Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

Maximum laser frequency

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Hey everyone,

I was just wondering. Does anyone here know how fast a laser can pulse before it won't do it properly anymore?

I had the random idea of making a long range Ethernet bridge using lasers and receivers to act like the wires of an Ethernet cable.

And how do you go about rapidly pulsing a laser? It can't be good for the driver to constantly be shut on and off repeatedly.. Maybe I'd just ground the power line between the driver and laser so that the diode doesn't turn off but goes down in power enough that the receiver can't see it?

But if a laser can't keep up with the rate that data goes through the cable I'd just scrap the idea for a slower medium of communication.

I believe that the maximum frequency of a cat5e cable is 100MHZ.

and on a side note, which wavelength of laser goes the furthest with least power?

I'm probably not going to make anything groundbreaking with this side project but it sounds interesting ;)
 

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
So as far as I know, laser DIODES can be pulsed extraordinarily quickly, and I don't think that 100MHz is out of that range. And for drivers... you need a driver that can handle a short on the load in order to pulse it this quickly. That is, you would need to be able to switch from with a load to shorted to with a load again in a nanosecond without dropped in current. Not sure what drivers can do this, but I am sure it wouldn't be difficult to design one... but then again, most switching ICs nowadays switch at around 1MHz, so maybe it would be difficult to design.

And on your side note... 808nm would be the best, because there is the least Rayleigh Scattering effect on the lower-frequency end of the visible spectrum (frak you guys who say that 808nm isn't visible. I can totally see it).
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
lol

I was going to talk to my electronics teacher about a driver design that could handle this. He's been designing precision power supplies for years before becoming a teacher, so I'm sure he knows of one.

Wow, I wasn't expecting this to be that simple. And those 808nm diodes are cheap!

Now I just have to come up with a way to receive them fast enough and then a way to translate the electrical ethernet pulses to laser pulses.

Maybe high speed mosfets? Dunno. I wonder if it could be fast enough to be seamless to the device on the thing, so it just assumes its a 100mbps connection.
 

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
Remember, to detech 808nm, you're going to need a NIR sensor because 808nm is just barely in the visible spectrum.

Further, yes, you have to figure out a way to detect the light and then use that as an on-off switch for a power supply. However, I would think an optical coupler would work there (I think that's what it's called, it essentially uses light as the gate for a transistor). Translating the electrical ethernet pulses shouldn't be that hard - just use a high-speed transistor that will open the gate when the ethernet pulse is HIGH and close it when it is LOW to connect the diode to the leads on the driver.

But what do I know? I'm just speculating (although I am pretty damn sure about the high-speed nature of diodes and 808nm lasers being used for high speed connections).
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Yeah, I recall that we have all of those types of components in the storage room. Can't wait for the year to start so I can get back to tinkering!

This should be interesting. Maybe I could build a tree house and use this to communicate? ;) lol, just kidding. I don't know what I'd use it for.
 

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
I wonder if it is possible to regulate current faster than it is to regulate on-off? Because maybe then you can actually encode data differently - you could use different power levels for different bits, instead of using a binary, ON-OFF system, you could use a LOW-MED-HIGH system or something. If you could encode it that way, you wouldn't need as high a speed in order to communicate the same information as a binary system is at 100Mbps.
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Maybe, but then you would need a device to go and encode/decode everything. I mean its possible, and I would probably do that if I wanted to move to gigabit, but for now this is meant to be a simple 'wonder if it'll work' thing.

And besides, that may cause issues if the outside conditions are spotty. Like maybe a fog preventing the laser from reaching it at full strength and then confusing the decoder? At least with binary its 'on or off' and no guessing.

Though I was thinking of multiple lasers for more data streams.
 

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
You may be right about that. I am just worried about getting a driver to pulse the laser that frequently.
 

SOG

New member
Joined
Jun 13, 2011
Messages
109
Likes
1
Points
0
Um.... but I thought optical cables uses lasers too? so I suppose they would work?

Actually I have seen something similar when I was in one of those exhibition show... it was for a security camera feed. I wasn't sure why they have it on a security camera feed thought...

But I think it won't work very well out doors? think about rain, fog... birds... not sure how your program will handle the error rates if you are going to use a PC for sending them on digital.

But hey, I have heard they are gonna use laser to shot to Mars, or any space stations, so they can have internet access... but I have heard that from like 5 years ago, not sure how they do it.
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Yeah. Maybe a different method of driver then?

And how do things like DDL drivers respond to rapid shorts? I'd have to test that.

And on top of that I need to find some sort of high speed transistor. I know that the common ones are too slow.

And, I need to find one of these NIR sensors you speak of. I've never messed with infared before so yeah..

Edit: SOG,
Yeah, thats true. Or led. I dunno.

And I imagine if its powerful enough it'll punch through fog and stuff. Dunno about rain. I was thinking of buffering the signal a bit maybe? I know that most network equipment is built to deal with packet losses. All it does is reduce the throughput.
 
Last edited:

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
A DDL driver actually may work, as long as you design the heatsink on the IC to be able to sustain the whole of the input voltage converted into heat (should be doable).

The only problem I see is that how will you ground the output without momentarily making an open circuit? At normal speeds, it would be fine, but at this speed, the actual switching from on to off may cause problems.
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Well I was thinking of doing it inline with the laser diode. So not actually disconnecting it, just bypassing it with a couple ohm resistor or something. Enough to get the ddl driver to lower the voltage significantly, in order to dim or stop the LD from emitting light.

And I would probably slap a way too large heat sink on everything anyway, so no worries :p
 

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
Or, what if you put a resistor in parallel with the LD? Finding out the current the LD is seeing would be a whole different game, but it should be doable, and then when you disconnect the LD, there still is no short because the resistor is still connects the outputs!
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Thats slightly different then what I was saying actually, but still sounds good!

What I was saying was to have the LD negative and resistor hooked together, then LD positive hooked to the driver, and then a transistor between the resistor and driver as well. So when you trigger the transistor, suddenly there is more load on the ddl driver, it lowers voltage to compensate, then the LD dims or shuts down. When signal is back, the transistor shuts off, cutting the resistor from the parallel link, causing the DDL to only see the diode, raise the voltage back to normal levels, and the LD to light up again.

Do you see any issues with that? I think it might be safer since there are no sudden connects/disconnects for the LD, since I've read they can be fragile.
 

Wolfman29

New member
Joined
Jan 14, 2011
Messages
3,830
Likes
200
Points
0
Eh. When it comes to diodes, I wouldn't really worry about disconnecting the diode completely. Your way would work, but it would just make it more difficult to make your detector NOT pick it up when it's dimmer. I would suggest my method, because then the only two states are OFF and ON, not HIGH and LOW.
 

ITman496

New member
Joined
Aug 19, 2011
Messages
185
Likes
9
Points
0
Good point. I'd probably try both and see which was more reliable in various conditions.

Also, can you explain to me what you meant by the NIR you mentioned earlier?
 




Top