This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors.

Rogue waves, which were first described as an oceanographic phenomenon, constitute an important factor in the dynamics of many physical systems. Most of these systems were analyzed by scalar fields, while some of them, and specifically in optics, are described by a vector field. Thus, they differ from scalar systems in several crucial aspects. In this work, we study experimentally twin-peak rogue waves with a temporal imaging system capable of measuring the Stokes vectors as a function of time. We found that the two peaks in optical twin-peak rogue waves have orthogonal states of polarization and similar intensities. We observed this with two different systems, however, we do not have a theoretical explanation for this phenomena and could not explain it with current models.

For an Er-doped fiber laser, for the first time, to the best of our knowledge, we demonstrate both experimentally and theoretically a novel mechanism of harmonic mode-locking based on the electrostriction effect leading to excitation of the torsional acoustic modes in the transverse section of the laser. The exited torsional acoustic modes modulate the fiber birefringence that results in synchronization of oscillations at the harmonic modes and the linewidth narrowing with the increased signal-to-noise ratio of 30 dB. By adjusting the in-cavity birefringence based on tuning the polarization controller, we enable the selection of the harmonic mode to be stabilized.

In this paper, we report an active Q-switching of an erbium-doped fiber laser with special modulation functions and novel laser geometry. We experimentally demonstrate that using such a smart Q-switch approach, Q-switch ripple-free pulses with Gaussian-like shape and 17.3 ns width can be easily obtained. The idea behind the smart Q-switch is to suppress one of two laser waves contra-propagating along the fiber cavity, which arises after Q-cell opening, and to eliminate the minor sub-pulses.

A distributed laser model is applied to explain the multi-peak shape of the pulses generated by the actively Q-switched erbium-doped fiber laser. In the model, all kinds of intra-cavity losses are taken into account, including the point losses produced by fiber splices and intra-cavity elements, and the distributed loss, such as the active fiber background loss and the loss caused by excited state absorption inherent in erbium-doped fibers. The model also takes into account the exact function that describes the switching dynamics of the Q-switch modulator. We show that the distributed model allows an accurate simulation of the laser pulse shape and energy, providing therefore a good agreement with the experimental results. The origin of a multi-peak pulse shape frequently observed in QS-EDFL and some other features that result from the model are discussed.

We report experimental evidence of bistable phase locking in nonlinear optics, in particular, in a photorefractive oscillator emitting in few transverse modes. Bistable phase locking is a recently proposed method for converting a laserlike system, which is phase invariant, into a phase-bistable one by injecting a suitable spatially modulated monochromatic beam, resonant with the laser emission, into the optical cavity. We experimentally demonstrate that the emission on the fundamental TEM${}_{00}$ mode becomes phase bistable by injection of a beam with the shape of the TEM${}_{10}$ mode with appropriate frequency, in accordance with recent theoretical predictions [K. Staliunas et al., Phys. Rev. A 80, 025801 (2009)]. The experimental observations are supported by an analytical study of a few-transverse-mode photorefractive oscillator model. DOI: http://dx.doi.org/10.1103/PhysRevA.85.025805 ©2012 American Physical Society