The present invention relates to an adjustable, fluid-filled lens and in particular a lens incorporating a diffractive pattern, and an article of eyewear comprising such a lens.
Fluid filled lenses of the kind in which the pressure of fluid is used to control the shape of an elastic membrane in contact with the fluid are known in the art. Generally these lenses may be of the “fluid injection” type, in which the amount of fluid is controlled within an envelope that is bouhded on one side by the membrane, or the “fluid compression” type in which the volume of an envelope is adjusted that is bounded on one side by the membrane and contains a fixed amount of fluid. In each case, the pressure of the fluid within the envelope is adjusted, either by adding or removing fluid to or from the envelope, or by changing the volume of the envelope, to control the fluid pressure acting on the membrane, thereby to control the shape of the membrane.
Whilst various applications of adjustable lenses are possible, for example in cameras and other optical equipment, one use is in eyewear. An adjustable lens is particularly useful for correction of presbyopia—a condition in which the eye exhibits a progressively diminished ability to focus on close objects with age. If the wearer additionally suffers from myopia—a condition in which the eye does not focus objects viewed at distance correctly (nearsightedness or shortsightedness)—the adjustable lens can be used in combination with a negative corrective lens to account for the myopia. An adjustable lens is advantageous because the wearer can obtain correct vision through a range of distances from long-distance to near vision. The lens is typically designed such that it can be adjusted when required for close tasks and the object may be brought into focus in the same region of the lens through which distant objects are viewed. This is more ergonomic than bifocal lenses in which near-vision correction is provided in a bottom region of the lens, thereby only allowing the user to see close objects in focus when looking downwardly.
A helmet mounted display (HMD) is an item of headwear which incorporates a display to project an image into the wearer's eye. The display may be transparent, thereby allowing the wearer to view the image whilst still being able to see his field of view. In this case the image may be projected across a part of or the whole field of view. Alternatively, the display may be configured to project the image into one eye, such that the wearer's field of view can be observed through the other eye. The projected image is generated by a projector and is usually received as data and processed into an image by the projector. The data often relates to the wearer's environment, for example a fighter pilot might use an HMD to view information such as airspeed, altitude or target range, whilst still being able to see around him to fly the plane. The image is typically generated by a cathode ray tube (CRT) imager or a micro display such as a liquid crystal display (LCD) with a light emitting diode (LED) illuminator.
A disadvantage of the type of HMD described above is that if the wearer needs any sort of vision correction, he would need to wear either eyeglasses or contact lenses in addition to the HMD. This would be inconvenient from a comfort point of view and also when changing focus from far objects to near objects, since the image projected from the display would likely be in a non-optimal location in one or both situations.
It would be desirable to provide an adjustable lens incorporating a display for viewing a projected image in addition to the field of view. It would further be desirable to provide an article of eyewear, such as an HMD, which mitigates the above-discussed problems.
According to a first aspect of the invention, there is provided an adjustable fluid-filled lens having a rear surface; and a front surface and a body of fluid therebetween, the lens incorporating a diffractive pattern within the fluid.
The diffractive pattern may be disposed either at an interface between the lens and the fluid or be supported in the fluid spaced apart from the front and rear surfaces.
The front surface of the adjustable lens preferably comprises an elastic or viscoelastic membrane held around its edge by a supporting member, the membrane being spaced apart from the rear surface. The pressure of the fluid may be adjustable for adjusting the shape of the membrane to thereby vary the power of the lens to focus the first image.
Advantageously the lens may be operable to focus a first image of an object viewed through the lens in a first region of the lens and the optical element may be operable to focus a second image projected onto the diffractive pattern in an overlapping region of the lens. Advantageously, the lens may have an optical centre which remains in a substantially constant position during a range of adjustment of the lens to focus the first image.
In some embodiments, the rear surface is defined by a rear cover on which the diffractive pattern is disposed.
