Lithium-niobate-on-insulator (LNOI) is a new material platform for integrated optics allowing for small bending radii, high intensities and superior electro-optical and nonlinear properties. Ridge waveguides of different width are fabricated on pure and Er-doped LNOI substrates using diamond-blade dicing, resulting in smooth side walls with lower roughness when compared to dry etching techniques. Propagation losses for polarized modes are measured by the Fabry-Perot method using a fiber coupling setup and a tunable laser at 1.5 μm. Loss values as low as ~1.4dBcm^-1 were obtained for quasi-TM (qTM) modes, while losses for qTE modes are slightly higher. Characterization of Er:LNOI ridges is performed using Raman and fluorescence spectroscopy. Spectral scans are obtained using a scanning confocal microscope and a 488nm laser. Besides line broadening that may be attributed to internal strain in the bonded layer and implantation induced defects, analysis of Raman spectra shows no significant difference between waveguide and bulk material. However, Er emission of ²H_11/2 and ⁴S_3/2 to ⁴I_15/2 contains small spatial differences across the layer thickness when compared to Er-doped bulk samples. While Raman intensity has a linear relationship with pump power, the intensity of the Er emission starts saturating already at pump levels of a few mW. To investigate fluorescence of the ⁴I_13/2–⁴I_15/2 transition inside the diced ridges, a fiber-coupled laser with wavelength 980nm is used for pumping. The emission is broadened and maxima are shifted to longer wavelengths, which may be attributed to defects induced by implantation, strain induced by the bonded LN-SiO₂ interface, and re-absorption of fluorescence light.

Date Published: 7 March 2014
PDF: 8 pages
Proc. SPIE 8982, Optical Components and Materials XI, 89821G (7 March 2014); doi: 10.1117/12.2036270

Published in SPIE Proceedings Vol. 8982:
Optical Components and Materials XI
Michel J. F. Digonnet; Shibin Jiang, Editor(s)