阅读说明：本技术 衍射光栅 (Diffraction grating ) 是由 卡西米尔·布卢姆斯泰特 尤西·拉霍梅基 伊斯莫·瓦尔蒂艾宁 于 2019-02-25 设计创作，主要内容包括：本发明涉及一种选择性衍射光栅及其应用。该光栅包括成周期性交替图案的具有第一色散曲线(n<Sub>1</Sub>)的第一材料和具有与第一色散曲线(n<Sub>1</Sub>)不同的第二色散曲线(n<Sub>2</Sub>)的第二材料。根据本发明,第一色散曲线和第二色散曲线(n-i、n2)在两个或更多个不同波长(λ<Sub>1</Sub>、λ<Sub>2</Sub>)处彼此相交。(The invention relates to a selective diffraction grating and application thereof. The grating includes a first dispersion curve (n) in a periodically alternating pattern 1 ) And has a first dispersion curve (n) with respect to the first material 1 ) A second, different dispersion curve (n) 2 ) Of the second material of (1). According to the invention, the first and second dispersion curves (n-i, n2) are at two or more different wavelengths(λ 1 、λ 2 ) Where they intersect each other.)

1. A two-dimensional waveguide comprising a diffraction grating disposed on a surface or within the waveguide, the diffraction grating comprising a periodic alternating pattern;

-a first material having a first dispersion curve,

-a second material having a second dispersion curve different from the first dispersion curve, wherein,

-the first and second dispersion curves intersect each other at two or more different wavelengths.

2. The waveguide of claim 1, wherein the different wavelengths are in the wavelength range of 380nm to 750nm, separated by at least 50 nm.

3. The waveguide according to claim 1 or 2, wherein at least one of the materials is SiN_x。

4. The waveguide of any one of the preceding claims, wherein at least one of the materials is TiO₂、HfO₂Or ZrO₂。

5. A waveguide according to any one of the preceding claims, wherein the dispersion curves differ by at least 0.05 units, in particular by at least 0.1 units, at least at a certain wavelength in the range 380nm to 750 nm.

6. A waveguide according to any preceding claim, wherein the grating is arranged on a major surface of the waveguide.

7. A waveguide according to any one of the preceding claims, comprising a stack of such gratings having different intersecting wavelengths.

8. The waveguide of claim 7, wherein the intersection wavelengths of the stack of gratings are adapted such that each grating has one intersection wavelength that is the same as one intersection wavelength of each other grating of the stack.

9. A waveguide according to claim 7 or 8, wherein the stack of such gratings forms one, two or all of: an in-coupler of the waveguide, an exit pupil expander of the waveguide, an out-coupler of the waveguide.

10. A diffractive waveguide stack comprising at least two superposed waveguide layers, wherein at least one of the waveguide layers comprises a waveguide according to any one of the preceding claims.

11. A personal display device, the personal display device comprising:

-the waveguide according to any one of claims 1 to 9 or the waveguide stack according to claim 10 for use as a see-through display element,

a projector for projecting an image into the waveguide or waveguide stack at least partly through and by means of one or more of the gratings in the waveguide or waveguide stack,

wherein the projector is a multi-color projector adapted to emit light of at least three different wavelengths, two of which correspond to the different intersecting wavelengths of one or more of the gratings in the waveguide or waveguide stack.

12. The personal display device of claim 11, wherein the projector is a laser projector.

13. The personal display device of claim 11 or 12, comprising at least three such gratings arranged as: a stack of gratings on a single waveguide or a stack of gratings on different waveguide layers arranged as a stack, the intersecting wavelengths of the gratings being aligned with the wavelength emitted by the projector.

14. The personal display device of claim 13, wherein the grating is arranged as a stack of gratings with a period set so as to diffract the three different wavelengths achromatic into a single waveguide.

15. A method of manufacturing a two-dimensional waveguide comprising a selectively transparent diffraction grating, the method comprising

-selecting two or more different wavelengths,

-selecting a diffraction pattern configuration using at least two different materials,

-selecting at least two different materials having different dispersion curves, the different dispersion curves intersecting each other at the two or more different wavelengths,

-manufacturing the grating on a surface or within the waveguide using the diffractive pattern configuration and the different materials therein.

16. The method of claim 15, wherein the different dispersion curves are provided by:

-selecting a first material from a first group of materials,

-selecting a second material from the group consisting of,

-selecting the stoichiometric ratio of the first material and/or the second material such that the dispersion curves of the first material and/or the second material intersect at two or more different wavelengths,

-producing the material with the stoichiometric ratio into an alternating pattern of the different materials to form the grating.

