Behaviour of minimum excess-noise figure and maximum transducer gain in a linear 2 port

In order to minimise the excess-noise figure (excess-noise figure = noise figure ? 1) of a linear 2 port, the source conductance gs must have an optimum value of gso. It is shown that this value of gso does not necessarily correspond to the condition for maximum transducer gain. Considering the excess-noise figure and transducer gain, a compromise value of gs is found for the minimum noise measure.     

Low-frequency noise behavior of Si NMOSTs stressed at 4.2 K

The low-frequency (LF) noise behavior of Si NMOSTs stressed at 4.2 K is investigated and compared with the stress-induced changes in the DC parameters. In linear operation, a reduction of the noise spectral density is observed, which can be explained by considering the reduction in the device transconductance. The excess noise, typically observed in the kink region, is reduced after stress, as is the noise hysteresis. This behaviour can be understood by substituting the changes in the substrate current characteristic in the excess-noise model derived     

Q dependence of IMPATT-diode f.m. noise

Measurement of IMPATT-diode-oscillator f.m. noise, for external Q factors ranging between 100 and 10 000, showed that the product of r.m.s. frequency deviation and square root of power output is inversely proportional to the Q factor, in accordance with the Edson formula for f.m. oscillator noise. The excess-noise temperature, varying between 30 and 50dB, rapidly increases with current through the diode. The correlation for f.m. and a.m. noise lies between 0.8 and 1.     

Computer model of a superluminescent LED with lateral confinement

We present a computer simulation of a strip-geometry superluminescent light emitting diode (SLD). One end of the strip waveguide has a finite reflectivity while the reflectivity vanishes at the other end because it is assumed that the strip waveguide terminates in a high-loss region. The gain of the structure is computed from the drive current and several intrinsic device parameters; gain saturation is taken into account. We discuss the dependence of the light power coupled into a fiber from an InGaAsP SLD at 1.3 μm as a function of the driving current, the reflectivity of one end of the strip waveguide, its numerical aperture (NA), and its length and width. A considerable improvement in power coupling efficiency can be realized when the waveguide NA equals the fiber NA or, in the absence of lateral confinement, when the fiber NA is much larger than the half-width to length ratio (times the refractive index) of the strip waveguide. Previous analyses have ignored lateral waveguiding effects.     

Gain-bandwidth product optimization of heterostructure avalanche photodiodes

A generalized history-dependent recurrence theory for the time-response analysis is derived for avalanche photodiodes with multilayer, heterojunction multiplication regions. The heterojunction multiplication region considered consists of two layers: a high-bandgap Al/sub 0.6/Ga/sub 0.4/As energy-buildup layer, which serves to heat up the primary electrons, and a GaAs layer, which serves as the primary avalanching layer. The model is used to optimize the gain-bandwidth product (GBP) by appropriate selection of the width of the energy-buildup layer for a given width of the avalanching layer. The enhanced GBP is a direct consequence of the heating of primary electrons in the energy-buildup layer, which results in a reduced first dead space for the carriers that are injected into the avalanche-active GaAs layer. This effect is akin to the initial-energy effect previously shown to enhance the excess-noise factor characteristics in thin avalanche photodiodes (APDs). Calculations show that the GBP optimization is insensitive to the operational gain and the optimized APD also minimizes the excess-noise factor.     

Double junction AlInAs/GaInAs multiquantum well avalanche photodiodes

A separate absorption, grading, and multiplication avalanche photodiode with an AlInAs/GaInAs multiquantum well multiplication region is reported. This device exhibits a low excess-noise factor and a gain-bandwidth product of 50 GHz, due to the high ratio of ionisation rates of the multiplication material. In addition, a large bandwidth is obtained owing to the use of an undoped (n type) GaInAs absorption layer, fully depleted when multiplication occurs.<>     

掺Yb3+双包层光纤激光器的自脉冲行为分析

为了对掺Yb3+双包层光纤激光器的自脉冲行为进行系统的理论研究,采用数值模拟方法,对光子数密度和反转粒子数密度随时间及抽运功率的变化、阻尼系数与后腔镜的反射率和掺杂粒子浓度的关系,以及光纤本身固有振荡频率随后腔镜反射率的变化进行了理论分析.结果表明,随抽运功率的增加,振荡频率增加,振幅度减小;降低输出端的反馈和粒子的浓度可以抑制自脉冲现象.另外提出了抑制光纤激光器自脉冲的措施,为设计掺Yb3+双包层光纤激光器提供了理论依据.     

