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Under investigation in this paper is a set of the-dimensional nonlinear Schrödinger–Maxwell–Bloch (NLS–MB) equations, which describes the optical pulse propagation in an erbium-doped fibre. Employing the Hirota method and symbolic computation, we obtain the one- two- and N-soliton solutions. We prove that the interactions between the two solitons are elastic through the asymptotic analysis on the soliton solutions. Figures are plotted to show the one soliton and the interaction between the two solitons. We find that the decrease of the frequency shift from the resonance can make the angle between the propagation directions and the amplitudes of the two MB solitons bigger, implying that the change of the amplitudes of the two MB solitons is closely related to the propagation directions of the two NLS solitons. [ABSTRACT FROM PUBLISHER]

Graphene oxide mode-locked Er-doped fiber lasers are investigated in this paper. The generalized nonlinear Schrödinger equation, which can be used to describe the fiber lasers, is studied analytically. Soliton solutions for this equation are obtained, and the stable solitons are generated in the fiber lasers. Physical effects, such as the gain bandwidth, distributed gain, group-velocity dispersion, and nonlinearity of fiber lasers, are analyzed. Soliton amplification techniques are proposed which can effectively restrain the appearance of pedestals during the evolution of solitons in the cavity. These analytic results are compared with the experimental ones. The results of this paper will be valuable to the study of the fiber lasers properties and provide theoretical guidance for the obtaining of high-power ultra-short pulses. [ABSTRACT FROM AUTHOR]

In this paper, a multiwavelength two-mode Brillouin fibre laser generated by two-mode optical fibre (TMOF) is proposed and demonstrated experimentally. The system comprises a 500 m long TMOF. A tunable laser source amplified by a high power erbium doped fibre amplifier acts as the Brillouin pump (BP) followed by a single mode fibre Bragg grating as a reflector in the cavity with a centre wavelength of 1544 nm. The BP is observed in the superposition ofandmodes in the few-mode fibre. The set-up is capable of generating a maximum of 12 clearly defined Stokes lines at the pump power of 28.6 dBm, spanning from 1543.88 to 1544.92 nm. [ABSTRACT FROM PUBLISHER]

In this paper, we construct soliton solutions for a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system, which can describe the ultrashort optical pulse propagation in a nonlinear, dispersive fiber doped with two-level resonant atoms. Under certain transformations and constraints, one- and two-soliton solutions are obtained via the Hirota method and symbolic computation, and soliton collisions are graphically presented and analyzed. One soliton is shown to maintain its amplitude and shape during the propagation. Soliton collision is elastic, while bright two-peak solitons and dark two-peak solitons are also observed. We discuss the influence of the coefficients for the group velocity, group-velocity dispersion (GVD), self-phase modulation, distribution of the dopant, and Stark shift on the soliton propagation and collision features, with those coefficients are set as some constants and functions, respectively. We find the group velocity and self-phase modulation can change the solitons’ amplitudes and widths, and the solitons become curved when the GVD and distribution of the dopant are chosen as some functions. When the Stark shift is chosen as a certain constant, the two peaks of bright two-peak solitons and dark two-peak solitons are not parallel. In addition, we observe the periodic collision of the two solitons. [ABSTRACT FROM AUTHOR]

In this paper, coupled higher order nonlinear Schrödinger–Maxwell–Bloch equations are studied for the ultrashort pulse propagation in erbium-doped birefringent fiber system. Lax pair is constructed for the CHNLS–MB system. Through the Darboux method and symbolic computation, analytic two-soliton solution is obtained. To analyze the specific problem, we design an optimal system by properly choosing the special form of variable coefficients. Here, using obtained two-soliton solution, tunneling of femtosecond soliton through barrier and well is investigated. While solitons are passing through barrier and well, some unexpected behavior is observed and hidden possibilities in switching action through tunneling is investigated. [ABSTRACT FROM PUBLISHER]

In this paper a tunable single-longitudinal mode (SLM), short-wavelength band (S-band) fiber laser using a conventional erbium-doped fiber (EDF) with a length of 3 m and a step index erbium dopant profile as opposed to the commonly used depressed cladding erbium-doped fiber (DC-EDF) is proposed and demonstrated. The proposed SLM fiber laser has a tuning range of 1496 to 1507 nm in a ring configuration using two 0.15 m of EDF which acts as saturable absorbers (SAs). The highest peak power measured is about −0.6 dBm at a wavelength range of 1502 to 1507 nm. The measured signal-to-noise ratio (SNR) is approximately 74 dB for the same wavelength range. The line-width of the SLM output is measured to be 140 kHz. [ABSTRACT FROM PUBLISHER]

