Optical and mechanical properties of infrared fibers

Optical and mechanical properties have been investigated for As ₂S₃ and As₂Se₃ glass fibers and a KRS-5 polycrystalline fiber. A bending effect was serious for a KRS-5 fiber but not for chalcogenide fibers. In an aging test, a KRS-5 fiber showed a deterioration of transmissivity due to adsorption of moisture as well as plastic deformation of the crystal. Optical loss spectra of chalcogenide fibers were observed to change characteristically due to environmental factors such as humidity, high temperature, and ultraviolet radiation. The potential usefulness of these fibers is discussed     

锆基非晶合金与不锈钢激光焊接的接头特性

为了优化非晶合金与晶体金属的激光焊接工艺,运用最大平均功率300 W脉冲红外激光焊接锆基非晶合金Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀与440、304、17-4PH不锈钢。采用材料分析手段和力学测试方法对实验焊接接头的材料微观组织、成分组成以及力学性能进行了表征,取得了合适的激光偏移量焊接工艺参数、焊接接头微观组织特性数据及其力学性能数据。结果表明,激光焦点往不锈钢侧偏移0.2 mm～0.3 mm可以使焊接熔化均匀并有效提高抗弯强度,通过合适的焊接工艺使非晶合金与17-4PH接头抗弯强度达339 MPa;非晶合金与3种不锈钢的激光焊接接头主要分为熔化混合区与热影响区,熔化混合区中发现了呈树枝状与颗粒状的结晶组织,焊后通过低温退火可使抗弯强度提升14%～48%。此研究结果对扩大锆基非晶合金在各个领域的应用具有指导意义。     

Influence of the grain boundary phase on the mechanical strength ataluminum nitride substrate surfaces

The influence of grain boundary phases on the mechanical strength at aluminum nitride (AlN) substrate surfaces, after a wet chemical process, was studied using AlN substrates doped with 2 wt% CaO or 4 wt% Y₂O₃. Mechanical strength was measured by pin pull-off, pin bending tests and Vickers hardness measurements. Test specimens were obtained by the processes of lapping, polishing, thin-film metallizing, photoengraving, plating, and brazing. The test results showed that the mechanical strength at the surface of Y₂ O₃-AlN substrates was higher than at CaO-AlN surfaces, where it was under the adhesion strength between the metallization layer and the AlN substrate. The mechanical strength at the surface of the CaO-AlN substrate was lost during patterning and plating. This was accompanied by an important weight loss in HNO₃ and K₂ O·n(B₂O₃) aqueous solution, due to dissolution of the grain boundary phase. The reason for the difference in the mechanical surface strength of AlN substrates after patterning and plating is that the CaO-AlN grain boundary phase dissolves in the chemical solution in the process more easily than the Y₂O₃-AlN gram boundary phase. The Y₂O ₃-AlN substrate showed unchanged pin pull-off and bending strength even after thermal cycling (1000 cycles) and 1000 h of a pressure cooker test. Although the CaO-AlN grain boundary phase seemed to cover all the grains, thermal conductivity was only slightly affected, because the grain boundary film was very thin     

Determination of the individual strain-optic coefficients insingle-mode optical fibres

A method to determine the individual strain-optic coefficients in single-mode fibers is described. It is based on two photoelastic experiments, namely, the polarimetric measurement of optical activity induced by mechanical twist and the interferometric measurement of optical-path-length change induced by static longitudinal strain. For fibers with pure silica core and B₂O₃ doped cladding, the optical activity per unit twist rate and the phase change per unit fiber elongation have been measured to be 0.1472 and 1.150×10⁷ rad/m, respectively. The strain-optic coefficients have been measured to be p₁₁=0.113 and p₁₂=0.252, 7% lower than those of bulk silica     

