Noise characteristics in repetitively pulsed semiconductor lasers

Timing jitter (phase noise) and power fluctuations (intensity noise) in a semiconductor laser driven with a periodic current waveform, in the large signal regime are investigated theoretically. The temporal behavior of the laser output power is calculated numerically from the modified rate equation with Monte Carlo simulation of the random processes, both free-running and active mode-locked configurations are treated. The temporal width and root-mean-square (rms) timing jitter and energy fluctuation of the pulses are calculated, as are the correlation and spectral properties of the noise     

Spectral measurement of the noise in continuous-wave mode-lockedlaser pulses

A theoretical analysis of the noise of a periodic optical pulse train is presented. It is shown that the amplitude fluctuation, the pulsewidth fluctuation, the pulse timing jitter, and the cross correlations between any two of these three noise parameters can be separately quantified by comparing the noise power spectra of the fundamental pulses and those of the second-harmonic pulses. The noise characteristics of an actively mode-locked Nd:YLF laser are presented to demonstrate this technique     

Measurement of the timing jitter and pulse energy fluctuation of aPLL regeneratively mode-locked fiber laser

We measured the timing jitter and pulse energy fluctuation from the noise RF power spectra of a 10-GHz regeneratively mode-locked erbium-doped fiber laser in both free-running and phase-locked-loop (PLL) operation. The measured timing jitter was 90 and 120 fs for free-running and PLL operation, respectively. These values are to our knowledge the smallest timing jitter reported in actively mode-locked fiber lasers. The pulse energy fluctuation was 0.24% for both operation     

Injection-Locked Mode-Locked Laser With Long-Term Stabilization and High Power-per-Combline

A novel method is presented to provide long-term stabilization of an injection-locked harmonically mode-locked laser to a narrow linewidth continuous-wave (CW) source for the first time. The method, based on the Pound-Drever-Hall method of laser frequency stabilization, exploits the phase shift across a laser cavity mode resonance to detect the offset between the CW frequency and the combline frequency desired for injection-locking. Long-term suppression of the radio-frequency supermode noise spurs is shown as well as 36-dB suppression of optical supermodes. Significant reductions in phase and amplitude noise are also shown due to injection. Postamplification noise results are presented, showing an increase in optical power per combline with no degradation in pulse-to-pulse energy fluctuation or timing jitter.     

氦镉激光器的噪音研究

本文在实验上研究了氮镉激光噪音的起因和特性，得到氦镉激光噪音的起因是多重的。行走辉纹、气压差及镉浓度波都是产生噪音的重要原因。气压差及镉浓度波可使噪音增大很多倍，浓度波主要增强了低频噪音。适当增大激光管内平均镉浓度和采用扩散迴路后，可显著降低激光噪音，获得大功率低噪音的氦镉激光器。     

太赫兹时域光谱仪中幅值噪声的分析

明确指出太赫兹时域光谱仪系统的幅值噪声的来源为延时线的重合抖动、采样抖动以及飞秒激光功率的波动。通过理论和实验相结合的方法证明,在测量样品的折射率和吸收系数等光学常量时,延时线的重合抖动和采样抖动影响着系统提取的折射率值的精确度;延时线的采样抖动和激光功率波动分别影响着系统提取的吸收系数的高频部分和低频部分的精确度。     

A theoretical analysis of the transient intensity noise ofsemiconductor lasers

The nonstationary intensity noise of a high-speed modulated semiconductor laser is investigated. The analysis is based on a rate equation method with Langevin fluctuation sources. The variance and the autocorrelation function of the intensity noise are calculated analytically with a state-space approach. The time-variant statistical properties of the intensity noise are evaluated numerically for the turn-on transient. The numerical calculation indicates that the difference between intensity noise and photon number fluctuations during the turn-on transient can be neglected. It a shown that is significant part of the nonstationary intensity noise can be described as timing jitter of the relaxation oscillations     

Noise of the stretched pulse fiber laser. II. Experiments

For pt.I see ibid., p.649, 1997. The noise characteristics of the stretched pulse fiber ring laser are determined from the power spectrum of the current of a detector illuminated by the output pulse train. Amplitude fluctuations as low as 0.05% of the pulse energy and jitter <80 fs (measurement time=0.09 s) are obtained with no external stabilization. These are the lowest noise levels reported to date for a passively mode-locked laser. The experimental results are compared with the noise theory of the companion paper. Good agreement is obtained between theory and experiment. Comparison with theory also shows that the jitter at frequencies higher than 60 Hz is due to amplified spontaneous emission (quantum) fluctuations when the measurement time is on the order of 0.1 s     

Turn-on jitter in nearly single-mode injection lasers

Computer modeling confirms recent experimental observations and shows that photon absorption and spontaneous emission cause as much as 50-60 ps jitter in the turn-on time delay of lasers with large mode-suppression ratios. Careful selection of the bias point can reduce this jitter to about 12 ps. Statistics are presented for the expected power level at fixed sampling time during the turn-on, and for the fluctuation in time delay for the laser power to rise to one-half the equilibrium power output.     