Technical Field

The present invention relates to diffractive optics. In particular, the invention relates to gratings that can be used to couple light into waveguides used in diffractive display elements and devices. The present invention may be used for personal display devices such as Head Mounted Displays (HMDs) and head mounted displays (HUDs). Such displays typically include a waveguide and at least one grating disposed on or in the waveguide.

Background

In many modern personal display devices, waveguides are key imaging elements. Using a diffraction grating arranged in the main plane of the waveguide, typically on its surface, the image to be displayed can be coupled into and out of the waveguide, as well as modified within the waveguide. For example, an in-coupling grating for coupling an image from a projector into a waveguide, an exit pupil expansion grating for expanding a light field in one or more in-plane dimensions of the waveguide, and an out-coupling grating for coupling the light field out of the waveguide to an eye of a user may be provided.

The waveguides, each layer carrying a different wavelength, may be arranged in a stack to provide a multi-colour display. The purpose of the in-coupling and out-coupling arrangements of such a stack is to achieve complete wavelength separation between the layers. In practice, however, at least a part of the light intended for one layer is coupled into the other layer. For this reason, in example or other applications where good control of wavelength is required, improved solutions are needed.

Disclosure of Invention

It is an object of the present invention to provide a novel solution for improved control of wavelength, in particular in waveguide based display applications.

It is a particular object to provide novel solutions for improving color separation in-and/or out-coupling arrangements of multi-color waveguides, waveguide stacks and display devices.

Said object is achieved by the invention as defined in the independent claims.

In one aspect, the present disclosure provides a selective diffraction grating comprising a periodic alternating pattern of a first material having a first dispersion curve and a second material having a second dispersion curve different from the first dispersion curve. The first dispersion curve and the second dispersion curve intersect each other at two or more different wavelengths, thereby making the grating completely transparent at these wavelengths. These wavelengths may be referred to as intersecting wavelengths.

In one aspect, the present invention provides a waveguide comprising a grating of the above-described type. The grating may be, for example, an in-coupling grating or an out-coupling grating. In one embodiment, a stack of gratings is provided, each grating being adapted to be transparent to two of the wavelengths and "visible" to one of the wavelengths, respectively, using the principles disclosed herein.

In one aspect, the present invention provides a waveguide stack having a plurality of layers, wherein at least one layer is a waveguide of the type described above. Typically, each of the layers includes an in-coupling grating and/or an out-coupling grating aligned with each other. For example, placing the grating of the present invention on the topmost waveguide layer allows two wavelengths corresponding to the intersecting wavelengths to pass through the topmost layer without interacting with it, and couples the third wavelength in the topmost layer.

The method for manufacturing the selective transparent diffraction grating comprises the following steps:

-selecting two or more different wavelengths,

-selecting a diffraction pattern configuration using at least two different materials,

-selecting at least two different solid materials having different dispersion curves, the dispersion curves intersecting each other at the two or more different wavelengths,

-manufacturing a grating using the diffraction pattern configuration and the different solid materials therein.

The present invention provides significant benefits.

These two intersecting wavelengths fully control the colors in a three-color display waveguide element implemented with a single waveguide or with a stack of waveguides each layer intended to carry only one color. The intersecting wavelengths may be set such that only one of the used wavelengths interacts with the grating and modifies the optical field in the waveguide. The other two wavelengths pass continuously through the grating and waveguide without interaction.

In particular, under control that is currently totally wavelength independent, only one waveguide can be used and still achieve the same wavelength spacing of the three colors as three separate monochromatic waveguides.

The invention is particularly suitable for use with RGB laser image projectors having narrow wavelength bands.

The dependent claims relate to selected embodiments of the invention.

Embodiments of the present invention and their advantages are discussed in more detail below with reference to the accompanying drawings.

Drawings

FIG. 1 shows a cross-sectional view of a grating according to one embodiment.

Fig. 2 shows an exemplary graph of suitable dispersion curves for two different materials.

Figure 3 illustrates a waveguide stack utilizing the present invention according to one embodiment.

FIG. 4 illustrates a single layer waveguide utilizing the present invention according to one embodiment.

Detailed Description

Figure 1 shows a grating made of two layers of different materials. The first layer 11 has a first wavelength-dependent refractive index n₁And the second layer 12 has a second wavelength-dependent refractive index n₂. At the interface of the layers, the materials are interleaved (interlave) so as to form a periodic diffractive structure, i.e. a grating.

