Abstract: A packer system for a wellbore includes a tubular member and a packer element having an inner layer that circumferentially overlies the tubular member and an outer layer that circumferentially overlies the inner layer. The inner layer includes an elastomer that swells upon contact with a swelling fluid. The outer layer includes a material that provides at least a partial barrier to the swelling fluid.

Abstract: The invention is directed to a method for determining the refractive index (n) of a substance wherein monochromatic light is conducted to a single-mode wave guide integrated into a substrate. The wave guide is brought into contact with the substance to be measured along a segment of predetermined length. In this way, the effective refractive index in this segment of the wave guide is changed. This effect is utilized for measuring the refractive index of the measured substance. The change of the effective refractive index causes a phase displacement of the light travelling through this measuring segment. This phase displacement is measured as a phase difference to a light component not influenced by the measuring substance. This measurement is preferably made interferometrically.