Embodiments include a device, apparatus, and a method. When the pilot signal is received by the node on the upstream side, the backward Raman pump light provided to the optical transmission link on the opposite link side is modulated to thereby send back a response signal to an own node. The flow stream leaves the tube and de-accelerates as the stream flows into a chamber. Teeth in the front portions of the driving belt supports and the driven belt supports and teeth in the rear portions of the driving belt supports and the driven belt supports are oriented in opposite directions.