Abstract: The present invention provides a bidirectional HDCP-based data transmission apparatus using an optical fiber which includes a core having a first facet and a second facet. The bidirectional HDCP-based data transmission apparatus includes a forward transmission module and a backward transmission module. The forward transmission module is used for emitting at least two forward light signals into a first end of a core of the optical fiber when being driven. Afterward, the at least two forward light signals are transmitted over the optical fiber immediately. The backward transmission module is used for receiving the at least two forward light signals transmitted over the optical fiber and emitting at least one backward light signal into a second end of the core of the optical fiber when being driven. Then, the backward light signal is immediately transmitted over the optical fiber, wherein the forward transmission module also receives the at least one backward light signal transmitted over the optical fiber.