Free Space Optical using LED as opposed to Laser

Thread Starter

lozza3951

Joined Jan 15, 2015
4
Hi all,

I am looking for some technical assistance with a current project I have been tasked with.

The project requires the construction of a working Free Space Optical (FSO) link. Although exact distances have not been stated as yet, it is hoped to achieve somewhere in the region of 500m to 1km. Most traditional FSO systems utilise a Laser as the light source but I have been tasked with experimenting with the use of high powered LEDs.

The end system needs to be required to transmit/receive data bi-directionally at low speeds of around 1Mbps.

Does anyone have any knowledge or experience in designing circuits that may be possible of achieving this? I have looked at the RONJA systems online but they seem to be very complex and manpower intensive.

Any help is massively appreciated!!

Lauren
 

crutschow

Joined Mar 14, 2008
34,285
A LED would be difficult to use for this task since it doesn't put out a narrow coherent beam of light that a laser does, so it's difficult to focus the light into the narrow beam required to transmit long distances. It likely will require much more power than a laser system.
Good luck.
 

MikeML

Joined Oct 2, 2009
5,444
A LED would be difficult to use for this task since it doesn't put out a narrow coherent beam of light that a laser does, so it's difficult to focus the light into the narrow beam required to transmit long distances. It likely will require much more power than a laser system.
Good luck.
However, as Clint shows in this article, the LED is much better at carrying modulation than is a laser because of scintillation. That might not matter in space.
 

wayneh

Joined Sep 9, 2010
17,496
Most traditional FSO systems utilise a Laser as the light source but I have been tasked with experimenting with the use of high powered LEDs.
My first boss taught us to always ask, "Why?" It seems an obvious question here: Why deviate from proven technology?
 

alfacliff

Joined Dec 13, 2013
2,458
at a ham club meeting about 7 years ago, some guys were demonstrating leght beam communications using led's with telescopes, worked pretty well.
 

Thread Starter

lozza3951

Joined Jan 15, 2015
4
I have asked that question to the project proposer and they have their own reasons behind using LEDs as opposed to Laser so unfortunately this is a must for this project.

Had a meeting with them today and we are now looking at just a basic one way working system with a simple transmitter at one end of the link and a receiver at the other.

Also we are playing around with the idea of implementing the modulation/demodulation part of the system using FPGA's as opposed to PCB's and component level electronics. There is quite a healthy budget available for the project so we are not restricted on what products we can buy.

The basic system block diagram at the minute is looking something along the lines of:

Transmitter
I/O Device (Probably TCP/UDP) >>> FPGA BOARD (To modulate the data and drive a high current to the LED) >>> LED ARRAY >>> FRESNEL LENS ------ free space

Receiver

free space >>> SPOTTING SCOPE >>> PHOTOSENSOR/PHOTODIODE >>> FPGA BOARD (To de-modulate the data) >>> I/O Device (TCP/UDP)

Now i am sure it is probably far more complex than I am making out but this is just an initial idea. Thankfully we have until April to deliver the project so i have plenty of time for learning!!

Lauren
 
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