Patrice Twardowski

Conceiving a specific holographic combiner for an augmented reality HMD dedicated to surgical applications

In this paper, we present the conception of a holographic combiner for an augmented reality Head Mounted Display (HMD) dedicated to surgical applications. The recording of this holographic component has been performed at the Laboratoire des Systemes Photoniques (LSP) in Strasbourg, France. We present in this paper two different approaches for the recording of such a component: one using plane waves, and the other using spherical waves. The setup linked to the first approach has been developed and built, so that measurments of the diffraction efficiency can be shown. For the other way of recording the holographic combiner, we have performed numerical simulations to find the best recording setup to fit our specifications.

Design of an optimal single-reflective holographic helmet display element

A holographic optical element (HOE) can serve both as an imaging lens and a combiner for the helmet-mounted display. The resulting image is created by points whose geometrical conditions at readout will differ from those at recording, and then severe aberrations occur. Using the method of Hasman and Friesem, the authors design an optimal single reflective holographic helmet display element. This theoretical method is based on an analytic ray-tracing procedure that uses the minimization of the mean-squared difference of the propagation vector components between the actual output wavefronts and the desired output wavefronts. Considering the two-dimensional and monochromatic case, the authors obtain integral equations for the optimal grating vector components that they solve. As an illustration, the grating vector is calculated and the performance of a holographic helmet display with a 16 deg X 16 deg field of view is determined. Spot sizes and distortions at the image plane and the mean-squared difference of the propagation vectors are determined, and the results are compared with the performance of an HOE recorded with a spherical wave and a plane wave.

Design of some achromatic imaging hybrid diffractive-refractive lenses

The authors consider only hybrid singlet lenses composed of a plano-convex or a plano- concave glass lens and of a volume phase holographic optical element (HOE) in dichromated gelatin, coated on the plane surface of the glass lens. A design method is described which combines usual ray-tracing through a refractive lens and, for the HOE, the method of Hasman and Friesem. This latter method is based on a ray-tracing procedure that uses the minimization of the mean-square difference of the propagation vector components between the actual output wave fronts and the desired output wave fronts. Considering the one-dimensional case and a given spectral bandwidth, the authors determine by simulation the image spot sizes, the distortions at the image plane, and the mean-square difference of the propagation vectors. At the end, the results are compared with the performance of the optimal HOE alone, the spherical HOE, the refractive lens alone, and a diffractive system made of two HOEs. In conclusion, the authors discuss the space bandwidth product of the optimal HOE used in the hybrid systems.

Dynamic aberration correction for an optical see-through head-mounted display

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 users 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.

Phase-diffractive coating for daylight control on smart window

Daylight can be processed by a smart window in a transmission, reflective, refractive, and diffractive mode. In the future an optimization will be realized by a mixing of these approaches depending on the applied cases. Non-imaging diffractive optics has its roots in the work done in holographic diffractive coating for head up displays (HUD) and helmet mounted displays. For having globally good results on smart window with diffractive coating, a very high diffraction efficiency must be reached close to 100% without having a too important lowering of the control of other parameters of the light processed by a smart window (direction and frequency control essentially). We propose a method for designing, realizing, and using diffractive coating for a smart window that is based on a new organic material and diffractive model that were already validated in HUD. Potential low cost is possible for mass production on a large surface with an adapted investment. We describe the present technology and its limits and the ones that can be reached in the future. In this work, we present a holographic way to modify the slant of sun rays through a window, and to filter infrared radiations by using dichromated gelatin material. In this way it would be able to ensure a more uniform lighting and a more pleasant temperature inside buildings or vehicles, without using dye or photochromics glasses.