The design and the analysis of an off-axis (50°) diffractive imaging optical system is presented in this paper. A 10°x15° field of view is considered. The optical system is composed of two diffractive optical elements. A static diffractive optical element having a frozen phase transfer function is used to perform a virtual point in the considered field of view. A dynamic diffractive optical element having an adapted calculated phase transfer function is used to compensate for aberrations of the static element. Using a sequential creation of virtual image points and considering human eye characteristics, it is shown that a nine points virtual image can be obtained with current technology. Moreover, it is presented that aberrations can be compensated whatever the position of the virtual point in the 10°x15° field of view. Finally, using rigorous coupled wave analysis, it is shown that an average diffraction efficiency of 79% can be reached across the considered field of view with a standard deviation of nearly 5%.
A hybrid system that allows a high quality (low distortion) imaging in strong off axis configuration (50°) is proposed and analyzed in this paper. This imaging system is composed of a Bragg volume hologram (BVH) operating in catadioptric conditions and a programmable transmission computer generated holographic optical element (PCG-HOE). The BVH is used to produce a point by point virtual image in a sequential way by varying the angle of incidence of the reading wave. The PCG-HOE provides sequential aberrations correction adapted to each point to improve the image quality. A method to calculate the phase transfer function (PTF) to be implemented into the PCG-HOE to compensate for the aberrations of each virtual image points is presented. By applying the proposed approach we first demonstrate that the compensation of the aberrations is theoretically possible to a certain extent. In the last part of the paper, we discuss the constraining experimental conditions which have to be met, as well as obstacles to be overcome in order to achieve the fabrication of the BVH.
The object of this paper is to present the experimental validation of aberration compensation into a novel design for seethrough head-mounted displays. The proximity of the user's head generates high geometrical constraints. To compensate for the resulting aberrations, we use both dynamic sequential image creation and dynamic adapted aberration compensation. The see-through head-mounted display is composed of a holographic mirror serving as a combiner and a phase modulation spatial light modulator which insures the dynamic phase correction. The first step of the work has consisted in the realization of the holographic combiner and the characterization of the phase modulation by the light modulator. An experimental analysis of the aberrations of the image beam has been conducted. Next, the implementation of the theoretical corrective phase function into the spatial light modulator has been realized. Finally, the experimental demonstration of the expected aberration compensation has been achieved.
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