Gain Fiber Length Research Articles

Erbium Fiber Oscillator With an Intracavity Pulse Shaper for High-Energy Low-Pedestal Wavelength-Tunable Femtosecond Pulse Generation

An erbium fiber oscillator with dominating gain fiber length and an intracavity pulse shaper is experimentally demonstrated. The Kerr nonlinear phase shift induced in the fibers is suppressed by the pulse shaper, enabling high-energy (8.9 nJ) high-compression efficiency (93%) pulses of less than 270 fs duration (after linear dechirping) at modest (320 mW) pump power. A stably mode-locked spectrum corresponding to 19 nJ, 83 fs transform-limited pulse is achieved at 720 mW pump power. Wave-breaking-free pulse energy can be further enhanced by introducing stronger spectral phase modulation via the pulse shaper if more pump budget is available. We also demonstrate manipulation of the central wavelength and bandwidth of the output pulse by intracavity spectral amplitude modulation via the pulse shaper.

Experimental Investigation of the Wavelength Tunability in All-Normal-Dispersion Ytterbium-Doped Mode-Locked Fiber Lasers

The wavelength tunability of all-normal-dispersion (ANDi) ytterbium (Yb)-doped mode-locked fiber laser is experimentally investigated, where the laser is mode-locked by nonlinear polarization rotation and the wavelength is adjusted by an intracavity tunable filter. The influences of pump power, gain fiber length, and cavity length (i.e., repetition rate) on the mode-locking wavelength and output spectrum are investigated. It is found that the tunable range of mode-locking wavelength depends on the length of the Yb-doped fiber, as well as the cavity loss, and is independent of the cavity length. Mode-locking in a longer wavelength regime can be obtained by increasing the gain fiber length, although the length depends on the cavity loss. Moreover, the effects of pump power, central wavelength, Yb-doped fiber length, and cavity length on other output parameters are discussed. The variation range of pump power to keep the mode-locking status is also analyzed. We find that the pump power range for keeping the mode-locking status decreases, and the typical output pulsewidth increases dramatically as the repetition rate decreases. Guidelines for designingANDi Yb-doped mode-locked fiber lasers are proposed.

Graphene Q-switched 278 μm Er^3+-doped fluoride fiber laser

We report a diode-pumped 2.78 μm Er3+-doped ZBLAN fiber laser passively Q switched by a graphene saturable absorber, which was directly deposited onto a fiber dichroic mirror by the method of optically driven deposition. Stable Q-switched operation with a pulse duration of 2.9 μs and a pulse energy of 1.67 μJ was achieved in a 10 m long gain fiber. The pulse duration was reduced to 1 μs when the gain fiber length was shortened to 2 m. This Letter demonstrates that graphene is a promising and reliable saturable absorber for mid-infrared pulse generation at 3 μm.

Stable single longitudinal mode erbium-doped silica fiber laser based on an asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode (SLM) erbium-doped silica fiber laser. It consists of four fiber Bragg gratings (FBGs) directly written in a section of photosensitive erbium-doped fiber (EDF) to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio (OSNR) of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer (OSA) for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.

Optimization of femtosecond Yb-doped fiber amplifiers for high-quality pulse compression

We both theoretically and experimentally investigate the optimization of femtosecond Yb-doped fiber amplifiers (YDFAs) to achieve high-quality, high-power, compressed pulses. Ultrashort pulses amplified inside YDFAs are modeled by the generalized nonlinear Schrödinger equation coupled to the steady-state propagation-rate equations. We use this model to study the dependence of compressed-pulse quality on the YDFA parameters, such as the gain fiber's doping concentration and length, and input pulse pre-chirp, duration, and power. The modeling results confirmed by experiments show that an optimum negative pre-chirp for the input pulse exists to achieve the best compression.

