Chaos dynamics in semiconductor lasers with polarization-rotated optical feedback

By using polarization-rotated optical feedback from the transverse-electric (TE) mode to the transverse-magnetic (TM) mode, chaotic oscillations for both polarization modes are excited in a semiconductor laser. We find different correlations between these chaotic oscillations than those found in previous studies. In this study, the dynamics are strongly dependent on their radio-frequency (RF) components and they are divided into three RF regions. For low-pass filtered signals lower than the laser relaxation oscillation, there is an antiphase correlation between the two polarization modes. On the other hand, the two polarization modes have an in-phase correlation for the RF components of the high-pass filtered signals, which are higher than the relaxation oscillation. However, no correlations were observed between the two modes for the intermediate RF components that include the relaxation oscillation frequency. We also perform numerical calculations for the model and obtain good agreement between the theoretical and experimental results.     

Optical feedback induces polarization mode hopping in vertical-cavity surface-emitting lasers

Vertical-cavity surface-emitting lasers subjected to weak polarization-insensitive optical feedback are studied experimentally and theoretically. We find that the feedback induces random anticorrelated hopping between the two orthogonal linearly polarized modes. This polarization mode hopping is accompanied by rapid anticorrelated oscillations in the linearly polarized intensities at the external-cavity frequency. The study of a simple stochastic delay differential equation suggests that these oscillations generated by the delay are typical of any hopping phenomenon between states.     

Experimental characterization of DFB and FP chaotic lasers with strong incoherent optical feedback

We have experimentally investigated chaotic power oscillations in single-longitudinal mode DFB and multi-longitudinal mode FP lasers as a function of incoherent optical feedback strengths of up to 42%. We have demonstrated the existence of chaos in the output oscillations of both laser types using classical experimental tools such as RF spectrum, standard deviation, and maximum Lyapunov exponent, which all increase with increasing of feedback strength for both in single-longitudinal mode DFB lasers and multi-longitudinal mode FP lasers. It is also shown that power switching among longitudinal modes of multimode FP semiconductor laser is a considerable portion of the chaotic power oscillations for both strong and weak incoherent optical feedback.     

TE-TM coupled mode dynamics in a semiconductor laser subject to feedback with variably rotated polarization

We report on the experimental observation of dynamical collapses which address selectively the TM-mode of a laser subject to optical feedback with variably rotated polarization. Simultaneously, the TE-mode which remains the dominant lasing mode exhibits power bursts. We analyze the relative phase shift between the feedback fields into the TE- and TM-mode and find that the dynamical collapses, observed in a specific range of polarization rotation angles, can be attributed to large phase shift feedback conditions applied on the TM-mode.     

光电负反馈下垂直腔表面发射激光器偏振开关特性研究

基于扩展的自旋反转模型, 对光电负反馈下垂直腔表面发射激光器的偏振开关特性进行了数值仿真和理论分析. 研究结果表明: 对于不同的自旋反转率, 反馈强度和延迟时间对激光器偏振开关特性产生较大影响.在慢自旋反转率下运行时, 随着反馈强度的增加, 开关点电流呈线性增加, 导致X偏振模被压缩, 这与报道的基于各向同性光反馈的情景相反, 产生这一现象的原因是由于光电负反馈提高了X偏振模的阈值; 延迟时间对开关点电流的影响随反馈强度的变化而不同.在快自旋反转率下运行时, 反馈强度对开关点电流的影响与慢自旋反转率时的情形不同, 开关点电流经历先增加后减小的过程, 开关点电流受反馈强度的影响更加敏感; 而延迟时间的影响规律和慢自旋反转率时相似. 此外, 还发现自发辐射噪声对激光器偏振开关特性有较大影响. 关键词： 垂直腔表面发射激光器 偏振开关 光电负反馈 自发辐射噪声     

Spatiotemporal polarization dynamics in a transverse multimode CO2 laser with optical feedback

We investigate the polarization dynamics in a quasi-isotropic CO₂ laser emitting on the TEM_01* mode subjected to an optical feedback. We observe a complex dynamics in which spatial mode and polarization competition are involved. The observed dynamics is well reproduced by a model that discriminates between the intrinsic asymmetry due to the kinetic coupling of molecules with different angular momenta and the anisotropy induced by the polarization feedback. We observe various dynamical regimes including chaotic dynamics and show that feedback changes these states from regular to chaotic and vice versa. Finally, the possible applications to polarization coding are discussed.     

