Abstract

An all-single-mode fiber intracavity displacement sensor based on U-shaped single-mode fiber interferometer (U-SMFI) is demonstrated theoretically and experimentally. The theoretical model for a cavity-loss-modulated Er-doped fiber ring laser is proposed to analyze the linewidth-narrowing and signal-to-noise ratio (SNR) enhancement mechanism. The evolutionary process of the spectra is calculated through solving the rate equations to investigate the role that the intracavity spectroscopy plays in narrowing the linewidth and reducing the bandwidth-broadening effect theoretically for the first time. Experimental setup for intracavity displacement sensing via a U-SMFI is established to verify the above principle. According to the experimental results, the linewidth and SNR characteristics have been improved a lot compared with the passive U-SMFI. Moreover, it is indicated that the sensitivity of the intracavity displacement-sensor can be optimized through adjusting the bending radius of the U-SMFI. The mode-hopping phenomenon is investigated and eliminated to make the wavelength stability of the output laser comparable to the highest resolution of the optical spectrum analyzer. When the displacement applied to the U-SMFI with a radius of 5.95 mm is changed from 0 to 200 μm, the sensitivity of the proposed intracavity-sensor is 52.92 pm/μm, which can be enhanced through a further optimization to the radius of the U-SMFI. Our proposed sensor design is expected to emerge as a new and promising alternative approach to achieve high-resolution displacement sensor.

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