Low-loss highly overcoupled fused couplers: fabrication andsensitivity to external pressure

A flame brush technique for fabrication of optical directional couplers that maintain low loss over many coupling cycles is discussed. Couplers with excess losses less than 3% and with 2500 power transfer cycles in the coupling are reported. Such couplers, which have a narrow wavelength band transmission (0.12 nm), can be tuned by applying an external hydrostatic pressure. The long fused couplers can also have application as optical fiber sensors     

Effects of structural parameters on the external optical feedbacksensitivity in DFB semiconductor lasers

External optical feedback sensitivity in distributed feedback (DFB) semiconductor lasers is analyzed with special attention to phase-shifted and complex-coupled lasers. The effects of various structural parameters such as coupling strength, facet reflectivity, and corrugation phase angle on external optical feedback sensitivity are studied. The λ/4 phase-shifted index-coupled DFB laser exhibits low external optical feedback sensitivity for large index-coupling coefficient and high facet reflectivity. Pure gain-coupled DFB lasers perform better than the phase-shiftless uniform index-coupled DFB lasers but worse than λ/4 phase-shifted index-coupled lasers with high coupling strengths. External optical feedback sensitivity of complex-coupled lasers depends significantly on the index-to-gain coupling ratio, the phase between the index and gain gratings, and the total coupling     

Signal processing methodology to study the cutaneous vasodilator response to a local external pressure application detected by laser Doppler flowmetry

The existence of a cutaneous pressure-induced vasodilation (PIV) has recently been reported. This paper proposes a signal processing methodology to improve PIV knowledge. Temporal variations of laser Doppler signals rhythmic activities are first analyzed on anesthetized rats. The results lead to a method that provides a better PIV understanding.     

光纤外腔对半导体激光器发光特性的影响

1.半导体激光器的张弛振荡、自脉动等光强起伏现象,以及用于光通信系统时,由光纤端面或光盘反射所引起的噪声对高速光通信的应用影响较大。为了抑制光强起伏,近年来外腔半导体激光器得到了较大发展。许多实验证明:外腔不仅能抑制张弛振荡和自脉动等光强起伏现象,而且还有很好的选模作用。甚至用外腔还做出了可调谐的单频激光器。这里,我们将一段光纤耦合到激光器上,利用光纤端面的反射形成光反馈作成了光纤外腔。 2.实验用的激光器是GaAlAs DH激光器,波长约为820nm,结构是质子轰击条形。用作耦合的光纤是标准的多模梯度光纤,芯径为50μm,数值孔径为0.2。激光器被烧焊在一个梯形的热沉上,其出光面直接与光纤耦合(见图1)。光纤的耦合端做成了球面,而另一端则做成平面,光反馈就是由此面反射形成的。光纤耦合端距激光器的距离约为50μm,     

压力对W-Cu合金电场快速烧结的影响

采用Gleeble—3500D热模拟机,用电场快速烧结的方法制得W-Cu合金。通过对烧结压坯的密度、显微结构以及硬度的分析,研究了压力对W-Cu合金烧结的影响。结果表明:W-Cu合金在800℃、3 min内快速烧结可获得晶粒较细小、显微组织较均匀的烧结体;在10~30 MPa范围内加压能有效促进烧结体的致密化,可获得相对密度为92.60%~94.84%的W-Cu合金烧结体。但是随着压力的增加,烧结体的相对密度增加不明显。压力可使该烧结体显微硬度增高。     

Effects of external fields on the excitonic emission from single InAs/GaAs quantum dots

A low-temperature micro-photoluminescence (μ-PL) investigation of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field is reported. It is demonstrated that the QDs PL signal could be increased several times by altering the external and/or the internal electric field. The internal field in the vicinity of the dots could be altered by means of an additional infra-red laser. We propose a model, which is based on an essentially faster lateral transport of the charge carriers achieved in an external electric field. Consequently, also the capture probability into the dots and subsequently the dot luminescence is also enhanced. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment.     

