why visible light communication is not replacing DSL/cable ?

[jeorge_kabbi]

if a light bulb is blinking from some hundred yard i probably can see it with my eye without the use of a binoculars.

so why don't we build a tall tower in the middle of residential neighborhood (the existing cell towers could work) and we install laser / visible light transceivers on the tower and on those houses and point those to each other.

multiple measures can be used to reduce the cost and increase the speed of communication:
1- if visible light will be used we can use more than one color.

2-interpolating those colors of the transceiver on the tower i.e. yellow transceiver placed next to blue transceiver next to green ... etc, so that the other end will have easier time reading the light signal

3-multiple transceivers per house can be used to increase the throughput .

4-transceivers could be built to have zoom . this kind of zoom lenses woudl be much much cheaper than camera zoom because the glass of a camera has much more to worry about than a few pixels of light to be detected.

5- directional light : e.g. if you installed the light with a reflector at the end of a regular plastic water pipe the light will be sort of directional. i am sure a cap with a relatively small hole at the other end will make it even more directional (other houses will not see it and that will decrease the noise on those transceivers.

i am not an engineer just saying what if we built such a system that replaces DSL/cable instead of the crappy DSL/cable we have in many places (the last mile problem).

any thoughts ?

 

[MongGrel]

https://en.wikipedia.org/wiki/Optical_fiber

 

[Gryz]

The main reason is probably that it'll get too expensive. E.g. you can see a light blinking far away. But if you want to run at gigabit speeds, you'll need to let the light blink once every nano-second. That is fast. Building an optical receiver that can detect such fast blinking is probably gonna be very very expensive. Also note, that in a fiberglass-cable, the strength of the signal that comes out is relatively strong. In your proposal it lessens in strength by a power of 3 per distance (because we live in a 3d world).

Also, weather will have severe impact. Simple rain might kill the signal. Fog surely will.

Not everybody will have a straight line of sight. Even if they do, the antennas need to be redirected once in a while. The practical implications that can cause stability/service/support issues are huge, I think.

Your solution kinda exists already. Only not with photons in the visible spectrum. But with electro-magnetic pulses with lower frequency. It's called radio, WiFi, GSM, G4, etc. E.g. you can buy directed transmitters and receivers to do exactly what you propose, but over radio-frequencies. I know someone in Norway who does that, because he's too far away to dig cables. But he has clear vision over the fjord to a directional station. It's low bandwidth (2 Mbps I believe). And he's got lots of problem with the weather. I think with optical signals, it'll be even worse.

 

[Fardringle]

To do it the way you described, you would have to have a separate transmitter on that tower for every single customer in range. Assume that each tower only gets 1 mile range (to be efficient it would have to be much larger than that), an average residential neighborhood is going to have somewhere around 7000 homes in that 1 square mile range. So 7000 separate transmitters on that tower..

And then with direct visible light, you have to deal with obstructions, atmospheric conditions, adjustments in the signal for daylight and nighttime usage, and each transmitter would have to be exactly aligned to the receiver on each customer's home.

Direct light transmission can be used for point-to-point connections and can work fairly well in some cases, but not for general public use..

 

[JeffMD]

foggy day? mass internet outage. -_- The reliability would be worse then dish. Also while fiberoptic can bundle different wavelengths into one wire, a WAN setup would need a one to one setup making the tower have a finite number of connections possible.

Also you clearly live in a city, take a drive in the suburbs with lots of trees around. My neighborhood in Fl has huge trees all over. Everyone would need cellular tower length poles stick out of the canopies.

That said, Businesses with several large buildings in an area HAVE built laser interconnects between them.

 

[dave_the_nerd]

Visible wavelength stuff (lasers) are more problematic and prone to interference than other wavelengths of stuff. Also, "you'll put your eye out, kid."

Between cell phone networks and municipal wifi (in cities) there are solutions to address it.

In rural areas where the "last mile" problem is more like a "last ten mile" problem, there are technologies like WiMax, in addition to LTE (cell phone internet) and Satellite dishes.

 

[azazel1024]

It just isn't viable for distributed networking. It can be fine for temporary point to point links, but distributed or long term you run in to weather issues as well as cost and difficulty to install. As others have mentioned rain, fog, snow would all hamper or render it inoperable. For installation, single emitter, single receiver and you have to pinpoint it very, very, very exactly. So the installation would be on the difficult end of the spectrum. Whatever tower you put up must have LoS to the end point. Where can you imagine there is where you can see most houses in a neighborhood? I know in mine there is no where unless maybe you built an 800ft tower, even then you probably couldn't see it 3 miles away because of the rolling terrain where I live.

It would be good for secure communications (and fast) in relatively clear weather from hilltop to hilltop maybe. The applications are just tiny.

 

[KingFatty]

There are already technologies that do this but for indoors instead of outdoors. I think by adding modulation to the artificial indoor lighting, and devices in the room use their light sensor to receive data.

 

[iunlock]

They have indoor light spectrum prototypes in S.Korea at some of the Universities.

Outdoor wise like a lot have mentioned is the weather, along with many other variables.

Things would be a lot different in a vacuum (space), but that's basically fiber as we have it now just with data traveling through a different medium. With limits I might add.

The future will be interesting....

 

[drebo]

Free space optics are a thing, and they can be quite fast.

They require line of sight, though, so they aren't feasible for anything other than engineered point-to-point links.

https://en.wikipedia.org/wiki/Free-space_optical_communication