This disclosure is directed to fiber-optic modulators that can be integrated in optical fibers to encode data in optical signals. In one aspect, a fiber-optic modulator includes a weak planar, sub-wavelength grating disposed between an end of a first optical fiber and an end of a second optical fiber. A first electrode is disposed on an edge of the grating and connected to an electronic signal source, and a second electrode is disposed on the edge of the grating opposite the first electrode and connected to the electronic signal source. The grating includes a grating pattern to reflect a channel input to the first optical fiber when a low or no current portion of an electronic signal to be generated by the electronic signal source is applied to the grating and to transmit the channel when a high current portion of the electronic signal is applied to the grating.