Study on absolute distance measurement based on a mode-locked erbium-doped fiber laser

The absolute distance measurement system based on phase shift and synthetic wavelength is developed. The repetition frequency of 250 MHz and corresponding forth harmonic frequency of a mode-locked erbium-doped fiber laser are used in measurement. The synthetic wavelength in introduced to enlarge the measuring ambiguity range of the system. Moreover, the repetition frequency is modulated by an acoustic optical modulator so that the large-scale and high-precision measurement is realized. The experimental results show the proposed system owns a micro-grade measurement uncertainty in a range up to 100 m. The difference between the measurement and actual distance agrees well.