Narrowing Spectral Linewidth in Brillouin Optical Time Domain Analyzers With Adjustable Spatial Resolution

In order to both adjust the spatial resolution (SR) and narrow the Brillouin gain spectrum (BGS) linewidth in Brillouin optical time domain analysis system, a novel scheme based on differential pulse pair technique is proposed. By designing the phase and amplitude of the pulse properly, the higher peak gain and narrower linewidth of BGS are achieved compared to the conventional single pulse scheme with same SR. The pulse parameters for different SR are analytically solved and the performances of the sensor are theoretically and experimentally studied. Experimental results show that the linewidth of BGS is narrowed to 19 and 22 MHz in the case of 2 m SR and 1 m SR, which indicates 2.3 times and 4.3 times frequency accuracy improvements are achieved, respectively. Furthermore, the advantages of our proposal for small Brillouin frequency shift change are also investigated.