  Fiber-delay measurement is one of the key fundamental technologies in
numerous fields. Here we propose and experimentally demonstrate a
high-precision and concise optical time delay measurement system based on the
technique of linear optical sampling, reaching the precision better than 100 fs
under averaging. The use of only two optical frequency combs without locking
the carrier-envelope-offset frequency greatly simplifies the structure of the
time-delay measurement system. We also experimentally investigate the current
limitations on the precision of the system. The timing jitter noises of two
sources are mainly non-common mode, and are both restricted to the frequency
sources. Our results indicate that the proposed device can measure fiber length
fluctuations below 10 $\mu {\rm{m}}$, paving the way for further analyses of
the external disturbances on the fiber link.
