This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2008-0119981, filed on Nov. 28, 2008, the disclosure of which is incorporated by reference in its entirety for all purposes.
1. Field
The following description relates to a hyper-lens, and more particularly, to a projecting type hyper-lens for enlarging an image of the object while converting evanescent waves into propagating waves.
2. Description of the Related Art
The shape of an object can be recognized by imaging light (electromagnetic waves) scattered by the object. With regards to humans, some of the visible rays scattered from an object enter the eyeball, pass through the cornea, and crystalline lens where the visible rays are bent, and finally form an image on the retina where brightness and color of the light are sensed in cells of the retina. Optical signals obtained by sensing the brightness and color of the light are sent to the brain in a manner which allows human to recognize the object.
In general, a resolving power is a degree to which an optical system is able to discern the detail of an image. For example, when an optical system is loosely said as having a resolving power of ‘d’, the optical system is able to distinguish two objects spaced a minimum distance ‘d’ apart from each other. In optical theory, the resolving power obtainable by an optical instrument has an absolute minimum value which is half the value of the wavelength of light used in the optical device.
Accordingly, a conventional optical microscope has a resolving power of just under 200 nm corresponding to half of the shortest wavelength of visible light. If an object to be viewed has a dimension smaller than 200 nm, for example viruses or giant molecules, an electron microscope using an electron beam having a wavelength much shorter than that of visible rays is needed. However, an electron microscope is a highly complicated and expensive piece of equipment compared with an optical microscope.
As an alternative solution to the above problems, an optical microscope having an improved resolving power based on the characteristics of light has come to light. In general, the light scattered from an object has components of evanescent waves and propagating waves having different properties to each other. The propagating wave suffers low loss but offers a maximum resolution of half a wavelength. In the other hand the evanescent wave provides several times higher resolution than propagation wave but suffers very high loss. So in using evanescent wave for image formation the object should be roughly within a half wavelength from the front face of the imaging system. For example in the case of λ/2 dipole antenna, the emitted propagating wave and the evanescent wave have nearly equal amplitude at λ/6 distance from the antenna where λ is the wavelength of the radiated electromagnetic wave and the evanescent wave attenuates to 1/10 of the propagating wave around the half wave distance.
Recently, a device known as a superlens has been developed which is capable of amplifying evanescent waves using surface plasmon [N. Fang, H. Lee, C. Sun, and X. Zhang, “Sub-diffraction-Limited Optical Imaging with a silver Superlens,” Science 308, 534, 2005.]. That is, the superlens allows evanescent waves to be used in forming an image, exceeding a resolution limit of a convention lens.
In this regard, in order for the superlens to amplify the evanescent wave scattered from an object, a distance between a front surface of the superlens and the object needs to be roughly smaller than a half-wavelength of the light. In addition, in order for the superlens to form an image using the amplified evanescent wave, a distance between a rear surface of the superlens and an image plane needs to be smaller than a half-wavelength of the light; and since the superlens offers a real size image, electron microscope is also needed to see the subwavelength image formed by a superlens.
On the other hand, the newly introduced hyperlens is capable of forming a magnified image using an evanescent wave. If a critical size is magnified up to a certain level such as over the half wavelength it is no longer an evanescent wave but a propagating wave. A hyperlens converts evanescent wave to propagating wave in this manner. Since the propagating wave has a low decay rate, the hyperlens can form a magnified image at a location remote from a rear surface of the hyperlens.
But like superlens when imaging an object using a hyperlens, the object needs to move as close as possible to the front face of the hyper-lens such that evanescent waves coming from the object are incident onto the hyper-lens before considerable decay.
Since the front face of a conventional hyperlens is a recessed shape as the inner surface of a cylinder the access of the object and the front face of the hyper-lens may be seriously limited due to the substrate contact problem. In this case, a substrate layer where a main lens layer of the hyperlens is mounted may come into contact with the substrate where the object is mounted, thus the access of the object to the hyper-lens is limited.
Accordingly, in one aspect, there is provided a hyperlens having an improved structure, which allows an object to be effectively moved towards a front surface of the hyperlens until a distance between a front surface of the hyper-lens and the object is smaller than a half-wavelength of the used light. In one general aspect, there is provided a projecting type hyper-lens for forming a magnified diffraction limited image of an object using an evanescent wave component of light coming from the object.
A conventional hyperlens is produced by staking a dielectric thin film and a metal thin film alternately as coaxial semi-cylinders in
The projecting type hyper-lens is made from the conventional hyperlens by etching out a depth of the peripheral region of the hyperlens with the surrounding substrate. In this case the object easily approach the front face of the hyperlens within a half wavelength as in
In another general aspect, there is provided method of manufacturing a projecting type hyperlens. The projecting type hyperlens manufacturing method is performed as follows. First a non-projecting type hyper-lens is formed. The non-projecting type hyper-lens includes a substrate layer and a main lens layer supported by the substrate layer and has a recessed shape. A masking process using photoresist is performed such that a front central portion of the main lens layer is masked with the mask width smaller than the inner diameter of the main lens layer. The unmasked regions are subject to an etching such that the masked front central portion of the main lens layer protrudes beyond a surface of the substrate layer. And the photoresist used for masking is removed finally.
The masking of photoresist comprises coating photoresist on front surfaces of the substrate layer and the main lens layer; and removing a portion of the photoresist, which does not correspond to the central portion of the main lens layer.
