All-fiber ellipsometer for nanoscale dielectric coatings
나노 개전 코팅에 사용되는 전광섬유 타원기
Elipsometro de fibra óptica completa para recubrimiento dieléctrico nanométrico
Ellipsomètre tout fibre pour revêtements nanodiélectriques
Полноволоконный эллипсометр для нано - диэлектрического покрытия
Jose Javier Imas ¹ ², Ignacio R. Matías ¹ ², Ignacio Del Villar ¹ ², Aritz Ozcáriz ¹ ², Carlos Ruiz Zamarreño ¹ ², Jacques Albert ³
¹ Department of Electrical, Electronic and Communications Engineering, Public University of Navarre, Pamplona 31006, Spain
² Institute of Smart Cities, Public University of Navarre, Pamplona 31006, Spain
³ Department of Electronics, Carleton University, Ottawa (Ontario) K1S 5B6, Canada
Multiple mode resonance shifts in tilted fiber Bragg gratings (TFBGs) are used to simultaneously measure the thickness and the refractive index of TiO₂ thin films formed by Atomic Layer Deposition (ALD) on optical fibers. This is achieved by comparing the experimental wavelength shifts of 8 TFBG resonances during the deposition process with simulated shifts from a range of thicknesses (T) and values of the real part of the refractive index (n).
The minimization of an error function computed for each (n,T) pair then provides a solution for the thickness and refractive index of the deposited film and, a posteriori, to verify the deposition rate throughout the process from the time evolution of the wavelength shift data. Validations of the results were carried out with a conventional ellipsometer on flat witness samples deposited simultaneously with the fiber and with scanning electron measurements on cut pieces of the fiber itself. The final values obtained by the TFBG (n= 2.25, final thickness of 185 nm) were both within 4% of the validation measurements.
This approach provides a method to measure the formation of nanoscale dielectric coatings on fibers in situ for applications that require precise thicknesses and refractive indices, such as the optical fiber sensor field. Furthermore, the TFBG can also be used as a process monitor for deposition on other substrates for deposition methods that produce uniform coatings on dissimilar shaped substrates, such as ALD.