Abstract
A time-division Brillouin optical correlation domain analysis system was successfully achieved using simplified laser diode (LD) modulation and pump lightwave optimization. A complicated transfer function for a precise output waveform of a LD was required for the conventional system. However, a very simple modulation function gave a power output very close to a required ideal rectangle waveform without sacrificing optical output spectrum. An electrical input waveform applied into a gate in the pump lightwave path was also optimized for eliminating a probe lightwave included in a pump lightwave and for passing consecutive pump pulses alternatively. So the stimulated Brillouin scattering gain was attained without seriously distorting FM modulation, and the targeted spatial resolution was clearly accomplished. Additionally, using high speed response of a semiconductor optical amplifier (SOA), unlike an erbium-doped fiber amplifier (EDFA), the possibility was investigated that an SOA was going to replace an EDFA and a modulator used as a gate in the same time.
Highlights
Optical fiber sensors using Brillouin scattering have become effective tools for distributed measurement sensing strain or temperature in construction materials and structures
The possibility was investigated for further system simplification that a single semiconductor optical amplifier (SOA) was going to replace an erbium-doped fiber amplifier (EDFA) and a modulator used as a gate together
Two modulation frequencies of 20 MHz and 50 kHz were simultaneously applied to a DFB laser diode (LD), the former for correlating probe and pump lightwaves, and the latter for generating the two time-divided lightwaves
Summary
Optical fiber sensors using Brillouin scattering have become effective tools for distributed measurement sensing strain or temperature in construction materials and structures. This technology made it possible to measure longer than a 10-km optical fiber.[4,5] Due to the finite time required for the acoustic wave to be excited by the interaction of pulse pump and continuous probe, the spatial resolution of the conventional BOTDA systems is known to be limited to ∼1 m.
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