IMPROVED LIGHT GUIDE AND OPTICAL SYSTEM

Description

Technical field

[0001] The present invention relates to the general technical field of optical devices and / or systems used in virtual or augmented reality. The invention relates in particular to the medical field, the educational and cultural field, and the field of games. The invention finds its application in particular in navigation, security, transport or prototyping systems in industry.

[0002] The optical system according to the invention operates with any polychromatic or monochromatic light, in the visible range.

[0003] The present invention relates more particularly to an optical guide used in devices, accessories or other instruments having a display near the eye, also called NED (Near Eye Display), such as helmets or special glasses. State of the art

[0004] Known near-eye display devices, particularly those with light rays propagating in the open air, have significant drawbacks. In these devices, the mirrors used have large dimensions, thus contributing to increasing the size of said devices. The weight of these devices is also a drawback. Such devices are described in particular in documents US 2012 / 0212400 A1 or FR 2 941 786 A1.

[0005] Also known from document FR 2 983 976 is an optical guide with superimposed guide elements. The guide elements, of lamellar shape, are joined on one of their faces and separated by a semi-reflective coating over at least part of their length. Precise positioning of the semi-reflective coating makes the manufacture of such optical guides complex and expensive. In addition, the joined assembly of the two guide elements must be free of dimensional irregularities or air pockets to ensure the perfect operation of the optical guide. Document US 2014 / 140653 A1 discloses a near-eye display device with two optical guides.

[0006] It is also difficult to control the losses suffered by optical signals propagating through such optical guides.

[0007] Known optical systems, especially those with such optical guides, often provide a restricted field of view in at least one direction, typically a field of view of 26° (horizontal direction) x 20° (vertical direction). This is very often a major drawback in their areas of use.

[0008] We also know the document JP 2004 158336 , which describes an optical guide for providing a surface light source allowing a mixture of colors and brightnesses in particular to produce a high brightness source, but does not allow the optical fields to be preserved during the transmission of light. Statement of the invention

[0009] The object of the present invention therefore aims to overcome the drawbacks of the prior art and to provide a new optical guide making it possible to substantially widen the field of vision.

[0010] Another object of the present invention is to provide a new optical guide which is more compact and less heavy.

[0011] Another object of the present invention is to increase the dimensions of the "eyebox". The area called "eyebox" is by definition the area of ​​movement of the user's eye in which acceptable detection is guaranteed. The dimensions of this area, called "eyebox" vary according to the exemplary embodiments.

[0012] The objects assigned to the invention are achieved using an optical guide for a near-eye display device according to claim 1.

[0013] According to a preferred embodiment of the optical guide according to the invention, the spacing between the guide elements has a thickness e of between 0.1 mm and 0.2 mm.

[0014] According to an exemplary embodiment of the optical guide according to the invention, the first guide element has the entry zone at its first free longitudinal end, in the form of an inclined face.

[0015] According to an exemplary embodiment of the optical guide according to the invention, the output zone is provided with a light extraction system comprising at least one extraction mirror.

[0016] According to another preferred embodiment of the optical guide according to the invention, the output zone is provided with a light extraction system comprising a succession of several semi-reflecting extraction mirrors, constituting an extraction guide.

[0017] According to a preferred embodiment of the optical guide according to the invention, the second guide element has a thickness e2 linked to the thickness e1 of the first guide element with the relation: e2 = e1 x (tanβ / tanα), with α and β respectively the minimum and maximum incidences of the light beams injected into the first guide element.

[0018] According to a preferred embodiment of the optical guide according to the invention, the first guide element and the second guide element have a length of between 40 mm and 50 mm, the width of said guide elements being identical and between 35 mm and 45 mm.

[0019] According to an exemplary embodiment in accordance with the invention, the optical guide has a total thickness e3 of between 4 mm and 7 mm.

[0020] According to an exemplary embodiment of the optical guide according to the invention, the guide elements are made with the same constituent material, of the PMMA type.

[0021] According to the invention, the optical reflection member is a cylindrical mirror covering the cylindrical end surface of the portion.

[0022] The objects of the invention are also achieved using an optical system near-eye display including: an optical guide conforming to claim 1, and a light injection system for injecting light into said optical guide, characterized in that the injection system comprises a micro-display for providing point sources of light, said injection system making it possible to obtain in the guide parallel beams of light in a given direction y and converging in an xz plane orthogonal to said direction y.

