A Study of the Lossy Mode Resonances during the Synthesis Process of Zinc Telluride Films

Abstract

Films of zinc telluride (ZnTe) were deposited on the surface of a chemically thinned section of an optical fiber by metalorganic chemical vapor deposition. The boundary values of temperatures and the concentration ratios of the initial tellurium and zinc precursors at which the synthesis of ZnTe coatings is possible are determined. The influence of the position of the thinned part of the optical fiber in the reactor on the growth rate of films on the side surface of the fiber was studied, on the basis of which, the parameters of the deposition zone were determined. By placing a section of an optical fiber with an etched cladding in the center of this zone, sensitive elements for refractometers were created. The principle of their operation is based on the dependence of the spectral position of the lossy mode resonance (LMR) maximum on the refractive index (RI) of the external medium. It has been found that even thin films deposited on a light guide in a continuous process have cracks. It is shown that the interruption of the deposition process makes it possible to avoid the appearance of defects in the zinc telluride layers even with the repeated deposition of the sensor. The sensitivity of the spectral position of the LMR to changes in the RI of aqueous sodium chloride solutions in the range from 1.33 to 1.35 for the first transverse electric and transverse magnetic LMRs was 6656 and 6240 nm per refractive index unit, respectively.

Various Types of Light Guides for Use in Lossy Mode Resonance-Based Sensors

“…And this is despite the fact that the NH 4 F-(NH 4 ) 2 SO 4 etchant used in the work is considered polishing for silica. In our earlier work, we showed [53] that the rate of growth of a zinc telluride coating on a single-mode fiber increases with a decrease in the diameter of the thinned fiber section. The formation of thin films on the surface of substrates most often occurs in two stages: the nucleation stage, at which critical nuclei capable of further growth appear, and the film growth stage, at which critical nuclei grow and merge with each other to form a continuous film.…”