains, due to the optical power divergence. In addition, they can also deliver a nontrivial sampling rate when fast line scan is performed, easily go beyond 50 GS/s, which overwhelms the conventional data processing system. In this paper, we demonstrate a 15-MHz discretely swept source at a bandwidth of ∼70 nm particularly for high-speed spectrally encoded applications. The wideband discretely swept laser exhibits higher peak power, which enhances the detection sensitivity of optical system by more than 3 dB. The discretely sweeping characterization of the proposed laser is also proved to have the potential of reducing the data stream for fast processing without compromising the line-scan rate. It is believed that the efforts made in this paper provide a promising resolution for <italic>in situ</italic> ultrafast optical diagnosis at a higher sensitivity./resource/bwmeta1.element.ieee-art-000008038771High-Power and High-Order Random Raman Fiber Lasers
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High-order random Raman fiber lasers are investigated for generating high-power widely wavelength-tunable light sources. By cascaded random Raman lasing and adjusting pump laser wavelength, continuous wavelength tuning from 1 to 1.9 μm is reported. For power scaling, a high-power Yb-doped fiber laser at 1064 nm with improved temporal stability is developed as the pump source. The ninth-order cascaded random Raman fiber laser with a spectral purity of 86.6% is achieved at 1806 nm. Up to 100.1-W inband power is obtained with an optical efficiency of 38.4% from 1064 nm and 27.2% from 915 nm. The results prove that cascaded random Raman  fiber laser is a versatile technology to generate  high-power fiber laser at wavelength  outside the rare earth emission bands./resource/bwmeta1.element.ieee-art-000008063932Switchable Dual-Wavelength Cylindrical Vector Beam Generation From a Passively Mode-Locked Fiber Laser Based on Carbon Nanotubes
/resource/bwmeta1.element.ieee-art-000008064690
Cylindrical vector beams (CVBs) with axial symmetry in both polarization and field intensity have attracted much attention because of their unique optical properties. Conventional methods to obtain CVBs including direct modulation of light beams in free space and high-order mode excitation by offset splicing single-mode fiber with few-mode fiber usually works at single wavelength with rather narrow bandwidth. Here, for the first time to the best of our knowledge, we demonstrate switchable dual-wavelength CVB generation from a passively mode-locked fiber laser using carbon nanotubes as saturable absorber for mode-locking and a home-made mode-selective coupler as both mode converter and birefringence filter. In experiments, the mode-locked fiber laser delivers CVB pulses of dual-wavelength (1532.5 nm and 1555.5 nm) and corresponding single wavelength with duration of hundreds of femtosecond, respectively. Moreover, the output polarization status is switchable between radially and azimuthally polarized states. The mode-locked CVBs with wavelength and polarization flexibility may have potential applications in mode-division multiplexing optical fiber communication, nanoparticle manipulation, material processing, nonlinear optics, and so on./resource/bwmeta1.element.ieee-art-000008064690Backward Supercontinuum Generation Excited By Random Lasing
/resource/bwmeta1.element.ieee-art-000008047943
Backward supercontinuum generation excited by random lasing is proposed and demonstrated for the first time. Unlike conventional supercontinuum generation, completely distributed random fiber laser is first used as an effective seeding laser to initiate supercontinuum emission in a composite configuration with TrueWave and dispersion compensated fibers. The two fibers provide both amplified random distributed feedback and nonlinear effect induced spectral broadening. Taking advantages of intrinsic characteristics of random distributed Rayleigh scattering and low-noise backward distributed Raman amplification of random lasing, backward supercontinuum is realized with much lower intensity fluctuation in time domain compared to the forward counterpart. The study of combined effects of random lasing and strong nonlinear mechanism not only enrich the research scope of supercontinuum and random fiber lasers, but also provide a practical way for the development of stable broadband light sources for various applications./resource/bwmeta1.element.ieee-art-000008047943Visible Raman-Shifted Fiber Lasers for Biophotonic Applications
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The efficient nonlinear conversion of Yb-doped fiber laser systems using a combination of stimulated Raman scattering and second-harmonic generation is an effective method for developing sources for biophotonic applications in the yellow–green spectral region. In this paper, we review recent progress in the development of these sources, compare the relative benefits of differing source architectures, and demonstrate stimulated emission depletion microscopy using an exemplar source./resource/bwmeta1.element.ieee-art-000008094929Modified Single Trench Fiber With Effective Single-Mode Operation for High-Power Application
/resource/bwmeta1.element.ieee-art-000008094902
