Patent Application
20240027823
This application claims the benefit under 35 USC 119 (a) of Korean Patent Application No. 10-2022-0088993 filed on Jul. 19, 2022 in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference for all purposes.
The present disclosure relates to a lens that can be used by a hologram, an augmented/virtual reality display, and the like, and more particularly to a meta-lens using a meta surface.
A meta surface is an ultra-thin planar optical device made by arranging nanostructures, also known as ‘metaatoms,’ smaller than a wavelength of incident light. Required light characteristics (amplitude, phase, polarization, and the like) can be adjusted through such nanostructures. A color filter enabling printing of a white light structural color while controlling a reflection amplitude for each pixel using such a meta-surface may be implemented, and a hologram may be implemented while adjusting a phase for each position. Meanwhile, it can also be applied to a lens adjusting a focus according to light characteristics (amplitude, phase, and the like) while passing light, known as a meta-lens.
Meanwhile, in order to implement a hologram, a virtual reality or an augmented reality display, use of a lens is essential. A lens for this purpose should be capable of implementing multifocality. A conventional lens for implementing multifocality consists of mechanically moving a bulky glass-based optical device.
However, the conventional method has limitations in that an entire system thereof is heavy and occupies a large volume.
Therefore, it has been proposed to use a light and thin meta-lens, but there were limitations in implementing multifocality. For example, when multifocality is implemented using light in a visible light wavelength range, there were limitations in that it is not easy to make the light in the visible light range has two or more multifocal points.
There is a growing interest and demand for a lightweight device capable of overcoming these limitations and implementing multifocality.
An aspect of the present disclosure relates to a metal lens, and relates to a multifocus meta-lens capable of forming two or more multifocal points.
The object of the present disclosure is not limited to the above. Those skilled in the art to which the present disclosure pertains will have no difficulty in understanding the additional tasks of the present disclosure from the overall details of the specification of the present disclosure.
According to an aspect of the present disclosure, a multifocus metal lens includes: a liquid crystal layer; and a meta-lens coupled to one or both surfaces of the liquid crystal layer, wherein a nanostructure is formed on a surface of the meta-lens.
The patent or patent application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing (s) will be provided by the Office upon request and payment of the necessary fee.
The above and other aspects, features, and advantages of the present disclosure will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:
The terms used herein are intended to describe the present disclosure and are not intended to limit the present disclosure. Also, the singular forms used herein include the plural forms unless the related definition clearly dictates the contrary.
The meaning of “comprising” as used in the specification specifies a component, and does not exclude the presence or addition of other components.
Unless defined otherwise, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present disclosure belongs. The terms defined in the dictionary are interpreted to have a meaning consistent with the related technical literature and the currently disclosed content.
Hereinafter, specific embodiments of the present disclosure will be described in detail with reference to the drawings.
The liquid crystal layer 120 and the meta-lens 110 may be one or more, and the meta-lens 110 may be bonded to both sides of the liquid crystal layer 120 as well as one surface thereof. The liquid crystal layer 120 and the meta-lens 110 are preferably disposed in parallel on a path of light, and in this case, the liquid crystal layer 120 and the meta-lens 110 may be bonded to each other through arrangement, adhesion, lamination, or the like.
The liquid crystal layer 120 is not particularly limited, and the type or form thereof is not limited as long as it can be applied to the present disclosure.
In the liquid crystal layer 120, an arrangement state of liquid crystal molecules is changed according to an applied voltage, and thus a polarization state of incident light is changed.
The meta-lens 110 has a nanostructure 111 formed on a substrate. The nanostructure 111 has different structural variables (height H, width Lx, length Ly, rotation angle α) on a plane of the substrate. The structural variables of the nanostructure 111 are determined by various factors such as a phase effect according to the polarization state of incident light, a target incident wavelength, a size and focus of a meta-lens, and the like.
The phase delay effect is determined by considering a propagation phase (φ(x,y)) and a geometric phase (θ(x,y)), while
For a detailed description of this, in order for the metal lens to operate and focus on one focal point, a phase equation should satisfy the following lens equation.
ψ(x,y) is a phase at a (x,y) coordinate, λ is an operating wavelength, and f is a focal length. In this case, since it has different focal lengths depending on the type of circular polarization (left-circularly polarized (LCP), right-circularly polarized (RCP)), an f value may vary depending on the incident light, and accordingly, the required phase may also change (ψRCP(x,y) and ψLCP(x,y)). As light of circular polarization passes through meta-atoms, two elements are generated: a propagation phase (φ(x,y)) and a geometric phase (θ(x,y)). In this case, in order to make the light converge at different focal lengths according to circular polarization, the following equation should be satisfied.
ΨRCP(x,y)=Φ(x,y)+2θ (Equation 2)
ΨLCP(x,y)=Φ(x,y)+2θ (Equation 3)
If equations 2 and 3 are combined and expressed as equations for the propagation phase and the geometric phase, which is as follows.
Meanwhile, as an example of the meta-lens 110, a nanostructure of hydrogenated amorphous silicon (a-Si:H) may be formed on a fused silica glass substrate. Since the fused silica substrate has an n value (refractive index) of about 1.46 and a k value (extinction index) close to 0 at a wavelength of 633 nm, which is a visible light region, it is suitable for making a transmissive metasurface.
As a material for the nanostructure 111, a material having a high n value to effectively refract light and a k value to minimize loss, should be used, a-Si:H, a material satisfying this requirement, was used. Using the same, a basic set was constructed by selecting 8 meta-atoms satisfying the condition that a transmittance is close to 1, and an average transmittance of the 8 meta-atoms was about 95%.
Meanwhile, in the method of manufacturing the meta-lens, a nanostructure is formed on a substrate of the meta-lens, and in this case, it may be manufactured using an E-beam lithography process. As an example of a method for manufacturing the meta-lens of the present disclosure, first, an a-Si:H layer having a thickness of 500 nm is deposited by plasma enhanced chemical vapor deposition (PECVD), and then an electron beam is focused on a coated positive tone photoresist, PMMA, so that a desired shape of the structure is formed. Next, after depositing a chromium layer to be used as an etching mask, and then removing the remaining etching mask after a dry etching process, the nanostructure of the metal lens is finally completed.
The light formed on the focal point while passing through the metal lens was enlarged through an objective lens, and an image was captured by the camera. A microscope set-up was mounted on a stage, and a total of 195 images per polarization were stacked by setting a moving distance of the stage to 0.03 mm to obtain a final focus test result of
Looking at the results of
As forth above, according to the present disclosure, an ultra thin lens may be provided by overcoming the limitations of an existing heavy and bulky multifocal lens system. In addition, a multifocus meta-lens capable of implementing multifocality, which was difficult to implement in a visible light region.
In particular, a lens that can change the focus in real time according to polarization through a liquid crystal, and can be applied to variable beam steering requiring fast focus conversion, hologram devices, augmented/virtual reality display technologies, and the like, since a conversion speed of the liquid crystal is fast, may be provided.
Various and beneficial advantages and effects of the present disclosure are not limited to the above description, and will be more easily understood in the process of describing specific embodiments of the present disclosure.
While the example embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0088993 | Jul 2022 | KR | national |
