Auxiliary resonant scanner to increase the scanning capability of coarse integral holographic displays

Abstract

This Letter proposes a scanned holographic display system that takes the advantage of a high-speed resonant scanner to augment a galvanometer and hence improves the opto-mechanical information distribution capabilities, thereby potentially achieving an increased image size and enlarged viewing angles.OCIS codes: 090.1995, 070.7345, 100.6890. doi: 10.3788/COL201715.040901. With the ability to provide all the necessary visual depth cues [1,2] , three-dimensional (3D) holographic displays have the potential to be the ultimate 3D images displays, attracting research efforts in the past decades [3,4] . To deliver 3D images with depth cues, the system needs to provide enough information with sufficient bandwidth both optically and digitally, regardless of the optical system.An example is illustrative of the requirements of a representative system. A 1000 × 1000 pixels phase-only hologram with a pixel pitch of 10 μm can project 3D images of 10 mm × 10 mm extent with a 3.6°× 3.6°viewing angle, assuming the wavelength is 633 nm (red light). The image size and the viewing angle are exchangeable, while their product is a constant because of the Lagrange invariant [5] . Having 50 mm × 50 mm × 10°× 10°× 3 ðR∕G∕BÞ × 30 frames∕ sec (fps) requires more than 17 Gpixels/sec. Note that shorter wavelengths, such as 520 nm (green) and 450 nm (blue), have smaller viewing angles than red light, so they require more bandwidths for the same visual range. Considering the necessary bits per pixel, which is expected to be 8 bits to meet the commercial graphic standard, the overall bandwidth will be more than 100 Gb/s. Furthermore, the size and the viewing angle of this example are smaller than what general applications need. It is likely that 1 Tb/s or more is necessary. Therefore, there is a need to develop high-bandwidth spatial light modulators (SLMs) to meet this requirement before a practical 3D holographic display is feasible.When we consider high-bandwidth devices, they can be categorized into two types: a high space bandwidth product (SBP) with a typical video rate frame rate, and a typical video-resolution SBP with a high frame rate. In the former case, for example, if the SLM can be made up to 100000 × 100000 pixels with 60 fps, it can directly be used to support a holographic image of a large image size and a wide viewing angle. Unfortunately, this is not feasible due to practical issues, such as pixel uniformity and the control of electronic signaling. Digital micro-mirror devices (DMDs) are a good example of the latter case. To fully utilize its bandwidth for holographic applications, there is a need to distribute frames efficiently so information contributes to visual imagery rather than being wasted. For example, a DMD supporting a 1024 × 768 frame resolution with 22727 fps provides 17 Gpixels/sec. Distributing this information for holographic 3D images requires careful system integration and the appropriate hologram computation. Our previous works in coarse integral holography (CIH) [6] and layer-based algorithms [7] we...