Experimental optical far-field images captured by an infrared camera at different modulation voltages. A diffraction-limited beam (λ0 = 1550 nm) is positioned on the input grating to symmetrically feed the coupling system. The structure design is superimposed as a guide to the eye. The scattering images are superimposed with the structure design. a The unbiased device (Vm = 0 V) exhibits equal power distribution of the scattered signal emitted from the output ports, due to the symmetry of the directional coupler. b When a negative bias voltage (Vm = −25 V) is applied, an enhancement of the optical output signal of the biased waveguide arm is observed, while the optical signal at the opposite output port is decreased in intensity. c By changing the polarity of the applied voltage, the intensity in the two output terminals is switched.