The Experts below are selected from a list of 80829 Experts worldwide ranked by ideXlab platform
W.a. Clarkson - One of the best experts on this subject based on the ideXlab platform.
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Influence of energy-transfer-upconversion on threshold Pump Power in quasi-three-level solid-state lasers
Optics Express, 2009Co-Authors: Jacob I. Mackenzie, W.a. ClarksonAbstract:A simple analytical expression for threshold Pump Power in an end-Pumped quasi-three-level solid-state laser, which takes into account the influence of energy-transfer-upconversion (ETU), is derived. This expression indicates that threshold Pump Power can be increased dramatically by ETU, especially in low gain lasers and lasers with pronounced three-level character due to the need for high excitation densities in the upper manifold to reach threshold. The analysis has been applied to an Er:YAG laser operating at 1645 nm in-band Pumped by an Er,Yb fiber laser at 1532 nm. Predicted values for threshold Pump Power as a function of erbium doping concentration are in very good agreement with measured values. The results indicate that very low erbium doping levels (~0.25 at.% or less) are required to avoid degradation in performance due to ETU even under continuous-wave lasing conditions in Er:YAG.
M A Mahdi - One of the best experts on this subject based on the ideXlab platform.
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analytical study of nonlinear phase shift through stimulated brillouin scattering in single mode fiber with the Pump Power recycling technique
Journal of Optics, 2011Co-Authors: Hamid Ali Abed Alasadi, F Mahamd R Adikan, Ahmad Ashrif A Bakar, M A MahdiAbstract:We present a theoretical study of nonlinear phase shift through stimulated Brillouin scattering in single mode optical fiber. Analytical expressions describing the nonlinear phase shift for the Pump and Stokes waves in the Pump Power recycling technique have been derived. The dependence of the nonlinear phase shift on the optical fiber length, the reflectivity of the optical mirror and the frequency detuning coefficient have been analyzed for different input Pump Power values. We found that with the recycling Pump technique, the nonlinear phase shift due to stimulated Brillouin scattering reduced to less than 0.1 rad for 5 km optical fiber length and 0.65 reflectivity of the optical mirror, respectively, at an input Pump Power equal to 30 mW.
L. Rapp - One of the best experts on this subject based on the ideXlab platform.
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Dynamics of Spectral Hole Burning in EDFAs: Dependency on Pump Wavelength and Pump Power
IEEE Photonics Technology Letters, 2010Co-Authors: L. Rapp, Joao M. FerreiraAbstract:Pump wavelength and Pump Power dependency of the dynamical response of spectral hole burning (SHB) in erbium-doped fiber amplifiers (EDFAs) is investigated. The experimental results show a clear dependency on Pump wavelength also in the 1480-nm range. Similar to other effects in EDFAs affecting transient performance, dynamics of SHB speeds up with increasing Pump Power. We conclude that the Pump has a significant contribution to SHB and has to be taken into account in numerical models for SHB.
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Transient Behavior of EDFA Stages Using Pump Power Splitting or Pump Bypass Technique
Journal of Lightwave Technology, 2007Co-Authors: L. RappAbstract:Power transients in optical networks impose challenging requirements on the design and control of optical amplifiers. In addition, reducing amplifier cost has become mandatory. Therefore, setups using a single Pump to supply Pump Power to several coils of erbium-doped fibers (EDFS) have become attractive. In most cases, the so-called Pump bypass technique is employed, but Pump Power splitting also constitutes a favorable solution. Both techniques are compared with respect to their transient behavior. The investigations focus on the characteristics of the optical setup representing the control path. Appropriate scenarios are considered to take into account the influence of feedforward and feedback control techniques. Simulation results reveal that the Pump Power splitting approach is favorable with respect to a feedback control, whereas there are no significant differences with respect to feedforward approaches
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Comparison of EDFA Stages using Pump Power Splitting or Pump Bypass Technique with Respect to Steady-state Performance
Journal of optical communications, 2006Co-Authors: L. RappAbstract:Providing the Pump Power emitted by a single Pump laser to several coils of erbium-doped fibers (EDFs) is a common way to reduce cost of optical amplifiers. Typically, this is achieved by using a Pump Power splitter or by employing the Pump bypass technique. Both techniques are compared with respect to steady-state performance. In addition to the standard parameters noise figure and output Power, gain variations induced by population of the third energy level are also considered. The investigations cover single EDFA stages, multistage EDFAs using the mentioned techniques for the first stage, and two-stage gain-flattened EDFAs with variable gain. Pump Power splitting offers good performance in all test cases and shows the most balanced behavior. Simulation results for a two stage EDFA with embedded variable attenuator reveal that the Pump Power splitting approach provides better noise performance for a given maximum Pump Power if the splitting ratio and the length of the coils are set at an optimum.
Qing Fang - One of the best experts on this subject based on the ideXlab platform.
