See-through head or helmet mounted display device

1. A see-through head or helmet mounted display device, comprising:

a see-through member defining a see-through area and having rear and front sides, the rear side facing a user's eye when the see-through head or helmet mounted display device is worn by a user and the front side facing away from the user's eye when the see-through head or helmet mounted display device is worn by the user;

a plurality of display segments arranged on the see-through member in the see-through area wherein the plurality of display segments is configured to emit either monochromatic visible light or polychromatic visible light but not both;

a plurality of holographic optical elements arranged on the see-through member in the see-through area, wherein each holographic optical element is arranged in front of a respective one of the plurality of display segments,

wherein each display segment is located in a focal plane of its associated holographic optical element and is adapted to emit visible light towards the associated holographic optical element,

wherein the plurality of display segments are arranged in a mutually spaced manner to define a see-through zone extending between each pair of adjacent display segments, the see-through zone allowing ambient light to pass therethrough,

wherein each holographic optical element is adapted to reflect visible light emitted by the associated display segment towards the rear side of the see-through member,

wherein, when the plurality of display segments emit monochromatic visible light, the plurality of display segments each include a plurality of mutually spaced monochromatic pixel units, each pixel unit defining a pixel of an image, and, when the plurality of display segments emit polychromatic visible light, the plurality of display segments each include a plurality of mutually space polychromatic pixel units, each pixel unit defining a pixel of an image and including a plurality of sub-pixel units each configured to emit visible light of a respective different color, and

wherein an interspace between adjacent display segments is larger than an interspace between adjacent pixel units of a display segment.

2. The see-through head or helmet mounted display device according to claim 1 , wherein each holographic optical element is adapted to reflect visible light within a reflection spectrum and transmit visible light within a transmission spectrum, wherein the reflection spectrum and the transmission spectrum are spectrally disjoint.

3. The see-through head or helmet mounted display device according to claim 2 ,

wherein the reflection spectrum is a wavelength band having a bandwidth of not more than about 30 nm.

4. The see-through head or helmet mounted display device according to claim 2 ,

wherein, when the plurality of display segments emits polychromatic visible light, the reflection spectrum includes a red wavelength band, a green wavelength band and a blue wavelength band, at least one of the red, green and blue wavelength bands having a bandwidth of not more than about 30 nm.

5. The see-through head or helmet mounted display device according to claim 2 , including a filter member arranged on the see-through member in front of each holographic optical element, wherein the filter member is designed as a band pass filter adapted to filter out visible light within the reflection spectrum and transmit visible light within the transmission spectrum.

6. The see-through head or helmet mounted display device according to claim 2 ,

wherein each display segment is adapted to emit light only within the reflection spectrum.

7. The see-through head or helmet mounted display device according to claim 1 , including a mask arranged on the see-through member at a rear side of each display segment, wherein the mask is made of a material that is opaque or reflective for the light emitted by the display segment.

8. The see-through head or helmet mounted display device according to claim 1 ,

wherein a holographic optical element associated with a center-located display segment among the plurality of display segments reflects a collimated beam of light having a first beam propagation direction towards the rear side of the see-through member and a holographic optical element associated with an off-centered display segment among the plurality of display segments reflects a collimated beam of light having a second beam propagation direction towards the rear side of the see-through member, wherein an angle between the first and second beam propagation directions increases as a distance of the off-centered from the center-located display segment increases.

9. The see-through head or helmet mounted display device according to claim 1 further comprising:

a frame;

an actuator adapted to tilt the plurality of display segments and the plurality of holographic optical elements relative to the frame;

an image capturing device adapted to capture an image of a pupil of a user's eye and generate a signal indicative of a position of the pupil; and

a controller adapted to control the actuator based on the signal.

10. The see-through head or helmet mounted display device according to claim 1 , further comprising:

a shifter adapted to shift the plurality of display segments relative to the plurality of holographic optical elements;

an image capturing device adapted to capture an image of a pupil of a user's eye and generate signal indicative of a position of the pupil; and

a controller adapted to control the shifter based on the signal.

11. The see-through head or helmet mounted display device according to claim 1 , comprising:

a beam expander arranged at a rear side of the plurality of display segments and adapted to expand visible light reflected from the holographic optical elements.

12. The see-through head or helmet mounted display device according to claim 1 , wherein the plurality of display segments are arranged on the see-through member in a two-dimensional distribution pattern.

13. The see-through head or helmet mounted display device according to claim 1 , wherein the plurality of display segments each include a plurality of four or more pixel units, wherein an interspace between adjacent display segments is larger than an interspace between adjacent pixel units of a display segment.

14. The see-through head or helmet mounted display device according to claim 1 , wherein the plurality of display segments each include a plurality of pixel units arranged in a row and column pattern, wherein an interspace between adjacent display segments is larger than an interspace between adjacent pixel units of a display segment.

15. The see-through head or helmet mounted display device according to claim 14 , wherein the number of pixel units is 2 n in each display segment, wherein n is an integer equal or larger than 2.

16. The see-through head or helmet mounted display device according to claim 1 , wherein when the plurality of display segments emit polychromatic visible light, the plurality of display segments each include a plurality of pixel units, each pixel unit including a plurality of sub-pixel units configured to emit light of different colors.

17. The see-through head or helmet mounted display device according to claim 1 , wherein each holographic optical element is effective as a parabolic mirror.

18. The see-through head or helmet mounted display device according to claim 1 , wherein the plurality of holographic optical elements are arranged in a mutually spaced manner, so that the see-through zone is also defined between each pair of adjacent holographic optical elements.