9 ms·

Harnessing light for wireless communications

76 points by dwaxe 10y ago

rosalinekarr 10y ago
Maybe with this technology, we can finally build the 80's neon cyberpunk future we've all been waiting for.
- liveshops_ 10y ago
  I wanted to upvote this twice.
hathym 10y ago
Are they trying to re-invent Li-Fi ? https://en.wikipedia.org/wiki/Li-Fi https://en.wikipedia.org/wiki/Li-Fi
- pyvpx 10y ago
  the article is easily digestible and you'll find that no, they aren't. not even close.
  - xigency 10y ago
    Hm, they seem similar because both Li-Fi and free-space optical communication (FSO) use visible or near-visible spectra to send and receive information. I guess they might be seen differently as Li-Fi is potentially designed for indoor use? I don't see why they are substantially different, however, or at least incomparable. What the post discusses: https://en.wikipedia.org/wiki/Free-space_optical_communication https://en.wikipedia.org/wiki/Free-space_optical_communicati...
    - metaobject 10y ago
      One significant difference is that FSO operates over a much longer distance and has to contend with atmospheric interference (clouds, turbulence, etc). Also, the transmitter/receiver hardware used is much different.
antonios 10y ago
Reminded me of the Ronja project: http://ronja.twibright.com/about.php http://ronja.twibright.com/about.php
deleted 10y ago
[deleted]
xigency 10y ago
> In addition, this portion of the spectrum is not regulated Apart from not pointing a laser at a flying aircraft. I'm guessing this would be affected by weather.
- metaobject 10y ago
  Clouds and optical turbulence are both problems that have to be mitigated by FSO systems
mdturnerphys 10y ago
After reading this post, I was left with the question of why bother with the luminescence--why not just collect the transmitted light with the fibers and transmit it directly to the detector. The linked journal article makes it clear that the transmitted light is not collected by it entering the ends of the fibers. Instead, the transmitted light "scatters" off of the dye (changing wavelengths in the process), regardless of where and at what angle it hits the fiber, and some of it is scattered in the proper angular range to be transmitted along the fiber.
- deleted 10y ago
  [deleted]
- ISL 10y ago
  Wavelength shifting should make the detector more effective. Most photodiodes prefer longer-wavelength photos. In addition, their goal with this project is to make it omni-directional, so capturing and coupling the incoming photons directly would be a challenge. There may also be a little bit of wavelength-dependent trickery, where green photons are better at staying coupled, but I'd have to dig more to decide.
- mstresh 10y ago
  Efficiently directing light into a fiber optic cable is a difficult problem, in general. The luminescence is their proposed solution to this problem and one of the key results in their journal article. You have to shine light end-on into a fiber--you can't couple light into the fiber by shining on it at the side. Even for large, visible-light scintillating fiber used in this paper, you only have a few degrees of possible incidence angles that direct the light into the fiber. See for example, (one of the first results from Google), the figure on page 4 of this datasheet [0]. [0] https://www.ethz.ch/content/dam/ethz/special-interest/phys/particle-physics/precisionphysicsatlowenergy-dam/TeachingContent/ASL/bicronfiber.pdf https://www.ethz.ch/content/dam/ethz/special-interest/phys/p...
zw123456 10y ago
One of the major challenges for FSO is that it requires direct line of sight (LoS). One reason that electromagnetic radiation in the RF range is more desirable for communications is because it can be non-Los (think about your cell phone, you do not have to see the tower for it to work, you can be indoors for example). The second issue is the free space pathloss (see https://en.wikipedia.org/wiki/Free-space_path_loss https://en.wikipedia.org/wiki/Free-space_path_loss ) you can see by the formula that the loss goes up exponentially by not only the distance but also the frequency, which is why the wireless carriers are so interested in the 600Mhz spectrum, you need to build fewer towers using 600Mhz than say 3.5Ghz. The sudden interest in mm-wave (e.g. 28Ghz) for 5G is because the spectrum is much wider, that is the channels can be very wide allowing more data to be encoded, the trade off is that you start losing the NLoS capability, or it becomes much more difficult. With light, all those problems are orders of magnitude more difficult to overcome. Also, there are regulations around the level of emissions