Contribution-guided compensation of edge-field wavefront aberrations in freeform off-axis reflective systems

Rectangular-field freeform off-axis reflective imaging systems are widely used in compact imaging and display applications, but their edge-field image quality is strongly affected by field-dependent pupil sampling on freeform reflectors. This work analyzes edge-field degradation as pupil-footprint-induced redistribution of freeform wavefront-error contributions, which reflects the change in equivalent aberration components caused by field-dependent local sampling on the freeform reflector. To address this problem, a vector-aberration-based contribution analysis and compensation method is proposed. By reformulating the Zernike wavefront representation into the same aperture-dependent form as the vector aberration expansion, locally sampled freeform surface terms are mapped to equivalent edge-field wavefront aberration coefficients. A freeform aberration contribution ratio is then defined to quantify the energy participation of the freeform reflector before inter-surface cancellation, and this ratio is introduced into relay-mirror compensation optimization. An AR-HUD off-axis reflective system is used for validation. Results show that edge-field sampling mainly redistributes freeform terms into astigmatism, coma, and field curvature. After contribution-guided compensation, RMS wavefront error decreases from 0.078 waves to 0.031 waves, and maximum distortion decreases from 2.85% to 1.18%. These results demonstrate a physically guided framework for balanced full-field optimization of rectangular-field freeform off-axis reflective imaging systems.