Effect of carrier lifetime on mode partition noise in multimodesemiconductor lasers

The dependence of mode partition noise (MPN), and its association with the eye diagram and power penalty, on carrier lifetime in 1.3 μm InGaAsP multimode semiconductor lasers for a 1.2 Gbit/s lightwave transmission system was investigated. It was found that lasers with shorter carrier lifetimes showed less MPN, and hence, a better eye opening and a lower power penalty, than the lasers with longer carrier lifetimes. The significant dependence of MPN, eye opening, and power penalty on carrier lifetime in multimode semiconductor lasers suggests that the carrier lifetime of the laser, which depends on the laser design, can be used as an important parameter for characterizing the performance of high-speed lightwave transmission systems     

Reduced spontaneous carrier lifetime in narrow stripe geometry GaAlAs DH lasers

We examined the dependence of spontaneous carrier lifetime on the stripe width in internally striped-planar GaAlAs DH lasers by measuring the turn-on delay time of lasing emission under step current injection. The measured carrier lifetime reduces in narrow stripe lasers. Reasonable interpretation of the results can be given by the increased carrier density at threshold which results from the increasing waveguide loss and the carrier loss by out-diffusion in narrow stripe lasers. There is also given another explicit explanation on the reduced carrier lifetime by using the rate equation.     

Compressively strained 1.3 μm InAsP/InP and GaInAsP/InP multiplequantum well lasers for high-speed parallel data transmission systems

Turn-on delay times in the pulse response of compressively strained InAsP/InP double-quantum-well (DOW) lasers and GaInAsP/InP multiple-quantum-well (MQW) lasers emitting at 1.3 μm were investigated. DQW lasers with 200-μm cavity length and high-reflection coating achieved both a very low threshold current (1.8 mA) and a small turn-on delay time (200 ps), even under a biasless 30-mA pulse current. Compressively strained or lattice-matched GaInAsP MQW lasers and GaInAsP double-heterostructure (DH) lasers were also fabricated and compared. It was observed that the carrier lifetime was enhanced for InAsP DQW lasers and strained GaInAsP MQW lasers compared to the lattice-matched GaInAsP MQW lasers and conventional double-heterostructure lasers. To explain this increase in the carrier lifetime, the effect of the carrier transport on the carrier lifetime was studied. The additional power penalty due to the laser turn-on delay was simulated and is discussed     

The phase shift of the light output in sinusoidally modulated semiconductor lasers

The dependence of the phase shift of the light output from sinusoidally modulated semiconductor lasers was investigated as a function of the modulation current. This measurement is effective in accurately determining the short damping time constant associated with the relaxation oscillation. The frequency half width of this phase shiftDelta fwas found to be inversely proportional to the damping time constant. For narrow stripe lasers, the phase shift occurs more gradually, which corresponds to the fact that the narrow stripe lasers have shorter damping time constants. To analyze the narrow stripe effect, the recently developed time-dependent self-consistent theory was applied, considering the transverse distribution of both optical field and carrier density and including the carrier diffusion term. This theory can explain the shorter damping time constant for narrow stripe lasers compared with broader stripe lasers.     

Effects of zinc doping in DFB lasers emitting at 1.3 and 1.55 mu m

Reports on the performance of GaInAsP/InP DFB lasers with Zn-doped active region. At both 1.3 and 1.55 mu m the authors achieved a large bandwidth owing to the increased differential gain. The carrier lifetime of the lasers decreased with doping level. The decreased carrier lifetime had the effect of reducing the pattern effect, and they could obtain a clear eye opening with 4 Gbit/s NRZ modulation.<>     

低反光纤光栅对光纤激光器光谱展宽影响研究

光纤激光器中的自相位调制(SPM)以及低功率下的空间烧孔效应(SHB)会导致输出光谱展宽。分析了SPM、SHB导致光谱展宽的理论模型,讨论了低反光纤光栅(OC)的带宽与反射率对激光器输出光谱展宽的影响。实验研究了不同输出功率下激光器输出光谱随OC带宽及反射率的变化关系。结果表明减小OC带宽能够有效减缓SPM、SHB导致的输出光谱展宽;减小OC反射率能降低SPM导致的输出光谱展宽速度,却促进了SHB导致的光谱展宽;但相同改变量的情况下,OC带宽所带来的影响较反射率更为显著。实验结果与理论分析一致,对光谱合束及窄线宽高功率光纤激光器的设计与应用具有重要意义。     

微波激励PIN二极管的时频响应研究

利用一种PIN二极管子电路模型,分析微波激励下的I区电导调制机理,通过ADS软件瞬态、谐波仿真,研究Ⅰ层厚度w和少数载流子寿命τ对PIN二极管时频响应的影响。结果表明,对于同一微波激励,w越大,尖峰泄漏功率越大,导通时隔离度越小;τ越大,尖峰泄漏脉宽越小,导通时隔离度越大。仿真结果与理论分析相符。     

Regime where zero-bias is the low-power solution for digitally modulated laser diodes

We demonstrate that when a laser diode is digitally modulated with zero-bias, the average electrical power consumption can be less than a threshold-biased scheme for the same bit error rate. We find that the power consumption of large threshold >10 mA lasers with zero-bias is comparable to or less than with threshold-bias modulation as long as B/spl tau/<1/ln(2), where B and /spl tau/ are the bit rate and the laser's carrier lifetime, respectively. Experiments with a buried crescent laser diode confirm this claim at both 300 K and 77 K. The power penalty of zero-bias at higher bit rates is also discussed.     