[0023] According to an exemplary embodiment of the optical system according to the invention, the injection system comprises members optimized for focusing, in a zx plane, orthogonal to the yx plane, each beam of light on a curved focal surface, which is located substantially at the focal distance of the cylindrical mirror.

[0024] According to another exemplary embodiment, the light injection system comprises two lenses having three free-form optical surfaces and a plane mirror.

[0025] According to another exemplary embodiment, the light injection system comprises two free-form mirrors and a lens having at least one free-form optical surface as well as a spherical lens.

[0026] According to another exemplary embodiment, the light injection system comprises a single-piece free-form prism having four free-form optical surfaces, two of which work in transmission, while the other two work in reflection, and a lens having a free-form optical surface.

[0027] The objects assigned to the invention are also achieved by means of a near-eye display optical system comprising an optical guide described above and a light injection system, which comprises a micro-display for providing point sources of light, said injection system making it possible to obtain parallel beams of light in the guide, three aspherical lenses arranged to have six aspherical optical surfaces and a spherical lens.

[0028] According to an exemplary embodiment, the aspherical lenses, having a symmetry of revolution, are produced by at least one of them with a constituent material different from that of the other lenses.

[0029] According to another exemplary embodiment, the light injection system, which comprises a micro-display for providing point sources of light, said injection system making it possible to obtain in the guide, parallel beams of light and eight spherical lenses.

[0030] Spherical lenses, exhibiting rotational symmetry, are advantageously made of optical glass or a combination of optical glass and plastics / polymers.

[0031] In these last two embodiments, the optical system according to the invention has the advantage of operating with plane waves in the first and second guide elements. The light injection system can therefore have rotational symmetry. Furthermore, the injection of plane waves into the optical guide makes it possible to simplify the optical system and reduce its cost.

[0032] The optical system according to the invention is advantageously integrated into a virtual or augmented reality headset.

[0033] The optical guide device according to the invention also has the enormous advantage of being very compact and lightweight. For a compactness similar to that of a known optical guide, the field of vision is significantly increased.

[0034] A remarkable advantage of the optical guide according to the invention lies in obtaining an enlarged field of vision. Indeed, the maximum field of vision obtained, expressed in the air, is at least 20° and up to 45° in the horizontal direction, at least 40° and up to 60° in the vertical direction, thus substantially and unexpectedly increasing the field of vision, in particular in the vertical direction.

[0035] The optical system according to the invention also makes it possible to increase the movement area of ​​the user's eye and thus guarantee acceptable detection. This area, called "eyebox", varies according to the embodiments according to the invention from 15 mm (H: horizontally) x 4 mm (V: vertically), up to 15 mm (H) x 12 mm (V) using a light extraction guide. Brief description of the figures

[0036] Other characteristics and advantages of the invention will appear on reading the detailed description which follows, a description made with reference to the appended drawings given as illustrative and non-limiting examples, in which: there figure 1 is a schematic and general and simplified illustration of a family of known optical guides to which the invention relates, the Figures 1a and 1b schematically illustrate two examples of arrangement between an optical guide according to the invention and a light injection system, the Figure 2a represents an exemplary embodiment, according to a longitudinal view, of an exemplary embodiment of an optical guide in accordance with the invention, the Figure 2b is a representation according to a top view of the optical guide of the Figure 2a , there figure 3 is a representation according to a perspective view of the optical guide of the figure 2a or 2b , THE Figures 4a, 4b and 4cschematically illustrate examples of propagations of light beams in a first exemplary embodiment of an optical guide according to the invention, respectively along a plane yx, zx and zy, the Figures 5a, 5b and 5c schematically illustrate in a zx plane, examples of propagation of light beams in an optical guide according to the invention, from different point sources, the figure 6 , illustrates schematically, with an enlargement of the Figure 2a , the minimum and maximum angles of incidence of a light beam propagating in an optical guide according to the invention, the figures 7, 8 And 9 schematically illustrate three embodiments of an optical system according to the invention, each comprising an exemplary embodiment of a specific light injection system, the figure 10 is a partial representation of another exemplary embodiment of an optical guide which is not part of the invention, the figure 11 illustrates an enlarged detail of the figure 10 , THE figures 12 and 13 schematically illustrate two other embodiments of an optical system, each comprising another example of embodiment of a light injection system and an optical guide of the figure 10 , THE Figures 14a, 14b and 14c schematically illustrate in a zx plane, examples of propagation of light beams in an optical guide illustrated in figure 10 , and the figure 15 is an illustration of an enlargement of an example of a light extraction system or guide arranged in an optical guide according to the invention. Detailed description of the invention

