The present invention is related to an optical communication module for transmitting high frequency signals (e.g., 10 Gbit/s and higher data rates) between an optical element and an external circuit. In an illustrative embodiment, the optical communication module includes signal transmission lines and ground lines formed on a ceramic substrate, a flexible wiring board, and a printed circuit board. The widths of the signal lines and the ground lines vary, as well as the spacing between the signal and ground lines. This facilitates characteristic impedance matching among the signal lines to within about 50.OMEGA..