Demonstration of ErSiO superlattice crystal waveguide toward optical amplifiers and emitters

Abstract

ErSiO superlattice crystal (SC) waveguide is demonstrated. ErSiO-SC film was formed on a SiO 2/Si substrate. After the ErSiO preform formation by sol-gel method, high temperature anneal for the crystallization was performed in Ar atmosphere. Then the ErSiO-SC layer thickness is 220 nm. Then refractive index of ErSiO-SC was estimated to be 1.8 by ellipsometry and reflection spectroscopy measurements. To obtain the lateral optical confinement, polymer cladding layer (n = 1.54) was coated on the ErSiO-SC film and the striploaded structures with 5 μm width were formed by focused ion beam (FIB) etching. The optical confinement factor F of the ErSiO-SC waveguide layer was estimated to be 0.42, assuming the lateral confinement factor was 1 because of the sufficient wide waveguide for the light. Optical pumping was performed by using a 1480 nm laser diode through the lensed fiber. The pumping power is 30 mW at the fiber input. Green light emissions corresponding to 4f intra-shell transitions from 4S 3/2 and 2H 11/2 to 4I 15/2 in the Er 3+ ions, indicating cooperative upconversion in the ErSiO-SC waveguide, can be observed by using a conventional CCD system at room temperature. The upconversion emission behaviour through the waveguide with a photon trap for the 1480 nm light reveals that the 1480 nm pumping light is well-confined into the waveguide. The cooperative upconversion as the gain limitting factor in the ErSiO-SC waveguide are discussed. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.