An optical modulator and related methods are described. In accordance with one embodiment, the optical modulator comprises a horizontal waveguide grating structure (WGS) receiving an incident radiation beam propagating in a non-horizontal direction. The WGS includes a horizontal waveguiding layer along which a lateral propagation mode is guided, the lateral propagation mode having a vertically extending mode profile. The optical modulator further comprises a multiple quantum well (MQW) layer sufficiently proximal to the horizontal waveguiding layer to be within a vertical extent of the mode profile of the lateral propagation mode. The optical modulator further comprises an electric field source applying a time-varying electric field to the MQW layer. The optical modulator modulates the incident radiation beam according to the time-varying electric field to generate a modulated radiation beam propagating in one of a transmitted direction and a reflected direction.