Abstract

The optical vortices are known as light waves with helical phase front and are associated with the Laguerre-Gaussian (LG) modes. In order to evaluate optical vortices quantitatively, measurement of orbital-angular-momentum (OAM)-resolved spectrum [1], which indicates power distribution as a function of topological charge m, has been widely utilized so far. It is reasonable because their unique characteristics come from the helicity of the phase front which is determined by topological charge (in different words, azimuthal index). However, the OAM resolution, as has been sometimes misunderstood, does not lead to the expansion into LG modes which are propagation eigenmodes in free space. For more precise evaluation of optical vortices, eigenmode expansion with respect to both azimuthal index m and radial index p is an important issue.

© 2015 IEEE