Abstract: “An improved lightguide element design for a keyboard with optical coding is proposed in the article, based on the phenomenon of light reflection from the interface of two optical transparent media. A feature of this element is the use of relatively large values of the reflection coefficient from the medium interface at large angles of incidence, which is expressed, in particular, by the Fresnel formulas. This effect occurs also in the case when light passes from an optically less dense medium (air) to an optically denser (polymer), which, in particular, makes it possible to use a hollow polymer tube as a lightguide element. A differential equation is obtained that describes the shape of the initial section of an improved lightguiding element of a given type, as well as its analytical solution. This type of solution corresponds to a surface optical trap whose shape corresponds to multiple reflection of the rays from the same non-planar surface.”

Keywords: media interface, reflection coefficient, lightguide elements, Fresnel formulas, optical trap