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Discussion Starter · #1 ·
Evening All,


I was sitting here passing away the time when I started to wonder why could the DMD engine of DPL be used in conjunction with tri-fold monochromatic lasers as a light source.


Having three lasers operating monochromatically at 460, 520 and 620 nanometers would provide for excellent colored light source, each of which c/would shine onto the mirror array, in On and Off fashion.


I do not know if lasers can be switched in such a high rate needed to fluid image on the far end of the light path, the idea to have a very well-defined color source was what got my attention.


The three source beams could be dispersed much the way ordinary daylight is dispersed when strike frosted glass, but then again maybe I need to stick to networking. :)
 

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What if you didnt have to switch the lasers on and off? Why not have them all 3 on at the same time, but use a wheel that allows only one color to hit the DMD at a time. Basically a 3 segment wheel with 2 blacks and one clear section (actually just a hole) Might not be as nice as switching, but atleast I dont think you would get any rainbows with this type of setup.


Mark
 

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This sounds intriguing! My question would be this:

I know focused lasers are pretty bright, but when you spread them to colour the DMD, and then project them, wouldn't that brightness go down the tubes?


I am ignorant with respect to laser technology, so I don't know how fast they can be turned on and off (Or for that matter, the size and heat produced by a tri-laser light source)


And re: colour separation artifacts, I think the issue would remain, as you are substituting alternating colour segment for alternating colour source. From wheel to DMD, you would have the same issue as we have now.
 

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I suspect laser and projector technology has come a long way, but about 20 years ago, I saw a prototype of a laser projector. Can't remember the company or the explanation of the technology involved. What I do remember is that is was surpisingly shaped, and the size of a Corvair if you are old enough to remember the Corvair. Also, it took either 220v or 440v to power it, 440 if I remember correctly. It also had to be hooked up to a flowing (hose) water source for cooling. Man, what a beast. The only thing they were able to show it do at the time was animated squiggly lines much like a computer screen saver. Even so, it was impressive. Never heard any more about it after that. This was circa 1980-82 in Dallas.

Marvin
 

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Quote:
Originally posted by WanMan
Evening All,


I was sitting here passing away the time when I started to wonder why could the DMD engine of DPL be used in conjunction with tri-fold monochromatic lasers as a light source.


Having three lasers operating monochromatically at 460, 520 and 620 nanometers would provide for excellent colored light source, each of which c/would shine onto the mirror array, in On and Off fashion.


I do not know if lasers can be switched in such a high rate needed to fluid image on the far end of the light path, the idea to have a very well-defined color source was what got my attention.


The three source beams could be dispersed much the way ordinary daylight is dispersed when strike frosted glass, but then again maybe I need to stick to networking. :)
Wan Man,


I'm afraid you should stick to networking.


The color bandwidth for a laser is very narrow. When you mix red, green, and blue light to get all the colors, what

you really want to mix is a bunch of color centered around red, a bunch of colors centered around green, and a bunch of

colors centered around blue. The spectrum of a laser is a single line - so you would be mixing just 3 frequencies.


You wouldn't have to switch the laser on/off - that's what the DLP array does, effectively. You don't switch the lamp

in a DLP on/off - the DLP chip "dumps" the beam for the "off" pixels.


The laser beam would be very narrow - hence the need to undo this with the frosted glass, as you suggest.


Additionally, lasers are notoriously inefficient - the more coherent / monochromatic they are - the less efficient. You

think a D-ILA Xenon bulb dumps heat - you should try a laser.


My main question is "Why a laser?" What advantages do you see with using a laser? The characteristics of a laser are

that it gives you a very narrow beam of very monochromatic light. For a projector, you don't want a narrow beam [hence

the frosted glass], and you don't want that degree of monochromaticity. On the down side, you have the inefficiency.


I'm sorry, but a laser is just the wrong solution for the projector problem. You have to negate it's "advantages"

for use in a projector, and the laser then brings its own set of disadvantages. So what are you trying to accomplish

with using a laser? [ using a laser just for the sake of using a laser?]


Dr. Gregory Greenman

Physicist
 

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"about 20 years ago, I saw a prototype of a laser projector. Can't remember the company or the explanation of the technology involved. "


That would probably have been the Cavendish Labs laser PJ system from Britain.


You should be able to switch the lasers on and off FAR faster than would be necessary for this application, and in fact that would probably be desireable from a minimizing heat perspective (both in general and in the laser emitter itself).


Also, you would likely not "spread" the laser beam, but rather scan the chip with the focused beam at a very high rate.


But now you've eliminated the need for the DMD. If you are pulsing and scanning the laser beams already, what do you need the DMD for?


BB
 

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Quote:
Originally posted by Brandon B
"That would probably have been the Cavendish Labs laser PJ system from Britain.

BB
Does this mean you actually remember the Corvair too?
 

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Quote:
Originally posted by Brandon B
"about 20 years ago, I saw a prototype of a laser projector. Can't remember the company or the explanation of the technology involved. "


That would probably have been the Cavendish Labs laser PJ system from Britain.


