Photorefractive polymeric optical spatial solitons

Optical spatial solitons: historical overview and recent advances

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 Schrödinger 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.

Electro-activation and electro-morphing of photorefractive funnel waveguides

We demonstrate the electro-activation of funnel waveguides through the quadratic electro-optic effect in paraelectric potassiumlithium- tantalate-niobate. This allows us to achieve electro-optic intensity modulation in a single optical beam, a 1x2 switch, and finally the electrically controlled morphing of a single waveguide into a 1x2 and a 1x4 divider.

Photorefractive solitons of arbitrary and controllable linear polarization determined by the local bias field

We discuss and experimentally demonstrate a scheme to achieve photorefractive solitons of arbitrary linear polarization using the quadratic electro-optic effect and describe the observation of the self-trapping of a set of linear polarized beams in different positions of a paraelectric photorefractive crystal of potassium-lithium-tantalate-niobate (KLTN) biased by the inhomogeneous field produced by two miniaturized top electrodes. The polarization of the single solitons of the set is determined by the local electrostatic configuration and the underlying tunable anisotropy, which is detected through zero-field electro-activation.

Circularly polarized optical spatial solitons

We present, experimentally and theoretically, a polymer material system that supports optical spatial solitons of circular polarization. We demonstrate one-dimensional circularly polarized dark solitons supported by photoisomerization nonlinearity in a bulk polymer.

Soliton-induced waveguides in an organic photorefractive glass

We demonstrate optical waveguiding of a probe beam at 980 nm by a soliton beam at 780 nm in an organic photorefractive monolithic glass. Both planar and circular waveguides induced by one- and two-dimensional spatial solitons formed as a result of orientationally enhanced photorefractive nonlinearity are produced in the organic glass. Possibilities for increasing the speed of waveguide formation are discussed.

Spontaneous one- and two-dimensional optical spatial solitons supported by photoisomerization nonlinearity in a bulk polymer

We present theoretically another type of optical spatial soliton in steady state, which is supported by photoisomerization nonlinearity in a polymer. For the photoisomerization nonlinearity with saturation, this type of one- or two-dimensional spatial soliton can be formed in a bulk polymer. The spontaneous soliton of this type can only be dark or gray. Not only a linearly polarized beam, but also a circularly polarized beam can be used to form the soliton, which is impossible for the photorefractive soliton. The effects of wavelength, polarization, and intensity of the beam on the formation of the soliton are discussed in detail.

Optical spatial solitons supported by photoisomerization nonlinearity in a polymer

We present a theory for a new type of optical spatial soliton that is based on the angle hole burning mechanism of photoisomerization in some polymers. We predict that the photoisomerization nonlinearity can support steady-state dark and bright spatial solitons in the polymer. We also discuss the dependence of the FWHM of the spatial soliton on wavelengths of the background beams and on the ratio of the intensity of the background beam to that of the signal beam.

Molding and stretched evolution of optical solitons in cumulative nonlinearities

The observation of initial time dynamics of self-trapping in photorefractive media indicates that optical spatial solitons supported by intense cumulative nonlinearities manifest temporally nonlocal signatures in the form of stretched exponential behavior. This general result, supported also by numerical predictions, is triggered by wave shaping in a time-constant buildup map, a consequence of the spatially resolved inertial response intrinsic to the geometrical transition from a diffracting to a self-focused beam, inherent to soliton appearance.

Self-trapping of light in an organic photorefractive glass

We report the first observation, to our knowledge, of self-trapping of light as well as optically induced focusing-to-defocusing switching in an organic photorefractive glass, owing to the orientationally enhanced photorefractive nonlinearity of the material.