Refractive index n₁And n₂A dispersion curve is defined, saidThe dispersion curves are adapted to intersect at two or more different wavelengths for which the grating is non-diffractive, i.e. completely transparent. For other wavelengths, the grating is diffractive (i.e., diffracting into non-zero transmission or reflection orders, such as +/-1 order). Thus, a diffraction grating having two passbands is obtained.

An exemplary dispersion curve is shown in FIG. 2, which shows curves n for different materials₁And n₂. Here, the wavelength λ₁And λ₂Corresponding to the crossing wavelength, and at a wavelength λ₃Here, the refractive index is significantly different. Fig. 2 illustrates an advantageous case in which the dispersion curves have suitably different "curvatures" such that they intersect twice in the visible wavelength range.

In one example, at least one of these materials is silicon nitride, in particular amorphous hydrogenated silicon nitride (SiN)_x). The stoichiometric ratio x thereof may be adjusted to suit the present use. Similar effects may be achieved using other materials, some of which are discussed below.

In one example, at least one of these materials is titanium dioxide (TiO)₂) Hafnium oxide (HfO)₂) Or zirconium dioxide (ZrO)₂) Or the like or mixed oxides in various stoichiometric forms. They can be used together with one another in the appropriate stoichiometric ratios, and in particular with SiN_xTogether as a combined material for implementing the grating of the present invention.

In a particular example, the grating is formed from one of the following materials: SiN_x-TiO₂、SiN_x-HfO₂Or SiN_x-ZrO₂。

It is also possible that different materials have the same elemental composition, but the stoichiometry is adjusted so that the materials have different dispersion curves.

For example, in Charifi, H.H., Slaoui, A.A., Stoquert, J.P., Chaib, H.and Hannour, A. (2016) Opto-Structural Properties of Silicon Nitride Films Deposited by ECR-PECVD, World Journal of CondensedMSiN suitable for use in the present invention is discussed in atter Physics (journal of condensed State Physics in the world), 6,7-16(http:// dx. doi. org/10.4236/wjcmp.2016.61002)_xTuning of dispersion curves and SiN_xAnd (4) preparing the material.

Such as the Influence of Material Composition on structured Optical Properties of HfO in Mazur M. et al₂-TiO₂Mixed Oxide Coatings (material composition to HfO)₂-TiO₂Effects of the structure and optical properties of mixed oxide Coatings), Coatings 2016,6,13, on TiO, are discussed₂And HfO₂Tuning of the mixed oxide dispersion curve.

Charaterization of low temperature disposed atomic layer disposition TiO in Huang Y₂for MEMS applications (low temperature deposited atomic layer deposited TiO for MEMS applications₂Characterization of (d), j.vac.sci.technol.a, volume 31, phase 1, in 2013, month 1/2, discussing the use of TiO₂Tuning of the dispersion curve.

Investigation of Optical, electric, and mechanical Properties of MOCVD-grown ZrO at Dang V-S et al₂Films (MOCVD grown ZrO)₂Study of optical, electrical and mechanical properties of thin films), chem.vap.displacement 2014,20,320-₂Tuning of the dispersion curve.

In a typical example, the different wavelengths in the visible wavelength range are preferably spaced at least 50nm apart. This makes the grating and the waveguide containing the grating suitable for display applications.

Typically, the grating of the present invention is disposed on one or both of the major surfaces of the waveguide or within the waveguide.

The diffractive waveguide stack of the present invention comprises at least two overlying (supersuperpose) waveguide layers, wherein at least one of the waveguide layers comprises a waveguide as described herein. This means that the grating is optically connected to the waveguide such that the grating is capable of coupling light into the waveguide and/or otherwise interacting with the optical field of the waveguide, at least at other wavelengths than the wavelength at which the dispersion curves intersect.

Fig. 3 shows an exemplary stack comprising three waveguide layers 30A-C, on each of which a coupling-in grating 33A-C is arranged, respectively. The grating 33A of the topmost layer 30A is of the type discussed herein. It therefore allows a wavelength of λ₁And λ₂Passes unhindered through the layer 30A but at a wavelength λ₁Is coupled into layer 30A. The next layer 30B and the grating 33B are configured such that the wavelength λ is₁Passes through to layer 30C and couples wavelength 2 to layer 30B. Finally, the last grating 33C will have a wavelength λ₁Into the last layer 30C.

In some embodiments, the second grating and/or the third grating are also gratings according to the present invention, however with differently tuned transmission wavelengths for preventing coupling of light inversely passing through the upper layer into the lower layer.

