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In this paper, a polarization-maintaining quad-wavelength (QW) single-frequency fiber laser (SFFL) at the C-band with the novel and compact structure is demonstrated. Applying the rate equations and multiple coupled nonlinear Schrödinger equations, the theoretical model of QW fiber lasers is established, and then the optical spectra, temporal evolution, and stability of the QW fiber laser are analyzed numerically. Based on the theoretical analysis, a QW-SFFL having an ultrashort linear distributed Bragg reflector cavity is proposed. Utilizing a wideband fiber Bragg grating coupled with a dual-channel polarization maintaining fiber Bragg grating as the wavelength selection and a 15-mm-long Er3+/Yb3+ co-doped phosphate fiber as the gain medium has realized a robust QW laser with the wavelength spacing of 0.4 nm. All the wavelengths maintain the single-frequency operation independently with the linewidths of 20 kHz. This type of compact SFFLs with quadruple wavelengths is widely adapted to lidar systems and fiber sensing. [ABSTRACT FROM AUTHOR]

Holey optical fibers with air-filled openings can be turned into unconventional optofluidic components by selectively introducing a suitable liquid into their internal holes. Enhanced interaction between the light guided by the fiber and molecular species suspended in the confined liquid then forms the basis for designing unique optofluidic devices—filters, sensors, or lasers—whose operating characteristics are extremely sensitive to minute changes in the liquid composition. We present a comprehensive mathematical analysis of dye lasers based on suspended-core and hollow-core fibers, with aqueous solution of Rhodamine B dye injected into the internal holes of the fibers acting as the gain medium. Our model consists of coupled first-order differential equations that characterize the population of lasing levels and the variation of pump and signal laser powers along the fiber length in the steady state. We obtain optimum operating conditions of the proposed holey fiber dye lasers, such as the optimum fiber length and dye concentration, and compare their performance to conventional dye jet lasers. We conclude that the fiber variant of dye laser using the hollow-core fiber is superior in terms of low lasing threshold and high slope efficiency. The presented theoretical framework can find applications in designing practical holey fiber dye lasers serving as fiber-based alternatives of conventional dye jet lasers as well as novel biological/chemical sensors and bio-lasers. [ABSTRACT FROM AUTHOR]

We report a 2.07-μm Holmium-doped all-fiber laser (HDFL) pumped by a 1.13-μm Ytterbium-doped fiber laser (YDFL). Home-made alumino–germano–silicate holmium-doped fiber (HDF) served here as an active medium, optimized in terms of chemical composition and co-dopants’ concentrations. Laser action at 2.07 μm was assessed in simple Fabry–Perot cavity, formed by a couple of home-made fiber Bragg gratings (FBGs), inscribed directly in the HDF; this allowed notable diminishing of intracavity loss of the 2.07-μm laser. HDF was in-core pumped by the 1.13-μm double-clad YDFL with a power of ∼12.5 W, in turn pumped in-clad by a laser diode (LD) operated at 0.97 μm with ∼24.5-W output. Using optimal length (∼5.0…5.5 m) of the HDF and employing FBG couplers with reflections of ∼99% and ∼33%, the HDFL provided ∼5.0-W output at 2.07 μm. At these conditions, maximal absolute (slope) efficiencies at 2.07 μm of 39% (42%) and 20% (22%) were measured with respect to 1.13-μm (YDFL) and 0.97-μm (LD) pumps, respectively. Moreover, the record slope efficiency (48%) was obtained for the powers ratio of 2.07-μm output (HDFL) to launched 1.13-μm input (YDFL), which is only slightly less than theoretical quantum efficiency limit (53%) for this kind of pump schemes. [ABSTRACT FROM AUTHOR]

