Highly efficient calculation method for computer-generated holographic stereogram using a lookup table

Acceleration of fully computed hologram stereogram using lookup table and wavefront recording plane methods

Lookup table (LUT) and wavefront recording plane (WRP) methods are proposed to accelerate the computation of fully computed hologram stereograms (HSs). In the LUT method, we precalculate large and complete spherical wave phases with varying depths, and each complex amplitude distribution segment of the object point can be obtained quickly by cropping a specific and small part of the precalculated spherical wave phases. Then, each hologram element (hogel) can be calculated by superposing all the related segments. In addition, setting a WRP near the 3D scene can further accelerate computation and reduce storage space. Because the proposed methods only replace the complex calculation using referencing LUT, they are accurate and have no limitation on the size of hogel compared with some methods of paraxial approximation. Simulations and optical experiments verify that the proposed methods can reconstruct quality 3D images with reduced computational load.

Fast calculation of high-definition depth-added computer-generated holographic stereogram by spectrum-domain look-up table [Invited]

High-definition depth-added computer-generated holographic stereogram (DA-CGHS) is superior in its high quality, easy realization, and auto-shading effect. However, its computing cost is extremely high because numerous scenes together with depth information must be calculated. Here, we proposed a fast calculation scheme of DA-CGHS by the spectrum-domain look-up table (SDLUT) method. In SDLUT, diffraction fields on the hogel plane of selected reference points in the object space are calculated. Subsequently, the fields are Fourier transformed to the spectrum domain. Because the signal energy always concentrates in a small spectrum region, these regions are cropped as the elemental tables. In the computing of the hogels, the field superposition is conducted in the spectrum domain by using the elemental tables. In our demonstration, the table size of SDLUT is only 0.44% that of the look-up table (LUT). Because the table size is very small, the computing time of SDLUT method can be nearly 80 times faster than that of conventional LUTs in the spatial domain, while the image quality is comparable.

DOE for the formation of the effect of switching between two images when an element is turned by 180 degrees

An optical security element forming different 2D images when it is turned by 180 degrees is developed and manufactured for the first time. A synthesis technology is developed that incorporates the computation of the beam pattern in elementary hogels with sizes smaller than 100 microns, computation of the phase function of the diffractive optical element (DOE), and formation of the microrelief of the DOE using electron-beam technology. The DOE employed is a multilevel kinoform with an asymmetrical microrelief shaped with a precision of 10 nm. The resulting security feature is easy to control visually, and the DOE is securely protected against counterfeiting. These DOEs are easy to replicate using standard technologies in the manufacturing of embossed holograms and can be used to protect bank notes, securities, and documents against counterfeiting.