Certain molecular lengths measured by an optical lever

Abstract

Concepts of electronic band structure theory can be used to describe the behavior of light waves in periodic dielectric media. The periodicity involved can be microscopic as well as macroscopic. This chapter discusses the realization of a photonic band structure with a macroscopic periodicity, namely an effectively rotating fiber ring. A dielectric structure was introduced by means of an air gap in the ring, and rotation was simulated by means of the Faraday effect. The “valence” and “conduction” bands of a photon band structure were mapped and band gaps were manifested as doublet and quartet splittings. Because of the macroscopic nature of the system, typical orders of magnitude of the quantities involved are very different from those in semiconductor physics. The light wave in the ring is a pure standing wave at the top of the “valence” band and also at the bottom of the “conduction” band. The difference between these two standing waves is that a node or an antinode is present at the air gap; the resulting difference in dielectric polarization energy determines the magnitude of the optical band gap. The macroscopic nature of the system has important advantages for basic study because it allows easy manipulation of the parameters of the band structure, which is not possible for the microscopic case.