Self-pulsing characteristics of a high-power single transverse mode Yb-doped CW fiber laser

We present an experimental study of self-pulsing characteristics of a high-power single transverse mode Yb-doped double-clad continuous wave (CW) fiber laser. The self-pulsing features under high-power single-end pumping and double-end pumping configurations have been shown to be distinct. Our experimental observation indicates that in single-end pumping configuration, self-pulsing is predominant due to saturable absorption effect, caused by the weakly pumped portion of the fiber at the farther end. However, in double-end pumping configuration, uniform pumping and hence gain uniformity along the fiber length avoids the onset of saturable absorption of signal along the fiber length and thereby reduces self-pulsing, which finally results in a much more stable output.     

Waveguiding effects in self-pulsing vertical-cavity surface-emitting lasers

Self-pulsing in semiconductor lasers containing a saturable absorber is well documented. We propose an alternative mechanism leading to self-pulsing in vertical-cavity surface-emitting lasers. We specifically consider waveguiding effects and determine the conditions for self-pulsing. Our theoretical and numerical results agree with experimental observations reported by Willemsen et al. [Appl. Phys. Lett. 77, 3514 (2000)].     

Self-pulsing in a double-clad ytterbium fiber laser induced by high scattering loss

The characteristics of self-pulsing behavior in a double-clad ytterbium-doped fiber laser are presented. The self-pulsing generates a supercontinuum spectrum that mostly propagates through the multimode structure of the fiber. In fact, 90% of the total power, including the fundamental laser wavelength and the generated supercontinuum spectrum, propagates trough the first cladding. The experimental evidence indicates that the main mechanism for the self-pulsing is the high scattering loss in the double-clad fiber.     

Experimental observation of bright-dark pulse emitting in an all-fiber ring cavity laser

We demonstrate the emission of bright pulse and dark pulse in a simple all-fiber ring cavity laser by using self-pulsing technique. The switching between bright pulse and dark pulse can be realized by properly rotating the polarization controller (PC). Meanwhile, the bright-dark pulse can also be generated in the fiber laser and is experimentally verified to be on two different orthogonal polarization axis of the cavity fiber. Our experimental results show that the bright pulse, the dark pulse or the bright-dark pulse can be obtained in an all-fiber laser by using self-pulsing technique.     

Instabilities in semiconductor lasers

One of the most relevant problems connected with optical fiber communication is that related to the presence of instabilities in the output of semiconductor lasers. These instabilities appear as nonlinearities in the optical power-current characteristic (kinks) or as dynamics instabilities (self-pulsing). These phenomena more frequently occur in devices without a refractive index profile introduced ad hoc in the junction plane (gain-guided lasers); self-pulsing, in particular, is present in aged lasers. Both of them, however, can appear also in nonaged lasers with lateral confinement of the e.m. field (index-guided lasers). In this paper the principal experimental results obtained studying instability phenomena and the physical mechanisms proposed for their explanation are reported and discussed.     

An organizing center for optical bistability and self-pulsing

The problem of self-pulsing in optically bistable systems is discussed within the framework of imperfect bifurcation theory. The joint appearance of a hysteresis cycle in the cw-transmission curve and of transitions to self-pulsing is described as an interaction between steady-state and Hopf bifurcations induced by varying the incident field intensity. The bifurcation equations for the most degenerate case are shown to be determined by a corank-two and codimension-four polynomial normal form. This form can be extracted from analytical and numerical studies on the Maxwell-Bloch equations, and acts as an organizing center for bistable switching and the self-pulsing mechanism. The structurally stable unfolded bifurcation diagrams are analyzed. Besides describing correctly and in a comprehensive way all bifurcations to self-pulsing that have so far been observed, a number of new generic transitions are predicted. These include self-pulsing from the low transmission branch and transitions leading to the formation of islands with self-pulsing behavior.     

