Optical switch and optical-switch control method

An optical switch comprising:

• a multiple-stage optical-switch unit that includes one input port and a plurality of output ports that are configured by connecting multiple stages of optical switching elements each of which includes three or more optical input-output ports, and
• a switching control unit that, when receiving a switching instruction to switch an output destination of light input from the input port, executes at first a first control that changes setting of an optical switching element that is included in part not overlapping with an optical transmission channel reaching an output port before switching in an optical transmission channel reaching an output port after switching and is positioned at a point other than a branch point from an overlapping part, and then executes a second control that changes setting of an optical switching element that is positioned at the branch point
• wherein the switching control unit includes
• a setting-state comparing unit that, when receiving a switching instruction to switch an output destination of light input from an input port, compares a setting state of each optical switching element positioned in a new channel that is an optical transmission channel after changing described by the switching instruction, with a setting state of each optical switching element positioned in an old channel that is a current optical transmission channel before switching, and
• an optical switching-element control unit that specifies an optical switching element to be controlled, and performs setting change control of specified optical switching element, based on a comparison result by the setting-state comparing unit, and wherein
• the switching control unit further includes a control-timing determining unit that determines control timing of each optical switching element by using as a trigger one of reception of a connection specifying signal that indicates a switching instruction to switch an output destination of light input from an input port and reception of an element-switching monitoring signal that indicates a state confirmation result of each optical switch port, and
• the optical switching-element control unit performs setting change control of the specified optical switching element, in accordance with control timing determined by the control-timing determining unit.