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First consider a single unsheathed optic fibre, eg. a solid cylinder of glass surrounded by air. Light passes down the fibre because of total internal reflection. If a piece of glass is placed on the optic fibre, the total internal reflection will be disrupted and the piece of glass will redirect some
of the light out of the fibre. If a piece of glass could be selectively moved on and off the optic fibre, redirected light could be switched on and off.
Instead of physically moving the glass piece on and off the fibre, a material with varying refractive index that varied with electric field could be used. Unfortunately variable refractive index materials require large electric fields for small changes in refractive index, and probably would not be practical.
A better solution would be to use a piezoelectric material. The piezoelectric material would be positioned close to the optic fibre. When electric field is applied, the piezoelectric material touches the optic fibre, redirecting light out of the optic fibre. Alternatively, the piezoelectric when activated would come slightly closer to the optic fibre (but still not touch it) and tap out the 'evanescent wave' of the optic fibre.
To make a diplay, place many optic fibres in parallel, with each optic fibre having several piezoelectric elements. Each piezoelectric element having electrodes on opposite sides to create electric field. For color display, adjacent optic fibres would carry red, green and blue respectively.
Advantages: flat screen, built to any size, low power.
Patent WO2004107015
http://v3.espacenet...DX=WO2004107015&F=0
The display comprises piezoelectric elements which are arranged to move the light extracting elements into and out of physical contact with the wave guide. [xaviergisz, Sep 10 2006]
US 5319491
http://v3.espacenet...US&NR=5319491A&KC=A
[xaviergisz, Oct 20 2009]
Time-multiplexed optical shutter
http://en.wikipedia...xed_optical_shutter
[xaviergisz, Oct 20 2009, last modified Jan 16 2012]
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Would it work that way?
I mean, touching two surfaces together: wouldn't there be a small air gap most of the time. I suppose it would need to be smaller than the wavelength of light (or something like that), in order for the light to not notice the join? |
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Yah, I'm not sure if fiber optics work this way. If they do, then great. |
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It's called an electro-optic modulator, we use them to pulse laser beams. |
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So what would provide the optical fibres with the appropriate light they require?
Perhaps a display may do the job... |
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And as to the complexity of a full display. Wow, not this decade.
Note high electric field = high voltage, we all know what happens with suitably high voltages and small gaps. |
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I voted for it because it seems imaginative and useful, however fanciful. |
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[not-arf], the light supplied to the optic fibres could come from a single LED, and redirected into the optic fibres, or each optic fibre could have it's own LED or laser. |
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If the piezoelectric elements could be activated by a reasonable voltage, I don't see why this display would be any more complex than an LCD or plasma screen. |
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I think the main problem with this invention is the minute movement of piezoelectric crystals, ie, only a nanometer or so. However this could be overcome by 'amplifying' the piezoelectric movement. For example, a small compressive force/displacement upon a plastic rod can lead to a large warping effect (try it with a plastic ruler). The warping plastic rod can then be used to to redirect the light out of the optic fibre rather than the piezoelectric material. |
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The complexity might be similar to that of a micro-mirror display. |
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The proportion of light transferred by the evanescent wave decays approximately exponentially with distance. That might be an advantage, as (assuming that the actuator is approximately linear) the precision curve would closely match the discrimination sensitivity curve of human vision, giving superb contrast in dark regions (a failing of current screens). Alternatively (or additionally) it could easily be pulse-width modulated. |
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Another advantage is that the light is neither polarised nor colour filtered. This immediately gives a potential 6 fold higher efficiency than LCD. |
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One LED or laser per fibre seems like a good thing. By modulating the per-fibre light supply to the sum of that required by the pixels in that row, both the efficiency and contrast could be enhanced even further! This is because the light is not blocked in any way; the light that does not escape at a particular pixel is not absorbed, but able to continue along the fibre. Current so-called LED displays (really LED back-lit LCD, or at best LDC-LED hybrids) do this, but only on the scale of a cluster of pixels, and without the ability of light rejected by one pixel to be emitted by another. |
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This might be a seriously good idea. |
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On the other hand, it's difficult to imagine that any means of modulating light (such as this one) has not been considered as a possible display technology. |
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I'm a bit dissapointed this idea hasn't made it into production yet. A company called Uni-Pixel Displays was on the way to commercialising similar technology (using electrostatic attration rather than piezoelectrics) a few years ago, but I haven't heard much about it since. |
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I like your idea of varying the time the piezoelectric element is activated as a means of modulating the pixel intensity. |
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One potential drawback of using rapidly moving elements is it might create audible noise. |
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