OPTICAL RESPONSE OF GRATING-COUPLER-INDUCED INTERSUBBAND RESONANCES: THE ROLE OF WOOD'S ANOMALIES

Grating-coupler-induced collective intersubband transitions in a quasi-twodimensional electron system are investigated both experimentally and theoretically. Far-infrared transmission experiments are performed on samples containing a quasi-two-dimensional electron gas quantum-confined in a parabolic quantum well. For rectangular shaped grating couplers of different periods we observe a strong dependence of the transmission line shape and peak height on the period of the grating, i.e. on the wave vector transfer from the diffracted beams to the collective intersubband resonance. It is shown that the line shape transforms with increasing grating period from a Lorentzian into a strongly asymmetric line shape. Theoretically, we treat the problem by using the transfer-matrix method of local optics and apply the modal-expansion method to calculate the influence of the grating. The optically uniaxial quasi