Spatial Resolution Improvement in OFDR Using Four Wave Mixing and DSB-SC Modulation

Spatial resolution in optical frequency domain reflectometry (OFDR) is a function of frequency sweep span. In this letter, a new method to enhance OFDR spatial resolution is proposed, by increasing the applied sweep span. The proposed method uses degenerated four wave mixing (FWM) with only a single light source, and this results in a preserved coherence length. The double sideband with suppress carrier (DSB-SC) modulation is used to create two sidebands, with each sideband treated as a separate light source. It is demonstrated by means of experiments that the proposed method can increase the spatial resolution by three times. Furthermore, it is also confirmed that DSB-SC modulation and FWM can be used to cancel the laser phase noise in OFDR and detect break point beyond laser coherence length with three times higher spatial resolution.