Measurement of gain spectrum for semiconductor lasers utilizing integrations of product of emission spectrum and a phase function over one mode interval

A technique based on the integration of the product of amplified spontaneous emission spectrum and a phase function over one mode interval is proposed for measuring the gain spectrum for Fabry-Perot semiconductor lasers, and a gain correction factor related to the response function of the optical spectrum analyzer (OSA) is obtained for improving the accuracy of the measured spectrum. Gain spectra with a difference less than 1.3 cm/sup -1/ from 1500 to 1600 nm are obtained for a 250-/spl mu/m-long semiconductor laser at an OSA resolution of 0.06, 0.1, 0.2, and 0.5 nm. The corresponding gain correction factor is about 9 cm/sup -1/ at a resolution of 0.5 nm. The gain spectrum measured at a resolution of 0.5 nm has the same accuracy as that obtained by the Hakki-Paoli method at a resolution of 0.06 nm for a laser with a mode interval of 1.3 nm.     

基于热电制冷器温控系统数学建模和参量辨识

为了实现对半导体激光器温度的高精度控制,利用热电制冷器、温度传感器与相应的散热装置,设计了一套半导体激光器温度控制的实验系统.首先采用热力学分析方法,对实验系统进行了理论分析,建立了该温控实验系统数学模型与相应的传递函数;其次,在取得了半导体激光器温度数据的条件下,根据模型参量的特点,提出了一种结合阶跃响应的实验曲线,应用非线性曲线最小二乘拟合进行模型参量的辨识;最后利用该模型参量进行了系统仿真和实验验证.结果表明,仿真曲线、拟合曲线与实验曲线结果一致,拟合的模型参量具有较高的预测精度.这些结果对优化调整温度控制实验是有帮助的.     

一种半导体激光自混合效应模型参数的测量方法

从半导体激光自混合干涉系统的一般模型公式出发,建立了一个非线性函数模型,利用非线性最小二乘法的曲线拟合,来估计半导体激光自混合效应的模型参数——线宽展宽因数和光反馈因数。经计算仿真分析表明,该算法有较好的收敛性,迭代次数少且参数估计精度高,是半导体激光自混合效应参数测量的一种有效方法。     

三段式F-P半导体激光器的光谱特性分析

通过微加工法可以在FP半导体激光器中引入具有反射功能的缺欠点或面来改进激光器的光谱特性。利用射线法,推导了含有两个缺欠点的微加工获得的FP半导体激光器的输出谱表达式,并根据平均载流子密度近似(MCA)计算出名义阈值载流子密度Nth与实际载流子密度N之差ΔN,从而对模式抑制比(MSR)可作计算分析。     

基于谱估计的Fabry-Perot标准具透过率曲线参数估计方法

直接探测多普勒测风激光雷达系统大多采用基于Fabry-Perot（F-P）标准具的条纹技术和边缘技术测量多普勒频移。但激光器频率漂移会使得透过率曲线的估计出现一定误差,为了抑制其影响,提出了一种基于谱估计的F-P标准具透过率曲线参数估计方法。首先将标准具全量程扫描结果进行重构得到观测矩阵。之后使用MUSIC算法得到透过率曲线的伪谱。对伪谱进行谱峰搜索后,将得到的谱峰位置进行线性拟合得到自由谱间距。然后将上步的拟合结果代入透过率函数,利用非线性最小二乘法对其他参数进行估计。在仿真分析的基础上,采用真实测量数据进行了实验验证。结果表明所提出的方法在扫描步点间隔达到50、信噪比大于10 dB的情况下,估计差小于1%。该算法扫描时间短,估计误差小,具有实际应用价值。     

Broadening mechanism in semiconductor (GaAs) lasers: Limitations to single mode power emission

