US Patent 7885494 Optical signaling for a package-on-package stack

A package-on-package stack may include an upper package, an optical interface, and a lower package. The upper package may send an optical signal from a first component in the upper package. The optical interface may receive the optical signal from the upper package, and may transmit the optical signal. The lower package may receive the optical signal from the optical interface, and may relay the optical signal to a second component in the lower package or at the motherboard.