Diffractive waveguide element, personal display device and method of providing images thereon

Abstract

The invention relates to a diffractive waveguide element for a personal display device, a personal display device and a method of providing an image thereon, the element comprising a waveguide body (21) and at least two grating regions (23, 24) arranged on the waveguide body (21), at least some of the grating regions being adapted to expand the exit pupil of the element. According to the invention, the grating regions (23, 24) are positioned relative to each other and gratings with different grating vectors are arranged so that the grating regions (23, 24) interact to combine the functions of exit pupil expansion and outcoupling on at least some parts of the element. The invention allows efficient use of the waveguide area.

Description

Technical Field

[0001] The present invention relates to optical devices. In particular, the present invention relates to grating arrangements for diffractive waveguides used in personal display devices such as near eye displays (NEDs), head mounted displays (HMDs), and heads up displays (HUDs). More specifically, grating arrangements for large field of view waveguides with compact form factors are disclosed. Background Art

[0002] NEDs, HMDs, and HUDs typically include a projector and a combiner element. The projector produces a virtual image that is superimposed on the user's real-world view with the help of a combiner element. In NEDs and HMDs, the combiner element is typically translucent and located 1 to 3 cm from the eye. The combiner element can be a translucent mirror, or a more complex optical component such as a diffractive, holographic, or reflective light guide, or a free-form prism. Diffractive waveguides typically include in-coupling (IC), exit pupil expansion (EPE), and out-coupling (OC) gratings. In traditional designs, these grating regions are spatially separated. The size of the EPE and OC gratings increases with the size of the field of view (FOV) and the eyebox. This hinders the application of this approach in wearable NED devices with high FOV (>50 degrees).

[0003] To illustrate this problem, when the display design disclosed in US2016 / 0231568 A1 is applied to a 50 degree FOV NED display with an eye range of 15 mm × 10 mm (height × width) and an eye relief of 20 mm, Figure 1 The structure includes a waveguide 11, an IC 12, an EPE 13, and an OC 14. Due to the large FOV, the EPE 13 is larger than the outcoupling grating 14 both vertically and horizontally. The total size of the light guide is 77 mm × 52 mm (height × width), which is too large for a compact glasses-type NED.

[0004] Therefore, it is necessary to improve the diffraction display scheme. Summary of the invention

[0005] It is an object of the invention to provide a waveguide element whose area is used efficiently. A particular object is to provide a solution by which the ratio of the display area to the total area of ​​the waveguide can be increased.

[0006] In particular, it aims to provide a grating arrangement for a high field of view diffractive waveguide in a form factor compatible with wearable NEDs, in particular glasses form factor NEDs and other compact form factor devices.

[0007] One object is to provide a solution suitable for use with see-through or augmented reality devices.

[0008] The invention is based on the idea of ​​combining the functions of exit pupil expansion and outcoupling in a waveguide element. In practice, there are several ways to achieve this, using a suitable configuration of the grating region positions and the grating pattern therein.

[0009] Thus, according to one aspect, there is provided a diffractive waveguide element for a personal display device, comprising a waveguide body and at least two grating regions arranged on the waveguide body, at least some of the grating regions being adapted to expand an exit pupil of the element. According to the invention, the grating regions are positioned and provided with gratings such that the grating regions interact to combine the functions of exit pupil expansion and outcoupling at least in some positions of the element.

[0010] In general, the first and second grating regions may be positioned on the same side or different sides of the waveguide in a non-overlapping or overlapping position.Several exemplary configurations are discussed below.

[0011] According to another aspect, a personal display device is provided, comprising a waveguide element as disclosed herein and further having at least one incoupling region. Additionally, the device comprises at least one projector for directing an image on the incoupling grating, from which the image is diffracted into the waveguide and proceeds to the grating region, where, due to the first and second gratings, the exit pupil is expanded and the image is outcoupled.

[0012] According to yet another aspect, there is provided a method for providing an image on a personal see-through display device, the method comprising:

[0013] - Use the inner coupler as the propagating ray to couple the image into the waveguide body,

[0014] - allowing the exit pupil of a first portion of the incoupled propagating rays to expand in the waveguide by means of a first grating arranged on the waveguide, the expanded rays propagating from said waveguide to a second grating arranged on the waveguide and having a grating vector different from the first grating, in order to be outcoupled therefrom,

[0015] - an exit pupil of a second portion of the propagating rays allowed to be incoupled, different from the first portion, is expanded in the waveguide by the second grating, the expanded rays propagating from the second grating to the first grating in order to be outcoupled therefrom.

