Free Free Space Optics?

With all the layoffs happening in telecom, and service providers under financial strain, perhaps you've been sitting in your bedroom, staring at the wall, listening to The Who with the bass turned all the way down, and wondering if it isn't high time people just started building their own optical networking gear, dammit!

That's what at least one person posted -- amid a predictable amount of derision and mockery -- on Slashdot, a technology discussion board owned by a subsidiary of VA Software.

"Lately I've been obscessed [sic] with grassroots community network projects, and the hardware that enables them," writes the poster using the handle Graham Wheeler. (Graham Wheeler, incidentally, is the author of "Brew Classic European Beers at Home" and other home brewing books. Light Reading was unable to confirm that the Graham Wheeler posting was indeed that Graham Wheeler -- though the research was fun.)

"Most sites I have seen focus on wireless RF networking, but I have noticed a few projects revolving around free space optical transceivers," the poster continues. "Twibright Labs' RONJA [Reasonable Optical Near Joint Access] is a good example of what I'm talking about." Twibright Labs is a handful of undergraduate students studying "Informatics" in Prague. Their RONJA program encourages folk to "Build your own optical data link from common elementary parts." These include: "old toothbrush," "ceramic capacitors," and a "multimeter with transistor amplification coefficient measurement (not mandatory)." Damn! Where we gonna find an old toothbrush?

Besides making homemade optical networking gear, Twibright's other projects include a "lighting system with rechargeable batteries" for bicycles.

"Not being an electronics hobbyist, however, makes the various plans for building a comm laser from scratch look rather daunting," the poster frets.

"It seems to me that it would be easier to just make a lens and housing system into which would go one of the many cheaply available copper-to-fiber media converters. Then you could simply modify it so that the laser ports were optically connected to the TX [transmission] and RX [receive] lens assemblies instead of the standard fiber interface." (Yeah, definitely that Graham Wheeler... or at least a dedicated follower.)

"So, what factor(s) am I overlooking that would explain why nobody seems to be doing this?" the poster asks in conclusion.

Whether a hoax or not, the poster got several replies, only a few of which were combative. One respondent gently pointed out that perhaps buying an 802.11-enabled gadget would be better for around-the-house data transfer than, say, constructing one's own telecom lasers out of spare parts.

Another respondent interpreted the post to be about why a commercial fiber laser could be modified to work in point-to-point applications. "Most freespace [laser] projects involve something a bit more powerful, which allows the laser to punch through smoke and fog a little better," the respondent writes. "I guess if you made the laser powerful enough, it could punch through interference such as pigeons, too."

Alas, yet another sincere discussion about saving a few bucks by building your own optical networking gear has devolved into blasting birds with deadly data.

PETA officials did not immediately return calls seeking comment.

— Phil Harvey, Senior Editor, Light Reading
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8point 12/4/2012 | 10:07:04 PM
re: Free Free Space Optics? you guys are all crazy. i think you are overestimating the complexity of this home-made system.

you'd get better qos and bitrate with much less power consumption with 20lb stren and a couple empty cans of dinty moore classic chunky.
fusionboy 12/4/2012 | 10:07:03 PM
re: Free Free Space Optics? Though the optics are complex, it is not impossible. People have been able to achieve links of a few tens of meter using infrared LEDs and lenses used in remote control devices. If you change your LED to a DFB laser which is going to provide more power and a more coherent light source, it is conceivable to achieve a link that goes over 100 yards without using very expensive or complicated lens subsystem. Maybe not at Gigabit speed, but for a 802.11b base station uplink, all you need is 11Mb/s.

Light Source coherence has little to do with the problem - nor do "complex" optics.

Most IR remotes use a highly divergent beam(which quickly loses coherence in a room), and a simple, fairly sensitive detector. The beam is highly divegent so one doesn't need high alignment accuracy - you can point the remote in the general vicinity of the CD player. Simply uping the power of your source will do little to increase the range (not to mention you'll eventually have hire power lasers running around the room, not particularly safe) What you'll eventually have to do is replace the divergent remote lens with a collimating type lens, so you have a narrow beam.
CogswellCogs 12/4/2012 | 10:06:58 PM
re: Free Free Space Optics? BubbleBuster wrote: "staring at the wall, listening to The Who with the bass turned all the way down..."

