The Chinese have learned to bug the premises with fiber
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The Chinese have learned to bug the premises with fiber optic cables

Researchers at Tsinghua University in China have developed a technique to eavesdrop on conversations in rooms where fiber optic cables run. For example, they are used to provide an internet connection so you can find them anywhere. The results of the work of scientists were recently released on the Internet.

    Image source: Pixabay

Image source: Pixabay

The fact is that sound vibrations create air pressure drops that create micro-vibrations in the fiber optic cable, which are modulated with light waves transmitted through the cable. The resulting distortions can be analyzed with a laser Mach-Zehnder interferometer at a sufficiently large distance.

During the course of the study, the scientists were able to fully recognize speech in the presence of a three-meter open stretch of fiber optic cable in space. The distortion analysis was performed at a distance of 1.1 km from the listening room. It is noted that the hearing range and ability to filter interference correlate with the length of fiber optic cable in the room.

    Image source: arxiv.org

Image source: arxiv.org

As a result, scientists found that the detection and recovery of an audio signal in optical communication networks can be implemented secretly for the hearing object and without violating the communication functions used. To secretly connect to the communication channel, the researchers used a wavelength division multiplexer (WDM). The background noise level can be reduced by additional balancing of the interferometer arms.

To counteract this method of eavesdropping, it is advisable to shorten optical cables in the room and lay them in rigid cable ducts. You can also reduce listening efficiency by using angled optical connectors (APC) instead of flat end connectors (PC) when connecting cables. Cable manufacturers are encouraged to use high modulus materials such as metal and glass to coat the fiber.

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Robbie Elmers

Robbie Elmers is a staff writer for Tech News Space, covering software, applications and services.

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