Experimental Investigation on 1018-nm High-Power Ytterbium-Doped Fiber Amplifier

We present an all-fibered 1018-nm ytterbium-doped double-clad fiber laser in master oscillation power amplification configuration. The output characteristics of 1018-nm laser with seed power, gain fiber length, and fiber type are experimentally investigated. The power of the seed laser needs to be much higher to suppress amplified spontaneous emission and enable the sufficient amplification of the 1018-nm seed laser than the case of 1080-nm amplification. And the requirement of the seed power increases with the gain fiber length. The experimental results also indicate that gain fiber with large pump fill factor and low Yb ion concentration is more appropriate for the high-power 1018-nm fiber laser. With this gain fiber, we demonstrate a 77-W near diffraction limited fiber amplifier emitting at 1018 nm with power conversion efficiency of 75%.

Direct Side Pumping of Double-Clad Fiber Laser by Laser Diode Array Through the Use of Subwavelength Grating Coupler

An electron-beam-fabricated subwavelength grating coupler for direct side coupling of light emission from a high-power laser diode array (LDA) was studied theoretically and implemented experimentally. A gold-embedded silica-based design for grating coupler was employed to minimize the thermal expansion caused by the accumulated heat from light absorption by metal part of the grating coupler. In addition, with the consideration of the backward diffraction loss and the groove wall nonverticality caused by fabrication distortion, the grating pitch and groove width were optimized for the highest coupling efficiency. According to the experimental results, the grating coupler is capable of coupling light power up to 21 W from a 976-nm continuous-wave-operated LDA into the inner clad of a 400-μm-diameter double-clad fiber with an overall coupling efficiency of 50%. Furthermore, an LDA side-pumped ytterbium-doped DCF laser by using the grating coupler was demonstrated. By fine tuning the slow-axis collimation lens array, the laser-pumping scheme can easily be switched between bidirectional pumping and unidirectional pumping. Compared with the unidirectionally pumped fiber laser of the same gain fiber length, the laser slope efficiency of the bidirectionally pumped fiber laser was increased by 18% because of a better gain distribution over the fiber length. Finally, the signal output power of 10 W with a slope efficiency of 61% was achieved for the bidirectional side-pumped fiber laser.

Simulation and experiment of erbium/ytterbium co‐doped double‐clad fiber amplifier

AbstractThe “eye‐safe” waveband infrared laser radiation with wavelength of around 1.5 μm has extensive applications in communication, medical care, remote control, etc. An erbium/ytterbium co‐doped double clad fiber amplifier operating at 1.5‐μm wavelength is studied in this article. Theory models, which include calculation of amplified spontaneous emission powers, is built on rate equations describing the energy level transition and intercross transfer, and power propagation equations. Influence of gain fiber length and input signal power on amplifier's output power is analyzed and the amplifier's optimal parameters are derived via simulations. The laser's power spectrums after amplification are found to be satisfactory. An experiment of erbium/ytterbium doped fiber amplifier is also performed. A set of input–output power curves with varying pump powers are measured, which confirm our theoretical analysis. A highest output power of 1.33 W is achieved in the experiment. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1332–1335, 2012

Experimental study on tandem pumped fiber amplifier

We present the experimental results of a 1083nm fiber amplifier tandem pumped by 1030nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083nm signal laser has not been efficiently amplified when cladding-pumped by 1030nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4W with power conversion efficiency of 60%.

Theoretical study of two-tone single frequency fiber amplifier with gain competition

Introducing the gain competition is an effective way to suppress stimulated Brillouin scattering (SBS) in single frequency fiber amplifier. Steady rate equation describing two-tone single frequency Yb-doped double cladding fiber amplifier with gain competition is deduced based on single frequency amplifier. A theoretical model of this kind of amplifier is set up. With this model, simulation is performed to analyze the influences of wavelength difference between signals, signal power ratio, pump configuration and length of gain fiber on output efficiency of single frequency laser, and the effect of SBS suppression.

Design of Yb Fiber High Power Amplifier through 915nm Pumping

Analyze the fiber amplified theory and obtain the transmission formula of pump and signal for the use of rate equation. In the experiment, take the Yb-doped double cladding fiber based on phosphor silicate as gain medium, high power single emitter in 915nm as pump source. According to gain fiber length obtained by the theory analyses, the output power achieves 20W above. Apply the cladding power stripper at the output end for stripping the remained pump power.

