New optical cell design for pollutant detection

Abstract

A new and simple optical gas cell, developed to perform as the transducer for a methane fiber optic sensor, is presented. Its main advantage lies in the fact that, employing low-cost components and an easy alignment process, the path where the light beam is in contact with the pollutant becomes maximized to as much as four times the physical length of the optical cell. This increment in optical length is directly related to the optimization of the fiber optic sensor since low levels of methane concentration can be measured as stated by Beer-Lambert's law. One of the main advantages of this design lies in the simplicity of the optic cell, which makes it very interesting when one has to deal with the manufacturing process. The cell is mounted on a reflective configuration which improves the connection as only one optical fiber is employed. The main elements of the cell are an optical fiber, a mirror of high reflectivity and a converging lens arranged in an appropriate fashion to obtain the desired result. With this relatively reduced and low cost set of devices the insertion losses achieved are in the range of the 4-5 dB's.