In some embodiments the supporting member and the rear cover are flexibly joined together around their edges to form a sealed envelope in which the fluid is contained. The lens may comprise an envelope in which the fluid is contained, one wall of the envelope defining said front surface. The rear face may be defined by another wall of the envelope, the wall being fixedly attached to the rear cover. The diffractive pattern may be disposed within the envelope.
Preferably the fluid and the diffractive pattern are index-matched.
In some embodiments, the second image may be received through the rear surface of the lens. The second image may be received at an angle of between 10 and 90° to the rear surface.
In other embodiments, the second image may be received through a side of the lens, substantially parallel to the rear surface.
The lens may be thought of as having an axis passing through the front and rear surfaces and as having a width across the lens between first and second sides. The diffractive pattern may be arranged: substantially perpendicular to the axis; at an acute angle to the axis; across a side region of the lens; across a central region of the lens; or across substantially the entire width of the lens, depending on the application or on preference.
The diffractive pattern may comprise one or more of: a diffractive element, a diffractive grating, a bulk holographic element. It could optionally be an exit pupil expander; an functions may be used in combination. In some embodiments the diffractive pattern may be applied to a surface within the fluid in the form of a film, etched onto the surface or as a surface relief.
According to a second aspect of the invention, there is provided an article of eyewear comprising a lens as described above.
The article of eyewear may further comprise or carry an image generating device, arranged to project a second image onto the diffractive pattern. The image generating device may comprise a micro LCD display or an OLED display. The OLED display may be monochromatic or polychromatic. The article of eyewear may further comprise or carry a camera configured to record images, for example images of a wearer's eye. The camera may be incorporated in or carried on the image generating device.
The article of eyewear in some embodiments comprises a frame for holding the lens and a temple attached to or formed as part of the frame. The image generating device and/or the camera may be carried on the frame or the temple. The image generating device and/or the camera may be disposed on one or more of: a bridge of the frame; in a region where the frame and the temple are joined for projecting the second image substantially parallel to the rear face of the lens; and in a region of the temple for projecting the second image at an angle of between 10 and 90° to the rear face.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
a is a perspective view from above and to the left of the left-hand side of the eyeglasses of
b is a perspective view from above and to the reverse side of the eyeglasses of
a shows a cross-section of the one lens assembly along the line IV-IV of
a shows a cross-section of the one lens assembly along the line V-V of
a-f show schematically a number of alternative configurations of an adjustable lens assembly incorporating an optical element;
a shows an example of an eyebox and
In the drawings, like reference numerals indicate like parts.
As shown in
As can be seen from
As shown in
At the one side held between the truncated temples 96, 96′ and the temples 94, 94′, it can be seen from
As illustrated in
The front cover plate 4 may be of glass or a suitable transparent polymeric material. In the lens assembly 1 of the present embodiment, the front cover plate is about 1.5 mm thick, but this may be varied. In some embodiments, the front cover plate 4 may comprise a lens of fixed focal power(s), for example a single vision (single power), multi-focal (two or more powers), progressive (graded power) or even an adjustable element. As shown in
The rear cover plate 16 may be made of glass or transparent polymer. In the present embodiment, the rear cover plate 16 is about 1.5 mm thick, but this may be varied as desired. As with the front cover plate 4, in some embodiments, the rear cover plate 16 may form a lens of a fixed focal power. In the present embodiment, for example, the rear cover plate 16 is a meniscus lens, as best seen in
To assemble the lens assembly 1, the front shell 6a and the rear shell 6b are pushed together, with other components of the lens assembly 1 (these components do not include the front cover plate 4 and the rear cover plate 6) between them. The rear shell 6b is dimensioned to fit contiguously against the front shell 6a. The front 6a and rear 6b shells can be fitted together whilst allowing room for the other components of the lens assembly 1 to be sandwiched between them. The two may be glued together.
As noted above, the rear cover plate 16 is shown in
As best seen in
The other components of the lens assembly 1 mentioned above are the moveable components and are described in the following.
