as the electric field will have a relatively strong quantum confined stark effect which will shift the confined levels to lower energy levels on the other hand excitons in the other opposite triangular bottom well will have no effect or an opposite effects and its confined energy will stay or shift to a higher energy level therefore the applied bias voltage causes an interchange of the heavy and light hole confined energy levels since heavy and light hole bands have different anisotropy in absorption interchange of the heavy and light hole bands provides a change in polarization or intensity of light passing through the device the preferred embodiment of the invention comprises a molecular beam epitaxy mbe grown inalas inalgaas inalas inp structure which is shown schematically in fig3 a referring now to fig3 a reference numeral 10 denotes a small n type inp substrate on which is grown an n type or p type in 0 52 al 0 48 as cladding layer and a barrier layer of undoped in 0 52 al 0 48 as over the barrier layer 12 is grown a variable strain layered multiple quantum well structure 14 comprised of undoped in x al y ga 1 x y as on top of the quantum well structure 14 there is grown a second barrier layer 16 also comprised of undoped in 0 52 al 0 48 as the barrier layer 16 is followed by a growth of a cladding layer comprised of p type or n type in 0 52 al 0 48 as the quantum well structure 14 comprises a pseudomorphic strained quantum well having a gradient in the in and al mole fractions as shown in fig3 b where the in fraction x changes gradually from a value.