PURPOSE: To reduce the cost of a light applied sensor, to increase its accuracy, and to improve the easiness in use by obtaining two light outputs required to remove light intensity and loss variations by using a polarization beam splitter, etc.

CONSTITUTION: Light emitted by a light emitting element 1 is incident on an opto-elastic material 51 through the polarization beam splitter 41, etc. The light passed through the material 51 has its optical path bent by 80° through a right-angled prism 61, but its two orthogonal polarized components become out of phase. The light passed through this prism 61 is incident on the splitter 41 again through the material 51. This splitter 41 operates as an analyzer. The incident on the splitter 41 is separated into two polarized components; one component is guided to an optical fiber 10 through a microlens 8 and the other polarized component is guided to an optical fiber 11 through a right-angled prism 61 and a microlens 9. The light components incident on the fibers 10 and 11 reach photodetecting elements 12 and 13 respectively, whose outputs are processed electrically to obtain an accurate pressure measured value.