Spectral tuning effect and refractive index sensing characteristics of graphene oxide coated excessively tilted fiber gratings

In this work, graphene oxide (GO) is coated on excessively tilted fiber grating (ExTFG) surface through hydrogen bond by using sodium hydroxide (NaOH) solution. The coating effect of GO is inspected by scanning electron microscopy (SEM) and energy spectrum technique. The tuning effects of GO film on the spectrum, the wavelength refractive index (RI) sensitivity and intensity change of TM and TE modes of ExTFG are investigated and analyzed in detail. Experimental results show that the GO film has similar but much less tuning effects on the polarization dependence spectra of ExTFG than that of graphene coated one, and both the wavelength RI sensitivities of TM and TE mode are enhanced by ~5% by GO film. For the TE mode of the GO-coated ExTFG, the reduction of the resonance peak is obviously greater than that of TM mode, which indicates that the surrounding RI change will induce a relatively larger change in imaginary part of TE mode, thus leading more adsorptions for the TE polarization. The coupling intensity change (~9dB) of the TE mode is ~3 times larger than that (~3dB) of the TM mode when the surrounding RI changes from ~1.333 to ~1.37 for the GO-coated ExTFG. In addition, further GO film coating has only a little improvement in the spectrum and sensing performance for the sensor.