Abstract: detailed survey of fibre optic pH sensors is made which illustrates and compares the mechanisms and advantages of three types of fibre optic pH sensors:optic absorption,fluores- cent characteristics and refraction index fluctuation. The application perspective of fibre optic pH sensors in on-line pH measurement for industrial process control and in biology,medical and physiology fields is also discussed.

Key words: pH, optical measuring instruments, sensors, fluorescence, refraction index