of light for safety reasons, if a laser is turned up too high it can harm a persons eyes if they happen to look at it, so although the spectrum itself is not regulated, the amount of power you can emit is. That makes it very difficult to implement an FSO system that can safely transmit more than one or two kilometers, but if you get fog, rain or snow, that distance quickly becomes 100's of meters at best. They are correct that the best way to overcome this issue is by developing sensors with much better sensitivity, by making them larger you can theoretically collect more photons, like a telescope. Since it is unlikely you can overcome the safety issue of increasing the transmission power level, it is smart to focus on the receive end and improve the sensitivity. But that does not help the LoS problem. But a very interesting development nevertheless.
- tlb 10y ago
  Loss goes up quadratically with distance, not exponentially. The graphs showing the quadratic dependence of loss vs. frequency assume a half-wave antenna, meaning the antenna size decreases inversely to wavelength, so most of the effect is from having a smaller antenna. In any case, path loss doesn't usually limit network capacity. Densely deployed systems are limited by interference, and the interference experiences the same path loss as the signal.
  - 10y ago
beloch 10y ago
I wonder what their detector's dark count rate and activation threshold is. If both are low enough, this is precisely the sort of detector people doing free space quantum crypto need.
vturner 10y ago
Isn't it amazing how we in the "developed" nations always presume that the "developing" nations need our technology? Colonial Europe assumed the savage nations needed railroads and hospitals, and now us enlightened 21st century liberals assume the developing world needs our internet, our network of connectivity. But do they? Are they not already connected, and are we truly connected? Consider our societies. We are epidemically depressed, living alone, and becoming increasingly friendless. The internet has undoubtedly created business opportunity (I'm work remotely as a researcher); but has it "connected" us as we were not already connected? Instead, has it in fact disconnected us in its facade of relationships?
- TheSpiceIsLife 10y ago
  Do you mean places like, for example, Daru, Papua New Guinea? You can see this place from Australian territory. I mean, we gave these people the OK Tedi mine disaster. There was a Cholera outbreak there around 2010-11. Electricity to run water pumps is available for about an hour a day. I feel absolutely no qualms with thinking it'd be at least okay, possible even great, if everyone had something even near the opportunities we have here in Australia. Also, your comment assumes a rose-tinted pasted that very well may not have existed. It wasn't that long ago (my grand parents era) where Polio was something we lived with. Where we really more connected 'back then'? Was domestic violence and alcoholism and less?
- seanalltogether 10y ago
  > (I'm work remotely as a researcher) Sounds like you're projecting your own existential crisis onto others. Maybe you should try quitting your job and finding something local and more hands on.
  - vturner 10y ago
    No projection of my own. I have a significant person in my life and friends. I'm commenting on the well-documented reality of some western cultures. I few searches brought these stories up: Depression: http://www.nimh.nih.gov/health/statistics/prevalence/major-depression-among-adults.shtml http://www.nimh.nih.gov/health/statistics/prevalence/major-d... Living Alone: https://www.washingtonpost.com/politics/more-americans-living-alone-census-says/2014/09/28/67e1d02e-473a-11e4-b72e-d60a9229cc10_story.html https://www.washingtonpost.com/politics/more-americans-livin... Friends in UK: http://www.telegraph.co.uk/men/active/mens-health/11996473/2.5-million-men-have-no-close-friends.html http://www.telegraph.co.uk/men/active/mens-health/11996473/2...
femto 10y ago
My immediate question was isn't their bundle of optical fibres performing essentially the same function as a lens? Why not use a lens? Answering my own question, having just read the abstract (in case anyone else had the same reaction). The claim is that they get the light collecting powers, combined with a wide field of view. A lens collects the light, but has a narrow field of view, which requires steering/alignment. Edit: Another possibility is a Luneburg lens, a type of lens that can focus plane waves from many directions to a small area? https://en.wikipedia.org/wiki/Luneburg_lens https://en.wikipedia.org/wiki/Luneburg_lens