In this paper, we propose and demonstrate a cost-effective wavelength converter utilising a highly nonlinear fibre (HNLF) and a tunable dual-wavelength fibre laser as the pump source. The proposed system uses only the pump source and a signal probe to generate a partially degenerate four-wave mixing (FWM) effect. An FWM conversion efficiency of -12 dB is obtained at pump and signal powers at +13.3 dBm and +5 dBm, respectively, and it is predicted that a higher conversion efficiency is possible if a high power dual-wavelength fibre laser source is used. [ABSTRACT FROM AUTHOR]

We investigate in this paper the influence of intensity-dependent losses on the dynamics of an erbium-doped fibre laser. On the basis of the ion-pair model, it is theoretically demonstrated that this feedback efficiently suppresses the self-pulsing occurring in heavily doped fibre lasers. [ABSTRACT FROM AUTHOR]

In our study, we employed a Mo2TiAlC2 thin film as a passive saturable absorber (SA) to create a stable pulsed fibre laser at 1564.52 nm. We synthesized a Mo2TiAlC2-PVA thin film with a 6% modulation depth and a 10 MW/cm2 saturation intensity. This thin film was integrated into the laser cavity between FC/PC fibre connectors, enabling Q-switching over a pump power range of 30 mW to 120 mW. This resulted in an increased repetition rate from 31.1 kHz to 66.83 kHz and a reduced pulse duration from 13.45 µs to 6.35 µs. The pulse train's stability was confirmed by a high signal-to-noise ratio (SNR) of 58 dB. The laser achieved a maximum output power of 6.56 mW and a pulse energy of 98.16 nJ. These results demonstrate Mo2TiAlC2 as a viable Q-switching modulator in the 1.55-µm wavelength range, with promising applications in compact and efficient pulsed fibre lasers. [ABSTRACT FROM AUTHOR]

We propose a coupled system of generalized nonlinear Schrödinger and Maxwell–Bloch equations with variable coefficients which describes propagation of an optical soliton in an inhomogeneous nonlinear waveguide doped with two-level resonant atoms. The Lax pair of this model is derived using the Ablowitz–Kaup–Newell–Segur (AKNS) formalism. The one-soliton solution is constructed through a Darboux–Bäcklund transformation (BT). The coupled system is found to allow soliton propagation. We explain the soliton control by the effect of distributed amplification with varying group velocity dispersion, nonlinearity and gain or loss parameters. [ABSTRACT FROM AUTHOR]

A new compact and wide-band erbium-doped fibre amplifier (EDFA) was demonstrated by combining Hafnia-bismuth Erbium co-doped fibre (HB-EDF) and zirconia–yttria–aluminum Erbium co-doped fibre (Zr-EDF) as a hybrid gain medium, in parallel double-pass configuration. The proposed amplifier comprises a 0.5 m long HB-EDF and 4 m long Zr-EDF optimized for C- and L-band operations, respectively. The HB-EDF and Zr-EDF has erbium ion concentration of 12,500 ppm and 2800 ppm, respectively. At -10 dBm input signal, a wide-band flat gain of 15.7 dB is achieved with gain fluctuation of less than 1.5 dB within a wavelength region from 1525 to 1600 nm. Compared to same configuration of HB-EDF and Zr-EDF amplifiers which are using two pieces of HB-EDF and Zr-EDF, respectively with the same total amount of erbium ions, the proposed EDFA with hybrid gain medium provides even better performances in term of flat gain, bandwidth and noise figure. [ABSTRACT FROM AUTHOR]

A C-band mode-locked fibre laser incorporating a boron nitride-doped graphene oxide (BN-GO)-based saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by depositing multiple layers of synthesized BN-GO nanoparticles onto the polished surface of a side-polished fibre, which is then inserted into an erbium-doped fibre laser cavity to generate the desired pulsed output. The strong nonlinear optical response and light absorption of the BN-GO nanoparticles induces the generation of a highly stable mode-locked pulse at 1567.32 nm with visible Kelly’s sidebands. The pulses have a measured repetition rate of 13.56 MHz and a pulse width of 1.18 ps at the maximum pump power of 280.5 mW. The pulses have a frequency signal-to-noise ratio of ∼53 dB, indicating a highly stable output. The proposed laser would find significant telecommunications applications, particularly for dense wavelength division multiplexing systems. [ABSTRACT FROM AUTHOR]

