Lasers

[Edisonian]

I have a question that I hope some will be kind enough to answer. Does anyone think it is possible to use a laser to transmit data instead of traditional delivery mechanisms (i.e., cable, telephone line)? What are the physical limitations?

[H2SO4]

i dont see why not. A longer pulse means 1, and a short one means 0. binary code. I dont see why not.

[Cap'n Refsmmat]

Infrared transmission is relatively common.

 

Only problem with laser is that you have to have it pointed at exactly the right spot...

[Rakdos]

Does anyone think it is possible to use a laser to transmit data instead of traditional delivery mechanisms (i.e., cable, telephone line)?

Fiber Optic Cable sometimes use lasers so they are already in use.

[-Demosthenes-]

Infrared transmission is relatively common.

 

Only problem with laser is that you have to have it pointed at exactly the right spot...

Line of sight. If there is anyhting in the way then it can't get by, whereas radio and other waves can.

[swansont]

Line of sight. If there is anyhting in the way then it can't get by, whereas radio and other waves can.

 

Fiber optic cable. As was already said, IR lasers (near 1560 nm) are in widespread use already. Lots and lots of fiber optic cable is already in the ground.

 

I did a demo in my lab in grad school - took a boom box output, modulated a laser diode (780 nm), sent the light across the room to a photodiode, sent the output into another boom box and played the music. I thought it was one of the coolest things I'd seen. Aside from setting up the laser system (which had happened already) it only took a few minutes plus the time to wire a BNC-RCA cable.

[swansont]

I have a question that I hope some will be kind enough to answer. Does anyone think it is possible to use a laser to transmit data instead of traditional delivery mechanisms (i.e., cable, telephone line)? What are the physical limitations?

 

wave division multiplexing

 

One limitation is dispersion, where the 0s and 1s blur into each other because the wave pulses spread out. The index of refraction of materials (e.g. optical fiber) is wavelength dependent, so the high- and low-wavelength parts of a pulse travel at slightly different speeds and spread out in time.

[-Demosthenes-]

Fiber optic cable. As was already said' date=' IR lasers (near 1560 nm) are in widespread use already. Lots and lots of fiber optic cable is already in the ground.

 

I did a demo in my lab in grad school - took a boom box output, modulated a laser diode (780 nm), sent the light across the room to a photodiode, sent the output into another boom box and played the music. I thought it was one of the coolest things I'd seen. Aside from setting up the laser system (which had happened already) it only took a few minutes plus the time to wire a BNC-RCA cable.[/quote']

But then you have to run cable everywhere, right? Why would we want to use lazers? Are they faster?

[xa]

Couldn't you set it so that there are two frequencies and that say 1 is 700nm and 0 is 680nm(2 awesome points to anyone who recognizes those frequencies)?

Well you know what's cool about light? It's really really fast. So say you wanted to transmit data from A to B. Light will get there near instantaneously, but electric data will take much longer.

[RedAlert]

Line of sight. If there is anyhting in the way then it can't get by, whereas radio and other waves can.

 

That would make it a useful means of communication for the Military though. The message can only be intercepted by people in it's LOS, so that is an added security bonus for them.

[swansont]

But then you have to run cable everywhere, right? Why would we want to use lazers? Are they faster?

 

Bandwidth. Read the WDM link in post #7. You can send multiple signals (currently up to 32) down each fiber.

[swansont]

Couldn't you set it so that there are two frequencies and that say 1 is 700nm and 0 is 680nm(2 awesome points to anyone who recognizes those frequencies)?

Well you know what's cool about light? It's really really fast. So say you wanted to transmit data from A to B. Light will get there near instantaneously' date=' but electric data will take much longer.[/quote']

 

Electrical information also travels near c. Not surprising since the electromagnetic interaction is mediated by photons. The information through an optical fiber will travel at c/n, where n is the index of the fiber, and n>1.

 

680 and 700nm (those are wavelengths, not frequencies) - photosynthesis pigment absorption peaks? They're too imprecise to have spectroscopy significance.