Interferometric noise reduction in fiber-optic links bysuperposition of high frequency modulation

The reduction of interferometric noise by superposition of high frequency modulation is analyzed. It is shown that the nature of this reduction is due to a redistribution of noise energy from baseband to higher frequencies where it can be discarded by low-pass filtering. Detailed analysis revealed the dependence of the noise reduction factor on the product f_0τ, and the modulation index of the high frequency superimposed modulation. The proper choice of parameters can lead to complete elimination of the converted phase noise from the system     

Hot-electron noise limitations in submillimetre-wave Schottky-barrier mixer diodes

The noise from small-area platinum gallium-arsenide Schottky-barrier mixer diodes has been measured at 4 GHz, to compare high-field (hot-electron) noise in diodes with different doping densities and anode areas. In the present state of technology, submillmmetre-wavelength mixer diodes should be fabricated from gallium arsenide with a doping density of about 1017 cm?3.     

Power and noise limitations of active circulators

In this paper, new simple formulas expressing the power and noise limitations for three three-way circulator architectures and three quasi-circulator architectures are derived. It is shown that the power-handling capability of the active three-way circulators is determined by the required transconductance of the transistors in the circuit, while the noise is determined by the drain noise current source. The suitability of the different active circulator architectures for transmit/receive applications is investigated, We conclude that the quasi-circulators based on passive isolation offer the highest performance     

Interferometric noise reduction through intrabit frequencyevolution of directly modulated DFB lasers

A new technique is demonstrated that improves the performance of optical networks subject to interferometric noise. Every transmitter comprises a selected DFB laser that is NRZ ASK directly modulated with a large modulation depth. Under modulation, the center frequency of the DFB laser is found to vary over the duration of each bit, falling during mark bits and rising during space bits with an exponential-like dependency of characteristic time constant ~20 ns. The optical frequency at the midpoint of each bit interval is not constant but depends upon the sequence of the preceding bits. Therefore, on the interference of a delayed-replica parasitic crosstalk waveform the interferometric noise generated on detection may be reduced by RF filtering according to the difference in center frequency of the interfering bits. This noise suppression which requires no additional hardware has been successfully modeled and experiment demonstrates little performance gain for a single interferer, as predicted. However, in the presence of multiple interferers significant improvement is predicted and observed at sub-Gb/s rates     

Comparative studies of noise limitations in superconducting thin-film radiation detectors

We report measurements on the noise limitations of superconducting thin films operating as thermal detectors (bolometers) and as current-dependent detectors. By making measurements in each mode on the same film it is possible to make a comparative study of the noise limitations for both detection mechanisms in the same device. Thin tin films with normal state sheet resistances on the order of 100 Ω per square have been studied. The devices were scribed to produce total normal state resistances on the order of 10 kΩ and were mounted in the vacuum chamber of a demountable tail Dewar so that they were not in direct contact with liquid helium. The resulting bolometers have response times and sensitivities similar to those of Martin and Bloor. The dominant noise mechanisms we have observed appear to be Johnson noise in the thermal mode and 1/f noise in the current mode. These results confirm previous conclusions regarding the sensitivity of these films as radiation detectors.     

Scaling and technological limitations of 1/f noise and oscillator phase noise in SiGe HBTs

This paper examines the impact of SiGe HBT scaling on 1/f noise and phase noise of oscillators and frequency synthesizers. The increase of transistor speed with scaling is shown to significantly increase the sensitivity of oscillation frequency to 1/f noise and, thus, degrade close-in phase noise, but decrease the sensitivity of oscillation frequency to base current shot noise and base resistance thermal noises. The results show that corner offset frequency defined by the intersect of the 1/f³ and 1/f² phase noise has little to do with the traditional 1/f corner frequency. The relative importance of individual noise sources in determining phase noise is examined as a function of technology scaling, device sizing, and oscillation frequency. The collector current shot noise and base resistance noise are shown to set the fundamental limits of phase noise reduction. A methodology to identify the maximum tolerable 1/f K factor is established and demonstrated for the HBTs used     

The switching dynamics and noise limitations of indium antimonidebistable elements

The switching dynamics of an InSb optically bistable etalon are analyzed in terms of effective time constants which change dramatically near the switch points. Results are presented which show nanosecond switching, critical slowing down, optical biomodality, and noise filtration. The influence of noise levels on both the switching dynamics and the system stability close to switching are discussed. The InSb-CO system has the merits of being extremely stable and reproducible so that the detailed switching dynamics and statistics can be reliably assessed. In addition, it may be regarded as a model system so that the results presented can be scaled with appropriate material time constants to other bistable systems     

Interferometric measurement of low-frequency phase noise characteristics of diode laser-pumped Nd:YAG ring laser

Reports the interferometric measurement of the phase noise characteristics of a diode laser-pumped solid-state Nd:YAG 1.3 mu m laser based on a nonplanar ring cavity. Results show that the device has a low-frequency phase noise approximately three orders of magnitude lower than that observed with semiconductor diode lasers. The use of this source in fibre sensing applications is discussed.<>     

Photonic switch size limitations imposed by phase noise fromsemiconductor optical amplifier gates

A possible way to design photonic switch matrices is by interconnecting multiple 2×2 switches based on semiconductor optical amplifier gates. The size of these matrices is limited by many phenomena including phase noise from the gates. The authors examine the limitations imposed by this noise in a system using DPSK direct detection     

On the limitations of transimpedance amplifiers as tools for low-frequency noise characterization

An experimental set-up for the characterization of low-frequency noise on two terminal devices is reported. The experimental set-up is based on the use of the commercial transimpedance amplifier (TA) EG&G5182. This paper addresses the influence of the TA on the noise characterization process by describing the TA as a non-ideal operational amplifier with a feedback resistor. The impact of the TA finite input resistance and voltage gain is highlighted through comparison with measurements carried out on resistors and diodes.     