We report on a widely tunable, dual-wavelength, continuous-wave, mid-infrared optical parametric oscillator (OPO), pumped by a dual-wavelength fiber source that was realized by combining two fiber lasers in series. The OPO was designed as a four-mirror singly resonant cavity, in which a periodically poled lithium niobate (PPLN) crystal was used as nonlinear crystal. Two idler emissions with different wavelengths were observed, one being basically fixed at 3140 nm and the other being tunable from 3227 to 3413 nm. Under the maximum pump power, the total idler power was over 6 W and the corresponding pump-to-idler slope efficiency reached 11.4%. The generated signal beam had just one central wavelength around 1600 nm. Through theoretical analysis and experimental verification, it was analyzed that two nonlinear processes, OPO and intracavity difference frequency generation (DFG), simultaneously occurred in the resonant cavity. The experimental phenomena revealed large widened DFG gain spectrum, which was in absolute contrast to simulation results based on classical DFG theory. It indicated great potential in practical application such ultra-wide nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

The light sources operating in the spectral range 1600–1800 nm are of great interest because of a number of potential scientific and practical applications. This stimulates a search for effective laser media for this wavelength region. Recent progress in the studying of bismuth (Bi)-doped fibers is related to the development of Bi-doped high-germania-core fibers for the mentioned wavelength region. This paper is concerned with the current state of the art in the research field of this kind of the laser-active fibers. The fabrication and spectroscopic properties of the Bi-doped high-germania-core fibers are described. The photo-induced bleaching and recovery stimulated by thermal treatment of luminescent centers in these fibers are presented. The review also includes the description of the basic parameters of the optical devices (continuous wave (CW) and pulsed lasers, amplifiers, superluminescent sources) developed using Bi-doped high-germania-core fibers. [ABSTRACT FROM AUTHOR]

We demonstrate a fiber-based femtosecond laser source, which can deliver 37 MHz, ~100 fs laser pulses tunable from 920 nm to 1030 nm with up to 10 nJ pulse energy. Pumped by an ultrafast Yb-doped fiber laser, a short piece of tapered photonic crystal fiber with lower dispersion was used to generate self-phase-modulation filtered for the tunable pulses. We believe that this new type of high-energy ultrafast fiber laser source can be an ideal solution for the two-photon fluorescence microscopy applications. [ABSTRACT FROM AUTHOR]

A soliton-locked Erbium-doped fiber laser is demonstrated for the first time using a pure Antimony (Sb) film as a saturable absorber (SA). The SA device is fabricated by depositing a 5 μm Sb layer onto a polyvinyl alcohol thin film via Physical vapor deposition process. Self-starting soliton mode-locked pulses train with a constant repetition rate of 0.99 MHz is obtained as the pump power increased from 101 mW to 142 mW. The laser operates at 1559 nm with a pulse width of 3.53 ps. At the pump power of 142 mW, the maximum peak power and pulse energy are calculated as 5.83 kW and 20.59 nJ, respectively. The obtainable pulse is very stable with a signal-to-noise ratio (SNR) of 70 dB. Our experimental results manifest that the pure Sb thin film-based SA is able to generate mode-locked pulsed laser at the 1.55-micron laser regime. [ABSTRACT FROM AUTHOR]

We report on a low-noise, robust, all-polarization-maintaining (PM) mode-locked Er-doped fiber ring laser, indicating an effective method to further optimize the phase noise by adjusting the pump power. Integrated from 10 Hz to 10 MHz, the optimized timing jitter is as low as 269 fs with an amplitude noise of 0.028%. The experimental results agree well with the prediction in a series of simulations and numerical analyses, revealing that the phase noise performance is improved by rebalancing the interactions between the gain, dispersion, and nonlinearity, and the high pulse energy and short pulse duration contribute to a reduction in the phase noise until the nonlinearities begin to neutralize the benefit. Consisting of a packaged semiconductor saturable absorber mirror and an all-PM-fiber ring structure, the laser performs well with reliable output pulses in vibrational environments, and most of the technical noise from external disturbances is also suppressed. [ABSTRACT FROM AUTHOR]

Distributed feedback Raman fiber lasers with $\pi $ -phase-shifted uniform gratings are modeled and simulated in the steady state, to optimize their performance. Using the parameters of realistic devices, it is found that the position change of the $\pi $ -phase-shift in a constant-strength uniform grating has a significant impact on the laser performance including right and left-hand-side output power and emission frequency, and linewidth. Also, it is shown that the optimum phase-shift position to maximize the laser uni-directionality is dependent on pump power and fiber loss value. A new design approach based on an engineered $\pi $ -phase-shifted step-like-strength uniform grating is presented demonstrating that even for a high-loss fiber (0.1 dB/m), the laser power and linewidth can be efficiently increased and decreased by ~25% and ~15%, respectively, for the same total device length and pumping condition, just by the proper choices of the phase-shift position and two coupling coefficients. [ABSTRACT FROM AUTHOR]

