Referenceless phase holography for reconstruction of complete optical wave fields for metrology and displays II (RELPH II)

• Applicant: Professor Dr. Ralf Bernhard Bergmann
• Subject Area: Measurement Systems
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 250959575

Referenceless phase holography (RELPH) is a concept for displaying 3D scenes with arbitrary intensity and phase distributions. It is not only superior to other 3D display methods in showing horizontal, vertical, and motion parallax while exhibiting no accommodation-convergence conflict, but also is better than conventional holography in producing no dc-term and no twin images. The technique is based on the interference of two collimated waves which are phase modulated by two spatial light modulators (SLM) of liquid crystal on silicon (LCOS) type. Although today still no SLMs with a space-bandwidth-product high enough are offered on market, the foundations of this promising method for future 3D TV and 3D movies have to be developed now.In the first phase of the project existence and uniqueness of the underlying theory has been proven and the feasibility of the method was confirmed experimentally. Experiments displaying sample 3D scenes proved the 3D features depth of focus, object occlusion, and parallax. It has become obvious that RELPH requires an exact mutual adjustment of the two LCOS. Experiments with a sample object suggested a strategy for mutual rigid body adjustment of the LCOS. But a remaining spurious interference pattern superposed to the desired complex wave field has to be eliminated by measuring the deformations and adding correcting phase distributions to the phase distributions of both LCOS.In the next phase of the project, which is proposed here, this calibration has to be developed and implemented. The deformation of each LCOS has to be measured by an external interferometer. The results of these measurements can be checked against the results of phase-shifting measurements, which yield the difference of the two erroneous phase distributions. The employment of laser diodes will be investigated, their combination in spatially or temporally multiplexed color display also will be an issue. The digital holographic capture of the 3D scenes to be displayed will be analyzed with the objective to discover easy and fast procedures to calculate the RELPH-data out of the holographic data. The optical magnification of the RELPH-generated wave fields for better vision has to be improved with compensation of the different magnifications in lateral and in longitudinal direction already in the calculation process. Embedded into a performance assessment of the RELPH method the suppression of image degradations like speckles will be investigated and carried out.

• DFG Programme: Research Grants
• International Connection: Turkey, USA
• Cooperation Partners: Professor Dr. Levent Onural; Professor Dr. Wolfgang Osten; Professor Dr. Ting-Chung Poon