Meta AR/VR Patent Introduces Pancake Lens with Controlled Curvature

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(XR Navigation Network March 06, 2024Pancake, which helps miniaturize devices, is becoming a mainstream XR headset. In a patent application titled "Pancake lens with controlled curvature," the patent application states thatMetaA Pancake lens with controlled curvature is presented.

The device 100 illustrated in FIG. 1 includes a display 105, a first lens 115 including a partial reflector 120, a quarter-wave sheet 125 including the partial reflector 120, and a reflective polarizer 135 and an optional substrate 140. if the reflective polarizer 135 includes a cholesteric reflective polarizer, the quarter-wave sheet 125 may be omitted.

FIG. 2 shows an apparatus including a display and an optical configuration containing a zoom lens assembly. The apparatus 200 includes a display 205, a first lens assembly 215, and a second lens assembly 230. the first lens assembly 215 has a partial reflector 220 supported by one surface of the first lens and a quarter-wave plate 225 supported on opposing surfaces of the first lens.

The second lens assembly 230 includes a reflective polarizer 232 on one surface of the second lens assembly and an actuator 235 on opposing surfaces of the second lens assembly.The first and second lens assemblies may each include a lens, such as a refractive lens. Said actuator 235 may be a multilayer actuator. The display 205 emits display light, illustrated by example ray bundles 210 that may form evanescent ray bundles 240 and 245. The distance from said image to the user's eye may be referred to as the adjustment distance, and said adjustment distance may be adjusted by controlling the actuator using one or more electrical signals.

In one example, the adjustable lens in the second lens assembly 230 may have a radius of curvature in the range of about flat to about 150 mm, such as about flat to about 50 mm.

FIG. 3 shows light propagation through a cross-section of the apparatus 300. The embodiment apparatus 300 includes a display 305, a first lens assembly 315, and a second lens assembly 330. the first lens assembly 315 may include a partial reflector 320 supported by one surface of the first lens and a quarter-wave wavelength 325 supported by an opposing surface.

The second lens assembly 330 may include a lens, said lens supporting a reflective polarizer 332 on one surface and an actuator 335 on the other surface.Said display 305 may be configured to emit light, such as a beam 310 that may form collimated ray beams 340 and 345.The collimation of the ray beams 340 and 345 may produce an image that is displayed at a greater distance from a user.

In one example, the second lens assembly 330 may include a lens, such as an adjustable lens, with a radius of curvature in the range of about flat to about -150 mm, such as about flat to about -50 mm. in one example, the transmittance of the second lens assembly may be adjustable using the actuator 335.

FIG. 4 is an example optical configuration of at least one lens having an adjustable transmittance. The device 400 may include a display 405 and an optical configuration including a first lens assembly 470 and a second lens assembly 475. the first lens assembly 470 may include an actuator 410, a reflector 415, and optionally a quarter-wave wavelength 420.

The second lens assembly 475 may include a reflective polarizer 425 and a second lens 430, the second lens 430 including an actuator supported on a surface of the second lens.

In one example, an exemplary device may include a display and at least one lens assembly. The exemplary lens assembly may generally be planar and may include, for example, a fluid lens, a diffractive element, or a Fresnel lens, or both, in one or both of the lens assemblies.

At least one of the first and second lens assemblies may have adjustable optical parameters, such as transmittance and/or cylindricity. For example, at least one of the first and second lens assemblies may include a surface having a controllable curvature, such as a membrane for a fluidic lens, a curved surface for a controllable electro-optical solid lens, or an actuator-controlled lens including an elastic material.

In one embodiment, the partial reflector layer may include one or more of three layers, such as an absorbing linear polarizer, a quarter-wave sheet, and a partial reflector layer. The partial reflector layer may be configured to reflect about 501 TP3T of light and transmit about 501 TP3T of light, e.g., for visible light of at least one wavelength.

FIG. 5 illustrates at least one example optical configuration of a device 5000 having a lens with adjustable transmittance and an absorptive optical polarizer. The device 500 may include a display 505, a first lens assembly 570, and a second lens assembly 575. the first lens assembly 570 may include an actuator 510, a reflector 515, and a first lens 520 that may further support an optional quarter-wave wavelength sheet. the second lens assembly 575 may include a reflective polarizer 525, a combination of the second lens and an absorptive polarizer 535, and a second actuator 530.

The optical structure of FIG. 5 may be modified to reduce reflections from objects, such as those external to the device. In this example, the lens 575 supports an absorbing polarizer 535, wherein the blocking polarization of the absorbing polarizer 535 may be parallel to the blocking polarization of the reflecting polarizer 525 to reduce reflection effects.

Another exemplary device 600 illustrated in FIG. 6 includes an optical structure having at least one lens with adjustable transmittance and at least one actuator. The device 600 includes a display 605, a first lens assembly 670, and a second lens assembly 675. the first lens assembly 670 may include an actuator 610, a reflector 615, an optional quarter-wave wafer 620, a partial reflector 625, and a first lens 630.

The second lens assembly 675 may include a reflective polarizer 635 disposed on a surface of the second lens 640 and a second actuator 645 disposed on an opposing surface of the second lens 640.The second lens assembly may also include an absorbing polarizer. For example, the second lens 640 may support an optional absorbing polarizer layer that absorbs any light polarization blocked by the reflective polarizer 635.

