OPTICAL FIBER SENSOR AND BRILLOUIN FREQUENCY SHIFT MEASUREMENT METHOD

To reduce costs by adopting a direct modulation system in which a semiconductor laser is directly modulated. An optical fiber sensor includes a light source configured to generate an optical pulse as probe light by a direct modulation system, an optical bandpass filter configured to extract anti-Stokes light that is a component on an anti-Stokes side of Brillouin scattered light from backscattered light generated by the probe light in an optical fiber to be measured, an interference signal acquisition unit configured to generate an interference signal by self-delayed heterodyne interference from the anti-Stokes light extracted at the optical bandpass filter and input to the interference signal acquisition unit and a Brillouin frequency shift acquisition unit configured to acquire a Brillouin frequency shift amount from the interference signal.