Fig. 1. Schematic diagram of condition monitoring structure for FOCT

Fig. 2. Display interfaces of the status parameters in the host computer

Fig. 3. Measuring device. (a) Integral structure; (b) 95∶5 coupler

Fig. 4. Measurement results of harmonic amplitude of each order

Fig. 5. Variation in amplitudes of the second and fourth harmonics with the power of the light source. (a) Harmonic amplitude; (b) harmonic amplitude ratio

Fig. 6. Mapping relation between the return signal and the modulated signal

Fig. 7. Variation in return signal with modulated signal

Fig. 8. Flowchart for fault diagnosis