High-efficiency self-focusing metamaterial grating coupler in silicon nitride with amorphous silicon overlay.

Efficient fiber-chip coupling interfaces are critically important for integrated photonics. Since surface gratings diffract optical signals vertically out of the chip, these couplers can be placed anywhere in the circuit allowing for wafer-scale testing. While state-of-the-art grating couplers have been developed for silicon-on-insulator (SOI) waveguides, the moderate index contrast of silicon nitride (SiN) presents an outstanding challenge for implementing efficient surface grating couplers on this platform.

High-Efficiency Metamaterial-Engineered Grating Couplers for Silicon Nitride Photonics.

Silicon nitride (SiN) is an ideal candidate for the development of low-loss photonic integrated circuits. However, efficient light coupling between standard optical fibers and SiN chips remains a significant challenge. For vertical grating couplers, the lower index contrast yields a weak grating strength, which translates to long diffractive structures, limiting the coupling performance.

Library of single-etch silicon nitride grating couplers for low-loss and fabrication-robust fiber-chip interconnection.

Silicon nitride (SiN) waveguides become an appealing choice to realize complex photonic integrated circuits for applications in telecom/datacom transceivers, sensing, and quantum information sciences. However, compared to high-index-contrast silicon-on-insulator platform, the index difference between the SiN waveguide core and its claddings is more moderate, which adversely affects the development of vertical grating-coupled optical interfaces. SiN grating couplers suffer from the reduced strength, therefore it is more challenging to radiate all the waveguide power out of the grating within a beam size that is comparable to the mode field diameter of standard optical fibers.

Low-loss grating coupler based on inter-layer mode interference in a hybrid silicon nitride platform.

Surface grating couplers are an important component for interfacing photonic integrated circuits with optical fibers. However, conventional coupler designs typically provide limited performance due to low directionality and poor fiber-to-grating field overlap. The efficiency can be improved by using non-uniform grating structures at the expense of small critical dimensions complicating the fabrication process.