We present a compact holographic near-eye display system with high-quality speckle-free optical reconstructions using camera-in-the-loop (CITL) optimization with phase constraint strategy. The CITL optimization with phase constraint is used to iteratively synthesize the computer-generated holograms (CGHs) based on the in-system optical feedback. The phase constraint embedded into the whole CGH optimization process can effectively smooth the phase profile of reconstructed wave field, which helps to suppress the speckle noise caused by the phase singularities in CGH reconstruction. Numerical and optical experiments have been performed to demonstrate that the proposed method can provide speckle-free optical reconstructions with excellent image fidelity for holographic near-eye display in a compact setup.
The property of space-bandwidth product in computer holography is investigated based on phase space analysis. Optimization of the hologram in joint space-frequency domain can exert comprehensive constraints on the diffraction fields for high-quality optical reconstructions.
Stochastic gradient descent (SGD) algorithm with weighted constraint strategy is proposed to solve the vortex stagnation problem in CGH optimization and improve the image quality for computational holographic near-eye display. The weighted constraint strategy includes weighted phase constraint and weighted amplitude constraint. The weighted phase constraint is used to smooth the phase profile of reconstructed field, which helps to solve the vortex stagnation problem caused by optical vortices and eliminate the speckles in reconstructed field. The weighted amplitude constraint is used to broaden the optimization space by introducing the amplitude freedom of non-signal region in the reconstructed field, which helps to further improve the image quality in the signal region. The weighted constraint SGD algorithm can ensure the stable convergence of CGH optimization and avoid the vortex stagnation, which helps to eliminate the speckles and improve the image quality for holographic near-eye display.
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