Fabrication, optical characterization, and device application of $Er_xY_{2-x}SiO_5$ for high gain per length optical material

Abstract

$Er_xY_{2-x}SiO_5$ for high gain per length optical material was fabricated in two different methods and investigated. High crystalline quality of $Er_xY_{2-x}SiO_5$ nanocrystalline particle was fabricated using Si nanowires by spin-coating with $ErCl_3 \dot 6H_2O$ and $YCl_3 \dot 6H_2O$ dissolved solution. Analysis of concentration and pump power dependence of the $Er^{3+}$ photoluminescence intensity and decay lifetime shows that while cooperative upconversion occurs at high Er concentrations, the cooperative upconversion coefficients are only (2.2 ± 1.1) × $10^{-18} cm^3$ /s and (5.4 ± 2.7) × $10^{-18} cm^{3}$ /s at an Er concentration of 1.2 × $10^{21} cm^{-3}$ and 2.0 × $10^{21} cm^{-3}$, respectively. This is nearly 10 times lower at 10 times higher Er concentration than that reported from Er-doped silica. Simulation shows that about 23 dB/cm optical gain is possible from $Er_xY_{2-x}SiO_5$ with 1.5 at. % Er at reasonable pump intensity due to low cooperative upconversion coefficient. For device applications, thin film $Er_xY_{2-x}SiO_5$ was fabricated using ion beam sputter deposition. Onset of transition to crystalline phase is observed at 1100 ℃ and maximum $Er^{3+}$ PL intensity is observed with annealing at 1200 ℃ for 10 min which is due to the increase of luminescence efficiency. However, longer or higher temperature annealing leads to larger grain size and rough surface that can lead to scattering which can cause waveguide propagation loss. The optimized annealing condition was 1150 ℃ for 3 min. To investigate the gain characteristics of $Er_xY_{2-x}SiO_5$, strip-loaded waveguides were fabricated with two Er concentrations. In gain measurement, the maximum inversion level of low Er concentration waveguide is 0.6 ~ 0.65, close to theoretical maximum when 1472 nm pump was used. However, the maximum inversion level of high Er concentration waveguide is 0.4 due to large cooperative upconversion coefficient. Simulation shows that inversion level of more...