Fig. 4: Working principle, simulation and calculation results of the MEMS-tunable directional coupler.

a Working principle of the MEMS-tunable directional coupler. b Simulated optical response of the MEMS-tunable directional coupler versus vertical offset. c Simulated natural frequency of the MEMS-tunable directional coupler. d Calculated response of the MEMS-tunable directional coupler