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     

Measurement and simulation of the turn-on delay time jitter ingain-switched semiconductor lasers

The turn-on delay time jitter of four different unbiased gain-switched laser types was determined by measuring the temporal probability distribution of the leading edge of the emitted optical pulse. One single-mode 1.5-μm distributed feedback laser and three multimode Fabry-Perot lasers emitting at 750 nm and 1.3 μm were investigated. The jitter was found to decrease for all lasers with increasing injection current. For multimode lasers it decreases from 8 ps excited slightly above threshold down to below 2 ps at three times the threshold current. The jitter of the distributed feedback (DFB) laser is a factor of 3-5 larger than the jitter of the three multimode lasers. A model for predicting the turn-on delay time jitter is presented and explains the experiments quantitatively     

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。     

Turn-on jitter in semiconductor lasers with moderate reflectingfeedback

Numerical simulations are used to investigate the impact of moderate external feedback on the turn-on timing jitter inherent in directly modulated semiconductor lasers. Enhanced turn-on jitter is found to be due to the feedback-induced intensity noise     

Turn-on jitter of external-cavity semiconductor lasers

Analytical expressions, validated by numerical simulations, are obtained for the turn-on delay jitter of semiconductor lasers subjected to weak optical feedback in short external cavities. The results show explicitly that displacement of the external reflector on optical wavelength scales causes significant changes in the switch-on dynamics of the laser. It is found that more than a 400% increase of jitter can occur under certain circumstances. The demonstrated sensitivity of laser switch-on dynamics to reflector location is considered to be particularly relevant to the performance of packaged laser diodes     

Timing jitter in semiconductor lasers under pseudorandom wordmodulation

Timing jitter of semiconductor lasers under pseudorandom word modulation was studied at 1 Gb/s. For lasers biased above threshold the timing jitter was Gaussian in distribution, with a turn-on timing jitter amplitude τ=2σ=±6 ps. For lasers biased below threshold, the turn-on timing jitter showed two peaks of Gaussian distribution, with an amplitude τ=60±10 ps and separated by about 80 ps. This phenomenon is due to a pattern-dependent effect of the laser turn-on delay. Theoretical calculations show that for data transmission above 2.2 Gb/s, the laser has to be biased above threshold to avoid excessive (>0.5 dB) jitter-induced power penalty     

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     

Dependence of timing jitter on bias level for single-modesemiconductor lasers under high speed operations

The dependence on the bias level of some quantities characterizing optical pulse statistics, such as the turn-on time, pulsewidth, maximum output photon number, and average output power, of single-mode semiconductor lasers is numerically analyzed at frequencies in the gigahertz range. Periodic modulation and pseudorandom word modulation are considered. In the former regime, timing jitter is shown to be rather independent of the bias current. In the latter regime, timing jitter becomes larger when biasing above threshold than when biasing below threshold. This larger jitter is found to be associated with a bimodal probability distribution of the turn-on time, which yields undesirable pattern effects. A privileged bias, slightly below threshold, suppresses these pattern effects making the laser response almost independent of previous input bits. For such bias value the probability distribution functions of the turn-on time in the case of the periodic and pseudorandom word modulation coincide     

Operation range of VCSEL-interconnect links with“below-threshold”-biasing

Biasing lasers below threshold in interconnect links yields a lower effort for the monitoring circuitry, but it leads to a significant turn-on jitter due to the bit-pattern effects and spontaneous emission. An analytical expression describing the probability density function (pdf) of the total turn-on delay for a single-mode vertical-cavity surface-emitting laser (VCSEL) biased below threshold is derived, which accounts for both bit-pattern effects and spontaneous emission. In a high speed digital transmission system both timing jitter as well as the signal-to-noise ratio (SNR) limit the system-performance, which can be measured by the resulting bit-error rate (BER). The measured BER is compared with the calculated BER yielding good agreement. Therefore, following the quite general guideline as presented here, the operation range for “below-threshold”-biased VCSEL-interconnect links can be determined     

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.     

Coupling coefficient dependence on oscillation frequency stability of self-pulsating DFB laser diodes

Grating coupling strength effects in self-pulsating distributed feedback lasers were investigated. Choosing the coupling coefficient appropriately, improvements in the timing jitter as well as the injection locking sensitivity were observed experimentally. The results are attributed to a co-ordination of optical feedback strengths between dual lasing modes.     