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Effects of waveguide length and Pump Power on the efficiency of wavelength conversion in silicon nanowire waveguides
Optics Letters, 2009Co-Authors: Minming Geng, Lei Zhang, Lin Yang, Ping Chen, Qing Fang, Mingbin YuAbstract:We point out the use of a wrong definition for conversion efficiency in the literature and analyze the effects of the waveguide length and Pump Power on conversion efficiency according to the correct definition. The existence of the locally optimal waveguide length and Pump Power is demonstrated theoretically and experimentally. Further analysis shows that the extremum of conversion efficiency can be achieved by global optimization of the waveguide length and Pump Power simultaneously, which is limited by just the linear propagation loss and the effective carrier lifetime. (C) 2009 Optical Society of America
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Effects of waveguide length and Pump Power on the efficiency of wavelength conversion in silicon nanowire waveguides
Optics letters, 2009Co-Authors: Lianxi Jia, Minming Geng, Lei Zhang, Lin Yang, Ping Chen, Yuliang Liu, Qing FangAbstract:We point out the use of a wrong definition for conversion efficiency in the literature and analyze the effects of the waveguide length and Pump Power on conversion efficiency according to the correct definition. The existence of the locally optimal waveguide length and Pump Power is demonstrated theoretically and experimentally. Further analysis shows that the extremum of conversion efficiency can be achieved by global optimization of the waveguide length and Pump Power simultaneously, which is limited by just the linear propagation loss and the effective carrier lifetime.
Georges Patrick - One of the best experts on this subject based on the ideXlab platform.
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Magic mode switching in Yb:CaGdAlO 4 laser under high Pump Power
Optics Letters, 2016Co-Authors: Druon Frédéric, Olivier Mickaël, Jaffrès Anaël, Loiseau Pascal, Aubry Nicolas, Didierjean Julien, Balembois François, Viana Bruno, Georges PatrickAbstract:We present unique spatial-mode switching in a cw Yb:CALGO laser when Pumped at a multihundred-watts Power level. It permits us to automatically stabilize to a TEM 00 mode from a highly spatial multimode regime. This stabilization is achievable thanks to polarization-mode switching allowed by the particular spectroscopic and thermal properties of Yb:CALGO crystal. This atypical and unexpected behavior is studied in detail in this Letter and explained by analysis of the thermo-optical coefficients for CALGO. Diode-Pumped high-Power lasers based on Yb-doped materials have raised intense interest in the laser community in the last few years. Among them, Yb-doped CaGdAlO 4 crystal (Yb:CALGO) is now recognized to exhibit exceptional and interesting properties for high-Power and ultra-short-pulse lasers. In fact, by combining both broad emission bandwidth and good thermal properties , it permits us to demonstrate ultra-short pulses [1,2] and high Power [3–6]. Very recently, this crystal also has been integrated in thin-disk geometry [7,8], demonstrating in cw up to 150 W (multimode) and 50 W (single mode) and up to 30 W in femtosecond regime [9]. These experiments clearly demonstrate the interest of Yb: CALGO in classical bulk or thin-disk configurations for high-Power femtosecond lasers. Increasing the Pump Power (typically > 100 W), the thermal issues start to be problematic in Yb:CALGO. Nevertheless, the analysis of the thermal lens in CALGO has never been carried out in detail up to now. Indeed, very few thermal parameters are known for Yb:CALGO. In this Letter, the thermal properties are studied carefully in order to explain an unexpected and, to our best knowledge, never-observed-before effect consisting of a drastic spatial mode stabilization by passive polarization switching. The laser cavity is shown in Fig. 1. It is a three-mirror V-shape cavity incorporating a plane dichroic mirror, a 500 mm radius-of-curvature mirror and a plane mirror as the output coupler. The Yb:CALGO is a 10 mm long 2 at. %-doped crystal with a section of 2 × 2 mm 2. The crystal is Pumped with a 400 μm diameter fiber-coupled (NA 0.22) diode delivering up to 200 W. The diode beam is imaged in the crystal with a magnification of 1. In this configuration, the crystal absorbs between 90% (at low Power) and 75% (at high Power) of the Pump Power, depending on the absorption saturation. The optimal output coupler transmission is 10%, allowing extraction of cw Power up to 43 W. The crystal is integrated in a copper mount, which is water cooled at 18°C. This module design, based on Taranis technology from Fibercryst, is used to optimize the heat-transfer coefficient and minimize mechanical stresses. The temperature elevation, measured with an IR 8 to 12 μm camera, at the entrance surface and in the center of the crystal is 0.66 K∕W (versus absorbed Power), which leads to a 100 K increase at full Power. Experimentally, we observe a spatial single-mode operation at " low " Pump Power, typically under 88 W of absorbed Pump Power (100 W incident). Multimode operation, due to thermal lens effects, appears above this value. Surprisingly, the spatial mode switches back abruptly to a nice TEM 00 mode when the Pump reaches 128 W of absorbed Pump Power (160 W incident) as shown in Fig. 2. Increasing furthermore the Pump Power, the spatial mode does not degrade back to highly multi-mode operation but stays almost TEM 00 with only a slight astigmatism and a small amount of TEM 20 (Fig. 2). We then observe a very different behavior before and after the switch. We investigated the spectral and thermal properties of Yb:CALGO in order to understand this magic mode switching. The first noticeable difference between the two laser beams before and after the switch is the polarization state. Actually, the linear polarization switches from vertical to horizontal. This corresponds with our crystal cut to a switch from a σ polarization Ejj ⃗a to a π-polarization Ejj⃗ c, see Fig. 1. Since these two axes have different gain cross sections (Fig. 3), the emission wavelength switches
