Apodized hollow conical occulter with gradient transmittance for stray-light suppression

• Radial thickness control enables smooth edge transition and diffraction reduction. • A hollow conical occulter with gradient transmittance is proposed for stray-light suppression. • Dual optimization of geometry and transmittance is achieved via modeling and TRACEPRO. • Unlike traditional apodized disks, the design avoids the limits of material uniformity and 2D transmittance control. • Simulations show ∼ 89% reduction vs. solid cone and ∼ 96% vs. disk-shaped occulters. This study addresses faint target detection under intense backgrounds by proposing a novel hollow truncated conical external occulter for stray light suppression in imaging systems. Unlike material-dependent transmittance control methods, the design innovatively optimizes transmittance distribution via geometric parameter tuning, significantly reducing edge diffraction and attenuating image-plane stray light. Leveraging TRACEPRO’s optimization capabilities and gradient transmittance diffraction theory, a precise optical model is established, with the occulter’s diffraction and stray light characteristics quantitatively analyzed through numerical optimization workflows. During optimization, the occulter structure and lens configuration are co-optimized to enhance imaging quality while boosting weak-signal detection capability. Combined with an internal occulter and Lyot stop in a multi-stage suppression scheme, the design reduces image-plane background irradiance to the 10 −8 order, maintaining effective imaging at a minimum angular separation of 0.5°. This approach discards the traditional method of achieving transmittance variation through multiple materials, but rather leverages flexible geometric structures to control a single material, enabling precise optimization of graded transmittance. It not only exhibits excellent diffraction light suppression performance but also opens up a novel technical pathway for the manufacturing of external occulters. Additionally, it effectively mitigates strong background interference such as solar radiation, significantly enhancing space target detection accuracy and providing reliable support for weak signal acquisition in space target monitoring and exploration missions.