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Hollow core optical fibers of numerous guiding mechanisms have been studied in the past decades for their advantages on guiding light in air core. This work demonstrates a new hollow core optical fiber based on a different guiding mechanism, which confines light with a cladding made of epsilon-near-zero (ENZ) material through total internal reflection. We show that the addition of a layer of ENZ material coating (e.g. indium tin oxide layer) significantly reduces the loss of the waveguide compared to the structure without the ENZ layer. We also show that the propagation loss of the ENZ hollow core fiber can be further improved by integrating ENZ materials with lower loss. This study presents a novel type of hollow core fiber, and can find advanced in-fiber photonic applications such as laser surgery/spectroscopy, novel gas-filled/discharge laser, in-fiber molecular/gas sensing, and low-latency optical fiber communication. [ABSTRACT FROM AUTHOR]

The generation and evolution of soliton molecules are investigated theoretically with the coupled nonlinear Schrodinger equations based on a vector field. The formation of second‐and third‐order soliton molecules is investigated. Besides this, various‐order soliton molecules from the 6th order to the 13th order have been observed by adjusting small‐signal gain and phase delay. Finally, we analyze the reason for the soliton molecule generation. Exploring soliton molecules is helpful for optical communication as well as for fiber laser design. [ABSTRACT FROM AUTHOR]

A broadly tunable erbium-doped fiber ring laser is proposed and demonstrated based on the tapered polarization maintaining fiber (PMF) Sagnac interferometer, in which the Sagnac and intermodal interferences are superimposed to generate one localized peak over a wide wavelength range in its transmission spectrum. By heating the tapered PMF, the localized peak may be discretely tuned with the temperature at the step, depending on the intermodal interference. Tunability may become continuous when additional stress is exerted longitudinally on the tapered PMF. The tapered PMF Sagnac interferometer is inserted into the laser cavity to achieve broadly and continuously tunable output. Specifically, by optimizing the PMF length and its tapering section to obtain proper channel intervals of the Sagnac and intermodal interference, the lasing wavelength is continuously tuned over 60 nm covering from 1565.1 nm to 1625.2 nm with sidemode suppression ratio higher than 50 dB and power uniformity better than 1 dB. The tuning responses to temperature and axial stress are both linear with sensitivity of −1.1 nm/°C and −29.4 pm/μϵ. Most importantly, the temperature and axial stress affect the Sagnac and intermodal interferences, respectively, which makes it convenient to set the lasing wavelength beforehand during operation. [ABSTRACT FROM AUTHOR]

In this letter, we report the first demonstration of a visible-wavelength-tunable, vortex-beam fiber laser based on a Sagnac-loop fiber filter and efficient long-period fiber grating. A 30 cm Pr3+/Yb3+-codoped ZBLAN fiber pumped by a 445 nm laser diode provides ~ 635 nm strong optical gain. A homemade dielectric mirror on the fiber end-facet and a Sagnac-loop fiber filter are used to build a wavelength-tunable fiber laser with a wavelength range of 633.89 to 636.02 nm. A self- fabricated long-period fiber grating acts as a mode converter in the cavity, and one-order vortex-beam including cylindrical vector beams (CVBs) and orbital angular momentum beams (OAMs) with a high mode purity are successfully obtained. Furthermore, we also measured the speckle contrast of the visible-wavelength fiber laser, and the speckle contrast is reduced by 17.13% through CVBs. This work could offer an effective approach to develop compact, wavelength-tunable vortex fiber lasers in the visible spectrum for applications to high-resolution imaging, laser display, visible light communications, and scientific research. [ABSTRACT FROM AUTHOR]

A gain-switched pulsed laser based on a commercial, heavily holmium-doped fluoroindate glass fiber, is designed to emit in the middle-infrared range, at the wavelength λ = 3.92 μm. The laser, pumped at λ = 888 nm is modeled by a six-level system, by taking into account experimental spectroscopic parameters, to identify a feasible laser configuration. An output signal peak power of about Pspeak = 14.62 W with a full width at half maximum (FWHM) pulse duration less than τs = 73 ns and pulse energy Es = 1.214 μJ is predicted, by considering an input peak power of Pppeak = 10 W, and pump repetition rate of ƒ = 100 kHz, by employing a 8 cm-long fluoroindate fiber with holmium concentration NHo = 100 000 ppm. The obtained result encourages the construction of a pulsed laser based on commercially available optical fiber, for applications in different fields as sensing and biomedicine. [ABSTRACT FROM AUTHOR]