Anomalous dispersion in Er3+ and Yb3+-dopedfibers

In experimental and theoretical study of anomalous dispersion in Er³⁺and Er³⁺-Yb³⁺-doped fibers has been developed. Anomalous time delay caused by both absorption and emission at 1.535 μm has been theoretically calculated and experimentally measured. A pump power dependence of anomalous time delay in rare-earth-doped fibers has been theoretically calculated and experimentally investigated. It has been shown that pump power fluctuations lead to propagation time jitter in Er³⁺-doped fiber amplifiers. The pulse interaction due to refractive index change caused by gain saturation is predicted. It has been shown that for Er ³⁺-doped fibers with SiO₂-GeO₂ core composition, the anomalous dispersion per 1-dB gain is twice that of fibers with SiO₂-Al₂O₃ core, which is caused by gain curve form difference. A scheme of mutual compensation of intrinsic fiber dispersion and anomalous dispersion caused by Er³⁺ in the region 1.532-1.537 μm has been suggested     

磁控管用新型直热式稀土铪酸钆陶瓷阴极研究

为了提高大功率磁控管的输出功率,延长其使用寿命,采用难熔稀土氧化钆和过渡金属氧化铪制备大功率磁控管用新型直热式稀土铪酸钆陶瓷阴极,并对该阴极的热发射特性和寿命特性等进行了测试,热发射测试结果显示该阴极在1300℃ br即可提供0.1A/cm²发射电流密度,1600℃ br下可提供超过1.93A/cm²的发射电流密度.寿命实验结果显示,该阴极在1500℃ br,直流负载为0.5A/cm²的条件下,寿命已经超过4000h.最后,利用X射线衍射仪、扫描电镜、能谱分析仪、氩离子深度刻蚀俄歇电镜等设备分别对该阴极活性物质的分子结构,阴极表面微观形貌、元素成分及含量等进行了分析.结果表明,高温烧结合成了单一的铪酸钆物相,烧结过程中当一种Gd³⁺价稀土氧化钆掺入Hf⁴⁺价的过渡金属氧化铪时,会发生离子置换固溶,为了保持铪酸钆晶格的电中性,晶格中就会产生一个氧空位.当阴极在激活、老练、热发射测试时,会加速氧空位的生成,产生的氧空位越多,阴极表面导电性就会越好,这间接降低了逸出功,从而提高了阴极的热发射能力.     

Decay of transmitted light during fiber breaks-implications forbreak location

The accuracy of a bit-counting method for locating fiber breaks in an optical communication system proposed by Rosher et al. is limited in part by the decay time of the transmitted light during fiber failure. In order to understand the nature of this limitation, decay times were measured for individual fibers using a variety of failure mechanisms. The mechanics of the break processes were considered and the implications for break location using the bit-counting technique were assessed. The fastest decay times (≈14 ns) occurred when fibers broke catastrophically under stress levels greater than 0.7×109 N/m². The decay times in this case implied a small break-location uncertainty of 3 m when employing the bit-counting scheme. Since the strength members of fiber cable break at much greater tensions, decay times for cable failures (for example, caused by a backhoe) should not significantly limit the break-location accuracy assuming that the fibers do not bend severely before breaking. For stresses below 0.7×109 N/m² the decay times increase as the stress decreases, attributable to a corresponding decrease in the speed with which the cores of the broken fiber sections tilt with respect to each other and/or separate     

Lifetime Estimation Using Only Failure Information From Warranty Database

Knowledge about product lifetime obtained from actual usage (field data) is of great importance to manufacturers who want to get information about the true reliability of their products. Warranty data are frequently used to estimate reliability characteristics because such databases are automatically generated and updated at no additional cost from repair claims during warranty coverage. For engineering purposes, usage time (e.g., mileage) is more relevant, and lifetime parameters measured in usage time is an integral part of reliability analysis using warranty data. Usually, warranty data consist of only failure information. Censored data (e.g., mileage of non-failure automobiles) are not obtainable, of which usage time distributions are different from those of failed ones. Effective usage-based estimation thus requires supplementary information about usage accumulation for non-failure units such as follow-up studies, or a usage time distribution which includes both failure, and non-failure products. However, sometimes usage-based data for non-failed units are expensive and difficult to obtain. Thus, the unavailability of the usage time of censored units makes it difficult to estimate the usage-based lifetime distribution of products. This paper deals with that problem, and discusses how to estimate the lifetime distribution using warranty data which consist of only failure information. The practical consequence of this finding is that supplemental information is not needed to obtain correct estimates of the lifetime parameters.      