In this paper, the modified single trench fiber (MSTF) is proposed. The core of MSTF is successively surrounded by the trench and ring whose refractive index is lower than that of the inner cladding and identical with that of the core, respectively. Performances of MSTF have been numerically investigated by the finite element method at 1-<italic> μ</italic>m region. Simulations show that the MSTF can provide much larger loss of least lossy high-order-mode than the step-index fiber (SIF) and even larger than the standard single trench fiber, which is beneficial to achieve effective single-mode (ESM) operation and enhance the threshold of transverse-mode instabilities. Furthermore, the MSTF fabricated by using a conventional technique (core NA ∼ 0.06) with 25 and 30 <italic>μ</italic>m core diameter can guarantee the ESM operation, which is much superior than the SIF with the same parameters. The MSTF with the core diameter of 25 <italic>μ</italic>m is fabricated by using a conventional fabrication method. Excellent high-order-mode suppression and ESM operation based on the MSTF are experimentally verified. Finally, the MSTF is employed in a high-power fiber laser (HPFL), and the ESM operation (<italic>M</italic><sup>2</sup>-factor <1.1) is obtained up to 807 W. The MSTF is a practical candidate aiming at industrial HPFLs requiring ESM./resource/bwmeta1.element.ieee-art-000008094902Polarization Rotation Dynamics in Harmonically Mode-Locked Vector Soliton Fiber Lasers
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Polarization rotation dynamics for group velocity locked vector solitons in higher order harmonically mode-locked soliton fiber lasers are studied for the first time, in a thulium/holmium fiber laser. In a linear ultrafast fiber laser with net anomalous dispersion, harmonically mode-locked states are generated continuously by increasing the pump power for specific net cavity birefringence settings. The polarization evolution frequency remains the same for all harmonically mode-locked pulse trains, converging toward a singular solution close to the maximum pulse intensity modulation depth for each respective harmonically mode-locked state. With a polarization resolved output, an intensity modulation of the ultrafast pulse train with varying pulse binning is recorded, corresponding to the polarization rotation of the vector solitons. In addition, a polarization rotation vector soliton state with two different sets of RF sidebands symmetric to the repetition rate is observed, which leads to a more complex modulated pulse train. The experimental results of the polarization evolution also matche well with the presented theoretical modeling. Similar relative intensity noise <0.4% for all harmonically mode-locked states is measured. This method to modulate the intensity of an ultrafast pulse train and tune its pulse spacing by integer fractions of the initial round trip time shows a strong potential for applications in optical communications, polarization de multiplexing schemes, and sensing./resource/bwmeta1.element.ieee-art-000008093984High-Repetition-Rate Ultrafast Fiber Lasers for Material Processing
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Ultrafast lasers operating at high repetition rates, in particular the GHz range, enable new possibilities in laser-material processing, particularly accessing the recently demonstrated ablation-cooled regime. We provide a unified perspective of the unique opportunities created by operating at high repetition rates together with our efforts into the development of enabling laser technology, including new results on further scaling up the capabilities of the laser systems. In order to access GHz repetition rates and microjoule-level pulse energies without requiring kilowatts of average power, we implement burst-mode operation. Our results can be grouped into two distinct directions: low- and high-power systems. Pulsed pumping is employed in the later stages of low-power systems, which have low burst repetition rates to achieve high pulse energies, whereas the technique of doping management is developed for the continuously pumped power amplifier stage of high power systems. While most of the developments have been at 1-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m wavelength range due to the relative maturity of the laser technology, we also report the development of Tm-fiber lasers around the 2- <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m region specifically for tissue processing and laser-surgery applications./resource/bwmeta1.element.ieee-art-000008103327Impact of Spectral Filtering on Multipulsing Instability in Mode-Locked Fiber Lasers
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We investigate the impact of spectral filtering in mode-locked fiber lasers with an extended geometrical model. Our iterative model, which includes gain, loss, and the pulse shaping effects of chromatic dispersion and self-phase modulation, is used to model the laser cavity dynamics. Simulations show that broadband pulses experience large losses from spectral filtering in the cavity, leading to a number of potential laser instabilities and outcomes such as multipulsing, periodic and chaotic states, or a single pulse which transits to a higher energy state. For narrow band spectral filtering, the laser dynamics is dominated by the gain–loss dynamics in the cavity which causes multipulsing. For broadband spectral filtering, the nonlinearity-induced spectral reshaping of the single pulse can lead to a discontinuous pulse energy transition that circumvents multipulsing. The inclusion of third-order dispersion shows that the multipulsing instability is induced even in the case of broadband spectral filtering./resource/bwmeta1.element.ieee-art-000008103744Dead-Band-Free, High-Resolution Microwave Frequency Measurement Using a Free-Running Triple-Comb Fiber Laser
/resource/bwmeta1.element.ieee-art-000008098584
