what the difference between light emitting diode&laser d

hi..i have a question..i want to do a project...its about free space communication..i want to send information " data, voice, video " by using a laser diode or light emitting diode and for recieving photo diode..ok.? like i talk using mic..mic converts voice signal to electric signal...then im gona use an amplifier to amplify the signal "is there will be noise? and if yes what gona do to solve this problem is there an amplifier that remove noise?"..then im gona use an exciter to change the frequency of the signal and i think im gona use red wavelength"infrared"..then the signal goes to the laser or light emitting diode"what the difference between them and what do u suggest?"..then the diode converts the signal to beam of light...what the distance between the laser diode or light emitting diode and photo diode? and can i increase the distance by using lens to strong the beam?..".one of my teachers told me that its impossible project..because after the photo diode converts the the light beam to an electric signal...the signal will be very small...which the amplifier cant detect the signal."...then the signal goes to an amplifier then to a demodulation to change the signal to its original frequency..then to a speaker...what do u think..? for the information im gona send voice coz its easier than others..what problems u think im gona face...pleez guys..help me.. if u can give me links or send me files that help me..i will be grateful...if u use MSN...can u add me RoNNy_Rm@hotmail.com

LED and LASER eventhough they both emit light on emits by stimulated emision and other by spontenious emission

A laser is like a high Q resonator oscillator. Like an oscillator, a lot of the properties of the light depend on the type of resonator used.

An LED is like a broadband noise source at high output power.

Basically Laser has a threshold current while LED does not.

this is some material

http://www.icnirp.de/documents/led.pdf

Hello Ronny
You want to use infrared right?
Then if u use laser u can reach up to 4-5 meters range and for LEDs this is quite smaller up to 2 meters due large beam pattern.you cant focus as well but if u use a large area receiver as well, u take more power so use APD but by this way ofcourse u will increase the input capacitance since u increase the area.
And there are also some lenses for the transmitters, search them on net. There are amplifiers both pre and back amp. used after the receivers. this shrinks the ambient noise and shot noise. But for infrared comm. u can't escape from noise, this is impossible. Best way is also to use a sector combining. Have u taken a course on mobile communications, if not just search about the max. ratio combining or best sector or equal ratio combining , then u select the best SNR and go on your way but as much as u add components u make it expensive and slower and complex so nowadays the scheme is to implement the circuit as simple as possible..This is the summary, I suggest u to use LD and APD..
Memo

using LED like using omni direction antenna but laser like directed one
if u want to concentrate ur power into a small area use laser but if u want to distribute the power use led it depend on the application u will implement but if u ask about the theory of operation u will find alot of document on the net talk about that sorry i do not have one now

Hello,
this is some characteristics of leds and LASER
laser : is more powrful than light emmiting LED, it's unidirectional, therefor it's much less sensitive to attenuation, and climat conditions
LED: is much less directive, and it gives less power (or if you want intensity), it's very attenuative light and it's easly dispersif one.
oh I hink it's all
best regards