Satellite link performance under rain and external interferences: Constraints to be imposed on the statistical behavior of the external interferences

This paper concerns an environment in which several communication systems share a common frequency band and, therefore, each system operates subject to the interference generated by the others. More specifically, the paper addresses the problem of establishing the limits that should be imposed on the transmitted interfering signals so that all systems sharing the band are able to operate adequately and none of them experiences harmful interferences. This is a well‐known problem for those working in the telecommunication regulation and standardization areas. Its solution requires studies and analysis that are usually complex and strongly depend on the technical characteristics of the systems involved. This paper presents a new technique that is able to determine, in a systematic way, the constraints to be imposed on the statistical behavior of the external interferences affecting a satellite link to guarantee that the link performance requirements are satisfied. The proposed technique considers the joint effect of the degradations due to rain and due to external interferences. In the method, a series expansion on the basis of orthonormal functions is used to represent the probability density function of the degradation due to external interferences and the limiting mask is obtained by solving a conveniently defined constrained optimization problem. The method is flexible enough to allow for the use of the rain attenuation models that are usually employed in link calculations. Two example applications are presented: one involving a satellite downlink in 19 GHz and the other an uplink in 29 GHz using power control. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of growth pressure on indium incorporation during the growth of InGaN by MOCVD

The effect of the growth pressure on the In incorporation in InGaN thin films, grown by metalorganic chemical vapor deposition (MOCVD) have been investigated. The InGaN thin films were grown by varying the growth pressures, while maintaining all other growth parameters constant. Photoluminescence and high resolution x-ray diffraction (XRD) measurements showed that the In incorporation in the InGaN thin film was drastically increased with decreasing growth pressures. XRD analysis also revealed that the In concentration in the films was increased by 7.5% as the growth pressure was decreased from 250 torr to 150 torr. This can be attributed to the enhanced mass transportation of precursor gases through the boundary-layer on the substrate in the MOCVD system.     

气体红外吸收特性受压强与温度的影响分析

气体的红外吸收特性是利用红外光学方法对气体进行定性定量分析的重要依据.吸收谱线的峰值吸收系数与全线宽是描述气体红外吸收特性的两个重要参量,参考HITRAN2004数据库,以乙炔在近红外的一段红外光谱为研究对象,对压强与温度对峰值吸收系数与全线宽的影响规律进行了研究,结果表明:当压强大于0.1MPa时,峰值吸收系数与全线...     

Effects of current modulation on timing jitter of single-modesemiconductor lasers in short external cavities

Turn-on jitter of single-mode semiconductor lasers with modulated injection current and weak optical feedback exhibits periodic oscillations as a function of the length of the external cavity, under configurations appropriate for packaged laser diodes. Numerical results for both periodic and pseudorandom word modulation show that the oscillations persist even when increasing the external cavity length to a few millimeters. It is found that under particular positions of the external reflector a large increase of jitter occurs as compared with the jitter without optical feedback     

Analysis of the response of lasers to external signal injection

The rate equation including the injection term was extended and solved numerically. The relation between the peak photon number in the onset of relaxation oscillations of lasers and the injected photon number is shown. The step response of the CW laser to the external signal injection and the reshaping property of the laser for the distorted optical pulse are reported.     

The effect of interference source proximity on cuff imbalance

The presence of cuff imbalance degrades the signal-to-interference (ENG/EMG) ratio in tripolar nerve cuff electrode recordings. Known causes of cuff imbalance include inhomogeneous tissue growth after cuff implantation and cuff manufacturing tolerances. In this paper, we report on an additional contribution to cuff imbalance that stems from variations in orientation and distance of the tripolar cuff relative to the external interference source. The latter is represented here by a dipole. Interference amplitude is also shown to depend on orientation and distance variations, here both factors included in the term "proximity." The study was conducted using field simulations and saline-bath experiments.     

