Abstract: An optical input/output (I/O) system includes at least one electronic circuit die on at least one first substrate on a first side of a printed circuit board (PCB), where the at least one electronic circuit die includes at least 4 electrical inputs and at least 4 electrical outputs that are each configured to operate with a speed of at least 10 Gb/s. The optical I/O system also includes at least one photonic circuit die on at least one second substrate on a second side of the PCB, opposite the first side of the PCB. A plurality of electrical connections are implemented through the PCB, and electrically connect the at least one photonic circuit die with the at least 4 electrical inputs and the at least 4 electrical outputs of the at least one electronic circuit die.