Liangying Xu

Nonvolatile photorefractive holograms in LiNbO 3 :Cu:Ce crystals

We report experimental and theoretical studies of nonvolatile photorefractive holographic recording in LiNbO(3):Cu:Ce crystals with two illumination schemes: (1) UV light for sensitization and a red interfering pattern for recording and (2) blue light for sensitization and a red pattern for recording. The results show that the oxidized LiNbO(3):Cu:Ce crystals can provide high, persistent refractive-index modulation with weak light-induced scattering. The optimal working conditions and the prescription for doping and oxidation-reduction processing that yields the maximum refractive-index modulation are discussed.

Experimental study of non-volatile holographic storage in doubly- and triply-doped lithium niobate crystals

Abstract Four kinds of lithium niobate crystals doped with Cu:Ce, Mn:Cu:Ce, Mn:Fe, and Mn:Fe:Mg processed under oxidation or reduction conditions were studied experimentally for the photorefractive non-volatile holographic storage with ultraviolet sensitizing and red light recording. It is shown that only highly oxidized crystals are able to realize non-volatile holographic storage. On the condition of non-volatile holographic storage with high signal-to-noise ratio, the non-volatile diffraction efficiency of the oxidized LiNbO 3 :Cu:Ce crystal is the highest among all studied samples, and the recording sensitivity and the dynamic range of the oxidized LiNbO 3 :Mn:Fe crystal are the highest.

Controllable real-time simple spatial filter based on selectively erasing in photorefractive two-beam coupling

Abstract Based on selectively erasing part of phase gratings of an image Fourier spectrum by an extra beam in photorefractive two-beam coupling in a SBN:Ce crystal, a new dynamic simple spatial filter is proposed, which has the advantages of both controllable operation and simple experimental arrangement. Computational simulation and experimental demonstration are made with an example of high pass filtering.

Accumulative recording of nonvolatile photorefractive holograms in LiNbO3:Fe:Mn crystals

Abstract A cyclic scheme of a recording period with a red interference pattern and an ultraviolet (UV) light and a following post-exposure period with an UV light is suggested to accumulate nonvolatile photorefractive holograms in LiNbO 3 :Fe:Mn with enhanced diffraction efficiency and suppressed scattering noise. Experimental results as well as an enhancement of diffraction efficiency up to 30% and a suppression of noise down to near zero are reported. Theoretical simulations and corresponding analyses on the optimization of working conditions are given, too. No additional equipment is needed in this method, and it is of potentials for applications.

Grating-encoded multichannel photorefractive incoherent-to-coherent optical conversion

A dynamic multichannel incoherent-to-coherent optical converter based on the photorefractive effect of SBN:Ce is described. A number of grating-encoded input images, illuminated by incoherent light, are projected onto the crystal to yield photoinduced phase gratings. Coherent positive replicas of these images are simultaneously reconstructed by a coherent read beam. A simple theoretical description of this converter and corresponding experimental results are presented.

Energy transfer in Sr0.56Ba0.44Nb2O6:Ce AT 633 nm

Abstract A steady-state solution for two-wave mixing equations in SBN:Ce is presented in which the absorption of light and the thermal generation of the carriers are taken into account. The energy transfer between the two writing beams in SBN:Ce are analyzed as a function of the following parameters: total incident intensity, incident beams ratio and spatial frequency. The experimental results show that an exponential gain coefficient Γ ≈ 22 cm -1 is reached for optimized writing conditions.

Single-block optical system using layer laser thermal fixed photorefractive holograms

Abstract A scheme using CO 2 laser beams to thermally fix layers of photorefractive holograms to implement a solid-state optical system in a single block of LiNbO 3 crystal is suggested. To limit the heating region with shape similar to the heating beam, two CO 2 laser beams of narrow width are used to laterally illuminate a layer of the crystal, and additional absorbers are attached to the crystal surfaces outside the heating region to guide the heating flows. Analytical discussions based on the heat-transfer equations are given. As a proof-of-principle example, a modified gamma network is adapted for demonstration, and a stage of such a network is constructed in a block of crystal. It can thus be seen that it is possible to package an optical system into a miniaturized single-block of photorefractive crystal.

Crystal substrate integration of free-space optical computing systems

This paper summarized our developments on the integration of miniaturized optical 3D systems using crystal substrates, which include a birefringence-customized stacking technique with the building blocks of double refraction and a photorefractive integration technique with the photorefractive local holograms thermally fixed by CO2 laser heating. The principles are introduced and the corresponding configurations are given, and the examples of various integrated digital optical computing systems such as logic processor, morphological image processor, and interconnection networks are shown.

Photorefractive single-block optical system using layered thermally fixed holograms

A scheme of using carbon-dioxide laser beams to thermally fix layers of photorefractive holograms to implement a solid-state optical system in a single block of LiNbO3 crystal is suggested. In this paper, a modified gamma network is adapted to demonstrate, and a stage of such a network is constructed in a block of crystal. To limit the heating region with the shape similar to the heating beam, two carbon-dioxide laser beams of narrow width are used to laterally illuminate a layer of crystal, and additional absorbers are attached on the crystal surfaces outside the heating region to guide the heating flows. Analytical discussion based on the heat- transfer equations and the proof-of-principle experimental result are given. It can be thus seen that it is possible to package an optical system into a miniaturized single-block of photorefractive crystal.