Lens thinner than the light it bends and focuses

Discussion in 'Architecture & Engineering' started by Plazma Inferno!, Jun 3, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

    A lens has been built that is thinner than the waves of light it focuses. Such lenses, made from light-warping metamaterials, might someday replace the heavier glass lenses used in everything from microscopes to phone cameras.
    In a normal lens, a curved glass surface a few millimetres or even centimetres thick redirects light rays to a common focal point. To improve the image – say, to take out distortions, or make sure different wavelengths of light all get focused correctly – you have to keep adding glass layers.
    As a result, cameras, microscopes and telescopes are limited in part by the size and heft of the lenses they require.
    Designers say that virtual reality has the same problem. In order to having high-resolution imaging systems, users end up wearing heavy helmets.
    Metamaterials, by contrast, can bend light towards a common point using structures that are as small or smaller than the wavelengths of the light waves themselves.


    I wonder would it be possible applying these metamaterials to contact lenses?
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  3. iceaura Valued Senior Member

    This first one requires not only monochromatic but - reading the offhand mention in the middle of the article - polarized light.

    The pattern, or rather apparent absence of pattern, of the "nanofins" is interesting - resembles to my eye acoustical tilings designed to dampen reflections. I can't tell - does anyone know where - or if - the center axis of the focus is in that photo?
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  5. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Making a huge glass lens for a light house beam was not possible until French physicist and engineer Augustin-Jean Fresnel made the multi-part thin lens for use in lighthouses. According to Smithsonian magazine, the first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary; its light could be seen from more than 20 miles (32 km) out.[4] Scottish physicist Sir David Brewster is credited with convincing the United Kingdom to adopt these lenses in their lighthouses.[5][6]

    They are much cheaper than regular lens of only 1/10 their area. I have square one, a foot on each edge, that is no more than a mm thick. I think I bought it from Edmond's Scientific for a couple of dollars + shipping, decades ago.

    If the micro structures has wave length of light size, or less, it will be more like a grading than lens - each wave length will be refracted differently and if they do not have very regular separation then the light will just be scattered, not focused.

    PS Once there were many more fresnel lens light houses than now, but other navigation aids replaced most of them. Sadly very few of these wonderful, complex glass structures now exit - most were just broken up for scrap glass. I guess that is "progress" but does not seem so to me. I'm ok with fax machines being destroyed for their scrap. - They were never technological "works of art."
    Last edited: Jun 4, 2016
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  7. Q-reeus Valued Senior Member

    From the NS article: "It still can’t compete with a glass lens in handling different colours at once, he points out."
    Indeed, and that is the bugbear of such metamaterials. In order to obtain spectacular changes in effective permittivity/permeability hence refractive index, resonant structures are required. And that always means much reduced bandwidth. Hence the limitation to monochromatic light. Which can be partially redressed via multi-layer arrangements - but there goes any perceived advantage in terms of simplicity vs complexity. The one real advantage is then reduced bulk.
    When such lenses can be cheaply made without recourse to inherently expensive electron beam lithography, a genuine competitive advantage may be there, but not before.
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  8. iceaura Valued Senior Member

    According to some supporting material, in Science et al, satisfactory ones can be made via high UV removal of the resist as is common in chip manufacturing. The key apparently was not the electron beam, but the technique of making the fins by cutting holes into a thick resist, filling them with the refractive material via an inherently smooth deposition method, then removing the overdeposition layer and the remaining resist.

    If I'm reading this stuff correctly.

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