Towards multifocal displays with dense focal stacks

Abstract

input Fig. 1. Producing strong focusing cues for the human eye requires rendering scenes with dense focal stacks. This would require a virtual reality display that can produce thousands of focal planes per second. We achieve this capability by exciting a focus-tunable lens with a high-frequency input and tracking its focal length at microsecond time resolution. Using a lab prototype, we demonstrate that the high-speed tracking of the focal length, coupled with a high-speed display, can render a very dense set of focal stacks. Our system is capable of generating 1600 focal planes per second, which we use to render 40 focal planes per frame at 40 frames per second. Shown are images captured with a 50mm f /2.8 lens focused at different depths away from the tunable lens.We present a virtual reality display that is capable of generating a dense collection of depth/focal planes. This is achieved by driving a focus-tunable lens to sweep a range of focal lengths at a high frequency and, subsequently, tracking the focal length precisely at microsecond time resolutions using an optical module. Precise tracking of the focal length, coupled with a highspeed display, enables our lab prototype to generate 1600 focal planes per second. This enables a novel first-of-its-kind virtual reality multifocal display that is capable of resolving the vergence-accommodation conflict endemic to today's displays.

Illuminated Focus: Vision Augmentation using Spatial Defocusing via Focal Sweep Eyeglasses and High-Speed Projector

“…The polymer-based ETLs achieve faster focal change than other types of ETL while maintaining a relatively large aperture size. Consequently, they have been exploited in a wide range of optical systems, from micro-scale systems, such as microscopes, to larger-scale systems, such as HMDs [6,29,43,46] and projectors [21]. Specifically, we inserted two ETLs (16 mm aperture, Optotune AG, EL-16-40-TC) in an eyeglass frame fabricated from an FDM 3D printer to form a wearable (69×128×67 mm, 200 g) device (Figure 1(a)).…”

Multifocal displays: review and prospect

“…In 2018, Chang et al [92] further increased the focal plane number yet lowered the frame rate, demonstrating a proof-of-concept grey near-eye display [ Fig. 10(c)] with a dense collection of 40 depths at a 40 Hz refresh rate.…”

AR Displays: Next-Generation Technologies to Solve the Vergence–Accommodation Conflict

“…In practice, the most widespread approach is to use time-multiplexing for representing series of focal planes, which, in contrast to varifocal designs, considerably decreases the maximum image brightness, as the single focal plane is shown only for a 1/n fraction of the time, where n is the number of focal planes. Though this concept has been one of the most widely studied subjects [13][14][15][16][17][18][19] as means for mitigating VAC in stereoscopic systems, in practice it is quite a challenge to derive a competitive design. One of the most interesting recently-proposed approaches is the utilization of an oscillating varifocal lens with a very-high image refresh rate-capable spatial light modulator.…”

“…A proof of concept for such a design has been provided by J.-H.R. Chang, where an ultra-fast digital micromirror device is used as an image source and a varifocal lens is driven continuously to yield 40 focal planes at a 40 Hz refresh rate [19]. One of the key parts of this solution is utilization of separate infrared beam-based focal length tracking, allowing very rapid real-time synchronization between given focal length and activation of the image source.…”

“…The alternative proposed by J.-H.R. Chang utilizes a liquid-tunable lens in conjunction with a real-time focus tracking system, meaning that the focal length is scanned continuously and there is no need to wait for the lens to settle [19]. As a consequence, this shifts the role of the limiting link from the lens to the image source (spatial light modulator).…”