A formal framework for scenario development in support of environmental decision-making

Scenarios are possible future states of the world that represent alternative plausible conditions under different assumptions. Often, scenarios are developed in a context relevant to stakeholders involved in their applications since the evaluation of scenario outcomes and implications can enhance decision-making activities. This paper reviews the state-of-the-art of scenario development and proposes a formal approach to scenario development in environmental decision-making. The discussion of current issues in scenario studies includes advantages and obstacles in utilizing a formal scenario development framework, and the different forms of uncertainty inherent in scenario development, as well as how they should be treated. An appendix for common scenario terminology has been attached for clarity. Major recommendations for future research in this area include proper consideration of uncertainty in scenario studies in particular in relation to stakeholder relevant information, construction of scenarios that are more diverse in nature, and sharing of information and resources among the scenario development research community.     

Microbend fiber-optic phase shifter

The use of spatially periodic microbend transducers to produce phase shift in single-mode fibers has been investigaed. Phase shift of32deg/mum²of transducer displacement per centimeter of trans-3.7deg/mum². cm for a 1023-μm peroid. Phase shifts as large as 560°/cm of transducer length were obtained with the shorter period transducer. These results are compared with predictions based on coupled-mode theory.     

Origins and control of polarization effects in single-mode fibers

The polarization state of light in single-mode fibers is very sensitive to any perturbation which is not symmetric about the fiber axis. While this is a source of noise, drift, or signal fading in some applications, it can also be exploited in novel guided-wave devices. The basic birefringences that couple the two modes and change the polarization state along the fiber are reviewed. The three cases of uniform, phase-matched, and random coupling are considered. Polarization preservation in both low- and high-birefringence fibers is achieved by reducing this coupling. In addition to polarization-state changes, bireftingent fibers can quickly reduce the polarization degree of nonmonochromatic light if both modes are excited, a characteristic that greatly simplifies evaluation of the degree of polarization preservation in these fibers. Current evaluations of the birefringence and the polarization-holding ability of state-of-the-art fibers are discussed, and it is concluded that fibers with good polarization-holding properties are becoming available.     

Asymmetric multimode couplers

An asymmetric multimode coupler consists of two dissimilar multimode fibers. A simple theoretical analysis of asymmetric multimode couplers that will enable couplers to be designed with specific performance parameters is presented. The theoretical predictions are compared with the measured behavior of specially fabricated couplers. A novel technique to determine the performance of a linear bus of identical asymmetric couplers from measurements on a single coupler is introduced     

Acousto-optic phase modulator for single-mode fibres

A compact fibre-optic phase modulator with a single-mode fibre positioned along the axis of a cylindrical PZT acoustic transducer is investigated. The fibre is bonded inside a glass capillary tube, which is in turn epoxied inside the transducing cylinder to give a solid, mechanically stable structure. The maximum sensitivity of the phase shifter is 0.058 rad/V cm at 6.02 MHz. No polarisation modulation is observed.     

Beamforming fibre optic sensor

An optical sensor using a twisted birefringent single mode fibre embedded in or cemented to the outside of a hollow cylinder is shown to exhibit an acoustic response which depends on the frequency and propagation angle of the incident wave. Experimental results verifying the predicted behaviour are reported.     

Polarization coupling in kinked single-mode fibers

When a fiber is stretched over a small ridge on a drum, the modifications of the distributions of curvature and of lateral force near the ridge induce extra birefringence in the fiber. Many such kinks, distributed randomly along a high-birefringence fiber, degrade the polarization-holding quality of the fiber. A theoretical analysis of these effects and pertinent experimental results are presented.     

Polarisation-holding in a high-birefringence fibre

The polarisation-holding ability of a 1 km length of high-birefringence fibre is reported. The fibre birefringence increases linearly with frequency and the polarisation-holding parameter h is independent of frequency with a value of 5.5 × 10?6 m?1, indicating average polarisation-holding to ?22 dB.     

Polarization properties of birefringent fibers with stress rods in the cladding

The polarization properties of fibers with high-expansion aluminum-doped stress rods in the cladding are described. Polarization beat lengths and polarization-holding parameters comparable to those of state-of-the-art high-birefringence fibers are obtained. The diameter of the outer cladding is not sufficient to provide optimum constraint on the stress rods. Increasing the diameter of this region should significantly reduce both the beat length and the polarization-holdingh- parameter. No anomalous behavior or thermal hysteresis is observed in the temperature dependence of the fiber birefringence below 600°C. Above 600°C, a permanent hysteresis which reduces the fiber birefringence is observed.     

Polarization holding in elliptical-core birefringent fibers

Polarization holding in high-birefringence elliptical-core fibers is evaluated for the fiber birefringence spatial frequency range 1.5 cm^-1< beta_{i} < 40cm^-1, corresponding to beat lengths from 1.6 mm to 4.2 cm. This range of spatial frequencies is spanned by making measurements with a broad-band light source on four fibers with different degrees of birefringence. In this way, the strength of the internal birefringence perturbations is mapped to give the first experimental measure of their power spectrum. It is shown that commonly available fiber jackets can significantly degrade the polarization holding. For low spatial frequencies, the strength of the perturbations decreases rapidly with increasing frequency, but this rate decreases by more than half over a one-and-a-half order of magnitude increase in spatial frequency. A possible origin of the perturbations is suggested and it is shown that the strength of these perturbations must be reduced if polarization holding to a very high degree is to be realized in elliptical-core fibers. Presently, internal perturbations limit the polarization holding to ≤ 14.4 dB over 1 km.