Can you carry more info through lasers than on radio waves?

[HRS]

I remember reading about a new form of communication where lasers are used in place of radio waves with one of the proposed applications being transmissions between space probes and such. For one it would not be faster. But would it be more accurate? Could it carry more information than radio? Why or why not?

[Enthalpy]

Many experiments are under way among space probes and satellites, exactly because designers hope to increase the data throughput using lasers.

 

The main reason is that light can be focussed to a narrower beam than radio waves using an antenna, lens or mirror of limited diameter. An other reason is that much mandwidth is available, which helps (a bit) transmit more throughput from the same link power budget. All the rest is worse with light: emitted power, receiver's sensitivity, modulation capability.

 

A narrower beam demands to point more accurately the transmitter and receiver - much so before improving over a radio link. This has been a hard nut up to now. One option is to transmit by light (say from a deep space probe) to a satellite on Earth orbit, then relay somehow to Earth: this eases weather requirements.

 

I've suggested to pump the transmitting laser by sunlight directly, for efficient conversion: no electricity in between. Yag lasers absorb sunlight well with a second absorption center (is it terbium in addition to erbium?): a Japanses university does it on Earth with >20% light-to-light conversion.

 

For all data transmissions by light, on Earth or not, especially unguided, my filter would attenuate noise:

http://www.scienceforums.net/topic/74445-evanescent-wave-optical-filter/

[John Cuthber]

Lasers are used to carry a lot of information. I suspect this message was probably carried on a laser beam at least once between my computer and yours.

http://en.wikipedia.org/wiki/Fiber-optic_communication#Transmitters

[HRS]

Thanks but I should have been more specific in that my inquiry was to nonphysical communications, such as future theoretical space communication networks, or at the least space probe communications. Though that does remind me that mass amounts of information can be transmitted through light.

 

Though would there be a difference between the light being contained within fiber optic cables with total internal refraction and the light in lasers being transmitted to a theoretical satellite or probe?

[studiot]

You may find that masers more generally make your question obsolete.

 

Look particularly at the part entitled 21st century developments.

 

http://en.wikipedia.org/wiki/Maser

[HRS]

I have never heard of masers before. Fascinating I will have to look into them more thank you

Edited May 10, 2014 by HRS

[Enthalpy]

Maser microwave sources wouldn't bring better transmissions than any other. They do serve as clocks, especially in some GPS satellites. Clocks were the goal of NIST as they made their maser on a chip.

 

The whole point of laser transmissions is the shorter wavelength that focusses the beam better. That's why they are developed presently.

 

My first answer deals with unguided transmissions.

[swansont]

The real advantage to lasers is that they can be spectrally narrow, so you can put more channels in a band and send information in beams that overlap, and you sort it out at the end. It's especially important with optical fibers, so you can put more channels in the low-loss band of the fiber.

http://en.wikipedia.org/wiki/Wavelength-division_multiplexing

Maser microwave sources wouldn't bring better transmissions than any other. They do serve as clocks, especially in some GPS satellites.

 

Galileo is planning to use them, but GPS does not currently use masers. Cesium (for older satellites) and rubidium clocks. Masers may be put on newer satellites supporting GPS III.

Clocks were the goal of NIST as they made their maser on a chip.

 

Link?

[jero25]

Can laser transmit data .

[swansont]

Can laser transmit data .

 

Yes. There's a whole bunch of the telecom industry that sends information with lasers via optical fibers.

[Enthalpy]

Pumping a laser by sunlight would bring heartening power for space probe data transmission.

 

Imagine a probe at Jupiter's moon Europa. Sunlight provides 50W/m² there. A D=4.4m concentrator to fit unfolded in a launcher fairing brings 700W. From a Nd:Cr:YAG, a team at Osaka university observed 38% conversion into laser light

http://www.icenes2007.org/icenes_proceedings/manuscripts.pdf/Session%207B/SOLAR%20PUMPED.pdf

but let's take 25%: that's still permanent 180W transmitted power from that difficult location, with the better focussing possibility of light.

 

At Mars, the same evaluation tells permanent 2kW transmitted power. Better than solar cells feeding laser diodes pumping a solid laser.

 

To reduce the cooling need at the YAG, I suggest to cover the concentrator (or put filters on light's path) so that it reflects only the wavelengths that pump the Nd:Cr:YAG.

Galileo is planning to use them [hydrogen maser suggested by Enthalpy], but GPS does not currently use masers. Cesium (for older satellites) and rubidium clocks. Masers may be put on newer satellites supporting GPS III.

 

My bad. A paper long ago presented a research effort as already flying technology, I believed it.

Would there be a difference between the light being contained within fiber optic cables with total internal refraction and the light in lasers being transmitted to a theoretical satellite or probe?

 

The attenuation law differs. In a fiber, light stays concentrated at any distance, but the material absorbs it. We luckily have pure silica that is very transparent (glass is opaque at 1m thickness), and big efforts developed laser diodes tuned to the best wavelength; as a result of exp(-distance), Australia can be crossed in one hop.

 

Compare with open-space propagation: no attenuation through vacuum (our atmosphere would be very bad), but light spreads its power density as distance^-2 which is more favourable at long range. Consequently, our Moon's distance is measured since Apollo by a laser beam on Earth illuminating a small reflector put on the Moon to send a fraction back.

 

Well beyond our Moon, radio enabled transmissions with the Pioneers and Voyagers. Light shall improve such links.