76 points by dwaxe 10y ago

rosalinekarr 10y ago

Maybe with this technology, we can finally build the 80's neon cyberpunk future we've all been waiting for.

liveshops_ 10y ago
I wanted to upvote this twice.

hathym 10y ago

Are they trying to re-invent Li-Fi ? https://en.wikipedia.org/wiki/Li-Fi https://en.wikipedia.org/wiki/Li-Fi

pyvpx 10y ago
the article is easily digestible and you'll find that no, they aren't. not even close.
- xigency 10y ago
  Hm, they seem similar because both Li-Fi and free-space optical communication (FSO) use visible or near-visible spectra to send and receive information. I guess they might be seen differently as Li-Fi is potentially designed for indoor use? I don't see why they are substantially different, however, or at least incomparable. What the post discusses: https://en.wikipedia.org/wiki/Free-space_optical_communication https://en.wikipedia.org/wiki/Free-space_optical_communicati...
  - metaobject 10y ago
    One significant difference is that FSO operates over a much longer distance and has to contend with atmospheric interference (clouds, turbulence, etc). Also, the transmitter/receiver hardware used is much different.

antonios 10y ago

Reminded me of the Ronja project: http://ronja.twibright.com/about.php http://ronja.twibright.com/about.php

deleted 10y ago

[deleted]

xigency 10y ago

> In addition, this portion of the spectrum is not regulated Apart from not pointing a laser at a flying aircraft. I'm guessing this would be affected by weather.

metaobject 10y ago
Clouds and optical turbulence are both problems that have to be mitigated by FSO systems

mdturnerphys 10y ago

After reading this post, I was left with the question of why bother with the luminescence--why not just collect the transmitted light with the fibers and transmit it directly to the detector. The linked journal article makes it clear that the transmitted light is not collected by it entering the ends of the fibers. Instead, the transmitted light "scatters" off of the dye (changing wavelengths in the process), regardless of where and at what angle it hits the fiber, and some of it is scattered in the proper angular range to be transmitted along the fiber.

deleted 10y ago
[deleted]
ISL 10y ago
Wavelength shifting should make the detector more effective. Most photodiodes prefer longer-wavelength photos. In addition, their goal with this project is to make it omni-directional, so capturing and coupling the incoming photons directly would be a challenge. There may also be a little bit of wavelength-dependent trickery, where green photons are better at staying coupled, but I'd have to dig more to decide.
mstresh 10y ago
Efficiently directing light into a fiber optic cable is a difficult problem, in general. The luminescence is their proposed solution to this problem and one of the key results in their journal article. You have to shine light end-on into a fiber--you can't couple light into the fiber by shining on it at the side. Even for large, visible-light scintillating fiber used in this paper, you only have a few degrees of possible incidence angles that direct the light into the fiber. See for example, (one of the first results from Google), the figure on page 4 of this datasheet [0]. [0] https://www.ethz.ch/content/dam/ethz/special-interest/phys/particle-physics/precisionphysicsatlowenergy-dam/TeachingContent/ASL/bicronfiber.pdf https://www.ethz.ch/content/dam/ethz/special-interest/phys/p...

zw123456 10y ago

One of the major challenges for FSO is that it requires direct line of sight (LoS). One reason that electromagnetic radiation in the RF range is more desirable for communications is because it can be non-Los (think about your cell phone, you do not have to see the tower for it to work, you can be indoors for example). The second issue is the free space pathloss (see https://en.wikipedia.org/wiki/Free-space_path_loss https://en.wikipedia.org/wiki/Free-space_path_loss ) you can see by the formula that the loss goes up exponentially by not only the distance but also the frequency, which is why the wireless carriers are so interested in the 600Mhz spectrum, you need to build fewer towers using 600Mhz than say 3.5Ghz. The sudden interest in mm-wave (e.g. 28Ghz) for 5G is because the spectrum is much wider, that is the channels can be very wide allowing more data to be encoded, the trade off is that you start losing the NLoS capability, or it becomes much more difficult. With light, all those problems are orders of magnitude more difficult to overcome. Also, there are regulations around the level of emissions of light for safety reasons, if a laser is turned up too high it can harm a persons eyes if they happen to look at it, so although the spectrum itself is not regulated, the amount of power you can emit is. That makes it very difficult to implement an FSO system that can safely transmit more than one or two kilometers, but if you get fog, rain or snow, that distance quickly becomes 100's of meters at best. They are correct that the best way to overcome this issue is by developing sensors with much better sensitivity, by making them larger you can theoretically collect more photons, like a telescope. Since it is unlikely you can overcome the safety issue of increasing the transmission power level, it is smart to focus on the receive end and improve the sensitivity. But that does not help the LoS problem. But a very interesting development nevertheless.