[0037] There figure 1 illustrates very schematically the general principle of the family of optical guides within which an optical guide 1 in accordance with the invention is developed.

[0038] These systems therefore comprise an optical guide 1 transporting a beam of light towards an eye 2 of a user.

[0039] The optical system also comprises a light injection system 3, making it possible to inject beams 3a of light into the optical guide 1 via an input zone 1a.

[0040] The injection system 3 comprises a micro-display 4 on which are located point sources of light generating the light beams as well as collimation members 5 making it possible to inject several parallel beams 3a of light into the optical guide 1.

[0041] In the example embodiment illustrated in the Figure 1a , the input zone 1a is an inclined face of the optical guide 1. The injection of light by the injection system 3 is carried out by choosing an adequate angle for the inclination of this inclined face.

[0042] In the example embodiment illustrated in the Figure 1b, the injection system 3 is perpendicular to the longitudinal extension of the optical guide 1. The input coupling into the optical guide is obtained by means of a coupling mirror 1c constituted by an inclined and metallized face of the optical guide 1. For example, the inclination angles α1 and α2 are respectively 45° and 24° for a material of the PMMA type. The light beams injected into the optical guide 1 propagate by total internal reflection.

[0043] The efficiency of the optical coupling is identical for the two examples of realization of the Figures 1a and 1b Only space constraints will lead to the use of one or other of these technical solutions.

[0044] There Figure 2a represents an exemplary embodiment, according to a longitudinal profile view, of the optical guide 1 according to the invention. The Figure 2a is a representation in an xy plane of an xyz space and the Figure 2bis a representation according to a top view of said optical guide 1 in a zx plane.

[0045] The optical guide 1 comprises a first guide element 6 arranged above a second guide element 7. The guide elements 6 and 7 advantageously have a single-piece lamellar shape and their respective faces facing each other are not contiguous over a portion of their length. A spacing 9, of small thickness, between the guide elements 6 and 7 thus makes it possible to produce an interface with a thin layer of air.

[0046] The guide elements 6 and 7 are connected to each other over a complementary portion 1b of their length L by means of a continuity of material so as to constitute a single-piece or monobloc shape of the optical guide 1.

[0047] The optical guide 1 also has at one of its longitudinal ends an optical reflection member. The latter is a cylindrical mirror 10a.

[0048] The cylindrical mirror 10a thus achieves, with the complementary portion L, the optical coupling between the first guide element 6 and the second guide element 7. The light beams thus propagate first in the first guide element 6 before propagating in the second guide element 7 in an opposite direction. But in no case does a portion of the light rays propagate simultaneously in the two guide elements 6 and 7 and in the same direction of propagation. The light beams passing through the complementary portion 1b and being reflected on an internal face of the cylindrical mirror 10a therefore remain confined in the material constituting the guide elements 6 and 7 and do not pass through any interface or discontinuity of material.

[0049] The guide element 6 comprises at its longitudinal end opposite that comprising the cylindrical mirror 10, the entry zone 1a. The latter is for example produced by a simple inclined face extending orthogonally to the xy plane.

[0050] The guide element 7 also integrates into an extraction zone, comprising for example an extraction mirror 11. According to the embodiment example illustrated in Figure 2b , the extraction zone comprises a cascade of three semi-reflecting extraction mirrors 11, making it possible to direct the light beams towards the eye 2.

[0051] The spacing 9, extending to a limit corresponding to the internal edge 9a of the material continuity zone of the guide elements 6 and 7, advantageously has a thickness e sufficient to avoid direct optical coupling between said guide elements 6 and 7. The propagation of the light therefore takes place independently in each guide element 6 and 7. The thickness e of the spacing 9 is however sufficient to avoid penetration of reflected light beams into said spacing 9 and thus avoid signal losses.

