低阈值光纤激光器稳频特性研究

为了实现低阈值光纤激光器的频率稳定输出,设计了环形腔光纤激光器,以光纤光栅作为波长选择元件,在未泵浦光纤饱和吸收体和其锥形化结构的协同作用下实现激光纵模选择,获得了短光纤饱和吸收体长度下的单纵模激光稳定输出。介绍了未泵浦光纤饱和吸收体选频原理和锥形结构滤波原理,实验研究了不同光纤饱和吸收体长度下激光纵模特性和波长稳定性,以及锥形化光纤饱和吸收体的激光输出特性。实验表明,引入锥形化结构的饱和吸收体后,激光器能够稳定输出1545 nm波长的单纵模激光,并有效降低光纤激光器阈值至7.58 mW,采用延迟自外差方法测得该光纤激光器的线宽小于8 kHz。     

Calculation of the colliding pulse mode locking in CW dye ring lasers

A calculation of the influence of a transient absorber grating on the pulse parameters of a dye laser in the "colliding pulse mode-locking" (CPM) regime is given. It is shown that, compared to other passive methods, considerably shorter pulses with a more favorable stability region can be obtained. Within the stability range of single pulse operation the shortest pulses in the CPM are obtained by operating far above threshold where the saturation energy of the amplifier is much greater than that of the absorber. Deviation from an amplifier position that is symmetric with respect to the amplification of the counter-running pulses leads to different energies of the pulses and to a strong decrease of the stability range. Taking the dispersive properties of absorber and amplifier into consideration, equations for the time dependent phase of the laser pulse are established and solved by an analytical ansatz. The resulting pulse chirp is shown to be mainly dependent on the detuning of the pulse frequency from the center frequency of the saturable absorber. The estimated values for the pulse duration and the down-chirp for typical experimental conditions of a rhodamine 6G-DODCI CPM laser agree well with the measured ones.     

Power output of 650-nm self-pulsating AlGaInP laser diodes foroptical storage applications

Self-pulsating laser diodes operating at a wavelength of 650 nm are required in optical storage devices. Pulsation can be achieved by including saturable absorbing quantum wells in the p-doped cladding layer of an AlGaInP laser. A rate equation model of this kind of device is used to analyze the power output of the pulses by varying the cavity length and the absorber quantum-well configuration. Results indicate that certain performance tradeoffs occur between the power output and other characteristics that are subject to optical storage device constraints     

Realization and modeling of a 27-GHz integrated passively mode-locked ring laser

We present a realization and the modeling of a 27-GHz integrated extended cavity ring laser that is passively mode-locked. The mode-locked ring laser is fabricated with active-passive integration. Experimental results show that internal reflections are the major factor affecting operation stability. Continuous-wave, self-pulsating, and in small windows of operation mode-locked regimes have been observed. Similar regimes have been observed in our bidirectional laser model. This model describes the semiconductor amplifier and the saturable absorber using rate equations. Our experimental and theoretical results are compared and discussed.     

内腔倍频被动调Q Nd:YVO4/KTP绿光的脉宽控制

分别改变饱和吸收体在激光腔内的位置及抽运光的束腰在激光晶体中的位置，实现了对激光二极管（LD）抽运Nd：Nd：YVO4／KTP腔内倍频Cr^4＋：YAG被动调Q绿光的脉宽控制。在抽运功率1．52w的条件下，脉冲宽度可以控制在388～616ns之间，同时获得了激光脉冲的重复频率、单脉冲能量及峰值功率的变化范围分别为4．4～26．3kHz，0．52～4．19μJ和1．0～7．2w。考虑腔内光子数密度的高斯空间分布以及抽运光的空间分布，给出了描述调Q激光器工作原理的耦合速率方程组，其数值解与实验结果相符。     

Molecular saturation and the criterion for passive Q switching

Rotational hole burning is known to be the main factor that determines saturation in molecular absorbers during a short pulse. Experimental results are presented that suggest that pulse transmission measurements, as opposed to CW transmission measurements, must be used in order to determine if a gas can be used as a saturable absorber in passiveQswitching. Rate equations are developed for a five-state model to explain saturation in SF6. This model is found to predict CW and pulse transmission through SF6at various lines of the 10.4-μm band of the CO2laser. A simplified model is developed for pulse transmission through saturable gases and is solved analytically for the peak of the pulse. It is found that the absorption coefficient of the absorber at the peak of the pulse is given by a simple expression, which leads directly to a new criterion for passiveQswitching. An experimental test of this criterion is carried out for several mixtures of SF6and He which act as saturable absorbers under varying conditions of irradiation. It is found that the transition from CW to pulsed operation is very sharp and occurs at a well-defined value of radiation intensity.     