tlb 10y ago
Loss goes up quadratically with distance, not exponentially. The graphs showing the quadratic dependence of loss vs. frequency assume a half-wave antenna, meaning the antenna size decreases inversely to wavelength, so most of the effect is from having a smaller antenna. In any case, path loss doesn't usually limit network capacity. Densely deployed systems are limited by interference, and the interference experiences the same path loss as the signal.
- 10y ago

beloch 10y ago

I wonder what their detector's dark count rate and activation threshold is. If both are low enough, this is precisely the sort of detector people doing free space quantum crypto need.

vturner 10y ago

Isn't it amazing how we in the "developed" nations always presume that the "developing" nations need our technology? Colonial Europe assumed the savage nations needed railroads and hospitals, and now us enlightened 21st century liberals assume the developing world needs our internet, our network of connectivity. But do they? Are they not already connected, and are we truly connected? Consider our societies. We are epidemically depressed, living alone, and becoming increasingly friendless. The internet has undoubtedly created business opportunity (I'm work remotely as a researcher); but has it "connected" us as we were not already connected? Instead, has it in fact disconnected us in its facade of relationships?

TheSpiceIsLife 10y ago
Do you mean places like, for example, Daru, Papua New Guinea? You can see this place from Australian territory. I mean, we gave these people the OK Tedi mine disaster. There was a Cholera outbreak there around 2010-11. Electricity to run water pumps is available for about an hour a day. I feel absolutely no qualms with thinking it'd be at least okay, possible even great, if everyone had something even near the opportunities we have here in Australia. Also, your comment assumes a rose-tinted pasted that very well may not have existed. It wasn't that long ago (my grand parents era) where Polio was something we lived with. Where we really more connected 'back then'? Was domestic violence and alcoholism and less?
seanalltogether 10y ago
> (I'm work remotely as a researcher) Sounds like you're projecting your own existential crisis onto others. Maybe you should try quitting your job and finding something local and more hands on.
- vturner 10y ago
  No projection of my own. I have a significant person in my life and friends. I'm commenting on the well-documented reality of some western cultures. I few searches brought these stories up: Depression: http://www.nimh.nih.gov/health/statistics/prevalence/major-depression-among-adults.shtml http://www.nimh.nih.gov/health/statistics/prevalence/major-d... Living Alone: https://www.washingtonpost.com/politics/more-americans-living-alone-census-says/2014/09/28/67e1d02e-473a-11e4-b72e-d60a9229cc10_story.html https://www.washingtonpost.com/politics/more-americans-livin... Friends in UK: http://www.telegraph.co.uk/men/active/mens-health/11996473/2.5-million-men-have-no-close-friends.html http://www.telegraph.co.uk/men/active/mens-health/11996473/2...

femto 10y ago

My immediate question was isn't their bundle of optical fibres performing essentially the same function as a lens? Why not use a lens? Answering my own question, having just read the abstract (in case anyone else had the same reaction). The claim is that they get the light collecting powers, combined with a wide field of view. A lens collects the light, but has a narrow field of view, which requires steering/alignment. Edit: Another possibility is a Luneburg lens, a type of lens that can focus plane waves from many directions to a small area? https://en.wikipedia.org/wiki/Luneburg_lens https://en.wikipedia.org/wiki/Luneburg_lens