We derive the analytical rogue wave solutions for the generalized inhomogeneous nonlinear Schrödinger-Maxwell-Bloch (GINLS-MB) equation describing the pulse propagation in erbiumdoped fibre system. Then by suitably choosing the inhomogeneous parameters, we delineate the tunneling properties of rogue waves through dispersion and nonlinearity barriers or wells. Finally, we demonstrate the propagating characteristics of optical solitons by considering their tunneling through periodic barriers by the proper choice of external potential. [ABSTRACT FROM AUTHOR]

We demonstrate a Q-switched Erbium-doped fibre laser (EDFL) utilizing cobalt oxide (Co3O4) nanocubes film based saturable absorber (SA) as a passive Q-switcher. Co3O4nanocubes are embedded into a polyethylene oxide film to produce a high nonlinear optical response, which is useful for SA application. It has saturation intensity and modulation depth of 3 MW/cm2and 0.35%, respectively. The proposed laser cavity successfully generates a stable pulse train where the pulse repetition rate is tunable from 29.8 to 70.92 kHz and the pulse-width reduces from 10.9 to 5.02 μs as the 980 nm pump power increases. This result indicates that the Co3O4is excellent for constructing an SA that can be used in producing a passively Q-switched fibre laser operating at a low pump intensity. To the best of our knowledge, this is the first demonstration of Co3O4film based fibre laser. [ABSTRACT FROM PUBLISHER]

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50?m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48?nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4?kHz as the pump power increases from the threshold power of 69.0?mW to the maximum pump power of 133.8?mW. The minimum pulse width of 4.4??s was obtained at the maximum pump power of 133.8?mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0?mW. [ABSTRACT FROM AUTHOR]

We demonstrate a self-seeded multi-wavelength Brillouin–erbium fibre laser with double Brillouin frequency gap. The twice channel gap is induced by the gain difference in different directions. Thirty-six stable output channels with 20?GHz frequency gap are obtained when the 980?nm pump power is 300?mW. The factor that induces the double frequency gap is investigated and proved. [ABSTRACT FROM AUTHOR]

We demonstrate a simple, compact, and low cost mode-locked erbium-doped fiber laser (EDFL) using a single-walled carbon nanotubes (SWCNTs) embedded in polyethylene oxide (PEO) thin film as a passive saturable absorber (SA). The film with a thickness of 50 μm was fabricated using a prepared homogeneous SWCNT solution with 0.1% loading percentage, which was mixed with a diluted PEO solution and casted onto a glass Petri dish to form a thin film by evaporation technique. The film is sandwiched between two fiber connectors to construct a SA, which is then integrated in an EDFL cavity to generate a self-started stable soliton pulses operating at 1558 nm. The soliton pulse starts to lase at pump power threshold of 17.6 mW with a repetition rate of 50 MHz, pulse width of 0.67 ps, average output power of 0.158 mW, pulse energy of 3.16 pJ, and peak power of 4.43 W. [ABSTRACT FROM AUTHOR]

An all-fiber amplification and compression system seed is demonstrated by using a chirped pulse oscillator at the telecommunication band. Dispersion management is applied successfully both in the oscillator and amplifier, allowing dissipative soliton (DS) generation and amplification. The oscillator generates 4-ps chirped pulses with 130 mW (4.55 nJ) average power. Benefiting from large chirp and the high energy of DSs from the oscillator, the amplification system can be simplified. The average power after amplification is increased to 324.2 mW, corresponding to a single pulse energy of 11.3 nJ. The minimum pulse duration is 190 fs after the single-mode fiber (SMF) is employed to compress the pulses. The repetition rate of pulses is 28.6 MHz. [ABSTRACT FROM AUTHOR]

Wavelength division multiplexing (WDM) systems, which are widely used in telecommunication, have the advantages of huge bandwidth support and reliability. A performance analysis is presented of a WDM system using an erbium-doped fiber amplifier (EDFA), with specific emphasis on bit error rate (BER) optimization. EDFA parameters, including doped fiber length and pump power, are optimized and performance evaluating parameters for different modulation schemes are observed. Simulation results provide optimized BER, noise figure, and gain flatness values. The WDM system is modeled from 1546 nm to 1558 nm bandwidth to obtain maximum gain uniformity, low noise figure, and low BER. This wavelength range is selected to investigate the 1550 nm wavelength commonly used in the telecommunication industry. Also, that we are using a WDM grid, so multiple channels can be accommodated in this range. [ABSTRACT FROM AUTHOR]

