Three-core nonlinear directional coupler with variable coupling coefficient

Three core nonlinear directional couplers (TCNLDCs) with variable coupling coefficients (VCCs) are proposed. Their linear operation is examined analytically. Three types of VCC TCNLDCs are investigated numerically. Their transmission features are compared with those of their two-core counterparts. It is shown that the switching curves of VCC TCNLDCs are sharper than those of their two-core counterparts. Also the features of different types of VCC TCNLDCs are compared to each other and to the constant coupling coefficient (CCC) TCNLDC. It is found that the sidelobes in the postswitching region can be suppressed with VCC TCNLDCs and the peak transmission of VCC TCNLDCs is higher. (C) 2003 Society of Photo-Optical Instrumentation Engineers.