Optical system for exit pupil expansion without magnification

Abstract

The invention relates to an optical system (17) with a magnification equal to 1, comprising a first set of lenses (19) configured to focus an input image on a first intermediate focal plane (21), an optical device (23) configured to achieve a magnification greater than 2 between the first intermediate focal plane (21) and a second intermediate focal plane (25), and a second set of lenses (29) configured to refract the second intermediate focal plane (25) at infinity.

Description

[0001] DESCRIPTION

[0002] TITLE: Non-magnification exit pupil enlargement optical system

[0003] Technical field

[0004] The present invention relates to an optical pupil enlargement system.

[0005] In particular, the present invention relates to an optical system configured to receive a light flux from a light source or a diaphragm, also called a restitution pupil, of small diameter, said optical system being intended to transmit the light flux with a constant magnification and with an exit pupil of larger diameter.

[0006] Previous techniques

[0007] Figure 1 schematically shows an example of a display system 1 comprising a digital screen 3 and an optical element 5 refracting rays coming from the digital screen 3 "to infinity", for example with an apparent field angle equal to 30°. "To infinity" is understood to mean the common designation in the field of optics for rays which emerge substantially parallel from said optical element 5.

[0008] The display system 1 can be positioned upstream of a binocular, or a particular sensor, but is not predestined to be used by a human eye.

[0009] As a result, certain display systems 1 of this type include a restitution pupil 7 of very small diameter, for example equal to 1 millimeter, which is also positioned a few millimeters from the last lens of the optical element 5.

[0010] Under these conditions, if a human user still wishes to be aware of the luminous flux returned by the optical element 5, the user will have difficulty in correctly positioning his eye in front of the display system. The diameter of the restitution pupil 7 is so small that the eye must be positioned almost in contact with the optical element 5 to be able to see the luminous flux, which is unpleasant and dangerous in the event of a false movement.

[0011] An illustrated solution to make observation by a human eye 9 more comfortable can be imagined by fixing a magnifying zoom 1 1 behind the optical element 5 in order to apply a magnification factor to the restitution pupil 7, for example a factor x5.

[0012] However, this solution greatly reduces the apparent field angle which will therefore be well below 30°, which is not acceptable.

[0013] Another solution, not illustrated, is the use of a module following the optical element 5, said module comprising a sensor on which an image is formed, said image then being sent to a screen restoring to the user, via or not another optical element, the image collected at the output of the display system.

[0014] However, this solution requires additional electronics, which is also not desirable because it complicates the display system.

[0015] Statement of the invention

[0016] The present invention therefore aims to overcome the aforementioned drawbacks and to provide an optical system which can be attached to an existing display system in order to form an exit pupil with a diameter greater than the restitution pupil of the existing system.

[0017] The present invention relates to an optical system with a magnification equal to 1, comprising a first set of lenses configured to focus an input image onto a first intermediate focal plane, an optical device configured to achieve a magnification greater than 2 between the first intermediate focal plane and a second intermediate focal plane, and a second set of lenses configured to refract the second intermediate focal plane to infinity. Thus, this optical system makes it possible, without any magnification, in other words without changing the apparent field angle, to increase the transverse size of the optical beam seen by the user at the output of said optical system. This is particularly advantageous when the optical system is positioned behind an optical element comprising a restitution pupil with a diameter too small for observation by this restitution pupil to be pleasant for a human eye.

[0018] In a first embodiment, the optical device comprises an array of microlenses, the microlenses being aspherical or holographic.

[0019] Advantageously, the optical device comprises a microlens array of at least 400 by 400 microlenses, each microlens having a magnification greater than 2.

[0020] Advantageously, the optical device has transverse dimensions of between 5 and 15 millimeters.

[0021] In a second embodiment, the optical device comprises an angular diffuser, the positions of the first intermediate focal plane, the second intermediate focal plane and said optical device being merged at the same location.

[0022] Advantageously, the angular diffuser comprises a granular surface with an average grain size of between 10 and 40 microns.

[0023] In a particular embodiment, the angular diffuser is a liquid crystal polymer or a metasurface.

[0024] Advantageously, the second set of lenses includes a dioptric adjustment for accommodation of a user's eye.

[0025] In a particular embodiment, the optical device is configured to achieve a magnification greater than or equal to 5, the optical system comprising an exit pupil of between 2.5 and 7.5 millimeters in diameter, preferably 5 millimeters in diameter.

