Abstract: An optical ring resonator modulator comprises a circular waveguide, or ring, evanescently coupled to a first straight waveguide and a second straight waveguide. The ring may be surrounded by an outer ring or member of doped silicon and the region inside the ring may comprise an oppositely doped member, making the ring itself the intrinsic region of a positive-intrinsic-negative (PIN) diode. When a voltage is applied between the outer and inner members the refractive index of the waveguide is changed. A photodiode at a throughput end of the first waveguide is connected to a feedback loop that controls the voltage to the members.