A new method for constructing optical zero-correlation zone (OZCZ) codes based on the Hadamard matrix and the concatenation operation is proposed. The most important property of the obtained codes is that the periodic correlation function of the proposed codes is zero for the phase shifts within the zero-correlation zone. The structure of the proposed OZCZ code is simple and their construction is more flexible. The proposed code is expected to be useful for reducing co-channel interference in optical code division multiple access system.