Welcome to Forth Dimension Displays

Microdisplay Operation

Our microdisplay is a highly reflective Liquid Crystal on Silicon (LCOS) device. The very high switching speed of our liquid crystal (LC) enables high speed light modulation with no spatial beam separation, no subpixels and no tilting mirrors.

The "in-plane" switching of the optical axis of the LC film provides for excellent viewing angles and enables simple optical architectures (Optical Principle). Together with our Application Specific Integrated Circuit (ASIC) the end user is given the flexibility to choose a mode of operation to suit their application.

In principle, the LCOS device comprises of two substrates. The first is a pixilated silicon-based CMOS substrate (backplane), which serves as both the active matrix to drive individual pixels and as a mirror, and the second, is a front glass substrate (see figure 1). Between the backplane and the front glass substrate is the LC material, which serves as the medium for light modulation.

Microdisplay Operation
Optical Principle
ASIC

Optical Principle

To understand how our microdisplay works, consider the display as a mirror with an electrically switchable quarter-wave plate (formed by the liquid crystal layer).

If a light source, a mirror, and a polarizing beamsplitter (PBS) are arranged as shown in Figure 2, and a quarter-wave plate (l/4) is inserted between the mirror and beam-splitter, and orientated at an angle of 45

relative to the S-polarized light, then the following sequence of events occurs:

1. The illuminator produces S- and P-polarized light, which hits the PBS.
2. The P-polarized light passes through the PBS and leaves the system.
3. The S-polarized light is reflected by the PBS onto the mirror, this time via the quarter-wave plate, so it is circularly polarized when it reaches the mirror.
4. The reflected light, is circularly polarized in the opposite direction, and having passed through the quarter-wave plate a second time, is once again linearly polarized, but this time rotated by 90

, i.e. P-polarized.
5. The PBS passes the P-polarized light through to the observer.

Now replace the mirror and quarter-wave plate with our microdisplay, the same sequence of events occurs when the panel is switched to its "ON" state. That is, it behaves just like the mirror and quarter-wave plate. However, when the panel is switched to its "OFF" state, then the S-light incident on the microdisplay does not have its' polarization state changed. It therefore reflects back to the PBS and is reflected back to the light source. The observer then does not see any light coming from the microdisplay, as it appears black.

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Application Specific Integrated Circuit (ASIC)

Our ASIC is an easy-to-use microdisplay driver. It is designed specifically to provide a seamless interface between external pixel data streams and the microdisplay. An industry standard 2-wire interface is incorporated for inter-device communication where the ASIC will appear as a slave device allowing set-up and control by the system controller.

A set of memory-mapped registers gives the user complete control over the ASIC allowing ease of use with a wide range of graphics processors/decoders, different image resolutions and image centering. The user also has access to sets of peripheral functions within the device. A test pattern generator allows test patterns to be displayed without valid video input.

Display orientation is selectable allowing the image to be flipped horizontally and/or vertically.

The ASIC provides all the processing power required to allow high quality full 24-bit colour images to be generated on our LCOS microdisplay.

Rather than display images using a single method of colour rendering, the ASIC can be programmed to show bit-planes in any order, and for any duration. The firmware that determines the sequence of bit-planes is called a sequence file. The operations performed by the ASIC on incoming pixel data generates the sequence of bit-planes that are uploaded onto our microdisplay.

For further information please contact sales@forthdd.com

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