OPTICAL PARAMETRIC OSCILLATORS WITHOUT PHASE-MATCHING

We show that optical parametric oscillators (OPO's) based on intersubb and transitions in quantum wells operate in a new and interesting regi me where the gain, loss, and momentum mismatch are all of the same ord er of magnitude. We find that such OPO's can oscillate without phase m atching. The threshold gain does not increase monotonically with idler loss, as one would expect intuitively, but experiences a minimum. Thi s minimum comes about because of a relaxation of the momentum selectio n rule or phase-matching condition. We derive these results by analyzi ng an OPO without making any of the usual assumptions on the relative magnitudes of the gain, loss, and momentum mismatch. We also consider in detail the design of a particular quantum-well structure, the asymm etric double quantum well, for realizing such an OPO experimentally. ( C) 1997 Optical Society of America.