Photovoltaic Solitons Research Articles

Steering the propagation of photovoltaic solitons by spatial phase modulation

A simple scheme is presented to steer the propagation of a spatial photovoltaic soliton in a photovoltaic crystal. The basic idea is to impose a sinusoidal phase modulation on the light beam before entering the crystal. It is found that the self-deflection, soliton-like propagation, annihilation and splitting of this spatial-phase-modulated (SPM) beam can be realized by choosing appropriate modulation parameters; besides, a SPM beam can produce a waveguide with strong stability to steer a non-phase-modulated beam. These unique properties would have potential applications in the optical switch, splitter, modulator, and waveguide, etc.

Effects of system parameters on bright dissipative holographic photovoltaic solitons

In a photovoltaic dissipative system, evolution and stability of a bright dissipative holographic photovoltaic (DHP) soliton are completely determined by the given dissipative system, i.e., they are impacted by the system parameters, such as the system temperature, the photovoltaic field of the crystal, the angle between two input beams, and the angle of polarized direction. Such DHP solitons can be easily amplified or absorbed by adjusting these system parameters. They have potential applications in optical switches or repeaters.

One-dimensional optical bright screening photovoltaic photorefractive solitons, soliton pairs and incoherent interaction between them in BaTiO 3 crystal

By the use of theory of optical solitons, nonlinear equations governed by screening photorefractive photovoltaic solitons are introduced. By means of numerical methods, intensity profile, refractive index change of the media and also stability under propagation are investigated. Self-bending of solitons under first-order diffusion is also studied. Besides, incoherent coupled bright–bright soliton pairs and incoherent interaction are studied.

Grey photovoltaic solitons in two-photon photorefractive materials under the open-circuit case

In steady-state conditions, we predicted that grey photovoltaic solitons of the optical wave evolution equation could exist in two-photon photorefractive materials under the open-circuit case. The characteristics of the grey photovoltaic soliton, such as the intensity profile, the intensity full width at half-maximum, the transverse velocity and the phase profiles of these grey photovoltaic solitons are discussed in detail.

Experimental study of bright photovoltaic solitons in lithium niobate crystal

The effect of background beam with different Glass constant on the relative spatial refractive perturbation in photovoltaic crystal was discussed, in which was introduced the concrete conditions for the formation of bright or dark photovoltaic spatial solitons in crystals with negative refractivity change. Based on the results, for what is to our knowledge the first time, the bright photovoltaic solitons was experimentally observed in LiNbO3:Fe by use of e-ray signal of 532nm and o-ray background illumination of 488nm.

Large self-deflection of bright and dark screening photovoltaic solitons in LiNbO3

We demonstrate large self-deflection of both bright and dark screening photovoltaic solitons existing in LiNbO3 crystal under an external applied field with numerical method, and we also demonstrate that the self-deflection is not only connected with the acceptor concentration NA but also with the external applied field E0. Under the same E0, when NA is lower, the self-deflection is more obvious. Under the same NA, when E0 is higher, the self-deflection is more obvious. We also find that self-deflection of the bright screening spatial soliton and that of the dark one are different: the bright screening photovoltaic soliton deflects obviously; while only one side of the dark soliton deflects, its extreme value point and the other side almost do not deflect.

Grey screening-photovoltaic soliton-induced waveguides

This paper shows that waveguides induced by grey screening-photovoltaic solitons are always single mode for all intensity ratios, which are the ratio between the peak intensity of the soliton and the dark irradiance. It finds that the confined energy near the centre of the grey soliton and the propagation constant of the guided mode increase monotonically with increasing intensity ratio. On the other hand, when the soliton greyness increases, the confined energy near the centre of the grey soliton and the propagation constant of the guided mode reduce monotonically. When the bulk photovoltaic effect is neglected for short circuits, these waveguides become waveguides induced by grey screening solitons. When the external bias field is absent, these waveguides become waveguides induced by grey photovoltaic solitons.

