Resonant Coupling for Active–Passive Monolithic Integration of Al2O3 and Si3N4

The developed double-layer Al
₂
O
₃
-Si
₃
N
₄
photonic platform monolithically combines the outstanding optical features of LPCVD Si
₃
N
₄
and the properties of rare-earth-ion-doped Al
₂
O
₃
active material. In this letter, a resonant coupling is studied in Al
₂
O
₃
-Si
₃
N
₄
couplers by introducing a lateral shift between a lateral Al
₂
O
₃
taper and a vertical Si
₃
N
₄
taper. The proposed resonant couplers enable to reduce mode mismatch losses at the taper tips, avoiding submicrometer lithography process while yielding a broadband and fabrication-tolerant performance. Undoped Al
₂
O
₃
-Si
₃
N
₄
resonant couplers are fabricated, with measured total losses less than 0.18 dB in the 1460-1635-nm spectral window. The first demonstration of active-passive integration is carried out using resonant couplers between Al
₂
O
₃
:Er
³⁺
and Si
₃
N
₄
waveguides, showing the great potential of our double-layer Al
₂
O
₃
-Si
₃
N
₄
platform for the realization of active-passive-integrated functionalities in the Si
₃
N
₄
technology.