Adjacent the rear retaining ring 6b is a dish-shaped part 12 having a flexible side wall 18 with a forward sealing flange 20 and a rear wall 19. In the present embodiment, the dish-shaped part 12 is made of transparent DuPont® boPET (biaxially-oriented polyethylene terephthalate) and is about 6μ thick, but other suitable materials for the dish-shaped part may be used and the thickness adjusted accordingly. The rear wall 19 of the dish-shaped part 12 is bonded contiguously to the front face 17 of the rear cover plate 16. For this purpose, a transparent pressure-sensitive adhesive (PSA) such, for example, as 3M® 8211 adhesive may be employed. In the present embodiment, a layer of PSA of about 25μ thickness is used, but this may be varied as required for the movable parts of the lens assembly 1.
The side wall 18 of the dish-shaped part 12 is free to move within the retaining ring 6a, 6b, adjacent the rear shell 6b. This floating arrangement allows the dish-shaped part to be compressed in use, and allows other moveable parts of the lens assembly 1 to operate unimpeded by the retaining ring 6a, 6b, as described in more detail below.
The forward sealing flange 20 of the dish-shaped part 12 is bonded to the rear surface of a transparent diaphragm comprising a disk 24. In the present embodiment, as best shown in
The front surface of the transparent disk 24 is sealed to a membrane sub-assembly comprising a transparent, non-porous, elastic membrane 8 that is sandwiched between a pair of resiliently bendable membrane supporting rings comprising a front ring 2 and a rear ring 10. The rings 2, 10 are of substantially the same overall geometry as each other and are dimensioned for being received within the retaining ring such that the front ring 2 sits adjacent the front shell 6a of the retaining ring. However, there is a space between the front ring 2 and the front shell 6a so that the rings 2, 10 can change shape or move during use of the lens. The front and rear rings 2, 10 together form a supporting member for the elastic membrane 8. In the present embodiment, the rings 2, 10 are cut from a sheet of stainless steel and the front ring 2 is about 0.3 mm thick, while the rear ring 10 is about 0.05 mm thick. Other materials may be used and the thickness adjusted accordingly to provide the desired stiffness. For example, the front ring 2 may have a thickness in the range 0.2-0.75 mm, suitably 0.3 or 0.4 mm to 0.5 mm. The rear ring 10 may have a thickness in the range 0.01-0.25 mm, suitably 0.025-0.1 mm, e.g. about 0.05 mm
In the present embodiment, the membrane 8 is made of polyethylene terephthalate (e.g. Mylar®) and is about 0.5 mm thick, but alternative materials with a suitable modulus of elasticity may be used as desired. For instance, the membrane 8 may alternatively be made of other polyesters, silicone elastomers (e.g. poly(dimethylsiloxane)), thermoplastic polyurethanes, including cross-linked polyurethanes (e.g. Tuftane®), vinylidene chloride polymers (e.g. Saran®) or glass of suitable thickness.
The front ring 2 comprises a number of tabs 120 around its extent, which protrude outwards from the general shape of the front ring 2 i.e. away from its central enclosed area but in plane with the central enclosed area of the ring 2. Apart from the thickness, the rear ring 10 is shaped and dimensioned similarly to the front ring 2, except it does not have any tabs. These tabs 120 are used as hinge points for hinging the sub-assembly to the retaining ring 6a, 6b at selected discrete locations and for preventing the lens 1 undergoing unwanted out-of-plane bending. In view of the flexibility of the rings, the disk 24 serves as a bending control member to mitigate unwanted in-plane bending.
Referring additionally to
Finally, also visible in
In operation, the adjuster wheel 108 is rotated, which, via a gear train 107, causes the cam plate 122 to undergo translational movement. The cam follower 126 is fixedly attached to the front ring 2 at three of the tabs 120 on the short side 7 of the lens assembly, and this causes the front and rear rings 2, 10 of the short side 7 to move relative to the rear shell 6b. Thus the volume of the cavity 22 can be selectively reduced or increased and therefore the fluid pressure is respectively increased or decreased. An increase in fluid pressure causes the membrane 8 to distend into a convex shape, thereby increasing the focal power of the lens. Rotation of the adjuster wheel 108 in the opposite direction causes the degree of distension to lessen and hence the focal power of the lens is decreased.