[0016] The present invention provides considerable benefits. The main benefit is that the footprint of the element is small compared to the effective outcoupling area of ​​the element. This allows display elements, for example the size of eyeglass lenses, to have large exit pupils and FOVs.

[0017] As illustrated by the embodiments described later, the present invention also allows a high FOV of 50×90 degrees (horizontal×vertical) with a single projector and an in-coupling region, and an extremely high FOV of 100×90 degrees (H×V) with two projectors and an in-coupling region to be propagated in a waveguide (where the refractive index of the waveguide is 2.0).

[0018] Next, selected embodiments of the present invention as advantages thereof are discussed with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A conventional diffractive waveguide of the prior art with exit pupil expansion is shown.

[0020] Figure 2 A grating arrangement without a dedicated out-coupling grating is shown.

[0021] Figure 3A and Figure 3B Shown for Figure 2 Wave vector diagram in the (kx, ky) plane of the grating arrangement.

[0022] Figure 4 A double-sided grating arrangement is shown.

[0023] Figure 5A Grating arrangements with 1D and 2D gratings are shown.

[0024] Figure 5B Possible diffraction orders produced by a hexagonal grating are shown.

[0025] Figure 6 A grating arrangement with a 2D inner coupler and a small-period extended grating on the second surface is shown.

[0026] Figure 7 Shown for Figure 6 The wave vector diagram in the (kx, ky) plane of the inner coupler and the wave vector of the small-period grating on the second surface.

[0027] Figure 8 Another embodiment of the present invention is shown.

[0028] Fig. 9 Still another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0029] As mentioned above, in order to reduce the surface area required for the grating, it is necessary to combine the optical functions of the EPE and OC gratings.

[0030] 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 at a first position of the waveguide body; and a second grating region provided with a second grating, the second grating region being positioned at a second position of the waveguide body, the second position being different from the first position. The second grating is arranged to outcouple rays that have been spread by the first grating, i.e. whose exit pupil has been expanded. On the other hand, the first grating outcouples rays whose exit pupil has been expanded by the second grating.

[0031] Figure 2 An example of such an element is shown without a dedicated outcoupling region. The waveguide 21 comprises only an inner coupler 21 and EPE gratings 23 and 24. The EPE grating 24 outcouples the rays rotated by the EPE grating 23, and the EPE grating 23 outcouples the rays rotated by the EPE grating 24.

[0032] In a preferred configuration, the inner coupler (G 1 ) and EPE(G 2 , G 3 ) are chosen so that their sum is the zero vector. Figure 3A and Figure 3B A field of view of 50×90 degrees (H×V) is illustrated in FIG.

[0033] In some embodiments, Figure 2 As shown, the first and second grating regions are arranged in a non-overlapping manner on the same or different sides of the waveguide body.

[0034] In an alternative embodiment, 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 advantageous for increasing the eye range of the element.

[0035] In fact, Figure 2 In the grating arrangement with small k y The FOV points of the components suffer from a small eye-range. The eye-range problem can be solved by placing EPE gratings on different sides of the waveguide and extending them laterally so that they overlap in the central area. Figure 4 4, wherein the first waveguide surface 41 comprises an inner coupler 43 and an EPE grating 44. The second waveguide surface 42 comprises a second EPE grating 45.

[0036] The overlapping area may be, for example, 10-50% of the area of ​​the first or second region, the two regions being generally equal in size to each other.

[0037] In all the above embodiments, the first and second gratings and the inner coupling grating may be linear gratings, ie single periodic gratings, which have a periodic diffraction pattern with a parallel line structure.

[0038] Figure 5A Another grating arrangement is illustrated, in which a waveguide surface 51 includes an inner coupler 52, first and second EPE gratings 53, 55, and a doubly periodic (2D) third grating 54. Figure 5B As shown, the grating 54 may be a hexagonal grating having six propagation directions.

[0039] 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 a third grating region having a third grating is provided between the first and second grating regions. The third grating is a double periodic grating, such as a hexagonal grating, and may be positioned on the same side of the waveguide as the first and second grating regions.

[0040] In some applications, the exit pupil for rays with small wave vector components in one dimension is expanded by an additional grating with a short period.