A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop WDM amplifiers relative to the low concentration erbium ions multi feedback-loop optical amplifiers and ion-pairs, which act as a saturable absorber to compensate the gain tilt caused by the OAGC laser spectral hole burning. The theoretical results are in complete agreement with the previous published experimental results.     

Self-locked He-Ne ring laser

Experimental conditions necessary for self-pulsing to occur in a He-Ne ring laser are reported. These results are compared with predictions that are based upon theoretical models that have been presented in the literature. Good qualitative agreement is found in that theory and experiment both show that self-pulsing will only occur over a range of excitation. Quantitative results differed enough to indicate that additional refinement is needed even though the models have identified many of the important parameters involved.Supported by the US Army Research Office.     

哈肯激光方程自脉冲解的稳定性分析

本文详细地研究了哈肯激光方程的自脉冲不稳定性,得出了自脉冲解的解析表达式,并对其进行了稳定性分析。结果表明,无论是对于第三类激光系统还是对于第四类激光系统,哈肯激光方程的自脉冲解都是不稳定的。     

Effect of steady-state conditions on self-pulsing characteristics of Yb-doped cw fiber lasers

Fiber laser resonator configurations have been analyzed theoretically on the basis of steady-state rate equations to optimize the laser conversion efficiency. Evolution of the pump- and signal powers and the saturated gain coefficient along the length of the laser medium has been simulated for high- and low-finesse resonators in forward- and backward pumping schemes. The corresponding fiber laser configurations have been setup to verify the results of simulation. Backward pumping configuration in an Yb-doped fiber laser has been found to be the most efficient, and in this configuration a maximum cw output power of 10.75 W in single transverse mode with an optical-to-optical conversion efficiency of 62.5% has been achieved. The laser output spectrum was peaked at 1093 nm with full-width at half-maximum (FWHM) line-width of about 9 nm. In the low-finesse resonator configuration, it has been found that experimental observations differ from theoretical simulation results. In this case, output power from both ends ceases to increase linearly beyond 1.8 W, and starts fluctuating due to the onset of strong random self-pulsing phenomenon. Our investigation shows that a non-uniform steady-state gain along the fiber length facilitates the self-pulsing process.     

The effect of Erbium concentration on the optical spectrum of Erbium-doped fiber laser

We report an experimental observation of the influence of concentration of Er³⁺ ions in an Erbiumdoped silica fiber on the spectral characteristics of an erbium fiber laser. Our basic conclusion is that an increase of erbium concentration in the fiber results in the laser optical spectrum narrowing. We also discuss possible mechanisms responsible for this effect.     

Residual pump light as a probe of self-pulsing instability in an ytterbium-doped fiber laser

Self-pulsing instability in the ytterbium-doped fiber (YDF) laser is investigated with the pump-bypassed cavity configuration. The residual pump light acts as a probe of the intracavity dynamics, and the temporal behavior of the light shows correlations with the self-mode locking instability in the original cavity and the sustained self-pulsing instability in the modified cavity of the YDF laser. The results suggest that the interactions among stimulated emission, pump absorption and/or reabsorption could account for self-pulsing instability in the YDF laser. The pump-bypassed laser cavity configuration can be used to investigate the instabilities of various kinds of fiber lasers.     

Erbium glass lasers and their applications

In this paper results of experimental investigations into erbium glass lasers and their likely applications are discussed. Regularities of the inversion energy accumulation, also as channels of energy losses, are covered in detail. Different erbium lasers, both flashtube and neodymium laser-pumped, are compared. Parameters of some erbium laser glasses are presented, including the new LGS-E7, which requires a smaller pumping energy density (less than 100–200 J cm^-2). Test data from experimental models are summarized.     

