Abstract
This paper discusses the influence of coating long-period gratings with a silicon nitride thin overlay on the grating’s spectral response. The overlays have been obtained with a radio frequency plasma enhanced chemical vapor deposition method. During the experiment, the structures were positioned on various heights over the electrode using specially developed sample holder. The results of the experiment show that the investigated long period grating structures have increased their sensitivity to variations of external medium refractive index in the range of n<sub>D</sub>=1.33 to 1.43 RIU. The relation between the height at which the long period grating was placed over the electrode and the deposited overlay symmetry is discussed. The highest sensitivity of 2080 nm/RIU has been observed for the grating placed at the highest positions of the holder out of the examined range of 3 to 8 mm over the electrode. This overlay also shows the highest symmetry around the fiber.
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