Fiber Ring Laser Directional Torsion Sensor with Ultra-Wide Linear Response

• Main Authors: Xianjin Liu, Fengjuan Wang, Jiuru Yang, Xudong Zhang, Xiliang Du
• Format: Article
• Language: English
• Published: MDPI AG 2019-08-01
• Series: Sensors
• Subjects: fiber laser sensor; Sagnac interferometer; torsion; linear response range; phase modulation
• Online Access: https://www.mdpi.com/1424-8220/19/16/3613

In this paper, a comprehensive passive torsion measurement is performed firstly in a 40-cm-long polarization maintaining fiber-based Sagnac interferometer (PMF-SI), and the non-linear torsion response is found and investigated. Then, a fiber laser torsion sensor (FLTS) with a dual-ring-cavity structure is proposed and experimentally demonstrated, in which the PMF-SI is utilized as the optical filter as well as the sensing unit. In particular, the highly sensitive linear range is adjusted through fine phase modulation, and owing to the flat-top feature of fringes, an ~83.6% sensitivity difference is effectively compressed by the generated lasing. The experimental results show that, without any pre-twisting, the ultra-wide linear response from −175 to 175 rad/m is gained, and the torsion sensitivities are 2.46 and 1.55 nm/rad with high linearity (>0.99) in the clockwise and anti-clockwise directions, respectively. Additionally, a high extinction ratio (>42 dB) and small line-width (~0.14 nm) are obtained in the proposed FLTS, and the corresponding detection limit reaches 0.015 rad/m.