The development is reported of a multi-longitudinal mode fiber laser sensor based on passive mode locking employing carbon nanotubes in the laser cavity. A polymer membrane is employed beneath the pre-strained erbium-doped fiber (EDF) to convert the sound pressure disturbance into axial strain, alter the cavity length, and induce a shift of the longitudinal modes beat. Hence, acoustic pressure measurement can be carried out by detecting the shift of the beat frequency. Experimental results show comparable strain and sound pressure sensitivity of ~0.5 kHz/?? and 147.2 Hz/Pa, respectively. The proposed sensor is an alternative for the measurement of acoustic pressure and possesses the advantages of good stability and ease of interrogation. [ABSTRACT FROM AUTHOR]

A detailed study is presented on the lasing properties of an erbium-doped photonic crystal fiber (PCF) laser. The effects of the host PCF’s structure and laser parameters on continuous-wave laser emission are analyzed by considering the confinement and overlap of pump and signal fields in the gain medium for varying values of pitch, hole diameter, and doping radius. For analysis, we used a finite-difference mode-calculation algorithm devised with standard population and propagation rate-equation solver. Our analysis, applied to an experimentally realized PCF laser, reproduces the observed/reported data, thereby showing the efficacy of our analysis. Finally, a fiber geometry to realize a laser with threshold as low as 6 mW using a short fiber length of 0.52 m is prescribed. The aim of the design is to greatly reduce splice loss with standard single-mode SM28/G.652 fiber while maintaining the optimum performance. These results are new in PCF laser research and should be useful in realizing high performance PCF-based laser devices. [ABSTRACT FROM PUBLISHER]

A new multi-wavelength Brillouin erbium fiber laser (BEFL), which operates in the L-band region with double frequency Brillouin spacing, is demonstrated. This design uses a Raman pump (RP) and a piece of 2 km highly nonlinear fiber as a gain medium. The double frequency spacing is achieved by employing a dual ring configuration, which is formed by utilizing a four-port circulator that removes the odd-order Stoke signals. Twenty Stokes and seventeen anti-Stokes lines, which have optical signal to noise ratio (OSNR) greater than 15 dB, are generated simultaneously with a spacing of 0.16 nm when Brillouin pump and RP powers were fixed at the optimum values of 8 dBm and 40 mW, respectively. The BEFL can be tuned in the range between 1591 nm to 1618 nm. The proposed configuration increases the number of lines generated and the OSNR, and thus allows a compact multi-wavelength laser source to be realized. [ABSTRACT FROM AUTHOR]

The electromagnetically induced left-handedness with zero absorption and large negative refractive index was investigated in a solid Er3+:YAG crystal with a four-level system proposed for an atomic medium. It was found that the frequency region with simultaneous negative permittivity and negative permeability, the zero absorption intervals, and the maximum values of the negative refractive index can be adjusted by changing the signal field, the coherent field, as well as the concentration of Er3+ ion in crystal. It is shown that wider zero absorption intervals with a higher index of refraction can be easily obtained when the signal field is only off resonance. The slab fabricated by the left-handed solid medium Er3+:YAG crystal with zero absorption may be a practical candidate for designing perfect lenses. [ABSTRACT FROM PUBLISHER]

A Bi2O3-based erbium-doped fiber (Bi-EDF) ring laser with a 70 nm tunable range is demonstrated with a 49 cm long Bi-EDF in which tuning range can be extended to larger than 100 nm using an optical switch to alter the length of Bi-EDF in the laser cavity. With an extinction ratio of better than 60 dB throughout the entire tuning range, the measured FWHM of laser lines are measured to be 0.09 nm. In addition, the common amplification parameters are measured and studied in detail for various pumping configurations. [ABSTRACT FROM PUBLISHER]

We have experimentally reported a passively harmonic mode-locked fiber laser at controllable repetition rates. The pulse train is continuously tunable and controllable from the fundamental cavity frequency to the eighth-order harmonic frequency. The pulses in the proposed laser disappear one by one when the pump power is decreased and, at the same time, the remaining pulses self-organize into a new, stable, uniform distribution in the cavity at each state. The experimental results indicate a supermode suppression of more than 40 dB. By appropriately increasing the coupler output ratio and lengthening the laser cavity, the enhanced mutual influence of the global and local soliton interactions induced by the CW components and the dispersive waves plays the key role in separating pulses stably and uniformly in the cavity. Our laser has the potential to generate chirp-free pulses at even higher rates and shorter pulses for use in future time-division multiplexing systems. [ABSTRACT FROM AUTHOR]

Gain flattened C-band erbium-doped fiber amplifier (EDFA) is demonstrated using a macro-bending method. Various bending diameter and length of high concentration aluminosilicate EDFA are theoretically and experimentally analyzed. By varying the bending radius and the length of the doped fiber, the gain saturation effect as well as the energy transfer from shorter wavelength to a longer wavelength can be controlled to obtain a flattened and broadened gain profile in the C-band region. The amplifier uses a 9 m long erbium-doped fiber (EDF) with erbium ion density of 1.6 × 1025 ions m-3 and bending radius of 6.5 mm as a gain medium. The gain variation of the EDFA is obtained within ±1 dB over 25 nm bandwidth of C-band region. [ABSTRACT FROM AUTHOR]

