Tuning of Fiber Optic Surface Reflectivity through Graphene Oxide-Based Layer-by-Layer Film Coatings

Abstract

The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, by mounting combined bilayers of polyethylenimine (PEI) and GO layers using the Layer-by-Layer (LbL) technique. The reflectivity of optical fibers coated with graphene oxide layers is investigated for the telecom region allowing to both monitor layer growth kinetics and cavity characterization. Tunable reflective surfaces are successfully attained in both cleaved optical fibers and hollow microsphere fiber-based sensors by simply coating them with PEI/GO layers through the LbL film technique.

Thermally Stimulated Desorption Optical Fiber-Based Interrogation System: An Analysis of Graphene Oxide Layers’ Stability

“…The obtained spectra presented electronic bands at 230, 247 and 299 nm that are associated with ππ* transitions of the aromatic ring (phenol) and with the n-π* transition of the group carboxylic acid, with transitions of π-π* type of the benzene aromatic ring and with n-π* transitions of the carbonyl group [44]. When the maximum absorbance values, achieved at the wavelength of 230 nm, are plotted as a function of the number of bilayers and for constant adsorption time, one can discern that PEI/GO films grew linearly with the number of bilayers (see Figure 2b), being in accordance with the behavior of PEI/GO bilayers deposited onto cleaved or hollow microspheres' optical fiber ends [38]. Slopes of the fitted straight line reveal that the adsorbed amount per unit of area and per bilayer increased with adsorption time up to a constant value, thus allowing us to calculate the GO adsorption kinetics curve, which will be described in the next section.…”

“…As recently demonstrated [38], reflectivity measurements enabled the in situ adsorption kinetics curve of a GO layer on a (PEI/GO) n /PEI thin film to be determined, demonstrating that the GO adsorption follows an exponential curve with a characteristic adsorption time of 600 ± 30 s, not revealing the common behavior of polyelectrolytes where the kinetics curves follow two mechanisms. However, at short adsorption times, i.e., at the initial stages of adsorption, the curves present some noise.…”

“…The optical power source used in the interrogation system was a broadband spectrum optical source centered at 1570 nm with 100 nm bandwidth. Upon reaching the end of the fiber, where the PEI/GO LBL film was deposited, this signal was reflected, returned to the optical circulator, and measured by the optical spectrum analyzer (OSA; Yokogawa AQ6370D) [38]. Figure 1b shows the reflected optical spectrum of a (PEI/GO) 12 thin film coating the optical fiber.…”

“…The reflectivity measurements allowed the observation of a linear growth of PEI/GO LbL thin films with the number of bilayers, in films deposited onto cleaved or hollow microspheres optical fiber ends [38]. To analyze the growth of PEI/GO LbL films onto quartz solid supports by spectrophotometry, thin films were prepared with different numbers of bilayers and with different adsorption time periods, namely 5, 15, 30, 60 and 300 s. The films' UV-VIS spectra were measured after the adsorption of each bilayer.…”

“…In recent years, optical fiber devices have been widely explored in the literature for hydrostatic pressure [13], lateral load [14], and strain [15,16] sensing. They have, therefore, general application as optical sensing devices; however, thin graphene oxide (GO) [17][18][19][20][21] films have gained acceptance in the development of several devices [22][23][24][25][26][27][28][29][30][31] and sensors [32][33][34][35][36][37][38][39][40]. Recently, it has been demonstrated that hollow microsphere fiberbased sensors, conforming to Fabry-Perot interferometers (FPI), can be used in sensing applications [41] by using GO as a tunable platform to enhance the spectral features of hollow microsphere FPI fiber sensor devices.…”