Microwave photonic solutions of frequency measurement have advantages in broad frequency coverage, but achieving high-resolution measurement remains a challenge. Those schemes based on optical frequency combs could achieve high-resolution measurement over a broad frequency range. Here, a dead-band-free, high-resolution microwave frequency measurement scheme based on undersampling the microwave signal by three pulse sequences generated from a triple-wavelength mode-locked fiber laser is proposed and demonstrated. The triple-wavelength ultrashort pulses generated in one laser cavity have slightly different repetition rates due to chromatic dispersion. This eliminates the needs of multiple mode-locked lasers and frequency control between them and drastically reduces the system complexity. The absolute frequency of the microwave signal can be determined based on three down-converted low-frequency beat notes of the microwave signal with the nearest comb lines without ambiguity. A 10<sup>–10 </sup> relative measurement precision at a sampling speed of 100 Hz is demonstrated from 1 to 20 GHz, and the measurement accuracy remains within 0.3 Hz. Microwave signal with an RF power as low as −75 dBm can be measured with a 10 Hz precision at 10 GHz by using RF frontend amplifiers. The simple and compact triple-comb fiber laser would enable the development of low-complexity, high-performance microwave characterization instrument./resource/bwmeta1.element.ieee-art-000008098584Route to Larger Pulse Energy in Ultrafast Fiber Lasers
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Principles of pulse shaping aiming larger pulse energy in fiber lasers are reviewed. From conventional solitons generated in the anomalous dispersion regime, stretched pulses in dispersion-managed fiber lasers, similaritons in normal dispersion regime, dissipative solitons in large normal dispersion regime, and amplifier similaritons in fiber lasers with narrow bandwidth filtering to dissipative-soliton-resonance (DSR) pulses in fiber lasers, scaling of pulse energy from picojoule level to microjoule is successfully achieved. DSR is a possible way to achieve endless pulse energy, which is limited by the available pump power and material damage threshold. Properties of DSR pulses are reviewed. Specifically, we experimentally and numerically demonstrate tilt-top DSR pulses in a normal dispersion mode-locked fiber laser. Two fronts of the tilt-top pulses exhibit different intensity, and the intensity disparity maintains while the pulses extend with increasing gain. The tilt-top DSR pulses have rectangular spectral pedestal and a peak. The spectral peak deviates from the center of the rectangle spectral pedestal. Further results show that the asymmetry of two fronts is closely related to the wavelength deviation of spectral peak. Numerical simulations reveal the importance of the saddle-type spectral filtering on asymmetric DSR pulse generation./resource/bwmeta1.element.ieee-art-000008100943Graphene-Assisted All-Fiber Optical-Controllable Laser
/resource/bwmeta1.element.ieee-art-000008085117
All-optical controlling provides the burgeoning, precise, and compact access in photonics and optoelectronics with tunable performance. Through tuning physical parameters of optical-controlled devices, such as effective index, bandwidth and dispersion, the output characteristics of free-running lasers can be manipulated for widespread applications in spectroscopy and laser biology. Among which the flexible optical-thermal tunability of graphene introduces an advantageous avenue for the enhancement of photosensitivity of optical-controlled devices to efficiently regulate laser properties. Here, we fabricate an optical-controllable fiber filter based on a graphene-assisted micro-fiber Bragg grating, whose wavelength can be linearly tuned by controlling pump light, and a tuning step of 3.1 pm is achieved. By cooperating it with a fiber laser operating at a Q-switched mode-locked state, the lasing wavelength is all-optically controlled with a linear tuning sensitivity of 23.5 pm/mW. Considering the optical controlling performances, such a wavelength-tunable fiber laser may find potential applications in all-optical computing, all-optical logic gating, and generation of microwave source./resource/bwmeta1.element.ieee-art-000008085117Multimode Fiber Raman Lasers Directly Pumped by Laser Diodes
/resource/bwmeta1.element.ieee-art-000008082791
Raman fiber lasers (RFLs) are usually based on single-mode fibers core-pumped by high-power rare-earth-doped fiber lasers with single transverse mode output that leads to a rather complicated design of RFLs. One of interesting possibilities to simplify the RFL design is its direct pumping by cheap and reliable high-power multimode laser diodes (LDs). It is attractive to use standard graded-index multimode passive fibers characterized by very high quality and low cost due to their wide use in telecom. In this case, one can directly couple the multimode radiation of high-power LDs with moderate brightness into the core of multimode graded-index fiber with much higher efficiency than into the core of single-mode fiber. Using commercially available multimode LDs with operating wavelengths of 915–940 nm, it is possible to obtain high-power high-beam-quality Raman lasing in wavelength range of 950–1000 nm, which is problematic for rare-earth-doped fiber lasers. Here, we review the results obtained in this direction and report on the demonstration of all-fiber LD-pumped CW Raman laser based on the graded-index fiber. A joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of fiber core, results in high-efficiency conversion of multimode (M<sup>2</sup>∼26) pump at 915 nm into a high-quality output beam at 954 nm. Fibers with core diameter of 62.5, 85, and 100 <italic> μ</italic>m are compared. With core enlargement, the conversion efficiency increases sufficiently (from 47% to 84%) at the expense of slight beam-quality parameter reduction (M<sup>2</sup> = 1.3–3). The generated spectrum remains to be rather narrow (<0.4 nm) at output power >60 W./resource/bwmeta1.element.ieee-art-000008082791Fiber Lasers of Prof. Okhotnikov: Review of the Main Achievements and Breakthrough Technologies
