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Fiber-Optic Mechanical Vibration Sensor Using Long-Period Fiber Grating

Long-period fiber gratings (LPGs) are fabricated by illuminating UV laser light to a photosensitized single-mode optical fiber. By applying the intensity modulation scheme, which is known to be effective as an interrogation method for fiber Bragg grating (FBG) vibration or sound sensors, we construct a fiber-optic mechanical vibration sensor that uses an LPG as a sensing element. It is confirmed that the LPG vibration sensor yields a clear and stable signal waveform and shows good linearity when the amplitude of the vibration strain is varied. In addition, the dynamic range of the sensor is more than 90 dB. Since an LPG shows higher sensitivity to static strain when an appropriate higher cladding mode is adopted, it is expected that with proper choice of the cladding mode an LPG vibration sensor will show much higher sensitivity.