1. Field of the Invention
The present invention relates to a system for the production of a dynamic image for display and has particular, although not exclusive, relevance to such systems employing liquid crystal display devices for use in holography.
2. Discussion of Prior Art
It has long been known to use holographic techniques to produce a three-dimensional image of an object which has all of the depth cues used by the human brain in its image processing. Conventionally a real three-dimensional object is used in the production of the hologram by known techniques.
It is also known to use holographic stereogram techniques which, rather than rely on real three-dimensional object in the production of the hologram, rely upon multiple flat, two-dimensional, objects having different perspectives of a scene encoded as light intensity or phase differences across the surface thereof which can be used to produce a hologram therefrom.
Interferometrically derived, so-called display holography requires high performance materials such as silver halide to both record and replay the holograms. In order to achieve a very wide field of view, it is desirable to have resolutions down to around 10 nm. This resolution also allows for high fidelity and colour to be recorded and faithfully reproduced.
It has been recognised that it would be desirable to produce a dynamic, rather than static object possibly using this two-dimensional display holography technique. This will be possible by simple substitution of the holographic recording material by some form of electronically addressable spatial light modulator. These may consist of two-dimensional arrays of electronically addressable light modulation elements, referred to as pixels.
The above desirable result, however, meets with drawbacks because whilst conventional spatial light modulators are fabricated using a wide variety of techniques, they all suffer from an number of problems. None of the conventional spatial light modulators offer the potential to achieve small pixel sizes which are necessary to achieve the desired field of view. Additionally, none offer the number of pixels typically seen in a latent image hologram. The low resolution due to the low number of pixels results simply from the limits of technology at the present time. Even in leading systems, using a acousto-optic modulators and passive addressed ferroelectric liquid crystal modulators, the maximum number of pixels is limited by various reasons. The acousto-optic systems are limited due to the modulation bandwidth of the acousto-optic modulator which is typically a few-several hundred MHz. In liquid crystal systems this is due to the manufacturability of very complex displays. Currently 3000xc3x972000 pixels has been achieved.
Accordingly, it would be desirable to be able to use an electronically addressable modulator to provide a dynamic image for display and possibly to be used for holography. The present invention therefore aims to at least alleviate the aforementioned shortcomings.
There is provided, in accordance with the present invention, a system for the production of a dynamic pattern for display comprising: a light source; first spatial light modulator means having an associated updating frame-rate in the path of the light source; relay optics means in the path of the light from the first spatial light modulator means for guiding the modulator light therefrom, and; second spatial light modulator means having an associated read-out frame-rate in the path of the guided light from the relay optics means and arranged to produce a real image therefrom for display, wherein the updating frame-rate of the first spatial light modulator means is greater than the read-out frame-rate of the second spatial light modulator means.
This enables the image produced at the second spatial light modulator means, which operates at a far slower read-out rate than the update rate of first spatial light modulator means, to be effectively governed by the operation of the first spatial light modulator means. This permits a trade off between the temporal information available in high frame-rate spatial light modulators and thereby obtain a high complexity system working at a lower frame rate. It will be apparent to those skilled in the art that the term complexity as used herein refers to the number of pixels capable of being displayed on the spatial light modulator.
Preferably the second spatial light modulator means comprises an optically addressable spatial light modulator. Use of an optically addressed spatial light modulator enables the active screen formed by the grid of pixels therein to be divided into independently addressable segments.
Additionally or alternatively the first spatial light modulator means maybe arranged to produce a plurality of modulated light sources from the light source to the relay optics means. In this way the first spatial light modulator may be used to provide a plurality of patterns for subsequent use within the system.
Additionally or alternatively the first spatial light modulator means may comprise a plurality of spatial light modulators. This allows an alternative way of producing a plurality of data patterns.
The first spatial light modulator means may be electrically addressable. This enables a fast rate of dynamic pattern to be produced.
Preferably the relay optics means guides modulated light from the first spatial light modulator means to the second spatial light modulator means in a predetermined pattern. Alternatively the relay optics means may modulate the phase or polarisation of light guided thereby. This permits for predetermined guiding/modulation of light by the relay optics means. The relay optics means may comprise a lens means or an array of individual lenses or a beam splitter or a shadow mask, or holographic optical element. Alternatively the relay optics means may comprise a diffractive array generator such as a diffractive array element or holographic array element.
The complexity of the first spatial light modulator means may be less than the complexity of the second spatial light modulator means. This allows, for example, for repeat patterns to be formed on the second spatial light modulator means. In a preferred embodiment, the modulated light from the first spatial light modulator means may be replicated at the second spatial light modulator means by the relay optics means. Additionally the replication of the modulated light may comprise a plurality of patterns. Usefully the relay optics means guides the replicated modulated light time-sequentially to predetermined portions of the second spatial light modulator. In this way the relay optics means may reproduce a pattern at the second spatial light modulator of that provided by the first spatial light modulator.
Preferably the second spatial light modulator means comprises a ferroelectric liquid crystal light modulator. Additionally the light source may be an incoherent light source. The light source may usefully be a point light source. In certain circumstances, though, the light source may be a plurality of individual light sources, even colour or colour sequential light sources. The liquid crystal light modulator may also be capable of itself acting as the light source.
According to a second aspect of the present invention there is provided a method of producing a dynamic image for use in display comprising:
providing a light source and passing light from this light source through or reflecting it from a first spatial light modulator means having an associated updating frame-rate; guiding the modulated light via a relay optics means, disposed in the path of the modulated light, to a second spatial light modulator means, which second spatial light modulator means has an associated read-out frame-rate less than the associated updating frame-rate of the first spatial light modulator; and providing a real image or pattern from the second spatial light modulator means.