Adjustable lenses of the present embodiment are described in more detail in co-pending international patent applications nos. PCT/EP2012/075549 and PCT/GB2012/051426, the contents of which are incorporated herein by reference.
As best seen in
In the present embodiment, the lens assembly 1 has a zero focal power when it is substantially planar. When operated as described above, the short side 7 of the front and rear rings 2, 10 is selectively moved towards the rear shell 6b of the retaining ring 6a, 6b, thus causing distension of the membrane 8, thereby increasing the focal power of the lens assembly 1 in view of the curvature of the membrane 8. By “prior to adjustment” herein is meant the lens assembly 1 when it is in a substantially planar state. It will be understood that when considering use of the lens by a real wearer this term is somewhat arbitrary as the lens could be in any of a range of possible states and then adjusted or re-adjusted. However, this terminology is used for convenience to explain embodiments of the invention.
a and 6b as discussed in the following show cross sectional views of the lens assembly 1. In terms of the light paths shown and the relative positions of other items in the figures, these drawings are purely illustrative and are not intended to show to scale the distances between components, or the relative sizes thereof. The light paths and beams are shown schematically as an indication of how embodiments of the invention work. An eye of a wearer of the spectacles 90 is also shown purely as a representation thereof; as the cross-section V-V is not taken on the optical centre OC, the centre of the wearer's eye 102 may in reality be disposed from the view of
Referring now to
A diffractive pattern in the form of an optical element 100 is disposed on the rear cover plate 16. In the present embodiment this is achieved by application of a film to the rear wall 19 of the envelope 12, which itself is glued to the rear cover 16. In practice it is very thin as it is formed as a film, but its size is shown exaggerated for convenience in the drawings. This optical element 100 is shown in
A visual representation of the design of the exit pupil expander is shown in
In
The optical element 100 applies one or more optical effects to the received second image. Optical effects could include focusing, expanding or contracting, diffracting, reflecting or transmitting or any combination thereof. In the case of the exit pupil expander used in this embodiment, the received image is mainly focused, reflected (a small amount, about 2% may pass through the optical element 100) and expanded, as discussed previously with reference to
In view of the position of the optical element 100 within the lens assembly 1, the wearer will view the image projected from the projector 108 as it appears on the optical element 100. Thus the second image will appear to the left of the wearer's eye and slightly higher than where the object O1 is observed via the optical centre OC of the lens assembly 1. It will be understood that the object O1 represents the user's distant field of view and hence that the wearer can observe both the field of view and the second image simultaneously because the second image is superimposed on a part of the first image. Although appearing to the user's left, the second image nevertheless appears sufficiently proximal to the optical centre OC of the lens that a wearer of the eyeglasses 90 can view it comfortably without having to move his or her eyes much, if at all.
Turning now to
Since the optical element 100 is disposed within the fluid 11 but the second image is not projected through the membrane 8, the second image can still be viewed correctly at the wearer's eye 102, even though the optical power of the lens to focus an image incoming from the wearer's field of view through the membrane 8 has changed. Furthermore, because the membrane 8 distends around the OC, the position of the object O2 in the user's field of view is viewed at substantially the same position in the X-Y plane as the object O1 is viewed in the situation shown in
Another important feature of this embodiment of the invention is that the film carrying the optical element 100 is transparent. The etched surface features as shown in
Furthermore, the refractive index of the optical element substantially matches the refractive index of the oil 11. Consequently, any light beams representing the first image which pass through the optical element 100 on their path in through the membrane 8 are not refracted any more than they would be if they did not pass through the optical element 100. Thus the first image is not distorted or is only negligibly distorted by the presence of the optical element 100. Additionally, the optical element 100 is substantially invisible to an onlooker observing the wearer's eyeglasses, thus improving the aesthetic appearance of the eyeglasses 90. These effects are achieved because the optical element 100 is disposed next to or within the oil 11.
