Heterodyne detection applied to a fiber Bragg grating-based sensor using a directly modulated distributed feedback laser

The heterodyne detection technique is applied to a fiber Bragg grating (FBG)-based sensor. Specifically, a directly modulated distributed feedback laser array is used as a frequency scanning light source. Weak reflections from the FBG are recorded as a beat signal with a high signal-to-noise ratio using heterodyne detection. A reflection signal is clearly observed from the FBG with a reflectivity of 1% located at 60 km from the detection port.