Embodiments may relate to a semiconductor package that includes a die and a package substrate. The package substrate may include one or more cavities that go through the package substrate from a first side of the package substrate that faces the die to a second side of the package substrate opposite the first side. The semiconductor package may further include a waveguide communicatively coupled with the die. The waveguide may extend through one of the one or more cavities such that the waveguide protrudes from the second side of the package substrate. Other embodiments may be described or claimed.