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This review is dedicated to the scientific work of Professor Oleg G. Okhotnikov (April 8, 1951 to April 8, 2016), an inspired scientist who has made a significant contribution to the development of fiber lasers. Prof. Okhotnikov published more than 280 journal articles, 100 conference papers, and numerous patents, many of which represented pioneering work in the area of fiber lasers. This article highlights the most valuable scientific and technological breakthroughs in fiber lasers achieved by Prof. Okhotnikov and his research groups./resource/bwmeta1.element.ieee-art-000008226808Complete Field Characterization of Ultrashort Pulses in Fiber Photonics
/resource/bwmeta1.element.ieee-art-000008186142
We report a simple fiber-implemented technique for complete reconstruction of intensity profile and phase of ultrashort laser pulses based on processing only pulse spectrum and two self-phase modulated spectra measured after a short piece of optical fiber. Its applicability is shown on an example of a fiber optical system in the telecommunication range. A retrieval algorithm in a dispersionless approximation and with considering dispersion effects is developed. The obtained results are confirmed by independent measurements using the second-harmonic generation frequency-resolved optical gating technique and by reconstructing purposely introduced signal features. We also provide estimates demonstrating great opportunities for implementing this technique in all-waveguide optical systems ranging from optical communications to nanophotonics with femtojoule pulses as well as to mid-IR photonics, where specialty fibers with huge optical nonlinearities can be used./resource/bwmeta1.element.ieee-art-000008186142Mode-Locked Erbium-Doped Fiber Lasers Using 45° Tilted Fiber Grating
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We have systematically studied the 45° tilted fiber grating (45TFG) as a functional device for erbium-doped fiber laser (EDFL) mode locking. A number of 45TFGs with different polarization-dependent loss (PDL) have been fabricated. Mode-locked (EDFL) using these devices have been characterized in terms of threshold, pulse duration, signal-to-noise ratio, and spectral width. Our results show that a 45TFG with higher PDL could achieve better laser results. By using a 45TFG with 24 dB PDL, the mode-locked laser has 8.1% conversion efficiency and a threshold of 200 mW./resource/bwmeta1.element.ieee-art-000008125082Octave Spanning Coherent Supercontinuum Comb Generation Based on Er-Doped Fiber Lasers and Their Characterization
/resource/bwmeta1.element.ieee-art-000008118181
Wideband, octave spanning, coherent supercontinuum (SC) with high flatness is very useful for many applications, but it has been difficult to achieve such ideal SC. In this paper, we investigated the octave spanning, coherent SC generation based on Er-doped ultrashort pulse fiber laser system. First, we developed a high power ultrashort pulse system using a single-wall carbon nanotube fiber laser and similariton amplifier. A 1.0–2.2 <italic>μ </italic>m octave-spanning coherent supercontinuum was successfully generated. Next, by use of a stabilized fiber laser comb system as the seed pulse, an octave spanning SC comb was demonstrated. An octave spanning, highly coherent comb with high flatness was generated with normally dispersive highly nonlinear fiber. The characteristics of the generated supercontinuum comb were examined via balanced heterodyne beat measurements with stable continuous-wave laser diodes. The SC comb was confirmed to have high coherence and low amplitude noise at the observed wavelengths. Finally, the SC generation in two kinds of highly nonlinear fibers with different dispersion properties and the characteristics of the generated comb were examined. The dependence on fiber length, wavelength, and dispersion properties were discussed./resource/bwmeta1.element.ieee-art-000008118181Resonant SRS Filtering Fiber for High Power Fiber Laser Applications
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We explore the properties of a novel stimulated Raman scattering (SRS) filtering fiber for high average or high peak optical power delivery applications. The fiber geometry is based on a series of circularly arranged high index rods embedded in a leaky silica cladding. The operation principle relies on the resonant coupling of the core and rod modes and the wavelength-dependent leaking of the structure. The fabricated fiber demonstrated wide transmission window and filtering of SRS with extinction in excess of 20 dB at the Raman Stokes wavelength, excellent robustness with bending, and high output beam quality. The fiber has been tested as a beam delivery fiber of a commercial pulsed fiber laser system in order to explore the filtering performance and its limitations./resource/bwmeta1.element.ieee-art-000008110630High Average Power Thulium-Doped Silica Fiber Lasers: Review of Systems and Concepts