Effect of external optical feedback on spectral properties of external cavity semiconductor lasers

The effects of external optical feedback on the spectral properties of single-mode external cavity semiconductor lasers that use a graded-index (GRIN) lens in the optical cavity have been investigated. Mode rejection ratio and intensity drop-out rate of the dominant mode as a function of optical strength have been measured. These measurements show that a laser with a short (160 ?m) GRIN-lens external cavity can tolerate optical feedback as large as ?20 dB without significant penalty. This minimum optical feedback can be larger when lasers with shorter cavity length are used.     

激光雷达用高性能光纤激光器

系统研究了窄线宽低噪声单频连续光纤激光器、高能量纳秒长脉冲单频光纤激光器以及高峰值功率纳秒短脉冲光纤激光器三类高性能光纤激光器:实现了工作于1、1.5及2 m波段的单频连续光纤激光器,典型光谱线宽小于3 kHz,强度噪声接近于散粒噪声极限;实现了高能量单频光纤激光器,脉冲能量超过200 J,重复频率20 kHz,脉冲宽度100~500 ns,激光波长位于1.5 m波段;实现了高峰值功率纳秒短脉冲光纤激光器,峰值功率超过700 kW,重复频率10 kHz,脉冲宽度3 ns;同时还实现了高重频高峰值功率纳秒短脉冲光纤激光器,峰值功率超过200 W,重复频率3 MHz,脉冲宽度1~5 ns。文中阐述了以上几类高性能光纤激光器在激光雷达探测系统中的应用前景。     

High power GaInP/AlGaInP visible lasers (/spl lambda/=646 nm) with narrow circular shaped far-field pattern

GaInP/AlGaInP visible lasers based on a longitudinal photonic bandgap crystal waveguide emitting at 646 nm show narrow circular shaped far field pattern. Vertical and lateral beam divergence of about 8/spl deg/ (full width at half maximum) that is independent of injection current is demonstrated. Differential quantum efficiency is up to 85%. Pulsed total optical output power is as high as 20 W for 100 /spl mu/m-wide stripe lasers and 6 W for 20 /spl mu/m-wide stripe lasers. Such values of output optical power are 2.5 higher with respect to ones obtained for the lasers fabricated from the state-of-the-art epiwafers for commercial 650 nm range DVD lasers.     

Analysis of Er-doped fiber laser stability by suppressing relaxation oscillation

For Er-doped fiber lasers, we show that the fluctuation of lasing power caused by resonant pump-power perturbations is inversely proportional to the lifetime of photon in the laser cavity. Analysis shows that Er-doped fibers with high-gain coefficient are favorable for fiber lasers in the view of point of suppressing the lasing-power instability caused by the resonant pump perturbation. The results obtained are especially useful for single-frequency Er-doped fiber lasers which have a very short cavity length, i.e., a short lifetime of photon in the cavity.     

Finite time of carrier energy relaxation as a cause of optical-power limitation in semiconductor lasers

It is shown that the reason why the maximum attainable optical power in semiconductor lasers is limited is the finite time of carrier energy relaxation via scattering by nonequilibrium optical phonons in the quantum-well active region. The power and spectral characteristics of semiconductor lasers are studied experimentally at high excitation levels (up to 100 kA/cm²) in pulsed lasing mode (100 ns, 10 kHz). As the drive current increases, the maximum intensity of stimulated emission tends to a constant value (“saturates”), and the emitted power increases owing to extension of the spectrum to shorter wavelengths. The intensity saturation is due to limitation of the rate of stimulated recombination, caused by a finite time of the electron energy relaxation via scattering by polar optical phonons. It is found that the broadening of the stimulated emission spectrum is related to an increase in carrier concentration in the active region, which enhances the escape of electrons into the waveguide layers. As the drive current increases, the carrier concentration in the waveguide reaches its threshold value and there appears an effective channel of current leakage from the active region. The experiment shows that the appearance of a band of waveguide lasing correlates with a sharp drop in the differential quantum efficiency of a semiconductor laser.     

