High selectivity of surface-plasmon polaritons on wavelength can be used for reconstruction of color holograms illuminated with white light. In such a case, a combination of plasmonic filter and holographic microstructure is used. Compared to other techniques for creating holograms for white light reconstruction, such as rainbow holograms, the plasmonic approach offers full angle color reconstruction.

The plasmonic structure consists of a holographic grating recorded in a photo-resist material and a thin metallic layer on top of the grating. The parameters of both components are tuned to transmit only a selected spectral range when illuminated with white light. For RGB reconstruction three independent structures can be combined on a single substrate.

An excitation of plasmonic effects usually requires a relatively complicated setup containing prisms for in-coupling of optical waves. In this paper, a modification of the plasmonic hologram is proposed, which consists of two gratings recorded on opposite surfaces of a substrate. The first grating serves as an in-coupling element which also partially tunes the spectral transmittance of the structure. The second grating is metallized and out-couples the energy stored in the surface plasmon to a transmitted wave.

However, there is still a problem of diffraction efficiency of such transmission holographic structures. In order to optimize the transmittance and spectral selectivity, numerical simulations of light propagation through the plasmonic structure have been performed using MEEP software. The dependencies of transmitted light on various parameters of the diffraction gratings and metallic layer are discussed in detail.

Optical document security represents an important field of application of analogue and synthetic diffractive structures. Most of the security elements are based on visual effects formed by diffraction on a structure with the details in the order of hundreds of nanometers. However, to improve the anti-counterfeiting properties of these structures, various types of hidden features are included within the area of the security elements. They are not visible under normal lighting but it is possible to easily reveal the hidden information under specially-defined geometry and/or type of illumination.

In this paper, theory and application of a novel type of hidden diffractive security element are presented. It combines standard visual properties of synthetic holograms with waveguide effects. The hidden information is recorded using a special grating, which is not visible under normal observation geometry. The encoded image can be reconstructed only when the proper guided mode appears in a substrate. During the reconstruction, light is coupled into a waveguide (holographic foil) using a grating coupler and after traveling through the substrate in a chosen direction it is selectively out-coupled within the areas containing the hidden information. Several elements with different properties have been designed, fabricated and compared with theory. Principles of diffraction and waveguide effects, realization technology and properties of the realized test samples are presented.

The advantage of the combination of diffractive and waveguide effects is that the resulting hidden effect is sophisticated but easily readable with no additional tools.