James from the Temple of Concave
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Is it possible to replace the wifi signal with sunlight to connect to the Internet and transmit data?
Someone did.
Researchers in Saudi Arabia have designed a smart glass system.
It can use the window as a modem (that is, the "cat" used to surf the Internet at home), and realize the transmission of information by changing the nature of sunlight.
The phone's camera receives the optical signal and converts it back into binary data.
Only a solar cell with a power of 1 watt is needed to get it running.
The study has been published in the IEEE Photonics Journal.
How exactly is it done? Look down.
Do you believe in the Light?
In the past, it was common to change the intensity of light to encode it.
However, in the air propagation of light, its intensity will be constantly changed by environmental influences such as air pressure, the transmission efficiency is too low, and the human eye is very sensitive to drastic changes in light intensity.
This time, the researchers turned to the polarization principle of light.
In middle school, I learned that light is a shear wave, and if it is allowed to pass through a specific medium (polarizer), only part of the light wave in a specific direction will be retained.
Through the above principles, the researchers designed a system that carries information into sunlight by changing the polarization of light waves, and the human eye is not easy to detect the changes.
Specific changes need to be achieved through liquid crystal materials. At different voltages, the molecular arrangement of such materials will change, which in turn will affect the polarization of the light in the medium.
But this is still not enough.
In order to improve the coding efficiency, the researchers also refer to the time response function of the liquid crystal shutter and consider the problems of birefringence of the light-transmitting medium, and stack the two reverse liquid crystal (LC) units on top of each other.
Finally, the entire modulation system consists of 3 polarizers and 2 reverse liquid crystal layers (one constant white, one constant black) -
Researchers call this a dual-unit liquid crystal shutter (DLS).
The benefits of this design are:
Compared with single-layer liquid crystal polarization systems, it can change the polarization of light waves faster, reduce coding errors, and reduce the effect of the "scintillation effect" of random fluctuations in the intensity of light in propagation.
As can be seen from the figure below, the red line is the output of the constant white mode to signal 1, and the blue line is the constant black mode, when the two are stacked, the pulse (green curve) of the signal "1" is shorter, changes more rapidly, and is more efficient in communication coding.
With DLS as the basic modulation unit, the researchers designed a complete set of information transmission system to replace wifi:
First let the sunlight shine through the smart glass window, the window itself is a modulator, through DLS to change the polarization of the light wave, modulation and coding.
The light wave carrying the information continues to enter the room, and then is received by terminal cameras such as mobile phones, and demodulates them back into binary data.
To further increase the transmission rate, the researchers also used time-division multiplexing (TDM).
Simply put, this technology is to cut the transmission time in a channel, assign transmission acceptance time to different devices in a certain order, and when it is the turn of a certain device, the device will open the transmission, and the transmission of other devices will be cut off.
Finally, the research team observed the transmission performance of the system they built through modeling.
At present, the more mainstream communication method of optical modulation and direct transmission will use semiconductor optical amplifiers (SoA), and the researchers chose two modulation modes for comparison: RetroTurbo with a modulation area of 66 square centimeters, and PassiveVLC with a modulation area of 14 square centimeters.
The results show that with the same modulation area and the same transmission distance, their system is superior to the current state-of-the-art method, and the maximum transmission rate can reach 16Kbps.
In terms of energy consumption, only 1W of solar panels are needed to drive the entire system.
Although the current rate of transmitting information is limited, the team believes that the results indicate that sunlight is not only an energy resource, but also an information resource, which will help us transmit information with lower energy consumption.
Regarding follow-up research planning, the team said:
Their next step is to increase the transmission rate to megabits per second, or even gigabits, and will apply to order the relevant test hardware.
Team introduction
Finally, get to know the research team members.
Sahar Ammar comes from the Department of Electrical and Mathematical Sciences and Engineering (CEMSE) of King Abdullah University of Science and Technology (KAUST), with a focus on optical communications;
the second work, Osama Amin, also from the Department of Electrical and Mathematical Sciences and Engineering (CEMSE) at King Abdullah University of Science and Technology;
Instructor Basem Shihada specializes in wireless and wired communications, as well as cybersecurity and cloud computing.
Reference Links:
[1]https://ieeexplore.ieee.org/document/9864223/authors#authors
[2]https://interestingengineering.com/innovation/researchers-devise-smart-glass-windows-that-can-polarize-sunlight-for-wireless-data-transmission
[3]https://www.alphagalileo.org/en-gb/Item-Display/ItemId/226738?returnurl=https://www.alphagalileo.org/en-gb/Item-Display/ItemId/226738
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