Pulse Position Modulation for Secure Optical Communication

As computer capabilities continue to increase, previous generations of encryption systems become vulnerable. Scientists have now discovered an “unbreakable” encryption system that could, in the near future, make our information permanently secure from theft.

The method transmits data via laser, converting the information into a stream of unrelated photons so that any monitoring of the channel only sees a chaotic collection of photons. This requires a special conversion system possessed only by the sender and the receiver, ensuring that only the two parties can decrypt the message. The experiment is organized by a research institute at the University of Massachusetts, which is currently developing this conversion system.

The technology enabling the system is called Pulse Position Modulation (PPM), which divides time into incoherent intervals, each representing a letter or symbol. Laser pulses carry the signal. The interval encoding is shared only with the receiver, who alone can decode it.

Researchers state that the transmission pulses contain only a few photons, while the fiber carrying the information contains a large number of unrelated photons. The converter's purpose is to segment the information so that it appears as background noise. Typical optical sensors ignore unknown photons, providing confidentiality. If the sender allows the signal to remain in the channel longer, it blends more thoroughly with background photons, effectively disappearing.

Researchers have demonstrated the system, though they have not specified potential users. While most parties care about protecting critical information—such as state intelligence or commercial secrets—this method is well suited for such transmissions. However, a major drawback is that the decoding key must be pre‑shared with the receiver, raising the question of how to keep that key confidential.