On 05/03/2012 10:10 PM, Erik Basilier wrote: > The May 2012 issue of the IEEE Spectrum magazine reports that researchers in > Italy and Sweden were able to conduct two separate instances of radio > communication on the exact same frequency, without increasing bandwidth, and > without time-division multiplexing, be making the transmissions differ in > angular momentum. One transmission used linear polarization, and the other > was given angular momentum by means of a dish with a radial cut, where the > metal was bent backwards/forwards on the two sides of the cut. Apparently > this is not just a case of linear vs circular polarization, as circular > polarization can be readily picked up by a linearly polarized antenna, and > apparently the two channels did not interfere with each other. The > researchers claim that this demonstration points to the possibility that the > radio photons can be given multiple, quanized levels of angular momentum, > making possible several more communication channels without increased > bandwidth. Other researchers say that this is just a form of MIMO. Wikipedia > describes MIMO as the technique of using multiple antennas as in diversity > reception or in gain increases obtained by phasing the antennas. > The only source of angular momentum in a photon is its intrinsic spin ( = 1). This can have two projections, +1 and -1 (only two, unlike for most spin one particles, which have three possible projections). However, these two projections are directly related to the left and right circularly polarized light, so I cannot quite see what other source of angular momentum could arise in this case? Having said this, I don't quite believe in the Swedish group explanation of this experiment.
Jussi Eloranta AA6KJ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
