We present an advanced optical design for a high-resolution ultra-compact VR headset for high-end applications based on multichannel freeform optics and 4 OLED WUXGA microdisplays developed under EU project LOMID . Conventional optical systems in VR headsets require large distance between lenses and displays that directly leads to the rather bulky and heavy commercial headsets we have at present. We managed to dramatically decrease the required display size itself and the display to eye distance, making it only 36 mm (to be compared to 60-75 mm in most conventional headsets). This ultra-compact optics allows reducing the headset weight and it occupies about a fourth of volume of a conventional headset with the same FOV. Additionally, our multichannel freeform optics provides an excellent image quality and a large field of view (FOV) leading to highly immersive experience. Unlike conventional microlens arrays, which are also multichannel devices, our design uses freeform optical surfaces to produce, even operating in oblique incidences, the highest optical resolution and Nyquist frequency of the VR pixels where it is needed. The LOMID microdisplays used in our headsets are large-area high-resolution (WUXGA) microdisplays with compact, high bandwidth circuitry, including special measures for high contrast by excellent blacks and low-power consumption. LOMID microdisplay diagonal is 0.98” with 16:10 aspect ratio. With two WUXGA microdisplays per eye, our headset has a total of 4,800x1,920 pixels, i.e. close to 5k. As a result, our multichannel freeform optics provides a VR resolution 24 pixels/deg and a monocular FOV of 92x75 degs (or 100x75 with a binocular superposition of 85%).
We present novel advanced optical designs with a dramatically smaller display to eye distance, excellent image quality and a large field of view (FOV). This enables headsets to be much more compact, typically occupying about a fourth of the volume of a conventional headset with the same FOV. The design strategy of these optics is based on a multichannel approach, which reduces the distance from the eye to the display and the display size itself. Unlike conventional microlens arrays, which are also multichannel devices, our designs use freeform optical surfaces to produce excellent imaging quality in the entire field of view, even when operating at very oblique incidences. We present two families of compact solutions that use different types of lenslets: (1) refractive designs, whose lenslets are composed typically of two refractive surfaces each; and (2) light-folding designs that use prism-like three-surface lenslets, in which rays undergo refraction, reflection, total internal reflection and refraction again. The number of lenslets is not fixed, so different configurations may arise, adaptable for flat or curved displays with different aspect ratios. In the refractive designs the distance between the optics and the display decreases with the number of lenslets, allowing for displaying a light-field when the lenslet becomes significantly small than the eye pupil. On the other hand, the correlation between number of lenslets and the optics to display distance is broken in light-folding designs, since their geometry permits achieving a very short display to eye distance with even a small number of lenslets.
In present commercial Virtual Reality (VR) headsets the resolution perceived is still limited, since the VR pixel density (typically 10-15 pixels/deg) is well below what the human eye can resolve (60 pixels/deg). We present here novel advanced optical design approaches that dramatically increase the perceived resolution of the VR keeping the large FoV required in VR applications. This approach can be applied to a vast number of optical architectures, including some advanced configurations, as multichannel designs. All this is done at the optical design stage, and no eye tracker is needed in the headset.