A low loss stable Fabry-Perot etalon is disclosed. In the preferred embodiment the Fabry-Perot etalon comprises a housing made of a material with a low coefficient of thermal expansion, an optical fiber connected to the housing for providing an optical signal and a reflecting surface preferably being part of the housing for receiving the optical signal from the optical fiber. In the preferred embodiment, the reflecting surface reflects the received optical signal substantially back to the optical fiber. If desired, a tuning plate may be positioned in a cavity between the reflecting surface and the optical fiber. The tuning plate may be used for tuning the cavity between the reflecting surface and the optical fiber to a desired wavelength.
