A compact retro-reflective module for use in electro-optical bar code readers includes components arranged to fold outgoing and incoming light along crossed optical paths. The auxiliary substance has a stabilizing action. Because of its optical properties, the display can also be attached, for example, on the curved exterior of the microscope body or also on an X-Y coupling that may be present. The LiNbO3 phase modulator imprints an RF signal onto one path of the MZM cavity, while the fiber wrapped PZT is used to control the path length difference between the two optical paths. 1 m100 m, such that when air passes through the filtering member, it is purified by the released negative ions and becomes oxygen-rich air for use in the combustion chambers of gasoline or diesel engines.