Because of the power imbalance between the two arms of an interferometer in an electro-optic modulator (EOM), the output of the EOM is combined amplitude modulation (AM) and phase modulation (PM) for the probe signal consisting of the pulse and the dc component. Because of this PM, the Brillouin gain-loss spectrum becomes asymmetric. The central Brillouin frequency is shifted from that of an AM pulse. The maximum extinction ratio of the EOM is limited to ∼29 dB for a power-splitting ratio of 51% to 49%. The asymmetric property induced by PM is not pulse shape dependent; for both Gaussian- and super-Gaussian-shaped pulses the Brillouin loss spectrum is symmetric for AM and asymmetric for combined AM and PM (power imbalance).
© 2005 Optical Society of America
(060.2310) Fiber optics and optical communications : Fiber optics
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(190.5890) Nonlinear optics : Scattering, stimulated
(290.5830) Scattering : Scattering, Brillouin
(290.5900) Scattering : Scattering, stimulated Brillouin
Xiaoyi Bao, Yidun Wan, Lufan Zou, and Liang Chen, "Effect of optical phase on a distributed Brillouin sensor at centimeter spatial resolution," Opt. Lett. 30, 827-829 (2005)