Abstract

The growing demand for Tbps/cm² transmission capacity necessitated the improvement in functional optical materials with suitable dopants for dense optical interconnects and its integration with semiconductor devices [1]. It is essential to have high density rare earth (RE) doping with CMOS process compatible, long photoluminescence lifetime optical materials [2]. This will enable the realisation of next generation optical systems in package with on-chip optical gain and loss compensated waveguides. However, the chemical limitation of silica in attaining higher RE doping as well as the physical limitation of concentration quenching in highly RE soluble materials like phosphates prevented the miniaturization of such optical gain elements. Here we report a potential solution to this issue, femtosecond laser assisted multi-ion doping in silica that enables pure silica with higher density Er/Yb doping while achieving the longest reported lifetime. This unique process relies on the hybrid integration of rare earth doped tellurite glass targets and pure silica glass substrates through ultrafast laser plasma implantation (ULPI) process [3]. The engineered material reveals the formation of a well-defined metastable and homogeneous glass structure with Er³⁺-Yb³⁺ -ions in a matrix of silica. Tellurite modified dense silicate layers subsequently display the spectroscopic properties of Er³⁺-ions corresponding to the intra-4f ⁴I_{13/2 →} ⁴I_15/2 transition. Rutherford backscattering spectrometry (RBS) and laser excitation techniques reveal that such fs-laser ion implanted glasses can be doped with significantly higher concentrations of RE, 2.8 at. % (1.687 × 10²² cm^-3), without clustering, validated by this record lifetime of 9.1 ms. Moreover, the optical characterisation of these modified layers on silica shows > 95 % optical transparency in the C-band with a step index of 1.6, at 1550 nm wavelength, that facilitate the fabrication of high index contrast (>10%) low foot-print waveguides on silica. A method of multi-target sequential implantation process to lower the fluorescence quenching at higher doping concentrations by maintaining the equilibrium distance between the doped ions in addition to the use of shadow masking to form active and passive regions will also be presented.

© 2015 IEEE