JPS646841A - Detecting device - Google Patents

Abstract

PURPOSE:To utilize incident light effectively, to make the optical waveguide in a photoconductive medium longer, and to reduce the size of a detecting device without increasing the capacity of the photoconductive medium by adding polarizing filters to an incident light part and a photodetection part. CONSTITUTION:At least part of the flank of the plate type photoconductive medium 1 is covered with a reflecting layer 2 and a sensing layer 3 varies in double refractive index by sensing a material to be measured which is present in gas or liquid. A polarizing filter 16 is added to the incident light part and the incident light beam is polarized by 45 deg. and made incident, so that the light incident on the reflecting layer 2 almost at right angles has its initial polarization state nearly maintained when reaching the photodetection part and the polarizing filter of the photodetection part cuts the majority of the light. Further, a light beam which is reflected totally by the border surface between the photoconductive medium 1 and sensing layer 3 changes in polarization state every time it is reflected totally and enters a nearly random polarization state when reaching the photodetection part, so that the light reaches a photodetecting element without reference to whether or not the polarizing filters are provided.