Methods, systems, and devices are disclosed for linear optical phase modulators. In some aspects, a linear optical phase modulator device is provided to include a substrate; a PN junction formed on the substrate to include a P region, a N region and a depletion region formed by the P and N regions; and an optical waveguide formed on the substrate and structured to guide light in one or more optical modes to have a spatial optical intensity distribution based on a free carrier density spatial distribution in the PN junction in such that the depletion region exhibits a substantially linear response with regard to a voltage applied to the PN junction to modulate a phase of the light guided by the optical waveguide.