doubts on twisted light
According to the BBC doubts are emerging about 'twisted light'. It is even being characterised as a physicist vs. engineer debate.
I have my doubts about it, as I find it difficult to imagine how the lowest orbital mode differs from normal circularly polarised radiation. However, one of the rebuttals contains a glaring error. A resistor connected to an N-mode antenna in a heat box will radiate only an Nth of its thermal power in each mode; the authors forget this and claim that N-mode antennas violate the 2nd Law and are therefore impossible. Their resistor could cool down without violating the 2nd Law by 'heating up' the previously empty N-2 radiation modes in the cavity. The resistor is transferring heat from a hot body (the cavity and the two normal radiation modes) to a cold 'body' (the other N-2 modes). They are on safer ground when they say that if N-mode was possible then black bodies would radiate more heat than has been measured - although I suppose it is possible that some suppression mechanism prevents this from normally happening. So their rebuttal contans a hole.
Sounds like polarization modulation.
Some patents on polarization modulation.
US 2273161 Polarized wave modulation by phase variation
US 2273911 System of radio communication by means of polarization modulation
US 3415995 Polarization modulation optical communication system
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