Fig. 11: Examples of waveguide-to-waveguide evanescent couplers.
From: Advances in waveguide to waveguide couplers for 3D integrated photonic packaging
a, b SiN on fused silica to SOI PIC (reprinted with permission from ref. 152, ©Optica Publishing Group). In (a), a perspective view of the coupler with the red indicating the double taper on the SOI PIC and the blue indicating the SiN double taper on the quartz interposer. In (b), a side view of an example fully packaged die showing the electronic-photonic integration of Cu micro pillar bumps as well as the use of an underfill epoxy for mechanical stability and refractive index matching. In (c), an IOX waveguide to SOI waveguide evanescent coupler cross section is shown along the propagation direction (reprinted with permission from ref. 154 ©2020 IEEE). d, e Polymer waveguide on board to SOI PIC. In (d), a perspective view of the coupler with the red indicating the multi-segmented taper on the SOI PIC and the blue indicating the polymer laminate on the board (reprinted with permission from ref. 373 ©2016 IEEE). In (e), a cross section of the evanescent coupler system with relevant parameters (reprinted with permission from ref. 374 ©2017 IEEE). In (f, g), SiN to SiN coupling with flip-chip Au–Au thermocompression bonding is shown including an oxide cladding opening on the interposer for decreasing the vertical gap between tapers (reprinted with permission from ref. 253 ©Optica Publishing Group). In (h), an SOI to Si evanescent coupler actuated by micro-electrical-mechanical system (MEMS) devices is shown along with how the coupler could be used as a switch for different layers or die (reprinted with permission from ref. 345 ©Optical Society of America). In (i), a cross sectional view of an evanescent coupler used to connect SOI waveguides to lithium niobate (LiNbO3) waveguides for modulator integration50 (©2019 M. He et al., reproduced with permission from SNCSC)