We demonstrate an all-polarization maintaining double-clad Er/Yb-codoped fiber laser with a nonlinear optical loop mirror, which delivers noiselike pulses (NLPs). The proposed configuration is featured for two different lengths of cavities (~210 and ~510 m), corresponding to the repetition rate of 985 and 402 KHz, respectively. The maximum pulse energy has reached to $1.54~\mu \text{J}$ , which is, to the best of our knowledge, the highest value increased by an order of magnitude than the previous work for NLPs directly generated from the laser output. The central wavelengths for both configurations have been obtained at 1616 and 1612.3 nm, which could fully cover the absorption lines of the ethane (C2H6) gas and could be applied in ethane gas detection. Simulation results are in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

We numerically investigated the compressibility of dissipative soliton pulses in an all-normal-dispersion fiber laser which was mode-locked with a nonlinear optical loop mirror. A transition state within the area between the traditional dissipative soliton regime and dissipative soliton resonance regime was revealed to have much higher dechirped peak power and shorter dechirped pulse duration than its vicinity. This phenomenon is reported for the first time to the best of our knowledge. The peak power and pulse width of the dechirped pulse were calculated using the linear compression method. The dynamics and the distribution of the transition state were systematically analyzed in laser parameter spaces. The nonlinear frequency chirp wasmainly induced by self-phase modulation and the pulse formation mechanism, which influenced the linear compressibility of the dissipative. We demonstrated that there were optimal filter bandwidth values corresponding to the best pulse compressibility under different laser parameters. The simulation results indicate that dechirped pulses with a pulse peak power of 0.5-1 MW, a pulse duration of the 100-fs level, and a pulse energy of ~100 nJ can be obtained using the optimal parameters. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a continuous-wave all-fiber ring laser generating cylindrical vector beams (CVBs) using a mode selective coupler (MSC) as transverse mode converter and mode splitter. The MSC is fabricated by a novel method free of pre-tapering, achieving LP11 mode with a high purity of >96% near the wavelength of 1064 nm. The CVB fiber laser operates at a center wavelength of 1053.9 nm, with a 3-dB linewidth of less than 0.04 nm and a signal-to-background ratio of >60 dB. The laser slope efficiency is >9%. The radially and azimuthally polarized beams can be switched by adjusting the polarization controllers in the fiber ring cavity, with a high mode purity measured to be >96%. [ABSTRACT FROM AUTHOR]

This paper presented a high-power 1018-nm ytterbium-doped fiber laser pumped bywavelength-stabilized laser diodes in bidirectional pumping structure. A record output power reaching 1150 W was achieved, along with a slope efficiency of 82.9% and a beam quality factor of M2 = 1.96. The output spectrum exhibited an efficient amplified spontaneous emission and parasitic lasing light suppression. The thermal effects were studied to verify the reliability of our 1018-nm FL as a practical 1-kW light source. Besides, an important investigation was made on the 1080-nm fiber laser tandem pumped by 1018-nm fiber lasers, the experimental result of which was reported to be 3712 W. [ABSTRACT FROM AUTHOR]

