Development Of Optical Coupling Technologies For Si-Photonics-Die Embedded Package Substrate

In high performance computer systems and large-scale data centers, data movement becomes a critical problem. To overcome this problem, co-packaged optics are attracted much attention for high performance LSIs like upcoming high-capacity switch ASICs. We proposed a new package substrate called active optical package (AOP) substrate. The AOP substrate is an organic package substrate where Si photonics dies are embedded. On the surface of the substrate, fan-out polymer waveguides, connecting high density Si-photonics I/O and low density single-mode fiber (SMF) array, are integrated. the AOP substrate will be used as same as conventional standard package substrates. Only a different point is to connect a pluggable optical fiber. Interlayer optical coupling between the Si and polymer waveguides was achieved with two micro mirrors. For example, light output from the Si waveguide end facet was reflected to upper side by the 1st micro mirror. The light was reflected again to the polymer waveguide end facet by the 2nd mirror fabricated above the 1st mirror. Compared to popular grating couplers, the mirror is suitable for low wavelength and polarization dependent optical coupling. Error free transmission of 28-GBaud NRZ optical signal through the Si waveguide, mirror coupling, and polymer waveguide was achieved without significant penalties. The optical coupling of the polymer waveguides to SMFs was also achieved by passive alignment using a low-cost MT-ferrule-compatible optical connector. The loss penalty of the passive alignment was about 3 dB.