DUAL-WAVELENGTH EMISSION FROM OPTICALLY CASCADED INTERSUBBAND TRANSITIONS

Dual-wavelength intersubband emission at 8 and 10 mu m is reported in a three-level quantum-well system in which one electronic state is at the same time the lower level of the first optical transition and the upper level of the second. Results are presented for two different AlI nAs/GaInAs quantum cascade structures featuring single-well active reg ions with two vertical transitions or double-well active regions with one diagonal and one vertical transition. Laser action has been achiev ed between the excited states of the single-well device and on the dia gonal transition of the double-well structure. In the latter case the wavelength can be electric-field tuned by means of the stark effect al so above threshold. (C) 1998 Optical Society of America.