Nonlinear distortions in the current modulation of non-self-pulsing and weakly self-pulsing GaAs/GaAlAs injection lasers

Nonlinear distortion characteristics of GaAs/GaAlAs injection lasers under analog current modulation were experimentally investigated. In non-self-pulsing lasers, relaxation oscillation (R.O.) plays a heavy role in generating harmonic distortions, in good agreement with theory. Additional distortions generated by microwave mixing in weakly self-pulsing lasers make such lasers unacceptable for wideband analog transmissions unless suitable negative feedback is applied. With such measure taken, both fundamental and the harmonic responses of a self-pulsing laser is indistinguishable from that of a laser with no R.O. resonance.     

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.     

Theoretical modelling of the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers

By employing a simple model of describing three-level lasers, we have theoretically investigated the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers. And based on the theoretical analysis we have proposed a promising method to suppress self-pulsing behaviour in the fibre lasers.     

Theoretical modelling of the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers

By employing a simple model of describing three-level lasers, we have theoretically investigated the effect of photon lifetime on the output dynamics of Er-doped distributed feedback fibre lasers. And based on the theoretical analysis we have proposed a promising method to suppress self-pulsing behaviour in the fibre lasers.     

Bistable mirrors for self-pulsing lasers

In this letter it is suggested that self-pulsing lasers can be realized by using optical bistable elements as decoupling mirrors.     

Influence of ion pairs on the dynamical behaviour of Er3+-doped fibre lasers

We demonstrate experimentally the influence of ion-pair concentration on the dynamical behaviour of erbium-doped fibre lasers. At low pair densities, the laser has a CW output, while at higher densities it exhibits a self-pulsing behaviour. For intermediate pair concentrations, the output intensity evolves continuously from an infinite train of pulses to a CW steady state as the pumping ratio is increased.     

Yb：Er共掺杂对掺铒光纤激光器中自脉冲行为的抑制作用

为了进一步提高镱铒共掺杂光纤激光器的实用性，对镱铒掺杂光纤激光器的自脉冲现象进行了理论分析。利用掺杂光纤中铒离子对的可饱和吸收的作用而引起自脉冲运转及离子对互作用模型作为理论基础建立系统模型，通过理论计算分析了共掺杂镱后掺铒光纤的有效抽运速率，证明了镱铒共掺杂可以提高有效抽运速率。使用这种光纤，可以使抑制光纤激光器中离子对导致的自脉冲效应所需的抽运功率水平大大降低。半导体激光器输出的抽运功率足以抑制由离子对导致的自脉冲，提供稳定激光运转。在研制稳定单频或高重复频率锁模光纤激光器方面，这种可用激光二极管抽运的镱铒共掺光纤具有很大的潜力。     

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.     

条形DH半导体激光器高频调制光输出的频率锁定、准周期、分岔和混沌

本文从解光场方程和载流子浓度以及光子密度速率方程的自洽解出发,研究条形DH半导体激光器高频调制下光输出的频率锁定、准周期、分岔和混沌现象。结果表明,不稳定的条形半导体激光器可能出现混沌的光输出;其通向混沌的途径是准周期到混沌。所得结果与实验符合得很好,并澄清了当前理论中的混乱之处。     

Stability analysis of two coupled Lorenz lasers and the coupling-induced periodic →chaotic transition

We have performed a linear stability analysis of two Lorenz lasers coupled by their electric fields and have shown that the bad cavity condition becomes a function of coupling and that a good cavity instability may occur if the injected fields are inverted before injection. In addition, we show that the symmetrically coupled Lorenz system is isomorphic to the original Lorenz system with new parameters. The stability analysis also predicts a lowering of the second laser threshold with coupling for both the chaotic and self-pulsing regimes. Numerical integration of the equations is in agreement with these predictions and has revealed a coupling induced transition from self-pulsing to chaotic behavior. The classification of the behavior of the coupled system in the parameter space of the coupling constants has been investigated and shows that the results of symmetric coupling allow enough of a margin for an experimental test of the theory. This would allow experimentalists to observe the actual Lorenz instability at excitations as low as 4–5 times above threshold.     

Self-pulsing and bichromatic emission in homogeneously broadened bidirectional ring lasers

We study the effects of saturation-induced Bragg gratings on the mode structure and dynamics of bidirectional homogeneously broadened ring lasers. The grating is viewed as a distributed feedback medium in a ring cavity and modes appropriate to such a structure are used. A Fourier decomposed rate equation model is developed to study the behavior of these modes above threshold. The difference in the properties of these solutions from the modes of an unfilled ring cavity lead to the possibility of bichromatic emission and both regular undamped and irregular damped self-pulsing.     

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.     

Self pulsing properties of optically pumped FIR NH3 lasers

We report on measurements of periodic and chaotic self-pulsing beyond the second threshold of far-infrared NH₃ lasers. While the instabilities of the 81 m¹⁴NH₃ laser follow a simple pattern, for the 374 m¹⁵NH₃ laser different pulsing properties are found in different parameter ranges.Pulses under conditions of high pumping power are measured in detail, in view of possible applications of these coherent, high-repetition rate far-infrared pulsed lasers.     

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.     

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.     

Upconversion assisted self-pulsing in a high-concentration erbium doped fibre laser

We report results on experimental and theoretical characterisation of self-pulsing in high concentration erbium doped fibre laser which is free from erbium clusters. Unlike previous models of self-pulsing accounting for pair-induced quenching (PIQ) on the clustered erbium ions, new model has been developed with accounting for statistical nature of the excitation migration and upconversion and resonance-like pumpto-signal intensity noise transfer. The obtained results are in a good agreement with the experimental data.     

Optical bistability,instabilities and higher order bifurcations

We discuss the transient and steady state behaviour of the self-pulsing instability of a bistable system using the dressed mode approach of Benza and Lugiato. This formalism, in a suitable limit, is shown to afford an exact adiabatic elimination of the atomic modes, and to lead to explicit and manageable equations of motion describing the evolution of the transmitted radiation. In steady state, the self-pulsing solutions display first and second order phase transition-type behavior. A higher bifurcation of the Hopf type, where the self-pulsing becomes unstable, is also identified, and the accompanying unstable limit cycle is displayed by integrating the equations of motion backward in time.     

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。     

High-power Yb-doped continuous-wave and pulsed fibre lasers

High-power laser generation using Yb-doped double-clad fibres with conversion efficiencies in excess of 80% have attracted much attention during the last decade due to their inherent advantages in terms of very high efficiency, no misalignment due to in-built intracore fibre Bragg gratings, low thermal problems due to large surface to volume ratio, diffraction-limited beam quality, compactness, reliability and fibre-optic beam delivery. Yb-doped fibres can also provide a wide emission band from ～1010 nm to ～1170 nm, which makes it a versatile laser medium to realize continuous-wave (CW), Q-switched short pulse, and mode-locked ultrashort pulse generation for various applications. In this article, a review of Yb-doped CW and pulsed fibre lasers along with our study on self-pulsing dynamics in CW fibre lasers to find its role in high-power fibre laser development and the physical mechanisms involved in its generation has been described. A study on the generation of high-power CW fibre laser of 165 W output power and generation of high peak power nanosecond pulses from acousto-optic Q-switched fibre laser has also been presented.