The second actuator 645 may be a single or dual actuator and may be omitted in particular examples. In this and other examples, the order of the optical elements within the lens assembly may be reversed and/or rearranged. The display 605 may be configured to emit unpolarized light.

Light 650, such as unpolarized light, may pass through the first lens assembly 670. the actuator 610 may include a transparent multilayer structure comprising a plurality of electrically active layers and an arrangement of transparent electrodes configured to apply an electrical signal to said electrically active layers. In one example, the controller may be used to provide an adjustable electrical signal to at least one layer of the multilayer actuator. The actuator 610 may be a monomorphic or bimorphic actuator.

The light 650 may pass through the reflector 615 and through the quarter-wave sheet 620 to form circularly polarized light. For example, the reflector 615 may include a linear polarizer. Light 650 passes through a first lens assembly including a partial reflector 625 and a first lens 630 to provide light 655. said first lens may support an optical retarder, such as said quarter-wave blade 620. light 655 may then be reflected by a second lens assembly 675 to form light 660, which may next be used as light 665 through the second lens assembly when the user is wearing the device reflected back towards, for example, the user's eyes.

The designation of the first lens assembly and the second lens assembly may be arbitrary. In one example, the device may be configured such that the display light passes through the first lens assembly, is reflected by a second reflector of the second lens assembly, is reflected by a first reflector of the first lens assembly, and then reaches the user's eye through the second lens assembly.

The actuator may be used to adjust an adjustable lens within said corresponding lens assembly. In one example, the at least one actuator may be combined with one or more optical elements in an example lens assembly, such as an adjustable lens or other optical element. A lens assembly including an actuator may be referred to as a first lens assembly, and a second lens assembly may include an actuator and an adjustable lens, or not include an actuator.

In one example, the actuator may change the polarization state of the light transmitted through the actuator, and this may be included in the optical design of the optical structure.

FIG. 7 illustrates an example actuator 700 with an actuator configuration that does not substantially change the polarization of light passing through the actuator 700, even for an actuator with a highly birefringent layer. The actuator 700 may include a clock stack of birefringent actuator layers.

The actuator 700 is shown having nine actuator layers. For example, the example actuator may include 1-50 layers, such as 1-20 layers, or some other number of layers. The first actuator layer through the ninth actuator layer are denoted as actuator layers 715, 720, 725, 730, 735, 740, 745, 750, and 755, respectively, wherein each actuator layer has a high in-plane refractive index nx, a low in-plane refractive index ny, and a refractive index orthogonal to the in-plane refractive index nz. The orthogonal component nz may have a value less than ny, greater than nx, or between nx and ny.

In this case, the clock stack of layers may comprise a multilayer structure comprising birefringent layers, each layer having an in-plane optical axis direction of a respective layer having an angular step difference from the optical axis direction of at least one neighboring layer.

In one example, the layer optical axis direction may be rotated in a stepwise manner along a direction perpendicular to the layers. The layer optical axis direction may describe a circle that advances through the multi-layer structure.

In one example, a proximate helix structure provided by rotation in the direction of the optical axis may provide a waveguide effect. The layer may include an oriented piezoelectric material. Example layers may include uniaxially oriented PVDF. example actuators may provide control over spherical, cylindrical, and optical axis parameters.

In one example, the multilayer actuator may include a plurality of electroactive layers interleaved with the electrode layers. The multilayer actuator may include a plurality of electrically active layers interleaved with the non-electrically active layers, the non-electrically active layers may support the electrode layers on one or both sides thereof.

The actuator 800 shown in FIG. 8 may include two single-axis actuator layers 850 and 855, where the nx vectors of each layer are approximately orthogonal to each other, as shown by arrows 830 and arrows 860.

The actuator 800 may be configured to reduce or substantially eliminate birefringent effects on the polarization of light transmitted through the actuator. In one example, the plurality of actuator layers includes two birefringent layers having orthogonal optical axes, wherein the optical axes of each layer may be located in the plane of a respective layer.

In one example, the actuator 800 may have a multilayer structure in which individual actuator layers may provide individually controllable uniaxial forces. The birefringent layer may be an optical uniaxial layer. The plurality of actuator layers may include a plurality of uniaxial layers, wherein each uniaxial layer has an optical axis, and wherein the direction of the optical axis in the plane of each uniaxial layer may differ by at least 10 degrees from the direction of an adjacent uniaxial layer.

In this case, adjacent electrically active layers may be separated by non-electrically active layers, but otherwise adjacent. During normal operation, the non-electrically active layers may not be able to respond to electrical signals provided to the actuator to alter the transmittance of the lens assembly to any perceptible degree.

In one example, an electric field applied to the one or more actuator layers may induce electrostriction of the actuator layers, such as in a direction parallel or orthogonal to the electric field. In one example, the electrical stretching within the one or more actuator layers may be used to adjust the curvature of the membrane, thereby, for example, adjusting the transmittance of the tunable fluid lens.

In one example, electrical stretching within one or more actuator layers may be used to adjust the transmittance and/or cylindricity of the tunable fluid lens. In one example, a symmetrical arrangement of electrostriction effects may be used to adjust the transmittance. In one example, an asymmetric arrangement of electrostriction effects may be used to obtain aspheric optical parameter adjustments, such as cylindricity adjustments.

The Meta patent application titled "Pancake lens with controlled curvature" was originally filed in August 2022 and was recently published by the USPTO.