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Home > Forums > Electrical / Electronic Engineers > Activities > Communication & Signal Processing engineering Forum

free space optical communication(2)

Read More Threads Like This One

daksein (Electrical)

31 May 12 13:01

Hi guys,
I want to ask anyone if you know about free space optical communication. Can you give me some insight about this technology. Whether it is accepted nowadays and used in any country?

VE1BLL (Military)

31 May 12 17:40

It's public knowledge that DARPA is funding investigations into use of blue-green lasers for free space (plus tens of meters of sea water) communications with submarines.

http://optics.org/news/1/4/21

Mid-1970s I sent audio across the classroom using an LED, reflector, phototransistor and a telescope.

One would think that it should be in more common use. But it practice it's unreliable because (for example) a passing bird can obviously block a laser beam or small sensor.

Off-hand I can't think of any wide spread applications.

IRstuff (Aerospace)

31 May 12 22:17

It's really a point to point type of system. What makes a laser intense is its beam's small divergence (angular diameter), but spreading out the signal to simplify alignment and aiming dilutes the signal.

TTFN
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MikeHalloran (Mechanical)

31 May 12 22:40

As of a few years ago, it was available commercially, and suitable for carrying what is now modest bandwidth (T1-ish) between buildings, e.g. rooftop to rooftop across a busy street.

It was also considerably more expensive than other technologies that became usable if you had any way to put a cable or fiber pair under the street.

Mike Halloran
Pembroke Pines, FL, USA

GregLocock (Automotive)

31 May 12 22:51

I always felt sorry for the guy waving the flags. The one with the telescope had a much easier job.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

LiteYear (Computer)

31 May 12 23:44

I find it pretty commonly between my couch and the TV. The advantage there I suppose is that you can physically aim the transmitter at the receiver until the short-length message is transmitted.

OperaHouse (Electrical)

1 Jun 12 5:28

Those remotes seem to have gotten a lot worse. I remember when You could point a remote in any direction and it would pick up the bounce. Now a deliberate aim is iffy. My father has IR headphones. You can walk anywhere in a room with no loss.

IRstuff (Aerospace)

1 Jun 12 10:06

"Those remotes seem to have gotten a lot worse. I remember when You could point a remote in any direction and it would pick up the bounce. Now a deliberate aim is iffy. "

Probably to minimize interference. It used to be that a single remote was about all you had, but now, there are remotes EVERYWHERE. The other problem is battery life; dimming the transmission probably substantially increases the battery life.

TTFN
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OperaHouse (Electrical)

1 Jun 12 11:14

My theory to everything is......Follow the money. Mad Man Muntz is storied to just clip out parts till a set stopped working. He is credited with reducing the sensitivity of TV tuners industry wide by eliminating the gain sections. His theory was 90% of the people lived in cities or had cable. Just no reason to have gain.

daksein (Electrical)

2 Jun 12 12:17

Quote (MikeHalloran)
As of a few years ago, it was available commercially, and suitable for carrying what is now modest bandwidth (T1-ish) between buildings, e.g. rooftop to rooftop across a busy street.

It was also considerably more expensive than other technologies that became usable if you had any way to put a cable or fiber pair under the street.

So how about nowadays? Is it still being used or implement for telecommunication? Can I know at which country it is being used?

MikeHalloran (Mechanical)

2 Jun 12 12:41

Well, how much bandwidth do you need, over what distance, in what country?

Mike Halloran
Pembroke Pines, FL, USA

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