# Can I turn Radio waves into light?

Wikipedia says that the frequency of light is 300 THz. I've made a radio waves transmitter that transmits about 100 MHz.

If I increase the frequency of the transmitter to 300 THz, will the antenna produce spark or light ?

Can I do this circuit practically o_O ? Is there any transistor or IC that can oscillate 300 THz ? Can I find an inductance ( coil ) of 0.0025 pH and capacitor of 1 pF ?

I know that it is a science fiction question but please, don't make fun of me :)

• Just run fast and make use of the effect of blue shifting.. – PlasmaHH Sep 29 '14 at 12:04
• Possible duplicate of a question I asked on physics.stack-exchange – Connor Wolf Sep 29 '14 at 14:26
• I like to think of an LED as molecular sized 2.5fF coil in series with a 1pH capacitor and a diode. ;-) – Michael Sep 30 '14 at 4:30
• This is a very good question. – Always Confused Jun 30 '16 at 14:16
• – Always Confused Jun 30 '16 at 14:59

300THz transmitter? (the band between infra red and microwaves) - with a lot of technology and know how perhaps. See http://www.rpi.edu/terahertz/about_us.html

300THz transistor/IC - no.

Use discrete inductors and capacitors at these frequencies? No. At very high frequencies conventional capacitors and inductors are replaced by other devices (see resonant cavities)

In theory there is only one basic difference between a 'photon' of radio waves, light waves, far infra red waves, microwaves, ultra violet waves, x-rays etc. and that difference is the energy the photon. This energy can be calculated using the simple formula:

                                       E = hf


where E = energy in joules, h = Planck' constant (6.626 × 10−34 J·s) and f is the frequency of the photon.

If you crunch the numbers you will see that the photonic energy of a radiowave is millions of times smaller than that of a visible light photon.

Light emitting 'transmitters' (into optical devices) use electrons jumping from one energy level to another rather than using a 'tuned circuit'. It turns out that the energy gap is just the right amount to give a visible light photon. There is no 'one technology fits all' that can produce photons of different frequencies (energies) across the entire spectrum. Even solid state devices become more exotic as you demand higher and higher frequencies and circuit boards start take on the appearance of complex plumbing.

Can it be done?

Perhaps. New developments in nanotechnology may well produce a single device capable of converting the energy from radio wave photons into TeraHertz , infra red or visible light photons etc.. They've already developed nanotube transmitters and receivers using graphene.

Unfortunately my crystal ball is on the fritz at the moment so I can't see in the future.

• I'm not an expert, but free-electron lasers might be in some way the closest thing to a conventional radio transmitter in the optical world, since they convince a bunch of unbound electrons to interact with each other in such a way as to resonate at light frequencies (or anywhere from microwave to X-ray, in fact). – hobbs Sep 29 '14 at 21:48

Can I do this circuit practically o_O?
Is there any transistor or IC that can oscillate 300 THz?
Can I find an inductance (coil) of 0.0025 pH and capacitor of 1 pF?

Not quite, no, and no. But this is an area of active research: The Truth About Terahertz.

The basic principle of the tuned LC radio emitter is resonance. The techniques for producing high frequency tuned signals at higher frequencies are also based on resonance, but because the frequency is higher the resonant elements need to be much smaller. You also need some system for amplifying the signal, bearing in mind that terahertz is above the operating speed of almost all transistors. You can get tuned light of a particular frequency using a LASER (Light Amplification by Stimulated Emission of Radiation), which is also a resonant process. Intermediate frequencies can be produced by a device called a Klystron, which is halfway between a vacuum tube and a laser in its operation.

It may be possible, but I don't know of practical devices that work in this fashion. If you search likely terms you'll find some work, but more along the lines of physics experiments than electronics. Transistors tend to stop amplifying at under 100GHz even for really good SiGe IC transistors.

In the reverse direction, there are (sort-of) practical light detection devices that use a nano-antenna array. I have seen some work in Germany that looked promising, and I'm sure they're not the only institute working on it. It's easier to go from light to DC than from DC to light.

• "It's easier to go from light to DC than from DC to light." What about a light bulb plugged on a battery? :P (ok a far too easy joke) – Doombot Sep 29 '14 at 13:25
• @Doombot- haha. But not with an antenna array, unless you get the antennas really, really hot. ;-) – Spehro Pefhany Sep 29 '14 at 15:55

An electro-optic modulator does what I believe you are asking about. Here's an extract from the wiki: -

Electro-optic modulator (EOM) is an optical device in which a signal-controlled element exhibiting the electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or polarization of the beam. Modulation bandwidths extending into the gigahertz range are possible with the use of laser-controlled modulators.

As you can see, AM, FM or PM are achievable.

• He wants to actually create light, not just modulate existing light. This is outside the realm of electronics despite specs written by noobs that specify the equivalent of 'DC-to-daylight' bandwidth (and zero noise and distortion). – Spehro Pefhany Sep 29 '14 at 12:51
• @SpehroPefhany, Well if you FM you do get a bit of "new" light in the side bands. But getting from 100MHz to 300THz that way will be even harder than doubling all the way up. :^) – George Herold Sep 29 '14 at 13:51
• @GeorgeHerold AO modulators are interesting. It would be nice to know as much as Phil H. about this stuff. You can do interesting closed loop sub-wavelength interferometry things with them. – Spehro Pefhany Sep 29 '14 at 13:54

Hmm, Well there are non-linear crystals whereby you can mix "light" of different wavelengths. Search for OPA's (optical parametric amplifiers). But you have to start with light... a laser. I guess in principle you could start with 100MHz and double up to 300THz, but that's a lot of doubling :^) If I stretched your question a bit, and asked how to turn electrons into light... (not in an atom) Then I would think about accelerators, where you get synchrotron radiation. And at the end of an electron beam you can build a free electron laser. (Years ago I worked at an FEL, not quite visible (3-10 um), but you could see it when it blew holes in things.)