[0026] The invention also relates to a display system comprising a camera, a digital screen configured to display an image taken by the camera, an optical element configured to refract the digital screen to infinity with an apparent field of between 20° and 40° and a restitution pupil of between 0.5 mm and 1.5 mm in diameter, the display system further comprising the optical system according to any one of claims 1 to 9, the digital screen refracted to infinity by the optical element being intended to form the input image.

[0027] Brief description of the drawings

[0028] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0029] [Fig 1] which has already been mentioned, is a schematic view of a display system according to the prior art;

[0030] [Fig 2] is a schematic view of a display system and its pupil enlargement optical system according to a first embodiment of the invention; and

[0031] [Fig 3] is a schematic view of a display system and its pupil enlargement optical system according to a second embodiment of the invention.

[0032] Detailed description of at least one embodiment

[0033] 2 schematically shows a display system 13 comprising a camera 15, preferably infrared, a digital screen 3 configured to display an image taken by the camera 15, and an optical element 5 configured to refract the digital screen 3 to infinity, in other words the light from an image displayed on the digital screen 3 is refracted to infinity by the optical element 5, with an apparent field of between 20° and 40°, preferably 30°, and a restitution pupil 7 of between 0.5 mm and 1.5 mm in diameter, preferably 1 millimeter in diameter.

[0034] Preferably, the digital screen comprises a matrix comprising between 100,000 and 1,000,000 pixels.

[0035] In Figure 2, the display system 13 further comprises a first embodiment of an optical system 17 aligned on an optical axis A. The optical system 17 has a magnification equal to 1, in other words the apparent field at the output of the optical system 17 is equivalent to the field at the input of said optical system 17. The optical system 17 being positioned after the optical element 5 whose apparent field is between 20° and 40°, the apparent field at the output of the optical system 17 will also be between 20° and 40°.

[0036] The optical system 17 comprises a first set of lenses 19 configured to focus an input image onto a first intermediate focal plane 21. The input image is in this case the light from an image displayed on the digital screen 3 and refracted to infinity by the optical element 5.

[0037] The optical system 17 further comprises an optical device 23 configured to achieve a magnification greater than 2 between the first intermediate focal plane 21 and a second intermediate focal plane 25. This magnification, preferably greater than 4, and more preferably equal to 5, makes it possible, at the output of the display system 13, to multiply the size of the restitution pupil 7 by said magnification, and thus to go for example from a restitution pupil 7 of 1 millimeter in diameter to an exit pupil 27 of 5 millimeters in diameter.

[0038] The optical system 17 finally comprises a second set of lenses 29 configured to refract the second intermediate focal plane 25 to infinity, so that the eye 31 of a user can take note of the information broadcast on the digital screen 3. The exit pupil 27 is measured near the second set of lenses 29, for example less than one millimeter from the second set of lenses 29, between the second set of lenses 29 and the eye 31 of the user. Advantageously, the second set of lenses 29 comprises a dioptric adjustment (not shown) to allow the accommodation of the eye 31 of a user to his sight.

[0039] In a particular embodiment, the first set of lenses 19 and the second set of lenses 29 each comprise at least two lenses.

[0040] In the first embodiment shown, the optical device 23 comprises a matrix of microlenses, the microlenses being aspherical or holographic or even spherical.

[0041] Advantageously, the optical device 23 has transverse dimensions of between 5 and 15 millimeters.

[0042] Advantageously, the optical device 23 comprises a matrix of microlenses of at least 400 by 400 microlenses, each microlens having a magnification greater than 2, preferably greater than 4 and more preferably equal to 5.

[0043] Thus, for a microlens array of 400 by 400 microlenses measuring 10 by 10 millimeters, each microlens is arranged every 25 micrometers.

[0044] Similarly, for a 2000 by 2000 microlens array of 10 by 10 millimeters, each microlens is arranged every 5 micrometers.

[0045] One of the features of the present invention is to use microlenses in an object-image configuration between the first intermediate focal plane 21 and the second intermediate focal plane 25, separated by a distance of between 50 and 400 micrometers, while the microlenses are usually used in an infinity-focus configuration.

[0046] This embodiment is also preferred because the microlenses can be produced at low cost.

[0047] Figure 3 schematically shows a display system 13 equivalent to the display system 13 of Figure 2 except for the optical device 23 which is slightly different.

[0048] In Figure 3, the display system 13 in fact comprises a second embodiment of an optical system 17 aligned on an optical axis A. The optical system 17 has a magnification equal to 1, in other words the apparent field at the output of the optical system 17 is equivalent to the field at the input of said optical system 17. The optical system 17 being positioned after the optical element 5, the apparent field of which is between 20° and 40°, the apparent field at the output of the optical system 17 will also be between 20° and 40°.

