The present invention connects two independent plastic optical fiber channels simultaneously, in which optic signals can be transmitted along two optic passes through a single mechanical rotational interface. The first channel of light path consists of a pair of plastic optic fibers with larger-core, co-axially fixed in 2 holders respectively. The light signal from one of the fiber can be directly coupled into another fiber. A number of smaller-core plastic optic fibers for second channel of light path are circumferentially arranged in the peripheral space of the first channel fibers. They are blind-spot free during rotation and are ideal for machine control applications such as SERCOS Interfaces. The rugged design permits underwater usage. Damaged fibers can be easily replaced without costly repairs of the device itself.