Abstract: An optical switch comprises a heterojunction transistor having a source electrode, a gate, a mesa, and three self-aligned waveguides, the mesa being ion implanted and having a single quantum well under the gate electrode, the single quantum well being comprises of undoped, narrow bandgap material bound on both sides by regions p-doped, wide bandgap material, both of said p-doped regions have symmetrically graded bandgaps, being most narrow next to the quantum well and increasing out to a wide and constant value away from the quantum well. A highly n-doped and totally depleted charge sheet is placed in a wide bandgap material, very near the gate side of the quantum well heterojunction. The charge sheet serves to induce a voltage controllable inversion channel within the quantum well.