Statistics of intensity of backscattered semiconductor laser radiation in single-mode optic fiber

We have studied the statistics of the intensity of backscattered radiation of a semiconductor laser in single-mode optic fiber as a function of the probing laser pulse duration and coherence time. It is shown that, at a given radiation source coherence time, the intensity distribution function varies, depending on the pulse duration, from nearly exponential to nearly Gaussian. The exponential statistics provides a better sensitivity for a coherent reflectometer with direct detection. Using the calculated distribution function, it is possible to qualitatively determine the degree of deterioration of the reflectometer sensitivity with respect to external factors during increasing probing pulse duration or decreasing laser coherence time. These data provide criteria for the optimum choice of a radiation source for the coherent fiber-optic reflectometer.     

Study on error calibration of fiber optic gyroscope under intense ambient temperature variation

A novel adaptive forward linear prediction (FLP) denoising algorithm and a temperature drift modeling and compensation concept based on ambient temperature change rate for fiber-optic gyroscope (FOG) are presented to calibrate the errors caused by intense ambient temperature variation. The intense ambient temperature variation will bring large temperature errors, which will degrade the performance of FOG. To analyze the temperature variation, characteristics of FOG temperature experiments are developed at first. Then the adaptive FLP denoising algorithm is employed to eliminate the noise aiming at reducing noise interference. After that, a simple modeling concept of building the compensation model between temperature drift and ambient temperature change rate is first to be given (we have not found a report of better results in any literature). The semiphysical simulation results show that the proposed method significantly reduces the noise and drift caused by intense ambient temperature variation.     

Optimum refractive-index profile of the graded-index polymer optical fiber, toward gigabit data links

The optimum refractive-index distribution of the high-bandwidth graded-index polymer optical fiber (POP) was clarified for the first time by consideration of both modal and material dispersions. The ultimate bandwidth achieved by the POP is investigated by a quantitative estimation of the material dispersion as well as the modal dispersion. The results indicate that even if the refractive-index distribution is tightly controlled, the bandwidth of the graded-index POP is dominated by the material dispersion when the required bit rate becomes larger than a few gigabits per second. It is also confirmed that the material dispersion strongly depends on the matrix polymer and that the use of a fluorinated polymer whose material dispersion [-0.078 ns/(nm km)] is lower than that of poly(methyl methacrylate) [-0.305 ns/(nm km)] allows for a 10-Gb/s signal transmission.     

Imaging of the optic disc and retinal nerve fiber layer: the effects of age, optic disc area, refractive error, and gender.

We cross-sectionally examined the relationship between age, optic disc area, refraction, and gender and optic disc topography and retinal nerve fiber layer (RNFL) measurements, using optical imaging techniques. One eye from each of 155 Caucasian subjects (age range 23.0-80.8 y) without ocular pathology was included. Measurements were obtained by using the Heidelberg Retina Tomography (HRT), the GDx Nerve Fiber Analyzer, and the Optical Coherence Tomograph (OCT). The effects of age were small (R2 < 17%) and were limited to specific HRT, GDx, and OCT parameters. Disc area was significantly associated with most HRT parameters and isolated GDx and OCT parameters. Refraction and gender were not significantly associated with any optic disc or RNFL parameters. Although effects of age on the optic disc and RNFL are small, they should be considered in monitoring ocular disease. Optic disc area should be considered when cross-sectionally evaluating disc topography and, to a lesser extent, RNFL thickness.     

光纤耦合问题的研究及球形端面光纤的应用

介绍了光源与光纤耦合的几种方法以及球形光纤的制作方法，采用射线理论分析了圆球形端面多模光纤的端面效应，给出了半导体激光器（LD）与圆球形端面光纤耦合的应用实例。实验结果表明该方法结构简单、调整方便，有实际应用的潜力。     

Differential group delay prediction in optical fiber links

We simulate the time evolution of differential group delay (DGD) in a fiber link in the hinge model with time series forecasting procedures, in particular, autoregressive (AR) models with Kalman filter, pattern imitation, and a Taylor expansion. In these studies, the furthest prediction horizon was attained with the AR accompanied by the Kalman filter procedure. We further discuss the influence of measurement noise on the prediction horizon. We also apply these methods to the measured DGD on 40 Gb/s fiber links and discuss the results.     

Aircraft crew radiation workplaces: comparison of measured and calculated ambient dose equivalent rate data using the EURADOS in-flight radiation data base

In May 2000, the chairman of the European Radiation Dosimetry Group (EURADOS) invited a number of experts with experience of cosmic radiation dosimetry to form a working group (WG 5) on aircraft crew dosimetry. Three observers from the Article 31 Group of Experts as well as one observer from the Joint Aviation Authorities (JAA) were also appointed. The European Commission funded the meetings. Full meetings were organised in January 2001 and in November 2001. An editorial group, who are the authors of this publication, started late in 2002 to finalise a draft report, which was submitted to the Article 31 Group of Experts in June 2003. The methods and data reported are the product of the work of 26 research institutes from the EU, USA and Canada. Some of the work was supported by contracts with the European Commission, Directorate General XII, Science, Research and Development. A first overview of the EC report was published late in 2004. In this publication we focus on a comparison of measured and calculated ambient dose rate data using the EURADOS In-Flight Data Base. The evaluation of results obtained by different methods and groups, and comparison of measurement results and the results of calculations were performed in terms of the operational quantity ambient dose equivalent, H*(10). Aspects of measurement uncertainty are reported also. The paper discusses the estimation of annual doses for given flight hours and gives an outline of further research needed in the field of aircraft crew dosimetry, such as the influence of solar particle events.     