Synchronized Chaos in a Modulated Bidirectional Ring Laser

Nonlinear dynamics of a pump-modulated bidirectional experimentally. Theoretical investigations are based on the pumped bidirectional ring laser that supports single mode in solid-state ring laser are studied theoretically and semiclassical equations of motion for an optically each direction. These equations include coupling of modes via their competition for gain as well as their coupling due to backscattering. Approximate analytical and numerical methods are used to study the dynamical behavior of the system when pump is square-wave modulated. It is found that depending on the depth and frequency of modulation, mode intensities exhibit a rich array of nonlinear dynamical behavior including synchronous and asynchronous chaos, and antiphase periodic and quasi-periodic oscillations.     

Polarization switching in a quasi-isotropic microchip Nd:YAG laser induced by optical feedback

This paper demonstrates the influence of external optical feedback on the polarization state of longitudinal modes in quasi-isotropic microchip Nd:YAG lasers. Under optical feedback, the polarization state of longitudinal modes in quasi-isotropic lasers relies strongly on the intracavity anisotropy loss and mode competition. When the intracavity anisotropy loss is small, external optical feedback can cause polarization switching and strong mode competition between two orthogonal linearly polarized eigenstates of one laser longitudinal mode, which leads to the distortion of laser intensity modulation waveform. The polarization switching is independent of the initial external cavity length. By increasing the intracavity anisotropy loss, one polarization eigenstate can be suppressed and the laser works in single-polarization state. A theoretical analysis based on the compound cavity model is presented, which is in good agreement with the experimental results. The results offer guidance to the development of laser feedback interferometers.     

Chaos synchronization in semiconductor lasers with polarization-rotated optical feedback

Chaotic oscillations of the transverse magnetic (TM) mode, which is not a common lasing mode, are excited by using polarization-rotated optical feedback from the transverse electric (TE) mode in a semiconductor laser. In our previous paper, we found that the dynamics were strongly dependent on their RF components under the condition of moderate optical feedback from the TE mode to the TM mode and that they were divided into three RF regions; low-pass filtered signals with a lower frequency than the laser relaxation oscillation frequency, intermediate RF components including the relaxation oscillation frequency, and high-pass filtered signals with a higher frequency higher than the relaxation oscillation frequency. Depending on the frequency bands, the laser outputs showed different correlations. In the present study, using such schemes, the polarization-rotated beam from a transmitter laser (i.e., the rotated TE-mode beam of a transmitter laser) is injected into a receiver laser. We experimentally observe chaos synchronization in accordance with the dynamics of RF components on the transmitter laser side. We also perform numerical calculations using a model and obtain good agreement between the theoretical and experimental results.     

Oscillations in Total Photodetachment Cross Sections of a Triatomic Anion

The total photodetachment cross section of a linear triatomic anion is derived for arbitrary laser polarization direction. The cross section is ,shown to be strongly oscillatory when the laser polarization direction is parallel to the axis of the system; the oscillation amplitude decreases and vanishes as the angle between the laser polarization and the anion axis increases and becomes perpendicular to the axis. The average cross section over the orientations of the triatomie system is also obtained. The cross section of the triatomic anion is compared with the cross section of a two-center system. We find there are two oscillation frequencies in the triatomie anion in contrast to only one oscillation frequency in the two-center case. Closed-orbit theory is used to explain the oscillations.     

Observation of low-frequency fluctuations in vertical-cavity surface-emitting lasers

Low-frequency fluctuations, which are typical irregular oscillations in edge-emitting semiconductor lasers, are experimentally observed for the y-polarization mode (y is the direction along the optical axis of a laser material) in a vertical-cavity surface-emitting laser with optical feedback.     

1550nm-VCSELs在偏振保持光反馈和正交光注入下的偏振转换特性

基于自旋反转模型,研究了1550 nm垂直腔面发射激光器(1550 nm-VCSELs)在偏振保持光反馈和正交光注入下的偏振转换特性.结果表明:正交光注入下的从激光器会随着注入强度的增加产生偏振转换.在归一化注入电流较小时,改变反馈强度,会使从激光器发生偏振转换的注入强度出现规律不同的变化;改变频率失谐,会使从激光器发生偏振转换的注入强度出现规律相同的变化.     

Observation of multi-path interference in broad-area semiconductor lasers with optical feedback

Multi-path interference effects induced by optical feedback in broad-area semiconductor lasers is experimentally studied. An external mirror and an internal laser cavity form a closed composite optical feedback loop. For a very small tilt of the external mirror for the exit facet along the stripe width of the active layer, the light emitted from the laser undergoes multi-path reflections in the composite cavity, and we therefore observe multi-path interference effects of the laser oscillations for a small mirror tilt. The laser output power always shows the fundamental mode of the single feedback loop together with an oscillation of a certain higher multi-path loop. The laser oscillation and the beam profile are strongly dependent on the tilt. We observed up to a nine-fold multi-path interference in the experiment.     

