Patent ID: 12253687

DETAILED DESCRIPTION OF EMBODIMENTS

As discussed above, to reduce the surface area required by gratings, the optical functions of EPE and OC grating need to be combined.

In some embodiments, there are at least two grating regions on or in the waveguide, the regions comprising a first grating region provided with a first grating, the first grating region being positioned on a first location of the waveguide body, and a second grating region provided with a second grating, the second grating region being positioned on a second location of the waveguide body, different from the first location. The second grating is arranged to out-couple rays that have been spread, i.e. whose exit pupil has been expanded, by the first grating. On the other hand, the first grating out-couples rays whose exit pupil has been expended by the second grating.

FIG.2shows an example of such element without a dedicated out-coupling area. The waveguide21contains only the in-coupler21, and the EPE gratings23and24. The EPE grating24out-couples the rays turned by the EPE grating23and vice versa.

In a preferred configuration, the grating vectors of the in-coupler (G1) and EPEs (G2, G3) are chosen so that that their sum is a zero vector. This is illustrated inFIGS.3A and3Bfor 50×90 deg (H×V) field of view.

In some embodiments, like that shown inFIG.2, the first and second grating regions are arranged in non-overlapping manner on the same or different sides of the waveguide body.

In alternative embodiments, the first and second grating regions are arranged on different sides of the waveguide body so that they partially overlap each other in the main plane of the waveguide. This is beneficial for increasing the eyebox of the element.

Indeed, in the grating arrangement ofFIG.2, the FOV points with small kycomponent suffer from the small eyebox. The eyebox problem can be fixed by placing EPE gratings on different sides of the waveguide and expanding them laterally so that they overlap in the center region. This is illustrated inFIG.4, where the first waveguide surface41contains the in-coupler43and the EPE grating44. The second waveguide surface42contains the second EPE grating45.

The overlapping area can be e.g. 10-50% of the area of the first or second region, which are typically equally sized with respect to each other.

In all embodiments described above, the first and second gratings, as well as the in-coupling grating, can be linear, i.e. singly periodic, gratings, having a periodic diffractive pattern of parallel line structures.

FIG.5Aillustrates another grating arrangement where the waveguide surface51contains the in-coupler51, first and second EPE gratings53,55, and a doubly periodic (2D) third grating54. The grating54can be a hexagonal grating with 6 propagation directions as shown inFIG.5B.

More generally, in some embodiments the first and second grating regions are arranged at a distance from each other in the main plane of the waveguide, and there is provided a third grating region having a third grating between the first and second grating regions. The third grating is a doubly periodic grating, such as a hexagonal grating and can be positioned on the same side of the waveguide as the first and second grating regions.

In some applications, the exit pupil of rays having a small wave vector component in one dimension is expanded by an additional grating having a short period.

Thus, in further embodiments there is provided also a fourth grating region arranged on the opposite surface of the waveguide body, the fourth grating region comprising a fourth grating being configured to expand exit pupil of rays having a small wave vector component in one dimension. The fourth grating is typically a linear grating having a period smaller than the first and second gratings. In this case, there is also preferably provided doubly periodic in-coupling grating, such as a hexagonal grating, adapted to diffract light directed thereto from the outside of the waveguide body towards the first, second, third and fourth grating regions.

FIG.6shows this kind of enhanced version of the grating arrangement ofFIG.5A. The first surface61of the waveguide contains the 2D in-coupler63, first and second EPE gratings64,66, and a 2D third grating65. The second surface62of the waveguide contains the fourth grating, i.e. a short period grating67. The operation of the 2D in-coupler63and the short period grating67in the (kx, ky) space is shown inFIG.7. The short period grating expands the exit pupil of FOV points with small kycomponent.

The term short period grating herein means a grating having a period shorter than the period of the first and second gratings. Thus, the grating is able to perform the do carry out the required small wave vector component exit pupil expansion.

The embodiments described above are directly suitable for one-projector display configurations and can be used to achieve a decent 50×90 deg (H×V) FOV propagation through the element. However, similar principles can be used to double the horizontal FOV in double-projector arrangements.

