Preference of Chaotic Synchronization in a Coupled Laser System

In a coupled laser system, the dynamics of the receiving laser is investigated when two separate transmitting lasers are injected into the receiving laser with different coupling strengths. It is shown that the phenomenon of preference of chaotic synchronization appears under appropriate coupling conditions. The receiving laser will entrain the pulses of either one or both transmitting lasers when the coupling is strong while it keeps its own dynamics when the coupling is weak.     

大口径谐振腔式固体激光中的动力学不稳定性研究

大口径谐振腔式固体激光定标到足够高功率后,由于非稳定腔内激光不对称振荡导致介质上激光强度横向不均匀,激光提取与介质产热耦合会引起激光输出功率和光束质量在时域上的不稳定性。针对三种激光器构型:Nd:YAG薄片、Yb:YAG薄片和浸入式液冷叠片激光器,通过理论分析与数值模拟揭示了其各自不同的光热耦合机制及其影响因素,给出了激光输出的瞬态演化规律。结果表明,前两种构型中基于激光动力学的光热耦合具有饱和效应,其动力学不稳定性只出现在特定参数区间,可以通过恰当的设计加以避免;第三种构型中动力学不稳定性表现出明显的阈值特征,在强光状态下只能通过减少冷却液吸收系数来抑制。     

Chaos synchronization and spontaneous symmetry-breaking in symmetrically delay-coupled semiconductor lasers

We present experimental and numerical investigations of the dynamics of two device-identical, optically coupled semiconductor lasers exhibiting a delay in the coupling. Our results give evidence for subnanosecond coupling-induced synchronized chaotic dynamics in conjunction with a spontaneous symmetry-breaking: we find a well-defined time lag between the dynamics of the two lasers, and an asymmetric physical role of the subsystems. We demonstrate that the leading laser synchronizes its lagging counterpart, whereas the synchronized lagging laser drives the coupling-induced instabilities.     

Phase locking and chaotic synchronization in an array of three lasers

A linear array of three lasers that are coupled mutually in space is investigated. It is shown that the phase of the laser fields is locked with intermediate coupling while the laser intensities are totally chaotic and chaotically synchronized. When the intensities of lasers reenter the regime of chaotic synchronization at smaller coupling constant, the laser fields show low degree of phase locking. The phase differences in the fields between three lasers show rich patterns when the coupling is changed. Received 3 August 2001 and Received in final form 27 September 2001     

Controlling the leader-laggard dynamics in delay-synchronized lasers

We study experimentally the collective dynamics of two delay-coupled semiconductor lasers. The lasers are coupled by mutual injection of their emitted light beams, at a distance for which coupling delay times are non-negligible. This system is known to exhibit lag synchronization, with one laser leading and the other one lagging the dynamics. Our setup is designed such that light travels along different paths in the two coupling directions, which allows independent control of the two coupling strengths. A comparison of unidirectional and bidirectional coupling reveals that the leader-laggard roles can be switched by acting upon the coupling architecture of the system. Additionally, numerical simulations show that a more extensive control of the network architecture can also lead to changes in the dynamics of the system. Finally, we discuss the relevance of these results for bidirectional chaotic communications.     

链式互耦合半导体激光器的实时混沌同步

通过在互耦合外腔半导体激光器之间增加中继激光器,建立了一种链式互耦合半导体激光器混沌同步系统模型.理论分析了系统的实时混沌同步条件,数值研究了注入电流、互耦合条件、反馈条件等对系统实时混沌同步品质的影响,揭示了同步质量在反馈强度和互耦合强度二维参数空间的分布规律.结果表明:注入电流较大时,满足互耦合强度和反馈强度相同,互耦合延时和反馈延时相等,系统中所有激光器之间可同时实现稳定高品质实时混沌同步;中心激光器和边激光器之间的稳定实时混沌同步分布在在互耦合强度和反馈强度较小的区域以及互耦合强度和反馈强度相近的区域;边激光器之间由于同时接收到中心激光器实施的相同注入,能够较容易的实现稳定高品质的实时混沌同步.该系统可进一步扩展成为实现远距离的双向实时混沌同步或阵列激光器系统的实时混沌同步.     

Dual-lag synchronization between coupled chaotic lasers due to path-delay interference

We study experimentally the synchronization dynamics of two semiconductor lasers coupled unidirectionally via two different delayed paths. The emitter laser operates in a chaotic regime characterized by low-frequency fluctuations due to optical feedback and induces a synchronized dynamical activity in the receiver laser, which operates in the continuous-wave regime when uncoupled. Different delays in the two coupling paths lead to the coexistence of two time lags in the synchronized dynamics of the oscillators. This dual-lag synchronization degrades the average synchronization quality of the system of coupled lasers and hinders the transmission of information between them. Numerical simulation results agree with the experimental observations, and allow us to explore this phenomenon in a wide parameter range, and quantify the degree of signal transmission degradation caused by this chaotic path-delay interference.     

