These kinds of lasers often called ultra-long have peculiar features: their enormous cavity lengths « miniaturize » the free spectral range of the cavity modes to a few kilohertz. Among the potential applications, we have focused our attention to the transmission of secure data between two end users. We have conceived a system and a protocol that are simple and cost effective and that can allow exchanging information in a secure way, thanks to a laser working-point that is common to two different and indistinguishable configurations. This laser is well suited for private key encryption. Although the level of security is lower than that of more complex systems based on quantum cryptography, these kinds of laser can operate in a normal optical infrastructure and can strengthen the security of a communication system using standard low-cost components.
This work has been carried out in the framework of a new collaboration with the Aston Institute of Photonic Technologies of Birmingham, UK and the Instituto de Óptica of the Consejo Superior de Investigaciones Científicas (CSIC) in Madrid, Spain.
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