Laser projector

[remp]

Correction
I mentioned I had prices for polygons. That should be "prices from manufacturers" for new polygons. 1 from USA 2 from Japan 1 from Germany.The prices were all over $2500 dollars.

Bitnick,
Many thanks for your information. Any further details of DIY EO modulators would be great.

Checked out the internet looking for light modulators. No cheap simple light modulators anywhere. Plenty of complicated ones, plenty of expensive ones. Plenty of state of the art modulators you need an advanced optics degree just to understand the first sentance but no simple no frills light modulators. Could be because modulating light is not a simple business.

To see the modulator problem in context as part of a DIY projector project even though a small scale investigation it is important to realise that good modulation of a light beam is a fundamental part of the whole thing. There would be no point going to all the trouble of building the scanner part and finding a suitable lighting system without being able to modulate the beam(s) with video information. The light beams are not flimsy little things they would be pretty powerful beams of light red green and blue and each beam has to be modulated at high speed. You see the results of modulation as pictures on the screen but behind that has to be some concrete means of modulating each of the light beams whether they be derived from a metal halide light or are three laser beams they still need modulated as the video information requires. This complicated modulation of the beams still has to be done in a way that is suitable for DIY people to duplicate.

Thats why I thought about using a movable lightweight obstruction in the light beam to act as a kind of modulator. Like a very fast shutter. Its a type of modulator that is easy to understand and could be easy to construct. I know it is not a good way to modulate. Normally you would have a light beam and modulate it so the whole beam reduces and increases in strenght according to the video information. The obstruction method does not do that. It simply stops part of the full strenght beam proceeding any further. Its all I have at the moment. It is possible the resultant obstructed beam could be homogenised into a correctly modulated beam.

Needs a very fast piezo-electric type material to move the obstruction and also needs high voltage to operate. The high operating voltage is inconvenient but not a serious problem. The real problem is speed of operation and amount of movement. High speed is usually associated with small movement. Piezo type materials can move at the speed required for a light obstructor but the movement is at most a tenth of a millimeter. That amount of movement would not obscure a 2 mm light beam but several of them might. Say four units forming an iris. There is also the method of optical leverage. If you reflect a light beam from a mirror, and move the mirror a small amount two feet away the light beam will move a lot. You could take this to extreme and measure the beam movement ten feet away. It will be a lot more. That means the mirror only has to move a tenth as far as without optical leverage so it could be possible to use a piezo device even with its small movement. Piezo elements can be stacked to give twice the movement. It is common practice to stack piezo elements say 5 or 10 elements but they can be expensive so that has to be considered. There are new types of piezo elements coming on the market with more movement. These could be useful.

Apart from that, still searching for modulator.

[BitNick]

Ok, here's some general info on EOMs (I'm not an expert but I have seen them in operation and during construction)...


EOMs work by "twisting" the polarization of light. An EOM setup would consist of

1) a polarizer (if your light source isn't polarized from the beginning, like most Gas and DPSS lasers)

2) the EOM crystal

3) an "analyzer" -- this can be either another polarizer or (for high power applications) a crystal that splits the beam by polarization -- one useful beam and one "waste" beam. The waste beam can be pointed to a black aluminium block or something similar that can take high amounts of power/heat.


When the light passes through the EOM crystal, its polarization is rotated (actually, this is due to phase shifts that is caused by birefringence in the crystal -- don't ask me about it because I don't really know what causes birefringence or how it really works).
Applying an electric field over the crystal changes the amount of phase shift, and therefore the amount of light blocked by the analyzer.

You could build an EOM by taking a fitting crystal (KDP?) cut in an appropriate way. It should be as high and wide as your beam diameter, and as long as possible. The thinner the crystal is the higher the electrical field per applied voltage -- this means lower voltage is needed. Therefore don't use a crystal higher than the beam diameter. Also, the crystal is not uniform so it is important to have the axles of the crystal right.
Glue one of the long sides (the correct one!) into place on a piece of copper (using conductive glue) -- the piece of copper will be your ground/earth and heat sink.
"Paint" the opposite (now upper) side of the crystal with more conductive glue, and connect it to your HVDC source. Place the laser so that it shines into one of the ends of the crystal and place the analyzer on the opposite side. Control the HVDC source with a video signal. Well, that's it!
Of course there will be a lot of problems -- how to change the voltage over the crystal (maybe 150V p-p) fast enough (12 MHz) is only one of them. Thermal stability is another.

I think if someone thinks themselves able to deal with the HVDC modulation, then go for it!

Also take a look at http://cord.org/cm/leot/course04_mod07/mod04_07.htm


// BitNick

[remp]

BitNick,

Thanks for the info. Sounds like the hardest job would be to locate a ready cut crystal. I might try the local University see if they can help or failing that someone in the gemstone business.
The other parts you mention would be readily avaliable and handling the high voltage is not a serious problem.