A further advantage of placing the optical element next to the oil 11, within a sealed unit of the lens is the optical element is protected from damage.
In
In the embodiment of
The optical element 100 thus comprises a diffractive pattern 24. The characteristics of the diffractive pattern 24 will need to be designed so that the light emitted by the projector 108 is diffracted through the angle between the optical element 100a and the wearer's pupil. The skilled person would be well aware how to do this without explicit instruction as he will know that the angle through which light is diffracted by a diffraction grating is given by:
where θm is the angle of diffraction; m is the order of diffraction; λ is the wavelength of light; d is the spacing between slits (or other diffractive features) in the diffractive pattern; and θi is the angle of incidence of the light from the projector 108. Given this equation, it is a straightforward matter to design a diffractive pattern by selecting a suitable value for d to cause light emitted by the projector 108 to be diffracted suitably so that the light will be diffracted into the user's pupil.
In
In
In
In
In
It will be appreciated that many variations may be made to the described embodiments of the invention. Firstly, the shape of the lens may be different from that of the embodiments shown, but the principles of the invention would still apply. For example, the shapes and sizes of the various elements of the lens assembly 1 could be different. The lens assembly 1 could be a different shape, for example round. It may not be necessary for the supporting member to comprise two rings, nor for it to be bendable, particularly for a round lens. The ring or rings may vary in thickness. The lens assembly may not require a support disk 24. The hinging mechanism provided by the tabs 120 is also not essential. The adjustment mechanism could be different from the cam plate mechanism shown; the adjustment mechanism could be mechanically, electrically or magnetically operated and/or may involve use of a phase change material, e.g. a shape memory alloy (SMA), wax or an electro-active polymer. The invention is equally applicable to fluid-filled lenses in which the pressure of the fluid is adjusted by addition of fluid (the “fluid injection” type). The lens assembly 1 does not have to be dynamically adjustable through all possible degrees of distension but may alternatively be adjustable at discrete lens powers. There may be more than one adjustable membrane and the shape of the front and rear covers or lenses could be different. Other types of fluid could be used than the above-described oil. It is not essential for the optical element 100 to be transparent, nor for it to be index-matched to the fluid, although these are preferred features.
In the above-described embodiments, the fluid is held in an envelope 12. In the above-described embodiments, the envelope 12 is disposed on the rear cover plate 16. This arrangement could be varied. For example, the rear face 19 of the envelope 12 could be omitted and instead, the flexible side walls 18 of the envelope 12 could be joined directly to the rear cover 16. Another alternative is for the envelope 12 additionally to hold the rear cover 16 therein. The optical element could thus be disposed on the rear cover 16 and if that rear cover comprises a lens, it could be etched into the lens. Alternatively it could be placed on the rear face 19 of the envelope 12.
The type of diffractive pattern could be different from the optical element 100 in the described embodiments. Other possibilities are a beam splitter, a thin film stack; a diffractive pattern in the form of other bulk holographic elements; an etched element; a film; and a coating. The optical element does not have to be in direct contact with the rear cover 16, provided it is in contact with the fluid. It could be suspended in the oil 11, supported in the region of its edges such that it does not contact any or all of the surfaces of the envelope 12 or the rear cover 16. Thus it could be at an interface between the front and/or rear covers 4, 16 and the oil or it could be supported in the oil such that it is spaced apart from the front and rear surfaces 4, 16. The optical element could be formed by various means such as etching, molding or grinding or by application of a film.
The arrangements of the various components of the embodiments shown can be varied. For example, the location of the projector 108 can be varied from the examples shown and discussed. The angle of projection of the image could also be different from that shown in the embodiment described with reference to
Number | Date | Country | Kind |
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1302717.2 | Feb 2013 | GB | national |
1302723.0 | Feb 2013 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/060810 | 5/24/2013 | WO | 00 |