An elegant method of nonlinear Fourier transform (NFT) has attracted worldwide research interests and such NFT methodology provides a new viewpoint on the physics of laser dynamics. Recently, the use of the NFT has been proposed for the investigation of laser radiation, indicating the capability to characterize the ultrashort pulse in the nonlinear frequency domain. Here, pure solitons are numerically separated from the resonant continuous wave (CW) background in a fiber laser by utilizing NFT. It is identified that the soliton and the resonant CW background have different eigenvalue distributions in the nonlinear frequency domain. Similar to water distillation, we propose the approach of soliton distillation, by making NFT on a steady pulse generated from a fiber laser, then filtering out the eigenvalues of the resonant CW background in the nonlinear frequency domain, and finally recovering the soliton by inverse NFT (INFT). Simulation results verify that the soliton can be distinguished from the resonant CW background in the nonlinear frequency domain and pure solitons can be obtained by INFT. [ABSTRACT FROM AUTHOR]

The performances of a fiber laser stabilized by a whispering-gallery-mode(WGM) resonator depends heavily on the coupling of the resonator and fiber system, and is labile due to the lasing mode competitions among excitable WGMs. Here, we propose a hybrid cavity where a linear fiber cavity is coupled by a WGM resonator for dual stabilizations of the laser mode, and experimentally demonstrate single-mode lasing emission with stable and high signal to noise ratio (up to 61 dB), narrow linewidth (low to ∼5 kHz) operations. By adjusting the coupling of the linear fiber cavity and the WGM resonator, the fiber laser can operate in two- to four- mode lasing without mode hopping as well. [ABSTRACT FROM AUTHOR]

We fabricate an oleic acid capped colloidal lead sulfide quantum dots (PbS QDs) by modified hot-injection method, and then drop them on the end of fiber connector to construct the fiber-based PbS QDs saturable absorber (SA). The modulation depth and saturation intensity of the PbS QDs SA are about 30% and 1.88 MW/cm2, respectively. The strong quantum confinement effect in PbS QDs enables wideband tunability. We get subpicosecond soliton pulses, wavelength-tunable between 1530 nm and 1560 nm, with stable mode-locking, by adjusting the orientations of the polarization controller. These results contribute to study the nonlinear optical properties of zero-dimensional nanomaterials and provide new opportunities for the applications of broadband photoelectronic devices. [ABSTRACT FROM AUTHOR]

We investigate optical property of polarization-maintaining fiber taper (PMFT) for tunable multi-wavelength laser generation in a fiber ring cavity. A panda-type polarization fiber is fused and tapered into a fiber taper with a diameter of about 2.5 μm. Optical and thermal properties of the PMFT are investigated theoretically and experimentally. As combined with a polarization dependent isolator, tunable multi-wavelength fiber laser operation is achieved by controlling of polarization-dependent loss in the fiber ring cavity. The laser wavelength number can be switched from 1 to 4. The 3 dB bandwidths of laser spectra are less than 0.05 nm for all wavelength numbers, with a maximum OSNR of about 54 dB. For single-wavelength laser operation near 1561.66 nm, the measured wavelength and power fluctuations are < 0.02 nm and 0.4 dB, respectively. [ABSTRACT FROM AUTHOR]

A tunable mode-locked ytterbium-doped fiber laser with a tuning range of 55 nm is demonstrated in this paper. Currently, this is the widest tuning range for all-normal dispersion (ANDi) ytterbium-doped mode-locked fiber laser based on new-material saturable absorber (SA). The combined effects of the single-walled carbon nanotubes (SWCNTs) SA and a reflective grating significantly improved laser performance: broad tuning range, superb stability, and repeatability. The experimental results indicate that SWCNTs can be a brilliant SA for achieving mode-locking operation in ANDi regime at 1 μm, with pulsewidth of 2.4 ps and optical spectral bandwidth of 1.6 nm across the full tuning range. The laser also shows that the optical spectrum can be tuned accurately and continuously, which gives possibility for various applications such as optical communications, spectroscopy, time-resolved measurement, etc. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a multi-wavelength actively mode-locked fiber laser around $2.07~\mu \text{m}$. A holmium-doped fiber is used as the gain medium which is pumped by a 1.93- $\mu \text{m}$ fiber laser. The multi-wavelength laser is achieved by employing a fiber Lyot filter in cavity, and actively mode-locking is achieved by driving a sinusoidal radio frequency signal on the electro-optic modulator. Stable actively mode-locked pulses can be obtained with up to 10.078-GHz repetition rate. The shortest measured pulse width is 16 ps. The wavelength channels can be accurately tuned under a fixed pump power by adjusting the polarization controllers and the BIAS voltage. Up to 27 channels can be obtained under a stable mode-locked operation. However, the increase of output channels leads to a significant increase in the threshold, and the maximum output channels have a strong dependence on the repetition rate. [ABSTRACT FROM AUTHOR]

