Security in information transfer is becoming increasingly important. Quantum key distribution (QKD) or quantum cryptography – a communication process that is based on quantum mechanics – is regarded as the most secure way of transferring information. However, its key-establishing rates and operational ranges can be restricted by signal attenuation, noise and detector dark counts.

To be free from these limitations, Scheuer and Yariv have proposed a new concept for secure key distribution – the giant fibre laser key distribution system (GFL-KDS)1. Fibre lasers are similar to conventional lasers, but they use an optical fibre with a suitable dopant, such as erbium, as the active region. The GFL-KDS is based on laser oscillations: the sender and receiver, at either end of this potentially very-long laser, each have three mirrors, labelled ‘0’, ‘1’ and ‘T’, that reflect at slightly different wavelengths. Independent choices of mirror by both users determine the lasing characteristics, allowing them to identify when they have selected the same mirror, thus constructing a key of ‘1’s and ‘0’s. Although this is simple to ascertain for legitimate users, it is very difficult for an eavesdropper. In contrast to current QKD systems, noise can even be used to conceal the exchanged data from an eavesdropper without affecting the primary laser oscillations. The researchers believe that with advantages such as higher key-establishing rates, longer link ranges and simple structure, this GFL-KDS paradigm could be an intriguing alternative, or at least a complementary technology, to QKD systems, especially for long haul links.