Meta AR/VR optical patent proposes refractive hollow unimodal folding lens structure

(XR Navigation Network November 20, 2023）对于头显设备，采用由两个简单透镜配对在一起的双透镜可以允许更多的光学表面和厚度，帮助纠正更多的光学像差并提高图像精度。然而，传统的双透镜可能在两个透镜之间的间隙中包含油脂或类似材料，并可能会增加头显的重量挑战。

A patent application titled "Reflective hollow singlet folded optical lens" is pending.MetaA refractive hollow unimodal folded lens structure is proposed.

简单来说，传统的双透镜在粘合时会用诸如油脂这样的液体填充间隙或者根本没有间隙。Meta的空心单峰折叠透镜结构则是沿着外围边缘机械或化学固定两个光学元件，保持间隙（中空），或者无需使用诸如油脂这样的液体填充间隙。在一个实施例中，间隙可以使用惰性气体或类似气体。

In one embodiment, the optical lens structure may include two optical elements with a gap therebetween. The surface of a single element can have any number of optical layers, such as reflective polarizer layers, quarter wave layers, semi-transparent mirrors or other optical layers.

Optical lens configurations can create refractive index through the surfaces of the cavities between reflective elements. Dual-element optical lens configuration provides non-chromatic aberration for improved optical imaging quality and increased compactness. More than two refractive surfaces can reduce spherical aberration, astigmatism and field curvature. In addition, this optical lens configuration can reduce the weight of the optical components of the head-mounted display device. The optical lens structure may allow for simpler, higher volume production compared to traditional lens systems.

Figure 5 illustrates several optical lens configurations of the present invention. Diagram 500 includes example optical lens configurations 502, 504, 506, 508, 510, and 512, where in each configuration the first optical element is identified as L1 and the second optical element is identified as L2. In the optical lens structure 502, L1 may be a uniform optical lens, and L2 may be a plano-convex optical lens.

In optical lens configuration 504, both L1 and L2 can be uniform optical lenses. In the optical lens structure 506, L1 may be a meniscus negative optical lens, and L2 may be a uniform optical lens. In the optical lens structure 508, L1 may be a uniform optical lens, and L2 may be a meniscus negative optical lens. In the optical lens structure 510, L1 may be a meniscus positive optical lens, and L2 may be a uniform optical lens. In the optical lens structure 512, L1 may be a uniform optical lens, and L2 may be a meniscus positive optical lens.

Diopter, or refractive index, refers to the degree to which an optical lens or similar optical system converges or diverges light. For two or more thin optical lenses in close proximity, the refractive index of the combined optical lens can be approximately equal to the sum of the refractive indices of each optical lens. Similarly, the refractive index of a single optical lens can be approximately equal to the sum of the refractive indices of each surface.

In one embodiment, additional surfaces of a single optical lens in an optical lens configuration may provide refractive surfaces for reducing spherical aberration, astigmatism, and/or field curvature. Therefore, the imaging accuracy of the window can be improved through optical lens configuration.

Figure 6 shows an optical lens structure having a reflective polarizer layer, a quarter wave layer, and a semi-transparent mirror according to an example. The optical lens structure in diagram 600 has two separate optical elements for reflection and refraction. Diagram 600 includes display 612, first optical element 604, second optical element 602, and window 620.

A reflective polarizer layer 606 is displayed on the first surface of the second optical element 602, a semi-transparent mirror 610 is displayed on the first surface of the first optical element 604, and a second surface of the first optical element 604 A quarter wave layer 608 is shown above. The light 626 passing through the first optical element 604, the light 624 located in the gap between the two optical elements, and the light 622 reaching the eyepiece 620 are shown in Figure 600.

In one embodiment, the first surface of the second optical element 602 (facing the first optical element 604) may be provided with a reflective polarizer layer 606. In optically transparent augmented reality systems, polarization management is crucial to improve the ambient contrast and brightness of the display.

Traditional polarizing beam splitter PBS for polarization management can provide excellent performance but may be too bulky for head-mounted devices, while compactness and lightweight are characteristics pursued by head-mounted AR displays.

In one example, a thin reflective polarizer layer 606 can be uniformly laminated over the first surface of the second optical element 602, providing similar performance to a polarizing beam splitter PBS. In a reflective polarizer, unpolarized ambient light can partially pass through, while polarized display light can be reflected by the reflective polarizer. Therefore, the head-mounted augmented reality system can effectively integrate the image displayed by the display 612 with the external world.

然而，反射偏振器可能会面临挑战。在实际实现中，只有大约一半的非偏振环境光可以通过，而另一半被反射回来。在一个示例中，可以在第一光学元件604的第二表面之上提供四分之一波层608，以弥补反射偏振片层606的透射率缺点。

Quarter wave layer 608 can change the polarization state of light waves passing through it by converting linearly polarized light to circularly polarized light. If unpolarized ambient light passes through quarter wave layer 608, it becomes linearly or circularly polarized. Therefore, the transmittance of ambient light can be increased through the reflective polarizer layer 606 .

Wave plates can be made from birefringent materials, such as quartz, mica, or plastic, whose refractive index may vary with linearly polarized light along one or the other of two perpendicular crystallographic axes. The properties of a wave plate depend on the thickness of the crystal, the wavelength of light, and changes in the refractive index. By selecting parameters, it is possible to introduce a controllable phase shift between the two polarization components of the light wave, thereby changing the polarization of the light wave.

In one embodiment, a semi-transparent mirror 610 may be disposed over the first surface of the first optical element 604. A semi-transparent mirror is also called a one-way mirror or a 50/50 mirror. A semi-transparent mirror is a mirror with one side reflecting and the other side transparent.

