Reciprocity in Classical Linear Optics

Masud Mansuripur

A recent informal survey of some optical science colleagues and students revealed that the notion of reciprocity in optics is not widely appreciated. One colleague even justified the prevailing ignorance by drawing a parallel between reciprocity in optics and the correspondence principle in quantum mechanics: "Both are true statements, which have little, if any, practical value in their respective domains." This column is an attempt at explaining the concept of reciprocity, clarifying some associated misconceptions, and pointing out its practical applications.