A flexible circuit assembly is described that integrates a first fiber optic die, for example a transmitter die, a second fiber optic die, for example a receiver die, a trans-impedance amplifier die and a transmitter driver die on a single flexible circuit. Alignment holes and multiple die are accurately placed on a single flexible circuit. The precise placement of alignment holes and fiber optic die facilitate micron alignment accuracy to a fiber optic connector, preferably a mechanical transfer (MT) connector. A heat sink is provided that transfers heat from the trans-impedance amplifier die and the transmitter driver die and isolates the fiber optic die from the heat source. Circuitry for the first fiber optic die, second fiber optic die, impedance die, and driver die, including isolated grounding circuitry, is also integrated on the flexible circuit assembly.