Filters (not shown) may also be used between layers to prevent incompletely coupled light from coupling to the next layer.

Similar arrangements may be used in the exit coupler or exit pupil expander of the waveguide element, in addition to the in-coupler discussed in detail above.

Instead of using a waveguide stack and "physical monochromatization", color separation can be achieved using a single waveguide layer and "virtual monochromatization", as described below by way of example.

Fig. 4 shows an exemplary single waveguide 40 comprising an in-coupler 45 having three in-coupling gratings 43A-C, respectively, arranged thereon as a grating stack. According to the invention, the gratings 43A-C are suitably configured such that each grating corresponds to the three wavelengths λ used₁、λ₂、λ₃Are transparent and therefore only visible at the third wavelength, i.e. diffractive. The gratings 43A-C are all different from each other so as to couple all wavelengths to the waveguide 40. In this way a single physical waveguide 40 can guide all the wavelengths required to produce a multicoloured image, but in practice appears as three monochromatic waveguides, where the different wavelengths can be controlled separately.

This embodiment allows better control of the light inside a single waveguide than a grating designed to work for all wavelengths simultaneously.

The period of the grating can be chosen relatively freely, for example, so that the diffraction angle is the same for each wavelength used. Thus, the stack of gratings can be effectively achromatic.

In addition to the in-coupler 45 discussed in detail above, a similar grating stack may also be used as the Exit Pupil Expander (EPE)46 and/or the out-coupler 47. In this way, color control is maintained throughout the waveguide.

In one embodiment, the intersection wavelengths of the stack of gratings are adapted such that each grating has one intersection wavelength which is the same as one intersection wavelength of the other gratings of the stack.

The three wavelengths used are typically selected in the blue, green and red visible wavelength ranges.

The personal display device of the present invention includes a waveguide or waveguide stack of the type described above as the display element of the device. Furthermore, there is a projector for projecting an image into a waveguide or waveguide stack at least partly through a grating and by means of the grating. The projector is a multi-color projector adapted to emit light at least three different wavelengths, two of which correspond to different wavelengths: the grating is transparent to said different wavelengths. In the case of several gratings according to the invention, the intersecting wavelengths of the gratings may be suitably aligned with the three wavelengths of the projector (permate).

Preferably, the projector is a three-color laser projector. The intersecting wavelengths are set to correspond to two of the three colors, while at the wavelength of the third color, the refractive indices of the two different materials are sufficiently different to cause significant diffraction. At this wavelength, the ratio may differ by, for example, 0.05 units or more, particularly 0.1 units or more, to obtain better diffraction efficiency.

Although described herein in the context of in-coupling, gratings may also be used in out-coupling arrangements and exit pupil expander arrangements.

In some applications, it may be beneficial to use one or more biphase-crossed dispersion curve gratings disclosed herein with gratings having single-crossed dispersion curve gratings.

The grating may be a linear grating having periodicity in only one direction or a two-dimensional grating having periodicity in two dimensions.

It should be noted that the grating may be formed as a separate entity on or within the waveguide, or one of the grating materials may be integral with the waveguide. Further, although also shown as a binary grating in fig. 1, the grating features may take any desired profile, such as a flame-like profile. Gratings of the type of the present invention may be used as part of a larger diffractive optical element.

In one embodiment of the method of the present invention, the different dispersion curves are provided by:

-selecting a base composition of a first material,

-selecting a base composition of the second material,

selecting the stoichiometric ratio of the first material and/or the second material such that their dispersion curves intersect at two or more different wavelengths,

-selecting a production method that yields said stoichiometric ratio,

-producing said material into an alternating pattern of said different materials with said production method and stoichiometric ratio to form a grating.

CITATION LIST

Non-patent document

Charifi,H.,Slaoui,A.,Stoquert,J.P.,Chaib,H.and Hannour,A.(2016)Opto-Structural Properties of Silicon Nitride Thin Films Deposited by ECR-PECVD.World Journal of Condensed Matter Physics,6,7-16.

Mazur M.,et al,Influence of Material Composition on Structural andOptical Properties of HfO2-TiO2 Mixed Oxide Coatings,Coatings 2016,6,13

Huang Y.,et al,Characterization of low temperature deposited atomiclayer deposition TiO2 for MEMS applications,J.Vac.Sci.Technol.A,Vol.31,No.1,Jan/Feb 2013.

Dang V-S.et al,Investigation of Optical,Electrical,and MechanicalProperties of MOCVD-grown ZrO2 Films,Chem.Vap.Deposition 2014,20,320–327.