A novel multi-wavelength mode-locked Erbium-doped fiber laser with tungsten disulfide (WS2) combined with a microfiber knot is described. This hybrid fiber structure facilitates strong light matter interaction between the saturated absorption of the WS2 material and high optical non-linearity of the microfiber knot. It is demonstrated experimentally that the novel fiber laser works stably in the absence of an external comb filter, with the generation of stable multi-wavelength picosecond pulses. In the multi-wavelength lasing regime, up to seven-wavelength stable mode-locked pulses are obtained using a polarization controller with the pump power at ∼250 mW. The pulse period and the pulsewidth are 188.7 ns and 16.3 ps, respectively. In addition, the number of multi-wavelength lasing channels can be changed by simply adjusting the microfiber knot size. Experimental results show the laser to have a stable output over 12-h recording period. The results of this investigation demonstrate that the optical microfiber knot with a WS2 overlay based fiber laser device can operate as a highly nonlinear optical component and a saturable absorber. The proposed multi-wavelength lasing device can therefore be widely used for non-linear and ultrafast photonics and has a number of advantages compared to similar devices using more conventional technologies, including low cost and good stability. [ABSTRACT FROM AUTHOR]

We report herein an all-fiber single-frequency master oscillator power amplifier (MOPA) at 1550 nm with Er/Yb-codoped active fiber and wavelength-stabilized 976-nm LD pump source. A pump-limited maximum continuous-wave output power of 56.4 W was achieved under the pump power of 150 W, with corresponding slope efficiency being 37.0%. Via the self-heterodyne method, the evolution of spectrum linewidth during the amplification was investigated for the high-power MOPA-based single-frequency fiber laser. The linewidth and relative intensity noise at the maximum output power are 4.21 kHz and −110 dBm/Hz, respectively. [ABSTRACT FROM PUBLISHER]

A few-mode Cr-doped crystalline core fiber (FMCDCCF) with high-index glass as a cladding is demonstrated. The FMCDCCF exhibits a core diameter of 34 μm and a V-value of 3.4, which could guide about two linear modes in theory, namely the LP01 and LP11 modes in fiber. A 4.1-dB gross gain of the FMCDCCF at wavelength of 1400-nm was obtained. Further study on higher gain is essential to open the possibility of utilizing the FMCDCCF as broadband fiber amplifiers for use in the next-generation optical transmission systems. [ABSTRACT FROM PUBLISHER]

Abstract: Evolution of dual-wavelength fiber laser from continuous wave to soliton pulses is investigated experimentally by using the nonlinear polarization rotation technique. With the increase of pump power, the proposed laser successively delivers the dual-wavelength continuous wave, the single-wavelength soliton pulses, and the dual-wavelength soliton pulses. The dual-wavelength laser operates at the central wavelengths of about 1533 and 1546nm with the separation of ∼13nm. The number of soliton pulses operating in the dual-wavelength state is much larger than that of the single-wavelength state, while the pulse intensity always keeps constant. Experimental results reveal that the dual-wavelength mode locking is determined by the combination of pump strength and the cavity filtering effect. [Copyright &y& Elsevier]

Abstract: We demonstrated stable pulses generation at 2μm in a passively Q-switched thulium-doped fiber laser using a few layer graphene thin film. The maximum output power was 4.5mW and the single pulse energy was 85nJ at 53kHz repetition rate, and the pulse width was about 1.4μs. The pulse width and the repetition rate of the Q-switched fiber laser can be changed along with the pump power. To the best of our knowledge, this is the first report of graphene saturable absorber for passively Q-switched 2μm fiber lasers. [Copyright &y& Elsevier]

A few-mode Cr-doped crystalline core fiber (FMCDCCF) is demonstrated. The fiber fabrication is a modified laser-heated pedestal growth (LHPG) technique that consists of over cladding a Cr:YAG crystal rod with silica and then fine tuning its core size with multiple core reduction through the LHPG system. The FMCDCCF exhibits a core diameter of 2 \mum and a V-value around 3.77 to provide the few-mode characteristics. The optical properties of the FMCDCCF are similar to that of a pristine Cr^4+:YAG crystalline. A gross gain of the FMCDCCF is measured around 2.3 dB at a wavelength of 1.4 \mum. [ABSTRACT FROM PUBLISHER]