[0052] The thickness e must therefore be as small as possible while avoiding the appearance of optical coupling between the guide elements 6 and 7. The thickness is advantageously between 0.1 mm and 0.2 mm.

[0053] This end of the optical guide 1 illustrated for example in the Figure 2b, shows the arrangement of the cylindrical mirror 10a, with its internal face in contact with the common longitudinal end of the guide elements 6 and 7.

[0054] There figure 3 is a perspective representation of the optical guide of the figure 2a or 2b .

[0055] The guide elements 6 and 7 advantageously have a lamellar shape, of substantially the same length and width.

[0056] According to a preferred embodiment, the thickness e2 of the second guide element 7 is substantially equal to twice the thickness e1 of the first guide element 6.

[0057] THE Figures 4a, 4b and 4c schematically illustrate examples of propagation of light beams in the optical guide 1 according to the invention, respectively along a plane yx, zx and zy.

[0058] THE Figures 5a, 5b and 5cschematically illustrate in a zx plane, examples of propagation of light beams in the optical guide 1 according to the invention, from different point sources located on the micro-display 4 associated with an inclined plane mirror 4a. The Figure 5a illustrates a beam of light extending substantially along the central x-axis. The Figure 5b illustrates a beam of light extending in an intermediate direction and the Figure 5c illustrates a beam of light extending in one extreme direction.

[0059] The optical guide 1 is advantageously integrated into an optical display system close to the eye, such as a headset or virtual or augmented reality glasses.

[0060] Such an optical system for near-eye display according to the invention comprises, in addition to the optical guide 1 described above, the light injection system 3 for injecting light into said optical guide 1. The injection system 3 comprises the micro-display 4 for providing point sources. The injection system 3 makes it possible to obtain parallel light beams in the guide 1 along a given direction y and converging in the zx plane.

[0061] The injection system 3 comprises for this purpose optimized members, in particular of the lens type, to focus, in the zx plane, orthogonal to the yx plane, each beam of light on a curved focal surface, approximately spherical. This focal surface is located at the focal distance of the cylindrical mirror 10 for the central light beam or close to this focal distance for the other beams.

[0062] The optimization is achieved, for example, by arranging lenses and machining special shapes such as free-form optical surfaces. This ensures that the light beams emerging from the guide element 7 are completely parallel in the form of plane waves.

[0063] The z axis therefore corresponds to the vertical direction in which the field of vision is substantially enlarged in accordance with the invention.

[0064] There figure 6 illustrates schematically, with an enlargement of the Figure 2a, the minimum α and maximum β angles of incidence of a light beam propagating in an optical guide 1 according to the invention. Thus, it is possible to determine the length L of the common end portion 1b of the guide elements 6 and 7, in particular as a function of the thicknesses e1 and e2 respectively of the guide elements 6 and 7. It is thus possible to calculate the minimum values ​​of the length L, as well as of the thickness e2 of the second guide element 7, starting from a thickness e1 of the first guide element 6.

[0065] The calculation elements given below assume that the material constituting the guide elements 6 and 7 and consequently the optical guide assembly 1 except for the cylindrical mirror 10a, is the same. For a given material, the value of the length L of the portion extending between the internal edge 9a and the mirror 10 is given by: L = e 1 / tanα

[0066] The value of the length L therefore depends on the minimum angle of incidence α. We also use the relationship: e 2 = L × tanβ

[0067] This condition determines the thickness e2 of the second guide element 7 as a function of the length L and the maximum angle of incidence β. It therefore follows that: e 2 = tanβ / tanα × e 1

[0068] We thus obtain the thickness e2 of the second guide element 7 as a function of the thickness e1 of the first guide element 6.

[0069] Thus, for example, with e1 = 1.5 mm, a minimum angle of incidence α equal to 28° and an angle of incidence β equal to 48°, we obtain a thickness of the second guide element 7 of e2 = 2.08 x e1, therefore approximately 3 mm, and the length L equal to 2.82 mm, for example for the PMMA material.

