The statistical distribution of switch-on delay in single-modesemiconductor lasers II: pattern effects

For part I see, p. 2006, 1995. The theory of stochastic processes as applied to photon emission and absorption events is used to calculate the distribution of switch-on delay in directly modulated semiconductor lasers down to a probability of 10^-10. In this second paper, the influence of a previous light pulse on the delay of a given pulse is investigated. The probability distribution of photon number in the dying remnants of the first pulse is examined under the relevant transient conditions of gain and loss, and is found to evolve in relative width and shape in a way which depends on only one parameter. This parameter, which consists of an integral over time of the reciprocal of the average photon number, is obtained from a solution of the deterministic rate equations and is used to deduce the delay distribution of the subsequent pulse. The results, although sensitively dependent on the conditions, are supported by experiment     

Photon statistics and quantum jumps: the picture of the dressedatom radiative cascade

The statistics of spontaneous photon emission times in single atom resonance fluorescence are investigated through the radiative cascade of the dressed atom. The delay function which gives the distribution of the delays between two successive emissions is calculated for a coherent as well as an incoherent laser excitation. For a two-level atom, various signals that reflect the fluorescence intensity (average value, photon counting, fluctuation spectrum, etc.) are reviewed by this method. For a three-level atom, this approach is applied to the analysis of the recently observed phenomenon of intermittent fluorescence and quantum jumps     

扩展目标光子测距回波特性及误差研究

光子测距具有灵敏度高,探测距离远的特点,目标形状和姿态对光子测距的影响不可忽略。针对扩展平面、球面和非球面三种典型目标,建立了扩展目标光子探测回波概率分布模型,推导出不同倾斜角下混有时空分布的光子回波概率分布一般方程。实验表明,扩展平面的光子回波概率分布与数值计算结果一致。理论仿真分析了扩展目标的光子回波概率分布特性,讨论了光子测距误差与扩展目标类型和倾斜角间的变化规律。结果表明:平均回波光子数为3.9,目标处激光光斑半径为0.2m,倾斜角小于20°时不同扩展目标间的光子测距误差小于1.23mm;光子测距误差随着目标倾斜角的增大逐渐增大,且扩展平面目标测距误差受倾斜角影响最大。     

基于基模高斯光束的单光子捕获概率研究

建立了一种自由空间量子密钥分配的单光子捕获概率理论模型。基于基模高斯光束,推导了单光子捕获概率的表达式。得到影响单光子捕获概率的主要参量是发射机的跟瞄误差、光束远场发散角、发射机和接收机的链路距离和接收机天线孔径。针对低轨卫星-地面站间链路进行了数值仿真分析,得到单光子捕获概率一般在10-3~10-5量级。     

Hot carrier evaluation of MOSFETs in ULSI circuits using the photonemission method

Photon emission from MOSFETs by hot carrier effect under AC operation is studied. A method to estimate the lifetime of MOSFETs in LSI chips, which uses the photon emission, is proposed. This method is based on experimental data showing that the lifetime of hot-carrier degradation is described by a universal curve with respect to the photon count at a wavelength of 200 nm. Quantitative estimations of lifetimes of MOSFETs in a real LSI are reported. This method is applied to the lifetime estimation of a CMOS microprocessor     

Evolution of the statistical properties of photons passed through atraveling-wave laser amplifier

The authors determine the evolution of the photon statistics of a light beam as it passes through a traveling-wave laser amplifier, modeled as a birth-death immigration (BDI) medium. The relationship between the input and output probability distributions and probability generating functions with given (but possibly varying) birth, death, and immigration rates for arbitrary input statistics is obtained. The case of constant birth, death, and immigration rates is considered in particular detail. The photon statistics at the output of a general BDI traveling-wave amplifier are always broader than those at the input, and they can take many forms. The most general solution can be applied when the input distribution to the amplifier takes the form of a negative-binomial transform     

Application of renewal theory to unslotted ALOHA in VSAT networks

Renewal theory is used to develop the probability of successfully transmitting variable-length packets in a finite-user unslotted ALOHA channel operating in an satellite network of very small aperture terminals (VSAT). This result, which does not depend on the arrival distribution, is then used to determine the equilibrium or operating point from which the normalized throughput, traffic and delay are estimated     

非相干变频转换实现室温下红外单光子源

纳米金刚石中的NV-center(Nitrogen-Vacancy center)是目前室温下具有高发射率和稳定性的可见光波段单光子源,而如何实现及优化红外单光子源则是未来实现量子信息和量子通信应用的一大挑战.介绍了一种近期提出的实现红外单光子源的新型机制.该方法以金刚石中的NV-center作为可见光波段的单光子源,利用非相干变频转换实现室温下近红外波段稳定、无闪烁的单光子源.具体的实施方案为在中空芯光子晶体光纤中选择性地填充含有量子点的溶液,以可见光波段的单光子源作为激励源,选择合适的量子点即可得到红外波段的单光子源.中空芯光子晶体光纤保证了较高的单光子吸收效率以及荧光收集效率.该方案的实施在理论上可以达到26%的转换效率,而初步的实验得到了0.1%的转换效率.进一步分析了一些影响转换效率的因素,并提出了一些解决方案.     