A nonlinear steady-state theory of the emission spectrum of semiconductor (GaAs) lasers above threshold is developed, and limitation to power in a single longitudinal mode is studied. The nonlinear steady-state rate equations describing the power and the gain are solved iteratively. The model is based on the well known idea that the gain always saturates somewhere below the loss, and power sharing among the modes is dependent on the relative gain of the modes with respect to the loss level. The limitation to single mode power is essentially due to the uneven rate of saturation of the gain of the different modes as they approach the loss level asymptotically, with the dominant mode having the fastest saturation. The rate of saturation of the gain of different modes depends on the power emission spectrum and the intraband relaxation rate of the carriers. In this work, the relaxation is accounted for by using the generalized spectral weight function to describe the carriers. The dependence of maximum single mode power on intraband relaxation time is obtained. It ranges from a few milliwatts for relaxation time of the order of 10^-12s to hundreds of milliwatts for relaxation time of 10^-13s. The predictions of the model on gain saturation spectra, and carrier lifetime spectra agree well with experimental observations. The gain is seen to saturate near the lasing energy but continues to increase at a reduced rate at higher energy levels. The carrier radiative lifetime is found to decrease sharply in the vicinity of the lasing mode energies.     

基于F-P腔的干涉/强度调制型光纤温度传感器

介绍了一种基于非本征F P腔的干涉/强度调制型光纤温度传感器。宽谱光源发光二极管(LED)发出的光经过2×2耦合器C1 传给F P传感头,传感头返回光信号再次经过耦合器C1 及C2 后分成两路,一路直接传给光电探测器D1,另一路经过窄带滤光片再传给D2,光信号经光电转换及放大后由计算机采集处理。给出了采用不同谱宽的两路光信号进行自补偿运算和温度测量的理论模型,并简单分析了影响这一温度传感器长期稳定性的原因。实验中利用Levenberg Marquardt非线性拟合得到与理论模型符合很好的温度定标曲线。该传感器在 20~200℃量程内,温度变化最小分辨率达到0 .1℃,长期测量精度达到±0. 2℃。     

Distributed feedback InGaAsP/InP lasers with window region emitting at 1.5 µm range

Distributed feedback (DFB) InGaAsP/InP lasers with a window region formed at an end of the corrugated DFB region were made in order to overcome the problems inherent in the previous structures of DFB lasers with cleaved, sawed, etched, or AR-coated facets, or with an unexcited corrugation region. The window structure DFB lasers showed linear current versus output (I-L) curves, in contrast to those with a hysteresis or a kink appearing in a DFB laser with an unexcited region. Suppression of Fabry-Perot (F-P) resonances due to the two facets were sufficient enough to keep a single longitudinal mode property by DFB up to high excitation level. CW operation up to 65°C was achieved at the 1.5 μm wavelength range. Axial modes concerning the corrugated resonator were measured at about the threshold current. A stop band of a DFB laser was clearly observed with two dominant modes and much smaller submodes, which almost agreed with the axial modes predicted from a basic DFB theory.     

Theoretical design for 120 GHz semiconductor junction circulators: effects of different numbers of terms in the Green's function

A theoretical analysis of the predicted performance and field distributions for semiconductor junction circulators is based on Bosma's Green's function approach which involves a summation of infinite series in the mathematical derivation. The effects are considered of taking a different number of terms in the series, looking at three different circulators centred at 120 GHz. The narrowband semiconductor circulators show a similar effect to the ferrite junction circulator because the field distributions inside the semiconductor discs can be approximated by only considering the dominant modes. However, there is no dominant mode in the broadband circulator and the higher order modes play an important role in the operation of this circulator. In order to obtain a precise representation of the circulation effects inside both narrowband and broadband circulators, at least up to the 6th term, or 18 terms in all, are required to be added in the summation of Green's functions.     

