A versatile twisted optical fiber sensor

An optical sensor sensitive to changes in light absorption and other optical interactions, and consisting of two fibers twisted around each other, is described. The sensor can be used as a refractometer, is very sensitive to the presence of water in oil, can be used to determine the amount of a solvent in oil, and might be useful in monitoring degradation of internal combustion engine oil. In addition, by surrounding the fibers with a film of solution, and observing the changes in ouput over time, additional information can be obtained. Used in this manner, the sensor can be used to identify specific solutions.