Temperature and Strain Sensitivity Measurements of High-Birefringent Polarization-Maintaining Fibers

The strain and temperature sensitivities of three common commercial high-birefringent polarization maintaining fibers (bow-tie, polarization-maintaining and absorption-reducing, and elliptical core fibers) have been measured by using a dynamic polarimetric method. The experimental setup and measuring process are described in detail. Where possible, the measuring data are compared with published data, and good agreement is obtained

Temperature and Strain Sensitivities of High-Birefringence Elliptical Fibers

We have analyzed and calculated the temperature and strain sensitivities of a high-birefringence double-clad elliptical fiber. We propose a method to minimize these sensitivities without increasing the fiber size or weight; this is achieved by selecting suitable fiber parameters—core ellipticity, refractive index difference, and thickness of the inner cladding. In addition, we discuss the design of temperature- or strain-insensitive fibers which may be used in polarimetric strain or temperature sensors. This method may also be used to minimize or enhance other external effects

Polarization Characteristics of Double-Clad Elliptical Fibers

A scalar variational analysis based on a Gaussian approximation of the fundamental mode of a double-clad elliptical fiber with a depressed inner cladding is studied. The polarization properties and graphic results are presented; they are given in terms of three parameters: the ratio of the major axis to the minor axis of the core, the ratio of the inner cladding major axis to the core major axis, and the difference between the core index and the inner cladding index. The variations of both the spot size and the field intensity with core ellipticity are examined. It is shown that high birefringence and dispersion-free orthogonal polarization modes can be obtained within the single-mode region and that the field intensity distribution may be more confined to the fiber center than in a single-clad elliptical fiber

Minimization of Temperature Effects of High-Birefringent Elliptical Fibers for Polarmetric Optical-Fiber Sensors

The temperature dependence of polarization-maintaining fibers is a problem in polarimetric optical-fiber sensors. We report a novel method for making a temperature-insensitive, polarization-maintaining fiber, which may be used for the sensing part in a polarimetric strain sensor. The fiber has a double-clad elliptical core with built-in stresses in the core and cladding regions. To minimize the temperature sensitivity, the built-in stresses are balanced with the refractive-index differences and the core ellipticity properly chosen. The temperature and strain sensitivities of the fiber are calculated. A practical design and some potential applications of such a temperature-insensitive fiber with a high strain sensitivity are presented

Maternal Employment and Childhood Obesity: A Search for Mechanisms in Time Use Data

Recent research has found that maternal employment is associated with an increased risk of childhood obesity. This paper explores mechanisms for that correlation. We estimate models of instrumental variables using a unique dataset, the American Time Use Survey, that measure the effect of maternal employment on the mother’s allocation of time to activities related to child diet and physical activity. We find that employed women spend significantly less time cooking, eating with their children, and playing with their children, and are more likely to purchase prepared foods. We find suggestive evidence that these decreases in time are only partly offset by husbands and partners. These findings offer plausible mechanisms for the association of maternal employment with childhood obesity.

Mechanisms for the Association Between Maternal Employment and Child Cognitive Development

Recent research has found that maternal employment is associated with worse child performance on tests of cognitive ability. This paper explores mechanisms for that correlation. We estimate models of instrumental variables using a unique dataset, the American Time Use Survey, that measure the effect of maternal employment on the mother's allocation of time to activities related to child cognitive development. We find that employed women spend significantly less time reading to their children, helping with homework, and in educational activities in general. We find no evidence that these decreases in time are offset by increases in time by husbands and partners. These findings offer plausible mechanisms for the association of maternal employment with child cognitive development.