Light from the display may pass through the semi-transparent mirror 610 and be focused by the first optical element 604 . As light exits the first optical element 604, its polarization may change as it passes through the quarter wave layer 608. Through the gap between the optical elements, light from the display can pass through the reflective polarizer layer 606 and be further focused by the second optical element 602 to the viewing window 620 .

Unpolarized light from the environment may pass through semi-transparent mirror 610 and be focused by first optical element 604 . When exiting the first optical element 604, light from the environment may be at least partially polarized by the quarter wave layer 608. Partially polarized light from the environment can pass through the gap between the optical elements and at least partially through the reflective polarizing layer 606 into the second optical element 602, and the second optical element 602 can further Focus on the window 620.

Some of the light from the environment that may be reflected by the reflective polarizer layer 606 may pass through the quarter wave layer 608 of the first optical element 604 and be reflected back by the semi-transparent mirror 610 . Since the reflected light is further polarized by the quarter wave layer 608 , the reflected light can pass through the reflective polarizing layer 606 and reach the viewing window 620 .

Therefore, light loss to the environment can be greatly reduced.

In one embodiment, the optical lens structure may comprise an assembly of two optical elements connected together with an air gap in between. Optical materials can be affected by chromatic dispersion, which can cause signals to be scattered at different wavelengths. Example optical lens structures may utilize two complementary dispersive optical elements to compensate for dispersion and have optical lens structures with similar focusing capabilities across the entire wavelength range.

Therefore, achromatic optical lens structures can limit the effects of chromatic and spherical aberration.

In one embodiment, one of the optical elements may be a negative (concave) element with higher dispersion, while the other optical element may be a positive (convex) element with lower dispersion.

Traditional dual-lens construction typically uses two lenses glued together without a gap or with a liquid such as grease to fill the gap, but this implementation may not solve the headset's size and weight issues. For example, an optical lens configuration with an air gap between two optical elements may allow for thinner, lighter optical lenses that may be easier to manufacture.

For example, an optical lens structure may be formed by mechanically or chemically securing two optical elements along its peripheral edges. In other cases, an inert gas or similar gas may be used to fill the void instead of air.

In diagram 600, first optical element 604 and second optical element 602 are shown as plano-convex optical lenses. Additionally, a reflective polarizer layer 606, a quarter wave layer 608, and a semi-transparent mirror 610 are shown on certain surfaces of the first optical element 604 and the second optical element 602.

7A-7E illustrate various configurations of reflective polarizer layers, quarter wave layers, and semi-transparent mirrors in optical lens configurations.

In diagram 700A, for simplicity, first optical element (L1) 710 and second optical element (L2) 712 are represented as uniform optical lenses. The first surface (facing the display) 702 of the first optical element (L1) 710 may be designated L1S1. The second surface (facing the viewing window) 704 of the first optical element (L1) 710 may be designated L1S2. The first surface (facing the display) 706 of the second optical element (L2) 712 may be designated L2S1. The second surface (facing the viewing window) 708 of the second optical element (L2) 712 may be designated L2S2.

Diagram 700B of FIG. 7B shows a first example structure, in which a reflective polarizing layer 722 can be disposed on the first surface of the second optical element (L2S1), and a quarter can be disposed on the second surface of the first optical element (L1S2). A wave layer 724 is provided, and a semi-transparent mirror (50/50 mirror) 726 may be provided on the first surface of the first optical element (L1S1).

Diagram 700C of Figure 7C shows a second example configuration in which a quarter wave layer 724 may be provided on the second surface of the first optical element (L2S1) and on the first surface of the first optical element (L1S1). A reflective polarizing layer 722 is provided, and a semi-transparent mirror 726 may be provided on the first surface of the first optical element (L1S1). In this configuration, the second optical element (L2) 714 may function as an aberration correcting lens.

Diagram 700D of Figure 7D shows a third example configuration in which a quarter wave layer 724 may be disposed on the second surface of the second optical element (L2S2) and on the second surface of the first optical element (L2S1) A reflective polarizing layer 722 may be provided, and a semi-transparent mirror (50/50 mirror) 726 may be provided on the second surface of the first optical element (L2S1).

Diagram 700E of Figure 7E shows a fourth example configuration, in which a reflective polarizing layer (RP) 722 can be provided on the first surface of the second optical element (L1S2), and a quarter wave layer can be provided on the reflective polarizing layer 722 724, a semi-transparent mirror 726 may be disposed on the first surface of the first optical element (L1S1).

Figure 8 shows a head-mounted display mounting system with an optical lens configuration according to the invention. Diagram 800 shows a controller 802 managing a lens unit 804, a reflective polarizer unit 896, a quarter wave unit 808, a translucent (50/50) mirror unit 810, and an assembly unit 812.

A single optical element may be provided by a lens unit 804, followed by a reflective polarizer unit 806 applying a reflective polarizer layer on one surface of one of the optical elements. The quarter wave layer can be applied to one surface of the optical element via quarter wave unit 808 or via a reflective polarizer layer and then a semi-transparent mirror is applied to one surface of the optical element via semi-transparent mirror unit 810 .

The processed lenses may be assembled together to form an optical lens structure and then assembled with the remaining components of the head mounted display device 832 by the assembly unit 812 .

Related patents:Meta Patent | Reflective hollow singlet folded optical lens structure

The Meta patent application titled "Reflective hollow singlet folded optical lens" was originally submitted in April 2022 and was recently published by the US Patent and Trademark Office.