Peculiarities of photoluminescence of erbium in silicon structures prepared by the sublimation molecular-beam epitaxy method

The photoluminescence of semiconducting structures Si: Er: O/Si grown by the molecular-beam epitaxy method is studied. The dependences of Er photoluminescence intensity on the intensity of pumping are measured at the liquid helium temperature. An analysis of the experimental results on the basis of the exciton model of excitation of Er ions in a crystalline silicon matrix reveals the significant role played by an alternative channel of free-exciton trapping (apart from the donor energy levels of erbium-oxygen complexes), as well as that played by the nonradiative channel in the recombination of excitons, bound to erbium donors, without the excitation of erbium. The ratio of the concentration of optically active centers of erbium luminescence to the total concentration of introduced erbium is estimated.     

碱土金属离子对掺铒磷酸盐玻璃除水性质的影响

以掺铒磷酸盐玻璃中铒离子寿命随OH含量变化为依据,系统研究了碱土金属离子类型和含量对磷酸盐铒玻璃除水性质的影响。结果表明,采用通干燥O2和CCl4除水工艺可有效降低玻璃中OH含量,除水效果在通气的最初阶段最为明显,玻璃中OH含量降低速率随通气时间延长而减慢,最终趋于动态平衡。值得指出的是,在相同通气时间,磷酸盐铒玻璃的荧光寿命随碱土金属离子半径增大而减短。含有较高浓度碱土金属离子的磷酸盐铒玻璃具有较短的荧光寿命,并且在停止通气后熔体重新吸水的能力变大。     

Self-pulsing in two-cavity optical bistability

We discuss two serially coupled ring cavities which contain media modelled by an ensemble of homogeneously broadened two-state atoms. This system produces pulsed outputs for appropriate CW inputs and values of the cooperativity parameters in the absorptive regime. In particular, self-pulsing occurs when both stable and unstable steady-state output versus input characteristics are everywhere monotomic with positive slope. An analytic requirement for this self-pulsing is obtained in the absorptive case.     

掺铒光纤环形激光器输出特性的研究

根据掺铒光纤激光器的速率方程，对环形腔光纤激光器的输出特性进行了理论分析，得到了光纤激光器在稳态条件下阈值抽运功率、激光输出功率和斜率效率的解析表达式。利用数值模拟结果对光纤激光器的这些基本特性参量进行了分析和讨论，为光纤环形激光器的优化设计提供了依据。并进行了980nm抽运的掺铒光纤激光器的实验，实验证明理论分析得到的基本特性是合理的。     

多功能有源光纤器件组合实验仪

多功能有源光纤器件组合实验仪由若干功能单元构成，通过简单的跳线插接就可组合成系列实验装置：掺铒光纤放大的自发辐射(ASE)光源，掺铒光纤放大器(EDFA)，掺铒光纤激光器(EDFL)和全光纤调Q激光器．该实验仪为学生做有源光纤器件专题系列实验提供了平台．     

YZr2OZr3:Er3+纳米晶anti-Stokes发光性质的研究

采用均相沉积法制备了不同Er³⁺离子浓度掺杂的Y₂O₃纳米晶, 应用XRD，SEM和PL光谱对该体系材料进行了表征.在Y₂O₃:Er³⁺纳米材料体系中, 观察和研究了Stokes及anti-Stokes PL谱强度与Er³⁺离子摩尔浓度变化的关系, 当Er³⁺离子浓度为2.0mol%时, anti-Stokes PL强度最强.粉末X 关键词： 氧化钇纳米晶 anti-Stokes PL 双光子吸收     

A distributed model for continuous-wave erbium-doped fiber laser

A distributed model of a continuous-wave erbium-doped fiber laser is discussed. The model is based on two contra-propagated traveling laser waves, and includes inhomogeneous pumping, excited state absorption at the pump and the laser wavelengths, amplified spontaneous emission and radial distribution of populations of erbium levels. It is shown that excited state absorption is a main limiting factor to the laser's efficiency. Moreover, consideration of radial distributions of erbium levels' populations in the model reduces laser efficiency and decreases optimal reflection of the laser output coupler. The modeling results are in excellent agreement with the experimental study on the EDFL efficiency.