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Characterization of Ultrasound Detection Using a Strain-Insensitive FBG Sensing System Incorporating Fiber Ring Laser



A fiber Bragg grating (FBG) ultrasonic sensing system incorporating a fiber ring laser was constructed. An FBG was used not only as a sensor but also as a ring cavity mirror in the system. The fiber ring laser emitted a laser at the Bragg wavelength of the FBG sensor. When ultrasound impinged on the FBG sensor, the intensity of the laser varied in accordance with the ultrasonic vibration. Ultrasound detection of this system is attributed to the wavelength dependence of optical gain in an optical amplifier used the fiber ring laser. Despite a considerable shift in the Bragg wavelength of an FBG sensor, this system could sensitively detect vibrations over a broad band ranging from a few Hz to hundreds of kHz.

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