[0041] Therefore, in a further embodiment, a fourth grating region arranged on the opposite surface of the waveguide body is further provided, the fourth grating region comprising a fourth grating configured to expand the exit pupil of rays having a small wave vector component in one dimension. The fourth grating is typically a linear grating having a smaller period than the first and second gratings. In this case, preferably a dual periodic inner coupling grating, such as a hexagonal grating, is further provided, which is adapted to diffract light directed thereto from the outside of the waveguide body towards the first, second, third and fourth grating regions.

[0042] Figure 6 Show Figure 5A The first surface 61 of the waveguide comprises a 2D inner coupler 63, first and second EPE gratings 64, 66, and a 2D third grating 65. The second surface 62 of the waveguide comprises a fourth grating, namely a short period grating 67. Figure 7 The 2D inner coupler 63 and the short period grating 67 are shown in (k x , k y ) space. Short-period gratings extend the y The exit pupil of the FOV point of the component.

[0043] The term short-period grating herein refers to a grating whose period is shorter than the period of the first and second gratings. Thus, the grating is able to perform the desired successful implementation of the exit pupil expansion of the wavelet vector component.

[0044] The implementation described above is directly applicable to a one projector display configuration and can be used to achieve a suitable 50 x 90 degree (H x V) FOV spread through the elements. However, similar principles can be used to double the horizontal FOV in a dual projector arrangement.

[0045] In some exemplary embodiments to this effect, a first grating region is disposed on a first side of the waveguide body, the first grating region comprising a doubly periodic first grating, and a second grating region is disposed on an 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. Two doubly periodic in-coupling gratings are also provided, adapted to diffract light directed thereto from outside the waveguide body from different lateral sides thereof towards the first and second grating regions. 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 along the grating line direction of the second grating.

[0046] Figure 8 This grating arrangement for increasing the FOV is illustrated, where the first surface 81 of the waveguide comprises 2D inner couplers 83, 84 and a single 2D EPE grating 85. The 2D grating may be, for example, a hexagonal grating. The second surface 82 of the waveguide comprises a small period grating 86. The FOV is split into two parts along the y-axis. x The FOV of the component is fed into IC 83, and the x The component FOVs are fed into IC 84. This arrangement allows a 100 x 90 degree FOV to be propagated within the waveguide.

[0047] In some embodiments, Figure 8 As shown in , the inner coupling gratings are arranged to be misaligned with each other in a direction perpendicular to the grating lines of the second grating. In some applications, it is desirable to achieve a high FOV and at the same time minimize the so-called rainbow effect produced by the diffractive element in the presence of ambient light. To achieve this, in some embodiments, a first grating region is arranged on a first side of the waveguide body, the first grating region includes a linear first grating, and one or more second grating regions are arranged on the opposite second side of the waveguide body, which partially overlaps with the first grating region, and the second grating region includes a linear second grating, whose grating vector is different from the first grating. In addition, two double periodic inner coupling gratings are provided, and the above-mentioned two double periodic inner coupling gratings are on the first side of the waveguide body and are suitable for diffracting light guided thereto from the outside of the waveguide body towards the first and second grating regions. In the non-overlapping area of ​​the grating area, there is only one linear grating on one surface of the element, thereby minimizing the rainbow effect.

[0048] The two in-coupling gratings are typically positioned on different sides of the first grating region in a direction perpendicular to the grating lines of the first grating and symmetrical to the second grating region. The second grating region may overlap the in-coupling gratings to maximize efficiency.

[0049] In some embodiments, a plurality of second regions are provided, and the second regions are arranged so that a void region on the second side of the waveguide body, i.e. a region without a grating, remains aligned with the first grating region. The void region produces a minimal rainbow effect.

[0050] These implementations utilize Figure 8 FOV segmentation with two 2D ICs used in Fig. 9 93, 94 and a linear grating 95. The second surface 92 comprises four EPE gratings 96, 97, 98, 99. For example, the inner coupling can be a hexagonal grating. The advantage of this approach is that the central part of the waveguide is only covered by vertical linear gratings, which are not very sensitive to interfering rainbow patterns due to ambient lighting.

[0051] In an alternative embodiment, the grating 95 on the first surface is a doubly periodic grating rather than a linear grating.

[0052] The EPE gratings 96, 97, 98, 99 may be positioned as follows Fig. 9 As shown, ie on four different sides of the clear space area. The grating lines can also be oriented as shown, ie "towards" the clear space area.

[0053] More generally, in all of the above embodiments, one of the first and second grating regions may include or define a blank area on one side of the waveguide body, i.e., an area without gratings, which is aligned with a linear grating disposed on the opposite side of the waveguide body to minimize rainbow effects.