Turn-on jitter of zero-biased nearly single-mode VCSEL's

The turn-on jitter of zero-biased nearly single-mode vertical-cavity surface-emitting lasers (VCSEL's) is experimentally investigated. Since during the turn-on event both the dominant and the suppressed polarization are exited, an analytical expression describing the probability density function of the turn-on delay for a single-mode VCSEL is derived, which accounts for both polarizations. The measurement results and the theory are in good agreement as long as the VCSEL is transversal single-mode     

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…     

Jitter Accumulation for Periodic Pattern Signals

It is important to accurately evaluate and reduce jitter accumulation in long-haul digital repeatered lines. Jitter accumulation caused by random pattern signals has already been analyzed. However, periodic pattern signals such as pseudorandom signals are usually used to measure jitter accumulation. This paper describes the difference between the jitter accumulation for both signals and the necessary conditions to accurately estimate jitter accumulation for random pattern signals by using periodic pattern signals. First, it is shown theoretically that systematic jitter for periodic signals saturates, showing a ripple pattern. The limit of increase is determined by the ratio of tank bandwidth and pattern repetition frequency. Up to a certain number of regenerators determined by the ratio, systematic jitter increases in rough proportion to thesqrt{N}slope. It is also shown that the equation to estimate random pattern jitter accumulation is determined by the measured value for periodic pattern signals. Second, jitter characteristics are simulated by optical signal circulating experiments. The results are in agreement with the analysis. In addition, the reduction effects on periodic signal jitter accumulation caused by timing signal delay and nonlinearity of the limiter in the timing circuit are shown.     

有光反馈的半导体激光器大信号SPICE电路模型

为了使半导体激光器的电路级模拟更容易,本文建立了一个有光反馈的半导体激光器大信号SP CE模型,并对激光器的开启延时、张驰振荡和稳定时的光功率与光纤到激光器发光端面的距离及反射光功率大小间的关系进行了研究.     

Jitter optimization based on phase-locked loop design parameters

This paper investigates the effects of varying phaselocked loop (PLL) design parameters on timing jitter. The noise due to voltage-controlled oscillator (WO), input clock and buffering clock are considered. First, a closed-form equations are derived that relate PLL output clock jitter to parameters of a second-order PLL, i.e., damping factor and bandwidth. Then the second-order analysis is extended to a third-order PLL with inherent feedback/sampling delay. The sensitivity study clearly illustrates how to select design parameters to obtain minimum output jitter. To verify the analysis experimentally, a digitally tunable PLL architecture is designed and fabricated that allows independent adjustment of loop parameters. The design not only demonstrates the agreement between analysis and theory, but also shows an architecture that minimizes jitter.     

基于FPGA的EoS系统中帧处理的改进与实现

根据ITU-TX.86协议的规定,设计了一种EoS系统,实现了IP数据包在基于SDH的骨干光传输网络中的高速传输。针对现有帧处理方案在帧同步时延和时钟抖动方面存在的问题,提出了改进的快速帧同步机制和时钟提取方案。采用廉价的FPGA硬件编程实现,通过电路综合与时序仿真表明,方案在缩短帧同步时延和消除时钟抖动方面具有较好的效果。     

160-gb/s optical clock recovery using a regeneratively mode-locked laser diode

Line rate optical clock recovery at 160-Gb/s has been demonstrated based on injection-locking and optical time-division multiplexing of a 40-GHz regeneratively mode-locked laser diode (RML-LD). Injection-locking is achieved by directly coupling the 160-Gb/s data streams to a photodetector in the RML-LD feedback loop. The pulsewidth and root-mean-square timing jitter of the recovered clocks are 2.31 ps and 225 fs (10 Hz-40 MHz), respectively.     

Differentail Board/Backplane Optical Interconnects for High-Speed Digital Systems Part II: Simulation Results

For pt.I see ibid., vol.11, no.7, p.1234-49 (1993). The performance of a DC-coupled fully-differential interconnect is analyzed in terms of the deterministic vertical and horizontal eye closure at Gb/s for different optical power levels and extinction ratios in the two complementary arms. Two types of transmitters are investigated, one based on an ideal optical modulator switch (IOMS) and the other based on conventional modulation of two separate lasers. In general, it is found that the timing jitter increases when the imbalance between the power levels in the two arms increases, when the difference between the laser turn-on delay in the two arms increases, and when the receiver and transmitter bandwidth is reduced. To achieve low latency and to accept a maximum power imbalance of 4-5 dB at the receiver, the IOMS and the lasers should be modulated to produce an extinction ratio of at least 10 dB, and the lasers should be biased above threshold. If low latency is not the main concern, an improvement in the maximum tolerable imbalance can be obtained with regular laser modulation by biasing the lasers below threshold. The fitter can be reduced and the maximum tolerable imbalance be increased if faster receivers and transmitters are employed     

Detailed Theoretical and Experimental Characterization of 10 Gb/s Clock Recovery Using a Q-Switched Self-Pulsating Laser

A detailed characterization of the clock recovery properties of a self-pulsating, three-section distributed feedback laser is presented by directly comparing simulation and experimental results for the dependence of the RMS timing jitter of the recovered clock signal on important properties of the input signal. These properties include the duty cycle, peak power, extinction ratio, state-of-polarization, optical signal-to-noise ratio (OSNR), and waveform distortion due to residual group velocity dispersion and polarization mode dispersion. The permissible range for each of these is identified in terms of the RMS timing jitter of the recovered clock signal being less than 2 ps. In particular, the self-pulsating laser is effective for input signals degraded by amplified spontaneous emission noise as it provides this level of jitter performance for input OSNRs larger than 8.8 dB (0.1 nm noise bandwidth).