Distributed Brillouin sensing with sub-meter spatial resolution based on four-section pulse OM3G.3(OFC2013) Presenter: Heng Kong Date:

Outline Content Introduction Operation Principle Experimental results and discussion Conclusion Four-section pulse based Brillouin distributed fiber sensor sub-meter spatial resolution mitigate the secondary “echo” directly without extra measurement time and post-processing algorithm” State Key Laboratory of Information Photonics & Optical Communications (Beijing University of Posts and Telecommunications)

Background Rayleigh Scattering Raman Scattering Brillouin Scattering Fresnel Reflection Brillouin Scattering Spontaneous Brillouin Scattering Stimulated Brillouin Scattering

Introduction Distributed fiber sensors based on Brillouin optical time- domain analysis(BOTDA): ProblemsSolutionsDisadvantages Spatial resolution < 1m Pre-pulse, dark-pulse,π- phase-shift pulse Exits the secondary “echo” Secondary “echo”Differential pulse pair,π- phase-shift pulse pair The measurement time is twice longer Long measurement time Brillouin gain-profile tracing; deconvolution based method Need use post-processing algorithm

Operation Principle Fig.1. (a): dark pump pulse. T determines the spatial resolution; (b) four-section pump pulse. T1 determines the spatial resolution. (c) Probe traces vs. position. Blue trace: probe trace based on dark pulse technique; Red trace: probe trace based on four section pulse technique. Features: a)Higher spatial resolution than bright pulse; T determines the spatial resolution b)T1 acts as sensing pulse;T2 plays the role of mitigating the secondary “echo”; The longer T1, the longer T2 c)four-section pulse is better

Experimental results and discussion Fig. 2. Experimental setup. PC: polarization controller: EOM: electro-optic modulator; EDFA: Erbium-doped fiber amplifier; PD: photo-detector; PG: pulse generator. 25 ℃ GHz(10m) 70 ℃ GHz(50cm) 20dBm 1550nm 3kHz 1mW β:5ns,β’:10ns α:100mW β:1mW β’:120mW γ:100mW 50:50 700MHz 500MHz 1G/s

Experimental results and discussion Fig. 3. (a) The 3D-mapping of Brillouin gain versus both location and frequency shift with dark pulse based technique. (b) The 3D-mapping of Brillouin gain versus both location and frequency shift with four-section pulse based technique. Fig. 4. (a) Top view of 3D-mapping with dark pulse based technique. (b) Spectral gain curves at two typical locations with dark pulse based technique. (c) Top view of 3D-mapping with four-section pulse based technique. (d) Spectral gain curves at two typical locations with four-section pulse based technique. 观测到 BFS

Conclusion A novel Brillouin distributed fiber sensor based on four- section pulse: Theoretical analysis and experimental demonstration (10m long, 50cm spatial resolution) Mitigate the secondary “echo” phenomenon directly Hope it can help the development in future

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