Abstract
In this paper, we demonstrate that the sensitivity of Faraday effect based heterodyning fiber laser sensors for magnetic field can be effectively enhanced by lowering the intrinsic linear birefringence inside the fiber laser cavity. Well explained by theoretical analysis and confirmed by birefringence tuning through transversal force, it shows that the sensitivity to magnetic field intensity is inversely proportional to the linear birefringence. A CO(2)-laser treatment is therefore proposed to tune the intra-cavity linear birefringence. With CO(2)-laser treatment, the intra-cavity linear birefringence can be lowered permanently to effectively enhance the sensitivity of a heterodyning fiber laser sensor to magnetic field.
Highlights
Fiber-optic magnetic field sensors are more attractive than their electronic counterparts in immunity to electromagnetic interference, light weight, compact size and large bandwidth and have been actively explored over years [1,2,3,4]
Many mechanisms can be employed to implement fiber-optic magnetic field sensors, such as magnetostrictive effect, magnetic force, Lorentzian force, etc, Faraday effect based schemes are frequently preferred for many applications as they measure magnetic fields directly without external transducers
A magnetic field parallel to the laser can induce a circular birefringence into the laser cavity through Faraday effect, which combines with the intracavity intrinsic linear birefringence to form an elliptical birefringence
Summary
Fiber-optic magnetic field sensors are more attractive than their electronic counterparts in immunity to electromagnetic interference, light weight, compact size and large bandwidth and have been actively explored over years [1,2,3,4]. Dual-polarization fiber grating laser based sensors have been attracting many attentions these years [7,8,9]. We have proposed a novel miniature fiber-optic magnetic field sensor based on a dual-polarization fiber grating laser less than 20 mm [1]. The dualpolarization fiber grating laser produces two orthogonally polarized lasing modes to generate a radio-frequency (RF) beat signal after a polarizer with the beat frequency proportional to the intra-cavity birefringence. We demonstrate that the sensitivity of a Faraday effect based heterodyning fiber laser magnetic field sensor can be effectively enhance by lowering the intra-cavity intrinsic linear birefringence. CO2-laser heat treatment of fiber laser is experimentally demonstrated as a practical technique to lower the birefringence and enhance the sensitivity
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