PURPOSE: To permit nonlinear action such as flip-flop action by coupling plural pieces of cells in a manner that the cells can cooperate with each other.

CONSTITUTION: This element has plural pieces of unit elements each containing a nonlinear refractive index medium and means for inputting light to the medium. These elements are so coupled as to cooperate with each other in the relation that the output of one of plural pieces of the unit elements is coupled to the input of the other unit element. For example, the unit element is constituted of both of the nonlinear refractive index media 1-1W1-N and reflecting mirrors 2-1W2-N and N-pieces of the elements (cells) as a whole are coupled to an annular shape to constitute an annular optical resonator in such a manner that the output light of one cell is entered to the next cell. The resonator is so constituted that light E1 is entered to the media 1-1W1-N by reflecting mirrors 2-1W2-N of the respective cells. The flip-flop action which is impossible with the conventional unit element is thereby realized with the assemblage of the cells.