Temperature-humidity-bias behavior and acceleration factors fornonhermetic uncooled InP-based lasers

The stability of uncooled InP-based laser diodes in humid ambients was studied. Nonhermetic devices were aged at two different temperatures and humidities at a constant current and at one temperature and humidity at six different drive currents. For all nonhermetic devices failure occurred as a result of a large increase in the threshold current. The reverse leakage current for the failures did not increase when the threshold current increased, indicating that the change in threshold was a result of a change in reflectivity of one or both facets. The hermetic control group of devices aged under many of the same conditions showed a gradual increase in both the threshold current and slope efficiency. The median lifetimes as determined by assuming a device was a failure when the threshold current increased by 50% was strongly dependent upon humidity temperature and drive current. The lifetime data was fit to and equation of the form lifetime exp(-E_α/kT) exp(-B_RH [RH²]). The values of E_α and B_RH were 0.52 eV and 4.9×10^-4/%², respectively. The current drive data was fit to and expression of the form lifetime a exp(I^αI_op) where I_α as 0.09 h/mA. The lifetime dependence on current drive was modeled by assuming that the drive current caused a local temperature rise through thermal resistance. This local temperature rise then caused a decrease in the local humidity at the diode surface through an expression of the form %RH_diodeα exp (-5990[1/(T_r+T_ambient)-1/T_ambient ])where where T_r is the local temperature rise due to thermal impedance. Finally, we present our preliminary results on the reliability of nonhermetic SiO_x passivated lasers. These results indicate that such lasers can be made with sufficient reliability for use in telecommunications application     

挠性光电印制电路板工艺光纤特性仿真与测试

挠性光电印制电路板(Flexible Electro-Optical Printed Circuit Board, FEOPCB)在高温层压制作过程中,埋入光纤会产生热应力,造成光纤损坏等缺陷,影响其可靠性和高速信号传输性能。为了降低FEOPCB弯曲半径并提升其可靠性,将在双面覆铜聚酰亚胺(PI)基板上设计制作高精度矩形光纤定位槽。首先建立有/无涂覆层光纤埋入挠性基板有限元仿真模型,对FEOPCB制造工艺进行模拟仿真,并对埋入光纤应力及影响因素进行分析。结果表明,有涂覆层光纤所受应力远小于无涂覆层光纤。针对有涂覆层光纤,采用激光刻蚀技术在双面覆铜PI基板上制作了高精度矩形定位槽,通过高温层压工艺完成了FEOPCB制作。FEOPCB完成了温度冲击、低温、高温、湿热和10万次弯曲疲劳可靠性试验,利用光学显微镜观察分析,埋入光纤无高温降解和破裂等缺陷。FEOPCB最小弯曲半径小至2 mm,弯曲损耗分别为0.57 dB (90°)和1.12 dB (180°),且相邻光纤之间无串扰,在850 nm波长条件下通信速率可达10 Gbps,误码率小于10^-16。     

Dispersion-shifted dual-shape core fibers. Optimization based onspot size definitions

Design features, for very low bend and splice losses, in dispersion-shifted dual-shape core (DSC) single-mode fibers are obtained in terms of characteristic mode spot sizes W¯ responsible for splice loss, and W_∞ responsible for bend loss. Dual-shape core fiber designs are given with W¯_∞/W lying between 1.16 and 1.33 while maintaining the mode spot size between 4 and 5 μm at the operating wavelength of 1550 nm. With this design goal it is shown that bending loss would be lower in a step-index than in a graded-index DSC fiber. Further, conventional single clad step-index or triangular-index dispersion-shifted fibers are seen to have higher bending loss than well-designed DSC fibers     

Subthreshold flaws and their failure prediction in long-distanceoptical fiber cables

A study of surface defects and static fatigue data is presented to support the view that subthreshold surface defects are responsible for failure in proof-tested optical fibers. For this type of defect, crack initiation, as opposed to crack growth, is the rate-limiting step. Classical crack propagation theory does not describe this process sufficiently well for lifetime production, but semiempirical techniques indicate that this popular treatment may be pessimistic. A more conventional reliability treatment, similar to that used for other system components, appears to offer the best available approach to the task of failure lifetime prediction in proof-tested fibers     

Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections. Part 1: Effects of Test Parameters

The work presented in part 1 of this study focuses on identifying the effects of thermal cycling test parameters on the lifetime of ball grid array (BGA) component boards. Detailed understanding about the effects of the thermal cycling parameters is essential because it provides means to develop more efficient and meaningful methods of reliability assessment for electronic products. The study was carried out with a single package type (BGA with 144 solder balls), printed wiring board (eight-layer build-up FR4 structure), and solder interconnection composition (Sn-3.1Ag-0.5Cu) to ensure that individual test results would be comparable with each other. The effects of (i) temperature difference (ΔT), (ii) lower dwell temperature and lower dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate were evaluated. Based on the characteristic lifetimes, the thermal cycling profiles were categorized into three lifetime groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. Thus, one might be tempted to use the highly accelerated conditions to produce lifetime statistics as quickly as possible. However, to do this one needs to know that the failure mechanisms do not change from one lifetime group to another and that the failure mechanisms correlate with real-use failures. Therefore, in part 2 the observed differences in component board lifetimes will be explained by studying the failure mechanisms that take place in the three lifetime groups.     

Spontaneous emission lifetime of the C → A band of the XeF molecule

The radiative lifetime of the blueC rightarrow Atransition of XeF has been measured to be 93 ± 5 ns by monitoring the exponentially decaying 460 nm emission following rapid electron impact dissociation of XeF2. By varying the XeF2partial pressure, the rate constant for quenching of XeF (C) by XeF2was determined to be(1.8 pm 0.5) cdot 10^{-10}cm³. s^-1. Finally, knowledge of the XeF B and C state lifetimes yields a revised value of 610 ± 60 cm^-1for theBtoCstate energy defect.     

Characterization and modeling of electromigration failures inmultilayered interconnects and barrier layer materials

Electromigration failure mechanisms of TiN/Al-alloy/TiN multilayered interconnect and TiN, TiW barrier layer materials have been studied. The stress induced in Al electromigration instead of severe joule-heating has been attributed to the damage healing or resistance oscillation observed in TiN/Al-alloy/TiN multilayered interconnects. The lifetime dependence on interconnect geometry (length and width) for multilayered structures has been investigated. The experimental results show that the failure observed in TiN and TiW barrier layer materials was not caused by electromigration, instead it was due to a thermally activated process. The activation energy of this thermal process for TiN was found to be 1.5 eV. A 10-year lifetime was projected to be attainable if the hottest spot in TiN film was kept below 408°C. This suggests that TiN may safely conduct 2.4×10⁷ A/cm ² for the typical thermal impedance of a hot spot     

Drawing influence on the lifetime of optical fibres

Strength and lifetime measurements carried out on optical fibers with different residual tensile stress at the surface are discussed. This stress was optically measured and included in the theory of fiber strength and lifetime. The strength results were compared with measurements done on pure silica fibers without residual stress. In lifetime predictions, this residual tensile stress in the outside region of the fiber has to be taken into account. However, the decrease in intrinsic strength was much larger than the increase in residual stress in the outside region of the fiber. This phenomenon, which is not well understood, depends on drawing conditions     

Electron transport across bulk(AlxGa1-x)0.5In0.5P barriersdetermined from the I-V characteristics of n-i-n diodes measured between60 and 310 K

The electron transport characteristics of five n-i-n diodes with (Al_xGa_1-x)_0.5In_0.5P intrinsic barrier regions of various aluminum composition x were determined from the measured I-V characteristics between 60 and 310 K. From these measurements, three different transport regimes were identified. Fowler-Nordheim tunneling was observed at temperatures below 215, 260, 110, 150, and 120 K for aluminum compositions of x=0.4, 0.5, 0.6, 0.7, and 1.0, respectively, with applied electric fields in excess of 5 MV/m. The temperature dependence of the Fowler-Nordheim tunneling currents is shown in AlGaInP for the first time with direct bandgap AlGaInP exhibiting a strong linear decrease in apparent barrier height with increasing temperature. The measured barrier height using the thermionic emission model yields values close to the expected conduction band offset between the GaInP spacer layers and the AlGaInP intrinsic barriers, as measured using high-pressure photoluminescence, and provides a novel technique for measuring the direct-indirect crossover composition in AlGaInP. It is shown that the lowest lying conduction band in AlGaInP is the dominant barrier to electron transport. This has important implications for the design of AlGaInP laser diodes     

