This paper presents new developments of the BNM-INM heterodyne compact refractometer. Air refractive index measurements have been made at 633 nm with a relative uncertainty of 10−8 and the realization of a new type of wavelength stabilized laser source has been demonstrated at 633 nm. We now have adapted this source to a commercial interferometric system working at 633 nm. Length variation measurements in air have been made. Results show that the wavelength of our source is insensitive to slow variations of the refractive index of air at a level of 10−8, demonstrating the possibility to make distance measurements in air without the need to make any index correction.