Development and application of SRSN:Er for compact on-chip photonic devices

Abstract

The limitation of oxide based material was investigated by using a Silicon-rich silicon oxide $(SRSO)/SiO_2:Er$ multilayer. Results showed that though high temperature annealing is essential in sensitizing $Er^{3+}$, the formation of Si nanocluster (nc-Si) also leads to de-activation of $Er^{3+}$ ions, lowering the fraction of active Er, suggesting that there is a limit to excess Si and Er contents that can be used. Thus as an alternative material, we used Er doped Silicon-rich silicon nitride (SRSN) which is known to be less sensitive to the thermal annealing process and suppresses the de-activation of Er. To see how much Er is active in nitride, Er doped SRSN waveguide was fabricated and pumped resonantly at wavelength 1480 nm. Results show a population inversion of 0.7~0.75, which is close to the maximum possible theoretical inversion level. This indicates that almost 100 % of Er are active even with high excess Si after high annealing temperature ($1100 \degC$) and at Er concentration of 0.2 at.%. Based on the results indicating Er doped SRSN as an efficient gain material for silicon based light source, the possibility of applications were investigated for two types of microdisks. By using e-beam lithography, a pedestal type Er doped SRSN microdisk was fabricated and characterized by using a U-bent tapered fiber in order to obatin a high Q value. The maximum measured $Q_{tot}$ for the fundamental TE-like mode was 5700, and the intrinsic Q without Er absorption loss was $4.5\times10^4$. Though we did not obtain a Q high enough for lasing, by top-pumping non-resonantly, we observed $Er^{3+}$ emission peaks matching the transmission dips that were excited by fundamental whispering gallery mode via nc-Si sensitized $Er^{3+}$. With a higher concentration of Er (0.43 at.%) than the pedestal type disk (Er 0.2 at.%), a planar type microdisk coupled to a polymer waveguide with cladding was fabricated by photo-lithography to investigate the feasibility of integrati...