Computer simulation of laser photon fluctuations: Single-cavity laser results

In this second paper of a series I present statistical results obtained from computer simulated experiments in single-cavity semiconductor lasers and show that the probability distribution for realistic lasers are much broader than the Poisson distribution. When the gain saturation parameter is properly chosen, the computer simulated probability distributions agree very well with published experimental results. The following is a summary of the results. 1) Only the longitudinal laser mode at the center of the gain peak shows a probability distribution whose peak coincides with the average photon number. The modes to either side of the central mode have noise-like character with probability maxima at zero photon number. 2) The photon probability distribution narrows with increasing power output, increasing cavity mirror reflectivity and decreasing cavity length. 3) For the photon probability distribution to approach the Poisson limit, the cavity mirrors must have reflectivity near unity and the cavity losses must be very low. 4) Two modes symmetrically located at either side of the gain peak have a probability distribution that is constant from zero photon number to a cutoff value, because the modes compete for power and fluctuate widely. 5) Pulsed single-cavity lasers do not turn on consistently in the same longitudinal mode even if they are biased above threshold. 6) The performance of coupled-cavity (C³) and distributed feedback lasers (to be discussed in a subsequent paper) is much better than that of single-cavity lasers.     

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     

利用激光器产生单模亚泊松光

对利用激光器产生单模亚泊松光进行了研究。提出了一个普遍的主方程,它适用于任意稳定的原子注入方式,并在该方程中,考虑了有限腔寿命的作用。得出了输出光子数的Mandel因子,并指出在泵噪声抑制的基础上通过减少腔寿命,可以代替抑制自发辐射,使输出光子数的涨落进一步减小。     

采用多像素光子计数器的探测率与虚警率

为了完善多像素光子计数器（MPPC）在激光测距和激光雷达等方面应用的理论基础,对MPPC作为激光测距或激光雷达光探测器的探测率与虚警率进行了系统研究,运用泊松理论提出了基于MPPC的探测率与虚警率模型,推导了相应的解析表达式,并进行了数值分析,发现了一些传统探测器不存在的有趣特性。数值结果显示,利用多像素光子计数器作为激光测距的光接收器时,即使不使用门控（选通）技术,仅仅依靠等效光电子数探测阈值调节技术就可以达到实际应用中激光测距的系统要求。其灵敏度可达到光子量级,并能进行光子数分辨。该模型和结果对于促进MPPC在激光测距和激光雷达方面的应用,实现高灵敏度快速探测有一定的理论和实用价值。     

A comparative analysis of substrate current generation mechanisms in tunneling MOS capacitors

This paper presents a critical analysis of the origin of majority and minority carrier substrate currents in tunneling MOS capacitors. For this purpose, a novel, physically-based model, which is comprehensive in terms of impact ionization and hot carrier photon emission and re-absorption in the substrate, is presented. The model provides a better quantitative understanding of the relative importance of different physical mechanisms on the origin of substrate currents in tunneling MOS capacitors featuring different oxide thickness. The results indicate that for thick oxides, the majority carrier substrate current is dominated by anode, hole injection, while the minority carrier current is consistent with a photon emission-absorption mechanism, at least in the range of oxide voltage and oxide thickness covered by the considered experiments. These two currents appear to be strictly correlated because of the relatively flat ratio between impact ionization and photon emission scattering rates and because of the weak dependence of hole transmission probability on oxide thickness and gate bias. Simulations also suggest that, for thinner oxides and smaller oxide voltage drop, the photon emission mechanism might become dominant in the generation of substrate holes.     

基于单光子计数激光雷达的Bayesian检测研究

在单光子计数激光雷达检测领域,目前的检测方法在低信噪比情况下虚警概率会增加,同时也无法适应噪声变化的问题。针对这些问题,提出了一种基于Bayesian的检测方法,该方法首先通过雷达方程估计回波信号光子数的范围,将其作为先验信息,而后结合二项分布建立了累计概率模型,基于Bayesian判决准则计算得到检测阈值,此阈值能够在检测概率与虚警概率中间择其平衡。这种方法不仅克服了低信噪比检测困难的情况,还减少了先验信息的获取难度。实验结果表明,对比固定阈值其虚警概率降低了10倍。对比“恒虚警”其检测概率提高了约20%。验证了方法具有良好的检测效果,具备一定的可操作性。     

