FIELD

The present disclosure relates to a display device and method of operating a display device. More specifically, some embodiments relate to a near-eye device, head-mounted display or head-up display, and method of operating the same. Some embodiments relate to a visor for a head-mounted device or an optical combiner for a head-up display. Some embodiments relate to a method of switchably-providing augmented reality. Some embodiments relate to a method of switchably-providing one of augmented reality and virtual reality.

BACKGROUND

Light scattered from an object contains both amplitude and phase information. This amplitude and phase information can be captured on, for example, a photosensitive plate by well-known interference techniques to form a holographic recording, or “hologram”, comprising interference fringes. The hologram may be reconstructed by illumination with suitable light to form a two-dimensional or three-dimensional holographic reconstruction, or replay image, representative of the original object.

Holography enables three-dimensional (3D) images to be recorded in an optical medium for later reconstruction and display. Typically, a hologram is recorded by optical interference of two coherent laser beams in a film or a grating. As such, the laser recording imparts static optical properties such as fixed depth encoded lights in the grating. The characteristics of the grating do not change once the recording is performed. As such, static optical properties of gratings can be difficult to use in Augmented Reality (AR) devices since the user's relative position is dynamic. AR devices allow users to observe a scene while simultaneously seeing relevant virtual content that may be aligned to items, images, objects, or environments in the field of view of the device or user. However, the user may move the devices relative to the items and stationary objects in space. Since the depth of field for the virtual content is fixed based on the previously recorded grating, the user may perceive a disparity between the real object and the virtual content.

Computer-generated holography may numerically simulate the interference process. A computer-generated hologram, “CGH”, may be calculated by a technique based on a mathematical transformation such as a Fresnel or Fourier transform. These types of holograms may be referred to as Fresnel or Fourier holograms. A Fourier hologram may be considered a Fourier domain representation of the object or a frequency domain representation of the object. A CGH may also be calculated by coherent ray tracing or a point cloud technique, for example.

A CGH may be encoded on a spatial light modulator, “SLM”, arranged to modulate the amplitude and/or phase of incident light. Light modulation may be achieved using electrically-addressable liquid crystals, optically-addressable liquid crystals or micro-mirrors, for example.

The SLM may comprise a plurality of individually-addressable pixels which may also be referred to as cells or elements. The light modulation scheme may be binary, multilevel or continuous. Alternatively, the device may be continuous (i.e. is not comprised of pixels) and light modulation may therefore be continuous across the device. The SLM may be reflective meaning that modulated light is output from the SLM in reflection. The SLM may equally be transmissive meaning that modulated light is output from the SLM is transmission.

A holographic projector for imaging may be provided using the described technology. Such projectors have found application in head-up displays, “HUD”, and head-mounted displays, “HMD”, including near-eye devices, for example.