Efficient continuous-wave laser emission of acetylene molecules at 3.1 μm wavelength has been demonstrated in low loss hollow-core fiber by optically pumping using a fiber-amplified diode laser around 1.53 μm. In this paper, we report and compare the continuous-wave laser performance of acetylene molecules in the cavity and single-pass configurations. The use of low-loss antiresonant hollow-core fiber makes the single-pass configuration ideal for high-power laser generation and enables over 1.1 W continuous-wave mid-infrared laser output with over 33% slope efficiency relative to the absorbed pump power. The systematic characterization of power-scaling and pump power absorption properties demonstrates that the molecular kinetics inside hollow core fiber determines the laser performance, and that low fiber attenuation is key to high-efficiency continuous-wave output. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In ultralong fiber laser key distribution, two sides use standard optical equipment to create kilometer long fiber lasers in a communication link to establish a secret key. Its security rests on the assumption that any attack to learn the generated key would be unpractical while the legitimate users only need to use standard equipment.We present a challenge to that assumption with a hidden probe attack in which the eavesdropper hides a weak signal in the unavoidable noise floor that appears in the laser during amplification and probes with it the configuration of one or both communication parties.We comment how this attack can compromise different proposals for ultralong laser key distribution and propose possible countermeasures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 850Wand energy as high as 0.55 nJ were extracted directly from the laser. [ABSTRACT FROM AUTHOR]

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 μm 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. [ABSTRACT FROM AUTHOR]

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-bandfree, 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 10–10 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 triplecomb fiber laser would enable the development of low-complexity, high-performance microwave characterization instrument. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The potential of Fe 3 O 4 nanoparticles as a base material for saturable absorbers (SAs) that can operate in the 2 μm-wavelength regime, was investigated. An SA was fabricated on a sandwich-structured fiber-ferrule platform through the deposition of an Fe 3 O 4 mixture with polyvinyl alcohol (PVA) onto the end surface of the fiber ferrule. Using the prepared Fe 3 O 4 /PVA-composite-based SA within a Tm-Ho codoped fiber laser, stable Q-switched pulses were readily produced at 1894 nm. The temporal characteristics of the output pulses were investigated as a function of the pump power, and the maximum energy of the output pulses was 322 nJ. The temporal width of the output pulses was measured as 2.6 µs at the maximum pulse-repetition rate of 37.2 kHz. The output performance of the passively Q-switched Tm-Ho-codoped fiber laser in this work was compared with those of recently demonstrated, passively Q-switched Tm-doped fiber lasers for which the other types of saturable-absorption materials. [ABSTRACT FROM AUTHOR]

For the first time, a backward-pumped random distributed feedback fiber laser is applied to the conventional distributed Raman amplification (DRA). A new asymmetric DRA scheme for improving the signal power variation (SPV) performance was achieved. The scheme was studied numerically and was shown to effectively reduce the SPV of all signals to less than 1.2 dB, whilst maintaining a flat ON–OFF gain over 40 nm bandwidth for a 61.5 km fiber span. Moreover, the nonlinear Fourier transform technique, which is utilized to deal with the nonlinear noise, could be realized on the proposed scheme with such a low SPV. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a switchable narrow linewidth single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser with LP 11 transverse mode output. The laser is based on a mode selective all-fiber fused coupler which is composed of a single-mode fiber (SMF) and a two-mode fiber (TMF). By controlling the polarization state of the output light, the laser can provide narrow linewidth SLM output with LP 11 transverse mode at two specific wavelengths, which correspond to two transmission peaks of the chirped moiré fiber grating (CMFBG). The 20 dB linewidth of the fiber laser for each wavelength is approximately 7.2 and 6.4 kHz. [ABSTRACT FROM AUTHOR]

We propose a novel saddle-shaped Yb-doped fiber design for high power generation in the spectral range near 0.976 μm. The fiber has a central single-mode part with a core diameter of approximately 12 μm and an ultra-thin silica clad of approximately 49 μm. At both ends of the fiber, the core/clad diameters were adiabatically increased up to 20/80 μm to be compatible with ordinary passive fibers. A monolithic 976-nm single-mode continuous wave laser based on the proposed fiber was created. The laser’s power was a record high compared with all-fiber laser schemes, with an output power of 10.6 W. Utilization of a photodarkening-free core glass matrix has allowed us to demonstrate perfect long-term stability (without any power degradation) of the developed laser over 45 h. [ABSTRACT FROM AUTHOR]

Ultra-high temperature ceramics are widely used in hypersonic vehicles, nuclear reactors, and in other equipment that operates under extreme conditions. In particular, Zirconium Boride (ZrB12) is an ultra-high temperature refractory ceramic material with a melting point above 3000 °C. The measured laser damage threshold of ZrB12 is 132 mJ/cm2, higher than in many materials commonly used as saturable absorbers, making it suitable for work in high-power laser systems. Zirconium Boride is also used as a saturable absorber in an ytterbium-doped Q-switched fiber laser, producing pulses between 239 and 2600 ns. [ABSTRACT FROM AUTHOR]

