Solar antenna invented

[Tormod]

Up until now, nobody has been able to make an antenna that picks up light. But now it apparently has happened:

 

CNN: Researchers invent antenna for light

http://www.cnn.com/2004/TECH/science/09/17/light.antenna.reut/index.html

 

Researchers said on Friday they have invented an antenna that captures visible light in much the same way that radio antennas capture radio waves. They say the device, using tiny carbon nanotubes, might serve as the basis for an optical television or for converting solar energy into electricity once properly developed.

 

The hopes is that this will make it possible to create technology that can convert solar energy more efficiently than today's solar panels.

[BlameTheEx]

These researchers should be congratulated on their achievement, but commercial applications might have to wait.

 

Light is in principle no different to radio waves except in wavelength, but in practice there are difficulties. The output of this arial would be a very high frequency signal indeed. There is no rectifier that could handle such a frequency for direct conversion to a DC current, and I am not planning on holding my breath while waiting for one to be developed.

[Freethinker]

Originally posted by: Tormod

The hopes is that this will make it possible to create technology that can convert solar energy more efficiently than today's solar panels.

What bothered me about the article is how they seemed to promote this technology as primarily a way to improve TV signals. Like that has value! Just what we need, better reception of Survivor 50. :-)

 

It would seem that this technology can dramatically increase the transmission of data thought. By controlling the size and positions of the nano-tubes, they can create a filter to allow each such antenna to be very selective as to which photon's each would pickup. Allowing datamuxing based on individual photon freq info. I understand they already utilize optical filters and polarizing to increase optical fiber data rates.

[TeleMad]

Freethinker: ... they can create a filter to allow each such antenna to be very selective as to which photon's each would pickup. Allowing datamuxing based on individual photon freq info. I understand they already utilize optical filters and polarizing to increase optical fiber data rates.

 

Yeah, multiplexing signals through optical fiber based on different frequencies is old news.

 

One way to leverage your installed base of optical fiber is to replace simple transmitters with transmitters that can transmit several light sources at slightly different frequencies. You can add signal capacity wihtout adding new fiber.

 

This simple idea is given the complex name wavelength division multiplexing (WDM). Not content with that, marketers created another term, dense wavelength division multiplexing (DWDM) for fiber that carries more than 40 light sources at differen frequencies." (Raymond R Panko, Business Data Networks and Telecommunications: Fourth Edition, Prentice Hall, 2003, p81-82)

[Tormod]

I actually went to a doctoral dissertation a few weeks ago where a friend of mine defended his thesis concerning the future of package switching in optical networks. Quite interesting stuff. (So he's now a Ph.D) He's been studying multiplexing at ultra high speeds via fiber optics for years.

[BlameTheEx]

In what ways are these aerials superior to mirrors, lenses, polarising filters, and prisms?

 

Also it is already more easy to create an optical filter by depositing alternating layers of 2 different transparent materials onto a glass plate. I am not quite sure, but i think they have to be 1/4 of the desired wavelength deep.

 

These aerials will only come into there own if there is need for ultra miniature light concentrators or filters.

[Freethinker]

Originally posted by: TeleMad

Yeah, multiplexing signals through optical fiber based on different frequencies is old news.

Not only freq's but also polarity. By polarizing the light the amoount of data can be increased even more than just by "color".

 

But an "antenna" is a far better, more efficient method of doing this than optical filters and overcoming barrier voltages as the current system needs.

[Freethinker]

Originally posted by: BlameTheEx

In what ways are these aerials superior to mirrors, lenses, polarising filters, and prisms?

 

Also it is already more easy to create an optical filter by depositing alternating layers of 2 different transparent materials onto a glass plate.

Actually only one layer is needed.

 

But there is a dramatic difference between the two systems.

 

first "mirrors, lenses, polarising filters, and prisms" requires passing the entire lightfiber signal. This reducing the intensity of the light. Thus requring additional light output on the transmitting end. More energy power dissapation. Thus larger devices.

 

2nd the reduced light levels then have to generate enough voltage at the pickup device to overcome the barrier voltage of the device. Nothing happens until the light level is strong enough.

 

With an antenna ANY photon of the proper freq will produde an output. No splitter is needed for filtering thus the transmitter does not need to compensate in front for loss downstream. Less power is needed to generate an output. Thus less power consumption and heat dissipation in the entire system.

These aerials will only come into there own if there is need for ultra miniature light concentrators or filters.

Such as data paths within a processor core or die.

[BlameTheEx]

Freethinker

 

An antenna would receive efficiently it is true, but only within its limits. It will only receive "ANY photon" if it is large enough to receive ALL photons from the end of the fibre optic. Alternately you can use an array of smaller ones. You are back to "passing the entire lightfiber signal".

 

Of course if you are only receiving at one frequency you don't have a problem, but then you didn't with more traditional means ether. The problem comes when you wish to receive on different frequencies. At that point you will find that aerials tuned to different frequencies will be competing for the same optimal position. The result will be compromise and loss of signal. To maintain efficiency we are still reduced to using traditional techniques for splitting the signal. Or were you thinking that once the light is converted to an electrical AC signal of the same frequency there are electrical components available to split the signal into different frequencies? Now that would be a breakthrough!

 

Regarding optical filters. Only one layer will create a filter, but multiple layers will be necessary to create a sharp narrow band filter. To give you an idea of the properties of a single layer filter, there is one on normal camera lenses. It is the cause of that slight blue coloration.

