Abstract: An electrically-tunable optical filter has an optical cavity that forms an absorption peak in light that is incident on the filter. The optical cavity includes a layer composed of a material with a high electro-optic coefficient so that the index of refraction of the layer changes in response to a voltage applied by a controller. By adjusting the voltage, the controller can control the index of refraction so that an absorption peak of the filter can be tuned as may be desired without having to alter the physical structure of the filter.

Abstract: A method and apparatus are provided for sensing the mass flow rate of a fluid flowing through a pipe. A light beam containing plural individual wavelengths is projected from one side of the pipe across the width of the pipe so as to pass through the fluid under test. Fiber optic couplers located at least two positions on the opposite side of the pipe are used to detect the light beam. A determination is then made of the relative strengths of the light beam for each wavelength at the at least two positions and based at least in part on these relative strengths, the mass flow rate of the fluid is determined.