[0070] According to an exemplary embodiment of the optical guide 1 according to the invention, the first guide element 6 and the second guide element 7 have a length of between 40 mm and 50 mm, the width of said guide elements 6 and 7 being identical and between 35 mm and 45 mm. These dimensions are, for example, particularly suitable for integration into glasses.

[0071] According to a preferred embodiment in accordance with the invention, the optical guide has a thickness e3 of between 4 mm and 7 mm.

[0072] There figure 7 schematically illustrates an embodiment of an optical system in which the light injection system 3 comprises two lenses 5a, 5b. The latter advantageously have three free-form optical surfaces S1, S2, S3 associated with an inclined plane mirror 4a.

[0073] There figure 8schematically illustrates an embodiment of an optical system in which the light injection system 3 comprises a free-form prism 3b in one piece. The free-form prism 3b has on the one hand four free-form optical surfaces S5, S6, S7, S8, two of which S5, S8 work in transmission, while the other two S7, S6 work in reflection and on the other hand, a lens 5c having a free-form optical surface S4.

[0074] In an example of realization illustrated in the figure 9 , the light injection system 3 comprises two free-form mirrors S9 and S10 and a lens 5d having a free-form optical surface as well as a spherical lens 5e. The latter has one or two spherical faces. Advantageously, the spherical lens 5e has a flat face making it easier to position it relative to the optical guide 1.

[0075] 5d and 5e lenses are made of different materials. One material is, for example, optical glass, and the other material is, for example, a plastic or polymer. This results in two free-form surfaces that function in reflection, at least one free-form surface that functions in transmission, and one spherical surface that functions in transmission.

[0076] In an exemplary embodiment according to the invention, the lens 5d has a free-form surface and a spherical face which is joined to the spherical face of the spherical lens 5e. The latter then has a second flat face.

[0077] In another embodiment according to the invention, the lenses 5d and 5e are not contiguous. The lens 5d then has free-form faces and the spherical lens 5e has a spherical face and a flat face.

[0078] There figure 10is a partial representation of another exemplary embodiment of an optical guide 1, used in an optical system which is not part of the invention. This optical system comprises a light injection system 3 in which

[0079] the cylindrical mirror 10a is replaced by sawtooth-shaped micro-reflectors 10b. The latter, illustrated in more detail in figure 11 , advantageously have a height h of between 0.2 mm and 1 mm and are distributed according to a cylindrical arrangement with a radius of 42.8 mm. Two consecutive faces forming such a sawtooth advantageously have a mutual angle of between 89.8° and 90.2° and preferably equal to 90°.

[0080] The optical reflection optical member is therefore made up of micro-reflectors 10b arranged in a cylindrical profile at the free end of the portion 1b. The sawtooth-shaped micro-reflectors 10b are advantageously metallized and produced in the cylindrical free end of the portion 1b, either by molding or by machining.

[0081] With this configuration of the optical reflection organ shown schematically in Figures 10 and 11 , the optical system comprises a light injection system 3 shown for example in figure 12 ou 13 .

[0082] In the example embodiment illustrated in the figure 12 , the light injection system 3, which comprises the micro-display 4 for providing point sources of light, also comprises three aspherical lenses 5f, 5g, 5i, arranged to have six aspherical optical surfaces and a spherical lens 5h which has at least one spherical surface.

[0083] The 5f, 5g, 5i aspherical lenses and the 5h spherical lens have rotational symmetry and at least one of them is made with a different constituent material than the others.

[0084] In the example embodiment illustrated in the figure 13 , the light injection system 3, which includes the micro-display 4 for providing point sources of light, also includes eight spherical lenses 5j, 5k, 5l, 5m, 5n, 5o, 5p, 5q.

[0085] The spherical lenses 5j, 5k, 5l, 5m, 5n, 5o, 5p, 5q, therefore have a symmetry of revolution, are made of optical glasses or a combination of optical glasses and plastics / polymers so as to produce an assembly of which at least one lens is made with a constituent material different from that of the other lenses.

[0086] THE figures 14a, 14b et 14c schematically illustrate in a zx plane, examples of propagation of light beams in the form of plane waves in an optical guide 1 illustrated in particular in figures 10 , 12 et 13

[0087] There figure 15 is an illustration of an enlargement of a light extraction system or guide arranged in an optical guide 1 according to the invention. The extraction guide is advantageously made up of a succession of semi-reflecting mirrors 11.

