Abstract
Atomic layer deposition (ALD) technology is introduced to fabricate a high sensitivity refractometer based on an adiabatic tapered optical fiber. Different thicknesses of titanium dioxide (TiO2) nanofilm were coated around the tapered fiber precisely and uniformly under different deposition cycles. Attributed to the higher refractive index of the TiO2 nanofilm compared to that of silica, an asymmetric Fabry–Perot (F-P) resonator could be constructed along the fiber taper. The central wavelength of the F-P resonator could be controlled by adjusting the thickness of the TiO2 nanofilm. Such a F-P resonator is sensitive to changes in the surrounding refractive index (SRI), which is utilized to realize a high sensitivity refractometer. The refractometer developed by depositing 50.9-nm-thickness TiO2 on the tapered fiber shows SRI sensitivity as high as 7096 nm/RIU in the SRI range of 1.3373–1.3500. Due to TiO2’s advantages of high refractive index, lack of toxicity, and good biocompatibility, this refractometer is expected to have wide applications in the biochemical sensing field.
Highlights
Optical fiber refractometers are of great importance to the biochemical sensing field due to the advantages of high sensitivity, compact size, and anti-electromagnetic interference
-coated adiabatic tapered fiber to is from air tofrom deionized which indicates that the TiOthat
Compared with the tapered fiber coated with Al2O3 nanofilm where the maximum sensitivity is 6008 nm/RIU [13], the sensitivity of the tapered fiber coated with TiO2 nanofilm has been improved, which results from the higher refractive index of TiO2
Summary
Optical fiber refractometers are of great importance to the biochemical sensing field due to the advantages of high sensitivity, compact size, and anti-electromagnetic interference. For LMR-based refractometers, the fiber is coated by high refractive index-absorbing nanofilm, whose real part of permittivity is positive and higher in magnitude than both its own imaginary part and the permittivity of the material surrounding the nanofilm, such as indium tin oxide (ITO) [10,11], titanium dioxide (TiO2 ) [12], aluminum oxide (Al2 O3 ) [13], and [PAH-PAA]X polymeric thin film [14]. Light guided in these structures is coupled to the lossy mode in the nanofilm. The refractometer developed by depositing 50.9-nm-thickness TiO2 on the tapered fiber shows an SRI sensitivity of 7096 nm/RIU in the SRI range of 1.3373–1.3500
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