Optical Wireless Communication

[karmax]

I want to design a simple system based on Line of Sight communication technique using LED in the visible spectrum, the range should be about 2-3 m. I am thinking on the lines of using RJ 45 to serial and then Frequency modulation (VCO). On the receiver end demodulation (PLL) and again interface to RJ 45.
Can someone please suggest some good resource with circuit diagrams and theory??
Will appreciate the help.

[Soeren]

Hi,

I want to design [...]
Can someone please suggest some good resource with circuit diagrams and theory??

If you want to design a system, you are the one designing and drawing the schematics and developing the theories for this system.
If you just want to copy someones else's design, don't claim you want to design it.
Copying andf designing are two very different disciplines.

a simple system based on Line of Sight communication technique using LED in the visible spectrum, the range should be about 2-3 m.

Why visible?
There's more power in IR-LEDs.

I am thinking on the lines of using RJ 45 to serial

"RJ45" is a connection standard (RJ=Registered Jack and strictly speaking, RJ45 is an 8P2C connector [8 positions 2 conductors]), "serial" is just a description of how multiple bits are transmitted one by one, so what do you mean?
Are you perhaps thinking Ethernet (which is serial) to EIA/TIA-232 ("RS-232")?

and then Frequency modulation (VCO). On the receiver end demodulation (PLL) and again interface to RJ 45.

What bit rate do you need (absolutely)?
FM might not be the best solution.
Did you consider IRDA or something like a TV-remote NRZ-scheme?

[dennyL]

hi,

I have to make(not design!) a similar thing for my college project. It needs to be optical since later it will adapted for underwater use (using blue-green wavelengths).

I am hoping to get some advice on what options to look for and just pointers in the right direction.

[z.s.tar.gz]

Why wouldn't infared work underwater?

[guncha]

http://www.imagineeringezine.com/ttaoc/preface.html is THE place to go for info on this. You can find schematics and everything there.

[madsci1016]

Why wouldn't infared work underwater?

Different wavelengths will scatter more/less. IR will scatter very quickly and lose signal strength. Even blue/green won't go very far.

The reason the sky is blue is because it is the only wavelength not scattered by the atmosphere.

[Soeren]

Hi,

2..3m should be manageable, even with whatever color, but for seawater, bluish green (teal?) is probably the one with the longest reach of the visible LEDs.
However, there's more energy in IR and IR have been used for underwater comms (between divers), so it do work (range will probably depend on which ocean though).