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Thulium-doped fiber lasers (TDFLs) have had the second highest growth in average output power next to ytterbium-doped fiber lasers. This has been enabled by access to high power, high brightness ∼790-nm pump diodes in conjunction with the cross-relaxation process that improves laser efficiency. While numerous high power TDFLs have been recently demonstrated, a 1-kW result from 2010 remains the highest output power system reported to date. This paper reviews these systems and the concepts behind high power TDFLs. The spectroscopic properties of Tm<sup>3+ </sup>-doped silica are first detailed, revealing complex processes and large variations among published measurements. Notable multi-100 W TDFLs are then summarized, with outputs ranging from 1908 to 2130 nm. Another route for power scaling is to in-band pump with another TDFL to enable >90% efficiencies. Both 790- and 1900-nm pumped TDFL architectures are theoretically modeled based on currently available systems. Hindered by high background losses and available pump sources, achieving >4 kW like ytterbium-fiber systems will be a substantial challenge./resource/bwmeta1.element.ieee-art-000008115290Dynamics of Dispersive Wave and Regimes of Different Kinds of Sideband Generation in Mode-Locked Soliton Fiber Lasers
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We give a thoroughly theoretical and numerical investigation of sidebands generation in mode-locked soliton fiber lasers for the first time. A simple and reliable numerical method is proposed to separate the dispersive wave and soliton in the ultrashort pulse of a mode-locked fiber laser. We find that the dip-type sideband generation can be regarded as a locally destructive interference between the resonance-enhanced dispersive waves and solitons, which can also be explained by the parametric process in the fiber laser. The dip-type sidebands are also Kelly sidebands according to their formation. Simulations confirm the rationality of our proposed explanation and method. Our work gives an insight into the dynamics of soliton mode-locked fiber lasers./resource/bwmeta1.element.ieee-art-000008128502Asymptotically Single-Mode Hybrid Fiber for Dispersion Management Near 1 μm
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In this paper, we demonstrated the possibility of efficient dispersion management using a newly developed asymptotically single-mode hybrid fiber that has anomalous dispersion in the 1 μm spectral range. Of the few internal modes of the hybrid fiber, only one mode can propagate at a length longer than 6 m because of the mode's differential optical absorption. This feature was achieved by inserting a highly absorbing ring layer at the position of the electric field minimum of the hybrid mode. About 10 m of an asymptotically single-mode hybrid fiber with an anomalous dispersion of ∼65 ps/(nm⋅km) at 1064 nm was used for the compression of 7 ps chirped pulses down to 440 fs duration. The use of the same hybrid fiber with a length of 6.5 m for intracavity dispersion management allowed us to demonstrate the stable operation of a ring soliton laser scheme based on a semiconductor satiable absorbing mirror. Pulses with duration of approximately 700 fs, a peak power of 850 W and energy as high as 0.55 nJ were extracted directly from the laser./resource/bwmeta1.element.ieee-art-000008125725Dissipative Rogue Waves Among Noise-Like Pulses in a Tm Fiber Laser Mode Locked by a Monolayer MoS2 Saturable Absorber
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We report on the experimental and numerical investigations of dissipative rogue waves (DRWs) among noise-like pulses, in a thulium-doped fiber laser mode locked by a monolayer MoS<sub>2</sub> saturable absorber. By increasing the pumping power or weakening the effective cavity spectral filtering, the statistics distributions of the pulse events deviate from the Gaussian statistics to the L-shaped distributions with long tail, accompanied by the increase of the DRWs proportion. Our observations reveal the dissipat-ive nature of rogue waves in dissipative systems./resource/bwmeta1.element.ieee-art-000008030045Identification of Coherent and Incoherent Spectral Sidebands in an Ultrafast Fiber Laser
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Ultrafast fiber lasers, as the soliton pulse sources, offer great platforms for the investigations of soliton dynamics. Since both the coherent and incoherent spectral sidebands could be shown on the soliton spectrum, herein we proposed a method to identify them by using the dispersion Fourier transformation (DFT) technique. According to the principle of DFT technology, for the coherent spectral sidebands, that is, Kelly sidebands in the mode-locked fiber laser, they could be mapped to the temporal waveforms after the DFT process. However, the incoherent spectral sidebands, namely continuous waves, would disappear on the shot-to-shot spectra after DFT due to their uncertain phase relation. The obtained results would deepen our understanding of spectral sidebands./resource/bwmeta1.element.ieee-art-000007987730Exploration in Performance Scaling and New Application Avenues of Superfluorescent Fiber Source