In the etching process, the main lens layer is etched such that a foremost portion of the main lens layer is higher than the front central portion by a distance smaller than a half-wavelength of used light.
Side walls of the remained main lens layer are inclined such that the main lens layer has a cross sectional area which is larger toward a rear surface of the main lens layer.
The forming of the non-projecting type hyper-lens includes forming a groove having a semicylindrical shape or a semisphere shape in the front surface of the substrate layer; and forming the main lens layer in the groove through a stacking scheme.
In the forming of the non-projecting type hyper-lens, the main lens layer is formed by alternately stacking a dielectric substance thin film and a metal thin film against on each other on a bottom surface of the groove.
Each of the dielectric substance thin film and the metal thin film has a thickness of about 100 nm or less.
The dielectric substance thin film includes aluminum oxide (Al2O3) and the metal thin film includes silver (Ag).
As apparent from the above description, such a projecting type hyper-lens has a structure allowing an object to be effectively moved towards the hyper-lens until a distance between the object and the hyper-lens is smaller than a half-wavelength of used light. As a result, a far field image of an object smaller than a half-wavelength of used light can be formed using the evanescent waves scattered from an object.
In addition, according to the method of manufacturing the projecting type hyperlens, the projecting type hyperlens can be easily manufactured by using a conventional cylindrical hyperlens having a recessed shape.
Other features will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the attached drawings, discloses exemplary embodiments of the invention.
Elements, features, and structures are denoted by the same reference numerals throughout the drawings and the detailed description, and the size and proportions of some elements may be exaggerated in the drawings for clarity and convenience.
The detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses and/or systems described herein. Various changes, modifications, and equivalents of the systems, apparatuses, and/or methods described herein will likely suggest themselves to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions are omitted to increase clarity and conciseness.
Hereinafter, a projecting type hyper-lens will be described with reference to accompanying drawings.
As shown in
The main lens layer 10 has a front surface having a recessed shape.
The substrate layer 20 supports the main lens layer 10 and is formed of quartz.
In particular, a front central portion 11 of the main lens layer 10 protrudes beyond a surface 21 of the substrate layer 20. Accordingly, a distance between a front surface of the main lens layer 10 and an object is smaller than a half-wavelength of used light. Such a projecting type hyper-lens is suitable for viewing a fine object having a size smaller than half a wavelength of the light.
That is, as show in
That is, such a projecting type hyper-lens is suitable for viewing an object having a size smaller than a half wavelength of used light as compared with a non-projecting type hyper-lens. Hereinafter, the projecting type lens will be described in terms of a structural improvement of the projecting type lens by comparing the projecting type lens with conventional non-projecting type hyper-lenses.
As shown in
If light having a wavelength of 365 nm is radiated normally to the front surface of the main lens layer 60, some evanescent components scattered by the objects propagates to the radial direction and form a magnified far field image behind the substrate.
In practice, the objects 80 are not engraved on the front surface of the main lens layer 60 but are placed on a substrate layer 90 as described in
Different from such a conventional hyper-lens, according to the projecting type hyper-lens of the present invention, the front central portion of the main lens layer protrudes beyond a front surface of the substrate layer, so that the object to be viewed can be effectively adjacent to the main lens layer as compared with the non-projecting type hyper-lens.
Meanwhile, as shown in
In addition, the main lens layer 10 has a sectional area which is larger toward the rear surface thereof. That is, the side walls of the main lens layer 10 are not parallel and converge to a point, so that the light incident onto the front surface of the main lens layer 10 is effectively emitted in a radial manner.
In addition, the main lens layer 10 is formed by alternately stacking a dielectric substance thin film and a metal thin film against on each other.
As shown in
The masking of the photoresist includes coating photoresist on the front surface of the substrate layer and the main lens layer (operation 200) and removing a portion of the photoresist which does not correspond to a central portion of the main lens layer (operation 300).
In the masking of the photoresist, the remaining photoresist is formed to extend vertically from the central portion of the main lens layer forward while maintaining a predetermined width.
The remaining photoresist has a width smaller than an inner diameter of the main lens layer.
Meanwhile, in the removing photoresist which does not correspond to the central portion of the main lens layer (i.e. the portion which is to be removed), an exposure process is performed on the portion of photoresist to be removed and then a development process is performed on the exposed portion.
As shown in
For example, the exposure is performed on the photoresist 52 through UV lithography or e-beam lithography. UV and e-beam cause a chemical reaction on the resist in the UV-lithograpy and the e-beam lithography, respectively.
The above description has been made in relation to the photoresis 52 having a positive property as an example with reference to
Meanwhile, in the etching (operation 400, in
In addition, in the etching (operation 400, in
Meanwhile, in the forming of the non-projecting type hyper-lens (operation 100, in
In this case, the main lens layer (51, in
Although few embodiments of the present invention have been shown and described, the above embodiment is illustrative purpose only. It will be apparent to those of ordinary skill in the art that various modifications can be made to the exemplary embodiments of the invention described above. However, as long as modifications fall within the scope of the appended claims and their equivalents, they should not be misconstrued as a departure from the scope of the invention itself.
Number | Date | Country | Kind |
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10-2008-0119981 | Nov 2008 | KR | national |
Number | Name | Date | Kind |
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20100134898 | Shalaev et al. | Jun 2010 | A1 |
Number | Date | Country | |
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20100134897 A1 | Jun 2010 | US |