Fig. 10: Examples of free form waveguide-to-waveguide couplers.
From: Advances in waveguide to waveguide couplers for 3D integrated photonic packaging
In (a, b), a 45° TIR mirror in a polymer waveguide is used to couple to an SOI grating on chip (reprinted from ref. 131, with the permission of AIP Publishing). In (c), a combination of a TIR mirror in InP and an SOI grating couple light between pick-and-placed InP die (reprinted with permission from ref. 335 ©Optical Society of America). d, e DNA self-assembled pyramids (reprinted with permission from ref. 136, ©2023 American Chemical Society). In (d), a schematic of how DNA forms faceted structures which can be used as out of plane reflectors. In (e), SEM images show how the facet angles can be controlled during self-assembly. In (f, g), a schematic and simulation data for a flip-chip coupler using TPP fabricated micro-reflectors are shown139 (©2023 S. Yu et al., licensed under CC BY-NC-ND 4.0). In (h), an experimental image of the reflector is shown which was used for fiber-to-PIC coupling (adapted with permission from ref. 141 ©2024 Chinese Laser Press). In (i), an SEM image showing a TPP fabricated micro-reflector connecting two separate chips which are not flip-chipped, but placed side-by-side142 (©2024 H. Huang, licensed under CC BY 4.0). In (j), a side view of a coupler fabricated using greyscale and NIL is shown58 (©2022 Nakamura et al., licensed under CC BY 4.0)
