A novel scheme is proposed to measure Brillouin gain spectrum in an optical fiber combining Brillouin gain and loss
effects. A dual-parallel Mach-Zehnder modulator is used to generate upshifted afterward downshifted single sideband
with suppressed carrier by periodically chopping the dc bias. The two successive single sidebands serve as Brillouin
pump and probe waves to amplify and absorb the carrier wave for lock-in detecting of the net Brillouin gain between
Brillouin gain and loss effects. The signal-to-noise ratio of the cost-effective measurement system with fewer optical
devices is twofold enhanced. Distributed strain sensing ability with a nominal spatial resolution of 1.6 cm is
experimentally demonstrated by utilization of this scheme into a Brillouin optical correlation domain analysis system.