Waveguides induced by steady-state gray solitons in biased photorefractive–photovoltaic crystals

We carry out a theoretical investigation of the properties of waveguides induced by photorefractive one-dimensional steady-state gray spatial solitons (i.e., screening solitons, photovoltaic solitons, and screening-photovoltaic solitons). We demonstrate that waveguides induced by photorefractive steady-state gray spatial solitons are only a single guided mode for both all soliton graynesses and all values of ρ, where ρ is the ratio between the soliton peak intensity and the dark irradiance, and moreover, waveguides induced by gray photovoltaic solitons for closed-circuit condition are also only a single guided mode for all electric current densities. We find that the confined energy near the center of a photorefractive steady-state gray spatial soliton increases with ρ and decreases with an increase in the soliton grayness. We also find that the confined energy near the center of a gray photovoltaic soliton for closed-circuit condition increases with the electric current density. On the other hand, waveguides induced by gray screening-photovoltaic solitons are gray screening soliton-induced waveguides when the bulk photovoltaic effect is neglectable and are gray photovoltaic soliton-induced waveguides when the external bias field is absent.

Photovoltaic spatial soliton pairs in two-photon photorefractive materials

We report the existence of incoherently coupled bright–bright steady state photovoltaic soliton pairs in two-photon photorefractive material under open circuit conditions. Based on WKBJ method and paraxial ray approximation, we have obtained coupled equations describing dynamical evolution of spatial soliton pairs. In the steady state regime, the present analysis leads to the identification of existence equation of bright–bright solitons, which captures a plethora of soliton pairs. We have undertaken linear stability analysis which shows that these solitons are stable.

Diffusion-induced deflection and the effect of two-wave mixing gain on dissipative photovoltaic solitons

In an open-circuit dissipative photovoltaic (PV) crystal, by considering the diffusion effect, the deflection of bright dissipative photovoltaic (DPV) solitons has been investigated by employing numerical technique and perturbational procedure. The relevant results show that the centre of the optical beam moves along a parabolic trajectory, while the central spatial-frequency component shifts linearly with the propagation distance; furthermore, both the spatial deflection and the angular derivation are associated with the photovoltaic field. Such DPV solitons have a fixed deflection degree completely determined by the parameters of the dissipative system. The small bending cannot affect the formation of the DPV soliton via two-wave mixing.

Incoherently coupled screening photovoltaic spatial solitons in biased photovoltaic photorefractive crystals

Propagation characteristics and stability properties of two-component composite screening photovoltaic spatial solitons have been analyzed in this paper. Employing paraxial ray approximation, we have identified a very large family of new two-component composite screening photovoltaic solitons in photovoltaic–photorefractive crystals. These composite solitons can exist only when the carrier beams have the same polarization, wavelength and are mutually incoherent. We have identified a wide parameter space involving spatial width and power where these composite solitons can exist as a stationary entity. The identified regions of existence of solitons give a deeper understanding of these solitons and reveal some interesting properties. We have shown that composite solitons with different widths cannot propagate as a stationary entity. A relevant example has been provided where the crystal is LiNbO 3 or BaTiO 3. In addition, we have shown that in the new family of solitons, a degenerate pair with equal peak power possesses bistable property. Both paraxial theory and numerical simulation show that the identified family of composite solitons is stable.

Photovoltaic solitons in two-photon photorefractive materials under open-circuit conditions

We present the evolution equation of one-dimensional spatial soliton in two-photon photorefractive media under open-circuit conditions. In the steady state regime, our solutions show that the dark and bright photovoltaic spatial solitons can be supported in two-photon photorefractive media under open-circuit conditions.

One type of high order coupled photovoltaic spatial solitons

By numerical simulation we theoretically study one type of high order coupled photovoltaic spatial solitons that can be realized by using four parallel beams with two different frequency components in photovoltaic crystals whose light-induced refractive index perturbation is positive. The numerical results show that this kind of coupled soliton can be approached by hyperbolic secant beams undersome suitable conditions. The optical steering properties of such a high ordercoupled soliton are investigated. It is shown that such a coupled soliton cannot be realized when the incident beams remarkably deviated from the lateral symmetry.

Interactions between counter-propagating photovoltaic spatial solitons

We study the interactions between two counter-propagating photovoltaic spatial solitons with different frequencies. Numerical results show that these two solitons display different dynamic characteristics during spatial evolution, which also differ obviously from the case of co-propagation. These two solitons exhibit different induced focusing or defocusing behavior when they propagate coaxially, which is sensitive to the specimen length. When they propagate in parallel and closely overlapping, the induced focusing or defocusing effects are weakened and the soliton with higher frequency attracts the one with lower frequency markedly. And their evolutions are different from the case of co-propagation.

