Jitter dynamics of a gain switched semiconductor laser underself-feedback and external optical injection

We investigate the jitter dynamics of a gain switched laser diode (LD) under the influence of strong optical injection due either to multiple reflections from an external cavity mirror, or from another LD. A numerical technique that considers both the spontaneous emission noise and multiple reflections from external optical components is implemented. At all times, the LD exhibits multi-longitudinal mode operation with a Gaussian-shaped spectral line profile that is centered around a fixed dominant output wavelength. We separately consider three (strong) optical injection conditions: 1) coherent self-feedback; 2) incoherent self-feedback; and 3) coherent, external continuous-wave (CW) optical injection. Incoherent self-feedback results in a reduction, by an order of magnitude, in both the intensity and timing jitter (0.5 ps), while maintaining the average peak power and pulsewidth. Eye pattern results show an opening of at least 90 %, which represents an improvement by a factor of two over the same LD that operates without optical injection. The external CW injection condition approaches that of incoherent self-feedback only at high external injection. Coherent self-feedback does not produce any significant change in the LD performance     

Effects of current modulation on timing jitter of single-modesemiconductor lasers in short external cavities

Turn-on jitter of single-mode semiconductor lasers with modulated injection current and weak optical feedback exhibits periodic oscillations as a function of the length of the external cavity, under configurations appropriate for packaged laser diodes. Numerical results for both periodic and pseudorandom word modulation show that the oscillations persist even when increasing the external cavity length to a few millimeters. It is found that under particular positions of the external reflector a large increase of jitter occurs as compared with the jitter without optical feedback     

Generation of low jitter and discrete tunable dual-wavelength optical pulses at arbitrary repetition rates

Recently there is an increasing interest in generatingshort optical pulses with lowti ming jitter and tuneablemulti-wavelength due toitsi mportant applicationin op-tical ti me division multiplexed(OTDM),wavelength di-vision multiplexed(WDM)systems,and opt…     

Frequency-stabilized mode-locked solid-state laser system forprecision range-Doppler imaging

We report measurements which show that an actively stabilized cw mode-locked Nd:YLF laser, in combination with a flashlamp-pumped Nd:glass amplifier, can achieve better than 1 cm resolution of distant rotating targets using range-Doppler imaging. To do this, we have produced trains of 50 ps mode-locked pulses with less than 25 kHz peak-to-peak optical frequency broadening and jitter of the laser modes. This frequency stability is achieved by active control of the oscillator cavity length using an external cavity as a reference. Cavity length stabilization can also reduce mode-locked laser timing jitter if the jitter is caused by cavity optical path length changes common to all laser modes. In our laser, however, the active optical-frequency-stabilization did not significantly improve laser pulse timing stability from the approximate 2-ps jitter levels achieved in our passively stabilized cavity. Analysis of the data indicates that a significant fraction of the timing jitter was due to laser cavity path length changes that varied from mode to mode     

The effect of external optical feedback on the turn-on delaystatistics of laser diodes under pseudorandom modulation

The turn-on delay statistics of laser diodes with optical feedback are investigated by numerical modeling. Under pseudorandom modulation the optical feedback causes an increase in the average turn-on delay and multiplies and jitter considerably. The jitter increase due to optical feedback is largest at highest bias currents. Optical feedback from an external reflectivity of greater than 0.1% can destroy the pattern effects which occur for some operating conditions     

40-GHz mode-locked fiber-ring laser using a Mach-Zehnder interferometer with integrated SOAs

A 40-GHz mode-locked fiber-ring laser based on an optically controlled modulator is presented and analyzed in detail. The modulator is a monolithic InGaAsP-InP Mach-Zehnder interferometer with integrated semiconductor optical amplifiers, which allows optical pulse generation synchronized to an external optical clock pulse stream. The laser generates nearly transform-limited Gaussian pulses of 2.5-ps width and up to 9-mW mean output power with less than 130 fs of timing jitter, and it is wavelength tunable over more than 30 nm. The relationship between key laser parameters and the output pulse characteristics is analyzed experimentally and numerically. An improved cavity design permits the generation of shorter pulses of 1.0-ps width.     

