Phase plate and phase plate manufacturing method

Abstract

The invention relates to a phase plate which is easy to manufacture such as to have a desirable characteristic and the like. The phase plate (10) is substantially shaped like a circular cylinder and has a fixed refractive index in a direction along a center axis (AX) of the circular cylinder. The phase plate (10) also has plural regions (11-18) sequentially arranged as concentric circles from the center in a cross section perpendicular to the center axis (AX). The boundary between two adjacent regions in the regions (11-18) can be distinguished by the difference between refractive indexes. Each of the regions (11, 13, 15, 17) has a refractive index n1, while each of the regions (12, 14, 16, 18) has a refractive index n2 (≠n1).

Dependencies are inferred from the claim text.