Chunfeng Hou

Incoherently coupled grey-grey screening-photovoltaic soliton pairs in biased photovoltaic-photorefractive crystals

Summary The incoherently coupled grey-grey screening-photovoltaic soliton pairs are predicted in biased photovoltaic-photorefractive crystals under steady-state conditions. These grey-grey screening-photovoltaic soliton pairs can be established provided that the incident beams have the same polarization, wavelength, and are mutually incoherent. Relevant example is presented where the photovoltaic-photorefractive crystal is of lithium niobate type. The grey-grey screening-photovoltaic soliton pairs can be considered as the united form of grey-grey screening soliton pairs and closed-circuit grey-grey photovoltaic soliton pairs. They reduce to grey-grey screening soliton pairs in the absence of photovoltaic effect, whereas they will become grey-grey photovoltaic pairs in the closed-circuit condition when the bias field is not applied.

Kinetics of the formation of space-charge field in photorefractive polymers

We derive a kinetic differential equation for the formation of space-charge field (SCF) in photorefractive polymers and give its general solution, which is based on Schildkraut’s work. It is found that SCF consists of two exponential decay waves and there are two decay factors corresponding to two response time constants of SCF. Changing the parameters in the solution, we can understand the formation of SCF for different cases. In this article, we discuss a case of no traps and find that both static and transient actions of SCF are determined by the grating wave vector k and total incident intensity Ii.

Spatial solitons in centrosymmetric photorefractive crystals due to the two-photon photorefractive effect

We present the evolution equation of one-dimensional spatial solitons in centrosymmetric photorefractive media due to the two-photon photorefractive effect. It is shown theoretically that both dark and bright spatial solitons can exist in two-photon centrosymmetric photorefractive media under steady-state conditions. Moreover, we also investigate the self-deflection of steady-state bright solitons arising from the diffusion effects.

Enhanced photorefractive properties of paraelectric potassium–lithium–tantalate–niobate by manganese doping

Paraelectric potassium–lithium–tantalate–niobate, or KLTN, crystals have been grown with two different Mn concentrations: 0.25 and 0.5 mol%. Detailed investigations have been made on the photorefractive (PR) properties of the as-grown crystals by the two-wave mixing technique. High diffraction efficiencies of 90% and 62.5% and PR sensitivities of 1.0 × 10−9E0 cm2 J−1 and 3.0 × 10−9E0 cm2 J−1 were achieved for 1.5 mm thick Mn0.25 : KLTN and Mn0.5 : KLTN, respectively. The measured two-wave mixing gains for 0.25 mol% and 0.5 mol% reached large values of 27 cm−1 at the external field of E0 = 3.4 kV cm−1 and of 25 cm−1 at E0 = 3.9 kV cm−1, respectively. The normalized PR response time under 1 W cm−2 illumination is less than 1 s at 532 nm. It is shown that Mn can effectively enhance the PR properties of KLTN which is a very promising ideal material for electroholographic applications.

Grey screening-photovoltaic spatial soliton in biased photovoltaic photorefractive crystals

Abstract Steady-state grey screening-photovoltaic spatial solitons are predicted for biased photovoltaic–photorefractive crystals when the diffraction of an optical beam is exactly compensated by nonlinear self-defocusing, due to the photovoltaic field and screening field set up in the photovoltaic–photorefractive crystal to which an external electric field is applied.

Incoherently coupled spatial soliton pairs due to both the linear and quadratic electro-optic effects

A number of new photorefractive materials, where refractive index changes in materials are simultaneously governed by both the linear and quadratic electro-optic effects, have been found in recent decades. Here we first present a comprehensively theoretical study of incoherently coupled spatial soliton pairs due to both the linear and quadratic electro-optic effects in all four possible realizations: dark–dark, bright–bright, gray–gray, and dark–bright. These soliton pairs owe their existence to the co-effects of both the linear and quadratic electro-optic effects where PR effect may be enhanced, weakened, or even counteracted because of the interaction of these two electro-optic effects. It is shown that these incoherently coupled spatial soliton pairs can be established provided that the incident beams have the same polarization, wavelength, and are mutually incoherent. At last, we give a simple elucidation on the stabilities of these incoherent coupled soliton pairs. Relevant examples are also provided.

Spatial solitons in biased photorefractive materials with both the linear and quadratic electro-optic effects

Unlike previous cases discussed, non-linear changes of refractive index in the photorefractive (PR) materials are governed by both the linear and quadratic electro-optic (EO) effects simultaneously now. Here, the evolution equations of one-dimension spatial solitons resulting from both the linear and quadratic EO effect are presented firstly. Under appropriate conditions, our analysis indicates that bright, dark, and gray solitons can exist in the steady-state regime. Moreover, stabilities of bright and dark soliton propagation are analyzed by means of beam propagation methods. The analytical solutions in the low-amplitude regime are also obtained. The self-deflection of such bright spatial solitons arising from diffusion effect in biased PR crystals involving both the linear and quadratic EO effects has been investigated symmetrically by the use of numerical techniques and perturbation methods.

Optical amplification in multilayer photorefractive liquid crystal films

Photorefractive two-beam coupling was performed in fullerene C60-doped nematic liquid crystal cell. Photorefractive gain coefficient as high as 1386cm−1 was obtained at an input pump power as weak as 16mW. However, the thin film nature led to a small gain of 16. By the use of several such cells stacked together to increase the overall interaction length, the optical gain was improved greatly, and the pump power to obtain the highest optical gain was reduced. At 1.2V, the highest gain of 141 was obtained for the 40μW signal at an input pump power of 12mW.

Optically controlled random lasing based on photothermal effect in dye-doped nematic liquid crystals

We presented a way to control the output of the nematic liquid crystal (NLC) random laser with a response time of hundreds of milliseconds by a continuous-wave laser beam with the power of several milliwatts. The lasing intensity can be tuned continuously by variation of the control power in the range from 0 to 5 mW or the lasing output can be switched on and off by turning off and on the control beam when the control power reaches 6 mW. The control power-dependent lasing polarisation and the self-phase modulation of the control beam indicate that the photothermal effect, which leads to the change of the order of the NLC and subsequently the change of the long-range fluctuation of the dielectric tensor, is mainly responsible for the controllability of the random lasing.

Incoherently coupled spatial soliton families in centrosymmetric two-photon photorefractive crystals

It is shown theoretically that incoherently coupled dark, bright and bright?dark hybrid soliton families can exist in centrosymmetric two-photon photorefractive crystals under steady-state conditions. These soliton families can be established provided that the incident optical beams share the same polarization and frequency, and are mutually incoherent.