A coherent optical time-domain reflectometer (COTDR) using flexible all-digital orthogonal phase code pulse is proposed for distributed acoustic sensing. All-digital orthogonal phase code pulse with frequency shift and time shift is used as probe. Coherent detection and balance photodetector are used to amplify interference signal and get rid of its direct-current (DC) component. The new scheme needs only single channel detection while keeping sampling frequency. Amplitude triangle modulation and frequency linear sweep modulation waveform are used for system performance investigation. The experiments on 15.4 km optical fiber showed that waveform information can be recovered well. The all-digital orthogonal phase code pulse will provide a flexible solution for different application requirement.