Graphene with zero-band gap can be easily saturated under strong excitation due to Pauli blocking. In this work, the graphene oxide membrane is reduced on the surface of microfiber by use of high temperature heating. Such reduced graphene oxide can interact with the strong evanescent field of the microfiber and enable saturable absorption in passively mode-locked fiber laser. The system can be effectively utilized to directly generate ultra-wide-band doublet pulses for high-capacity wireless communication applications. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, we implemented a vibration or displacement system using the well-known self-mixing effect in an Er3+–Yb3+ codoped Distributed Bragg reflector (EYDBR) fiber laser. The experimental Signal-to-Noise ratio (SNR) was measured up to be 60.25dB at 2km. This paper also focuses on the theoretical description of the self-mixing effect which applies to our specific implementation, followed by some experimental results. From the experiment results, the compact structure and high SNR up to 60.25dB of self-mixing effect sensor can be earned by combining the self-mixing interference technique and EYDBR fiber laser. It is also proved potential using self-mixing interference with ASE source in EYDBR fiber laser for high sensitivity and wide range measurement. [Copyright &y& Elsevier]

Abstract: We demonstrate a tunable and switchable dual-wavelength passively mode-locked fiber ring laser in the anomalous dispersion regime that generates high-energy pulses at a sub-100kHz repetition rate. The nonlinear polarization rotation (NPR) technique is employed in this configuration to allow for passively mode-locked operation. By exploiting the intensity-dependent loss caused by NPR, the mode competition could be efficiently alleviated. Moreover, taking advantage of the intrinsic spectral filter induced by the intracavity birefringence, the dual-wavelength separations as well as the wavelength lasing locations could be flexibly tuned by properly rotating the polarization controller. With a repetition rate of 85.8kHz, the laser delivers the single pulse energy of 198nJ at a pump power of 250mW. The combination of high per-pulse energy and flexible tunability in this fiber laser is useful for practical applications. [Copyright &y& Elsevier]

Abstract: In this paper we report passive harmonic mode-locking of an Erbium/Ytterbium-doped double-clad fiber laser with repetition rates up to 10GHz. The modes synchronization was obtained using Nonlinear Polarization Rotation mechanism. The stable operation at 634th harmonic of the fundamental (15.8MHz) repetition frequency was achieved. Soliton pulses with the duration of less than 900fs and 300mW average output power were obtained. [Copyright &y& Elsevier]

Abstract: A tunable and switchable single-longitudinal-mode (SLM) dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach–Zehnder interferometer (MZI) filter was proposed and demonstrated, which can be applied in microwave generation. By incorporating a high extinction ratio (ER) dual-pass MZI into an erbium-doped fiber ring cavity, SLM dual-wavelength lasing can be achieved even using a MZI with relatively little free spectrum range (FSR), and by beating the two wavelengths at a photodetector, a 9.76GHz microwave signal with a 3-dB bandwidth of less than 10kHz is obtained. Moreover, by direct linking the two outputs of the MZI, the high ER dual-pass MZI is easily reconfigured as a half FSR dual-pass MZI. Using this structure, switchable SLM dual-wavelength lasing can be conveniently realized. [Copyright &y& Elsevier]

Abstract: We demonstrate coherent beam combining of two-dimensional fiber amplifier arrays with a total of 137W output power using stochastic parallel gradient descent (SPGD) algorithm. Compact all-fiber polarization-maintained single frequency fiber amplifier chains are developed and four fiber amplifiers are arranged to 2×2 laser array with a fill factor of 70% in the near-field. Active phase control is implemented by a digital signal processor (DSP) based SPGD controller. The fringe visibility of the coherent combined beam profile is as high as 81% when the system is closed-loop controlled despite perturbations of the environment. [Copyright &y& Elsevier]

Abstract: We experimentally investigate the soliton pairs in a passively mode-locked erbium-doped fiber laser with large normal cavity dispersion. By adjusting the polarization state, four different kinds of soliton pairs are achieved. The pulses in soliton pairs exhibit different temporal separations, and show randomly distributed spikes on the top-flat of spectra. The pulse–pulse interactions in the soliton pairs are investigated, and it is suggested that the pulse separation, pulse duration, and their relative intensities all determine the strength of pulse interactions. [Copyright &y& Elsevier]

Abstract: We report efficient laser demonstration and spectroscopic characteristics of a Yb-doped Y2O3 (or Y3Al5O12) nanoparticle silica fiber developed by conventional fiber fabrication technique. The spectroscopy study evidences modification in the environment of Yb ions by the Y2O3 nanoparticles. As a result, photodarkening induced loss is reduced by 20 times relative to Yb-doped aluminosilicate fibers. The fiber is suitable for power scaling with good laser slope efficiency of 79%. [Copyright &y& Elsevier]

