Miniature Fiber-Optic Magnetic Field Sensor Based on Ampere Force and Fiber Laser
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Miniature Fiber-Optic Magnetic Field Sensor Based on Ampere Force and Fiber Laser Weiren CHENG, Tianming LUO, Linghao CHENG*, Hao LIANG, and Bai-ou GUAN Institute of Photonics Technology, Jinan University, Guangzhou 510632, China *Corresponding author: Linghao CHENG
E-mail: [email protected]
Abstract: A compact fiber-optic magnetic field sensor is proposed by packaging an orthogonal dual-frequency fiber grating laser and a copper wire with alternating electrical current together inside epoxy resin. The alternating current generates Ampere force in a magnetic field, which changes the birefringence of the fiber laser and hence tunes the frequency of the beat signal after photodetection. The magnetic field magnitude can then be detected by measuring the frequency change of the beat signal. The sensitivity of the sensor can be tuned with a maximum response of 35.21 kHz/kGs demonstrated. Moreover, the sensor shows good immunity to environment interference. Keywords: Fiber laser; optical magnetic field sensors; fiber-optic sensors; Ampere force Citation: Weiren CHENG, Tianming LUO, Linghao CHENG, Hao LIANG, and Bai-ou GUAN, “Miniature Fiber-Optic Magnetic Field Sensor Based on Ampere Force and Fiber Laser,” Photonic Sensors, DOI: 10.1007/s13320-020-0590-5.
1. Introduction Magnetic field is of great importance in various areas and its detection has always been a research hotspot in the world [1], attracting the attention of institutions in many countries. Compared with traditional sensing methods, fiber-optic based magnetic field sensing technology shows advantages in small size, large bandwidth, light weight, and immunity to electromagnetic interference [2]. Various technologies have been proposed to implement fiber-optic magnetic field sensors, such as magnetic force, Lorentz force, Faraday effect, magnetostrictive effect, and magnetic fluid materials [3–6]. Among them, Faraday effect is popular because it can directly measure magnetic field. However, since the Verdet constant of silica fiber is small, the sensitivity of Faraday effect based methods is normally quite low [7, 8] even with magneto-optical crystal introduced to increase the
sensitivity [9]. Sensing techniques based on other mechanisms typically measure magnetic field indirectly through external transducers to increase sensitivity, such as through magnetostrictive transducer and Ampere force [10–12]. Such schemes generally convert magnetic field to an intermediate physical measurand which can be measured through fiber-optics with high sensitivity. Recently, sensing techniques using orthogonal dual-frequency fiber grating lasers have attracted widespread attentions. The dual-polarization mode in the same longitudinal mode of an orthogonal dual frequency laser produces a beat signal after photodetection, and its frequency varies with changes in birefringence within the laser cavity [13]. A very low cavity birefringence change of 10–8 can cause the beat frequency to vary in megahertz range. Therefore, the orthogonal dual-frequency fiber grating laser can re
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