There is provided an optical rotation measurement apparatus and a measuring system which are user-friendly, capable of measuring glucose concentration in drawn blood and living bodies with high accuracy in real time such that it is available for use at an actual medical site without depending on a reagent, and capable of measuring glucose concentration in a living body noninvasively with high accuracy, a new polarized light converting optical system that can be used for the measuring system, and an optical rotation measurement method using the optical system.The problems are resolved by inserting a non-reciprocal optical system sandwiching a specimen in an optical fiber ring interferometer, using input/ output optical fibers of the non-reciprocal optical system, which are comprised of a large core diameter low NA single mode optical fiber, as an input/ output part, connected via a mode-matching unit to a small core diameter and high NA polarization preserving fiber as a transmission part, and employing a defocused configuration without deploying the optical fiber ends at focal points of lenses.