被动锁模掺Er3+氟化物光纤激光器理论研究

根据非线性薛定谔方程建立了基于可饱和吸收体被动锁模掺Er3+氟化物光纤激光器的理论模型,研究了中红外超短脉冲在掺Er3+氟化物光纤激光器中形成的物理机制,数值模拟了被动锁模掺Er3+氟化物光纤激光器中中红外超短脉冲的演化过程,重点分析了掺Er3+增益光纤长度,可饱和吸收体不饱和损耗对被动锁模掺Er3+氟化物光纤激光器产生中红外超短脉冲的影响,并给出了参数设置范围。研究发现:当小信号增益系数、可饱和吸收体不饱和损耗、腔内净色散量为一定值,掺Er3+氟化物光纤长度在一定范围时,才会出现稳定的锁模脉冲,且随着掺Er3+氟化物光纤长度增加脉冲宽度变窄、光谱变宽、峰值功率增高;当掺Er3+氟化物光纤长度、腔内净色散量、小信号增益系数为一定值时,可饱和吸收体不饱和损耗在一定的范围时可以得到稳定的锁模脉冲,且随着可饱和吸收体不饱和损耗的增加脉冲宽度变窄,光谱先变宽后变窄变化范围不大,峰值功率增加。     

Parameter ranges for CW passive mode locking

CW passive mode locking of a homogeneously broadened laser is considered. In the coordinate plane, whose abscissa is proportional to the small-signal saturable absorber loading, and whose ordinate is proportional to the small-signal gain, the following regimes are laid out: 1) steady-state single-pulse mode-locking solutions; 2) stability against relaxation oscillations; 3) self-starting of mode locking. The assumption is made that CW mode locking can be obtained only for a choice of parameters for which all three regimes overlap. We require further that the overlap regime be reached by a monotonic increase of small-signal gain (pumping), without passing outside regime 2). Under these conditions one may state requirements on the system parameters for the obtainment of single-pulse mode locking by a saturable absorber. The analysis explains why it has been impossible to mode lock passively the CW Nd:YAG laser, but passive mode locking of the CW dye-laser system is possible.     

1300-nm pulsed fiber lasers mode-locked by purified carbon nanotubes

For the first time, we demonstrate a novel passively mode-locked fiber laser operating at 1300 nm using purified single-walled carbon nanotubes (CNTs) as a saturable absorber. The saturable absorber incorporates diameter-controlled CNTs with peak absorption /spl sim/1300 nm, guaranteeing mode-locking over the same wavelength region. The ring laser uses praseodymium-doped fiber as a gain medium. The pulse repetition rate is 3.18 MHz, and the spectral half-width is 0.15 nm. Dual-wavelength mode-locking is also demonstrated with a channel spacing of 1.1 nm.     

Analysis of stability in two-mode laser systems

Stability in two-mode laser systems is analyzed by considering both the gain saturation and the absorption saturation. The analysis shows that the two-mode laser systems could exhibit new types of stability other than previously predicted and have at most triple stable steady states. The influences of the saturation coefficients on the stability are studied. The cross saturation of the gain and that of the saturable absorber are found to have an opposite influence on the stability. Analysis also shows that an increasing ratio of the self-saturation coefficient of the saturable absorber to that of the gain favors the new types of stability, including the tristability     

饱和吸收体调Q的反转粒子数分析

从描述饱和吸收体调Ｑ的速率方程出发，推导出了实现有激发态吸收的饱和吸收体调Ｑ所需的反转粒子数理论上应满足的条件，并对其进行了讨论与分析，与参考文献的相关叙述相符。     

Dynamics of passively Q-switched microchip lasers

Self-pulsing in passively Q-switched microchip lasers is investigated in detail. The typical range of values of the parameters motivates a new analysis of the laser rate equations. We determine basic properties of the laser intensity oscillations such as threshold conditions, repetition rate, pulsewidth, peak power, and pulse energy. We show that these oscillations appear through a quasi-vertical Hopf bifurcation located slightly above the lasing threshold. Our bifurcation results are verified numerically by modeling a microchip laser experiment with Nd:YAG as the gain medium and YAG:Cr as saturable absorber. Our results agree with the experiment to within 10%     

Dynamic analysis of mode-locked sampled-grating distributed Braggreflector laser diodes

