Photorefractive screening solitons of high and low intensity

Segev, Mordechai; Shih, Ming-Feng; Valley, George C.

doi:10.1364/josab.13.000706

Cited by 230 publications

(131 citation statements)

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“…This dependence is unique to this type of soliton and as opposed to the dependence of V on u 0 for screening solitons that rely on the linear electro-optic effect [in that case Dj~pV and at high intensity ratios Dj~u 0 (Ref. 7)]. This result confirms that these solitons indeed rely on the quadratic electro-optic effect.…”

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confidence: 58%

One-dimensional steady-state photorefractive spatial solitons in centrosymmetric paraelectric potassium lithium tantalate niobate

et al. 1998

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We report the first observation of spatial one-dimensional photorefractive screening solitons in centrosymmetric media and compare the experimental results with recent theoretical predictions. We find good qualitative agreement with theory. © 1998 Optical Society of America OCIS codes: 190.5330, 230.6120. Photorefractive spatial solitons have been a subject of intense study over the past few years. They have been predicted and observed in the quasi-steady-state regime, 1,2 in photovoltaic materials, 3,4 in the screening configuration, 5 -9 and in photorefractive semiconductors. 10More-complicated phenomena have also been reported, giving rise to intriguing observations, such as self-trapping of incoherent light beams. 11All these phenomena have been observed in noncentrosymmetric materials, in which soliton formation is governed by a change in refractive index that is due to the linear electro-optic response to an internal photoinduced space-charge field. Recently, spatial screening solitons of a different nature that should exist in photorefractive centrosymmetric materials were predicted. 12 We report the f irst observation of such solitons and compare our experimental results with the theoretical predictions.Centrosymmetric screening solitons arise from the index change produced by the quadratic electro-optic response to a photoinduced internal f ield. The f ield has, in this case, the double role both of polarizing the crystalline structure and of distorting the electronic polarization. In centrosymmetric crystals the change in refractive index is proportional to the square of the polarization ͑1͞Dn͒ ij g ijkl P k P l and is expressed by Dn 2͑1͞2͒n b 3 g eff e 0 2 ͑e r 2 1͒ 2 E 2 , where E is the internal field, g eff is the effective quadratic electrooptic coeff icient, and n b is the background refractive index and it is assumed that the (dc) polarization is in the linear regime, i.e., P e 0 ͑e r 2 1͒E.Our experiments are performed in potassium lithium tantalate niobate 13 (KLTN), which is treated to have a first-order ferroelectric -paraelectric phase transition slightly below room temperature. Working at room temperature enables one to operate in a centrosymmetric phase close to that transition, thereby enhancing the electro-optic response, 13 making centrosymmetric soliton observation possible with moderate electric fields. In Fig. 1 we show e r as a function of temperature and observe the large increase of e r at the vicinity of the ferroelectric -paraelectric transition (which occurs at ϳ12 ± C). Because Dn scales with ͑e r 2 1͒ 2 , operation at temperatures slightly above the Curie temperature results in an increase of the quadratic electro-optic response. In the specif ic case of KLTN, g eff is positive and thus only bright solitons can be observed; i.e., in the screening regime KLTN is a self-focusing medium. 12Bright centrosymmetric screening solitons in ͑1 1 1͒ D obey the wave equationwhere u͑j͒ is the soliton amplitude normalized to the square root of the sum of background and dark irradianc...

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confidence: 58%

One-dimensional steady-state photorefractive spatial solitons in centrosymmetric paraelectric potassium lithium tantalate niobate

et al. 1998

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“…For these intensities, however, the excited free-carrier density is no longer smaller than that of the acceptors, and the space-charge f ield is due both to the free carrier and to the ionized donor contributions. 7 In this Letter we report what we believe to be the first experimental observation of high-intensity screening solitons, along with a comparison between experimental results and theoretical predictions. To work in the high-intensity regime, one must satisfy the requirement that 1͞r , , a͑u 0 2 1 1͒ ,, 1, where…”

