Compressed OpticsOptical function multiplexing
A DigiLens typically comprises a stack of SBGs each engineered to perform one or more of the functions of light: deflection, focusing, beams and illumination shaping, spectral filtering, and distortion and aberration correction and others. A DigiLens™ can be used to replace bulky systems of optical elements.
Form factor compression
Multiplexing optical functionality leads to compact designs unachievable using conventional optics. A DigiLens™ allows much more extreme deflection of light rays than is possible in conventional optical elements, enabling radically compact form factors.
- Non-CRT displays have fixed pixel resolution
- Requires high resolution panel
- Lower resolutions must be scaled up
- HDTV resolution panels require a significant increase in the size of the microdisplay backplane, with a severe reduction in yield and consequently higher costs. Alternatively the pixel feature size must be reduced, but this is typically limited by the display technology itself or the resolution of any practical optical system to couple to the display
- "Tiling" builds a higher resolution composite image from a lower resolution display by using the excess bandwidth of the chip for temporal multiplexing.
- The DigiLens™ ASIL changes magnification for each mode to provide full screen image
- A preset hologram configuration is provided for each tile position and magnification within a compound multi-resolution ASIL. Critical registration alignments are preset at the hologram recording stage, thus minimizing the tolerance requirements of the overall optical system.
- The switching time of the DigiLens™ ASIL between tiles is less than 100µs, so very fast multiplexing is possible, and is typically considerably faster than the refresh time of the input display.
HDTV Display Modes
- Single 640x1080 display (less than XGA resolution)
- Central portion of display used for interlaced or progressive display
- Preset optical characteristics of the ASIL give correct aspect ratio and full screen magnification
- Progressive scan HDTV modes use 1280 x 720 at 60Hz
- Single 640x1080 panel multiplexed twice (2:1 tiling)
- Display is run at 120Hz
- Interlaced scan HDTV modes use 1920x1080 at 30Hz
- Single 640x1080 panel multiplexed three times (3:1 tiling)
- Display runs at 180Hz
- Progressive (line doubled) scan possible for ultimate quality
- The fast switching properties of the DigiLens™ technology, combined with its optical transparency when inactive allows the combination of multiple optical functions within a single space envelope.
- A DigiLens™ ASIL could primarily be used as part of a display system, presenting the eye with a seemingly constant, flicker-free image.
- During short periods in the image integration time, (such as the refresh time of the display), the optical system could temporarily assume a completely separate function. As an example, a DigiLens™ stack used in reflection for display could switch to transmission mode in order to image the outside scene onto a CCD or CMOS image sensor.
- The secondary optical system re-uses much of the space occupied by the primary display, leading to very compact, multi-function systems.
- As well as performing the multiplexing function, the ASIL acts as two separate high quality optical elements, further minimizing bulk.
- Combines imaging and display optics in a compact configuration.
- Very fast switching of the ASIL allows different functionality to be "spliced" into the view without being noticed by the eye.
- Night vision display achieved by multiplexing with Infra-Red CCD, allowing processed IR scene to be displayed.
- Augmented display capability superimposes IR display with direct ambient light since they share the same perspective. Provides a unified image in all lighting conditions.
- Alternatively rapid multiplexing with low resolution IR sensor allows imaging of pupil. Local processing extracts direction of view and controls the tiling mode of the display for area of interest displays.
- Applications of this bi-directional imaging include night vision goggles, and as the eye-tracking optics at the heart of an Area-of-Interest display system.
Transparent ModeElectrical fields applied across the DigiLens™ cause the Bragg grating to disappear, and the efficiency of the hologram to fall to zero - leaving an optically transparent element.
A DigiLens™ operates over a controlled range of angles and wavelengths. Light outside this angular and spectral range is unaffected by the hologram and will see only a transparent element. Hence a full color ambient scene can be seen through the DigiLens™, even whilst it is active.
Unlike surface holograms, which have a theoretical maximum efficiency of 42% into any order, the Bragg holograms in a DigiLens™ can approach 100% efficiency. Efficiencies of greater than 95% have been demonstrated.
A DigiLens™ provides high diffractive efficiency for spectral bandwidths from 20-50 nm
Angular bandwidths in excess of 20 degrees (FWHM in air) can be achieved by suitable selection of refractive index modulation, incidence angle and grating thickness.
Unlike surface holograms, which have a theoretical maximum efficiency of 42% into any order, the Bragg holograms in a DigiLens™ ASIL can approach 100% efficiency. Typical efficiencies of 70 - 80% are currently observed, with greater than 95% already demonstrated.
Spectral bandwidths of 10nm to over 50nm are achievable. With local angular bandwidths of over +/-7° , this makes DigiLens™ technology applicable to most narrow and broadband optical problems.
Color sequential illumination
Color illumination is achieved by providing a stack of red, green, and blue sensitive SBGs, which are switched in sequence with red, green, and blue light sources.
The angle and polarization selectivity properties of a DigiLens™ may be used very effectively in beam splitters.
A DigiLens™ may combined spectral filtering with a range of other optical functions.
The optical effect of a DigiLens™ can be varied continuously or simply switched on or off.
A DigiLens™ can provide a range of bi-directional optical devices – for example a device for providing color sequential illuinations and transmitting/receiving infrared light
SBGs can be designed to operate anywhere in visible and near infrared and UV bands. A DigiLens™ may incorporate SBGs design to operate in different spectral bands – for example, combining visible imaging and infrared sensing.