Analysis of backscatter waveforms from single-mode fibres

Backscatter measurements have been made on single-mode fibres with high precision and good spatial resolution. Apparent changes in local attenuation are revealed which occur over short fibre lengths and result from backscatter factor variations. The latter are compared to known fluctuations in fibre parameters. It is found that the backscatter signal is less sensitive to diameter variations in single-mode fibres than in multimode fibres. Longitudinal variations of numerical aperture, scattering loss coefficient or core radius preclude an accurate determination of local attenuation derived from backscatter measurements made at one end only of the fibre

Remote measurement of temperature distribution using an optical fibre

A new fibre sensor which measures temperature-distribution is proposed. The sensor uses optical-time-domain reflectometry to determine temperature-induced changes in the levels of the backscatter signal. Experiments using liquid-core fibres have demonstrated a sensitivity of 0.018 dBk over distances of more than 100m. The proposed sensor is able to monitor the temperature of over 100 points simultaneously. Solid core fibres have also been used; they exhibit a wide temperature range, but somewhat reduced sensitivity

Long-range single-mode OTDR, ultimate performance and potential uses

A high-performance single-mode optical time-domain reflectometer (OTDR) is described. Dynamic ranges of 30dB and 41dB one-way are achieved using laser diode and Nd:YAG laser sources respectively. A new OTDR technique allows absolute splice-loss measurements as well as active splice alignment to be performed from one cable end only

A fibre-optic temperature-distribution sensor

The development of all-optical fibre-sensors for monitoring a wide range of physical parameters is currently of considerably interest. It is attractive to consider an optical measurement of temperature, pressure, strain and vibration at a remote location situated in a hazardous environment or which suffers from severe electrical interference. In many cases it is desirable to determine the spatial distribution of the sensed quantity. For example, in certain applications it is necessary to monitor the variation of temperature within a machine, pipe or oven, or within a reservoir

Comparison of measured and predicted bandwidth of graded-index multimode fibres

Measurements of pulse spreading in three graded index fibers have been performed over an extensive range of wavelengths, including regions in which the index profiles become optimal and the bandwidths correspondingly high. The refractive index distributions and profile dispersion parameter have been measured and used in a ray-tracing algorithm in order to predict bandwidths. Comparison reveals that averaging processes on the index data are usually necessary to account for noncircularity of the fiber and small variations in the deduced profile caused by the wavelength dependence of the near-field intensity distribution. Results obtained by this means usually tend to slightly underestimate the true fiber bandwidth, while alpha-profile predictions always result in overestimates by about one order of magnitude. Remaining discrepancies between measured and predicted bandwidths are attributed to small variations of the index profiles along the fiber length

Polarisation measurements on monomode fibres using optical time-domain reflectometry

The feasibility of polarisation optical time-domain reflectometry in single-mode fibres is demonstrated. Polarisation analysis of the backscattered light clearly shows the evolution of the state of polarisation in the fibre. It is further shown that the polarised nature of the scatter return from single-mode fibres can cause errors in conventional backscatter measurements

Polarisation optical-time-domain reflectometry : experimental results and application to loss and birefringence measurements in single-mode optical fibres

Optical time-domain reflectometry is now a well established means of examining the length-dependence of attenuation in multimode optical fibres. Theoretical work has shown that the technique is similarly applicable to monomode fibres and experimental results have lately appeared in the literature. It has recently been noted that in monomode fibres the scatter return contains additional information concerning the local state of polarisation (SOP) in the fibre, since at any point the scattered light mirrors the SOP at that position. A polarisation optical time-domain reflectometry technique (POTDR) has thus been proposed, in which the backscattered light is analysed by means of a polariser to reveal the variation of polarisation along a mononode fibre. Such a technique would be invaluable in the study of the properties of polarisation-maintaining fibres for sensor applications (e.g. gyroscopes, hydrophones) and of low-birefringence fibres for the Faraday Current Monitor and telecommunications. In the latter case, information could be obtained relating to the polarisation dispersion in the fibre and to the variation of the SOP with time, an effect which is expected to produce problems when interfacing to integrated-optics devices. We present here the first measurement to be made using POTDR. Our results clearly establish the feasibility of the technique and, furthermore, show that polarisation effects can cause substantial errors in conventional backscatter attenuation measurements on monomode fibres. Consequently, care must be taken to eliminate the polarisation sensitivity of the measurement and caution exercised in the interpretation of backscatter curves

