Abstract: Heavy-haul locomotives operate in complex and dynamic environments. Drivers are required to frequently monitor numerous displays within the cab and track conditions, and switching the line of sight will result in driving blind for a certain distance. This can easily lead to visual fatigue and safety incidents over extended periods. In this paper, we propose a dual-focal-plane augmented reality head-up display (AR-HUD) system adapted for heavy-haul locomotives, integrating dual picture generation units (PGUs) with two freeform surfaces to achieve the display of near-field and far-field. Due to the large inclination angle of the windshield in heavy-haul locomotives, there are significant aberrations of the optical system and the virtual image quality of the far-field needs to be improved. To address this issue, we introduce two freeform surfaces into the optical path of the far-field to reduce aberration. The increased structural degrees of freedom facilitate subsequent optimization. Following optimization of the system, the maximum root mean square (RMS) radius within the eyebox regions E1 to E5 was smaller than the Airy disk radius, and the modulation transfer function (MTF) value at the cutoff frequency exceeded 0.3. Grid distortion was less than 5%, and at the cutoff frequency of 4.31 line pairs per millimeter (lp/mm), over 98% of the MTF was greater than 0.3. The image quality and overall imaging performance were excellent, with reasonable tolerance distribution, demonstrating the feasibility of this design. This configuration allows for the simultaneous display of both far-field and near-field images, enhancing its applicability in rail transport. The feasibility of this innovative AR-HUD system has been validated through user interface (UI) simulation.

Key words: Optical system; Off-axis reflective structure; Freeform surface; User interface (UI) simulation

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