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FrozenGate by Avery

Homemade Scanning Laser Color Projector/TV

GooeyGus said:
hmm... Still doesn't make a whole lot of sense to me. If these motors are fast enough to scan tv that well (I assume it's 'rastering' the image) then I would think that laser projectors would be using this same technology but they dont. Galvo's are still the scanning method of choice. I would think if these are that much faster that they would be more widely used.
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When you think about it, any tweeter or other small speaker is capable of 15Khz very easily. As long as it's a concisely defined and repetitive path, it can be engineered without much of a problem. The part I don't understand is the modulation.

625 is on one axis, and assuming 16x9 ratio, 350 on the other. With a framerate of 25fps, your modulation speed would therefore have to be 5.5Mhz. That's 200-600 times faster than lasers I'm aware of.
 





Cyparagon said:
[quote author=GooeyGus link=1240948547/0#10 date=1241043070] The part I don't understand is the modulation.

625 is on one axis, and assuming 16x9 ratio, 350 on the other. With a framerate of 25fps, your modulation speed would therefore have to be 5.5Mhz. That's 200-600 times faster than lasers I'm aware of.
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No problem

LDs are fast enough.
 
sltvm2007 said:
[quote author=Cyparagon link=1240948547/0#17 date=1241280040][quote author=GooeyGus link=1240948547/0#10 date=1241043070] The part I don't understand is the modulation.

625 is on one axis, and assuming 16x9 ratio, 350 on the other. With a framerate of 25fps, your modulation speed would therefore have to be 5.5Mhz. That's 200-600 times faster than lasers I'm aware of.
Click to expand...


No problem

LDs are fast enough.[/quote]


And you have Green LDs ? ::)

Also, the drivers can't go this fast too easily.
 
I'd really like to see a diode running at 5+MHz. Sure the diode can do it, but probably not the driving electronics.

I mean, 5+MHz AND it's modulating power... I dont know about that.

Even upon special request most laser manufacturers can only do up to 30kHz modulation... I've seen as high as 50kHz.

If it were using PWM modulation it would make a whole lot more sense to have such a super fast modulation rate, because that's how it works. But analog at a few mHz just doesn't sound right to me.
 
With respect to DVDs, 10.5Mbps is 1X and we've seen 22X. That's 231 million pulses per second (231MHz TTL). So why are no lasers (outside of optical drives) capable of more than 50KHz?
 
The lasers themselves are quite capable of modulation up into the MHz range, it's the drive circuitry that comes with them that is not. You could use a DPSS laser for high-speed data transmission if you wanted to, but the usual DPSS wavelengths are not the best suited for fiber transmission. Laser diodes are by far the most efficient, low-cost solution for high-speed modulation in fibers and consequently are the most common lasers to see being modulated at MHz speeds. Any diode is capable of very high-speed modulation, as well as any DPSS laser head, so long as the modulation circuitry can provide pulses at these speeds.
 
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Isn't it so that DPSS has some sort of delays in the cristal which implay that it cant react that fast?
 
Not that I know of. Light typically propagates faster in solids than liquids or gasses, so the transmission through the crystal will still be plenty quick. When you consider the math, it would take one hell of a propagation delay in the crystal to cause issues modulating in the MHz range. I'm not sure just what the limits are, and there are limits, but DPSS lasers can definitely be modulated very fast. Stability in DPSS lasers during modulation is another matter, however. This makes them unsuitable for high speed modulation more than any propagation delay problems.

FrothyChimp is the man when it comes to this stuff, so I'm sure he could set the record straight.
 
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I thought more of a delay before the pumping energy is high enough in the cristall bevore it emits green laser light. seriously i forgot all the details and where i read this but it was something about that dpss "turns on" slover than a diode and "turns off" with a delay too. thats why a user at PL developed the "DPSS correction circuit" to remove "tails" in scanning projections.
 
You may be right.. like I said, FrothyChimp is the man when it comes to DPSS stuff. What you are describing sounds like power sags and surges (instability). In a green DPSS laser, when the pulse of pump energy hits the crystal, it does take a brief instant for the power level to come up, so if that is what you're describing then yes, there is a delay. I believe however, that even though it is not at full power, green light is emitted the instant the pump beam hits the crystal. There is most likely enough power present that data communication could still take place, and like I said in my last post, these stability issues are far more of a problem than propagation delay.
 
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Sound as well.. In lenses and prisms, refraction occurs because the light slows down (its phase velocity decreases) slightly as it leaves the solid material and enters the air, which causes the light waves to change direction slightly..
 
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Mmm.. I'm still not too sure about that. That statement is comparing an unknown transparent material (could be solid, liquid, or gas) to a vacuum (which has unique properties when it comes to transmitting energy), whereas my statement is comparing a solid transparent material to a gaseous transparent material.

You may be correct, but I'll have to do more research later. I'm at work presently, so I'm a bit limited, and I can't remember all my high school physics ATM..:)

Regardless of the order of things, I still don't think that the speed change would slow or delay the transmission of light enough to prevent modulation up into the MHz range..
 
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You are correct, cyparagon.. Here's a link that describes this in more detail. Thanks for your input!

http://www.physlink.com/Education/AskExperts/ae81.cfm?CFID=17088478&CFTOKEN=62018254

So, any delay would depend on the type of solid medium, and on its specific properties. It is true that DPSS lasers are more limited in terms of modulation speed than their diode counterparts, but just how much more limited I have no idea..

My own personal experience with high speed optical data transmission has always been with diodes only, and I'd imagine that has to do with what is described in the link above. That, coupled with the instability that DPSS lasers tend to display while being modulated is pretty much a deal-killer for this type of application.
 
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