We report an ytterbium-doped all-fiber laser generating dissipative soliton resonance (DSR) pulses with kilowatt-level peak power. The laser cavity was constructed with all-10/125 large-mode-area fibers to alleviate excessive nonlinear effects caused by high peak power. DSR pulse breaking and Raman-induced instability are avoided by carefully placing the fiber sections. Numerical and experimental investigation of high-peak-power DSR laser mode-locked with nonlinear optical loop mirrors is presented. Up to 1.66 W, 161-nJ energetic pulses are obtained without pulse-breaking. In particular, the laser generates pulses with 48-146 ps tunable pulse duration and an almost fixed peak power as high as 1.1 kW. To the best of our knowledge, this letter presents the first demonstration of DSR pulses with kilowatt-level peak power in mode-locked fiber lasers. [ABSTRACT FROM PUBLISHER]

We demonstrate multi-stage ytterbium-doped fiber amplifiers (YDFAs) seeded with a superluminescent light emitting diode (SLED). Laser pulses with four pulse durations, such as 350-ps, 6-ns, 55-ns, and 183-ns (full width half maximum), have been studied. The peak powers reach 332, 95, 119, and 92 kW for the four types of laser pulses, respectively. The 350-ps laser pulses are generated through gain switching. Thanks to the broadband optical spectrum of the seed laser from the SLED, the stimulated Brillouin scattering is avoided. The configuration of such YDFAs seeded by an SLED with adjustable laser pulse durations (from picosecond to nanosecond) is desirable for many industrial applications. [ABSTRACT FROM PUBLISHER]

A self-started stable tunable mode-locked soliton fiber laser in a linear cavity structure composed by commercial passive elements is presented in this paper. It is based on the combination of an erbium-doped fiber as the active medium, and a saturated fiber Bragg grating (FBG) as a partial mirror of the cavity. The other side of the cavity consists of a semiconductor saturable absorber mirror acting also as the mode-locking device. The central wavelength of the FBG is selected by the application of axial strain giving rise to a tunable soliton over 8.6 nm on the C band with a variable spacing of 0.01 nm. The laser delivers 18.9 ps long pulses with a 0.14 nm bandwidth, an 8.2 MHz repetition rate, a pulse energy of 89 pJ, and a peak power of 4.71 W. [ABSTRACT FROM PUBLISHER]

We reported an efficient ytterbium-doped vectorial fiber laser modulated by a low loss q-plate, which can manipulate the intra-cavity polarization evolution in a flexible and compact way. The vectorial fiber laser can deliver watt-level radially and azimuthally polarized laser around 1~\mu \textm from the same laser cavity with slope efficiency greater than 70.6%, and the polarization extinction ratio exceeding 97%. The polarization behavior of the radial and azimuthal polarization beams can be switched by simply controlling the intra-cavity polarization element. [ABSTRACT FROM PUBLISHER]

We report on the successful operation of a dissipative soliton fiber laser mode-locked with a bulk InGaAs-based saturable absorber mirror forming a resonant micro-cavity. Highly-chirped pulses with several nanojoules of energy are thus produced. Remarkably, the laser performances in terms of output power and amplitude stability are comparable to those obtained with their multiple-quantum-well-based counterparts. This letter suggests that this simplified approach for saturable absorber mirrors can be considered as a promising alternative regarding ultrafast optics applications. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate a narrow linewidth single-longitudinal-mode erbium-doped fiber ring laser with an output of tunable second-order optical vortex beams (OVB). The laser is based on a mode selective all-fiber fused coupler, which is composed of a single-mode fiber (SMF) and a few-mode fiber (FMF). The fused SMF–FMF coupler inserted in the cavity of the laser acts as a mode converter, which converts LP01 mode to LP21 mode group. The tunable OVB is produced by combing two even LP21 modes with orthogonal polarization directions. The tunability of second order OVB in the fiber laser is experimentally realized by adjusting a polarizer at the output end of the fiber. The 20 dB linewidth of the fiber laser is approximate 7.2 kHz. [ABSTRACT FROM PUBLISHER]

