High contrast holography through dual modulation

TL;DR

This paper presents a novel dual modulation architecture for holographic displays that significantly enhances image contrast at short propagation distances, enabling more compact and high-quality head-mounted holographic devices.

Contribution

Introducing a low resolution amplitude SLM placed near a phase SLM to improve contrast, demonstrated through simulation and experimental validation.

Findings

Peak SNR improved up to 31 dB in simulation

Experimental SNR improvement of 6.5 dB

Low resolution amplitude modulation suffices for contrast enhancement

Abstract

Holographic displays are a promising technology for immersive visual experiences, and their potential for compact form factor makes them a strong candidate for head-mounted displays. However, at the short propagation distances needed for a compact, head-mounted architecture, image contrast is low when using a traditional phase-only spatial light modulator (SLM). Although a complex SLM could restore contrast, these modulators require bulky lenses to optically co-locate the amplitude and phase components, making them poorly suited for a compact head-mounted design. In this work, we introduce a novel architecture to improve contrast: by adding a low resolution amplitude SLM a short distance away from the phase modulator, we demonstrate peak signal-to-noise ratio improvement up to 31 dB in simulation and 6.5 dB experimentally compared to phase-only modulation, even when the amplitude modulator is 60$\times$ lower resolution than its phase counterpart. We analyze the relationship between diffraction angle and amplitude modulator pixel size, and validate the concept with a benchtop experimental prototype. By showing that low resolution modulation is sufficient to improve contrast, we open new design spaces for high-contrast holographic displays.