A mode-locked sampled-grating distributed-Bragg-reflector (SGDBR) laser diode for generating a train of light pulses at terahertz repetition rates is proposed with a numerical analysis based on a time-domain large-signal model. The device consists of three parts: the saturable absorber section which serves as a mode-locker, the gain section as an amplifier, and the SGDBR as a spectrum filter. It is predicted that spectrum filtering of the SGDBR along with passive mode locking due to the saturable absorber is effective in generating a train of transform-limited mode-locked pulses at a high repetition rate     

被动调Q固体激光器参数计算及优化设计

在考虑可饱和吸收体受激态吸收的条件下,用拉格朗日乘数法求出了被动调Q激光器输出关键参数的解析解,给出了被动调Q激光器输出能量与输出耦合镜反射率的解析表达式,并通过数值解来优化选择被动调Q激光器可饱和吸收体的初始透过率、耦合输出镜反射率等关键性参数,计算和分析了红宝石被动调Q激光实验数据,计算结果十分接近实验的真实值,较好的说明了被动调Q激光器关键参数的优化效果.     

Extreme timing jitter reduction of a passively mode-locked laserdiode by optical pulse injection

Reduction of the timing jitter to less than that of the master laser pulses was achieved for a passively mode-locked laser diode stabilized by subharmonic-frequency optical pulse injection. Detailed investigation revealed that this phenomenon originates from the short-term stability of the mode locking frequency under passively mode-locking operation with suitable bias conditions of the saturable absorber and the gain sections     

被动调Q腔内单共振光参变振荡器和Cr4+:YAG激光器

分析了以Cr4+:YAG作为饱和吸收体和激光增益介质的被动Q开关Cr4+:YAG激光器腔内抽运的Cr4+:YAG激光器和单共振光学参变振荡器(SRO)的特性.建立了描述这类激光器和单共振光学参变振荡器的动力学特性的速率方程.结果表明,适当条件下作为激光增益介质的Cr4+:YAG同时具有对二阶非线性作用过程产生的处于Cr4+:YAG激光增益谱范围内的SRO信号波的放大作用.分析中考虑了Cr4+:YAG较高激发态和激光上能级之间的弛豫时间约为100ns的中间能级对Cr4+:YAG饱和吸收体和激光器以及ICSRO的影响.     

Relaxation Oscillations and Pulse Stability in Harmonically Mode-Locked Semiconductor Lasers

In this paper, we discuss pulse dynamics in harmonically mode-locked semiconductor lasers and present the conditions necessary for stability. In a laser mode-locked at the Nth harmonic, the pulse energy fluctuations have (N+1) different modes of relaxation oscillations. Different modes correspond to different patterns for the energy fluctuations in the N different pulses inside the laser cavity. In the higher order relaxation oscillation modes, the energy fluctuations are negatively correlated in different pulses inside the laser cavity, and these modes can cause instability. Gain saturation on time scales of the order of the pulse width (dynamic gain saturation) stabilizes pulse energy fluctuations with respect to relaxation oscillations. The precise limits on the stable operating regime depend on the gain dynamics at both slow and fast time scales. We also discuss harmonic mode-locking in the presence of a slow saturable absorber. Dynamic loss saturation in a saturable absorber can work against dynamic gain saturation and limit the stability range for harmonic mode-locking.     

Study of fiber laser micro-nano sensor based on colloidal crystal

A fiber laser micro-nano sensor based on colloidal crystal structure is proposed in this paper.The fiber laser has stable frequency and narrow linewidth.It is realized by using an unpumped erbium-doped fiber（EDF）as the saturable absorber.The saturable absorber possesses the shape of taper.The laser threshold can be effectively reduced by the tapered saturable absorber.The tapered fiber coated with colloidal crystal as sensing unit is studied.The concentration of ethanol can be obtained from the detection of the output laser wavelength.It can be extensively used in chemical,medical and biological detections.     

New two-mode bistability in an asymmetric absorptive multisectionlaser diode: theoretical analysis

A novel two-mode bistable laser diode (TMBLD) with an asymmetric cavity configuration is proposed and analyzed. It consists of a gain region, a saturable absorber region, and a set of mode-selective mirrors (or filters). These elements are arranged such that the saturable absorber acts as an intracavity loss for one mode and a bleachable absorber external to the cavity of the other mode. Both modes share the same gain medium and compete for the same gain. Bleaching of the absorber leads to a switching of the modes and possible bistability. This two-mode bistability results from the complementary processes of mode competition in the gain section and the mode-dependent effective cross section of the saturable absorber. A rate equation analysis of the device indicates that a switching time less than 200 ps and a modulation rate over 3 Gb/s should be obtainable