注入锁定法布里-珀罗激光器的单模工作特性

使用分布式反馈(DFB)激光器对法布里-珀罗(F-P)激光器进行单模注入锁定.通过改变F-P激光器的偏置电流,DFB激光器的输出功率以及两激光器间的波长失谐量,对注入锁定F-P激光器的光谱特性、功率特性以及频率响应特性进行实验分析.找出影响注入锁定F-P激光器稳定性的因素,并测量注入锁定F-P激光器的稳定锁定区;通过优化注人条件实现F-P激光器的高边模抑制比(SMSR)输出,最高可达55 dB;通过与自由运转F-P激光器比较,发现注入锁定可以明显抑制半导体激光器在高频调制下光谱的展宽.注入锁定后F-P激光器的3 dB调制带宽接近14 GHz.实验结果表明,通过合理设计光注入条件,注入锁定技术可以明显改善F-P激光器的光谱特性以及高频响应特性,并在高速光纤通信领域中得到广泛应用.     

1.25-Gb/s Operation at 50-GHz Channel Spacing Based on Intensity Noise Suppression of Wavelength-Locked Fabry–PÉrot Laser Diode

We demonstrate 1.25-Gb/s operation at 50-GHz channel spacing and 10-km single-mode fiber, which is based on a wavelength-locked Fabry-Perot laser diode (F-P LD) and an intensity noise suppression by a gain saturation of F-P LD in front of the receiver. The wavelength-locked F-P LD employs the spectrum-sliced incoherent light with narrow bandwidth of 35 GHz. The intensity noise of wavelength-locked F-P LD is suppressed about 6 dB by the F-P LD in the front of the receiver. As a result, the bit-error-rate curves exhibit the error-free performances over the detuning conditions to cover a whole mode spacing period of F-P LD.     

注入锁定半导体激光器全光波长转换技术

波长转换器是光通信网络中的一个重要器件。而除半导体光放大器（SOA）外，半导体激光器也是进行波长变换的一种很好选择。基于半导体激光器的注入锁定波长变换技术具有转换带宽较大、啁啾小、消光比特性好、结构简单、成本低廉等诸多优点。将探测光与信号光同步注入法布里-珀罗（F-P）半导体激光器，可以通过信号光功率的变化控制激光器锁模与失锁，导致腔内纵模变化，探测光随之被共振放大或减弱，从而将信息由信号光转换到探测光频率上。从静态实验入手，对半导体激光器的注入锁定现象及光信号控制法布里-珀罗纵模移动等问题分别进行了研究。分析了动态转换激光器工作点的选取问题，在动态实验中实现了较宽范围的正相与反相波长转换，转换速率达到了10Gb／s。     

Linear-time prediction mode reduction method for intracoding in H.264/AVC

We present a linear-time elimination method to adaptively reduce the nine intraprediction modes in H.264/AVC to two, three, five, or nine modes while preserving a satisfactory reconstructed video quality. Resemblance between prediction modes and appearing frequency for each prediction mode are first determined in an off-line way from the training video sequences. Prediction modes are modeled as vertices and resemblance between two prediction modes as the weight of the connecting edge in a complete graph. Then, find the Hamilton cycle with the minimum sum of weights. When encoding each intrablock, prediction modes corresponding to the adjacent vertices along the Hamilton cycle are examined for similarity. The prediction mode which appears less frequently in a pair of similar prediction modes is declared as redundant and eliminated. When compared with Laroche et al.’s method which aims to reduce the bitrate, experimental results demonstrate that the proposed elimination method can substantially reduce the execution time while preserving the peak signal-to-noise ratio and bitrate performance.     

