Interferometric method for measuring the refractive index profile of optical waveguides directly written in glass substrates by femtosecond laser
Year: 2005
Authors: Ferraro P., Aiello L., De Nicola S., Finizio A., Osellame R., Chiodo N., Maselli V., Cerullo G., Laporta P.
Autors Affiliation: Istituto Nazionale di Ottica Applicata, Via Campi Flegrei 34 80078 Pozzuoli (NA), Italy;
Istituto di Cibernetica del CNR “E. Caianiello” Via Campi Flegrei 34 80078 Pozzuoli (NA), Italy;
Istituto di Fotonica e Nanotecnologie del CNR – Dip. Fisica del Politecnico di Milano – P.zza L. da Vinci 32, 20133 Milano, Italy
Abstract: Direct waveguide writing by femtosecond lasers is rapidly becoming a promising valid alternative to standard fabrication techniques. Significant research efforts are devoted to understanding the effects of interaction of the radiation with the material and determining the key parameters in the writing process. The assessment of a reliable fabrication process depends crucially also on the availability of high resolution inspection and measurement methods. In this paper we employ digital holography (DH) in a microscope configuration as the characterization tool for measuring the refractive index profile of the waveguides. The method offers the advantages of high spatial resolution, high sensitivity and it allows to determine an absolute value of refractive index change without the need of any calibration. We report on the optical characterization of optical waveguides operating at 1.5 micron wavelength in two commercial glasses written by a stretched-cavity femtosecond Ti:sapphire oscillator. Measurements made by DH have evidenced a strong dependence of the fabrication process on the type of glass substrate.
Journal/Review: PROCEEDINGS OF SPIE
Volume: 5858 Pages from: 585804-1 to: 585804-11
KeyWords: interferometer; optical waveguides; DOI: 10.1117/12.612889