You should be able to switch the lasers on and off FAR faster than would be necessary for this application, and in fact that would probably be desireable from a minimizing heat perspective (both in general and in the laser emitter itself).
Brandon,


Depends on the type of laser being used.


Quote:


Also, you would likely not "spread" the laser beam, but rather scan the chip with the focused beam at a very high rate.


But now you've eliminated the need for the DMD. If you are pulsing and scanning the laser beams already, what do you need the DMD for?


BB
Exactly! If you want to use a laser to scan and "paint" an image on your screen, like in laser light shows; then you've

totally obviated the need for the DLP [DMD] chip.


The DLP chip is made to modulate a diffuse light source like a typical projector lamp - to produce an image.


The scanning laser; and the diffuse light source with DLP chip; are two very different paradigms for producing a

projected image.


In that sense, the laser and DLP are "incompatible".


Dr. Gregory Greenman

Physicist
 

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We could add a cluster of laser pointers to the projector with long life batteries.

No more bulb or fan or power needed to the projector.
 

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Quote:
Originally posted by Morbius
Wan Man,



The color bandwidth for a laser is very narrow. When you mix red, green, and blue light to get all the colors, what

you really want to mix is a bunch of color centered around red, a bunch of colors centered around green, and a bunch of

colors centered around blue. The spectrum of a laser is a single line - so you would be mixing just 3 frequencies.


You wouldn't have to switch the laser on/off - that's what the DLP array does, effectively. You don't switch the lamp

in a DLP on/off - the DLP chip "dumps" the beam for the "off" pixels.


The laser beam would be very narrow - hence the need to undo this with the frosted glass, as you suggest.


Dr. Gregory Greenman

Physicist
Morbius, why then sony is trying to use 3 lasers in their GLV system ?

They even did a prototype of Laser CRT.

Projector will get to laser technology someday...

A laser could be used in a dlp system if instead of a color wheel you were to use a scanning device for each laser. The beam of each laser wouldn't have to be enlarged (actually it would need to be focused at the size of a DLP mirror) and a set of rotating mirrors could scan the DLP ship pixel by pixel at a high frequency (a couple hundred hertz could do i guess).


In a DLP system, isn't the use of the colorwheel to try block all unwanted frequencies in the spectrum sequentially ? So i don't see the problem of the monochromaticity of lasers... they would deliver the purest primary colors.

http://www.avsforum.com/avs-vb/showt...&highlight=GLV


Pierre.
 

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Quote:
Originally posted by toxic candy
Morbius, why then sony is trying to use 3 lasers in their GLV system ?

They even did a prototype of Laser CRT.
Because GLV and DLP [DMD] are very different technogies.


A GLV modulates the light via diffraction. Diffraction is dependent on the frequency of the light. A diffraction

grating that does one thing for one frequency will do something else for another frequency. That's why a diffraction

grating will split white light into a rainbow - the different frequencies are affected differently by the

diffraction grating.


Because of this - in GLV - you HAVE to use a laser because you want a single frequency to be diffracted by the GLV.

If you were to shine light with multiple frequencies present - then you would have the different frequencies behaving

differently.


A GLV takes advantage, and in fact REQUIRES, a particular property of the laser light - the fact that it is monochromatic.

This is a proper use of a laser.


A DLP is reflecting light, not diffracting it - so it doesn't require the light to be monochromatic.

Quote:


Projector will get to laser technology someday...

A laser could be used in a dlp system if instead of a color wheel you were to use a scanning device for each laser. The beam of each laser wouldn't have to be enlarged (actually it would need to be focused at the size of a DLP mirror) and a set of rotating mirrors could scan the DLP ship pixel by pixel at a high frequency (a couple hundred hertz could do i guess).
In this case, you would have the scanning / painting laser system that I spoke of in my response to Brandon's post.


If you are going to be modulating and scanning the laser - then you don't scan the DLP chip with it - you just scan

the screen. The ability to scan / modulate the laser TOTALLY OBVIATES the function of the DLP chip. The DLP

chip becomes totally superfluous if you can scan and modulate the laser.

Quote:


In a DLP system, isn't the use of the colorwheel to try block all unwanted frequencies in the spectrum sequentially ?
No - the purpose of the color wheel is to make one chip do the job of three chips. If you have a 3-chip DLP - then

you totally dispense with the color wheel.

Quote:


So i don't see the problem of the monochromaticity of lasers... they would deliver the purest primary colors.
You think you get the "purest white" by mixing 3 frequencies - that is a 3-line spectrum is "purest white"? Afraid not.


Dr. Gregory Greenman

Physicist
 

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Thanks Dr. G


I realize some types of laser don't really have heat issues as far as their lasing mediums, but since heat in PJs creates the need for fans, seems worthwhile to minimize it.


Marvin -


Yes I remember the corvair. But I was 2 when we had one.