Nonlinear gain coefficients in semiconductor lasers: effects ofcarrier heating

Nonlinear gain coefficients due to the effects of carrier heating are derived from the rate equations of carrier energy transfer in semiconductor lasers. We find that, in the modulation responses of semiconductor lasers, stimulated recombination heating will affect the resonant frequency and damping rate in a same form as the effects of spectral hole burning, while free carrier absorption heating will only affect the damping rate. The effects of injection heating and nonstimulated recombination heating are also discussed. The carrier energy relaxation time is calculated from first principles by considering the interactions between carriers and polar optical phonons, deformation potential optical phonons, deformation potential acoustic phonons, piezoelectric acoustic phonons. At the same time, the hot phonon effects associated with the optical phonons are evaluated because their negligible group velocity and finite decay time. We show that the carrier-polar longitudinal optical phonon interaction is the major channel of carrier energy relaxation processes for both electron and holes. We also point out the importance of the longitudinal optical phonon lifetime in evaluating the carrier energy relaxation time. Neglecting the finite decay time of longitudinal optical phonons will significantly underestimate the carrier energy relaxation time, this not only contradicts the experimental results but also severely underestimates the nonlinear gain coefficients due to carrier heating. The effects of spectral hole burning, stimulated recombination heating, and free carrier absorption heating on limiting the modulation bandwidth in semiconductor lasers are also discussed     

Performance degradations of multigigabit-per-second NRZ/RZlightwave systems due to gain saturation in traveling-wave semiconductoroptical amplifiers

A nonlinear model for a travelling-wave semiconductor optical amplifier has been used to determine eye closure degradations for 2.4 and 10 Gb/s NRZ/RZ lightwave systems due to gain saturation effects in the optical amplifier. At 10 Gb/s, with a carrier lifetime of 300 ps, the results indicate that the penalty is less than 1 dB for both NRZ and RZ systems provided that the ratio of the input power (P_in ) to the saturation output power (P_sat) is less than -17 dB. The NRZ system penalty is slightly larger than the RZ penalty when P_in/P_sat is larger than -17 dB. For example, with P_in/P_sat=-10 dB, the NRZ system penalty is about 2.8 dB versus 2 dB for the RZ system. The system penalty at 2.4 Gb/s is slightly less than that at 10 Gb/s. At P _in/P_sat=-10 dB, the NRZ system penalty is about 2.5 dB versus 1.5 dB for RZ     

基于氧化石墨烯被动锁模的窄线宽皮秒脉冲掺铒光纤激光器

报道了用氧化石墨烯作为可饱和吸收体的全光纤结构皮秒脉冲掺铒光纤激光器。该激光器的线形谐振腔由窄带的光纤布拉格光栅和氧化石墨烯可饱和吸收镜构成。当抽运功率为22mW时,实现了稳定的重复频率为5.82MHz的锁模激光脉冲输出,脉宽为87ps,光谱中心波长为1549.3nm,3dB谱宽为0.06nm,信噪比为66dB。     

Short-wavelength current tuning of InAsSb/InAsSbP heterostructure lasers caused by an injection nonuniformity

A reduction in the emission wavelength in the preferred mode of InAsSbP/InAsSb/InAsSbP heterostructure lasers by 50Å is observed when the current is raised from 1.8 to 5 times the threshold with dc and pulsed power. A comparison of the spectral and spatial distributions of the output as functions of current shows that this short-wavelength tuning is caused by a change in the distribution of the nonequilibrium charge carrier concentration over the strip width as the current is varied. This effect is modeled mathematically, taking into account the increase in the injection density and the drop in the output intensity from the middle to the sides of the waveguide. The results of the model calculation are in good agreement with experiment.     

Comparison of simulation and measurement of dynamic fiber-coupling effects for high-speed multimode VCSELs

Static and dynamic measurements are performed with GaAs oxide-confined vertical-cavity surface-emitting lasers (VCSELs), using multimode fibers with a core diameter of 50 and 62.5 /spl mu/m and different numerical apertures (NAs). They show that a small NA can have a severe impact on the eye opening and thus also on the bit-error rate. The measurements are analyzed with a spatiotemporal two-dimensional (2-D) multimode VCSEL model. The required parameter extraction for the model is verified with small- and large-signal measurements. The analysis shows that the change of the eye opening can be explained by the interaction between the mode- and the current-injection profile, carrier diffusion, and intermodal gain compression (IGC). IGC increases differences in the modal power distribution caused by the interaction between the mode profiles and the current-injection profile. Carrier diffusion is able to compensate these increased differences of the modal power distribution. Its impact, however, on dynamic changes caused by IGC is moderate.     

光纤激光器光谱合束技术综述

对实现高功率、高光束质量输出的光纤激光器光谱合束技术进行了综述。针对体布拉格光栅合束和多层介质膜光栅合束两种技术方案进行介绍,从合束原理、高功率窄线宽光纤激光器单元、光栅器件以及合束方案等方面进行分析。同时,针对近年来国内外在光纤激光光谱合束技术领域的发展也进行了归纳性的介绍。     

Effects of hot phonons on carrier heating in quantum-well lasers

The hot phonon effects on carrier heating in quantum-well lasers are theoretically investigated. We show that the neglect of the finite lifetime of LO phonons will significantly underestimate the carrier energy relaxation time and thus underestimate the effect of carrier heating in quantum-wed lasers. We investigate the effects of carrier heating with hot phonons on the saturation and degradation of the resonant frequency in high-speed quantum-well lasers. The implications of the hot phonon effects on the design of high-speed quantum-well lasers are also discussed