KEYWORDS: Spatial resolution, Sensors, Signal to noise ratio, Sensing systems, Signal detection, Single mode fibers, Signal processing, Sun, Time metrology, Continuous wave operation
A Brillouin optical time-domain analysis (BOTDA) sensor that combines the conventional complementary coding with the pulse prepump technique for high-accuracy and long-range distributed sensing is implemented and analyzed. The employment of the complementary coding provides an enhanced signal-to-noise ratio (SNR) of the sensing system and an extended sensing distance, and the measurement time is also reduced compared with a BOTDA sensor using linear coding. The combination of pulse prepump technique enables the establishment of a preactivated acoustic field in each pump pulse of the complementary codeword, which ensures measurements of high spatial resolution and high frequency accuracy. The feasibility of the prepumped complementary coding is analyzed theoretically and experimentally. The experiments are carried out beyond 50-km single-mode fiber, and experimental results show the capabilities of the proposed scheme to achieve 1-m spatial resolution with temperature and strain resolutions equal to ∼1.6°C and ∼32 μϵ, and 2-m spatial resolution with temperature and strain resolutions equal to ∼0.3°C and ∼6 μϵ, respectively. A longer sensing distance with the same spatial resolution and measurement accuracy can be achieved through increasing the code length of the prepumped complementary code.
We report for the first time a unique multi-parameter optical fiber sensor based on the stimulated scattering of higher order acoustic modes of Orbital Angular Momentum (OAM) guiding fiber. Both optical modes and acoustic modes guided within the core region of OAM fiber are characterized and demonstrated theoretically and experimentally. Simulation analysis shows that the multi-peak feature in the Brillouin gain spectrum (BGS) of OAM fiber is attributed to the couplings among the guided optical modes and higher-order acoustic modes. The frequency shifts of first two Brillouin peaks are successfully monitored to discriminate the temperature and strain with an accuracy of 0.21oC and 4.6με.
We present a new approach to characterize dispersion of group birefringence in a long polarization-maintaining fiber (PMF). Two sinusoidal optical signals are respectively launched into fast and slow axes of a PMF under test. Wavelength dependent group-delay difference between two sinusoidal optical signals induced by group birefringence in the PMF is measured using a Kerr phase-interrogator, and dispersion of group birefringence is characterized from the group-delay difference. Measurements of wavelength dependent group birefringence and group birefringence dispersion for a 459.4-m Panda PMF are experimentally demonstrated.
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