Secret key exchange in ultra-long lasers by radio-frequency spectrum coding

Alessandro Tonello, Alain Barthélémy, Katarzyna Krupa, Vincent Kermène, Agnès Desfarges-Berthelemot, Badr Mohamed Shalaby, Sonia Boscolo, Sergei K. Turitsyn, Juan Diego Ania-Castañón

Research output: Contribution to journalArticlepeer-review


We propose a new approach to the generation of an alphabet for secret key exchange relying on small variations in the cavity length of an ultra-long fiber laser. This new concept is supported by experimental results showing how the radio-frequency spectrum of the laser can be exploited as a carrier to exchange information. The test bench for our proof of principle is a 50 km-long fiber laser linking two users, Alice and Bob, where each user can randomly add an extra 1 km-long segment of fiber. The choice of laser length is driven by two independent random binary values, which makes such length become itself a random variable. The security of key exchange is ensured whenever the two independent random choices lead to the same laser length and, hence, to the same free spectral range.
Original languageEnglish
Article numbere276
Number of pages5
Issue number2
Early online date27 Jan 2015
Publication statusPublished - 24 Apr 2015

Bibliographical note

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Funding: French National Research Agency (grants LABEX SIGMALIM and ANR 08-JCJC-0122 PARADHOQS); European Research Council (project ULTRALASER); Leverhulme Trust (grant RPG-278); Spanish MICINN project TEC2011-27314 (RAMAS); and XLIM Institute (grant VIP2013).


  • fiber lasers
  • fiber optics communications
  • optical security
  • encryption


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