Wafer-level testing of inverse-designed and adjoint-inspired dual layer Si-SiN vertical grating couplers

Abstract

Recently, silicon photonics foundries started providing access to new dielectric stacks which can be utilized to reduce optical I/O losses. For example, in a hybrid c-Si/SiN platform, inverse design techniques can be used to create novel dual layer grating coupler (GC) designs which, in simulations, reach state-of-the-art performance. In this paper, we experimentally validate such designs for perfectly vertical single-polarization GCs in the O-band consisting of a single-etch c-Si layer with a patterned SiN overlay, fabricated using a 193nm DUV immersion lithography process on 300mm wafers. Here, we investigate designs generated by two different design paradigms: inverse design based on the adjoint method and adjoint-inspired design. Using wafer-level testing, we experimentally demonstrate a record low median insertion loss (IL) of 1.3 dB (with interquartile range of ∼ 0.1 − 0.2 dB) for perfectly vertical coupling in DUV lithography compatible devices which is a ∼ 0.5 dB improvement over previously demonstrated single-layer, single-etch c-Si 0 deg GCs.

Vertical Coupling Between Waveguides and Optical Fibers Utilizing Polarization Gratings

“…In these methods asymmetry is introduced into the grating to enhance coupling efficiency in the vertical direction. Other options are using non-uniform periodic grating couplers [9][10][11], the implementing double-layer grating couplers [12,13] or making 2D variation of grating couplers [14] with the goal of achieving vertical coupling. These approaches demand the application of high-resolution deep ultraviolet (DUV) etch.…”

High-performance grating couplers on 220-nm thick silicon by inverse design for perfectly vertical coupling

“…The free-space optical beams should be collimated and the optical mode field should have a Gaussian-like distribution in 3D FSO systems 6 . Especially in some focal plane array (FPA) systems, GCs can be used as receiver to receive 3D FSO information, making the system miniaturized and flat, as show in the supplement materials of reference 7 and the direction of the free-space beams should be perfectly vertical to the surface of the silicon chips 8 – 10 .In addition, the perfect vertical optical coupling makes the alignment for wafer-level testing and for coupling of light to multicore fibers easier 11 , 12 . Therefore, high-performance GCs for perfectly vertical coupling are extremely important elements in silicon photonics.…”