[0088] Obviously, the invention is not limited to the preferred embodiments described above and shown in the various figures, and those skilled in the art can make numerous modifications and imagine other variants without departing from the scope or framework of the invention defined by the claims.

Claims

1. An optical guide (1) for a near-eye display device comprising: - a first guide element (6) having an inlet zone to inject a beam of light therein, - a second guide element (7) having an outlet zone to extract the beam of light therefrom, the first guide element (6) being superimposed on said second guide element (7), and - an optical coupling system between the first guide element (6) and the second guide element (7), - the first and second guide elements (6, 7) having, over a first part of their length, a mutual spacing (9) so as to delimit a thin layer of air between said guide elements (6, 7) extending between a first longitudinal end of the guide elements (6, 7) and the optical coupling system being of sufficient thickness to prevent the reflected beams of light to enter into said spacing, characterised in that: - the optical coupling system, located at a second longitudinal end of the first and second guide elements (6, 7), comprises a one-piece portion (1b) of said guide elements (6, 7), associated with an optical reflection element (10) for propagating the beams of light from the inlet zone to the outlet zone, the optical reflection element (10) being a cylindrical mirror (10a) covering the cylindrical end surface of the portion (1b).

2. The optical guide (1) according to claim 1, characterised in that the thickness e of the spacing (9) between the guide elements (6, 7) is of between 0.1 mm and 0.2 mm.

3. The optical guide (1) according to claim 1 or 2, characterised in that the first guide element (6) has the inlet zone at its first free longitudinal end, as an inclined face (1a).

4. The optical guide (1) according to any one of claims 1 to 3, characterised in that the outlet zone is provided with a light extraction system comprising at least one extraction mirror (11).

5. The optical guide (1) according to any one of claims 1 to 4, characterised in that the outlet zone is provided with a light extraction system comprising a succession of several semi-reflective extraction mirrors (11), constituting an extraction guide.

6. The optical guide (1) according to any one of claims 1 to 5, characterised in that the second guide element (7) has a thickness e2 related to the thickness e1 of the first guide element (6) with the relation: e2 = e1 x (tanβ / tanα), with α and β respectively the minimum and maximum incidences of the beams of light injected into the first guide element (6).

7. The optical guide (1) according to any one of claims 1 to 6, characterised in that the first guide element (6) and the second guide element (7) have a length of between 40 mm and 50 mm, the width of said guide elements (6, 7) being identical and of between 35 mm and 45 mm.

8. The optical guide (1) according to any one of claims 1 to 7, characterised in that it has a thickness e3 of between 4 mm and 7 mm.

9. An optical guide (1) according to any one of claims 1 to 8, characterised in that the guide elements (6, 7) are made of the same constituent material, of the PMMA type.

10. An optical near-eye display system comprising: - an optical guide (1) according to claim 1, and - a light injection system (3) for injecting light into said optical guide (1), the injection system (3) comprising a micro-display (4) for providing point light sources, said injection system (3) making it possible to obtain, in the guide (1), beams of light that are parallel along a given direction y and convergent in a plane xz orthogonal to said direction y.

11. The near-eye optical display system according to claim 10, characterised in that the injection system (3) comprises members optimised for focusing, in a plane zx, orthogonal to the plane yx, each beam of light on a curved focal surface, which is located substantially at the focal distance of the cylindrical mirror (10a).

12. The optical system according to claim 11, characterised in that the light injection system (3) comprises two lenses (5a, 5b) having three free-form optical surfaces (S1, S2, S3) and a planar mirror (4a).

13. The optical system according to claim 11, characterised in that the light injection system (3) comprises two free-form mirrors (S9, S10) and a lens (5d) having at least one free-form optical surface as well as a spherical lens (5e).

14. The optical system according to claim 11, characterised in that the light injection system (3) comprises a one-piece free-form prism (3b) having four free-form optical surfaces (S5, S6, S7, S8), two of which (S5, S8) work in transmission, while the other two (S7, S6) work in reflection, and a lens (5c) having a free-form optical surface (S4).

15. Virtual or augmented reality headphones or glasses, characterized in that they integrate an optical system according to any one of claims 10 to 14.