We report efficient high-average-power, high-energy passively Q-switched operation of an Er3+-doped fluoride fiber laser at room temperature with wavelength-tunable resonator configuration utilizing a plane ruled grating for wavelength selection. The fiber laser produced stable Q-switched pulses with a maximum average output power of 5.16 W at 2811.7 nm and a maximum pulse energy of 27.7~\mu \textJ at 2834.6 nm for 30.5-W launched pump power and could be tuned over a wavelength range of 90 nm from 2762.5 to 2852.5 nm, with > 4-W average power over the range of 76.1 nm. Our results present fivefold increase in output power over previously published values directly attained from ~3- \mu \textm passively Q-switched fiber lasers and firmly establish a fiber laser as a compact, wavelength-tunable, multiwatt, tens of microjoules mid-infrared pulse source with large scope of both industrial and scientific applications. [ABSTRACT FROM PUBLISHER]

For the first time, to the best of our knowledge, we demonstrate an all-fiber passively mode-locked thulium-doped fiber ring laser using evanescent field coupling in a tapered fiber with a single-layer graphene as a saturable absorber. The modulation depth limitation of a single-layer graphene is overcome by incorporating the graphene layer along the fiber longitudinal plane, effectively extending the interaction length between the single-layer graphene and the evanescent field. The fiber oscillator produces stable 0.98 ps soliton pulses with a pulse energy of 544 pJ, a 3 dB spectral bandwidth of 4.6 nm, and an RF signal-to-noise ratio of 70 dB. [ABSTRACT FROM PUBLISHER]

We propose a single, integrated fiber-optic device that possesses both passive Q-switching and active mode-locking functions. The structure of the integrated fiber-optic device consists of a bulk-structured Bi2Te3 topological insulator (TI) layer sandwiched between the surface of a piezoelectric transducer and the flat side of a side-polished fiber. The Bi2Te3 TI is used as a saturable absorption material to induce Q-switching while the piezoelectric transducer is used to produce an acousto-optical modulation function for mode-locking. The integrated fiber-optic device is used within an erbium fiber ring cavity to readily produce stable Q-switched mode-locked pulses at 1559 nm. Control of the modulation index of the acousto-optic modulation part together with the pump power was also shown to be able to change the laser operating regimes among CW, Q-switching, Q-switched mode-locking, and mode locking. [ABSTRACT FROM PUBLISHER]

We report a graphene Q-switched ytterbium-doped fiber laser with switchable cylindrical vector beam output. The 6–8 layers CVD-grown graphene films were transferred to the target substrate by an ultrasonic processing method, and its saturation intensity and modulation depth are measured to be about 0.61 MW/cm2 and 13.2% at 1072 nm by the Z-scan technique. We used a nanograting spatially variant waveplate as an intracavity polarization controlling element to convert pulsed Gaussian beam to radially or azimuthally polarized beam in the fiber laser cavity. Stable Q-switching operation can be achieved with the output power up to 253 mW and pulse energy 7.73 μJ at the maximum incident pump power. The polarization extinction ratio of radially and azimuthally polarized beam is 97.4% and 96.9%, respectively. The experimental results suggest that the graphene can act as a potential nonlinear optical material to modulate pulsed fiber lasers with spatially inhomogeneous polarizations. [ABSTRACT FROM PUBLISHER]

The redshift of the long wavelength plasmonic absorption band is essential to the use of gold nanorods (GNRs) for the implementation of the infrared broadband saturable absorbers (SAs). A common method to obtain the GNR-based SAs with a substantially broad absorption bandwidth from 1 to 2 μm is to use GNRs with a large aspect ratio. Here, a simple self-assembly technique is demonstrated, which enables us to obtain a significant redshift of the long wavelength plasmonic absorption peak of GNRs with a small aspect ratio, together with substantial spectral broadening of the absorption band. The proposed technique is based on an end-to-end self-assembly of the GNRs through hot air induced rapid drying of the GNRs in a deionized water solution, which makes the GNRs reassemble by attaching to one another by their ends. Using the proposed end-to-end self-assembly method for GNRs with an aspect ratio of 5.1, a single broadband SA that can operate from 1.5 to 1.9 μm was fabricated on a fiber ferrule based sandwich platform. The saturable absorption performance was tested by incorporating the fabricated GNR-based SA into two different optical fiber based ring cavities: One was based on an erbium-doped fiber and the other was a thulium–holmium codoped fiber. Our fabricated single SA readily produced stable Q-switched pulses from both the cavities. [ABSTRACT FROM PUBLISHER]

