Improving accuracy of distance measurements based on an optoelectronic oscillator by measuring variation of fiber delay

The ultra-long optical fiber of an optoelectronic oscillator (OEO) and the high spectral purity of its high frequency oscillation signal open the possibility of high-accuracy distance measurements at a long range. However, the longer the fiber length in an OEO, the more prone the system is to surrounding disturbance, which in turn leads to fluctuation of the loop delay and a reduction in distance measurement accuracy. In this paper, an intensity modulated light signal is combined with the light signal of an OEO in terms of wavelength division multiplexing (WDM) and is propagated through the fiber. The phase shift has been measured in real time to compensate for variations in fiber delay. With this method, experimental results showed a standard deviation of 14.8 μm.