Advanced Physical Research

We theoretically investigate Rashba spin–orbit coupling in low-dimensional semiconductor quantum wires characterized by position-dependent effective mass (PDEM) and asymmetric confinement profiles. Employing the Ben Daniel-Duke formalism, we derive coupled spinor equations describing electron dynamics under structural inversion asymmetry and Rashba interaction. Our analysis reveals the appearance of momentum-dependent Rashba spin splitting while preserving the degeneracy of timereversed states at zero longitudinal momentum, a phenomenon that does not occur in symmetric parabolic confinements. The position-dependent effective mass modifies the confinement energies and spatial localization of the electronic states, whereas Rashba coupling governs the momentum-dependent spin splitting Moreover, intersubband optical absorption spectra display relaxed parity-based selection rules, activating transitions that are forbidden in symmetric systems, such as 1 → 3, alongside enhanced spin-flip absorption channels. The 1 → 3 transition may acquire finite oscillator strength due to the relaxation of parity-based selection rules under asymmetric confinement. Rashba-induced state mixing redistributes oscillator strength among the optically accessible transitions. Confinement asymmetry and mass gradation jointly modify the intersubband transition energies and optical respons. These results open new avenues for the development of spin-sensitive optoelectronic devices, modulators and quantum-information platforms based on engineered confinement asymmetry and spatially varying effective mass.