PURPOSE: To obtain a high sensitivity and high accuracy optical magnetic flux meter, by applying magnetic field to be measured to the magnetostriction material sheathed on a polarization plane naintaining optical fiber to which light is incident from a light source, and interfering light propagating the fiber and reference light while subjecting the inteferred light output to photoelectric conversion to perform phase detection.

CONSTITUTION: Laser beam from a laser source 1 is linearily polarized by a polarizer 2 and beam straightly advanced through a half mirror 3 is incident on a polarization plane maintaining optical fiber 5 through a condensing lens 4a. A magnetostriction material 7 comprising Ni is sheathed on the outer periphery of the fiber 5 through an epoxy resin layer 6 and the direction of the incident end of the fiber 5 is adjusted so that linearly polarized beam is incident on the inherent polarization axis of the fiber 5. The emitted beam of the fiber 5 is subjected to S-polarization through a collimating lens 4b and imparted to a phase detector 9 while reflected by a beam splitter 8. On the other hand, the beam reflected by the mirror 3 is subjected to P-polarization to be incident on the splitter 8 as reference beam while transmitted beam is imparted to the detector 9. The detector 9 applies photoelectric conversion to beam output to detect phase difference and high sensitivity and high accuracy optical magnetic flux meter can be formed.