In some exemplary embodiments to this effect the first grating region is provided on first side of the waveguide body, the first grating region comprising a doubly periodic first grating, and the second grating region is provided on the opposite, second side of the waveguide body, overlapping or fully aligned with the first grating region, the second grating region comprising a linear second grating. There is also provided two doubly periodic in-coupling gratings adapted to diffract light directed thereto from the outside of the waveguide body towards the first and second grating regions from different laterla sides thereof. The in-coupling gratings are configured to couple different field-of-view components to the waveguide body. The in-coupling gratings are typically positioned on different sides of the element in the direction of grating lines of the second grating.

FIG.8illustrates this kind of increased-FOV grating arrangement where the first surface81of the waveguide contains 2D in-couplers83,84and a single 2D EPE grating85. The 2D gratings can be, for example, hexagonal gratings. The second surface82of the waveguide contains a small period grating86. The FOV is split along the y-axis into two parts. FOV with negative kxcomponents are fed into IC83and FOV with positive kxcomponents are fed into IC84. This arrangement allows to propagate 100×90 deg FOV inside the waveguide.

In some embodiments, like shown inFIG.8, the in-coupling gratings are arranged non-aligned with each other in the direction perpendicular to the grating lines of the second grating. In some applications, it is desired achieve high FOV and simultaneously minimize so-called rainbow effects that the diffractive element produces in the presence of ambient light. To achieve this, in some embodiments the first grating region is provided on a first side of the waveguide body, the first grating region comprising a linear first grating, and there are provided one or more second gratings region on the opposite second side of the waveguide body, partially overlapping with the first grating region, the second grating region(s) comprising linear second grating(s) having grating vector(s) different from the first grating. In addition, there is provided two doubly periodic in-coupling gratings on the first side of the waveguide body and adapted to diffract light directed thereto from the outside of the waveguide body towards the first and second grating regions. In the non-overlapping region of the grating regions, there is only one linear grating present on one surface of the element, whereby rainbow effect is minimized.

The two in-coupling gratings are typically positioned on different sides of the first grating region in the direction perpendicular to the grating lines of the first grating, and symmetrically to the second grating regions. The second grating regions can overlap with the in-coupling grating to maximize efficiency.

In some embodiments, there are provided a plurality of second regions arranged so that a void, i.e. a region without grating, on the second side of the waveguide body remains aligned with the first grating region. The void produces minimal rainbow effect.

These embodiments, utilizing FOV splitting used inFIG.8with two 2D ICs are illustrated inFIG.9. The first surface91of the waveguide contains only 2D ICs93,94, and a linear grating95. The second surface92contains four EPE gratings96,97,98,99. The in-couples can be hexagonal gratings, for example. An advantage of this approach is that the center part of the waveguide is covered only by a vertical linear grating that is not very sensitive to produce disturbing rainbow patterns due to ambient lighting.

In an alternative embodiment, the grating95on the first surface is a doubly periodic grating instead of a linear grating.

The EPE gratings96,97,98,99can be positioned e.g. as shown inFIG.9, i.e. on four different sides of the void area. Also the grating lines can be oriented as shown, i.e. “towards” the void area.

More generally, in all embodiments described above, one of the first and second grating regions may comprise or define a void, i.e. a region without grating, on one side of the waveguide body, aligned with a linear grating provided on the opposite side of the waveguide body to minimize the rainbow effect.

A common preferable feature of all embodiments described above is that the in-coupling grating(s) couple light to at least two different grating regions having different grating configurations represented by their grating vectors so that their co-effect is exit pupil expansion and out-coupling simultaneously at each or several locations of the regions. As shown, the regions can locate laterally to each other on the same surface of the waveguide, e.g. abutting each other, or partially or entirely overlapping with each other on different surfaces of the waveguide. The gratings configurations may be singly or doubly periodic as long as they interact as described herein.

The waveguide body can be e.g. a high refractive index (≥1.7, such as ≥2.0) body of e.g. glass and having a planar or curved shape.

The present element can be used in a personal display device, such as near-to-eye glasses, other augmented reality displays, such as head-mounted displays, or head-up displays.

The invention s in no way limited to the examples described above but is to be interpreted in full scope of the claims.

CITATIONS LIST

Patent Literature

US 2016/0231568 A1