In the article [1], a profile of the refractive-index contrast (relative to the background medium) for the graded-index microsphere was used for the numerical simulations. However, a typo appeared associated with the material parameters of the graded-index microsphere. This is corrected below.

Specifically, Eq. (1) provides the refractive-index contrast profile n(r) for the graded-index microsphere. This equation should read:

ε_r,max is set to 2 for all of the numerical simulations in this paper. Thus, the refractive-index contrast n(r) properly has a maximum value of 2 at the center of the microsphere, and decreases in the radial direction to a minimum value of 1 at the microsphere surface. Before this correction, the maximum n(r) at the microsphere center in Ref [1]. was improperly given as 2.

The authors regret the typo. Please note, however, that it does not affect any of the numerical results presented in [1].