Measurement of Brillouin gain spectrum with dual-frequency laser for optical fibre sensor

• Published in: Electronics letters 2020-06, Vol.56 (13), p.672-674
• Main Authors: Salhi, M, Kemlin, V, Faci, S, Baili, G, Khadour, A, Mostarshedi, S, Billabert, A.-L
• Format: Article
• Language: English
• Subjects: balanced detection technique; Brillouin backscattered spectrum; Brillouin frequency shift; Brillouin gain spectrum measurement; Brillouin spectra; Brillouin spectrum line‐width; coherent detection; cross‐polarised field; direct measurement; dual‐frequency solid‐state laser; Engineering Sciences; fibre optic sensors; high dynamic range measurements; low‐frequency benefits; measurement by laser beam; optical fibre sensor; Optics; photodetection; photodetectors; Photonic; Photonics; spectral line breadth; standard single‐mode fibre‐28; temperature coefficients
• ISSN: 0013-5194; 1350-911X; 1350-911X
• DOI: 10.1049/el.2019.4101

In this Letter, the authors present a first measurement of Brillouin gain spectrum with dual-frequency solid-state laser. This allows a coherent detection of the Brillouin backscattered spectrum in a frequency range below the hundreds of MHz by fine-tuning of the difference between the two cross-polarised fields emitted by the laser. The photodetection at low-frequency benefits from the balanced detection technique where high dynamic range measurements are largely available. The narrow line-width of the cross-polarised field permits also the direct measurement of the Brillouin spectrum line-width. The system is demonstrated by measuring the Brillouin frequency shift with temperature when standard single-mode fibre-28 (SMF-28) and large effective area fibre (LEAF) are fully heated. This gives temperature coefficients close to theoretical expectations with values of 1.16 MHz/°C for SMF-28 and 1.15 MHz/°C for LEAF.