Excess-noise and receiver sensitivity measurements of In0.53Ga0.47As/InP avalanche photodiodes

We report the results of excess-noise and normalised receiver sensitivity measurements for In0.53Ga0.47As/InP avalanche photodiodes for use in the ?=0.95 ?m to 1.65 ?m spectral region. The excess-noise measurements are consistent with a hole-to-electron ionisation rate ratio in InP of ~ 0.4. The receiver sensitivity, measured at 45 Mbit/s and 10?9 bit-error-rate, was ?53.2 dBm at a gain of 20 assuming unity quantum efficiency for the detector. This sensitivity is the highest reported at ?=1.3 ?m and represents an improvement over a PIN detector using the same amplifier.     

加法色噪声对双模激光竞争效应的影响

研究了加法色噪声对双模激光竞争效应的影响。通过线性稳定性分析以及小τ近似得到一些很有意义的结论。     

推–推振荡器共用谐振器分析与低相位噪声设计

为实现低相位噪声平面振荡器,对推-推振荡器的共用谐振器与相位噪声优化方法进行了研究。提出一种基于多环式开口谐振环的差分传输线,通过加载一对耦合谐振环的方式实现2个单元振荡器之间的弱耦合,提高了共用谐振器的频率选择特性。基于该结构设计并实现了一种X波段推-推振荡器,在设计中采用一种基于振荡器有源品质因子的相位噪声优化方法。测试结果表明：该振荡器在输出二次谐波9.52 GHz处的相位噪声为-115.48 dBc/Hz@100 kHz,基波抑制度达到-54.55 dBc。     

Gain clamping in semiconductor optical amplifiers with second-order index-coupled DFB grating

A systematic investigation of gain-clamped semiconductor optical amplifiers (GC-SOAs) based on the second-order index-coupled DFB gratings is carried out by way of simulation. In particular, we focus on the main effects of the radiation loss caused by the first-order diffraction of the gratings on the amplifier performance. The magnitude of the total complex coupling coefficient is the main factor to determine the level of gain clamping. We demonstrate that a high-performance GC-SOA can be realized by using purely loss-coupled second-order DFB gratings with more relaxed tolerance on grating strength and period. It is shown that, in the presence of weak reflection-related coupling, the parasitic radiation loss associated with the second-order grating always helps to expand the linear amplification region and to reduce the longitudinal spatial hole burning along the cavity. Further, we demonstrate through comparison that the GC-SOAs have higher saturation power and much shorter carrier lifetime than the conventional SOAs. An improved design by longitudinal variation of the grating duty cycle is proposed such that the noise performance of the amplifier can be enhanced without much sacrifice on the linear amplification regime.     

Noise figure of vertical-cavity semiconductor optical amplifiers

The noise figure of vertical-cavity semiconductor optical amplifiers (VCSOAs) is investigated theoretically and experimentally. Limitations on the noise figure set by the reflectivity of the mirrors are studied. Highly reflective mirrors lead to increased output noise as well as lasing at moderate carrier densities, which imposes a limit on the obtainable population inversion. Expressions for the excess noise coefficient, which governs signal-spontaneous beat noise enhancement due to finite mirror reflectivity, are presented for transmission and reflection-mode operation. Experimental results from a VCSOA operating in the reflection mode at 1.3 μm are presented. The results, from optical as well as electrical measurement techniques, are analyzed and compared to theoretical values     

Excess noise in the radiation from c.w. d.h. GaAlAs-diode lasers

The dependence of excess noise in the radiation from c.w. d.h. GaAlAs-diode lasers as a function of d.c.-pump current has been investigated at microwave frequencies (1 and 4 GHz) in the temperature range from ?30°C to +20°C. Measurements are compared to the results of excess-noise computations obtained from a simple, analytical, laser model.     