谱线和耦合系数对光纤激光器相互注入锁定的影响

相互注入锁定是相干合成技术中最具发展前景的方案之一. 在两个光纤激光器相互注入锁定的基础上,利用可调节光纤光栅改变其中一个激光器的中心谱线和利用不同的分束器改变两个激光器间的耦合系数,同时监测两个激光器的远场光斑和谱线,判断激光器谱线和耦合系数对相互注入锁定的影响. 通过理论和实验得到：提高耦合系数可以提高锁定的频率差;两个激光器的谱线越接近锁定的效果越好,当激光器的谱线超过一定范围时,两个激光器将不能被锁定. 关键词： 光纤激光器 相干合成 相位锁定     

GENERAL SYNCHRONIZATION OF CHAOS IN A SYSTEM OF TWO NON-IDENTICAL LASERS

General synchronization of the chaotic intensity fluctuations of two spatially coupled Nd:YAG lasers with pump modulation is investigated theoretically when the losses of the two lasers are different. It is shown that the chaotic synchronization still exists for medium coupling even though the two lasers are different. For strong coupling the system shows periodic motion of laser intensities. While for weak coupling, the two lasers oscillate independently. It is obvious that the increase of difference between the two lasers reduces the degree of chaotic synchronization.     

频率漂移对耦合激光器阵列锁相状态的影响

耦合激光器阵列可以通过激光器之间的倏逝波耦合实现相位锁定,是有望实现光束相干合成的方案之一。为了探究该阵列锁相状态的稳定性,分析了频率漂移对两路激光器阵列相位锁定状态的影响。通过对耦合激光器阵列动力学方程的数值研究发现,频率漂移将破坏激光器阵列的锁相状态,并引入相位噪声,导致输出远场光强分布不稳定; 研究还发现：倏逝波耦合能够对频率漂移的影响起到一定的抑制作用,但这种抑制只在频率漂移较弱时才有效,因此,如果将该阵列用于光束合成,加入相应的抗干扰措施还是很必要的。数值分析的结果还表明：频率漂移的低频成分对于阵列相位锁定状态的影响更为剧烈,因此,抗干扰措施应主要针对低频干扰来进行。     

Mutual injection locking and coherent beam combining of two thulium doped fiber lasers

We demonstrate which we believe the first investigation on mutual injection-locking and coherent combining of two thulium-doped fiber lasers. Mutual coherence between the two fiber lasers is established by means of mutual coupling through two 3 dB couplers. High combining efficiency of 99% for two fiber laser has been obtained, and the fringe contrast of the intensity pattern at the receiving plane is as high as 93%. The solution to scale to high power coherent beam combining is briefly discussed.     

Stable all-fiber dual-wavelength thulium-doped fiber laser and its coherent beam combination

We demonstrate which we believe the first investigation on mutual injection-locking and coherent combining of two thulium-doped fiber lasers. Mutual coherence between the two fiber lasers is established by means of mutual coupling through two 3 dB couplers. High combining efficiency of 99% for two fiber laser has been obtained, and the fringe contrast of the intensity pattern at the receiving plane is as high as 93%. The solution to scale to high power coherent beam combining is briefly discussed.     

Synchronization and control of chaos in coupled chaotic multimode Nd:YAG lasers

In this Letter we numerically investigate the dynamics of a system of two coupled chaotic multimode Nd:YAG lasers with two mode and three mode outputs. Unidirectional and bidirectional coupling schemes are adopted; intensity time series plots, phase space plots and synchronization plots are used for studying the dynamics. Quality of synchronization is measured using correlation index plots. It is found that for laser with two mode output bidirectional direct coupling scheme is found to be effective in achieving complete synchronization, control of chaos and amplification in output intensity. For laser with three mode output, bidirectional difference coupling scheme gives much better chaotic synchronization as compared to unidirectional difference coupling but at the cost of higher coupling strength. We also conclude that the coupling scheme and system properties play an important role in determining the type of synchronization exhibited by the system.     

Enhanced coherence of weakly coupled lasers

We present the phase-locking and coherence properties between two weakly coupled lasers. We show how the degree of coherence between the two lasers can be enhanced by nearly 1 order of magnitude after taking into account the effects of coupling on both their phases as well as their amplitudes. Specifically, correlations between synchronized spikes in the amplitude dynamics and the phase dynamics of the lasers allow for an interference pattern with a fringe visibility of 90%, even when the coupling strength is far below the critical value and they are not phase locked.     

