L-band erbium-doped fiber amplifier incorporating an inline fibergrating laser

Wide-band erbium-doped fiber amplifiers (EDFAs) having an inherently flat gain spectrum in the long-wavelength-band (L-band) between 1570 nm and 1600 nm have recently been realized. The L-band amplification has been achieved by simply using a longer length of EDF than in the conventional-wavelength-band (C-band) EDFAs. In the paper, we investigate the improvement of the gain flatness in an L-band EDFA co-pumped with the high-power pump light at 1.48 μm and the medium-power auxiliary pump light at 1.55-1.565 μm. We also propose a novel L-band EDFA incorporating an inline fiber grating laser (FGL) operating at the auxiliary pump wavelength, and demonstrate that the proposed EDFA has better gain flatness as well as the gain clamping characteristics     

Miniature erbium:ytterbium fiber Fabry-Perot multiwavelength lasers

We demonstrate stable simultaneous lasing of up to 29 wavelengths in miniature 1- and 2-mm-long Er³⁺:Yb³⁺ fiber Fabry-Perot lasers. The wavelengths are separated by 0.8 (100 GHz) and 0.4 nm (50 GHz), respectively, corresponding to the free spectral range of the laser cavity. The number of lasing wavelengths and the power stability of the individual modes are greatly enhanced by cooling the laser in liquid nitrogen (77 K). The polarization modes and linewidth of each wavelength are measured with high resolution by heterodyning with a local oscillator. The homogeneous linewidth of the Er³⁺:Yb ³⁺ fiber at 77 K is determined to be ~0.5 nm, from spectral-hole-burning measurements, which accounts for the generation of a stable multiwavelength lasing comb with wavelength separations of 0.4 nm     

Optical and Photoluminescence Properties of Erbium-Doped Chalcogenide Glasses (GeGaS:Er)

We have examined the optical and photoluminescence (PL) properties of Er³⁺-doped GeGaS glasses of near-stoichiometric composition Ge₂₈Ga_6.2S_65.3:Er_0.5. We have also used powdered samples of various mean sizes (L) to examine the dependence of the 1.54 -mum PL emission spectrum and the PL decay time on the average sample size. Optical absorption spectra of Er³⁺ ions arising from transitions between different energy manifolds, such as 4 I_{15 /2} -⁴ I_13/2,⁴ I_{15 /2} -⁴ I_{11 /2} , etc., have been used to extract Omega₂, Omega₄, and Omega₆ values using the Judd-Ofelt analysis and a Judd-Ofelt radiative lifetime T_JO = 2.6 ms for the ⁴ I_{13 / 2} -⁴ I_{15 / 2} transition. The PL emission spectra and the decay time have been found to depend on the mean sample size. The spectra are broader and the decay times are longer for larger sample sizes, due to photon trapping occurring in the sample. The extrapolated decay time to zero particle size yields a decay time that matches the Judd-Ofelt radiative lifetime almost perfectly, and confirms the argument that the true PL lifetime needs to be measured in fine powders to avoid reabsorption effects. We have estimated the maximum emission cross section as 15.5 X 10^-21 cm².     

Optimization of Broadband Gain Spectra of Cr $^{hbox{4}+}$:YAG Crystal Fiber Amplifier

In this paper, we present energy level, transition configuration, and numerical model of Cr³⁺/Cr⁴⁺:YAG crystal fiber amplifier for the first time, to the best of our knowledge. The rate and power propagation equations of the numerical model are solved and analyzed. The active ion concentration, length of the doped fiber, and pump power are optimized to maximize the bandwidth of the gain spectra. The effect of temperature on the gain spectra is also discussed. It is shown that based on analysis of the absorption spectra and emission spectra, Cr⁴⁺:YAG crystal is a three-level system, and the broadband gain of Cr ³⁺/Cr ⁴⁺ :YAG crystal fiber is attributed to the broad emission of Cr⁴⁺ ions, especially tetrahedral Cr ⁴⁺ in YAG. When excited at 800 nm, optimal fibers have ultrabroad gain spectra in the range of 1.2-1.65 mum, which cover the low-loss windows of the all-wave fiber without absorption peak caused by OH^- group.     