A novel analytical framework compounding statistical traffic modeling and aggregate-level service curve disciplines: network performance and efficiency implications

This paper demonstrates that higher network resource efficiency can be achieved by using resource management protocols which consider service disciplines based on service curves together with statistical traffic modeling. To this end, an appropriate analytical framework is introduced which allows calculation of the performance statistically guaranteed to any flow out of an aggregate. This feature enables the analytical framework to be applied to the elements of the core network where aggregates of traffic are considered instead of single flows in order to avoid scalability problems. Given that flows are modeled in the analytical framework through switched batch Bernoulli processes (SBBPs), the whole queueing system is denoted as SBBP/Sc/1/K. The performance is calculated in terms of loss probability and delay distribution. The proposed framework is applied in a significant multinode case study.     

Solid geometry-based object model for Monte Carlo simulated emission and transmission tomographic imaging systems

An object model based on combinations of object primitives is proposed for Monte Carlo simulated emission and transmission tomographic imaging systems. The primitives include ellipsoids, elliptic cylinders, tapered elliptic cylinders, rectangular solids, and their subsets: half, quarter, and eighth. The probability of a photon surviving interactions with the phantom medium is used as a weight for variance reduction. Calculation of the probability can be computationally intensive without properly organizing the inclusion of subregions within larger regions. A tree data structure is introduced to organize this inclusion relationship and used as the basis for two computationally efficient schemes for determining the intersection locations of a photon path with primitives and for identifying the attenuation coefficients for adjacent intersections for the survival probability computation. The approach has been validated by emission as well as transmission simulations. A thorax phantom containing overlapped ellipsoids and a heart composed of twelve overlapped quarter ellipsoids are employed to demonstrate the capability of the model.     

Simultaneous maximum a posteriori reconstruction of attenuation andactivity distributions from emission sinograms

In order to perform attenuation correction in emission tomography an attenuation map is required. We propose a new method to compute this map directly from the emission sinogram, eliminating the transmission scan from the acquisition protocol. The problem is formulated as an optimization task where the objective function is a combination of the likelihood and an a priori probability. The latter uses a Gibbs prior distribution to encourage local smoothness and a multimodal distribution for the attenuation coefficients. Since the attenuation process is different in positron emission tomography (PET) and single photon emission tomography (SPECT), a separate algorithm for each case is derived. The method has been tested on mathematical phantoms and on a few clinical studies. For PET, good agreement was found between the images obtained with transmission measurements and those produced by the new algorithm in an abdominal study. For SPECT, promising simulation results have been obtained for nonhomogeneous attenuation due to the presence of the lungs.     

White-light emission from GaAs m.o.s. structures

Emission of light from GaAs m.o.s. structures with anodic native oxides is reported. The spectrum is continuous, covers the visible range and has substantial parts that have higher photon energies than the GaAs energy gap. A part of the emission therefore seems to originate from the amorphous native GaAs oxide with its wide energy gap of about 4.5 eV. The light appears white to the eye and its intensity, but not its spectral distribution, can be controlled by the bias applied to the m.o.s. structure.     

Double balanced differential configuration for high speed InGaAs/InP single photon detector at telecommunication wavelengths

Recently,some kinds of structures have been found to show the property of extraordinary optical transmission(EOT).In this paper,we present a novel composite structure based on array of annular apertures(AAA)with compound lattice.The lattice includes two kinds of annular apertures with the same outer radius and different inner radii.The transmission spectrum of this compound periodic AAA can be achieved by adding up the spectra of two corresponding simple periodic AAAs,and the transmission shows EOT property.The transmission peaks of this kind of structure can be adjusted to desire wavelengths by changing the inner radius of aperture or the index of the dielectric material in the aperture.This structure can be used as a filter with dual pass bands when the difference between inner radii or indices of dielectric inside is large enough for two kinds of apertures.     

“Exciton” photoconductivity in GaAs crystals

The spectral dependence of the photoconductivity in epitaxial GaAs of high purity and crystalline perfection grown on a semiinsulating GaAs substrate are measured at 1.7 and 77 K and analyzed theoretically. The developed theory of photoconductivity spectra takes into consideration the analytical shape of the exciton absorption edge in semiconductor crystals, the transport of photogenerated charge carriers, the finite thickness of the crystal, and the presence of surface recombination centers. It is shown that, when the excitation photon energy is lower than the band gap, the photoconductivity spectrum is determined by elementary excitations of the exciton type, while at higher excitation energies the spectrum is determined by surface states as well as by processes associated with optical-phonon emission. It is found that, in the samples under study, the probability of the direct formation of excitons upon the absorption of light can be comparable to the probability of their formation from a thermalized electron-hole gas.