I don't think that anyone is going to detect single RF photons. At 1 GHz, each photon packs 6e-25 joules.
Detecting single visible-light photons is possible.
I don't think that anyone is going to detect single RF photons. At 1 GHz, each photon packs 6e-25 joules.
Detecting single visible-light photons is possible.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
You would see mainly background noise from the 4K microwave background.
Easy - as it is for moderate infrared photons too. Royal Holloway London are aiming for something quantum based good for 1-20GHz at present. I am not sure what the current state of the art is now.
It begs the question what is the longest wavelength for which individual photons can be detected using cost no object detectors.
-- Regards, Martin Brown
There are materials that become nonlinear in their optical response (the index of refraction is variant with electric field strength), that can mix optical and radio frequencies. Typically, to get a high field, one puts them inside a laser-driven resonant cavity. A resonant cavity for a 700 MHz transmitter means a BIG cavity full of the nonlinear stuff, but it'd work.
A search on "KDP" and "nonlinear optics" would pull up lots of examples...
I know basically nothing about this, but I recall having seen something involving Rydberg atoms in RF cavities.
Jeroen Belleman
Thanks to both you and whit3rd for the answers. I don't have a pressing need to make or use one, I was just wondering if that part existed and what it was called.
Matt Roberds
You can just modulate the diode laser current at RF. (People have done this up into the GHz range.) Besides the obvious amplitude modulation the current also changes the frequency.. .that's the easiest way to put side bands on a laser.
George H.
1) ASS-u-ME a photon exists; if such a beast was detected for light, where the hell is it for RF? 2) Knowing, that in RF work, that a few milliwatts or less allows communications over long distances (eg: DX work, moon bounce,etc). And no quantized phenomena has been reported. However, such "impossible" communication feats done with RF seem to be absent with light. "Slight" discrepancy. 3) LINEAR RF amplifiers easy to make and use at power levels from microwatts or less) to megawatts. No such beasties for light. "Slight" discrepancy.
As someone said, "where is the beef?"
Do the math. The energy of a ~MHz photon is down in the ueV, orders of magnitude below thermal noise, including black body radiation (which is pervasive at those frequencies -- from any source, from cosmic background to room ambient), let alone physical sources (like the incessant din of lightning bouncing around within the ionosphere, which plagues SW and MW communication).
So in the same way that room-temperature things tend to not behave quantum-like, or that large ensembles tend not to behave quantum-like, so too are the EM fields consisting of large ensembles, sufficiently peppered with noise and scattering, that you can't really tell.
Superconducting cryo experiments still produce evidence of it, e.g. Josephson junctions.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
So, it is MICRO eV? Then that makes it WORSE..makes communications more impossible, say from San Francisco to the OTHER Brisbane.
What's worse? Obviously it's still possible, given suitable propagation means (SW trapped by ionosphere, VHF+ repeated via ground station or satellite). Quantum encryption isn't going to be possible, but so what.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Isn't the theory that it takes energy to transmit a signal? Micro and Nano energy is WORSE than One or so eV; seems impossible to interact with any kind of receiver, even one at the "local" Brisbane. Do not confuse this with stupid FACTs of what one has seen. Seems theory virtually guarantees the mentioned impossibility, and your MICRO eV just compounds the situation.
Free-space optical communication is far harder than radio, for a number of reasons that mostly involve having to detect photons incoherently rather than collectively as in an antenna.
For instance:
A two-element antenna at 20 metres has an intercepted area of about 100 m**2, figuring a beam width of a steradian and 50% efficiency. In the analogous optical case that would get you 310 uV rms noise in a SSB phone channel. The atmosphere's not as noisy as that, even at HF.
SNR_max = N/(2B)
where N is the photon arrival rate and B is the video bandwidth. The photon energy goes as 1/lambda, so for a constant power level, this is
70 dB lower at 500 THz (green) than at 50 MHz.And then there are circuit details and so on that I won't belabour.
So radio is dramatically easier than optics for free space communications.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Well, yes... over a certain amount of time.
If you can wait forever, information theory says you can do it in arbitrarily little energy (potentially zero, for truly infinite time).
You also seem to be forgetting that you're not going it a photon at a time... lasers get quite good SNR when they do their stuff with stupidly large numbers of photons (like 10^18). (And that's with incoherent detectors, as Phil notes.) Can you calculate how many photons/sec (coherent photons, at that, and over a wide cross sectional area, also as Phil notes) are contained in an wavefront of 1W continuous radiated power at 100MHz?
So if your goal is to save power, one would presume arbitrarily low energy photons (assuming you can tease them out of the noise, since Shannon doesn't simply go away, even if you ignore it) would be a rather optimal choice!
:-)
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
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