Polarization-maintaining fibers and their applications are reviewed. The classification of high-birefringent fibers and low-birefringent fibers and their fabrication methods and characteristics are discussed in Section II. Analytical methods and numerical methods for fiber design on the birefringence are presented in Section III. Degradation factors of polarization maintenance expressed as crosstalk or mode-coupling parameters caused by internal origins such as structural imperfections, wavelength, and nonlinear effects, and by external origins such as temperature fluctuations, mechanical perturbations, and electromagnetic effects, are discussed in Section IV. Characterization methods on beat length, mode coupling, stress distribution, and mechanical strength are presented in Section V. Applications to the fiber devices and nonlinear effects, and splicing methods for the polarization-maintaining fibers are described in Sections VI and VII.

Polarization-maintaining fibers and their applications

This paper aims to examine the sustainability and environmental performance of PV-based electricity generation systems by conducting a thorough review of the life cycle assessment (LCA) studies of five common photovoltaic (PV) systems, i.e., mono-crystalline (mono-Si), multi-crystalline (multi-Si), amorphous silicon (a-Si), CdTe thin film (CdTe) and CIS thin film (CIS), and some advanced PV systems. The results show that, among the five common PV systems, the CdTe PV system presents the best environmental performance in terms of energy payback time (EPBT) and greenhouse gases (GHG) emission rate due to its low life-cycle energy requirement and relatively high conversion efficiency. Meanwhile, the mono-Si PV system demonstrates the worst because of its high energy intensity during the solar cells’ production process. The EPBT and GHG emission rate of thin film PV systems are within the range of 0.75–3.5 years and 10.5–50 g CO 2 -eq./kW h, respectively. In general, the EPBT of mono-Si PV systems range from 1.7 to 2.7 years with GHG emission rate from 29 to 45 g CO 2 -eq./kW h, which is an order of magnitude smaller than that of fossil-based electricity. This paper also reviews the EPBT and GHG emission rates of some advanced PV systems, such as high-concentration, heterojunction and dye-sensitized technologies. The EBPT of high-concentration PV system is lower, ranging from 0.7 to 2.0 years, but the CO 2 emission rate of dye-sensitized PV system is higher than the ones of other PV systems at the moment. The LCA results show that PV technologies are already proved to be very sustainable and environmental-friendly in the state of the art. With the emerging of new manufacturing technologies, the environmental performance of PV technologies is expected to be further improved in the near future. In addition, considering the existing limitations in the previous LCA studies, a few suggestions are recommended.

Review on life cycle assessment of energy payback and greenhouse gas emission of solar photovoltaic systems

Photovoltaic (PV) technologies have shown remarkable progress recently in terms of annual production capacity and life cycle environmental performances, which necessitate timely updates of environmental indicators. Based on PV production data of 2004-2006, this study presents the life-cycle greenhouse gas emissions, criteria pollutant emissions, and heavy metal emissions from four types of major commercial PV systems: multicrystalline silicon, monocrystalline silicon, ribbon silicon, and thin-film cadmium telluride. Life-cycle emissions were determined by employing average electricity mixtures in Europe and the United States during the materials and module production for each PV system. Among the current vintage of PV technologies, thin-film cadmium telluride (CdTe) PV emits the least amount of harmful air emissions as it requires the least amount of energy during the module production. However, the differences in the emissions between different PV technologies are very small in comparison to the emissions from conventional energy technologies that PV could displace. As a part of prospective analysis, the effect of PV breeder was investigated. Overall, all PV technologies generate far less life-cycle air emissions per GWh than conventional fossil-fuel-based electricity generation technologies. At least 89% of air emissions associated with electricity generation could be prevented if electricity from photovoltaics displaces electricity from the grid.

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Emissions from photovoltaic life cycles

Origins and control of polarization effects in single-mode fibers (A)

Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.

Polarization in optical fibers

A number of applications require single-mode optical fi­ bers in which the state of polarization of the guided light is sustained. The solid-core optical fibers described in the literature generally exhibit strong birefringence and also usually have a depolarizing effect. In this Letter we describe experiments on single-mode fi­ bers that were prepared under carefully controlled conditions and studied for their polarization behavior. The most fa­ vorable results were noted for fibers prepared by chemical vapor deposition (CVD). First, a Si02-B2O3 glass was de­ posited from the gas phase as cladding on the inside wall of a fused-silica tube, followed by pure quartz glass as the core material. The tube was then collapsed into a rod by raising the temperature and thereafter drawn into a fiber. Directly after leaving the furnace, the fiber was coated with silicon resin. Through precise control of the various step of the process, especially during the collapsing of the tube, a circular cross section in preform and fiber were realized. Figure 1 shows a transmission micrograph of a cross section of the preform. A comparison of round and oval fibers made of glass of the same composition showed a circularly symmetrical cross

Low-birefringence single-mode optical fibers: preparation and polarization characteristics.

The generation of electricity with solar cells is considered to be one of the key technologies of the new century. Over the past ten years the photovoltaic (PV) industry has grown by more than a factor of five to approximately 200 MWp in the year 2000. This impressive growth is mainly based on solar cells made from crystalline silicon. One of the key factors for this growth has been the supply of economically priced silicon from the semiconductor industry. This paper gives an overview on the current silicon feedstock supply and outlines a supply and demand scenario for the next five years. The importance of better silicon utilization per Wp module power through thinner Si wafers and higher solar cell efficiency is stressed. The impact of a growing thin-film technology on the silicon feedstock demand is considered as well. Copyright © 2002 John Wiley & Sons, Ltd.

Crystalline silicon feedstock for solar cells

The present invention is directed to an improvement in a magneto-optical device having a light waveguide for conducting light characterized by the light waveguide being a cladded optical fiber having a core of quartz glass and a cladding of synthetic material. This improvement provides an improved method of using the magneto-optical device by suppressing distortions of polarized light by reducing birefringence in the waveguide by using a waveguide comprising an optical fiber having a quartz glass core and a cladding of synthetic material.

Waveguides with a low birefringence

An optical unit having at least one longitudinal side coupling zone characterized by the unit comprising at least one glass fiber having a glass core with a glass cladding layer surrounding the core with a step in the index of refraction from a greater to a lower value occurring at the junction between the glass core and cladding layer, the cross section of the glass fiber remaining uniform along the entire length and the core having at least one constriction to form the longitudinal coupling zone. To form the optical unit, a device utilizing a double crucible with a nozzle opening of the inner crucible being arranged to discharge into the nozzle opening of the outer crucible and provided with a means for regulating the flow therethrough is utilized. If the unit includes a plurality of optical fibers, these fibers may be individually formed and held together by an adhesive, the cladding of the fiber may be fused together or the unit may be formed jointly by utilizing a crucible having a plurality of nozzle openings for the inner crucible so that a continuous cladding layer is disposed around a plurality of cores.

Optical unit having a longitudinal side coupling zone

In this second part, the most important components of a magnetooptical current transformer are described and their suitability is discussed Today He–Ne gas lasers and laser diodes seem to meet best the requirements of the light source Single-mode optical fibers are capable of transmitting polarized light without depolarization A fiber coil wound on a special coil former is used as a measuring sensor Two P-I-N photodiodes, together with an analog electronic circuit, transform the optical into an electrical measuring signal

Hubert Aulich

Papers

Low-birefringence single-mode optical fibers: preparation and polarization characteristics.

Crystalline silicon feedstock for solar cells

Waveguides with a low birefringence

Optical unit having a longitudinal side coupling zone

Magnetooptical current transformer. 2: Components.