Analysis of the frequency noise of tunable multisection DBR lasers

A theoretical analysis is performed of the frequency noise in tunable two- and three-section distributed Bragg reflector (DBR) laser diodes (LDs), taking into account the nonlinear gain compression effect. For a two-section DBR LD the frequency noise is shown to depend significantly on the tuning current, particularly at low frequencies (below the gigahertz range) and for low and moderate values of the grating coupling coefficient. For high values of this coefficient the tuning dependence is generally negligible when the tuning is performed only through the DBR section, but it becomes significant when using the phase control current in a three-section device. It is shown that the enhancement factor for the spontaneous emission rate due to the longitudinal field dependence increases significantly with tuning for low values of the grating coupling coefficient     

雾的雷达后向散射特性研究

利用流雾与辐射雾的能见度与含水量的经验公式导出的Gamma雾滴谱分布,得到了平流雾和辐射雾的雷达反射因子Z与雾的能见度、含水量的关系式。以94GHz雷达为例,研究了雾的雷达后向散射特性。最后利用毫米波衰减数据和能见度反演的几场湿海雾参数,研究了湿海雾的后向散射特性,研究结果表明：湿海雾的雷达反射因子可与中到大雨相当。     

Mode conversion and filtering of bound modes in planar waveguideBragg reflectors

A formalism for computing the reflectivity at oblique incidence of grating Bragg reflectors in integrated optics is developed. Attention is focused on the wavelength region near the Bragg wavelengths, where efficient reflection and strong Te-TM mode coupling occurs. The waveguide fields are expanded in normal modes of a waveguide film without the grating, and an answer is given to the question of how to define this film. Polarization resolved reflectivity spectra for a number of Bragg reflectors are calculated, and implications for device design in integrated optics are discussed     

A New Outer Bound and the Noisy-Interference Sum–Rate Capacity for Gaussian Interference Channels

A new outer bound on the capacity region of Gaussian interference channels is developed. The bound combines and improves existing genie-aided methods and is shown to give the sum–rate capacity for noisy interference as defined in this paper. Specifically, it is shown that if the channel crosstalk coefficient magnitudes lie below thresholds defined by the power constraints then single-user detection at each receiver is sum–rate optimal, i.e., treating the interference as noise incurs no loss in performance. This is the first capacity result for the Gaussian interference channel with weak to moderate interference. Furthermore, for certain mixed (weak and strong) interference scenarios, the new outer bounds give a corner point of the capacity region.      

Analysis of the phase-amplitude coupling factor and spectrallinewidth of distributed feedback and composite-cavity semiconductorlasers

A Green's function approach to the analysis of semiconductor lasers is formulated in a form suitable for complex cavity structures. Both the spontaneous emission rate and the effective phase-amplitude coupling factor can be accurately evaluated. For distributed-feedback (DFB) lasers, the spontaneous emission rate is strongly dependent on both the facet reflectivities and the grating coupling coefficients. The effective phase-amplitude coupling factor depends on the wavelength detuning from the gain maximum. The calculated linewidth of DFB lasers differs considerably from previous calculated results and gives better agreement with experimental results. For composite-cavity lasers, the frequency dependence of the equivalent reflectivity has a strong impact on the phase-amplitude coupling factor and the spontaneous emission rate. Distributed Bragg reflector (DBR) lasers are investigated as an example of a composite-cavity structure     

基于锥形尺度变换的弱小舰船目标检测

该文提出一种低信杂噪比下弱小舰船目标的检测方法。该方法对回波的慢时间瞬时自相关函数进行锥形尺度变换(Taper Scale Transform, TST),解除时延和慢时间的耦合。然后将TST后的信号相干积累,达到很好的检测效果。另外,该文分析了交叉项对检测的影响以及尺度因子的选择标准。实测数据的处理结果验证了该方法的有效性。     

利用由折射率表示的权重因子研究多层介质镜

利用反射系数的递推表达式研究了弱吸收1/4波长(QW)多层介质镜的反射特性,引入了一个具有普适性的权重因子来定量描述镜子中各层对反射时延、反射率下降的贡献。为了方便使用,用介质折射率表示出了权重因子,并以此讨论了折射率对反射时延及反射率下降的影响。