We report on infrared spontaneous emission between subbands in GaAs quantum wells excited by an interband optical pumping. The active region consists of 15 periods of four coupled quantum wells which are embedded in a mid-infrared optical waveguide. Electrons are selectively injected from the valence band in the excited subbands of the quantum wells using interband optical pumping. Intersubband spontaneous emission is observed at low temperature between theE5andE4subbands of the quantum wells(E5−E4≈162 meV≈7.7 &mgr;m).The intersubband luminescence vanishes when theE5subband is not selectively populated. The emission is polarized along the growth axis of the quantum wells as expected for intersubband transitions. The collected infrared power exhibits a linear dependence with the interband optical power with a slope≈560 pW/W.©1997 American Institute of Physics.