Understanding the Design and Implementation of SMDG HOEs

The basic principle of Spatially Modulated Diffractive Gratings (SMDG) Holographic Optical Elements (HOE) involves the recording of holographic patterns using a photomask and multiple laser sources. The experimental setup includes a diode-pumped laser emitting at different wavelengths, a spatial filter, a polarization beam splitter, and a photopolymer substrate affixed to a slide glass. By spatially modulating the holographic optical element with a photomask, the diffraction of red, green, and blue light is achieved, broadening the color gamut.

The design of the SMDG pattern considers factors such as pixel pitch, optical characteristics of the HOE, and spectral response of the human eye or camera. To prevent visual artifacts like the screen door effect, subpixel pitches are configured to be 3 μm, ensuring a high pixel density. The SMDG pattern is tailored to match these subpixel pitches, allowing for the diffraction of R, G, and B light through spatial modulation.

Efficiency spectra analysis reveals non-uniform efficiencies across the R, G, and B spectral bands, impacting color gamut. By adjusting subpixel pitch dimensions, a Trisected, TCB, and TSB-type HOE are designed to optimize color reproduction. The TSB-HOE achieves a uniform ratio of B, G, and R values, enhancing color gamut and color reproduction in the holographic display system.

Overall, the implementation of SMDG HOEs offers a sophisticated method for recording holographic patterns and expanding the color gamut in display technologies. By fine-tuning the design and optical characteristics, researchers can achieve improved color representation and immersive visual experiences in holographic displays.