The Effects of Spherical Surface and Laser Polarization on the Photodetachment Cross Section of H~-

We report the combined effects of laser polarization and curvature of the spherical surface on the detached electron spectra from H-.The Theoretical imaging method is used as a tool of investigation.The photodetachment cross sections for various polarization angles,radii of curvatures and inter ion surface distances are displayed.The analysis of the spectra reveals that the laser polarization angle θL,curvature of the surface rc and inter ion surface distance d strongly affect oscillations in the spectra.Therefore,a fine control on the laser polarization and that of curvature in the surface can be used to control oscillations in the photodetachment of negative ions.     

各向异性光反馈注入的垂直表面发射激光器的矢量偏振模转换机理

数值研究了各向异性光反馈注入的垂直表面发射激光器(VCSEL)的矢量偏振模转换机理,研究结果表明,首先,当注入电流接近阈值电流时,由VCSEL的外部参数和偏振器控制的光反馈注入量中各偏振模的能量决定VCSEL 输出的偏振态.其次,由偏振器控制的各向异性光反馈注入引起的VCSEL输出偏振态呈周期性变化.另外,当由偏振器控制的反馈注入量中的x^偏振和y^偏振模能量相当时, x^偏振模和y^偏振模之间竞争激烈,而激光器外部微小的扰动都会打破这两种偏振模竞争 关键词： 各向异性光反馈 垂直表面发射激光器 矢量偏振模     

Influence of polarization mode competition on the synchronization of two unidirectionally coupled vertical-cavity surface-emitting lasers

We analyze theoretically the effect of polarization mode competition on the synchronization of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs). Chaos in the master laser is induced by delayed optical feedback, and the slave laser is subject to isotropic optical injection from the master VCSEL. We show that the synchronization quality can be enhanced when the chaotic regime in the master VCSEL involves both fundamental orthogonal linearly polarized modes.     

Dynamics of a filtered-feedback laser: influence of the filter width

The behavior of a semiconductor laser subject to filtered optical feedback is studied in dependence on the width of the filter. Of special interest are pure frequency oscillations where the laser intensity is practically constant. We show that frequency oscillations are stable in a large region of intermediate values of the filter width, where the dispersion of the filter is able to compensate for the well-known phase-amplitude coupling of the semiconductor laser. Our stability diagram covers the entire range from a very narrow filter, when the system behaves like a laser with monochromatic optical injection, to a very broad filter, when the laser effectively receives conventional (i.e., unfiltered) optical feedback.     

Eigenmode analysis for the radiating stationary state of N two-level atoms in a slab geometry near threshold

We explore steady states of an open, no end-mirrors, low-Q cw laser pumped above the threshold for laser oscillations. We find that the spatial field profile of the steady state just above the threshold is the same as that of the eigenmode that dominates superradiance in the late linear regime from an initially inverted state without continued pumping. The threshold pumping rate and emission frequency are related to the real and imaginary parts of the eigenvalue of this dominant mode.     

短外腔偏振旋转光反馈下1550nm垂直腔面发射激光器的动力学特性研究

基于扩展的自旋反转模型,对短外腔偏振旋转光反馈下1550 nm垂直腔面发射激光器的动力学特性进行了数值仿真和理论分析.研究结果表明:增加反馈强度会导致多个偏振开关现象出现,中等反馈强度下呈现丰富的动力学状态,譬如单周期、倍周期、准周期及混沌态,增加注入电流使Y方向线偏振模的工作区域被压缩;随着反馈延迟时间的增加,在弱光反馈时,偏振模跳变现象将会以特定的频率发生,施加中等的反馈强度将会导致模式跳变的频率增加,并且出现各种新的动力学状态,包括拍频单周期、拍频脉冲包络、拍频准周期和拍频混沌态.新动力学行为的出现是由于短外腔区激光器的动力学特性对相位变化非常敏感,从而使外腔模式间的拍频效应发挥了关键作用.此外还发现各种动力学状态之间会伴随模式间的跳变而发生相互跳变.     

Coherent combining of tunable erbium-doped fiber lasers by a single-mode fiber feedback loop

We experimentally demonstrate the coherent combining of two tunable erbium-doped fiber lasers by using a single-mode fiber feedback loop configuration. A single-mode fiber is arranged in the feedback loop to filter the far-field pattern, and the energy of desired in-phase mode is collected and injected into the resonators of two component fiber lasers. The coherently combined laser is tunable over a wide spectrum ranging from 1536 to 1569 nm, which means that the combining scheme is compatible with wavelength tuning. The effects and necessity of whether adopting polarization controlling measures or not in component lasers are investigated in detail. The results indicate that adding polarization controlling can improve the array＇s coherence, whereas it will decrease the output power and efficiency simultaneously.