Inventors from the University of Illinois have developed novel phase-separated optical fibers for use in a distributed sensor. These phase-separated optical fibers have high loss (0.05 to 5 dB/m @ 1550 nm) when compared with conventional optical fibers, and the loss dominated by Rayleigh scattering. Moreover, these phase separated fibers are produced through a molten core method (MCM) which makes the cost of production relatively low when compared with conventional fibers. When employed in a Rayleigh based distributed sensor these phase-separated optical fibers provide short-range sensitivity that is orders of magnitude greater than conventional fibers.