Optical die structures and associated package substrates are generally described. In one example, an electronic device includes a package substrate having a package substrate core, a dielectric layer coupled with the package substrate core, and one or more input/output (I/O) optical fibers coupled with the package substrate core or coupled with the build-up dielectric layer, or combinations thereof, the one or more I/O optical fibers to guide I/O optical signals to and from the package substrate wherein the one or more I/O optical fibers allow both input and output optical signals to travel through the one or more I/O optical fibers.