On the basis of the cascade of multiple four-wave mixing (FWM) processes, the energy stability function of multiple lightwaves propagating through fibers is proved theoretically and confirmed experimentally. This function can help multiple lasers to redistribute power from those that have more to those that have less. Theoretical and experimental results show that the ability of the FWM-induced stability effect gradually becomes weaker with the increase of pump number. The stability effect of waves by multiple FWM processes can effectively overcome the homogeneous gain broadening of an erbium-doped fiber (EDF). By adjusting the attenuators and tuning fiber Bragg gratings, dual-, triple-, and four-wavelength EDF lasers with good stability are demonstrated experimentally at room temperature. [ABSTRACT FROM AUTHOR]

We report on the generation of superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber laser, in which the cavity is made of purely anomalous dispersion fibers. The maximum 3 dB spectral bandwidth of the pulse is about 98 nm. We show numerically that the superbroad spectrum of the pulse is caused by the fiber birefringence. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a novel switchable multiwavelength erbium-doped fiber laser with a overlapping linear cavity, which is formed by a dual-section Lyot-Sagnac filter and three fiber Bragg gratings (FBGs). Taking advantage of the high extinction of the Lyot-Sagnac filter, independent controlling of the different wavelength losses and the spatial hole burning in the overlapping linear cavities, with this structure we realize stable switchable multiwavelength laser emission at room temperature. An output signal to background noise ratio of ∼43 dB and less than 3 dB fluctuation on output power were observed for all wavelength switching cases. [ABSTRACT FROM AUTHOR]

Gain improvement in a dual-stage S-band erbium-doped fiber amplifier (S-band EDFA) is demonstrated using a broadband fiber Bragg grating (FBG) operating in the conventional-band (C-band) region or a C-band/S-band wavelength division multiplexing (WDM) coupler which filters out the forward C-band amplified spontaneous emission (ASE) in the amplifier system, thus increasing the population inversion in the S-band region. The gain for the amplifier with the WDM coupler increases by about 8.5 dB with an input signal power of -40 dBm, compared to that of the conventional dual-stage amplifier. The gain improvement varies from 4.0-9.2 dB at a wavelength region between 1480 to 1512 nm without a significant noise figure penalty. [ABSTRACT FROM AUTHOR]

A simple theoretical model for erbium-doped fibre ring lasers is presented. This model is experimentally verified by means of the comparison between theoretical values and measurements of efficiency, threshold pump power and output laser power employing a wide set of experimental situations. This model provides semi-analytical equations, which characterise the erbium-doped fibre, determining its absorption and emission spectral coefficients. [ABSTRACT FROM AUTHOR]

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) operating in the 1573 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a bismuth-based erbium-doped fiber (Bi-EDF) approximately 215 cm long and a single mode fiber (SMF) of various lengths to generate an optical comb with a spacing of approximately 0.089 nm. Two 3 dB couplers were used to form a looping arm in the system in order to produce cascaded Brillouin Stokes waves as internal feedback for multi-wavelength operation. A stable output laser comb with 10 lines at more than - 13 dBm was obtained with 4.85 dBm Brillouin pump power and two 140 mW pumps at 1480 nm. The 1480 nm pumps' power and SMF length have a significant effect on the number of wavelengths and on the output power of the generated wavelength comb. [ABSTRACT FROM AUTHOR]

A new, simple EDF characterization method is presented. Departing from well-known equations, some approximations, applicable in WDM working conditions, are introduced. Thanks to them, the number of active parameters necessary to describe the EDF behaviour is sensibly reduced. Afterwards, a simple experiment to find such parameters is proposed. Finally, the characterization method is applied to an EDF and the parameters' values obtained are used to predict gain results. A good agreement between these predictions and experimental data is observed. [ABSTRACT FROM AUTHOR]

A theoretical model of a passively mode-locked erbium-doped fibre ring laser using nonlinear polarization rotation is developed. Numerical simulations are used to study mode-locking and pulse dynamics in a typical ring configuration. The simulations show that stable operation can exist in both isotropic and birefringent fibres, and stable pulses with a FWHM as short as 45fs can be generated. It is found that there is an optimal regime of ellipticity such that the stable mode-locking can be obtained. In addition, the condition for high birefringence approximation is also found. [ABSTRACT FROM AUTHOR]