Comparison between Analytical Solution and Experimental Setup of a Short Long Ytterbium Doped Fiber Laser

In this paper, the usefulness of parabolic index profile with single clad as well as double clad fiber structure has been investigated for the design of erbium doped fiber amplifier (EDFA) and laser (EDFL). The characteristics of parabolic profile fiber lasers in terms of couple pump power and cavity length have been simulated for 980 nm pump and 1550 nm signal. At pump wavelength, the power confinement of double clad (94.55%) is higher than single clad (93.30%). At signal wavelength, the power confinement of double clad (83.80%) is much higher than single clad (67.88%). We found that, EDFL exhibits very high gain. Output power of 68.68 mw (18.36dBm) for single clad and 68.92 mw (18.38 dBm) for double clad is obtained at 140 mW pump power and 50 cm fiber length. It is observed that EDFA provides very high small signal gain in expense of low pump power and small fiber length. We obtained 40 dB small signal gain with 120 mW pump and 1m fiber length. Therefore, parabolic index profile may be useful to design EDFA and EDFL. In the case of EDFL, both geometry offer almost same performance but double clad shows very well result for EDFA.

This work analyses gain property of an erbium doped fibre (EDF) pumped at 830 nm. Particularly, gain at 1550 nm obtained from an EDF is numerically investigated by solving a number of rate and propagation equations incorporating the effect of amplified spontaneous emission (ASE). In addition, the impact of forward and backward ASE on the propagation of pump and signal powers along the fibre length is studied. ASEs are observed to increase if pump power or signal power or EDF length is increased. However, the impact of ASE on gain is very much sensitive with fibre length and power levels. For instance, gain at 1550 nm is found to be more affected by ASE at lower pump and signal powers. It is observed that, gain difference (AG) between gain estimated with ASE effect and without ASE effect is higher for pump powers lower than 50 mW at 830 nm. Thus, the analysis of gain properties in EDF under 830 nm pump are significant to model and design amplifiers using EDF.

Scaling the pulse energy and peak power in high-power, narrow-linewidth Thulium-doped fiber lasers (TDFLs) is fundamentally limited by parasitic lasing, amplified spontaneous emission (ASE), and nonlinear effects. We present a nanosecond-pulsed Tm-doped photonic crystal fiber MOPA that successfully pushes these performance boundaries, delivering 2.07 mJ nearly rectangular-shaped pulses, with 52 kW peak power at 207 W average power, linear polarization, a narrow 390 pm linewidth at 2048 nm and excellent beam quality (M²<1.3). Based on these results, we provide a detailed analysis of these limiting mechanisms, supported by theory and experiment. We examine the impact of fiber geometry (core diameter, fiber length) and operational parameters of the TDFL (pump and signal wavelength, temporal pulse shape, pulse repetition frequency) on the spatial, temporal and spectral output characteristics. Thus, this work provides a comprehensive framework for understanding and optimizing high-energy pulsed fiber lasers and aims to clarify common misconceptions in the field.

We report the experimental demonstration of an Ytterbium doped fiber laser (YDFL) composed by two stages in cascade. Two sorts of Ytterbium doped fiber (YDF) with different concentration have been used. A proper characterization of the YDFs has been performed in order to find the optimum YDF length. To this end, the output power and the slope-efficiency have been calculated and the signal amplification and the amplified spontaneous emission (ASE) spectra have been analyzed, which are strictly related to the absorption and emission cross-section of the YDF. The first stage has been studied for both continuous wave (CW) and pulsed regime. The results show that by using an YDF with a high slope-efficiency, up to 66%, it is possible to reach an emitted peak power of 30 W in a pulsed regime.

We develop a simulation tool for an all-optical gain-clamped erbium-doped fiber amplifier (GC-EDFA) based on an amplified spontaneous emission (ASE) reflector and thoroughly verify its validity by comparing simulation data with experimental ones. We carry out simulation work as changing conditions like reflection ratio and bandwidth of the ASE reflector, EDF length, and pump power. From this work, we have an exact understanding about the gain clamping principle that a reflected ASE acts like an intensity reservoir against input signal intensity variation. In general, as a reflected ASE power becomes higher, both a dynamic range and a noise figure (NF) increase; on the other hand, a clamped gain value decreases. The ASE reflector-based gain clamping scheme can be used for EDFAs with low NF characteristics at small input signal range in case a reflected ASE power is set at a level much lower than powers required for normal gain clamping function.

In recent years, infrared light sources have attracted great attention for their application in remote sensing, sensors, optical communication, medical and military technology, and so on. Innovative erbium-doped microstructured optical fiber ring lasers (EDFRLs) have been proposed in order to increase the performance of the conventional fiber lasers, enabling a number of advantages such as smaller size, higher power, better beam quality. In a previous work, the authors proposed a design of a Fabry Perot laser made of a novel erbium-doped Ga 5 Ge 20 Sb 10 S 65 chalcogenide glass, operating in the Mid-IR wavelength range. This work reports the design of a ring laser, made of the same glass, operating at the signal wavelength λ s = 4600 nm and at the pump wavelength λ p = 806 nm. The design and optimization has been performed in order to improve the laser performance. The numerical computer code, implemented ad-hoc to investigate the fiber ring laser, takes into account the rate equations of the 5-level erbium ion system, the pump and signal power propagation, the energy transfer of the up-conversion and cross-relaxation phenomena, the cavity losses and the coupling losses. The measured amplified spontaneous emission ASE power spectrum has been accurately sampled in 150 wavelength slots from λ 1 =4200 nm to λ 2 =4800 nm, to obtain more realistic simulations.

