Xu Ke-Bin

Incoherently coupled screening-photovoltaic soliton families in biased photovoltaic photorefractive crystals

It is shown that the existence of incoherently coupled screening-photovoltaic soliton families is possible in biased photovoltaic photorefractive crystals under steady-state conditions. These screening-photovoltaic soliton families can be established provided the multiple incident beams have the same polarization and wavelength and are mutually incoherent. Such soliton families reduce to screening-photovoltaic soliton pairs when they contain only two components. Relevant examples are presented where the photovoltaic photorefractive crystal is of the lithium niobate type.

Coherent Mutually Pumped Phase Conjugation Induced with High-Efficiency by Self-Pumped Phase Conjugate Reflection

A new scheme of coherent mutually pumped phase conjugate (MPPC) reflection that depends on the formation of self-pumped phase conjugate reflection of another beam has been demonstrated in a Cu:KNSBN crystal. The dependences of the MPPC reflectivity on the intensity ratio of the two incident beams and on the incident position of the signal beam were measured. We obtain phase conjugate reflectivities of greater than 90% at 488 nm.

Very High Photorefractive Gain in Two-Beam Coupling with Thin Iron-Doped LiNbO3 Crystal

The largest exponential gain coefficient (Γ = 250 cm-1), to our knowledge, is obtained in thin (d = 0.20 mm) iron-doped LiNbO3 crystal. The dependence of two-beam coupling coefficients on beam crossing angle are measured and compared in two samples fabricated from the same material with different values of thickness. The explanation based on light climbing effect is given.

THEORY OF PHOTOREFRACTIVE EFFECT FOR DOUBLE CARRIERS WITH TWO DEEP TRAPS AND A SHALLOW HOLE TRAP

We propose a new theoretical model of photorefractivity which consists of both electron and hole carriers with two deep traps and a shallow hole trap. The model predicts that, if the shallow trap accumulates a large density of charge carriers, the photoconductivity will be a sublinear (or superlinear) function of light intensity, and the space-charge field will increase (or decrease) to a saturated value as the light intensity increases, depending on the sign of the dominant carrier. The comparison of this model with previous ones shows that it provides a more common description about the dependences of photoconductivity and space-charge field on the light intensity.

Theoretical study on transmission of rapidly phase-modulated signal in photorefractive two-wave mixing

The transmission of rapidly phase modulated signal beams in photorefractive two-wave mixing is studied theoretically. The analytical expressions of output intensities are given both in diffusion regime and in drift regime.

Effect of light-induced scattering on diffraction efficiency in photorefractive crystals

The coupled wave equations and their analytic solutions in photorefractive crystals are presented for the case of two-beam writing, while the light-induced scattering is considered. Using this result, the diffraction efficiency for each writing beam is discussed in doped KNSBN crystals with unidirectional fan, which is explained theoretically and verified experimentally.

GROWTH AND PHOTOREFRACTIVE PROPERTIES OF KNSBN:Co CRYSTAL

Growth and photorefractive properties of KNSBN:Co crystal are reported for the the first time.Crystals were grown by CZ technique and the growth habits of them are severly affected by the amount of Co ions.New energy levels are formed in the energy band gap. Comparing to undoped KNSBN, KNSBN:Co has larger two-wave coupling coefficient, shorter response time and larger photo-induced free electron concentration in the experiment of two-wave coupling. Phase conjugation reflectivity of 56% and response time of 150ms were determined in the experiment of degenerate four-wave mixing.