Scientists edge closer to ultra-high-speed Wi-Fi using lasers

Cal Jeffrey

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Staff member

A paper published in the Proceedings of the National Academy of Sciences titled, “Radio frequency transmitter based on a laser frequency comb” outlines how engineers were able to use a laser to modulate and transmit microwaves wirelessly and receive radio frequency signals.

“The research opens the door to new types of hybrid electronic-photonic devices and is the first step toward ultra-high-speed Wi-Fi,” said senior author Federico Capasso.

The breakthrough came from research conducted in Capasso’s lab in 2017. The engineers discovered that terahertz frequencies could be generated using an infrared frequency comb within a quantum cascade laser. They found the ultra-short wavelengths could move data “hundreds of times faster” than contemporary wireless.

Then in 2018, the team found that quantum cascade laser frequency combs could also be used to encode, transmit and receive data.

“Now, the researchers have figured out a way to extract and transmit wireless signals from laser frequency combs,” Harvard notes.

"These results pave the way for applications and functionality in optical frequency combs, such as wireless radio communication and wireless synchronization to a reference source."

Conventional lasers only emit one frequency. Conversely, laser frequency combs are capable of emitting several frequencies all at once, which are evenly spaced like the teeth of a comb. It is these different frequencies beating together that emit the microwave radiation, which lies in our communication spectrum.

Up until this year, their work was mostly theoretical. It only became practical once they figured out how to build a device to transmit and receive information.

“If you want to use this device for Wi-Fi, you need to be able to put useful information in the microwave signals and extract that information from the device,” said co-author of the research Marco Piccardo.

Oversimplified, they created a dipole antenna on the laser configuration, used the frequency comb to modulate the information and transmit it in all directions as microwaves, and then received it using a horn antenna filtering it to a computer.

They also showed that the device could receive radio signals sent. The team could control the laser remotely from another radio transmitter.

“This all-in-one, integrated device, holds great promise for wireless communication,” said Piccardo. “While the dream of terahertz wireless communication is still a ways away, this research provides a clear roadmap showing how to get there.”

The device is patent pending, and the Harvard Office of Technology Development is exploring avenues for commercialization.

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QuantumPhysics

Posts: 3,349   +3,173
Thermodynamics dictates that lasers being transmitted over long distances will suffer from signal degradation. Latency is unavoidable.

And at the end of the day, no matter how fast your transmitters and recievers are, your CPU better be faster or else: bottlenecks.
 

wiyosaya

Posts: 5,363   +3,444
Thermodynamics dictates that lasers being transmitted over long distances will suffer from signal degradation. Latency is unavoidable.
Any signal, regardless of wavelength will technically degrade given enough distance. The inverse square law at play.

A careful reading of the article reveals that it is not the laser wavelength, per se, that is used to transmit the data, rather, it is a beat frequency generated from a laser frequency comb at a much longer wavelength - microwave region - that carries the data. What they are describing is a unique way of generating microwave radiation. How well this will propagate will, I suspect, depend on how carefully that frequency is chosen and how well that frequency propagates through air and obstacles just like any other means of generating useful radiation.

And at the end of the day, no matter how fast your transmitters and recievers are, your CPU better be faster or else: bottlenecks.
Devices like this tend to have their own dedicated processors. Data can be spooled to disk or other storage means. At this time, no consumer data needs would require that that amount of data be continuously sent.

However, something like this could be used to implement some sort of multiplexing where multiple channels of data are sent on one carrier thus, potentially, serving many data consumers at the same time.
 

elementalSG

Posts: 135   +127
Any signal, regardless of wavelength will technically degrade given enough distance. The inverse square law at play.

A careful reading of the article reveals that it is not the laser wavelength, per se, that is used to transmit the data, rather, it is a beat frequency generated from a laser frequency comb at a much longer wavelength - microwave region - that carries the data. What they are describing is a unique way of generating microwave radiation. How well this will propagate will, I suspect, depend on how carefully that frequency is chosen and how well that frequency propagates through air and obstacles just like any other means of generating useful radiation.


Devices like this tend to have their own dedicated processors. Data can be spooled to disk or other storage means. At this time, no consumer data needs would require that that amount of data be continuously sent.

However, something like this could be used to implement some sort of multiplexing where multiple channels of data are sent on one carrier thus, potentially, serving many data consumers at the same time.
It is curious that lasers are generating microwaves that are creating the signal to carry the data. If this is so, and they are already having problems propagating 5G signals long distances or even through walls (which run at about ~30-70Ghz for High Band), do you think this technology would only serve very short distances or perhaps need a very large relay network (a repeater every 25-100 ft or something)? I'm assuming that using lower frequencies in the microwave spectrum would probably result in speeds similar to what we experience on 4G LTE or 802.11ac right now, which probably isn't that different from what we currently have, but I could be wrong.
 

wiyosaya

Posts: 5,363   +3,444
You can't beat a bit of quantum cascade laser frequency combing on a Friday morning
:laughing:
Absolutely! The vibrations from that comb are a rather exhilarating and awakening experience, so much so, I decided to skip my morning coffee! :joy:

It is curious that lasers are generating microwaves that are creating the signal to carry the data. If this is so, and they are already having problems propagating 5G signals long distances or even through walls (which run at about ~30-70Ghz for High Band), do you think this technology would only serve very short distances or perhaps need a very large relay network (a repeater every 25-100 ft or something)? I'm assuming that using lower frequencies in the microwave spectrum would probably result in speeds similar to what we experience on 4G LTE or 802.11ac right now, which probably isn't that different from what we currently have, but I could be wrong.
I really do not consider myself an expert, however, as I understand it, the plan for mm wave 5G is to have repeaters - I do not know what the spacing is on them. Also, for 5G, use inside a building requires an antenna on the outside of the building because mm waves cannot penetrate the shell of a structure, and, if there is not some sort of frequency down-conversion that is done on the transition between outdoors and indoors, I would not be surprised to learn that repeaters would be required internally to any structure.

In the laser realm, frequency down or up conversion is common. The green lasers that you see, unless they are Argon lasers - and the most common ones are not, use a process of frequency up conversion to make them green. 1.06 micrometer wavelength infrared lasers are frequency doubled through a non-linear crystal to make the green that is seen at 532 nanometers wavelength.

What is happening in this case, at least as I understand it, is that the laser is making the teeth of the comb vibrate, and there is a beat frequency between those teeth that is responsible for the RF radiation that is generated. Simply put, it is a frequency down-conversion process.

As to speeds - as I understand it, it seems to me that it would depend on how much data can be carried at any particular frequency. Vastly simplified, the absolute theoretical limit of the data rate is, to the best of my understanding, equivalent to 1/2 of the frequency of the carrier. However, it is much more complicated than that in real life. Here is a more technical discussion of what is involved - https://en.wikipedia.org/wiki/Shannon–Hartley_theorem
 
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