High temperature nano-coated electric-arc-induced long-period gratings working at the dispersion turning point for refractive index sensing

摘要

In this paper we present for the first time electric-arc-induced long-period gratings (LPGs) working at the dispersion turning point (DTP) in the wavelength range of about 1550 nm. The DTP is achieved by reducing the grating period down to about 190 μm. In contrast to LPGs fabricated with the typical UV laser-based method, arc-induced gratings show high thermal stability and excellent long-term performance. These advantages make it possible to coat the LPGs using thin-film deposition methods, which require high temperatures. We present the effect of thin silicon nitride (SiN_x) overlay deposited by the radio-frequency plasma-enhanced chemical vapor deposition (RF PECVD) method. This technique increased the refractive index sensitivity of the LPGs from 400-700 nm/refractive index unit (RIU) to 887-2146 nm/RIU.