Secret key exchange in ultralong lasers by radiofrequency spectrum coding

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 ultralong fiber laser.This new concept is supported by experimental results showing how the radiofrequency 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.

The effect of self-focusing on laser space-debris cleaning

A ground-based laser system for space-debris cleaning will use powerful laser pulses that can self-focus while propagating through the atmosphere.We demonstrate that for the relevant laser parameters,this self-focusing can noticeably decrease the laser intensity on the target.We show that the detrimental effect can be,to a great extent,compensated for by applying the optimal initial beam defocusing.The effect of laser elevation on the system performance is discussed.

Spiral attractor created by vector solitons

Mode-locked lasers emitting a train of femtosecond pulses called dissipative solitons are an enabling technology for metrology,high-resolution spectroscopy,fibre optic communications,nano-optics and many other fields of science and applications.Recently,the vector nature of dissipative solitons has been exploited to demonstrate mode locked lasing with both locked and rapidly evolving states of polarisation.Here,for an erbium-doped fibre laser mode locked with carbon nanotubes,we demonstrate the first experimental and theoretical evidence of a new class of slowly evolving vector solitons characterized by a double-scroll chaotic polarisation attractor substantially different from Lorenz,Ro¨ssler and Ikeda strange attractors.The underlying physics comprises a long time scale coherent coupling of two polarisation modes.The observed phenomena,apart from the fundamental interest,provide a base for advances in secure communications,trapping and manipulation of atoms and nanoparticles,control of magnetisation in data storage devices and many other areas.

Multi-scale polarisation phenomena

Multi-scale methods that separate different time or spatial scales are among the most powerful techniques in physics,especially in applications that study nonlinear systems with noise.When the time scales(noise and perturbation)are of the same order,the scales separation becomes impossible.Thus,the multi-scale approach has to be modified to characterise a variety of noise-induced phenomena.Here,based on stochastic modelling and analytical study,we demonstrate in terms of the fluctuation-induced phenomena and Hurst R/S analysis metrics that the matching scales of random birefringence and pump–signal states of polarisation interaction in a fibre Raman amplifier results in a new random birefringence-mediated phenomenon,which is similar to stochastic anti-resonance.The observed phenomenon,apart from the fundamental interest,provides a base for advancing multi-scale methods with application to different coupled nonlinear systems ranging from lasers(multimode,mode-locked,random,etc.)to nanostructures(light-mediated conformation of molecules and chemical reactions,Brownian motors,etc.).