GS-DFB半导体激光器的光自注入技术

报道了一种光脉冲自注入的新方法 ,它能使增益开关 DFB激光器输出光脉冲的时间抖动从 5.7ps减小到 1.2 ps,分析了注入光延迟时间及功率对时间抖动的影响 ,指出为取得抑制时间抖动的最佳效果 ,必须选择合适的反馈光脉冲延迟时间和适当的反馈光功率。实验中观察到在增益开关 DFB激光器光脉冲建立期间注入反馈光时 ,输出光脉冲会发生严重畸变。     

低抖动准分子激光放大器光源的研究

为了获得低抖动的准分子激光放大器光源,设计了一种以氢闸流管作为高压开关的低抖动准分子激光放大器系统。利用抖动小于4 ns的闸流管触发电路来触发导通氢闸流管,从外部触发信号到准分子光信号之间有一定的延时时间。研究了以氢闸流管作为高压开关的准分子激光放电回路,外部控制信号发生电路产生外部充电信号和出光信号,转换电路将外部充电信号和出光信号转换成固定脉宽的光信号,在实现低抖动出光前,准分子激光放大器系统热平衡过程中会有一定的出光延时漂移现象。讨论了激光运行重复率、激光运行电压和气体状态在热平衡过程中对稳定延迟时间大小的影响。实验表明,在相同运行电压下,稳定延迟时间随着激光运行重复频率的提高而增大;运行电压越高,稳定延迟时间上升的幅度越大。气体恶化后,光脉冲稳定延迟时间变小。激光运行电压和重复频率越高,延时漂移时间越大。在温漂一定时间后,准分子激光放大器内部系统达到热平衡,以外部触发信号为基准,准分子光脉冲信号实现在5、10、15 Hz重复频率下的5 ns内低抖动出光。     

Bistable characteristics and all-optical set-reset operations of1.55-μm two-segment strained multiquantum-well DFB lasers

Bistable characteristics and all-optical set-reset operations in 1.55-μm two-segment InGaAsP-InP strained multiquantum-well (MQW) DFB lasers were studied. An extinction ratio as high as 20 dB with a lasing output power of 4 mW was obtained, partially due to the dispersion effect of strained MQW DFB structures. The detailed transient dynamics of the optical set-reset operations were observed for the first time, with optical injection from a single-mode laser, implying a potential for high-speed applications. A switch-on time in subnanosecond region and a switch-off time of 2.5 ns were measured using input pulses with a peak power of 500 μW     

19 ps switching of a bistable laser diode with 30 fJ optical pulses

19-ps optical switch-on of a bistable laser diode with only 30-fJ input coupled optical energy at a repetition rate of 500 MHz is reported. The bistable laser was an inhomogeneously pumped three-section Fabry-Periot laser diode. The switch-off time was 94 ps, probably limited by the duration of the electrical reset pulse. Longer turn-on delay times were recorded when switching with less input energy     

增益开关F-P激光器抖动的计算和测量

为了能够精确测量增益开关激光脉冲的抖动,应用傅里叶变换和自相关函数．理论分析了谐波频谱分析法测量激光脉冲抖动的数学模型、测量原理。修正了David A．Leep等人建立的基于功率谱测量脉冲抖动的误差,推导出了普适的测量激光脉冲抖动的数学表达式,并数值模拟了不同情况下激光脉冲功率谱的表现形式;利用谐波频谱分析法测量了外连续光注入下增益开关F-P激光脉冲的抖动,时基抖动为0．905ps、振幅噪声为2．83％,并与取样示波器的测量结果进行比较。结果表明在脉冲抖动较小、且重复频率较低的情况下,利用谐波频谱分析法测量脉冲抖动具有更高的精确度。其精确度可以达到飞秒量级。     

外部光注入分布反馈激光器的非线性动力学特性

实验研究了外部光注入分布反馈(DFB)激光器的非线性动力学行为,并给出了其输出特性随注入光强度和频率失谐量变化的动力学特征图.实验结果表明,激光器的动力学行为对外部的微扰十分敏感;在不同外部光注入条件下,激光器可以呈现出单周期、倍周期、多周期以及混沌等多种非线性动力学特征;在注入光强度和频率失谐量变化空间存在三个复杂动力学区域;激光器表现出的复杂动力学行为总是与周期行为有关;当激光器处于复杂动力学区域时,其频谱为连续谱,在连续谱上存在多个明显的峰,所对应的频率定义为特征频率,特征频率的大小不随注入光的强弱以及频率变化.     

Optical clock distribution using a mode-locked semiconductor laserdiode system

An experiment in which a high-power mode-locked femtosecond semiconductor laser system was used as a source of extremely low jitter intense optical pulses in the distribution of a clock to 1024 ports via optical fibers is described. The total accumulated dynamic clock jitter between any two ports, which contains both correlated and uncorrelated sources, was measured to be less than 12 ps. This laser system produced a train of 460-fs optical pulses with over 70 W of peak power at 302 MHz. These results represent the largest fanout with the minimum timing jitter for an optically distributed clocking network     

Impact of saturable absorption on performance of optical clock recovery using a mode-locked multisection semiconductor laser

This paper investigates the impact of saturable absorption (SA) on the performance of optical clock recovery using a mode-locked multisection laser diode. Optical clock at 40 GHz is recovered from the multisection laser with SA section operated under a range of bias conditions. The dependence of extinction ratio and timing jitter of the recovered clock on required optical injection power, data rate detuning, and mark ratio is also evaluated under these operation conditions. The experimental results show that strong SA effect in laser cavity improves extinction ratio and suppresses timing jitter of the recovered clock, while weak or no SA effect in laser cavity offers clock recovery with larger date rate detuning range defined by timing jitter and less dependence on the variation of data mark ratio for extremely low mark ratio.     