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Thanks to the unique properties such as spatially coherent, broadband emission spectrum, and high temporal stability, superfluorescent fiber source (SFS) has shown tremendous potential in wide applications of sensing, imaging, spectroscopy, and material processing. The fast development of active fiber and pump diode provides unprecedented opportunity for the performance scaling of SFS. In this paper, the new horizon opened by the recently developed SFS will be reviewed. First, the output power scaling of SFS with different architectures will be summarized, and a kilowatt-level high power SFS based on a tandem pumping technique will be demonstrated for the first time. Second, spectrum manipulation of SFS, including coverage extending and spectrum shaping, will be introduced in detail. What is more, the spectrum evolution of narrowband SFS in power scaling will be numerically modeled and evaluated. Third, several novel applications of SFS, including midinfrared laser generation, nonlinear effect suppression, sensing, and imaging, will be given, indicating the versatile performance of SFS compared with traditional fiber laser oscillators. Based on the new developed SFS, we will present the first hundred-watt level linearly polarized random fiber laser. In the last section, future endeavors on SFS will be presented./resource/bwmeta1.element.ieee-art-000007974747Continuous-Wave 3.1–3.6 μm Difference-Frequency Generation of Dual Wavelength-Tunable Fiber Sources in PPMgLN-Based Rapid-Tuning Design
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We report on a single-frequency continuous wave (CW) difference-frequency generation (DFG) source based on single-frequency wavelength-tunable polarization-maintaining ytterbium- and erbium-doped fiber master oscillator–power amplifiers (MOPAs), acting as the pump and signal source, respectively, and a 40-mm long periodically poled MgO-doped LiNbO<sub>3</sub> (PPMgLN) crystal. Owing to the dual wavelength-tuning of the MOPAs, the generated idler light reaches a wavelength-tuning range of close to 500 nm, from ∼3117.2 to ∼3598.8 nm, only by tuning the launched pump and signal wavelengths from 1040 to 1084.6 nm and from 1545.2 to 1561.4 nm, respectively, without any change of temperature or grating period of the PPMgLN. Compared to temperature-based idler-wavelength-tuning, this method is potentially faster in speed. The maximum idler power exceeds 60 mW, which is the highest reported power for a wavelength-tunable single-frequency CW DFG source. A rapidly wideband-tunable DFG source with tens of milliwatts of output power in a narrow line can be a practical tool for mid-infrared molecular spectroscopy, detection, and sensing at high measurement rates./resource/bwmeta1.element.ieee-art-000007973076Tunable High-Power Q-Switched Fiber Laser Based on BP-PVA Saturable Absorber
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Black phosphors (BP) nano-materials have been extensively investigated in the past years. However, the character of easily oxidizable limits BP's stability. Here a long-term-stable tunable Q-switched fiber laser with BP polymer composite (polyvinyl alcohol, PVA) as saturable absorber is realized. The modulation depth and the saturation power intensity of the BP-PVA film are 8.3% and 7.9 MW/cm<sup>2</sup>, respectively. A high average output power of 12.03 mW is obtained under the pump power of 400 mW. The shortest pulse width and maximum single pulse energy are 1.365 μs and 148.63 nJ, respectively. Meanwhile, the output spectra have a 2.5-nm blue shift when the pump power increases. The results prove that as a Q-switcher, BP polymer composite has a good performance on high power and excellent stability pulsed laser./resource/bwmeta1.element.ieee-art-000007953480Multiwavelength Coherent Brillouin Random Fiber Laser With Ultrahigh Optical Signal-to-Noise Ratio
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A narrow-linewidth multiwavelength Brillouin random fiber laser (MW-BRFL) was experimentally demonstrated and characterized, which was achieved by mutually combining Brillouin amplification with randomly distributed Rayleigh feedback in optical fibers. By cascading process through a sub-fiber loop, up to six orders Stokes emissions simultaneously resonate in a coherent lasing fashion under the acoustic coupling of stimulated Brillouin scattering in the presence of coherent Rayleigh scattered random feedback, which acts as an optical filter with the high reflection coefficient for lowest order longitudinal mode of each Stokes line to ensure single longitudinal mode operation. Consequently, random laser output with an unprecedented ultra-high optical signal-to-noise ratio of ∼47 dB and an optimal peak power discrepancy of 1.8 dB were obtained. Furthermore, each Stokes random lasing emission with narrow linewidth of ∼1 kHz was achieved thanks to coherent random lasing. Relative intensity noise transfer was observed in sequence from the first-to sixth-order Stokes emission. In this MW-BRFL, a wide tunable range over 30 nm of the operating wavelength was validated by shifting the central wavelength of the input pump from 1530 to 1560 nm. Meanwhile, the statistical properties of the MW-BRFL and the performance optimization were also experimentally investigated./resource/bwmeta1.element.ieee-art-000007940072Passively Q-Switched and Mode-Locked Fiber Laser Based on an ReS2 Saturable Absorber