Ce掺杂对空间激光通信掺铒光纤的耐辐照影响研究

辐照环境下掺铒光纤性能下降严重影响了其在空间环境中的应用,而Ce可以凭借其变价能力抑制光纤的辐致损伤效应。利用螯合物气相沉积法制备了不同Ce掺杂量的掺铒光纤,在常温下使用⁶⁰Co辐照源对光纤进行了累积剂量100 krad、剂量率6.17 rad/s的辐照实验。通过吸收损耗谱的测试发现Ce掺杂含量高的光纤在辐照后损耗为419.185 dB/km@1 200 nm,且荧光寿命变化量减小了0.578 ms。通过切片芯层透过率及电子顺磁共振测试发现Ce掺杂可以有效降低光纤中Al和Ge相关的色心缺陷数量。最后通过增益测试验证了Ce掺杂对掺铒光纤抗辐照能力的改善,辐照后高Ce掺杂的光纤比未掺杂Ce光纤的增益高出4.15 dB。实验结果表明,Ce掺杂可以有效增强掺铒光纤抗辐照性能,这一结论对掺铒光纤在太空中的应用具有重要意义,该研究结果能够为后续掺铒光纤的耐辐照加固及其在空间中的应用提供参考。     

Junction-current-confinement planar light-emitting diodes and optical coupling into large-core diameter fibers using lenses

High-radiance AlGaAs-GaAs double-heterostructure light-emitting diodes utilizing junction current confinement are described. Diode resistance and junction ideality factor are investigated as a function of emission diameters from 10 to 75 µm. Near-field intensity profiles indicate tight current confinement over the full range of emission diameters. Rise-time measurements are consistent with a simple carrier lifetime model for >25-µm emission diameters. An effective radiative-recombination constant, B = 1.5(±0.5) × 10-¹⁰cm³/s is deduced from the rise-time data and model. Peak wavelength and spectral width data are discussed in terms of junction current density and temperature. With decreasing emission diameter, the optical coupling efficiencies into 100- and 200-µm core diam high-numerical-aperture fibers increased from 10 to 25 percent and 25 to 50 percent, respectivley, using spherical glass lenses.     

非故意掺杂吸收层InP/InGaAs异质结探测器研究

为了获得低噪声铟镓砷（InGaAs）焦平面,需要采用高质量的非故意掺杂InGaAs（u-InGaAs）吸收层进行探测器的制备。采用闭管扩散方式,实现了Zn元素在u-InGaAs吸收层晶格匹配InP/In_0.53Ga_0.47As异质结构材料中的P型掺杂,利用扫描电容显微技术(SCM)对Zn在材料中的扩散过程进行了研究,结果表明,随着扩散温度和时间增加,p-n结结深显著增加,u-InGaAs吸收层材料的扩散界面相比较高吸收层浓度材料（5×1016 cm?3）趋于缓变。根据实验结果计算了530 ℃下Zn在InP中的扩散系数为1.27×10?12 cm2/s。采用微波光电导衰退法(μ-PCD)提取了InGaAs吸收层的少子寿命为5.2 μs。采用激光诱导电流技术(LBIC)研究了室温下u-InGaAs吸收层器件的光响应分布,结果表明:有效光敏面积显著增大,对实验数据的拟合求出了少子扩散长度L_D为63 μm,与理论计算基本一致。采用u-InGaAs吸收层研制的器件在室温(296 K)下暗电流密度为7.9 nA/cm2,变温测试得到激活能E_a为0.66 eV,通过拟合器件的暗电流成分,得到器件的吸收层少子寿命τ_p约为5.11 μs,与微波光电导衰退法测得的少子寿命基本一致。