Quantum well infrared photodetectors (QWIPs) based on GaAs have attracted much attention owing to its matured material growth technique. In order to obey the selection rule of polarization, various grating structures have been attached to planar QWIPs. Recently, we experimentally demonstrated that strained planar QWIPs could be self-rolled up into an out-of-plane tubular geometry so that the polarization selection rule is sufficiently subdued without any extra grating structure. Such self-rolled-up QWIPs show a broadband enhancement of responsivity and detectivity over a wide incident angle. In this paper, both wave-optics and ray-optics simulations are performed to clarify the underlying physics. The well-defined curved QWIPs pave a path towards flexible QWIPs for flexible optoelectronics.