BB
 

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Quote:
Originally posted by Brandon B
Thanks Dr. G


I realize some types of laser don't really have heat issues as far as their lasing mediums, but since heat in PJs creates the need for fans, seems worthwhile to minimize it.
Brandon,


Here's an ultra short pulse laser - 100 fs - that's 1.E-13 seconds or 1/10 of a trillionth of a second. But it can

only do that once every 3 minutes.

http://www-phys.llnl.gov/V_Div/spl/

http://www-phys.llnl.gov/V_Div/spl/s...eshaping1.html


It uses "chirped-pulse" technology - to stretch the pulse, amplify it, and then recompress back to original duration.


Dr. Gregory Greenman

Physicist
 

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Discussion Starter · #15 ·
Quote:
Originally posted by Morbius
Wan Man,

I'm afraid you should stick to networking.

Physicist
Ouch! That's hurt. I don't know if I'll be able to sit down after that jab! :)


Ok, Greg, I was simply playing off the Laser-CRT model in which they used three distinct color sources. I suppose that idea was just as immature, too, but I let you explain via rebuttal. :p


BTW, the idea behind the 'laser toggles between On/Off was so that the flipping of the mirrors could be used for other things, such as the mixing of colored light sources. I do fully understand the original design role of the tilting of mirrors in the DLP engine. Stupid I am, but not Chemistry stupid! :D (see wife for explanation)

Quote:
The characteristics of a laser are that it gives you a very narrow beam of very monochromatic light. For a projector, you don't want a narrow beam [hence the frosted glass], and you don't want that degree of monochromaticity.
Why?

Quote:
So what are you trying to accomplish with using a laser?
I suppose that in my infinite boredom at work I was trying to eliminate the color wheel in order to eliminate the rainbow effects. I did not do sufficient research on the origin (cause) of rainbows but still I proceeded forth.


BTW, could you explain the disadvantages of using a laser-based light system? I would be more than willing to learn, just like most people. So, teach us; class is in session.
 

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Discussion Starter · #16 ·
Quote:
Originally posted by Morbius
The DLP chip is made to modulate a diffuse light source like a typical projector lamp - to produce an image.

The scanning laser; and the diffuse light source with DLP chip; are two very different paradigms for producing a projected image.
Yes, their original design was set for in stone in order to proceed to market. BUT, it is not the law of the land that such incremental technology (i.e. component technology) can ONLY be used for one purpose. I suppose I am trying to find alternative uses for deployed technology.
Quote:
In that sense, the laser and DLP are "incompatible".
Why should 'digital light processing (processor) be incompatible with laser technology? I do not see why two of three monochromatic light sources could not use a tilting-mirror compilation to 'mix' light sources to paint a picture.


Sorry, I am trying not to be narrow minded in what can and cannot be done. Actually, I suppose this makes my Physics background even more invalid as I am starting to act more and more like an engineer. HAH!
 

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Discussion Starter · #17 ·
Quote:
Originally posted by Alan Gouger
We could add a cluster of laser pointers to the projector with long life batteries.

No more bulb or fan or power needed to the projector.
I would be more than willing to have my local power company supply me with a high-power photo-light wall outlet right next to the electrical outlet.


Hmm, where are those idiot venture capitalists when you need them ...
 

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Discussion Starter · #18 ·
Quote:
Originally posted by Alan Gouger
We could add a cluster of laser pointers to the projector with long life batteries. No more bulb or fan or power needed to the projector.
Dang, I missed that thread. This is what happens when you spend a day off either in an HT shop or eying the bottom of a bottle. Lemme go read this ...
 

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Well, actually this is not that bad of an idea if you could make a few changes.


First, there is nothing wrong with using lasers. The problem occurs in the types of lasers available in each wavelength range, in particularily the blue color. Both red and green can use standard diode lasers, but diode lasers in a blue color are currently *very* expensive and have a short lifespan. (In fact the person who invented this laser technology just moved from Nochia Chemical Japan to UC-Santa Barbara).


But, blue LEDs are currently available. (Remember the LEDs are basically lasers without the cavity mirror). Also (more importantly), companies are starting to sample multiwavelength LEDs capable of red-to-blue color wavelengths. Hence, instead of a rotated color filter it might be possible to have an array of multiwavelength LEDs (surface mounted since you want a high density for better light output) that are modulated in color wavelength. The modulation frequency could easily be in the 10s of Megahertz for those of us who see rainbows.
 

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Many lasers that are currently available do not produce much heat - in fact the opposite is true, that is, they produce significantly less heat than a standard projector lamp and are actually far MORE efficient producer of light than a bulb.


Also, while it is true that most lasers produce a relatively narrow range of frequencies - not all do. There are relatively broadband laser sources.


You could also expand the laser beam so that it hits all of the DLP chip without using ground glass - just use a beam expander.


Finally, you do not HAVE to use a laser with a diffraction grating - one could easily shine white light from a bulb at the grating and then just place one or more fixed or movable slits in the rainbow pattern of light that emerges from the grating to select the color or colors of interest.
 
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