Abstract: Device for stabilizing the wavelength in air of a laser diode for an Interferometer which measures length in waveguide technology. To stablize the wavelength in air, an interference phenomenon, according to Young, is produced and detected in an air chamber of constant and stable length with two point-shaped light waves of a coherent beam. The point-shaped light waves are formed by the ends of waveguides. The photo-detectors and the control device control the frequency of the laser diode so that the interference phenomenon, and therefore the wavelength in air, remain stable inside the reference chamber. The arrangement is simple and compact.