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Backward light scattering can cause passive Q switching in fiber lasers. We propose a self-consistent description of the laser dynamics. Our model quantitatively reproduces the temporal structure of pulsation and is also attractive for analysis of laser stability and statistics. The validity of the model is directly verified in an experiment.

We propose a secure communication scheme based on anticipating synchronization of two chaotic laser diodes, one subject to incoherent optical feedback and the other to incoherent optical injection. This scheme does not require fine tuning of the optical frequencies of both lasers as is the case for other schemes based on chaotic laser diodes subject to coherent optical feedback and injection. Our secure communication scheme is therefore attractive for experimental investigation.

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We analyze the bifurcation mechanism responsible for the experimentally observed polarization selfmodulation ͑PSM͒ in a vertical-cavity surface-emitting laser subject to optical feedback. We show that closed branches of time-periodic intensity solutions connecting distinct external-cavity modes ͑ECMs͒ exhibit PSM. Along these bridges, the linearly polarized components of the optical field oscillate in antiphase and with a frequency close to the difference between two ECM frequencies. A beating mechanism between stable ECMs then explains the PSM phenomenon. Our results also substantiate recent theoretical studies of edge-emitting lasers subject to optical feedback.

We report on the effect of MGy dose level γ-irradiation on the parameters of fibre Bragg gratings intended for sensing applications. The γ-radiation sensitivities of gratings written with near-UV 330 nm light in hydrogen loaded Ge-doped fibres and of a grating written in a N-doped fibre were found to be higher than that of gratings written in a 10 mol.% Gedoped fibre without hydrogen loading. In the former cases, changes in the amplitude and the width of the Bragg peak were observed during γ-irradiation while no change was observed in the latter case. For the grating written in the Ndoped fibre, the radiation-induced shift of the Bragg peak did not saturate while for gratings written in hydrogen-loaded Gedoped fibres it saturated to a higher level than for gratings written in unloaded Ge-doped fibre.

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