orbital angular momentum proposals ...
Since these typically generate a bit of debate here on the Reg, the interested reader might also look at this recent paper:
Orbital angular momentum modes do not increase the channel capacity in communication links
Mauritz Andersson, Eilert Berglind and Gunnar Björk
http://dx.doi.org/10.1088/1367-2630/17/4/043040
The orbital momentum of optical or radio waves can be used as a degree of freedom to transmit information. However, mainly for technical reasons, this degree of freedom has not been widely used in communication channels. The question is if this degree of freedom opens up a new, hitherto unused 'communication window'supporting 'an infinite number of channels in a given, fixed bandwidth' in free space communication as has been claimed? We answer this question in the negative by showing that on the fundamental level, the mode density, and thus room for mode multiplexing, is the same for this degree of freedom as for sets of modes lacking angular momentum. In addition we show that modes with angular momentum are unsuitable for broadcasting applications due to excessive crosstalk or a poor signal-to-noise ratio.