Strain Characteristics of Cascaded-Chirped Long Period Fiber Gratings Depending on Order of Cladding Mode

We have investigated optical frequency-shift sensitivity of the transmittance channeled spectrum of cascaded-chirped long period fiber gratings (C-CLPGs) to an applied strain from the viewpoint of the sensor use. In the experiment, eight different kinds of C-CLPGs have been fabricated by changing the cascaded distance for two types of CLPGs and the strain-induced spectral shifts are measured by use of a cross-correlation technique which provides highly precise determination of the spectral shift. As a result, it is confirmed that the higher frequency-shift sensitivities of the C-CLPGs to the strain obtain with the higher order of cladding mode.