Dark optical solitons: physics and applications

Spatial solitons, beams that do not spread owing to diffraction when they propagate, have been demonstrated to exist by virtue of a variety of nonlinear self-trapping mechanisms. Despite the diversity of these mechanisms, many of the features of soliton interactions and collisions are universal. Spatial solitons exhibit a richness of phenomena not found with temporal solitons in fibers, including effects such as fusion, fission, annihilation, and stable orbiting in three dimensions. Here the current state of knowledge on spatial soliton interactions is reviewed.

https://science.sciencemag.org/content/sci/286/5444/1518.full.pdf

Optical Spatial Solitons and Their Interactions: Universality and Diversity.

Solitons, nonlinear self-trapped wavepackets, have been extensively studied in many and diverse branches of physics such as optics, plasmas, condensed matter physics, fluid mechanics, particle physics and even astrophysics. Interestingly, over the past two decades, the field of solitons and related nonlinear phenomena has been substantially advanced and enriched by research and discoveries in nonlinear optics. While optical solitons have been vigorously investigated in both spatial and temporal domains, it is now fair to say that much soliton research has been mainly driven by the work on optical spatial solitons. This is partly due to the fact that although temporal solitons as realized in fiber optic systems are fundamentally one-dimensional entities, the high dimensionality associated with their spatial counterparts has opened up altogether new scientific possibilities in soliton research. Another reason is related to the response time of the nonlinearity. Unlike temporal optical solitons, spatial solitons have been realized by employing a variety of noninstantaneous nonlinearities, ranging from the nonlinearities in photorefractive materials and liquid crystals to the nonlinearities mediated by the thermal effect, thermophoresis and the gradient force in colloidal suspensions. Such a diversity of nonlinear effects has given rise to numerous soliton phenomena that could otherwise not be envisioned, because for decades scientists were of the mindset that solitons must strictly be the exact solutions of the cubic nonlinear Schrodinger equation as established for ideal Kerr nonlinear media. As such, the discoveries of optical spatial solitons in different systems and associated new phenomena have stimulated broad interest in soliton research. In particular, the study of incoherent solitons and discrete spatial solitons in optical periodic media not only led to advances in our understanding of fundamental processes in nonlinear optics and photonics, but also had a very important impact on a variety of other disciplines in nonlinear science. In this paper, we provide a brief overview of optical spatial solitons. This review will cover a variety of issues pertaining to self-trapped waves supported by different types of nonlinearities, as well as various families of spatial solitons such as optical lattice solitons and surface solitons. Recent developments in the area of optical spatial solitons, such as 3D light bullets, subwavelength solitons, self-trapping in soft condensed matter and spatial solitons in systems with parity-time symmetry will also be discussed briefly.

http://www.physics.sfsu.edu/~laser/pdf/rop347172p20.pdf

Optical spatial solitons: historical overview and recent advances

The investigation of nonlinear wave phenomena has been one of the main direc tions of research in optics for the last few decades. Soliton concepts applied to the description of intense electromagnetic beams and ultrashort pulse propagation in various media have contributed much to this field. The notion of solitons has proved to be very useful in describing wave processes in hydrodynamics, plasma physics and condensed matter physics. Moreover, it is also of great importance in optics for ultrafast information transmission and storage, radiation propagation in resonant media, etc. In 1973, Hasegawa and Tappert made a significant contribution to optical soliton physics when they predicted the existence of an envelope soliton in the regime of short pulses in optical fibres. In 1980, Mollenauer et al. conducted ex periments to elucidate this phenomenon. Since then the theory of optical solitons as well as their experimental investigation has progressed rapidly. The effects of inhomogeneities of the medium and energy pumping on optical solitons, the interaction between optical solitons and their generation in fibres, etc. have all been investigated and reported. Logical devices using optical solitons have been developed; new types of optical solitons in media with Kerr-type nonlinearity and in resonant media have been described.

Optical Solitons

Chapter 2 - Variational methods in nonlinear fiber optics and related fields

We show experimentally the trapping of two spatial solitons of the same wavelength but with slightly different propagation directions, which results from the collision of two initially overlapped solitons beams. This is the spatial analog of soliton pulse trapping in birefringent optical fibers. Adjustment of the phase shift between each beam permits the switching of one soliton to the other without disturbing their trajectory.

Experimental spatial soliton trapping and switching

We report the experimental observation of the nonlinear interaction between two fundamental spatial solitons with a π/2 phase difference in carbon disulfide. An energy flow from the phase-advanced soliton to the phase-delayed soliton was observed, which leads to a single self-trapped beam. The position of the output beam can be switched by reversing the sign of the solitons’ initial phase difference.

Experimental observation of spatial soliton interactions with a π/2 relative phase difference

Experimental results are presented showing the simultaneous propagation of a dark and bright spatial solitary waves of different colors (1064 and 532 nm) in a homogeneous Kerr medium of the focusing type, owing to cross-phase modulation. They correspond to a soliton pair, already proposed as a particular analytical solution of the two coupled wave equations. The intensity ratio between the two beams at which solitary propagation occurs is close to the theoretical value, and the observed phenomena are consistent with numerical simulations of the experiment. >

Observation of the self-guided propagation of a dark and bright spatial soliton pair in a focusing nonlinear medium

In this letter, we report a wide tuning range MEMS-based swept laser source using deep reactive ion etching on an SoI substrate. A MEMS Fabry-Perot filter with a free-spectral range and a tuning range wider than 94 nm is presented. The measured transmission loss of the filter is between -10.2 and -13.6 dB. This filter is used to construct a swept laser source with 85 nm tuning range. These results represent the widest tuning range reported in literature for an in-plane SoI-MEMS based swept laser source using deeply-etched free-standing distributed-Bragg-reflection mirrors. The recorded tuning range enables the use of the in-plane MEMS filter in optical coherence tomography applications.

Deeply-Etched Optical MEMS Tunable Filter for Swept Laser Source Applications

We have studied the increase of the power contained in Bessel beams generated using the Durnin ring technique, which is compatible with microelectromechanical systems technology. Increasing the ring width to increase the output power will lead to deviation from the Bessel beam profile and its diffraction properties. In this work, the effect of the ring width on the generated beam is investigated. An analytical expression for the generated beam depth of focus (DOF) is obtained. A Fourier optics model is also developed to estimate the transverse field profile. The theoretical predictions are assisted by numerical simulations and experimental measurements. The developed models allow engineering the beam diffraction properties to make the necessary compromise between the DOF and the amount of energy carried by the beam depending on the targeted application.

M. Shalaby

Papers

Experimental spatial soliton trapping and switching

Experimental observation of spatial soliton interactions with a π/2 relative phase difference

Observation of the self-guided propagation of a dark and bright spatial soliton pair in a focusing nonlinear medium

Deeply-Etched Optical MEMS Tunable Filter for Swept Laser Source Applications

Propagation of Bessel beams generated using finite-width Durnin ring.