Dual-sweep frequency scanning interferometry using four wave mixing

Frequency scanning interferometry is a well-known technique to measure the distance to a reflecting target. However, variations in the optical path length during the finite measurement time severely limit the applicability of the method in real-world environments. By the use of a second swept source measurements become immune to these variations. The use of a second source implies a great increase in costs and complexity. In this letter, we explore the possibility of using four wave mixing for the generation of the secondary swept frequency source. This greatly reduces the increase in costs and solves the synchronization issues often encountered by dual laser systems. A prototype has been built and tested against induced variations in the optical path length, proving the ability of the technique to improve distance measurements in industrial environments.