Multiple Holographic Gratings Research Articles

Dynamics of peristrophic multiplexing in holographic polymer-dispersed liquid crystal

In this article, we derive a two-dimensional nonlocal diffusion model utilising finite difference time domain method, which describes the dynamics of how multiple holographic gratings are formed in a polymer-dispersed liquid crystal film for peristrophic multiplexing storage. This model takes into account the diffusion processes of both the free monomer and the liquid crystal molecules, and the polymerisation kinetics in the overlapped regions of multiple holographic gratings. We have experimentally found out that there exists a bounce in the diffraction efficiency for multiplexed gratings at relatively low-exposure intensities, which is undesirable for recording the equal-strength holograms. Instead, the equal-strength holograms can be stored under relatively high-exposure intensities. To predict the occurrence of bounce, the temporal evolutions of the refractive index modulation are estimated and then verified by the experimental results. The appropriate holographic exposure intensity for recording the equal-strength hologram is suggested.

Formation mechanisms of multiple holographic gratings in spirooxazine-doped polymer films

Multiple holographic gratings were stored in the same location of spirooxazine doped polymer films using peristrophic multiplexing techniques. Accompanied by UV irradiation, three sets of holographic gratings with different directions were recorded and readout by the He–Ne laser (632.8nm) and the Nd:YAG laser (532nm), respectively. Diffraction efficiency of each grating was controlled almost uniform by adjusting recording time. It was found that the growth rate of the holographic grating recorded later was lower than that of the earlier one, resulting from the weakened anisotropic distribution and the decreased population of photomerocyanine molecules. A kinetics description of isomerization gratings, competing with orientation gratings, agrees well with experimental results. Due to the thermal stability of the isomerization grating, multiple interference fringes in the photochromic film were reserved and observed by Confocal Laser Scanning Microscope.

Recording multiple holographic gratings in silver-doped photopolymer using peristrophic multiplexing

Plane-wave transmission gratings were stored in the same location of silverdoped photopolymer film using peristrophic multiplexing techniques. Constant and variable exposure scheduling methods were adopted for storing gratings in the film using He-Ne laser (632.8 nm). The role of recording geometry on the dynamic range of the material was studied by comparing the results obtained from both techniques. Peristrophic multiplexing with rotation of the film in a plane normal to the bisector of the incident beams resulted in better homogenization of diffraction efficiencies and larger M/# value.

Microwave spatial beam splitter/combiner using artificial microwave volume hologram technology

The artificial microwave volume hologram technique has been applied to design a new microwave spatial beam splitter/combiner. It uses the multiplexing concept and has multiple holographic gratings integrated into a single hologram slab. A prototype has been fabricated and measured to verify the design concept.

Imaging spectral device based on multiple volume holographic gratings

A spectral device based on multiple holographic gratings is proposed. Several volume holograms are superimposed into a common volume of photorefractive crystal Fe:LiNbO 3 using the wavelength and angular multiplexing method. This device is implemented by only one single wavelength laser using a two-lambda method. The imaging function of the device is realized with convergent recording beams. It can reduce the spectral system because the focusing lens is removed. Because the diffraction efficiency and the spectral resolution of the superimposed volume holographic gratings could be very high, the spectral device could achieve attracting characteristics of the diffraction efficiency and spectral resolution. Theoretical analysis and model design are presented and a discrete spectral device working at four wavelengths is demonstrated. The device has a uniform diffraction efficiency of 10% and the resolution of 1 to 2 nm. In addition, it has the advantages of wide spectral coverage, simple structure, and flexible design.