The instant disclosure relates to bi-direction data transmission method, high-frequency connector and an optical connector using the same. The method may include transmitting a signal from a locomotive controller to the tender car. The flexible portion biases the electrically conductive surface towards a tissue surface. A recess is provided in a region between the source electrode and the drain electrode, wherein the recess goes through the electron supplying layer to a depth that exposes the channel layer, and the gate electrode is disposed on a gate insulating film that covers a bottom surface and an inner wall surface of the recess.