Abstract: An object of the present invention is to provide an optical communication system and an optical communication method capable of achieving a long transmission distance with a passive element and obtaining redundancy of a ring topology. The optical communication system according to the present invention is a PON system having a ring configuration, in which an unequal branch optical splitter having a left-right symmetrical configuration is disposed in a trunk fiber wired in a loop shape. An OLT and an ONU have a configuration in which two sets of Tx (transmitter) and Rx (receiver) are mounted. Two sets of Tx (transmitters) and Rx (receivers) in each of a plurality of ONUs are respectively connected to left and right symmetrical ports of one unequally branched light beam SP.

Abstract: A robot for removing an unnecessary portion on a workpiece, comprises a tool for removing the unnecessary portion, a tool positioning apparatus which contains a reference coordinate system, carries the tool attached thereon, and is movable to change a position and a posture of the tool in the reference coordinate system, a jig on which the workpiece is securely fixed to maintain a desired position and a desired posture of the workpiece with respect to the reference coordinate system of the tool positioning apparatus, and an arithmetic unit for calculating a movement path and a posture of the tool moved by the tool positioning apparatus on the basis of a position of the unnecessary portion on a desired shape of the workpiece, in which the arithmetic unit corrects the movement path and the posture of the tool not in accordance with the position of the unnecessary portion on the desired shape of the workpiece, but in accordance with a shape of at least one of the workpiece, the tool and the jig.