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Absolute distance measurement (ADM) over a long range has been studiedintensely over the last several decades, due to its important applications inlarge-scale manufacturing and outer space explorations [1-5]. Traditionalabsolute distance measurements utilize detection of time-of-flight information,detection of phase shift, or a combination of the two [6-17]. In this paper, wepresent a novel scheme for high-precision ADM over a long range based onfrequency detection by using two optoelectronic oscillators (OEO) to convertdistance information to frequency information. By taking advantage ofaccumulative magnification theory, the absolute error of the measured distanceis magnified by about 2*10E5 times, which makes the precision of the measureddistance significantly improved. In our experiments, the maximum error is 1.5um at the emulated ~6 km distance, including the drift error of about 1 um inthe air path due to the change in environmental conditions. In addition, themeasurable distance using this scheme could be further extended. The highestrelative measurement precision is 2*10E10 in our current system while theactual relative measurement precision of our experimental system is limited bythe variation of atmospheric conditions and is about 4*10E9.

High-precision Absolute Distance Measurements over a Long Range Based on Two Optoelectronic Oscillators