A direct-detecting COTDR based on wavelet smoothing DSP technique

Coherent optical time-domain reflectometer (COTDR) has shown high sensing resolution, but it is sensitive to noise, polarization and frequency shift. Wavelet smoothing DSP (Digital Signal Processing), combined with direct-detecting method and precise optical frequency shift controlled by microwave electro-optical modulation, is proposed for improving the performance of COTDR. A resolution of 0.1°C can be obtained in a 4.5-km-long fiber and a 25-km-long fiber. Besides that, the signals' correlation keeps longer than 10 minutes in the 4.5-km-long fiber.