The health problems connected with the use of high frequency EM are now a threat to the entire human race and something must be done.
Firstly, we need to frame the entire issue by definition:
Why do we have this problem ?
Humans exhibit a strong desire for fast and convenient communications.
Thus far, the available technological solutions have proven to be dangerous to the health of humans, animals and probably plants.
Our addiction to ever faster data transfer rates can only be temporarily satisfied in the current format by the use of higher frequency carrier waves.
At this time, carrier frequencies of at least 30 Gigahertz are routinely used in urban areas and higher for military applications.
The next area up is in the Terahertz region - 10^12 to 10^15 waves per second (or 1Thz to 1Phz). This represents a band that includes both high end microwaves and far infrared. By about 10^14, the health problems are much greatly reduced as we are now dealing with thermal radiation whose wavelength is so short that it can only cause atoms and molecules to vibrate (heat up) and not cause electronic changes (orbital electron trajectories).
By the time we get to visible light, we are in a relatively safe zone. The sun gives off much visible light and all the colours of nature would suggest that visible light is biologically safe (obviously up to a certain level - at least up to that of the Sun (~1kw/m^2).
After leaving the visible range of EM, we again enter dangerous areas - ultraviolet, soft X-ray, hard X-ray, Gamma and Cosmic, with increasing biological danger as the frequency climbs.
One might first think that because of the above facts, the near IR (upper Infrared) region might be a good choice for carrier frequencies - being around 100 or more times faster and relatively safe however, the penetration capacity of IR waves is much less that that of microwaves and thus, their use could only be virtually line of sight, barring fortunate reflections off walls and/or other structures - basically similiar to that of visible light.
The safest and fastest frequency to use would be that of visible light itself. This is why optical communications are so fast however whilst we can use optic fiber for fixed installations, it is useless for mobile (personal) applications which require no physical connections.
Since it is demonstrably possible to modulate visible light at the data rates desired, it seems that this band can be the only possible choice for mass communications if the human race is to survive. If we end up needing faster data transfer rates than that of downloading an entire movie in less than a millisecond, then faster communications will (imho) not save us.
We could create a communications network using visible light by making all street lights modulatable emitters. Normal street lights are incapable of being modulated at any kind of useful rates.
At this time, the fastest practical devices are laser diodes. Spintronic devices are as yet incapable of being modulated at the required frequencies.
Most lasers are set up to produce a beam of light, but with a little engineering, laser diodes can be made to emit a spread beam or even omnidirectionally.
If all street lights could be converted to laser-based visible light transmitters, they could then continue their present services as illumination and also be the transducers for a communications network.
* High power laser diodes are currently produced in quantity.
* Modulation is routinely achieved via modern high speed electronics.
* The optics for beam shaping are also in existence.
* The fact of the coherence of laser light, which causes "speckling" of illumination could be easily countered by designing the laser diodes for minimum coherence, by shining the light through a substance that de-coheres it or mixing laser outputs of differing colours. Thus an RGB (white) laser would be a good candidate.** (These exist now and are readily obtainable, however they require beam shaping optics for this application).
* Laser diodes are capable of greater longevity than regular incandescent/gas discharge based light sources
Such a system would obviously have some limitations - the main being that where there is no light or little light, there would be communications as the carrier strength would be too low. It would only function in reasonably lit areas.
Having said that, by the time such an industry were to be developed, the investment of profits arising from it could well fund research to minimize or even negate the above.
However, at this point, the author feels that the problems associated with the existing system FAR outweigh the limitations imposed by the use of visible/near IR carrier-based systems.
(c) 2017 Michael H. Goebel
** If anyone ever manages to create a SHEWL (Spherical High Energy White Laser), then ALL would be schweet.
nb. If anyone wishes to fund me, I'd be very happy to build a prototype
At this point, I would need around $5000 - and that is only because I have to find some premises for my workshop in which to build it.
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