Investigation of tightly bunched solitons generated from the nonlinear polarization rotation (NPR) governed mode-locked erbium-doped fiber laser (ML-EDFL) is demonstrated. By changing the intra-cavity polarization, the solitons can be switched from the tightly bunched state to coarse bunched state. In the tightly bunched state (stable state), the energy fluctuation of soliton is substantially suppressed to ΔE/E = 2.5 × 10 −3 with a timing jitter of Δt = 16 ps. In addition, the dynamic evolution of bunched solitons in the NPRML-EDFL is also explored by configuring two output ports at different positions. As compared to the output node before the EDF, the tightly bunched solitons delivered from the output node after the EDF performs the shorter pulsewidth of 380 fs with the lower noises with ΔE/E = 1.6 × 10−3 (timing jitter Δt = 12 ps). Enlarging pump power promotes the split number of bunched solitons within one mode-locked pulse envelope. The individual soliton of different orders experiences different amounts of long-range attractive force from solitons, which leads to an unequalized spacing between the adjacent solitons occurred within bunched pulse envelope. The chirp parameter of C = −0.022 is dominated by the cooperation of group-delay dispersion and self-phase modulation effects, which can further compress the EDFL pulse to <400 fs. [ABSTRACT FROM PUBLISHER]

We demonstrate a single-mode Tm/Ho co-doped mode-locked fiber laser with a repetition rate of 253 MHz that is directly core pumped at a wavelength of 790 nm. In a soliton mode-locked linear fiber laser cavity, femtosecond pulses with transform-limited pulse durations of 315 fs are generated. With single-mode core pumping, the high peak absorption of the gain medium is utilized to obtain an optical spectrum with suppressed ripples and high signal-to-background levels in the RF spectrum above 70 dB. Good noise performance with a rms relative intensity noise of 0.11% [10 Hz, 2 MHz] and a timing jitter of 20 fs [100 Hz, 2 MHz] is demonstrated. For a single pulsing mode-locking regime, a reproducible and stable peak wavelength tunability of the optical spectrum is achieved over 11 nm by pump power tuning. [ABSTRACT FROM PUBLISHER]

An Yb-doped, all-polarization-maintaining fiber laser oscillator with a nonlinear amplifying loop mirror is presented in this letter. A new compact non-reciprocal phase shifter biased fiber loop mirror was engaged inside the fiber laser, which results in a low threshold and stable mode locking. With a 2.8-nm filter inside the cavity, the mode locked output power is 4.1 mW with the repetition rate of 31.35 MHz at the pump power of 80 mW. The spectral bandwidth of the pulse is 3.1 nm. The pulsewidth of the direct output and the dechirped pulse are 2.13 ps and 538 fs, respectively. The filter bandwidth plays a significant role in the spectrum bandwidth and the direct output pulse width. [ABSTRACT FROM PUBLISHER]

We propose a chemical wet etching technique that does not make use of toxic Hydrofluoric solution to produce cladding-etched optical fiber intended for use as a platform for a fiberized saturable absorber. The wet etching technique is based on the use of a mixed solution of NH4F and (NH4)2SO4, which is not toxic, and a small, specially-devised etching cradle to achieve precise control of the etched fiber length. A fiberized saturable absorber was implemented by depositing the graphene oxide particles on top of the residual cladding for our cladding-etched fiber by using the drop & dry method. The saturable absorber was incorporated into an erbium-doped fiber ring cavity to test its suitability as a mode-locker with a modulation depth larger than 4.3%. Femtosecond pulses with a temporal width of ∼615 fs were readily obtained at a repetition rate of ∼17.09 MHz. The saturable absorption and laser performance of our saturable absorber were compared to those of an absorber on a core-etched fiber platform prepared through the formation of microdroplets of HF and surface tension-driven flow, as in [57]. [ABSTRACT FROM PUBLISHER]