Optical signal generation at millimeter-wave repetition rates usingsemiconductor lasers with pulsed subharmonic optical injection

A new technique is presented and investigated systematically which generates optical signals at millimeter-wave repetition rates from a semiconductor laser, without the need for an intracavity saturable absorber. Optical pulses are generated from a long-cavity semiconductor laser with a repetition rate equal to its cavity resonant frequency by injecting short optical pulses at one of the cavity resonance subharmonics. A rate-equation model is proposed to explain the mechanism of this subharmonic optical injection method. Optical pulses with repetition rates of 35 and 56 GHz are generated using the proposed scheme from a semiconductor laser with a distributed Bragg reflector and a Fabry-Perot laser diode, respectively. The performance of the generated pulses is also evaluated in terms of detected RF power at the repetition frequencies, the subharmonic suppression ratio, phase noise, and timing jitter as a function of frequency detuning, injected optical power, laser bias current, and, finally, the subharmonic number. It is found that the generated optical pulses exhibit large subharmonic suppression ratio (>17 dB), large locking ranges >400 MHz, low levels of phase noise (~-93 dBc/Hz@10 kHz) and timing jitter (<0.41 ps over 100 Hz to 10 MHz), and large tolerance to variations in operating parameters     

MOPA结构准分子激光电源的高精度电压控制研究

为了减小激光器双腔放电时间的相对抖动、稳定激光器输出能量,采用闭环控制回路电压泄放方法,设计了一套主振荡功率放大结构准分子激光谐振充电高精度电压控制方案。通过对电容电压取样处理,动态监测储能电容电压,当电容电压大于目标电压时,由泄放电路泄放电压至目标值,得到高精度的充电电压,使用此电压控制方案后,充电电压的波动由1.67减小到0.83。结果表明,该方案很好地提高了谐振电源储能电容上的电压精度,减小了激光器双腔放电时间的相对抖动,并为后期的激光器能量输出稳定控制打下良好基础。     

干涉噪声对基于以太的千兆接入网的影响

由于激光器输出相位的随机波动，光信号经多次反射后相互叠加将形成干涉噪声．在基于以太的千兆接入网中，由于EFM(Ethernet First Mile)链路1．25Gbit／s的工作速率，所以干涉噪声对其的影响必须予以考虑．文章分析了干涉噪声对系统性能的影响及其导致的功率代价，可以作为工程设计时的参考．     

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。     

低时间抖动的增益开关型被动调Q激光器

被动调Q激光器的输出抖动一般较大,为了降低这一输出时间抖动,同时实现激光器的小型化,可以根据增益开关工作原理,利用电源控制抽运功率密度变化,实现被动调Q情况下的增益开关.根据这一原理研制了环形激光二极管(LD)抽运增益开关调Q激光器.这种新型被动调Q激光器的输出能量为30 mJ,输出脉冲宽度约16 ns.实验中将传统的两套抽运源减少为一套,通过控制电源波形直接形成抽运功率的增益台阶脉冲,减少了影响时间跳动的因素.多发次统计测量结果表明,激光脉冲与电源输出外触发信号的时间抖动小于1 μs.根据测量的抽运预脉冲功率稳定性和阶跃脉冲的瞬时抽运功率计算的输出抖动与实验结果基本相符.     

自相似抛物线脉冲的噪声扰动分析

为了研究自相似脉冲系统中的噪声扰动，我们从非线性薛定谔方程出发，推导出了时间抖动方差和能量抖动方差表达式。数值研究结果表明噪声使得自相似抛物线脉冲形状，频谱和啁啾的畸变非常严重。噪声扰动导致了脉冲振荡和频谱抖动。虽然脉冲仍具有线性啁啾，但却在前后沿出现起伏波动。在初始阶段，噪声扰动很小，可以忽略，但随着传输距离增大，噪声扰动的影响将迅速增大。不同的正色散和增益对时间抖动和能量抖动方差影响不同。     

双模激光场强度起伏的噪声功率密度谱及其时谱特性

采用光场的量子理论导出了自由运转双模激光场强度起伏的噪声功率密度谱及其时谱公式，重点分析讨论了双模激光场的量子统计特性及其拍频噪声的时谱特性和频率调谐特性。研究发现双模激光拍频噪声的时谱特性也可用于双模激光的稳频稳幅。     

Analysis of mode partition noise in laser transmission systems

Mode partition noise can be the dominant limitation on a system error rate for single-mode-fiber laser transmission systems. The distribution of power among the longitudinal modes of the laser fluctuates and, as a consequence of chromatic dispersion in the fiber, causes an amplitude fluctuation of the signal at the decision circuit in the receiver. The effect is in essence a pulse-delay fluctuation, and the error rate cannot be reduced by increasing the received signal power. We derive a simple formula describing this mode partition noise, give useful design relations, and verify the analysis by comparison with system experiments.     

Theory of timing jitter in actively mode-locked lasers

An analysis of the pulse-to-pulse timing jitter in an actively mode-locked laser is presented. The model includes spontaneous emission noise, mode-locker driver phase noise, and cavity length detuning. Analytical expressions for the laser pulse train phase noise spectrum, the intensity power spectrum, and the RMS timing jitter are given. The timing fluctuations are characterized by a time constant proportional to the cavity round-trip time times the number of locked modes squared divided by the modulation depth. The contribution from the mode-locker driver phase noise will dominate unless high-stability RF sources are used. The residual timing jitter due to spontaneous emission noise is very sensitive to cavity detuning     

基于锁相环电源噪声引起的周期抖动分析

针对电源噪声在时钟电路的锁相环中引起的抖动问题，通过分析周期抖动和相位抖动与电源噪声间的关系，提出了用于预测电源噪声引起的锁相环抖动峰峰值的计算公式。文中预测的抖动峰峰值与HSPICE的仿真结果间的误差最大为3%，说明了文中公式的有效性。