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from the lasers-not-just-for-blasters-anymore dept.
City College of New York researchers have manipulated the polarization of a laser beam to create shapes that could boost data transmission rates:
Using special devices called "q-plates," the researchers manipulated a laser beam's polarization into novel shapes some of which Milione referred to as "radial" and "azimuthal." "While light's polarization (linear and circular) is used for many modern technologies, such as, 3D television, its shape is often left untouched," he said.
The researchers showed that each shape could carry an additional data stream. While the researchers used only four shapes, in principal, the number that can be used is unlimited. "The amount of data that can be transmitted on a single laser beam can be scaled to terabits or even petabits," said Alfano. "This technology is potentially compatible with building to building communication in NYC or even between Google data centers."
The research is published in Optics Letters [abstract].
(Score: 3, Informative) by bd on Tuesday April 28 2015, @08:27AM
Sorry, I am afraid you got this all wrong.
When you focus light of only one color, the smallest thing you could theoretically get has the form of a spot with a diameter that is related to its wavelength.
This is due to something called diffraction.
A single mode fiber is an optical waveguide (a pipe, sort of) that has a diameter that is roughly the size of this spot. Therefore, the light has no wiggle-room in
the fiber and only takes one propagation path through it, countering an effect where the same bit in your data stream takes paths of different length in
your fiber by being reflected at different angles at the same time, therefore having the same bit arriving at different times at the other end of the fiber.
Now, whenever light has structure in it that would, say, create an image of a "+", such an image in the focal plane of a lens would be a "+", that you
can think of as being composed of a lot of these diffraction limited spots. This is a fundamental limit of optics. Now, the single mode fiber will only let one of these dots inside.
Actually, if you would put the fiber on two translation stages, you could create an image of the "+" by moving the fiber. This would be the world's slowest image sensor.
So, whenever something is giving structure to light, such as higher order spatial modes as used in this paper, it means you cannot use it for fiber communications.
The aforementioned effect in multi-mode fibers also distorts the image that you see at the other end of the fiber.
What's more, the so-called beam quality of your light goes down if it contains higher-order modes. This means that it loses the ability of light to stay roughly
the same spot size over a given distance, as all higher-order modes have a larger divergence angle than the fundamental mode (that corresponds to a diffraction limited spot).
This means this method should be not really nice for very long distance free-space optical communications.
Of course, the researchers know this, and probably target a propagation distance where these effects for the modes they are using is not too much of a disturbance.
But it would certainly not work for communications between, say, earth and moon.
Your post contained a quite clever use of the number one for the letter i in the word shit, actually. Did you know you are allowed to use swear words on here?
(Score: 0) by Anonymous Coward on Tuesday April 28 2015, @03:07PM
I think fiber optics is generally unsuitable for earth-to-moon communication.
(Score: 0) by Anonymous Coward on Tuesday April 28 2015, @03:16PM
thanks for the info.
seems i got it wrong ... a bit. i found a good explaination to fiber optic multiplexers here: http://en.wikipedia.org/wiki/Arrayed_waveguide_grating. [wikipedia.org]
seems it is being "shaped" but not with a 2-dimensional cardboard punch out but rather "only" one dimensional.
the one that can potentially do unlimited dimensions seems to be OAM: http://en.wikipedia.org/wiki/Orbital_angular_momentum_multiplexing [wikipedia.org]
the article seems to refer to this OAM thingy ... seems we dont know all and every property of light just yet ... amazing.