Charge-transfer-induced optical bistability in an asymmetric quantum-well structure

We present self-consistent calculations of the energy levels in an asymmetric coupled quantum-well structure coupled to a CO2 laser source which is nearly resonant with an intersubband transition. Solving Schrödinger’s and Poisson’s equations concurrently with a set of rate equations, it is shown that intrinsic optical bistability can be achieved. The bistability arises from charge transfer and a subsequent, self-consistent shift of the energy levels which feeds back to the absorption rate. Using realistic parameters, an on-off intensity ratio of 4:1 at switching powers of a few 100 kW/cm2 is predicted at about 10-μm wavelength.