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Transition metal dichalcogenides, a family of two-dimensional material with unusual electronic, optical, mechanical, and electrochemical properties, have received much research attention in recent years. Here we demonstrate that, another type of few-layer transition metal dichalcogenides, rhenium disulfide (ReS<sub>2</sub>) nanosheets display saturable absorption property at 1.55 μm. By incorporating the ReS<sub>2</sub> nanosheets with the polyvinyl alcohol (PVA), a film-type ReS<sub>2</sub>-PVA saturable absorber is fabricated to realize Q-switching and mode locking of erbium-doped fiber lasers. The repetition rate of the Q-switched laser pulses varies from 12.6 to 19 KHz while the duration changes from 23 to 5.496 μs by tuning the pump from 45 to 120 mW. By optimizing the polarization state, the mode-locked operation is also obtained, emitting a train of pulses centered at 1558.6 nm with the duration of 1.6 ps and the fundamental repetition rate of 5.48 MHz. It is demonstrated that ReS<sub>2</sub> nanosheets have the similar saturable absorption property as that of MoS<sub>2</sub> and WS<sub>2</sub>, and may find potential applications in pulsed laser, optical modulators, and sensors./resource/bwmeta1.element.ieee-art-0000079454798.3 mJ, 166 W Burst Mode Pulse Fiber Amplifier Based on a Q-Switched Mode-Locked Fiber Seed Laser
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We report a 166 W burst mode pulse fiber amplifier seeded by a Q-switched mode-locked all-fiber laser at 1064 nm based on a fiber-coupled semiconductor saturable absorber mirror. With a pump power of 230 W at 976 nm, the output corresponds to a power conversion efficiency of 74%. The repetition rate of the burst pulse is 20 kHz, the burst energy is 8.3 mJ, and the burst duration is ∼ 20 <italic>μ</italic>s, which including about 800 mode-locked pulses at a repetition rate of 40 MHz and the width of the individual mode-locked pulse is measured to be 112 ps at the maximum output power. To avoid optical damage to the fiber, the initial mode-locked pulses were stretched to 72 ps by a bandwidth-limited fiber bragg grating. After a two-stage preamplifier, the pulse width was further stretched to 112 ps, which is a result of self-phase modulation of the pulse burst during the amplification./resource/bwmeta1.element.ieee-art-000007926357Fiber Optofluidic Microlaser With Lateral Single Mode Emission
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We report a low threshold fiber optofluidic microlaser, based on a microstructured optical fiber (MOF). The particular MOF structure is used not only as the microfluidic channel for sampling the liquid gain, but also as a spectral filter to achieve the single mode emission. Lateral laser emission from the MOF is observed when 1 mM Rhodamine 6G in ethanol is sucked into the MOF by the capillary force and pumped with a pulsed laser. It requires a low volume, ∼470 pL, of the gain materials. Single mode emission with a full width at half-maximum (FWHM) of 53 pm is obtained with a threshold of 13.2 μJ/mm<sup>2</sup>. The filtering effect is investigated both experimentally and theoretically by the interference within the cavity. The dependence of the number of modes on the lateral position of the pump with respect to the MOF is also discussed By using the single mode emission, it is promising for the multiplexing of optofluidic lasers in the spectral domain./resource/bwmeta1.element.ieee-art-000007940047Power Scaling of Linearly Polarized Random Fiber Laser
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The power scaling of linearly polarized random fiber lasers (RFLs) is investigated in detail based on master oscillator power amplifier configuration. A 442-W linearly polarized output with a narrow 3-dB linewidth of 0.28 nm and a 621-W linearly polarized output with a relatively wider 3-dB linewidth of 2.7 nm are realized. Besides, near-diffraction-limited beam quality and high polarization extinction ratio are obtained in both situations, and further power scaling is limited by the onset of mode instability (MI). To the best of our knowledge, these results are highest output powers of linearly polarized RFLs for the time being, in the narrow-linewidth and wide-linewidth situations, respectively. Meanwhile, the differences in the spectral broadening factor and the MI threshold between the narrow-linewidth linearly polarized RFL and the wide-linewidth one are discovered and discussed for the first time. It is experimentally demonstrated that relatively wider linewidth of the RFL seed is in favor of reducing the spectral broadening and increasing the MI threshold, providing significant reference for power scaling of linearly polarized RFL./resource/bwmeta1.element.ieee-art-000007964668Widely Wavelength-Tunable Mid-Infrared Fluoride Fiber Lasers
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We demonstrate widely wavelength-tunable conti-nuous-wave (CW) and Q-switched Er<sup>3+</sup>-doped ZBLAN fluoride fiber lasers operating around 3 μm enabled by a volume Bragg grating (VBG). In the CW operation regime, a total wavelength tuning range of over 160-nm spanning from 2694 to 2854 nm has been achieved. For the Q-switched mode of operation, a slightly modified resonator configuration, incorporating a passive Q-switcher, topological insulator Bi<sub>2</sub>Te<sub>3</sub> nanosheets, can produce stable pulse trains with a pulse width of 880 ns at a repetition rate of 81 kHz, while maintaining a wavelength tuning range of 62 nm from 2762 to 2824 nm through adjusting the VBG. In both operation regimes, the output spectral width is measured to be <0.3 nm (full-width at half-maximum) over the whole tuning range. Our work both demonstrates the great wavelength-tuning potential of the Er<sup>3+</sup> -doped fluoride fiber laser, and also paves a way for the development of a range of high-performance midinfrared laser sources./resource/bwmeta1.element.ieee-art-000007961266Ge-Rich SiGe Mode-Locker for Erbium-Doped Fiber Lasers