Fabrication and emission properties of Er 3+/Yb 3+ codoped tellurite glass fiber for broadband optical amplification

Measurement of the spontaneous emission and gain spectra provides a complete characterization of a semiconductor gain medium, however, this requires the observation of emission in two directions to avoid amplification of the spontaneous emission spectrum. We show that both the gain spectrum and the true spontaneous emission spectrum can be obtained from amplified spontaneous emission (ASE) spectra measured from the end of a segmented-contact device. The spontaneous emission spectra agree with spectra measured through a top contact window. If the carrier populations are fully inverted at low photon energy, it is possible to convert the ASE-derived spontaneous emission into real units.

We report an experimental study of the effect of fiber length and laser linewidth on self-pulsing dynamics and output stabilization of a single-mode Yb-doped double-clad CW fiber laser. It is found that initiation of self-pulsing under low-level pumping conditions is due to relaxation oscillations and saturable absorption in the weakly pumped region of the doped fiber, irrespective of the fiber length and the laser linewidth. However, with an increase in pump power, depending on fiber length and laser linewidth, the pulses initiated due to relaxation oscillation get amplified, and result in short-duration giant pulses due to either stimulated Brillouin scattering (SBS) or stimulated Raman scattering (SRS). In the case of fiber lasers that employ a broadband mirror and wherein the fiber length is sufficient to reach the SRS threshold, the giant self-pulses are generated by SRS, whereas in the case of fiber lasers using a fiber Bragg grating, characterized by narrowband reflection and with sufficient fiber length to reach the SBS threshold, the giant self-pulses are generated by SBS. Output stabilization and, hence, elimination of self-pulsations can be achieved either by suppressing the relaxation oscillations with the addition of an appropriate length of a passive fiber to sufficiently increase the cavity photon lifetime, or by increasing the pump power to achieve gain uniformity along the doped fiber such that relaxation oscillations and reabsorption effects are suppressed.

A novel super-fluorescence fiber source (SFS) in the wavelength range that covers the C+L-band with stable spectrum, high output power and high slope efficiency is demonstrated. The topology consists of two stages: the first stage provides primarily the L-band gain spectrum whilst the second is solely for the C-band. These two stages are combined in series. We merely used the low erbium-doped fiber (EDF) 10.8m long as a gain medium in the second stage, which was pumped backward by a 980nm semiconductor laser diode (LD). As a result, the Amplified Spontaneous Emission (ASE) spectrum had a threshold of 5.1mW and a slope efficiency of 13.48% in the C-band. With a 980 nm LD pumping forward at 11-m-long moderate EDF and 58-m-long low EDF in series, L-band ASE was yielded with 52.3 mW threshold and a slope efficiency of 35.82% in the first stage. The ASE in the L-band was put into the second stage through an isolator and combined with C-band ASE as an output then a broad ASE spectrum of C+L-band was observed. The maximum output power of the C+L-band source was 33mW (15.3dBm) and its power stability was better than ±0.02 dB. Through the optimization of fiber parameters and the adjustment of pumping power in both stages, the flatness of ASE spectrum was improved. The optical bandwidth for the SFS output power, which ripples in 3 dB, was 63.7 nm (1536.92-1600.62 nm) of optical bandwidth without gain flattening filter.