Pupil-size effects in fiber optic stellar interferometry.

The effects of finite telescope pupil sizes on the measurement of fringe visibility in fiber optic stellar interferometry are described. It is shown theoretically that the measured fringe visibility is equal to the cross correlation of the magnitude of the source's mutual coherence function with the cross correlation of the telescopes' effective pupil functions. If the telescopes' effective pupil diameters are not small compared with the width of the source's mutual coherence function, then the measured fringe visibility will be correspondingly distorted. The theoretical results are verified experimentally in a fiber optic Mach-Zehnder interferometer.     

Improvement of bit error rate and page alignment in the holographic data storage system by using the structural similarity method

Although widely recognized as a promising candidate for the next generation of data storage devices, holographic data storage systems (HDSS) incur adverse effects such as noise, misalignment, and aberration. Therefore, based on the structural similarity (SSIM) concept, this work presents a more accurate locating approach than the gray level weighting method (GLWM). Three case studies demonstrate the effectiveness of the proposed approach. Case 1 focuses on achieving a high performance of a Fourier lens in HDSS, Cases 2 and 3 replace the Fourier lens with a normal lens to decrease the quality of the HDSS, and Case 3 demonstrates the feasibility of a defocus system in the worst-case scenario. Moreover, the bit error rate (BER) is evaluated in several average matrices extended from the located position. Experimental results demonstrate that the proposed SSIM method renders a more accurate centering and a lower BER, lower BER of 2 dB than those of the GLWM in Cases 1 and 2, and BER of 1.5 dB in Case 3.     

Temperature error in radiation thermometry caused by emissivity and reflectance measurement error

A general expression for the temperature error caused by emissivity uncertainty is developed, and it is concluded that lower-wavelength systems provide significantly less temperature error. A technique to measure the normal emissivity is proposed that uses a normally incident light beam and an aperture to collect a portion of the energy reflected from the surface and to measure essentially both the specular component and the biangular reflectance at the edge of the aperture. The theoretical results show that the aperture size need not be substantial to provide reasonably low temperature errors for a broad class of materials and surface reflectance conditions.     

成组光纤水听器特性研究

成组光纤水听器具有能抑制流噪声、有指向性、灵敏度高等优点,可应用于全光拖曳阵.介绍了成组光纤水听器的概念,建立了其拾取水声信号的水声信号检测模型,理论分析了其灵敏度和指向性.完成了四子单元的芯轴型成组光纤水听器的光学设计和机械设计.在非消声水池中,采用脉冲法测定了其灵敏度和指向性.结果显示:此结构的成组光纤水听器灵敏度为-152dB(0dB=1rad/Pa),与理论值-151dB基本符合;当时,指向性函数主瓣宽度为28°,与理论值26°度基本吻合.     

Theoretical analysis of the membrane parameters of the fiber optic microphone

In the membrane displacement equation of fiber optic microphone, there are, beside the pressure, two kinds of parameters: membrane parameters and damping mechanism parameters. The first kind, which consists of the membrane radius, surface density and border tension, has an effect on the sensitivity and the acoustic frequency band (sonic and ultrasonic), whereas the second kind has almost no effect. The theoretical analysis of these parameters shows that some ultrasonic frequencies can cover a band close to 100 kHz, for a radius of 0.1 mm, with the increase of the sensitivity. This analysis provides a general approach useful to design a fiber optic microphone for a particular application.     

评价光纤水听器探头的性能参数

光纤水听器声学性能的准确评价一直是人们非常关心的问题。简要叙述了相位干涉型光纤水听器的工作原理,指出了光纤水听器探头和光纤水听器系统的区别。作为光纤水听器的关键技术之一,光纤水听器探头声学性能的测试还没有明确的规范或标准。为此,提出了有关评价光纤水听器探头声学性能的参数,如相移灵敏度、加速度相移灵敏度、相对加速度相移灵敏度、指向性、相移灵敏度随静水压的变化、相移灵敏度随温度的变化等的定义,并给出了相关的表达式,对准确测量和评价光纤水听器探头的声学性能有一定的借鉴意义。并希望通过这样的讨论,促进光纤水听器探头性能测试的规范和相关标准的制定。     

光纤隔离型存储测试技术研究

电热化学炮发射实验时存在强电磁干扰和地电位浮动问题,严重影响膛压数据的准确性和仪器的安全性.采用不同材料多层组合的屏蔽技术,有效地实现了强电磁环境下的电磁屏蔽,确保测试系统的安全性、可靠性和精度.利用存储测试技术和光纤通信,同时实现了膛压信号的存储测试和实时传输,保证了电热化学炮膛压信号获取的可靠性,并实现了双工通信,方便了电热化学炮的测试试验.     

Performance of 3 m fiber optic light guides

We describe the performance of 3 m long fiber optic light guides that we have fabricated as part of a search for the rare decay μ⁺ → e⁺ + γ at LAMPF. The acceptance cone of the light guides is narrow, leading to substantial ( ≈ 80%) light loss entering th guides. But those photons that do fall within the acceptance cone are transmitted long distances without significant further loss. We discuss our fabrication techniques and the results of both bench tests and in-beam tests of complete assemblies.