Question about Lasers, LCDs, and assorted Optics.

[Raukk]

I apologize if this question is dumb.

I understand that LCDs work by polarized light and by the ability to change that polarization of light passing through the Liquid crystals, and the light is normally provided by a back light. If that back light was removed and replaced by a laser would the laser light pass through the LCD the same as normal light and if it does; once it exited the LCD would the laser light still be a laser (ie. not expanding)?

As a rough example, could an image be projected at a distance by a laser traveling through an LCD screen?

Thanks for any input, my optics knowledge is a bit rusty.

[*Aqua*]

That's how LCD projectors work.

[N_las]

A laser would pass throgh the LCD, but some scattering will take place. But you could project an image with that.

LCD projectors do the same without lasers (they need lenses to focus the image at a fixed distance).

There are laser projectors out there, but they don't use LCDs. Think of a red, green and blue laser with moving mirrors.

[Raukk]

A laser would pass throgh the LCD, but some scattering will take place. But you could project an image with that.

LCD projectors do the same without lasers (they need lenses to focus the image at a fixed distance).

There are laser projectors out there, but they don't use LCDs. Think of a red, green and blue laser with moving mirrors.

That was what I thought!

Could you then in theory make a projector that would go very long distances?

[N_las]

That was what I thought!

Could you then in theory make a projector that would go very long distances?

We have the technology:

http://en.wikipedia.org/wiki/Laser_video_display

But even a Laser spreads out all the time. It is a common misconeption that a Laser is just a straight beam of light.

For short distances this doesn't matter. But for example the size of the "laser spot" we send on the moon to measure its distance is 70 km² on the moons surface.

I don't think a projector will work for distances that long.

Edited December 11, 2014 by N_las

[Raukk]

We have the technology:

http://en.wikipedia.org/wiki/Laser_video_display

But even a Laser spreads out all the time. It is a common misconeption that a Laser is just a straight beam of light.

For short distances this doesn't matter. But for example the size of the "laser spot" we send on the moon to measure its distance is 70 km² on the moons surface.

I don't think a projector will work for distances that long.

The longest range I've heard for a projector is 300m (on one that costs as much as my car) and I was thinking ranges of 1-2 mile(s) as very long distances.

If I wanted to project an image on the moon I think the laser would melt the LCD. Lol, now I want to project my face on the moon.

[QuesoExplosivo]

https://what-if.xkcd.com/13/

Not very easy to do . . .

[Idobox]

Lasers are very inefficient light sources, and monochromatic, so you'll need at least three to get colour pictures, and a way to "fuse" them, maybe switching from one to another very fast?

Expensive video-projectors use 3 optics with DLPs (tiny moving mirrors for each pixel), one for each colour, so that would be easier to adapt with lasers. That being said, using larger lenses would give you equivalent results.

Finally, what's the point of projecting a small image to such ranges? Because if you want a very large screen very far away, you just need a more powerful lamp and conventional optics.

[Raukk]

Lasers are very inefficient light sources, and monochromatic, so you'll need at least three to get colour pictures, and a way to "fuse" them, maybe switching from one to another very fast?

Expensive video-projectors use 3 optics with DLPs (tiny moving mirrors for each pixel), one for each colour, so that would be easier to adapt with lasers. That being said, using larger lenses would give you equivalent results.

Finally, what's the point of projecting a small image to such ranges? Because if you want a very large screen very far away, you just need a more powerful lamp and conventional optics.

The original idea that spurred this question is the idea of free-space optical communication and that "a picture is worth 1,000 words."

In theory I could shine a laser through a beam-expander and then an LCD display (or DLP) to a receiving station some distance away that would take the image an turn it into data.

If no data was lost in transmission (not realistic) my cellphone's screen could transmit 300+ MB/s (2560x1440, 30hz, 24bit color depth).

I know that example is simplistic and flawed but you get my point.

[N_las]

The original idea that spurred this question is the idea of free-space optical communication and that "a picture is worth 1,000 words."

In theory I could shine a laser through a beam-expander and then an LCD display (or DLP) to a receiving station some distance away that would take the image an turn it into data.

If no data was lost in transmission (not realistic) my cellphone's screen could transmit 300+ MB/s (2560x1440, 30hz, 24bit color depth).

I know that example is simplistic and flawed but you get my point.

We can already do much better data transfer with optical fibers.

http://en.wikipedia.org/wiki/Optical_fiber

"As of 2011 the record for bandwidth on a single core was 101 Tbit/s (370 channels at 273 Gbit/s each).[28] The record for a multi-core fiber as of January 2013 was 1.05 petabits per second. [29] In 2009, Bell Labs broke the 100 (petabit per second)×kilometer barrier (15.5 Tbit/s over a single 7000 km fiber)."

If you are watching a HD video on your screen, it had to get there over the internet. So, the communication technology of the internet has to be already better than your phone's screen could ever be.

[Raukk]

We can already do much better data transfer with optical fibers.

http://en.wikipedia.org/wiki/Optical_fiber

"As of 2011 the record for bandwidth on a single core was 101 Tbit/s (370 channels at 273 Gbit/s each).[28] The record for a multi-core fiber as of January 2013 was 1.05 petabits per second. [29] In 2009, Bell Labs broke the 100 (petabit per second)×kilometer barrier (15.5 Tbit/s over a single 7000 km fiber)."

If you are watching a HD video on your screen, it had to get there over the internet. So, the communication technology of the internet has to be already better than your phone's screen could ever be.

The idea was never intended for backbone networking, but for "Last Mile," given the low cost of a LCD screen it may be possible to get decent bandwidth (100+Mb/s) for less than $1000 per mile, which I think is several times cheaper than Fiber-optic.

Also, my question was, "is it possible", not "is it practical".

[N_las]

The idea was never intended for backbone networking, but for "Last Mile," given the low cost of a LCD screen it may be possible to get decent bandwidth (100+Mb/s) for less than $1000 per mile, which I think is several times cheaper than Fiber-optic.

Also, my question was, "is it possible", not "is it practical".

We can already do 1 Gbit/s over 2 km with laser free space communication:

http://en.wikipedia.org/wiki/Free-space_optical_communication

[Raukk]

We can already do 1 Gbit/s over 2 km with laser free space communication:

http://en.wikipedia.org/wiki/Free-space_optical_communication

Thank you, I heave read that. Sadly the cost of those systems was not disclosed in the article.

[N_las]

Those systems suffer from huge disadvantages. If the atmospheric condition is not perfect, than you won't get any significant amounts of data across.

The cost of the system are the laser and the detector. Both are things you would need for your idea too. Basically this IS your idea, just with way fewer pixels.

Your idea of "less than $1000" is flawed. The display in your phone may cost less than $1000, but the expensive parts of the system will be the laser and the detector.