Nonlinear digital optical switch, optical limiter and optical power stabilizator are proposed and analyzed, which consist of a number of cascaded single-input excitation nonlinear dual-core couplers. These devices utilize the nonlinear restrain effect of the nonlinear coherent coupler on the input-power. As a example, four kinds of switch structures are discussed, numerical results show that the off/on extinction ratio can be less than -90 dB and the dynamic switching range can be less than 0.03 Pc/100, and as an optical stabilizator, the fluctuation of the limiting power level can be less than 10-7Pc.