We demonstrated a passively Q-switched 2.8- \mu \textm Er3+-doped ZBLAN fiber laser with topological insulator Bi2Te3 nanosheets prepared by the solvothermal method. Enabled by the gold mirror with self-assembled Bi2Te3 nanosheets film sandwiched by polymethyl methacrylate polymer, the Q-switched fiber laser can deliver a maximum average power of 856 mW with corresponding pulse energy of 9.3 \mu \textJ and a pulse width of 1.3 \mu \texts at a repetition rate of 92 kHz under the pump power 5.9 W. To the best of our knowledge, this is the highest output power for the pulsed fluoride fiber laser around 2.8 \mu \textm modulated by the two-dimensional Dirac material. This letter reveals that the topological insulator can be a kind of promising nonlinear modulator for a mid-infrared laser. [ABSTRACT FROM PUBLISHER]

A fiber laser-pumped high-power burst-mode-operated picosecond mid-infrared (IR) laser at 3.8 \mu\textm is reported. A gain-switched distributed Bragg reflector laser diode with a pulse repetition rate (PRR) of 138 MHz and pulse duration around 200 ps was applied as the seed laser of a master oscillator power amplifier (MOPA)-structured Yb fiber laser. The PRR of the MOPA was increased to about 1.1 GHz through a pulse multiplier consisting of four cascaded 2 $\times$ 2 fiber couplers. A fiber-pigtailed acousto-optic modulator was used to carve the pulse train into pulse bursts so that the peak power of the final linearly polarized fiber laser output could be optimized by adjusting the duty cycle of the pulse bursts correspondingly. The output of the fiber laser was directed to pump a periodically poled magnesium-oxide-doped lithium niobate-based optical parametric oscillator through the quasi-synchronized pump scheme. Efficient parametric conversion was realized with a maximum average power output of 7.3 W at 3.8 \mu\textm under pump power of 45 W at 1.064 \mu\textm with pump-to-idler conversion efficiency exceeding 16%. [ABSTRACT FROM PUBLISHER]

We demonstrated a record standard deviation <100 μHz of stabilized repetition rate for a mode-locked laser in an environmentally stable figure-eight fiber laser cavity with a polarization maintaining active fiber located asymmetrically in the nonlinear amplifying loop. A laser diode with a maximum pumping power of 250 mW was applied to excite the polarization maintaining active fiber in the nonlinear amplifying loop and acted upon the active fiber to create refractive index change by both resonantly enhanced nonlinear effects and thermal effects. The tuning range, tuning slope, and tuning resolution of the repetition rate are measured to be 10 Hz, -55 mHz/mW, and 110 μHz, respectively, resulting in a standard deviation as low as 77 μHz for 1-s gate time and 24 μHz for 10-s gate time over 4 h. [ABSTRACT FROM PUBLISHER]

Germanosilicate and phosphosilicate-based glasses are two of the most common materials used to amplify light in the near and shortwave infrared wavelengths by stimulated Raman scattering in optical fiber, but are limited in total output power and efficiency that can be achieved due to the onset of stimulated Brillouin scattering (SBS). We experimentally investigate both germanosilicate and phosphosilicate Raman gain fibers with selective transverse doping profiles in the context of altering the fiber acoustic waveguide properties for increasing the threshold at which total Raman amplified power is saturated by SBS. It is shown that selective transverse doping offers greater potential for SBS suppression in germanosilicate gain fibers in contrast to those manufactured from phosphosilicate glasses. Initial SBS suppressed germanoslicate fibers are demonstrated with a 5 to 6 dB reduction in the maximum peak Brillouin gain as compared to a standard step-index fiber such as Corning HI-1060, which allows for over 5 dB in SBS suppression and an increase in saturated Raman amplifier gain from 15 dB to greater than 22 dB. [ABSTRACT FROM PUBLISHER]