Effects of pressure and hydrogen on the formation of vacancies and divacancies in crystalline silicon

The electron-density functional and pseudopotential methods are used to study the effects of hydrogen and pressure on the formation of vacancies and divacancies in silicon. It is shown that the formation energy of vacancies can be reduced by 1.8–3.5 eV and that of divacancies by 2.0–5.4 eV in the presence of hydrogen. As a result, the spontaneous generation of vacancies and vacancy-containing complexes becomes possible at high concentrations of hydrogen. At the same time, the presence of hydrogen makes silicon less sensitive to pressure and, at high hydrogen concentrations, can completely suppress the tendency toward additional formation of vacancies in the sample exposed to pressure.     

Supervisory adaptive control of arterial pressure during cardiacsurgery

A supervisory adaptive controller has been designed for the closed-loop control of mean arterial pressure during cardiac surgery, using sodium nitroprusside. This controller consists of a pole-placement and proportional-plus-integral feedback regulator, multiple-model adaptation, and a supervisor. The pole-placement and proportional-plus-integral regulator was designed to meet aggressive step response characteristics. Multiple-model adaptation was chosen to ensure rapid and stable adjustments for changes in key patients parameters. The supervisor was designed to provide safety and efficacy of control during disturbances that are common during cardiac surgery. We studied the ability of this supervisory adaptive controller to regulate arterial pressure during cardiac surgery on nineteen patients. The controller, through the action of the supervisor, detected and responded appropriately to the great majority of disturbances. This study demonstrated that supervisory adaptive control has the potential to provide clinically acceptable regulation of arterial pressure.     

外腔长度变化对光纤光栅外腔LD激射波长的影响

密集波分复用(DWDM)光纤通信系统对光源的波长稳定性有很高的要求。主要就可供DWDM系统选用的光源之一光纤光栅外腔半导体激光器(FGESL)的波长稳定性进行讨论。通过计及半导体激光器(LD)、外腔及光纤光栅(FG)三者的共同作用,根据光纤光栅外腔半导体激光器的相位条件确定FGESL的激光纵模分布后,理论上研究了FGESL的激射波长随FG外腔长度的变化。结果表明,外腔较短时,外腔长度的微小变化可以导致FGESL的激射波长产生显著的变化;外腔较长(大于10 cm)时,外腔长度的变化对FGESL的激射波长基本没有影响。     

血管参数对皮肤组织选择性光热解作用中光热响应规律的影响

利朋选择性光热解(SP)的三维光热作用模型,对血管尺寸、位置和数目等血管参数对皮肤组织选择性光热解作用中光热响应规律的影响进行了理论分析和数值求解.数值结果表明,当利用选择性光热解效应热损伤皮肤组织内的特定血管时,假如一定区域内有其他血管存在,则目标血管的热损伤率会受区域内其他血管的影响而减小.这个区域的大小与激光光斑大小及激光波长有关.一般来说,当血管处于激光光斑以外或深度超过1 mm(对于585 nm激光)时,这些血管的影响可忽略不计.     

Spectral analysis of arterial blood pressure in the rat during atrial fibrillation

This paper describes the development of a systems identification protocol in the rat for use in studies of the dynamics of blood pressure control The method is based on Taylor's canine random heart model and employs electrically induced atrial fibrillation to generate random fluctuations in arterial blood pressure. In order to evaluate the utility of the protocol, recordings of pulsatile blood pressure were obtained from the femoral arteries of anesthetized rats during atrial fibrillation. The data were reduced to spectral density function estimates using standard techniques of discrete spectral analysis. The results indicate that during atrial fibrillation, the time course of arterial blood pressure constitutes a white noise source in the frequency band from 0.01 to 10 Hz, in sharp contrast to the concentration of energy from the normal cardiac cycle into narrow frequency bands within this range. Thus, the protocol should be useful in the analysis of the dynamics of most physiological processes which respond to changes in blood pressure.     

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.