Illumination principle of phase-modulated laser light and application in high-dynamic-range laser display system

Laser displays commonly utilize spatial light modulators (SLM) as imaging devices, but the contrast ratio is limited by uniform illumination and the diffraction properties of SLM, which hinder the realization of high dynamic range (HDR) within a single frame. We investigate the fundamental diffraction properties of a phase light modulator (PLM) using the blazed grating model, explore its capability to steer beams, and evaluate its uniformity as a light field modulator. By employing PLM to modulate various light field distributions and conducting contrast ratio tests in laser display systems, we examine the illumination characteristics of PLM. We specifically select a representative light field distribution to assess the contrast ratio and analyze how altering the light field distribution through PLM affects it. Our findings reveal that reducing the proportion of individual spot size relative to the entire image area enhances the contrast ratio when there is a single spot area present in the modulated light field; conversely, increasing their number decreases the contrast ratio when multiple spots are present in the modulated image. By integrating PLM with a digital micromirror device (DMD), we have validated the feasibility of manipulating light field illumination in display systems, resulting in a remarkable improvement of over 300 times in contrast ratio and achieving HDR of projected images. Through utilization of the central light spot image to confirm its smaller proportion within the entire image, we can enhance the contrast ratio by more than 100 times and peak brightness by over 70 times. These findings demonstrate the viability of employing this approach to achieve HDR in laser displays.