Effects of strain and temperature change on the spectra of superstructure fiber gratings

For the superstructure fiber grating (SFG) consisting of a fiber Bragg grating (FBG) and a long period fiber grating (LPFG), a similarity transformation method for the coupled mode equations is presented, the effects of strain gradient and temperature gradient along the SFG on the transmission and reflection spectra of SFG have been investigated. The simulations show that the reflection spectrum and the transmission spectrum corresponding to v-order cladding mode will shift independently with the strain gradient or temperature gradient along the SFG according to a certain law.