High power with low electric power consumption activemulti-mode-interferometer laser diode for fibre-amplifier

Active multi-mode interferometer laser diodes (LDs), implemented in InGaAsP/InP, achieved a significant reduction of 40% (at 0.4 W output) in electric power consumption compared to regular single lobe LDs. With them, a high output power of 0.7 W was also obtained at 14XX nm     

合成孔径雷达干涉测量中的相位展开

合成孔径雷达干涉测量技术 (InSAR)是以合成孔径雷达复数据提取的相位信息作为信息源来获取地表的三维信息和变化信息的一项技术。相位展开是InSAR数据处理中的关键步骤之一。本文介绍了合成孔径雷达干涉测量的原理 ,重点讨论了InSAR中的相位展开算法 ,特别对与路径有关的算法和与路径无关的算法进行了分析 ,比较了各类方法的优缺点。指出一些在结构照明型计量中有效的相位展开算法也可以用于合成孔径雷达干涉测量之中的相位展开     

常州微至光电子有限公司 干涉条纹数字分析系统

加拿大微至（WZ）光电子有限公司研制开发的“干涉条纹数字分析系统”能够高精度数字分析干涉条纹，测量精度达到λ／20～λ／50，系统由图像采集卡、个人计算机、软件和软件加密狗组成，实时采集或输入干涉条纹，自动分析处理干涉条纹，输出检测报告，包括波面误差参数：峰谷值（P—V）误差、标准偏差（RMS）、赛德尔（Seidel）像差、光圈数（N）、局部光圈数（△N）。     

干涉条纹数字分析系统

加拿大微至（WZ）光电子有限公司研制开发的“干涉条纹数字分析系统”能够高精度数字分析干涉条纹，测量精度达到λ／20-λ／50，系统由图像采集卡、个人计算机、软件和软件加密狗组成，实时采集或输入干涉条纹，自动分析处理干涉条纹，输出检测报告，包括波面误差参数：峰谷值（P-V）误差、标准偏差（RMS）、赛德尔（Seidel）像差、光圈数（N）、局部光圈数（△N）。     

近柱面干涉检测研究

采用计算机仿真技术模拟了近柱非球面的正入射式检测装置。获取并分析了理想近柱面和理想柱透镜下的干涉图。讨论了降低干涉图P-V值的方法以及不同面形的近柱面在该装置下的可检性。     

Interferometric Analysis of Thermomechanical Deformations in Thermoelectric Generators

In thermoelectric applications, optimized thermal contacts are essential to enable efficient and homogeneous flow of heat currents. Thermomechanical stresses may lead to surface deformation, which alters the thermal contact. As a result, the heat current density is reduced and no longer homogeneous. Also an undesired temperature gradient perpendicular to the heat flow develops, and hence this temperature gradient again causes thermomechanical stresses. The described thermomechanical problems are particularly important in applications where high operating temperatures and hence large temperature differences are used. Also, system durability is a crucial aspect, especially in applications where thermal cycles occur (i.e., in the field of waste heat regeneration of car combustion engines). We describe a measuring technique to detect and evaluate the influence of these deformations. To analyze the surface and external points of contact of a thermoelectric generator (TEG), a measurement setup based on speckle interferometry is used. Temperature gradients as well as small surface deflections in the μm range have to be measured simultaneously. Therefore, an optical as well as a thermography camera are used to create a holistic image of the deformation and to analyze the influence of this deformation on the TEG structure.     

Interferometric determination of dispersion variations in single-mode fibers

Interferometry is used to study the variation of the zero dispersion wavelength (λ0) and the absolute group index (Ng) along the lengths of depressed cladding single-mode fibers. All of the results are for 34-cm samples of AT&T fibers drawn on production facilities. For two 7.5-km fibers sampled approximately every 1 km,bar{lambda_{0}} = 1299.6 pm 2.7and 1300.5 ± 2.9 nm. For five additional 0.8-km fibers, the average of the end-to-end differences of λ0is 2.0 nm. These results indicate the feasibility of inferring λ0for long lengths of these fibers from measurements made on a 34-cm length. At 1.30 μm,bar{N_{g}}and σ are 1.4659 and 0.0003, respectively (60 fibers from 28 preforms). The corresponding values at 1.55 μm are 1.4666 and 0.0003 (46 fibers from 19 preforms). These results place a lower limit of 0.02 percent on the accuracy of pulse delay measurements of unstressed lengths of AT&T production fibers.     

On non-scale-invariant infinitely divisible cascades

Multiplicative processes, multifractals, and more recently also infinitely divisible cascades have seen increased popularity in a host of applications requiring versatile multiscale models, ranging from hydrodynamic turbulence to computer network traffic, from image processing to economics. The methodologies prevalent as of today rely to a large extent on iterative schemes used to produce infinite detail and repetitive structure across scales. While appealing, due to their simplicity, these constructions have limited applicability as they lead by default to power-law progression of moments through scales, to nonstationary increments and often to inherent log-periodic scaling which favors an exponential set of scales. This paper studies and develops a wide class of infinitely divisible cascades (IDC), thereby establishing the first reported cases of controllable scaling of moments in non-power-law form. Embedded in the framework of IDC, these processes exhibit stationary increments and scaling over a continuous range of scales. Criteria for convergence, further statistical properties, as well as MATLAB routines are provided.     

Interferometric current sensors using optical fibres

Two types of fibre-optic current sensor have been developed and successfully tested in the laboratory: magnetostrictive jacketing materials and a heating effect, to produce a phase shift in the optical fibre. A ruggedised all-fibre interferometer powered by a diode laser was used to detect the phase changes induced by the electrical current.