卫星激光通信均匀信标光的研究

采用信标光是完成卫星激光通信捕获过程的一种重要手段,信标光的远场分布对捕捉概率和捕获时间有较大的影响。为满足通信系统的性能要求,对信标的远场分布提出一定的要求是必要的。首先从理论计算的角度,分析了远场高斯分布信标光对卫星激光通信捕获过程的影响,认为在存在光束抖动的情况下,均匀信标光在捕获阶段具有明显的优势。基于多激光器合束技术,利用半导体激光器设计了一个能实现远场均匀分布的信标光模块。给出了模块结构,分析了均匀信标光产生的机理,并从理论上推导了该模块的远场光强分布表达式。实验表明,所研制的均匀信标光模块可出射功率超过3.8 W,不均匀度小于11%的远场均匀信标光,通光效率为54%,从而证明了所设计的信标光模块的可行性。     

采用光纤消光法检测脉冲激光测距仪消光比的研究

阐述了光纤消光法检测脉冲激光测距仪消光比的测试原理,采用光纤消光法分析了光纤对大功率脉冲激光的耦合与传输等关键技术问题,提出了0．22NA、400μm大功率传能光纤方案,并设计了耦合器和光学系统,分析了聚焦透镜的损耗、光纤端面的损耗、光纤耦合器与光纤的对准误差等影响耦合效率的因素,计算了光学系统弥散斑数据,接收光学系统和发射光学系统在1ω视场的弥散斑分别为9．03μm和10．6μm。设计分析结果对光纤消光法的工程应用具有一定的研究价值。     

雾对激光的衰减特性研究

基于gamma雾滴分布模型以及辐射雾和平流雾粒径分布与能见度的经验关系,计算并分析了不同波长激光在两种雾中的衰减率随能见度的变化,透射率随传输距离的变化.结果表明,不同波长激光在两种雾中传输时,波长较长激光的衰减率都比波长较短激光的衰减率低;10.6μm激光在平流雾中衰减率大于在辐射雾中的衰减率;对不同波长激光在两种雾...     

Dynamics of symmetrical mode beating in complex coupling two-section DFB lasers

The effect of gain/loss coupling on the modal dynamics of weakly-coupled self-pulsating two section DFB lasers is studied in detail. A purely symmetrical mode-beating regime exists for imaginary coupling values between  ? 5% and 12.5%. The minimum required static detuning, the modulation index, and the tuning range of the predicted self-pulsations are sensitive to the magnitude of the gain/loss coupling. For the 10% gain-coupled DFB laser above 90% modulation index is predicted for self-pulsations between 34% and 123 GHz. For the 5% loss-coupled DFB laser above 50% modulation index is predicted for self-pulsations between 27 and 155 GHz.     

Control of dynamical instability in semiconductor quantum nanostructures diode lasers: Role of phase-amplitude coupling

We numerically investigate the complex nonlinear dynamics for two independently coupled laser systems consisting of (i) mutually delay-coupled edge emitting diode lasers and (ii) injection-locked quantum nanostructures lasers. A comparative study in dependence on the dynamical role of α parameter, which determine the phase-amplitude coupling of the optical field, in both the cases is probed. The variation of α lead to conspicuous changes in the dynamics of both the systems, which are characterized and investigated as a function of optical injection strength η for the fixed coupled-cavity delay time τ. Our analysis is based on the observation that the cross-correlation and bifurcation measures unveil the signature of enhancement of amplitude-death islands in which the coupled lasers mutually stay in stable phase-locked states. In addition, we provide a qualitative understanding of the physical mechanisms underlying the observed dynamical behavior and its dependence on α. The amplitude death and the existence of multiple amplitude death islands could be implemented for applications including diode lasers stabilization.     

固体激光器与光纤激光器对光子晶体光纤棒耦合的分析与对比

耦合效率的高低与耦合后光斑的好坏直接影响着光子晶体光纤棒的放大效果,因此需要对种子光的耦合效果进行研究,选择合适的激光器作为种子源。本文对光子晶体光纤棒在固体激光器与光纤激光器两种情况下的耦合效率进行了理论分析;模拟计算了两种激光器情况下耦合效率的变化规律以及对准误差对耦合效率的影响;选择合适的透镜或透镜组,使用两种激光器对光子晶体光纤棒进行了耦合实验;对比两种激光器的耦合效果可知:固体激光器的耦合效率最高只能达到62.4%,而光纤激光器的耦合效率可以达到80%以上;在光纤激光器耦合情况下,对不同功率注入时耦合效率,以及耦合后光斑进行了实验分析。得到的实验结果对后续光纤棒的放大实验具有指导作用。