高精度测量F-P标准具间距的光谱方法

利用高分辨率光谱分析仪对空气隙F P标准具透射谐振峰频率进行测量 ,然后通过直线拟合获得自由谱域 ,从而计算得出F P标准具的间距。对F P标准具间距测量的精度进行分析 ,F P标准具间距测量的相对误差为2× 10 -3 。提出了一种新颖的入射光与F P标准具垂直的精确调节方法     

抑制Nd:YAG激光器自锁模的实验研究

用于抽运钛宝石的电光调Q Nd:YAG激光器会出现自锁模调制,导致峰值功率不稳从而损伤钛宝石晶体,为了抑制这种自锁模调制,分析了产生该现象的原因,研究了谐振腔内插入法布里-珀罗(F-P)标准具的技术方案。实验采用单个厚度20mm,膜层反射率60%的标准具,有效抑制了该Nd:YAG激光器的自锁模调制,实现了脉宽约70ns,脉冲能量约600mJ的1064nm激光的稳定输出,既避免了引入较大的插入损耗,又防止了对F-P标准具膜层的损伤。分析认为单个厚度合适、膜层反射率不太高的标准具可有效抑制Nd:YAG激光器自锁模现象的原因在于:标准具一个透射峰半峰全宽(FWHM)内理论上虽有约5个纵模,但偏离透射峰中心的纵模损耗较大,使得单个透射峰内实际起振的纵模可能只有1个;激光器的增益线宽内虽存在标准具的多个透射峰,但起振纵模因不相邻避免了形成相位锁定。     

Nonlinear Influence of T-Channels in an in silico Relay Neuron

Thalamic relay cells express distinctive response modes based on the state of a low-threshold calcium channel (T-channel). When the channel is fully active (burst mode), the cell responds to inputs with a high-frequency burst of spikes; with the channel inactive ( tonic mode), the cell responds at a rate proportional to the input. Due to the T-channel's dynamics, we expect the cell's response to become more nonlinear as the channel becomes more active. To test this hypothesis, we study the response of an in silico relay cell to Poisson spike trains. We first validate our model cell by comparing its responses with in vitro responses. To characterize the model cell's nonlinearity, we calculate Poisson kernels, an approach akin to white noise analysis but using the randomness of Poisson input spikes instead of Gaussian white noise. We find that a relay cell with active T-channels requires at least a third-order system to achieve a characterization as good as a second-order system for a relay cell without T-channels.      

Characteristic analysis of a novel F-P interferometer based on a pair of FBGs with built-in LPFGs

The transmission characteristics of a Fabry-Pérot (F-P) interferometer based on a fiber Bragg grating (FBG) pair with a built-in long-period fiber grating (LPFG) are theoretically analyzed, and the shift of transmission interference fringe as a function of environmental refractive index is acquired. The influence of the lengths of F-P cavity, LPFG and FBG on the transmission characteristics of the proposed interferometer has been numerically investigated, and the simulation results indicate that the sensitivity of refractive index reaches 2.27 × 10-6 for an optical spectrum analyzer (OSA) with a resolution of 1 pm.     

光纤弯曲对掺镱光纤激光器光束质量的影响

通过改变F-P腔全光纤激光器中的光纤盘绕半径,对输出激光光束质量进行了研究.搭建了百瓦级全光纤激光器.最大泵浦功率为436 W的条件下,获得了300 W波长1 080 nm的激光输出.光束质量M2=1.13.光-光转换效率为69%.理论分析并计算了20/400 m大模场面积双包层光纤中的两种导波模式LP01模和LP11模沿光纤径向的功率分布和弯曲损耗;利用光纤弯曲选模方法,实验上探究了光纤弯曲半径对输出激光模式及光束质量的影响.实验发现,通过光纤弯曲方式可以有效地消除高阶模式,再经过包层光剥除可以获得更好的光束质量M2=1.06.     

Second-harmonic generation efficiency in periodically poled LiNbO3 waveguides

Quasi-phase-matched second-harmonic generation efficiency in periodically poled LiNbO₃ using titanium indiffusion, has been theoretically investigated. This permits clarifying how the involved guided modes convert the triangle-shaped form of the ferroelectric polarization in the crystal, via the overlap integral between this form and these modes, into an effective periodic nonlinear coefficient. As a consequence, the periodic function that really permits the quasi-phase-matching operation is the modulation of this effective nonlinear coefficient, the shape of which can be far from a triangular shape, as shown using different cases of mode profiles