Highly efficient diode-pumped 3-μm Er3+:BaY2F8 laser

A systematic investigation on a series of monoclinic Er³⁺ :BaY₂F₈ crystals with different dopant concentrations (C_Er=5%-30%) and crystal orientations was conducted to optimize the laser performance in this new 3-μm laser medium by laser diode pumping. The highest slope efficiency of 32% near the quantum defect (35%) was obtained with a 10% doped Er³⁺:BaY₂F₈ crystal with the orientation (010) and a length of 3.5 mm. A maximum output power of 160 mW was achieved at an absorbed pump power of 550 mW at a wavelength of 970 nm     

Wavelength-swept fiber laser with frequency shifted feedback andresonantly swept intra-cavity acoustooptic tunable filter

This paper concerns a wavelength-swept fiber laser (WSFL) incorporating frequency shifted feedback and an intracavity passband filter, in which the wavelength of the modeless output is linearly, continuously and repeatedly tuned (in time) over a given range by modulation of the filter peak wavelength and filter strength. We show both numerically and experimentally that amplifier noise plays a key role in determining the operation of frequency-shifted fiber laser systems and that a “noisy” amplifier can be used to suppress the natural tendency of such lasers to pulse, allowing for continuous wave, modeless operation. Furthermore, we show that significant narrowing of a WSFL instantaneous swept linewidth can be obtained if the filter peak transmission wavelength is resonantly swept so as to follow the wavelength shift per pass due to the acoustooptic frequency shift. Using these ideas we go on to demonstrate and characterize a high-power diode-driven Er³⁺/Yb³⁺ WSFL incorporating a bulk-optic acoustooptic tunable filter (AOTF). Linewidths as narrow as 9 GHz, sweep ranges up to 38 nm and output powers as high as 100 mW are obtained. Furthermore, we demonstrate the generation of user definable average spectral output by synchronous modulation of the filter strength and multiwavelength pulsed output at higher sweep rates. Excellent agreement between the experimental results and those of the numerical modeling is obtained. Our simulations show that reduced linewidth (<0.02 nm) and improved scan linearity should be readily achievable with realistic system improvements. We believe such sources to be of considerable physical and practical interest, with applications ranging from sensor array monitoring and device characterization through to low-coherence interferometry     

A broadly tunable erbium-doped fiber ring laser: experimentationand modeling

Broad-band tunability of erbium-doped silica fiber ring lasers in the 1.48-1.62 μm wavelength band is demonstrated through modeling and experiment. Tunability over the erbium-doped fiber amplifier (EDFA) C- and L-bands is achieved with a simple laser design using a single gain medium working in deep saturation. A comprehensive numerical model based on an iterative solution of propagation rate equations and spectrally resolved Giles parameters was used to analyze the impact of various laser variables. The dependence of laser output power on total cavity loss, erbium-doped fiber length, pump power, and lasing wavelength has been investigated. The calculated laser characteristics have been found in good quantitative agreement with the experimentally obtained data. Experimental results concerning wavelength tunability, output power, and lasing wavelength repeatability/stability and spectral purity are also presented     

Er3+-doped channel optical waveguide amplifiers for WDMsystems: a comparison of tellurite, alumina and Al/P silicate materials

Er³⁺-doped tellurite and Er³⁺-doped alumina optical waveguide amplifiers are analyzed both as single amplifiers and as elements of 16-channel wavelength-division multiplexing (WDM) systems; their performances are compared with that from Er³⁺-doped Al/P silica waveguide amplifiers. The amplifier model is based on propagation and population-rate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that Er³⁺-doped tellurite waveguides exhibit improved gain characteristics compared with alumina and Al/P silica waveguides. Using Er³⁺-doped tellurite waveguide amplifiers, it is suggested that 16 WDM channels may be transmitted to a maximum distance of 4250 km. By using in-line notch gain equalizing filters, the maximum transmission distance can be increased to 5250 km     

全光通信网中的L波段光纤激光器研究

本文首先介绍了光纤激光器(特别是掺铒光纤激光器)的工作原理。进而对L波段光纤激光器进行了深入的探讨,并分析了影响激光器输出的因素:谐振腔长、掺铒光纤长度,且做了相应的理论分析。     

Electrical relaxation in iron-containing glasses

Glasses with composition 70 mol%(SiO₂, B₂O ₃, P₂O₅, TeO₂)-15 mol% Fe ₂O₃-15 mol%(BaO, CaO) were prepared by the conventional melt quenching technique. The electrical relaxation of these glasses has been studied in the frequency range 20 to 10⁵ Hz. The small polaron hopping between iron ions in a different valence state Fe²⁺ to Fe³⁺ is found to be the principal conduction mechanism. The ratio of Fe²⁺ ions to the total iron content, C=Fe²⁺/Fe_tot, is one of the factors determining the electrical conductivity. The glass former has a minor influence on dc conductivity, except of TeO₂ glass where conductivity is three order of magnitude higher than those of other glasses. The ac conductivity as a function frequency is divided into two domains, a dc plateau, followed by a power law in frequency. These two regions are well distinguished in the complex plot of electric modulus where all data points for different temperatures reside on the single plot. The results are discussed in the frame of the Hunt theory of dielectric relaxation in glasses containing mobile charge carriers     