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A nonstoichiometric Si<sub>1−</sub><italic><sub>x</sub></italic>Ge<italic><sub>x</sub></italic> with composition ratio dependent saturable absorption prepared by vaporized synthesis and chemical exfoliation is performed to passively mode-lock the Erbium-doped fiber laser (EDFL). The Si<sub>1−</sub><italic><sub>x</sub></italic>Ge <italic><sub>x</sub></italic> with varied Ge/Si composition ratio from 3 to 16 exhibits tunable nonlinear modulation depth from 17% to 22%, where the Si<sub>1−</sub><italic><sub>x</sub></italic>Ge<italic> <sub>x</sub></italic> with the highest Ge content performs the largest nonlinear modulation depth. When operating the EDFL in the self-amplitude modulation region, the Si<sub>1−</sub><italic><sub>x</sub></italic>Ge<italic><sub>x </sub></italic> with Ge/Si composition ratios of 3, 9, and 16 self-starts the EDFL pulsation with pulsewidths of 820, 760, and 730 fs. When operating the EDFL in high gain region, the self-phase modulation induced soliton compression dominates the repulsation of passively mode-locked EDFL, which slightly shrinks the EDFL pulsewidth from 346 to 338 fs. All these demonstrations are premier and important to explore the superior nonstoichiometric Si<sub> 1−</sub><italic><sub>x</sub></italic>Ge<italic><sub>x</sub></italic> saturable absorbers for ultrafast fiber lasers./resource/bwmeta1.element.ieee-art-000007914665Effects of Nanomaterial Saturable Absorption on Passively Mode-Locked Fiber Lasers in an Anomalous Dispersion Regime: Simulations and Experiments
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In recent years, several kinds of nanomaterials have been successfully used for passive mode-locking, but it is not fully understand how the mode-locking performance is influenced by the different characteristics of these saturable absorbers (SAs). In this paper, we numerically and experimentally investigate the effects of nanomaterial saturable absorption (e.g., modulation depth and saturation intensity) on a passively mode-locked fiber laser in an anomalous dispersion regime. First, by numerically solving the Ginzburg–Landau equation, we analyze the evolution of the output performances (spectral bandwidth, pulse duration, and peak power) of passively mode-locked Er<inline-formula> <tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula>-doped fiber laser as the SA's modulation depth or saturation intensity. Then, we fabricate four nanomaterial-based SAs, which have the different modulation depth from 1.8% to 19.1%, the different saturation intensity from 11 to 180 MW/cm<inline-formula> <tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula>, and the similar insertion loss of <inline-formula> <tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>3 dB. Finally, we perform the experimental comparison of passively mode-locked Er<inline-formula><tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula>-doped fiber laser using the four nanomaterial-based SAs, respectively. Our results reveal that: 1) as the modulation depth increases, the mode-locked spectral bandwidth becomes wide and the pulse duration becomes short; and 2) the SA's saturation intensity has little influence on the output performance. The experimental results are in good agreement with the numerical simulations. This work could provide a useful guideline for choosing proper nanomaterial-based SA for different practical applications./resource/bwmeta1.element.ieee-art-000007907246Compact Single-Mode Nd-Doped Silicate Glass Multitrench Fiber With 40 μm Core Diameter
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We report a 40 μm core-diameter single-mode multitrench fiber (MTF) based on Nd-doped silicate glass. Both the delocalization effect and leaky nature were considered in the design of the MTF. The silicate MTF was designed and fabricated using the rod-in-tube method. A maximum laser output power of ∼8.4 W with a slope efficiency of 54% was obtained from a 10-cm-long single-mode MTF./resource/bwmeta1.element.ieee-art-000007823011Passively Mode-Locked Tm3+-Doped Fiber Laser With Gigahertz Fundamental Repetition Rate
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We propose and demonstrate a compact passively mode-locked <inline-formula><tex-math notation="LaTeX"> $\text{Tm}^{\text{3+}}\hbox{--}\text{doped}$</tex-math></inline-formula> fiber laser with a fundamental repetition rate up to 1.6 GHz. A 5.9 cm home-made, heavily <inline-formula><tex-math notation="LaTeX"> $\text{Tm}^{\text{3+}}\hbox{--}\text{doped}$</tex-math></inline-formula> barium gallo-germanate glass fiber with a gain coefficient of 2.3 dB/cm at 1950 nm is employed as gain medium. The compact Fabry-Pérot (FP) laser cavity contains a fiber mirror by directly coating the SiO<sub>2</sub>/Ta<sub>2</sub>O<sub>5</sub> dielectric films on a fiber ferrule. The miniature FP laser pumped by a 793-nm laser diode is passively mode-locked by a semiconductor saturable absorber mirror. Stable self-started mode-locking is successfully achieved at a low pump threshold of 107 mW. The mode-locked operation at the central wavelength of 1959.7 nm has a spectral bandwidth of 12.2 nm, and the pulse duration of 7.2 ps. In particular, the pulse repetition frequency of the fundamental mode-locking can be as high as 1.6 GHz. Moreover, numerical simulation for the 2-μm mode-locked Tm-doped fiber lasers is performed using the lumped model, and the numerical results are in good agreement with the experimental ones. This is, to the best of our knowledge, the highest fundamental repetition frequency for the 2-μm mode-locked fiber lasers./resource/bwmeta1.element.ieee-art-000007833181