[0054] A preferred feature common to all the above embodiments is that the in-coupling grating couples light into at least two different grating regions having different grating configurations represented by their grating vectors such that their common effect is simultaneous exit pupil expansion and out-coupling at each or several positions of the region. As shown, these regions may be located laterally to each other on the same surface of the waveguide, e.g. adjacent to each other, or partially or fully overlapping each other on different surfaces of the waveguide. The grating configurations may be mono-periodic or bi-periodic, as long as they interact as described herein.

[0055] The waveguide body may be, for example, a high refractive index (≥1.7, such as ≥2.0) body, such as glass, and have a planar or curved shape.

[0056] The present elements may be used in personal display devices such as near-eye glasses, other augmented reality displays such as head-mounted displays or heads-up displays.

[0057] The invention is by no means limited to the examples described above but should be interpreted within the full scope of the claims.

[0058] Reference List

[0059] Patent Literature

[0060] US2016 / 0231568 A1.

Claims

1. A diffractive waveguide element for a personal display device, comprising: - waveguide body, - at least two grating regions arranged on the waveguide body, at least some of the grating regions being adapted to expand an exit pupil of the diffractive waveguide element, in, The grating regions are positioned relative to each other and gratings having different grating vectors are arranged so that the grating regions interact to combine the functions of exit pupil expansion and outcoupling over at least some portions of the diffractive waveguide element; Wherein, the grating region includes a first grating region and a second grating region, - the first grating region and the second grating region are arranged at a distance from each other in a main plane of the waveguide, a third grating region having a third grating is arranged between the first grating region and the second grating region, and - the third grating is a double periodic grating; And among them, - the first grating region, the second grating region and the third grating region are arranged on the same side of the waveguide body, A fourth grating region is arranged on an opposite surface of the waveguide body, the fourth grating region comprising a fourth grating configured to expand an exit pupil for rays having a small wave vector component in one dimension.

2. The diffractive waveguide element for a personal display device according to claim 1, wherein: - the first grating region is provided with a first grating, the first grating region being positioned at a first position of the waveguide body, - the second grating region is provided with a second grating, the second grating region being positioned at a second position of the waveguide body, the second position being different from the first position, Thereby, the second grating is arranged to couple out the rays rotated by the first grating and the first grating is arranged to couple out the rays rotated by the second grating.

3. A diffractive waveguide element for a personal display device according to any one of the preceding claims, wherein: The first grating region and the second grating region are arranged on the same side of the waveguide body in a non-overlapping manner.

4. The diffractive waveguide element for a personal display device according to claim 1 or 2, wherein: The first grating and the second grating are linear gratings.

5. The diffractive waveguide element for a personal display device according to claim 1 or 2, wherein: The third grating is a hexagonal grating.

6. The diffractive waveguide element for a personal display device according to claim 1, wherein: The fourth grating is a linear grating having a smaller period than the first grating and the second grating.

7. The diffractive waveguide element for a personal display device according to claim 6, comprising a double-periodic inner coupling grating, which is suitable for diffracting light guided thereto from the outside of the waveguide body toward the first grating region, the second grating region, the third grating region and the fourth grating region.

8. The diffractive waveguide element for a personal display device according to claim 7, wherein: The double-periodic inner coupling grating is a hexagonal grating.

9. A personal display device comprising - a diffractive waveguide element according to any one of the preceding claims, and - at least one projector for directing an image on an in-coupling grating, from which the image is diffracted into the waveguide and proceeds to the first and second grating regions, where the exit pupil is expanded and the image is out-coupled due to the first, second and fourth gratings.

10. A method of providing an image on a personal perspective display device, the personal perspective display device being the personal display device according to claim 9, the method comprising - Use the inner coupler as the propagating ray to couple the image into the waveguide body, - allowing an exit pupil of a first portion of the propagating rays coupled inwardly to expand in the waveguide by a first grating arranged on the waveguide, the expanded rays propagating from the first grating to a second grating arranged on the waveguide and having a grating vector different from the first grating, so as to be coupled outwardly therefrom, - an exit pupil of a second portion of the propagating rays that are allowed to be incoupled, different from the first portion, is expanded in the waveguide by means of a second grating, the expanded rays propagating from said second grating to said first grating in order to be outcoupled therefrom, and - allowing the exit pupil for rays having a small wave vector component in one dimension to be expanded by an additional grating having a shorter period than said first grating and said second grating.

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