Generation of sub-50 fs pulses from a high-power Yb-doped fiber amplifier

We demonstrate the generation of 48 fs pulses with 18 W average power and 226 nJ of pulse energy from a Yb-doped fiber amplifier. The system uses a simple stretcher-free single-stage amplifier configuration operating in the parabolic pulse regime. The gain fiber length and pump wavelength are chosen in order to reduce the gain per unit length and generate both shorter pulses and higher pulse energy.

Stimulated Brillouin scattering in single-frequency fiber amplifiers with delivery fibers

For an all-fiber-based single-frequency amplifier, a passive delivery fiber carrying the amplified signal out of the pump combiner may induce unwanted stimulated Brillouin scattering (SBS) and affect amplifier performance. To evaluate the impact, a rate-equation based model has been adopted to study SBS characteristics in the fiber amplifier with a delivery fiber. The model allows independent inputs of many critical parameters, such as the delivery fiber length, temperature distribution, core size, Brillouin gain coefficient, as well as the gain fiber length. The SBS thresholds of the amplifiers under various conditions are computed. The results indicate that the delivery fiber lengths, core diameter, and Brillouin gain coefficient are the most influential parameters which make great impacts on amplifier performance. In addition, the gain fiber length also plays a role on SBS thresholds, but its impact is modest and normally less than a few percent. For an amplifier with a 25 microm gain fiber, to achieve more than 400 W output, the delivery fiber should have a Brillouin gain coefficient <1 x 10(-11) m/W with a length of less than 2 m and a core diameter of greater than 35 microm.

Performance of two-stage discrete fiber Raman amplifiers with and without all-optical gain clamping

Using numerical simulations, we analyze the properties of two-stage discrete fiber Raman amplifiers without and with all-optical gain clamping. In both cases a two-stage amplifier can be designed to have the same gain characteristics as a single-stage amplifier with improved noise performance by use of either the same total length of gain fiber (but with increased pump power) or total pump power (but with increased total length of gain fiber).

Cortisol secretion and growth in ewe lambs chronically exposed to electric and magnetic fields of a 60-Hertz 500-kilovolt AC transmission line.

A study was conducted to determine whether chronic exposure of ewe lambs to the electric and magnetic fields (EMF) of a high-voltage ac transmission line affected cortisol secretion and growth. Twenty Suffolk ewe lambs were assigned randomly in equal numbers to a control and treatment group. Treatment from 2 to 10 mo of age consisted of continuous exposure within the electrical environment of a 60-Hz, 500-kV transmission line (mean electric field 6 kV/m, mean magnetic field 40 mG). Treated lambs were confined directly beneath the transmission line; control lambs were maintained in a pen of similar construction 229 m from the line where the EMF were at ambient levels (mean electric field < 10 V/m, mean magnetic field < .3 mG). Cortisol was analyzed by RIA in serum of blood samples collected at .5- to 3-h intervals over eight 48-h periods. All ewe lambs were weighed weekly and side-patch wool growth was measured biweekly. Cortisol secretion occurred in a circadian rhythm; daytime serum concentrations were greater (P < .05) than nighttime concentrations for both groups. Concentrations of cortisol did not differ between the control and exposed ewe lambs. Weight gain and wool fiber length and diameter also were not affected by treatment. These data suggest that chronic exposure of developing ewe lambs to 60-Hz environmental EMF does not affect concentrations of cortisol secretion, body weight gain, and wool growth.

The gain and optimal length in the erbium-doped fiber amplifiers with 1480 nm pumping

The approximate analytic expressions for the gain and optimal length of the 1480-nm-pumped erbium-doped fiber amplifier with an arbitrary dopant distribution are obtained when the saturation by amplified spontaneous emission (ASE) is neglected. Numerical calculations show that the values predicted from the analytic expressions of the maximal gain and optimal fiber length as functions of input signal and pump powers are very accurate for narrow dopant distributions confined to the center of the fiber core.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>