[0049] The optical system 17 comprises a first set of lenses 19 configured to focus an input image onto a first intermediate focal plane 21. The input image is in this case the light from an image displayed on the digital screen 3 and refracted to infinity by the optical element 5.

[0050] The optical system 17 further comprises an optical device 23 configured to achieve a magnification greater than 2 between the first intermediate focal plane 21 and a second intermediate focal plane 25. This magnification, preferably greater than 4, more preferably equal to 5, makes it possible, at the output of the display system 13, to multiply the size of the restitution pupil 7 by said magnification, and thus to go for example from a restitution pupil 7 of 1 millimeter in diameter to an exit pupil 27 of 5 millimeters in diameter.

[0051] The optical system 17 finally comprises a second set of lenses 29 configured to refract the second intermediate focal plane 25 to infinity, so that the eye 31 of a user can take note of the information broadcast on the digital screen 3. The exit pupil 27 is measured near the second set of lenses 29, for example less than one millimeter from the second set of lenses 29, between the second set of lenses 29 and the eye 31 of the user.

[0052] Advantageously, the second set of lenses 29 includes a dioptric adjustment (not shown) to allow the eye 31 of a user to accommodate his or her eyesight.

[0053] In a particular embodiment, the first set of lenses 19 and the second set of lenses 29 each comprise at least two lenses. In the second embodiment shown, the optical device 23 comprises an angular diffuser, the positions of the first intermediate focal plane 21, of the second intermediate focal plane 25 and of said optical device 23 being merged at the same location. Indeed, the angular diffuser acts at a single point and is configured to effect a magnification greater than 2 directly at the level of the first intermediate focal plane 21.

[0054] In a particular embodiment, the angular diffuser is a liquid crystal polymer or metasurface, or a holographic diffuser.

[0055] One of the features of the present invention is to use an angular diffuser on a focusing plane, the first intermediate focal plane, where the diffusing effect must be obtained on a small scale.

[0056] For this, the angular diffuser comprises a granular surface whose average grain size is between 10 and 40 microns, according to the definition of the digital screen 3. For a magnification of 5, these grains are thus configured to transform an incident illumination cone of 2° into an illumination cone of 10°.

Claims

CLAIMS 1. Optical system (17) with a magnification equal to 1, characterized in that it comprises a first set of lenses (19) configured to focus an input image on a first intermediate focal plane (21), an optical device (23) configured to achieve a magnification greater than 2 between the first intermediate focal plane (21) and a second intermediate focal plane (25), and a second set of lenses (29) configured to refract the second intermediate focal plane (25) to infinity.

2. Optical system (17) according to claim 1, wherein the optical device (23) comprises an array of microlenses, the microlenses being aspherical or holographic.

3. The optical system (17) of claim 2, wherein the optical device (23) comprises a microlens array of at least 400 by 400 microlenses, each microlens having a magnification greater than 2.

4. Optical system (17) according to claim 1, wherein the optical device (23) comprises an angular diffuser, the positions of the first intermediate focal plane (21), of the second intermediate focal plane (25) and of said optical device (23) being merged at the same location.

5. Optical system (17) according to claim 4, wherein the angular diffuser comprises a granular surface whose average grain size is between 10 and 40 microns.

6. Optical system (17) according to one of claims 4 and 5, in which the angular diffuser is a liquid crystal polymer or a metasurface.

7. Optical system (17) according to any one of claims 1 to 6, wherein the optical device (23) has transverse dimensions of between 5 and 15 millimeters.

8. An optical system (17) according to any one of claims 1 to 7, wherein the second set of lenses (29) comprises a dioptric adjustment for accommodating an eye (31) of a user.

9. Optical system (17) according to any one of claims 1 to 8, wherein the optical device (23) is configured to achieve a magnification greater than or equal to 5, the optical system (17) comprising an exit pupil (27) between 2.5 and 7.5 millimeters in diameter, preferably 5 millimeters in diameter.

10. Display system (13) comprising a camera (15), a digital screen (3) configured to display an image taken by the camera (15), an optical element (5) configured to refract the digital screen (3) to infinity with an apparent field of between 20° and 40° and a restitution pupil (7) of between 0.5 mm and 1.5 mm in diameter, the display system (13) further comprising the optical system (17) according to any one of claims 1 to 9, the digital screen (3) refracted to infinity by the optical element (5) being intended to form the input image.

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