Intensity transmitted by a Fabry-Perot etalon with another internal Fabry-Perot interferometer

The intensity transmitted by a device made up of a F.P. etalon that contains another internal tunable F.P. has been studied. The theoretical predictions about the wavelengths of the intensity transmission maxima of the device are derived as functions of the optical path length of the internal F.P. An experimental check of the theoretical predictions is also presented.