  Monitoring the optical phase change in a fiber enables a wide range of
applications where fast phase variations are induced by acoustic signals or
vibrations in general. However, the quality of the estimated fiber response
strongly depends on the method used to modulate the light sent to the fiber and
capture the variations of the optical field. In this paper, we show that
distributed optical fiber sensing systems can advantageously exploit techniques
from the telecommunication domain, as those used in coherent optical
transmission, to enhance their performance in detecting mechanical events,
while jointly offering a simpler setup than widespread pulse-cloning or
spectral-sweep based schemes with acousto-optic modulators. We periodically
capture an overall fiber Jones matrix estimate thanks to a novel probing
technique using two mutually orthogonal complementary (Golay) pairs of binary
sequences applied simultaneously in phase and quadrature on two orthogonal
polarization states. A perfect channel response estimation of the sensor array
is achieved, subject to conditions detailed in the paper, thus enhancing the
sensitivity and bandwidth of coherent phase-OTDR systems. High sensitivity,
linear response, and bandwidth coverage up to 18 kHz are demonstrated with a
sensor array composed of 10 fiber Bragg gratings (FBGs).

Signal Processing