On the simulation of digital optical links with EDFA's: an accuratemethod for estimating BER through Gaussian approximation

A new method for the semi-analytical estimation of the bit-error rate (BER) of digital optical systems is presented. It is based on system simulation and accurately considers the performance degradation caused by waveform distortion. The method profits from the simplicity of Gaussian approximation for noise statistics, though explicitly accounting for intersymbol interference (ISI) effects in noise during the BER estimation. Optically preamplified and avalanche photodiodes (APD) receivers are considered, for which signal-dependent noise components are dominant. The system parameters influence on receiver sensitivity is studied. A digital optical transmission link with a single in-line erbium-doped fiber amplifier (EDFA) and with an EDFA chain is then analyzed. The influence of the EDFA chain characteristics on system performance is investigated: amplifier gain, noise figure and spacing are considered. The tradeoffs between EDFA parameters and system optimization are addressed     

An output power stabilized erbium-doped fiber amplifier withautomatic gain control

Based on the cross-saturation between two different-wavelength optical signals in an erbium-doped fiber amplifier (EDFA), we have developed an output power stabilized EDFA system with automatic gain control. The developed system shows 18.5-dB dynamic range of the output power limitation with the ability to set the output power level arbitrarily. When a temporally varying optical signal is input, the system works as a fluctuation remover for the input signal modulated at low frequency up to 1 kHz and does not have any deteriorative effect on high-frequency modulated optical signals. The degree of modulation in the fluctuated optical signal can be reduced down to as low as 0.003     

Determination of charge mobility in He gas from current-voltagemeasurements in point-plane geometry

In order to clarify whether or not is it possible to extract reliable values of positive and negative mobility for ions and even for electrons in gas when using sharp point-plane geometry, the authors have undertaken a systematic study using He gas. Monitoring the purity level of the same gas filling two different cells (point-plane and plane-parallel), they have compared mobility values deduced from current-voltage curves (mobility K) with time of flight measurements (actual mobility μ) as a function of gas pressure (0.1-15 MPa) and purity. For negative charge carriers (ions or electrons), they have directly measured K^- and μ^- and then compared the results. They observed, as expected, that the measured negative charge carriers mobility was strongly dependent on gas purification. For commercial gas (O₂ of the order of 100 ppm), K^- was very close to the data obtained for negative O₂^- ions (i.e., K^- ≅ μ(O₂^-)) but, for better purification level, K^- increases quickly and can reach electronic values μ_e (K^- → μ _e). For positive ions, in all the range of studied pressure, it was shown that one can extract easily from I(V) measurements, mobility values K⁺ in accordance with the values of μ⁺ of He⁺ previously given in the literature     

The ion-specific behavior of watertree growth in LDPE

The growth of water trees in low-density polyethylene (PE) has been studied. Trees were grown in solutions containing a fixed anion, Cl ^-, but different cations with valences of +1 (Li⁺), +2 (Mn²⁺) and +3 (Fe³⁺). An ion-specific effect on tree growth and tree appearance has been found. Generally, these results have been shown to be correlated with either the ion-water interactions or the interionic attractions. However, for the specific case of adding small amounts of 3+ cations into univalent ion solutions, such a correlation was not found: it is likely that the hydrogen ions, introduced by the multivalent ions through their electrostatic interaction with water molecules, play an important role. The abnormal transport behavior of such hydrogen ions in the solution and probably in the polymer, may expand the overall region affected by treeing but reduce the visibility of the individual trees themselves. A similar process may account for the particularly translucent appearance of trees formed with pure FeCl₃ solutions. This argument is further demonstrated through tree growth experiments using KCl solution and its mixtures with small amounts of HCl. It was found that this additive accelerated tree growth. It is argued that small amounts of KOH might be expected to show an effect similar to HCl because of the similar transport behavior of OH^- ions and H⁺ ions respectively and such enhanced tree growth was demonstrated, using small quantities of KOH added to KC1 solutions     

Silver tree

In this paper, AgNO₃ (silver nitrate) solution was used as liquid electrode to accelerate the growth of water trees in polyethylene. It was found that water trees grown in AgNO₃ solution can be colored spontaneously during their formation, their areas are brownish-yellow, and they grow fast. Scanning electron microscopy (SEM) revealed microchannels in the AgNO₃-grown water tree with diameters from 0.2 to 0.5 μm. In fact, these microchannels are possibly filled with metallic silver reduced from silver ions, and these water trees are referred to as `silver trees'. The structure of the silver trees is studied and analyzed in comparison with sulfide trees and blue water trees. The effects of silver ions (Ag ⁺) in the silver tree region are investigated and a comparison is made with other ions such as K⁺, Na⁺, Mg⁺⁺, and Cu⁺⁺ in water trees. The trees from AgNO₃ solution grow much faster than trees from the other solutions. Finally, the mechanism of the formation of silver trees is suggested     

