Technical University of Graz 1 article published in JoVE Engineering Fabrication of a Low-Cost, Fiber-Coupled, and Air-Spaced Fabry-Pérot Etalon Manuel Tanzer1, Benjamin Lang1, Alexander Bergmann1 1Institute of Electrical Measurement and Sensor Systems, Technical University of Graz This protocol describes the construction of a low-cost, discrete, fiber-coupled, and air-spaced Fabry-Perot etalon with various applications, such as in trace-gas spectroscopy. The fabrication is possible in any facility with standard optical laboratory equipment available.