Abstract: We have demonstrated a continuous-wave (CW) all fiber laser operation at 1558.4nm of a diode-pumped erbium-doped PCF laser based on 9.6m erbium-doped PCF. The maximum output power and the threshold of the fiber laser are 49.4mW and 6.67mW, respectively. We show that it is possible to achieve a high stability and beam quality laser, which has a great application potential in optical communication field in future. [Copyright &y& Elsevier]

Abstract: In this paper we present an actively switched fiber laser with an all-fiber long-period grating-based interferometer used as an intra-cavity loss modulator. The modulator consists of two equal long-period gratings written sequentially in the same piece of a double-clad optical fiber. One of the gratings is fixed onto a piezoceramic cylinder producing fast modulation of the interferometer transmission spectrum. The laser demonstrates a stable regime of pulsed emission at repetition rates in the range of tens of kHz. [Copyright &y& Elsevier]

Abstract: In order to improve the performance of the double-clad fiber laser, the optimum laser length needs to be estimated prior to the experiment. Previous expressions for the optimum length of fiber laser have been established under some assumptions, such as the output power without laser scattering loss and the pump power without reflection in the output-end. In this work, the issue of optimum laser length has been analyzed theoretically based on the strongly pumped fiber laser model. An extended expression for the optimum length of the linear cavity Yb3+-doped double-clad fiber laser is obtained. The respective effects of the laser scattering loss, the pump power, the Yb3+ dopant concentration, and the pump reflection on the optimum laser length are identified. [Copyright &y& Elsevier]

Abstract: An erbium-doped fiber laser (EDFL) constructed in a master oscillator and power amplifier (MOPA) configuration is analyzed. The pump powers for the fiber cavity laser and the booster amplifier stages are managed properly to achieve maximal pump conversion efficiency. Our design achieves a pump conversion efficiency of 91.4%, corresponding to a quantum efficiency of 96.6%, for a 1565.8nm MOPA laser pumped by a total power of 300mW at 1480nm. The optimized MOPA laser shows a 25% enhancement in the pump conversion efficiency, compared to a non-MOPA fiber laser. A side lobe suppression ratio of 48dB for the optimized MOPA laser is observed. [Copyright &y& Elsevier]

Abstract: We demonstrate a multiwavelength fiber laser with ultradense wavelength spacing and ultrabroad bandwidth based on inhomogeneous loss mechanism with assistance of nonlinear polarization rotation. The inhomogeneous loss, implemented by incorporating a section of highly nonlinear fiber (HNLF) and a Sagnac filter in the laser cavity, can balance mode competition in erbium-doped fiber and result in ultradense multiwavelength generation. The bandwidth of the multiwavelength spectrum is greatly broadened owing to the intensity-dependent loss induced by nonlinear polarization rotation. Stable multiwavelength lasing with wavelength spacing of 0.08nm and wavelength number up to 254 is achieved at room temperature. Moreover, multiwavelength tuning is realized through modifying polarization-dependent cavity loss. [Copyright &y& Elsevier]

Abstract: Passively mode-locked stretched-pulse erbium fiber laser is presented. With all-fiber configuration 111fs pulses were achieved with the fundamental repetition rate of 169MHz and an average output power of more than 30mW. Proposed setup shows excellent stability, reliability and ‘turn-key’ operation. The impact of the pump power on laser parameters is described. [Copyright &y& Elsevier]

Abstract: Erbium-doped fiber lasers are normally actively mode-locked through amplitude modulation or phase modulation. In this paper, we demonstrate that the laser can also be mode-locked by employing polarization modulation with a polarization-dependent cavity loss. We obtain a nearly transform-limited mode-locked pulse train at 10GHz repetition rate with timing jitter as low as 164fs. The timing jitter is only limited by the timing jitter of the driving signal. [ABSTRACT FROM AUTHOR]

This paper describes a very simple and stable harmonically mode-locked erbium-doped fiber ring laser that produces high-peak-power, 1 ps transform-limited sech2 optical pulses at 1564 nm at a repetition rate of 1 GHz. This very short pulse duration is attributed to the insertion of a comb generator in the modulation scheme. The temporal and spectral characteristics of the pulses are studied. Soliton transmission over 40 km of standard nondispersion-shifted single-mode fiber is demonstrated using this laser. ©2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 285–287, 2000. [ABSTRACT FROM AUTHOR]