[piGuy]

Hey everyone,
Sorry I haven't posted in a while. I did some research into CRT projectors, and found that some very nice HDTV grade projectors can be had for sometimes less than $1000. So I sort of lost interest in building a projector. Anyways, I decided to come by and see if there have been any developments. I was just thinking about the possibility of creating a single scan line display and then scanning that to produce the full display. It would reduce the required operating frequency of the mirror by roughly an order of 3. I guess the hard part would be everything else: creating the electronics necessary to drive the display one scan line at a time, actually creating the display (led array?) and focusing the light from the display to a coherent beam. Kinda crazy, I know. I was just thinking that if there's absolutely no way to get a fast enough mirror, maybe we should think about ways to get around that? Oh well, just a thought.

[remp]

Greetings

Hi Piguy. Thanks for info. An HDTV projector for less than $1000. Second hand ??.
Creating one line of video would solve the scan problem because you would only need to scan a horizontal line down the screen. The scan down would be a piece of cake to do. Creating one line I presume you mean a Horizontal raster line of video has been tried before. You can easily (=expensively) get one complete video line to register in a crystal with the correct drive then display that whole line with a very high power fast pulsed light source. If you use a pulsed laser at the power required it would be far too dangerous to have front project has to be rear projection and even then have to go to extraordinary trouble to make sure no high level light pulses come through the rear projection screen. There have been attempts using a whole lot of light beams extracted from a powerful light source but the one problem you keep running into is if you have say 600 light beams to make up a complete horizontal line, you also need 600 modulators and 600 modulator control circuits. There are people working on the method you say. For example Silicon Light I believe is the name of one company. Dawoo Hitachi Matsushita and many others with a variety of all at once methods.

It is very difficult as you say to make a mirror scan correctly at TV speed and other methods of H scanning are impractical for DIY or expensive like very expensive. Polygons can do it, Acousto-optic deflectors can do it, Electro-optic can do it. Several other techniques can also be used but when you look right into it they are expensive or have some really serious problem as far as a DIY person is concerned. Light shows are using modern equipment which is coming close to TV raster scanning but check the prices of their equipment.
If somebody seriously wanted to build a laser projector with good specs you can. White light lasers are avaliable off the shelf. Polygon high speed scanners are avaliable off the shelf. Modulators likewise. For a small setup suitable for home use you would be looking at $15,000 - $20,000. Who would spend that sort of money when you can buy a very high spec LCD projector for half or a quarter that price. Price is the determining factor that is why you do not see home laser projectors for sale.

But I am not put off by that. Sooner or later I will have a cheap usable laser projector. May not be for a while but the technical challenge is just too good to pass up.

There has been a large upheavel in the large screen projection industry which traditionaly has been dominated by LCD and DLD and that is the appearance from the laboratories of a new projector technology using a large screen covered in I understand ORGANIC Led material. These are like having a screen with a whole lot of led's fitted and where the picture should be bright red the red led lights up. They say these can be printed or silkscreened and you dont need any form of projector just a screen and control box. They can even be rolled up. Search for OLED. In the shops in a year or two.

[xblocker]

Richard,
this OLED developement is indeed exiting, there are even existing prototypes, but i think if you want LARGE images it's hard to handle. Look at the limitations of plasma screens.. The size of a modern PJ isn't much more than a radio clock, it can project 600" on a white wall, have an 1800:1 contrast ratio (like the expected 12° mirror HP-projector), has zoom lenses, lightweight...
The only, but main disadvantage is expensive bulb.
I don't know how they handle the power consumption of let's say 2.500.000 OLEDs for XGA res. And if they built it in various sizes, there is an amount of production costs. For now i would not hope for quick products. The same with lasers as far i can see.

BTW, i did it! Bought a 3-panel projector of ebay, 800 ANSI, 300:1 contrast, 1 year WRNTY for 1300 EURO. All i can say, compared to my OHP setup it's another quantum step! Simply GREAT!!
So i hope to see a good final soccer game!

Cheers
xblocker

[remp]

Greetings

Hi Xblocker. I agree. Modern small 3 panel projectors certainly are a very useful device easy to carry light weight low power dont even need to carry round a screen just project to a white wall but the display market is so large there is a very big driving force to find and market alternatives to LCD. There are as well long term very difficult problems with LCD particulary the panel production yield and light bulb cost and service life. For the present there is no low cost high output light alternative except for the new contactless 100,000 lumen lamps smaller than a golf ball driven by microwaves which are just becoming avaliable in the $1000-$1500 price range. They may come down in price and compete or be better/cheaper than present bulbs.
Congrats on getting a 3 panel projector. Isn't that world cup soccer fantastic. We have good TV free to air coverage here in New Zealand and I sit glued to my large screen every night. Comes on at 11 each night for couple of hours with live coverage and replays.

[Aluminium]

Today I have heard of the sucessful experimentattion of scientists also the country of New Zealand making first transportation of matter repeatedley! the have sent a laser beam from one place to the others with matter transportation devices!a
are you include this research also?
i can not believe and it is so fascination!
it is a same idea as seen in star trek movies transporter I think!

i see also news for prediction of small particle assembleyr for prediction in coming 5 years!
please request a answer to discuss if free
thank you for time here
AL