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The paper conducts a research on a new type of long period fiber grating with a local micro-structured defect, we analyze and simulate its spectral characteristics by the coupled mode theory and transfer matrix method. Gaining this new type of long period fiber grating method is etching a long period fiber grating by the hydrofluoric acid (HF). This method will etch the local couple of long period fiber grating. The result shows that with the change of the etching depth, length and the position of the defect state, it will open a transmission window and break up into two transmission peaks in the spectra of the stop-band of long period fiber grating, the depth of the two transmission peaks have some relationship with the etching depth, length and the position of the defect state. When the corrosion depth is shallow, the depth of the left peak is higher than the right peak, with the increase of the corrosion depth, the depth of right peak gradually is increasing and over the left peak, the two peaks will return to the state of a single peak, if the corrosion depth continues to increase. With the increase in the length of the corrosion, the depth of the left transmission peak is greater than the right peak, with the continued increase of the corrosion length, the right peak’s depth will gradually increase and over the left peak, if the corrosion length continues to increase, showing that the depth of the two peaks are equal, however, compared with previous cycles the transmission peaks depth decreases. With the change of the corrosion position LTH off the center, the transmittance of the peak’s depth gradually decreases. This research offers a theoretical basis for making the new type of local micro-structured long period fiber grating and achieving double parameters sensing applications.
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