CURRENT MEASURING APPARATUS USING POLARIZATION PLANE-PRESERVING OPTICAL FIBER

PURPOSE:To achieve a proper stability respect to external force and temperature characteristic of the light source along with a high accuracy by arranging incident and emission side polarization preserving optical fibers on a transmission path to receive incident light from a branch unit with light receiving element through two polarizers. CONSTITUTION:Light from a light source 11 is made linear polarized light with a polarizer 12 and a 1/2 wavelength plate 13 enters an incident side polarization plane preserving optical fiber 14 at an azimuth the same as in one axial direction. The linear polarized light propagated through the fiber 14 passes through a Faraday rotation element 16 as parallel beam with a rod lens 17 at the emission end and enters an emission side polarization plane preserving optical fiber 19 with a rod lens 18. Light from the fiber 19 is made to enter a branch unit 20 for the polarization plane preserving optical fiber and divided into two parts, which are respectively received with light receiving elements 23 and 24 through two polarizers 21 and 22 with the azimuths respectively aligning two axes of the fiber 19. This ensures a proper stability respect to external force and temperature characteristic of a light source along with a high accuracy.