Actions of sodium nitrite on long period fiber grating with self-assembled polyelectrolyte films

In this paper, the ultrathin membranes of poly(sodium-p-styrenesulfonate) (PSS) and poly-dimethyl diallyl ammonium chloride (PDDA) are assembled on the surface of long period fiber gratings (LPFGs). The experiments indicate that the transmission spectra characteristics of LPFGs have greater change when bilayer number changed from 75 to 130. The action of sodium nitrite on the LPFGs is researched. The LPFGs without assembled films are not able to distinguish the concentrations of sodium nitrite solutions in the range of 0.001–0.2 mol/L. However, LPFGs assembled polyelectrolyte films of 130 bilayers have a higher distinguishability for these concentrations of sodium nitrite. With the increase of sodium nitrite concentrations, the center wavelengths of attenuation bands gradually shift towards the longer wavelength and represent a good linear relationship with concentrations. The method has the advantages such as low cost, no toxin, fast speed, no time limit. It is hopeful to be applied in real-time and on-line monitoring of sodium nitrite.