Dynamische Erzeugung von Lichtwellenfeldern mit Hilfe von Computer-Generierten Volumen-Hologrammen (DynaHolo)

• Applicant: Professor Dr. Ralf Bernhard Bergmann
• Subject Area: Measurement Systems
• Term: from 2011 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 190601146

• Final Report Year: 2015

Final Report Abstract

In the course of this project, a novel approach for the synthesis of dynamic wave fields using computer generated volume holograms (CGVH) was successfully demonstrated. Hereby, a hybrid system that consists of a CGVH as a static element and a spatial light modulator (SLM) as the dynamic element was developed. It was shown that this system facilitates cross-talk free synthesis of predefined wave fields with a much larger space-bandwidth product as compared to the current state of the art. The major findings and results of the project are: • Firstly, the design process and functionality of this SLM-CGVH hybrid system was modeled mathematically. Using optimization theory, a CGVH was designed for a set of predefined far-field projections and the resulting 3D refractive index distribution was studied by means of numerical simulations. Thereby, design constraints and parameters for this model were chosen to suit microfabrication of the CGVHs in nonlinear optical materials and the dynamic decoding by means of an SLM. These numerical experiments were used to predict the performance of the hybrid system in terms of diffraction efficiency. • In the next step, a method for fabricating CGVHs in the bulk of photosensitive glass ceramics by means of a nonlinear laser induced 3D modification of refractive index was developed. This essentially involved characterizing a direct laser writing lithographic process. Hereby, volume phase gratings were used as test holograms to assess the feasibility of modulating the materials refractive index locally with voxel sizes on the order of 1 µm. This preliminary studies paved way to the successful fabrication of functional CGVHs in photosensitive glass ceramics. • Finally, a concept for coupling a set of plane reference waves into the CGVH and thereby simultaneously decoupling a linear combination of the corresponding projections was developed. The experimental feasibility of this concept was then explored by realizing a demonstrational setup comprising essentially of a spatial light modulator, high precision positioning stages for the CGVH and an imaging unit. Using methods of signal and image processing, the proposed SLM-CGVH system was characterized experimentally in terms of signal fidelity, Bragg selectivity and diffraction efficiency.

Publications

• A new approach to dynamic wave field synthesis using computer generated volume holograms, in: 12th Workshop on Information Optics (WIO), IEEE, pp. 1-3 (2013)
  Kamau, E. N.; Falldorf, C.; and Bergmann, R. B.
  
• Fabrication of Multiplexed Computer Generated Volume Holograms in Photosensitive Glass, in: Frontiers in Optics. Optical Society of America, pp. FTh4G-2 (2014)
  Kamau, E. N.; Parsi Sreenivas, V. V.; Bülters, M.; Falldorf, C. and Bergmann, R. B.
  
• Three dimensional Modification of the Refractive Index in Photosensitive Foturan Glass, in: DGaO Proceedings 2014
  Bülters, M.; Kamau, E. N.; Sanchez-Alvarez, C.; Parsi Sreenivas, V. V.; Falldorf, C. and Bergmann, R. B.
  
• Dynamic wave field synthesis: enabling the generation of field distributions with a large space-bandwidth product. Optics Express, Vol. 23, No. 22
  Kamau, E. N.; Heine, J.; Falldorf, C. and Bergmann, R. B.