title: Comment on the expression of a distributed index.
abstract: The expression of a distributed index by way of power series expansion is commented on from the viewpoints of wave optics and ray optics. A 3-D expression is also proposed.
authors.affiliation: Tokyo Institute of Technology, Research Laboratories of Precision Machinery & Electronics, 4259, Nagatsuta, Midoriku, Yokohama, 227, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Iga