Re: MIT Mirror Technology

Ron Kean (
Mon, 22 Feb 1999 21:12:10 -0500

On Mon, 22 Feb 1999 10:48:37 -0800 (PST) Terry Donaghe <> writes:
>I remember reading an article a couple of months ago about a new
>technology some guys at MIT were working on that involved mirrors
>were nearly 100% reflective. One of the things they built using
>new ideas was a fiber optic cable that was coated on the inside with
>this kind of mirror.
>Does anyone know what I'm talking about and does anyone have links to
>somewhere where I can find out more...
>I have no idea where I read this or if it's even true.
>Any help is greatly appreciated!

There are two kinds of 'mirrors'. (1) opaque (generally metal) , and (2) refractive. A given metal mirror exhibits just about the same reflectivity, regardless of angle of incidence, for any given wavelength.

Refractive materials (which are usually not called mirrors), exhibit high or total reflection when the light hits the index change interface at a shallow enough angle. Light which hits a glass window at a shallow angle reflects off the window in proportion to the cosine of the angle between the light direction and the plane of the glass. Light inside glass bounces off the glass to air interface (100% if the angle is small enough). That phenomenon is often called 'total internal reflection'. A simple glass fiber generally internally reflects light travelling thru it without any reflection loss, without the designer doing anything special, because the direction of incidence is nearly parallel to the axis of the fiber, and the fiber has a higher index than the air or vacuum around it. 'Graded index' fibers are also used which bend the light in the outer layers towards the central axis of the fiber.

I don't have any info on a new mirror from MIT.

Ron Kean

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