Contrasts in Oxidative Potential and Other Particulate Matter Characteristics Collected Near Major Streets and Background Locations

Background: Measuring the oxidative potential of airborne particulate matter (PM) may provide a more health-based exposure measure by integrating various biologically relevant properties of PM into a single predictor of biological activity

Can We Identify Sources of Fine Particles Responsible for Exercise-Induced Ischemia on Days with Elevated Air Pollution? The ULTRA Study

Epidemiologic studies have shown that ambient particulate matter (PM) has adverse effects on cardiovascular health. Effective mitigation of the health effects requires identification of the most harmful PM sources. The objective of our study was to evaluate relative effects of fine PM [aerodynamic diameter ≤ 2.5 μm (PM(2.5))] from different sources on exercise-induced ischemia. We collected daily outdoor PM(2.5) samples between autumn 1998 and spring 1999 in Helsinki, Finland. The mass of PM(2.5) was apportioned between five sources. Forty-five elderly nonsmoking persons with stable coronary heart disease visited a clinic biweekly for submaximal exercise testing, during which the occurrence of ST segment depressions was recorded. Levels of PM(2.5) originating from local traffic and long-range transport were associated with ST segment depressions > 0.1 mV, with odds ratios at 2-day lag of 1.53 [95% confidence interval (CI), 1.19–1.97] and 1.11 (95% CI, 1.02–1.20) per 1 μg/m(3), respectively. In multipollutant models, where we used indicator elements for sources instead of source-specific PM(2.5), only absorbance (elemental carbon), an indicator of local traffic and other combustion, was associated with ST segment depressions. Our results suggest that the PM fraction originating from combustion processes, notably traffic, exacerbates ischemic heart diseases associated with PM mass

Associations between PM2.5 and Heart Rate Variability Are Modified by Particle Composition and Beta-Blocker Use in Patients with Coronary Heart Disease

BACKGROUND: It has been hypothesized that ambient particulate air pollution is able to modify the autonomic nervous control of the heart, measured as heart rate variability (HRV). Previously we reported heterogeneous associations between particulate matter with aerodynamic diameter < 2.5 mu m (PM2.5) and HRV across three study centers. OBJECTIVE: We evaluated whether exposure misclassification, effect modification by medication, or differences in particle composition could explain die inconsistencies. METHODS: Subjects with coronary heart disease visited clinics biweekly in Amsterdam, the Netherlands; Erfurt, Germany; and Helsinki, Finland for 6-8 months. The standard deviation (SD) of NN intervals on an electrocardiogram (ECG; SDNN) and high frequency (HF) power of HRV was measured with ambulatory ECG during paced breathing. Outdoor levels of PM2.5 were measured at a central site. In Amsterdam and Helsinki, indoor and personal PM2.5 were measured during the 24 hr preceding the clinic visit. PM2.5 was apportioned between sources using principal component analyses. We analyzed associations of indoor/personal PM2.5 elements of PM2.5 and source-specific PM2.5 With HRV using linear regression. RESULTS: Indoor and personal PM2.5 were not associated with HRV. Increased outdoor PM2.5 was associated with decreased SDNN and HF at lags of 2 and 3 days only among persons not using beta-blocker medication. Traffic-related PM2.5 was associated with decreased SDNN, and long-range transported PM2.5 with decreased SDNN and HF, most strongly among persons not using beta blockers. Indicators for PM2.5 from traffic and long-range transport were also associated with decreased HRV. CONCLUSIONS: Our results suggest that differences in the composition of particles, beta-blocker use, and obesity of study subjects may explain some inconsistencies among previous studies on HRV