Locking bandwidth of actively mode-locked semiconductor lasersusing fiber-grating external cavities

We demonstrate numerically that actively mode-locked semiconductor lasers employing a linearly-chirped fiber grating in an external cavity can exhibit multiple drive frequency ranges of stable pulse generation, and thus give a large locking bandwidth. The locking bandwidth defines the range of RF drive frequencies over which the laser will generate pulses with low timing jitter. The stable optical pulses are generated with leading or trailing subpulses due to optical energy circulating within the fiber grating. The multiple stable ranges merge if loss is introduced into the fiber-grating region. We also show that the locking bandwidth can be improved if chirp is introduced into the grating. Suprisingly, however, chirp of either sign improves the locking bandwidth     

极低时间抖动的飞秒激光技术（特邀）

飞秒激光器的时间抖动（或定时抖动）是指其输出脉冲的时域位置相对于理想周期信号的短期随机偏差。在毫秒量级的时间尺度上，飞秒激光器的脉冲序列具有严格的一致性，其定时抖动甚至低至阿秒量级。飞秒激光器的这种独特性质及其支持的前沿应用构成了“阿秒时间精度的超快光子学”这一全新的超快研究分支。文中回顾了近年来飞秒激光器定时抖动研究进展、高时间分辨率的定时抖动测量技术、以及不同类型的飞秒激光源能够达到的最低抖动水平。最后介绍了低抖动飞秒激光器在大科学装置同步、高速模数转换、绝对测距、相干脉冲合成等领域的应用。     

An optoelectronic oscillator using an 850-nm VCSEL for generating low jitter optical pulses

We demonstrate an optoelectronic oscillator using a gain-switched vertical-cavity surface-emitting laser in a fiber-feedback configuration. We simultaneously generate a 2-GHz optical pulse stream at 850 nm with 750-fs timing jitter (over 100 Hz-10 MHz range) along with an electrical signal that is locked to the repetition rate of the optical pulses. The timing jitter performance is confirmed by measuring higher harmonic phase noise.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

Jitter reduction through feedback for picosecond pulsed InGaAsPlasers

Following a comparison of picosecond-pulse generation techniques, feedback schemes are reported for the generation of picosecond pulse trains with improved jitter for both multicontact and conventional single-contact InGaAsP-InP lasers. Subpicosecond jitter is achieved for Q-switched laser sources using a novel optoelectronic feedback scheme. The use of resonant electrical feedback is shown to improve the timing jitter of gain-switched pulses by up to six times. Pulse-to-pulse timing jitter as low as 250 fs is demonstrated for a hybrid of optical and electrical feedback schemes. Limits for timing jitter in diode lasers are established for optoelectronic, electrical, and optical feedback schemes, and the key picosecond pulse generation schemes are compared in terms of timing jitter for the first time     

A high-speed optical star network using TDMA and all-opticaldemultiplexing techniques

The authors demonstrate the use of time-division multiplexing (TDM) to realize a high capacity optical star network. The fundamental element of the demonstration network is a 10 ps, wavelength tunable, low jitter, pulse source. Electrical data is encoded onto three optical pulse trains, and the resultant low duty cycle optical data channels are multiplexed together using 25 ps fiber delay lines. This gives an overall network capacity of 40 Gb/s. A nonlinear optical loop mirror (NOLM) is used to carry out the demultiplexing at the station receiver. The channel to be switched out can be selected by adjusting the phase of the electrical signal used to generate the control pulses for the NOLM. By using external injection into a gain-switched distributed feedback (DFB) laser we are able to obtain very low jitter control pulses of 4-ps duration (RMS jitter <1 ps) after compression of the highly chirped gain switched pulses in a normal dispersive fiber. This enables us to achieve excellent eye openings for the three demultiplexed channels. The difficulty in obtaining complete switching of the signal pulses is presented. This is shown to be due to the deformation of the control pulse in the NOLM (caused by the soliton effect compression). The use of optical time-division multiplexing (OTDM) with all-optical switching devices is shown to be an excellent method to allow us to exploit as efficiently as possible the available fiber bandwidth, and to achieve very high bit-rate optical networks