In this paper, the ways to construct dual-channel fiber optic rotary joint (FORJ) are introduced. Furthermore, a new symmetrical optical system for the two-pass interconnection is proposed. We also analyze the designing principle of the optical system and calculate the light path in detail. Whenever there is a rotating interface in such a fiber optic communication system, data have to be transmitted from the stationary side to the rotational side of the system by a FORJ.