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confidence: 81%

High-intensity nanosecond photorefractive spatial solitons

1998

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We report the observation of high-intensity solitons in a bulk strontium barium niobate crystal. The solitons are observed by use of 8-ns optical pulses with optical intensities greater than 100 MW͞cm 2 . Each soliton forms and attains its minimum width after roughly ten pulses and reaches e 21 of the steady-state width after the first pulse. We find good agreement between experimental observations and theoretical predictions for the soliton existence curve. 4,5 For the most part these demonstrations generally require high intensities in the megawatt range. Interestingly, although Kerr solitons form as a result of the presence of a refractive-index change that is proportional to the optical intensity, it is precisely this dependence that prevents the existence of stable two-dimensional (2D) bright Kerr solitons. Recently, a new type of spatial soliton 1 based on the photorefractive effect was predicted and observed both in a quasi-steadystate regime 2,3 and more recently in the steady-state regime. 4 -10 Compared with those of Kerr 11 -14 spatial solitons, the most distinctive features of photorefractive spatial solitons are that they are observed at low light intensities [in the milliwatts per square centimeter ͑mW͞cm 2 ͒ range] and that robust trapping occurs in both transverse dimensions. Both of these attributes make photorefractive solitons attractive for applications and for fundamental studies involving the interaction between spatial solitons. 15 -22 One transverse-dimension theory of photorefractive screening solitons 5 -7 predicts a universal relationship among the width of the soliton, the applied electric field, and the ratio of the soliton intensity to the sum of the equivalent dark irradiance and a uniform background intensity. We refer to this curve as the soliton existence curve. This curve is important because experiments show that considerable deviations (ϳ20% or more) from the curve lead to instability and breakup of the soliton beam, 10,22 whereas much smaller deviations are typically tolerated and are arrested by the soliton stability properties. In the case of a low-intensity photorefractive soliton beam, i.e., a beam with an intensity in the mW͞cm 2 to kW͞cm 2 range, recent 1D experiments have known good agreement with this universal relationship. 10,20Although the low-intensity feature of photorefractive spatial solitons is attractive for applications, high-intensity ͑MW͞cm 2 to GW͞cm 2 ͒ photorefractive solitons are also interesting, since the speed with which the steady-state screening soliton forms is inversely proportional to the optical intensity. As we show below, solitons in strontium barium niobate (SBN) can form at nanosecond speeds for GW͞cm 2 intensities, which implies that for photorefractive semiconductors, which have mobilities 100 -1000 times larger than those of the photorefractive oxides, soliton formation should occur at picosecond time scales for similar intensities. For these intensities, however, the excited free-carrier density is no longer smaller than that o...

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“…11 'Depth' meaning the variation of the refractive index in the guide/anti-guide with respect to the refractive index in the bulk crystal 12 Around I inv the beam profile is not Gaussian anymore. Unlike the previously mentioned beam breakup, in this case diameter measurements are still meaningful.…”

Section: Discussionmentioning

confidence: 99%

“…As such, their properties are well known in typical PR materials (such as SBN, Bi 12 TiO 20 and BaTiO 3 [5][6][7][8]), in which the PR effect is due mainly to only one type of charge carriers and occurs at visible wavelengths. The dynamics of self focusing and soliton formation have been studied and characterized at steady state [9][10][11][12] as well as in transient regime [13,14], together with its dependency on various parameters (temperature, background illumination) for two different iron dopings.…”

Section: Introductionmentioning

confidence: 99%

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

2011

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This paper reports an experimental study of the self-focusing process in iron doped indium phosphide at an 1.06 micron wavelength, identifying the influence of temperature, beam intensity and background illumination for two different iron dopings. We point out that the iron ionization ratio is at the origin of different qualitative behavior previously reported and we show that it is possible to reproduce the said behaviors in the same crystal by applying a uniform illumination, allowing their eventual control for dynamic wave-guiding.

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Photorefractive screening solitons of high and low intensity

Cited by 230 publications

References 24 publications

One-dimensional steady-state photorefractive spatial solitons in centrosymmetric paraelectric potassium lithium tantalate niobate

One-dimensional steady-state photorefractive spatial solitons in centrosymmetric paraelectric potassium lithium tantalate niobate

High-intensity nanosecond photorefractive spatial solitons

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

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