Most virtual reality (VR) headsets nowadays use conventional, rotationally symmetric optics to create a wide field of view
(FOV > 90°) virtual scene enabling the required “immersion” or “presence” feeling. These optics require a long total track
length (TTL, distance between the actual panel displaying the contents and user’s pupil) to work well, and headsets become
very bulky. The so-called CLOVER is an optic, compatible with VR and video-see-through mixed reality (MR) able to
work around the TTL problem by using a freeform multi-channel, light folding approach. In its simplest version, it can
reduce the TTL down to a half, compared to conventional solutions, for the same FOV and angular resolution. Along with
a review of the original 4-channel CLOVER, this work shows recent results of upscale versions of the optic that utilize
myopia and color correction, pupil tracking and staggered surfaces to, respectively, avoid the need of prescription lenses,
improve the image quality for all colors, rise the resolution (by a 20%) and reduce the size (20% TTL reduction) of the
precursor.
Reducing the size of Virtual Reality head-mounted displays is of main interest to improve the comfort of users, which is a particularly complex design problem due to the very large field of view needed to feel the immersion. High compactness with high transmission efficiency and high contrast can be achieved by multichannel optics, whose design for high performance is carried out at LIMBAK introducing intensively freeform optical surfaces, increased resolution via variable magnification, dynamic mapping control and super-sampling via pixel interlacing. This presentation will cover the growing variety of geometries, how to address their challenges and envision their future.
Reducing the size of Virtual Reality head-mounted displays is of main interest to improve the comfort of users, which is a particularly complex design problem due to the very large field of view needed to feel the immersion. Such reduction can be achieve via folded polarization “pancake” optics, but at the expense of a very low transmission efficiency and poor contrast. High compactness without those drawbacks can be achieved by multichannel optics, whose design for high performance is carried out at LIMBAK intensively introducing freeform optical surfaces, adding variable magnification to maximize the VR display resolution where it is to be normally gazed, and applying two-dimensional distortion software corrections to each channel. This presentation will cover the recent advances in these systems, the growing variety of geometries, the benefits obtained when including gaze-tracking and the resolution boosts obtained by the application of pixel interlacing strategies.
Compared to conventional, rotationally-symmetric optics, free-form optics provide additional degrees of freedom that enable special geometrical and performance features. For instance, in AR and VR, some approaches based on free-forms have shown their ability to reduce the display to pupil distance (total track length, or TTL), to increase the Field of view (FOV) or to improve the apparent resolution of the VR scene. This work will discuss different forms to treat design problems with free-forms, ranging from the direct calculation of point-clouds using the so-called SMS method (followed by a NURBS representation of results) to the combination of direct calculation + optimization. In the latter approach, different types of polynomial descriptions of the free-form surfaces will be considered, with special emphasis on the importance of using a basis that is orthogonal, either with a sag metric or a gradient one.
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