 

Like you I do see possibilities for combining aerials with integrated circuits. Processors that use light rather than electricity have been proposed. My thought is that it is more likely that these aerials will be used in digital cameras, with one arial for every pixel as light concentrators. Still, this won't be soon. Fixing millions of aerials into precise positions cheaply is no small problem. Nor is the problem of manufacturing millions of aerials to tight specification. Even then, won't it be easier to use some printing technique to create aerials on an integrated circuit?

[Freethinker]

Originally posted by: BlameTheEx

Freethinker

 

An antenna would receive efficiently it is true, but only within its limits. It will only receive "ANY photon" if it is large enough to receive ALL photons from the end of the fibre optic. Alternately you can use an array of smaller ones. You are back to "passing the entire lightfiber signal".

After review, I think we are approaching this from the wrong angle.

 

A recieving "antenna" is a device for ACCUMLATING and perhaps secondarily CONVERTING energy. e.g. an RF antenna accumulates the RF energy which happens to exist around it's physical location. In many cases the accumulated energy is converted directly into electical energy. But not always. "Dish" type antenna's accumulate energy, but then redirects or focuses onto a device or region that does the conversion seperately.

 

In a conventional optical system, such as fiber cable, an optical concentrator, typically a lens, accumulates the photons and focuses them onto some device that converts them into electrical energy.

 

It would seem then that this new photon antenna combines the concentrator and conversion functions, previously seperate functions, into one device. And since it directly captures the photon, as opposed to passing it thru some substance such as the glass of the concentrator lens currently used, would be far more efficient. Fewer materials for the photon to travel thru. Less scattering or nonfunctional absorption. It would occupy less area for a given efficiency.

Of course if you are only receiving at one frequency you don't have a problem, but then you didn't with more traditional means ether. The problem comes when you wish to receive on different frequencies. At that point you will find that aerials tuned to different frequencies will be competing for the same optimal position.

But the optimal position is determined by wavelength related distances. Perhaps the optimal distance for differening freqs would actually improve the available "sweet spot"?

Regarding optical filters. Only one layer will create a filter,

Glad we can now agree on this.

but multiple layers will be necessary to create a sharp narrow band filter.

this is not correct. there are numerous sources for single layer film of highly selective wavelength bandpass. Both thru simple coloration of the surface, such as colored celophane, or actual wavelength dependant coating depth.

To give you an idea of the properties of a single layer filter, there is one on normal camera lenses. It is the cause of that slight blue coloration.

The dichroic coating of the lens is typically a bandpass type.

My thought is that it is more likely that these aerials will be used in digital cameras, with one arial for every pixel as light concentrators.

These antennas could dramtically increase optical pickup resolution and low light capabilites. Depending on the method used, most digital cameras today need 3 elements to determine one pixel's full color detail. One each for RGB. The option being a 3 chip system with optical prism block. Both systems thus require 3+ times the amount of photons for a given output. While each antenna would be designed for certain bandpass (RGB?), they would possibly be able to be placed directly adjacent to the other antenna. A much greater density. Currently less than half of the current chip's surface area is available for actual image area. Plus they may not require an accumulater bubble lens.

[BlameTheEx]

Freethinker

 

"A receiving "antenna" is a device for ACCUMLATING and perhaps secondarily CONVERTING energy"

 

Sadly it is the converting part that is the problem. Until you connect some sort of electronics to an antenna it is just an accumulator. There is no suitable electronics, not even a rectifier, available. In this situation the antenna is no more than an alternative to lenses or filters.

 

Should somebody invent something (presumably a large molecule) that can directly use the output from the antenna, things will be much more exciting. To emphasise the relative difficulty of this....

 

A group of scientist in communist Russia were given 5 years to turn cow **** into butter. After 2 1/2 years they were asked for a progress report. They replied "well we are half way there. It still tastes like ****, but it spreads like butter."

[Freethinker]

Originally posted by: BlameTheEx

Sadly it is the converting part that is the problem. Until you connect some sort of electronics to an antenna it is just an accumulator. There is no suitable electronics, not even a rectifier, available.

Actually information could be transmitted using simple binar. A string of photons for a given duration would indicate a "ON" state, or binary "1". A rectifier would only be needed as a detector for analog decoding. And even that isn't needed in PCM.

In this situation the antenna is no more than an alternative to lenses or filters.

Perhaps, but as an advancement over existing options.

Half full?

[BlameTheEx]

Freethinke.

 

Could you elaborate a tad? How do expect to transmit or receive information without any electronics?

 

Half full? Er, no. The glass is barely damp.

[Freethinker]

Originally posted by: BlameTheEx

Could you elaborate a tad? How do expect to transmit or receive information without any electronics?

 

Half full? Er, no. The glass is barely damp.

Ah see, one of the big differences. I see the glass as always full. It's just a matter of with what?

 

As to the antenna, the article states

The light excites miniature electrical currents

Which specifies that no other electronics are needed to produce the electrical current. Even if the frequency of this current is too high to pass thru current electrical devices, binary states can be. By producing pulses of appropriate duty cycles, data can be transmitted. A simple digital PCM design can decode the data based only on digital (on/ off) state of the pulses.

 

This would not allow for maximum utilization of the spectrum by any means. But because of the pilot/ carrier freq being in the light spectrum the duty cycle could be such that the data rate would still be extremely high.