A two-wavelength interferometer for space applications

We present a two wavelength interferometer that we have developed and characterized for space applications. It is based on the synthetic wavelength technique together with a super-heterodyne detection scheme. This set-up has all the optoelectronic components in fiber. The synthetic wavelength is generated by superposing two fiber-coupled external cavity diode lasers and can be changed with continuity by tuning the laser frequency without mode-jumps, ranging from 7.5 mm to a long enough value to solve the phase ambiguity. We have characterized the system in air in our laboratory and outdoor up to a distance of 137 m. Using a synthetic wavelength of 15 mm the interferometer has a resolution of 7 nm/√Hz and an Allan deviation of tens of micrometers at 10 s. Due to its compactness and simplicity it could be used for surveying applications.