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Measurements of vibration resonant responses of lightweight components are difficult if the sensor's mass is comparable to the mass of the specimen. Fiber optic sensors, which are lightweight, are particularly attractive for this special application. To demonstrate the capability of fiber optic sensors for this unique application, a polarimetric fiber optic vibration monitoring system was developed to measure the resonant response of a capacitor (0.34 g) mounted vertically on a printed circuit board during a laboratory vibration test. A pronounced resonance peak around 1200 Hz was detected; this is in agreement with the first vibrational mode of the capacitor (1260 Hz) predicted by a NASTRAN finite element analysis. This resonance was suppressed by encapsulating the capacitor leads in RTV silicon rubber adhesive.