Holographic visualization promises to offer a natural 3D experience for multiple viewers, without the undesirable side-effects of current 3D stereoscopic visualization (uncomfortable glasses, strained eyes, fatiguing experience). Imec's vision is to design the ultimate 3D display: a holographic display with a 60° diffraction angle and a high-definition visual experience. An example of such a simple test hologram is shown in fig. 1.
Figure 1: Different photographs of the same hologram. Photographs taken with different depth of field and point of view of one of our experimental static hologram - illustrating the nature of holographic 3D visualization, such as whole scene focus, natural depth cues and continuous viewing angle.
Realization of such a high-definition computer-generated holography (CGH) system remains an open challenge mainly due to the two following reasons: CGH is extremely computationally intensive, which complicates its real-time (video) applications and the quality of the visualization is to a major extend determined by the physical properties of the display device. To achieve wide viewing angle the light-diffracting element of the holographic display must be sized close to the wavelength of the used light, e.g. 600nm for red. Moreover, millions of such individually controlled elements are needed to achieve high 'image' quality.
Existing solutions are based on liquid-crystal display (LCD), liquid-crystal-on- silicon (LCoS) and micro-mirror micro-electro mechanical systems (MEMS) technologies. All these technologies, however, reach the scaling limits at around 2-4µm, limiting the viewing angle to less than 15°, see fig. 2. Furthermore, highest resolution displays using these technologies have at most up to 8 million pixels.
Figure 2: Diffraction angle of a projection system is proportional to the size of its pixels. Pixel size close to or below the wavelength of the used visible light are necessary to achieve diffraction angles of 60˚ or higher. Sub-micron imec DND devices reaching the 60˚ diffraction angle, as compared to existing commercial and academic state-of-the-art technologies.
As a solution, we develop HoloDis, a high-definition holographic display based on imec MEMS technology. As a first step we have concluded experimental verification of the theoretical assumptions from the state of the art studies. In our in-house facilities we have manufactured test structures ranging from 250nm to 2400nm pixel size, see fig. 3. These structures allow us to simulate and study the diffractive optical behavior and efficiency of our future diffractive nano devices (DNDs). In a short term we are going to develop our first prototype HoloDis system featuring 1million DNDs on a chip with a single DND sized below 1.5µm. This device will be the first working prototype demonstrating holographic video display with approximately 25° diffraction angle. The architecture of these devices is developed with further scaling in mind. In a longer term we will realize the ultimate HoloDis system comprising up to 900 million devices with pixel pitch of 500nm. Such HoloDis system is the central building block for true 3D visualization systems with roughly 60° diffraction angle and HD quality of experience.
Figure 3: Imec test chips with sub-micron piston-like structures simulating diffractive optical behavior of the DND system. A holographic visualization, similar to fig. 1, consisting of geometrical test patterns, has been realized, proving that binary piston-like DND-based system can be used to build a high-definition video holographic display.
HoloDis system architecture is being designed alongside the MEMS development as scaling the driver and control circuitry is yet another challenge. The complete DND driver circuitry needs to be scaled down to sub-micron area of a single DND. Furthermore, each of the millions of devices must be individually programmable, bringing extra challenges to the control logic and system design.top