Cascaded long period grating coated with polymethyl methacrylate

Experimental results of refractive index response of cascaded long period grating (CLPG) coated with polymethyl methacrylate (PMMA) are presented in this work. The response of the grating to environmental refractive index changes is investigated by grating immersion into glycerin-water blends with several concentrations. The results indicate that CLPG refractometers with PMMA nanocoating allow refractive index measurement beyond the limit imposed by the cladding refractive index.