Optical Response of Grating-Coupler-Induced Intersubband Resonances: The Role of Wood's Anomalies

TL;DR

This study investigates how grating-coupler parameters influence intersubband resonances in a quantum well, revealing the significant role of Wood's anomalies in shaping optical transmission line shapes through combined experimental and theoretical analysis.

Contribution

The paper provides a combined experimental and theoretical analysis of grating-coupler-induced intersubband resonances, highlighting the impact of Wood's anomalies on transmission line shapes.

Findings

Transmission line shape depends on grating period.

Line shape transforms from Lorentzian to asymmetric with increasing period.

Theory accurately reproduces experimental results and explains anomalies.

Abstract

Grating-coupler-induced collective intersubband transitions in a quasi-two-dimensional 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-two-dimensional electron gas is described in the long-wavelength limit of the random-phase approximation by a local dielectric tensor, which includes size quantization effects. Our theory reproduces excellently the experimental line shapes. The deformation of the transmission line shapes we explain by the occurrence of both types of Wood's anomalies.