Er-doped high-index materials for compact, on-chip devices

Er-doping of high-index materials for compact on-chip optical devices are investigated. Two sets of materials, SiN_x and Er_xY_2-xSiO₅, are used as high-index host materials. We find that in the case of Er_xY_2-xSiO₅, crystallization-induced surface roughness can limit the optical activation of Er and cause significant propagation loss, while in the case of SiN_x, very high temperatures can be used without clustering or optical de-activation of Er. In both cases, cooperative upconversion limits the amount of Er that can be doped, with SiN_x providing the lower cooperative upconversion coefficient.