Self-deflection of dark and gray photovoltaic solitons

We use both the numerical method and the perturbation technique to investigate the self-deflection process of a dark photovoltaic spatial soliton in a photovoltaic photorefractive crystal with diffusion effect. It is found that the dark soliton does not propagate along a parabolic trajectory, and it becomes grayer during the propagation in the photorefractive crystal. In the normalized coordinate system(ξ,ζ), the dark soliton deflects to the direction of ξ>0, which is different from that of the bright soliton. Besides, the deflection of dark solitons can be controlled effectively by modulating the ratio of effective Glass coefficient r and the intensity of the signal beam. We also investigated numerically the self-deflection characteristic of gray solitons, which depend on the direction of its initial transverse velocity v. When v>0, gray soliton deflects to the direction of ξ>0 in the coordinate system(ξ,ζ); when vξξ>0 after propagating for a small distance.

Top- and side-view method for measuring photorefractive spatial optical solitons

Basing on CCD technology and software processing, a new method, namely top- and side-view method, is presented for the observation of spatial optical solitons in photorefractive crystals. When a laser beam is propagating in a crystal, this method has an ability to show the horizontal and vertical outline of the beam at any location of the crystal very intuitively. By use of this method, we have experimentally observed the two-dimension bright photovoltaic solitons in a KNSBN crystal, and the measured results are qualitatively in agreement with the results of numerical simulation.

Soliton-induced waveguides in photorefractive photovoltaic materials

Waveguides induced by one-dimensional spatial photovoltaic solitons are investigated in both self-defocusing-type and self-focusing-type photorefractive photovoltaic materials. The number of possible guided modes in a waveguide induced by a bright photovoltaic soliton is obtained using numerical techniques. This number of guided modes increases monotonically with increasing intensity ratio, which is the ratio between the peak intensity of the soliton and the sum of the background illumination and the dark irradiance. On the other hand, waveguides induced by dark photovoltaic solitons are always single mode for all intensity ratios, and the higher the intensity ratio, the more confined is the optical energy near the centre of the dark photovoltaic soliton. Relevant examples are provided where photorefractive photovoltaic materials are of self-defocusing and self-focusing types. The properties of soliton-induced waveguides in both self-defocusing-type and self-focusing-type materials are also discussed.

Waveguides Induced by Screening-Photovoltaic Solitons inBiased Photorefractive–Photovoltaic Crystals

We investigate theoretically waveguides induced byscreening-photovoltaic solitons in biased photorefractive–photovoltaiccrystals. We show that the number of guided modes in a waveguide inducedby a bright screening-photovoltaic soliton increases monotonically withthe increasing intensity ratio of the soliton, which is the ratiobetween the peak intensity of the soliton and the dark irradiance. Onthe other hand, waveguides induced by dark screening-photovoltaicsolitons are always single mode for all intensity ratios and theconfined energy near the centre of a dark screening-photovoltaic solitonincreases monotonically with the increasing intensity ratio. When thebulk photovoltaic effect is neglectable, these waveguides are thoseinduced by screening solitons. When the external field is absent, thesewaveguides predict those induced by photovoltaic solitons.

Experimental investigation of phase-dependent interactions of photovoltaic bright spatial solitons in photorefractive Fe:LiNbO3

Phase-dependent interactions of two photovoltaic bright spatial solitons in photorefractive Fe:LiNbO3 have been studied experimentally. We have observed that in-phase solitons attract each other and fuse together for a small enough crossing angle, whereas out-of-phase solitons repel each other. These results are similar to interactions of bright screening spatial solitons found in saturable photorefractive media such as strontium barium niobate.

Higher-order space-charge field effects on the self-deflection of photovoltaic dark spatial solitons

We investigate theoretically the effects of higher-order space-charge field on the self-deflection of photovoltaic dark spatial solitons by numerical method under steady-state conditions. The expression for an induced space-charge electric field, including higher-order space-charge field terms is obtained. Numerical results indicate that photovoltaic dark solitons possess self-deflection process during propagation, and the solitons always bend in the direction of the c-axis of the crystal. The self-deflection of dark solitons can experience considerable increase especially in the regime of high photovoltaic field strengths. Relevant examples are provided.