Magnetic sensor

A magnetic sensor utilizing a phenomenon in which a plane of polarization of light traveling through a Faraday element rotates in proportion to the strength of a magnetic field, said magnetic sensor comprising:

• light output means;
• light branching means connected to said light output means through first light transmitting means;
• a sensor head connected to said light branching means through second light transmitting means;
• light detecting means connected to said light branching means through third light transmitting means;
• and
• computing means for receiving detected signals from said light detecting means;
• said sensor head including optical means, a first birefringent plate, a first Faraday element and reflecting means arranged in series from an end of said sensor head connected to said second light transmitting means;
• said light output means outputting light;
• said light branching means receiving the light transmitted from said light output means through said first light transmitting means, and emitting the light to said second light transmitting means;
• said optical means of said sensor head converting the light transmitted from said light branching means through said second light transmitting means into parallel light;
• said first birefringent plate of said sensor head separating the parallel light received from said optical means into two polarized rays having planes of polarization orthogonal to each other with respect to an optical axis of said first birefringent plate;
• said first Faraday element of said sensor head transmitting the two polarized rays from said first birefringent plate, and converting the strength of a magnetic field to be detected into a rotating angle of the planes of polarization of the two polarized rays;
• said reflecting means of said sensor head reflecting the two polarized rays transmitted through said first Faraday element, back into said first Faraday element, such that each of the two polarized rays reciprocates along the same optical path;
• said first birefringent plate of said sensor head separating each of said two polarized rays returned from said first Faraday element into two polarized rays (four polarized rays in total) orthogonal to each other and having an amplitude level corresponding to the rotating angle of the respective polarized rays;
• said optical means of said sensor head selectively transmitting two orthogonal polarized rays returning along optical paths substantially the same as incidence optical paths, among the four polarized rays emitted from said first birefringent plate;
• said light branching means branching the two polarized rays transmitted from said optical means through said second light transmitting means, to said third light transmitting means:
• said light detecting means detecting light intensities of the two polarized rays transmitted from said light branching means through said third light transmitting means;
• and
• said computing means deriving the strength of the magnetic field from the light intensities detected by said light detecting means.