Am I the only one who found this quote extremely offensive?...

Cogs replied: Yeah, I think so.

Hope this helps

freespaceman 12/4/2012 | 10:06:55 PM
re: Free Free Space Optics? I think they meant well. Don't want to be reminded that he is gone (although no bass might remind you).

I say all the way up to but I think it was meant to be a compliment.
freespaceman 12/4/2012 | 10:06:54 PM
re: Free Free Space Optics? The optics are not complex at all for large detectors or fibers. You can pretty mych do it with one lens.

The issue is that for no alignment issues, the beam must be diverged and then it rapidly looses power.

For the long links (Terabeam esque) they are diverging the beam but not that much. Now they have to hit the opposing received and this requires active control to account for everything from building sway to floor vibrations.

It's the active component (scan mirror, moving detector, etc, that makes this complicated and expensive.
bitdropper 12/4/2012 | 10:06:53 PM
re: Free Free Space Optics? "Calm down. We mourn Mr. Entwistle's passing. Didn't intend to offend.


Although I can understand why it could be taken the wrong way, I wasn't offended at all. Turning the bass down is a way of honouring John. I see it in the dame way I see a respectful "moment of silence", or the jet fighters in the "missing man formation".

There's possibly no better way of emphasizing and honouring John's contribution to THE WHO, than listening to what their music would have sounded like without him.
arch_dude 12/4/2012 | 10:06:49 PM
re: Free Free Space Optics? These systems work. Slashdot has mentioned several of them over the past two years. The construction details and the test results appear to be quite credible, and all of the theoretical objectins raised here have been addressed. In all cases, the projects have used off-the-shelf optics such as binoculars or small telescope lenses. Range is usually about 1000 meters.

There are also a series of projects to use wireless LAN technology in conjunction with homebrew antennae. These project can usually achieve a 10Km range at 11Mbit. The biggest problem in both cases is that they require line-of-sight.
willywilson 12/4/2012 | 10:06:28 PM
re: Free Free Space Optics? The biggest problem in both cases is that they require line-of-sight.


No problem at all. Cut down all trees. Telecom recovery takes precedence. Who needs vegetation anyway?
rtfm 12/4/2012 | 10:06:12 PM
re: Free Free Space Optics? Re: 802.11 systems

802.11 (b, that is) based systems can do large distances reasonably well. The issues are:

1) Line of sight - Here, in addition to LoS, one needs ground clearance beyond just the curvative of the earth. Part of the signal is carried in an ellipsoid-like envelope, which means clearance in between the end-points (above ground clearance).

2) 802.11b has needs ack-like messaging within about 100 microseconds, so speed of light limits the distance this native protocol can go. However, modifed versions, running in bridging mode (point to point) can do much longer distance.

3) Regulatory - FCC allows much higher powers (EIRP), with good antennae gain (sliding scale, allowing transmission capabilities of tens of miles). ETSI, on the other hand, limits one to 20 dBm, period. If you have an antenna, lower the Tx power. Most bridging stations with 802.11b have good strengths, just the laptop cards and like have lower powers.

4) Uplinking. Even if one uses 802.11 as a distribution means (last mile access), one still has to uplink. Or, if one runs pt-to-pt bridging with 802.11, then this can't "wire up a developing country" as the signals are daisy chaining.

But, there are some really neat pringles can (yagi-like) antennae out there.

5) One other problem might be ISPs. The NYTimes had articles on how some ISPs are cracking down on free 802.11 networks (ones that use DSL or cable for uplinking).

My $0.50

DevilsAdvocate 12/4/2012 | 10:06:12 PM
re: Free Free Space Optics? Commercial optical free space comms is not that new, since 1998 there's Terawave, and some others as well, they even have been cited here at LR a couple of times.

After cleaning out my garage today I ran came across two photocopies of articles on this subject published in 1985 and 1986.
The one from 1985 is a publication from an amateur electronics magazine with a complete description how to build your own system (for voice/audio transmission, e.g for use as an optical wireless headphone).
It also describes some interesting history of optical wireless:
19 Feb 1880: Alexander Graham Bell and Sumner Tainter demonstrate their "Photophone" which is capable to cover a distance of approx. 600 feet.

During WW2, the German company Carl Zeiss developed a system for military use capable to bridge upto 20 miles.
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