Projection unit comprising a volume hologram having a volume grating, and projection device having a projection unit
A projection unit images a multi-color image having a first and a second wavelength into an exit pupil such that an observer can perceive said image as a virtual image when an eye of the observer is positioned in the exit pupil and the observer views the projection unit at a predefined angle of observation. Each volume grating of the projection unit has a deflection efficiency curve dependent on the angle of observation with a maximal for the predefined angle of observation. The deflection efficiency curves are set equal for a predefined angle range around the predefined angle of observation by virtue of the fact that, for each of the volume gratings applied by exposure, the number of interference maxima applied by exposure is the same and the refractive index modulation for the corresponding wavelength, which refractive index modulation is applied by exposure, is the same.
1 . A projection unit which images a fed multicolored image having a first and a second wavelength into an exit pupil such that an observer can perceive said image as a virtual image when an eye of the observer is positioned in the exit pupil and the observer looks at the projection unit at a predetermined viewing angle, the projection unit comprising:
a volume hologram, which deflects the multicolored image into the exit pupil for imaging purposes,
wherein the volume hologram comprises a volume grating introduced by exposure for each wavelength of the color sub-images, the volume grating having a respective deflection efficiency profile which is dependent on the viewing angle and which is maximal for the predetermined viewing angle, and
wherein the deflection efficiency profiles for a predetermined angular range around the predetermined viewing angle are set to be equal by virtue of the fact that, for each of the volume gratings introduced by exposure, the number of interference maxima introduced by exposure is the same and refractive index modulation introduced by exposure for the corresponding wavelength is the same for the volume gratings introduced by exposure.
2 . The projection unit of claim 1 , wherein each volume grating is formed in a separate layer.
3 . The projection unit of claim 2 , wherein a thickness of the layers is chosen such that a ratio of the layer thicknesses corresponds to a ratio of wavelengths for which the volume gratings are designed.
4 . The projection unit of claim 1 , wherein the volume gratings are configured as reflective volume gratings.
5 . The projection unit of claim 1 , wherein the volume hologram is embedded in a transparent carrier.
6 . The projection unit of claim 1 , wherein the projection unit includes an image waveguide, into which the multicolored image is couplable for feeding purposes and is then guided via reflection as far as the volume hologram, which causes the deflection of the multicolored image and hence the output coupling from the image waveguide.
7 . The projection unit of claim 1 , wherein the fed multicolored image has a third wavelength, and the first wavelength lies in a blue wavelength range, the second wavelength lies in a green wavelength range, and the third wavelength lies in a red wavelength range.
8 . A projection device, comprising:
the projection unit of claim 1 ; and
an image module, which generates the multicolored image by generating a first color sub-image having a first wavelength and a second color sub-image having a second wavelength.