This paper analyzes the characteristics of the variable coupling coefficient nonlinear directional coupler (VCC NLDC) in detail. The self-switching transmission curves of three types of NLDC with different coupler length are compared. Their phase-controlled transmission curves are compared, and these device acting as pump-controlled switches are analyzed. It is found that the VCC NLDCs show digital characteristics with the increase of the input power. As phase-controlled devices, the response of the VCC NLDC is binarylike when the input power is high. As pump-controlled devices, the transmission curves of the signal are similar to their self-switching transmission curves, except for some specific details.
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