Electro‐optical modulators based on intersubband transitions induced by normal‐incidence radiation in GaSb‐AlSb‐family asymmetric double quantum wells are proposed. An applied field transfers electrons from &Ggr;‐valley states in one well toL‐valley states in the other well, thereby radically altering the selection rules, resonance energies, and in‐plane effective masses. ©1995 American Institute of Physics.