Highly sensitive operation of LPG vibration sensor using bending-induced spectral change

Bending-characteristics of long period fiber gratings (LPGs) are investigated for use in LPG vibration sensors based on an intensity modulation scheme, in which a tunable laser is used for an optical source with its wavelength tuned to a transmission spectrum curve of an attenuation dip of an LPG and the partially transmitted light through the LPG is modulated in intensity by applied vibrations. In the experiment, LPGs are fabricated by use of an UV irradiation technique and their bending-induced spectral changes are examined in terms of the wavelength and transmittance of the attenuation dip. In contrast to the axial strain, it is confirmed that the much larger spectral changes are obtained when bending deformations are applied to the LPGs. The intensity-based vibration sensor is then demonstrated by adopting the bending effects on a LPG spectrum and its highly sensitive operation is successfully performed.