Journal of Computer Engineering 1 (2009) 3-11 13 The Design of half-subtractor Logic Function Based on Nonlinear Directional Coupler L. A.Bakhtiar 1 , E. Yaghoubi 2 , A. Adami 2 , S. M. Hamidi 3 , M. Hosseinzadeh 2 (1) rak bra slamic za versity, rak, ran (2) Science and Researc ra slamic za versity, T ran, ran (3) aser and Plasma Resear stitute, S a B niversity, G. C. T ran, ran lei mail.com rbiau.ac.ir; ir m gmail.com; m_ham r; hosseinzade rbiau.ac.ir Received:2011/02/18 ;Accepted: 2011/04/20 Pages: 13-20 Abstract n this paper a novel design of all-optical half-subtractor based on nonlinear directional coupler is proposed. By using four waveguides and appropriately adjusting the refractive indices and selecting the proper length of waveguides, half- subtractor function can be obtained. The operation of this function is simulated by RSoft C - ayout (BeamPROP) simulator. The simulation results confirm the all- optical half-subtractor circuit without any optoelectronic conversions. e ords: all-optical half subtractor, coupling, nonlinear directional coupler, refractive index, waveguide. 1. Introduction In conventional optical communication and computation which is still performing in the electrical domain, optoelectronic conversion is inevitable. Optoelectronic conversion not only requires extra power, but also induces speed bottleneck in data transmission [1]. In recent years, the requirement for high speed and high bandwidth information processing has provided more attention to the all-optical devices and circuits. all-optical signal processing has capability of handling large bandwidth signals and large information flows and it is able to work with transmissions rates up to hundreds Gb.s -1 . ccording to these advantages, all-optical signal processing is expected to have many applications such as binary addition, header recognition, parity checking, addressing, demultiplexing, regenerating and switching with very high speed [2]. Many researches propose various schemes for implementing of all-optical devices by means of semiconductor optical amplifier [3], Mach-Zehnder Interferometer, micro-ring resonators [ ], a Nonlinear Interferometer [ ], cross gain modulation (XGM), four- wave mixing and Kerr effect at high-Q cavity [ ]. Many all-optical logic gates and all- optical arithmetic circuits have been proposed using above mentioned methods. mong these arithmetic circuits, a binary half-subtractor is one of the most importance operations of two digits. The half-subtractor can be implementing a full subtractor. In electrical domain this circuit constructed by use of and NOT gates. Figure 1 illustrated a particular half-subtractor circuit.