Average inversion level, modeling, and physics of erbium-dopedfiber amplifiers

We present a detailed study of a set of models for characterizing the gain, the input and output powers of single erbium-doped fiber amplifiers (EDFAs) and networks of EDFAs. The time dependent gain is described by a single ordinary differential equation for the average inversion level of an EDFA with arbitrary number of signal channels with arbitrary power levels and propagation directions. In steady state, this ordinary differential equation becomes a transcendental equation from which many important parameters are derived. Through perturbation analysis of the time dependent model, the output perturbation can be expressed explicitly in terms of the input perturbations, which is useful for tone calculations. Therefore, this set of models can be applied to the steady state, and to large- and small-signal transient states in wavelength-division multiplexed (WDM) optical communication networks with EDFAs. The models are applied to analyze fast power transients in networks of EDFAs     

海水直流冷却电厂烟气脱硫废水处理工艺的研究

某海水直流冷却电厂除脱硫废水外,所有生产废水均已处理回用。为达到废水零排放目的,拟采用软化预处理–微滤–反渗透–电渗析工艺对脱硫废水进行膜法减量浓缩处理。对浓缩减量核心工艺进行了试验研究,结果表明反渗透装置在75%回收率下将微滤处理后的脱硫废水进行初步浓缩,反渗透系统运行压力、压差稳定,水中的Ca²⁺、Mg²⁺可被基本去除,单支膜脱盐率可达99%以上;采用电渗析将反渗透浓水进一步浓缩,可将反渗透浓水可溶解固形物质量分数由7%浓缩至21%;最终脱硫废水流量由20 m³/h浓缩减量至2 m³/h,大幅降低了后续结晶设备的成本及能耗。此工艺方案实施后,可提高水资源利用率,实现全厂废水零排放。     

Laser-Induced Line Patterning of Nonlinear Optical Crystals in Glass

This paper reports the progress in the patterning of nonlinear optical crystal lines on a glass surface by laser irradiation techniques. Two techniques for the patterning of crystal lines have been developed, i.e., rare-earth atom heat processing and transition metal atom heat processing, in which continuous-wave lasers such as Nd:YAG laser (wavelength: lambda = 1064 nm) are irradiated onto the glasses containing rare-earth ions such as Sm³⁺ and Dy³⁺ or transition metal ions such as Ni²⁺ and Cu²⁺. The patterning of lines consisting of nonlinear optical crystals such as beta-BaB₂O₄, SmxBi_1- xBO₃, (Sr,Ba)Nb₂O₆, and LiNbO₃ has been achieved. It is clarified from the azimuthal dependence of second harmonic intensities and polarized micro-Raman scattering spectra that nonlinear optical crystals in the lines are highly oriented along the laser scanning direction, i.e., the patterning of single-like crystal lines. It is also possible to pattern two-dimensional crystal bending or curved lines by just changing the laser scanning direction, and such bending crystal lines have a potential for optical waveguides.     

RESALT技术在燃煤电厂脱硫废水浓缩处理中的应用

基于电渗析技术的离子重组技术（简称RESALT技术）能够将废水中的钙离子和硫酸根离子分开,因而可避免形成硫酸钙垢,同时可实现废水的浓缩减量。在华电莱州发电有限公司现场进行了脱硫废水处理量为3~4 m³/h规模的RESALT技术中试研究。脱硫废水在RESALT装置中的运行结果表明,利用RESALT技术能够实现硫酸根离子和钙离子的有效分离,并且同时可实现含盐废水的浓缩处理,RESALT装置运行的电耗成本随进水含盐量及浓水含盐量的升高而升高,系统运行无须加药软化预处理,运行的成本主要为电费;以硫酸根、钙离子、镁离子、氯离子、钠离子质量浓度分别为6 480 mg/L、1 820 mg/L、2 462 mg/L、20 680 mg/L、10 465 mg/L的脱硫废水为例,系统回收率为70%,水处理电耗总计为49.5 kW·h/t,水处理直接成本为22.6元/t。     

Widely tunable erbium-doped fiber ring laser covering both C-bandand L-band

We demonstrate a widely tunable erbium-doped fiber (EDF) ring laser covering both the conventional wavelength band (C-band) and the long wavelength band (L-band). It features a wide tunable range, high output power, low-coherent, and depolarized output. A tunable range over 80 nm (1520-1600 nm) has been achieved by optimizing the length of the EDF and by using an intracavity fiber Fabry-Perot (FFP) filter