Tunable sign reversal of giant Goos–Hänchen shifts in graphene-covered quantum wells

Abstract

We theoretically investigate tunable sign reversal of giant Goos–Hänchen shifts in a graphene-covered semiconductor quantum-well cavity. A coherently driven four-subband semiconductor quantum-well medium induces ultra-steep 2π phase wraps of the TM reflection coefficient vs incidence angle, which convert—via the stationary-phase relation—into giant positive or negative lateral displacements reaching 103−104 times the free-space wavelength λ. The shift polarity and magnitude can be independently engineered by varying the incidence angle, the effective cavity thickness, and the control-field strength, while the graphene overlayer enhances confinement and phase sensitivity. Moreover, electrostatic tuning of the graphene Fermi level reconfigures the reflection resonances and enables active switching between large forward and backward beam displacements. These results suggest a compact platform for angle- and voltage-programmable beam steering, optical switching, and position-encoded sensing.