Faraday rotator and optical device employing the same

A Faraday rotator comprising:

• a magneto-optic crystal provided in a light propagation path;
• a first permanent magnet located so that its magnetic field direction forms a first angle with respect to said light propagation path, said first permanent magnet having a first temperature coefficient of a field strength;
• and
• a second permanent magnet located so that its magnetic field direction forms a second angle larger than said first angle with respect to said light propagation path, said second permanent magnet having a second temperature coefficient of a field strength larger than said first temperature coefficient;
• wherein a Faraday rotation angle exhibited on the light passing through said magneto-optic crystal by a synthetic magnetic field generated by said first and second permanent magnets is controlled substantially constant regardless of temperature changes.

An optical device comprising:

• a Faraday rotator comprising a magneto-optic crystal provided in a light propagation path, magnetic field applying means for applying first and second magnetic fields having different directions to said magneto-optic crystal so that a strength of a synthetic magnetic field exceeds a predetermined value, said magnetic field applying means including an electromagnet for generating at least one of said first and second magnetic fields, and driving means for driving said electromagnet;
• a temperature sensor provided adjacent to said Faraday rotator, said temperature sensor being capable of converting a temperature change into a current change;
• and
• control means for controlling said driving means so that a Faraday rotation angle becomes constant according to a temperature detected by said temperature sensor, said control means incorporating data on temperature dependence of the Faraday rotation angle of said magneto-optic crystal.