Optical fiber refractometers based on indium tin oxide coatings fabricated by sputtering

Abstract

This Letter presents the fabrication of optical fiber refractometers based on indium tin oxide (ITO) coatings deposited by sputtering with response in the visible region. ITO thin films have been sputtered by means of a rotating mechanism that enables the fabrication of smooth and homogeneous coatings onto the optical fiber core. The ITO coating acts as a resonance supporting layer. This permits us to couple light from the waveguide to the ITO-coating/external medium region at specific wavelength ranges. The device is sensitive to external medium refractive index, which allows its utilization as a refractometer. The sensitivity is dependent on the coating thickness, ranging from 523.21 to 1221 nm/refractive index unit in the explored sensors. The sensor development process is time effective compared to other techniques such as dip coating or layer-by-layer self-assembly, which is interesting in terms of mass production.

Lossy Mode Resonance (LMR) Based Fiber Optic Sensors: A Review

“…The dispersion curve of ITO is plotted in Fig. 4 using the ITO dispersion relation [25] (see the appendix). It is seen from the dispersion curve that ITO acts as a suitable material for LMR generation in visible-near infra-red (VIS-NIR) wavelength range (400-1366 nm) whereas beyond 1366 nm (mid-IR) it acts as a plasmonic material.…”

“…Since the properties of thin films vary depending upon the deposition techniques [34]- [36], LMR based optical fiber refractometer with ITO coating deposited by the sputtering technique were also explored [25]. Sputtering technique is beneficial for mass production of refractometers due to its relatively less deposition time as compared to LbL and dip coating techniques reported in literature [5], [16], [18].…”

Micro and Nanostructured Materials for the Development of Optical Fibre Sensors

“…LMRs are affected by refractive index changes, so, taking that into consideration, coatings sensitive to different materials can be deposited onto the ITO thin layer to implement sensing devices: in this manner, Layer-by-Layer nanostructures [ 108 ] were used to develop humidity sensors. Thanks to the chemical nature of the oxide, it can be also deposited by sputtering, which shortens the construction process [ 109 ]. Other compounds can be coated around the sputtered ITO film: it is the case of polyvinylidene (PVdF), a conducting polymer that is sandwiched between two ITO layers to get a tuneable optical filter by electric signals: it can be used for electric field sensing too [ 110 ].…”

Tunable electro-optic wavelength filter based on lossy-guided mode resonances

“…Since the sputtering technique is mainly intended to be used with planar substrates, it was necessary to implement a new mechanism in order to rotate the optical fiber during the deposition at constant speed. More details of this fabrication procedure can be found in [29]. This first ITO layer of thickness of 85 nm is where the LGMR is generated and also forms the inner electrode necessary to apply the voltage to the final device.…”