= Nicholas X. Fang
{c}
= Nick Fang
{c}
{synonym}
A researcher in optics whose MIT teaching develops the connection between wave propagation and optical ray models. The <eikonal equation> relates the local phase gradient to <refractive index>, while optical path length describes how rays traverse an inhomogeneous medium. Deriving these relations from wave physics shows what information a ray model retains and why geometrical optics has a limited regime of validity.<MIT 2.71 and 2.710 Optics, Spring 2014 by Nicholas X. Fang/Optics, Lecture 10: Eikonal Equations, Superposition of EM Waves>[Lecture notes pp. 1–3: eikonal equation, optical path and ray direction]{ref}
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