Summary form only given. There is rapid progress in the development of high-power fiber lasers due to their robust operation, low cost, high beam quality at high powers. There are various applications, such as laser sensing, LIDAR applications, processing of specific materials, which require robust and high-power pulsed laser sources at 1550 nm with high beam quality. Achievement of high peak power with low repetition rate is challenging due to well-known problems of strong nonlinear effects and amplified spontaneous emission (ASE) build-up between pulses. In order to reach highest efficiency, the design of each stage of amplification should be carefully optimized. Numerical modeling can be a great tool due to the large number of parameters involved. To date, most modeling efforts of fiber amplification have assumed either a lumped gain model for pulse propagation or a distributed, position-dependent gain model for CW signal for computational simplicity. Here, we investigate both time- and position-dependent gain dynamics numerically, which are used to optimize experimental results. We solve rate equations for Er-doped fiber (three-level system) and Er-Yb-co-doped fiber (six-level system) using finite differences method. The fiber is divided into small segments and for each segment, the rate equations are solved for both forward and backward propagating signals for a fixed time interval. Next, the time step is increased, and the process is iterated. This scheme allows us to analyze pulse propagation with population levels dependent both on time and position along the fiber. This treatment is evidently necessary to correctly model processes such as dynamic gain saturation and ASE creation, since the physical length of a few-ns pulse is comparable to the length of a typical gain fiber. Simulation results were confirmed by experiments, based on which the experimental setup was iteratively optimized. It consists of a seed source, which is a current-modulated diode laser, a core-pumped Er-fiber preamplifier, an acousto-optic modulator to reduce repetition rate to 50 kHz or 100 kHz and a three-stage amplifier system. The first stage comprises of a single-clad Er-doped fiber and the last two stages are based on cladding-pumped Er-Yb co-doped fiber with 10μm and 12-μm core diameter. Following the final amplifier, pulses traverse standard singlemode fiber (SMF-28) to clean up any residual high-order modes before being extracted from fiber. In simulations, the seed source is modeled with Gaussian pulses with peak and average power of 50 mW and 0.3 mW, respectively, corresponding to our experimental values. Simulation results confirm that sufficient seed power is needed from each stage to the next for its saturation and prevention of ASE creation. However, even at high pulse energy and average power after the middle stage (1.2 W in simulation and experiment), at 50 kHz repetition rate we observe significant amount of ASE creation between pulses. By comparison, at 100 kHz, the ASE generation was negligible. In conclusion, we report on time and space-dependent modeling of amplification of nanosecond pulses in a multi-stage fiber amplifier with good agreement to experiments. The influence of seed pulse shape on amplified pulse shape, and ASE creation are investigated. Guided by numerical simulation, we optimized our setup and generated 10-W, 5-ns, 100-kHz pulses from an all-fiber, diffraction-limited and ASE-free fiber amplifier.

A new three-stage quadruple pass (QP) EDFA is presented in this paper. The mathematical models for designing this proposed EDFA are developed. In the mathematical models, the effects of amplified spontaneous emission (ASE) of prior stages are included. Performance analysis of this QP EDFA is carried out with the variation of input pump power ratio and signal power. Change in Erbium ions concentration in energy level 1 and energy level 2 with the variation of fiber length is also analyzed to determine optimum fiber length. From the obtained results the optimum design parameters (pump power, signal power, fiber length) are recommended for practical implementation.

Mid-infrared (mid-IR) fiber lasers that are based on dysprosium (Dy) as the active laser ion provide emission in the wavelength range between 2.6–3.4 μm and can thus bridge the spectral gap between holmium (Ho) and erbium (Er) based mid-IR lasers. Another distinct feature is the wide choice of pump wavelengths (1.1 μm, 1.3 μm, 1.7 μm, and 2.8 μm) that can be used. To date, pump wavelengths shorter than 1.1 μm have not been reported and all demonstrated pump wavelengths apart from in-band pumping suffer from pump excited state absorption (ESA). In this paper, we report new excitation wavelengths, 0.8 μm and 0.9 μm, for Dy-doped mid-IR fiber lasers. We have measured 18.5% and 23.7% slope efficiency (relative to launched pump power) for 0.8 μm and 0.9 μm pumping wavelengths, respectively. By comparing the residual pump power of experimental and numerical simulation data of a 0.5 m Dy-doped fiber, we have found that these new excitation wavelengths are free from pump ESA. Moreover, the high power laser diodes are commercially available at these new excitation wavelengths; therefore, the realization of a diode-pumped Dy-doped mid-infrared fiber laser might become feasible in the near future.

In this study, single-pass (SP), double-pass (DP), and double pass with passive erbium doped fiber (EDF) configurations are designed as erbium-doped fiber amplifier (EDFA). All configurations have been experimentally investigated for four different EDF. EDFA configurations are simulated at the fixed pump and signal power, pump wavelength and channel numbers. In simulation, EDF length of each fiber optimized for maximum gain and minimum gain ripple. After then, output spectrums are examined for each system. As a result, the gain is low level in the SP-EDFA configuration, despite the improvement of the gain factor with the DP-EDFA scheme, the amplified spontaneous emission (ASE) power adversely affected the noise figure because it propagates both forward and backward along the fiber. The best gain and noise values have been observed in the double pass with passive EDF system.

Guided mode resonance filters (GMRF) were used to spectrally-stabilize and line-narrow the output spectrum from Tm fiber lasers operating in the 2 μm wavelength regime. The GMRFs were placed in the output path of an amplified spontaneous emission (ASE) light source and the transmitted light was measured as a notch in the spectrum on resonance. The GMRFs were characterized to determine their peak reflectivity, resonance wavelength, and spectral linewidth of each element. These measurements showed various resonance wavelengths and linewidths varying from 0.50-1.5 nm depending on the individual GMRF parameters. Using GMRFs as feedback elements in Tm fiber laser oscillators resulted in output powers up to 10 W and slope efficiencies of 30-45% with respect to launched 790 nm pump power. In order to scale to higher powers and maintain narrow linewidths, a master oscillator power amplifier (MOPA) setup was employed with a GMRF stabilized master oscillator. In addition to the laser and amplifier characteristics, thermal and damage testing of the GMRFs is reported.