Reflective variable light attenuator

A reflection-type variable optical attenuator comprising:

• a main attenuator unit including a first birefringent crystal plate, a Faraday rotational angle varying unit, and a second birefringent crystal plate arranged in this order, said Faraday rotational angle varying unit including a Faraday element, a permanent magnet that magnetically saturates said Faraday element, and an electromagnet that applies a variable magnetic field to said Faraday element;
• an input port and an output port that are arranged on a side of one end of said main attenuator unit;
• and
• a two-point reflection-type optical path varying reflector that is arranged on a side of the other end of said main attenuator unit;
• wherein said Faraday element has a structure in which a compensating film Faraday element that has a high coercive force and in which a Faraday rotational angle scarcely changes with respect to a magnetic field caused by said electromagnet is arranged between basic film Faraday elements that have been divided into two and in which Faraday rotational angles change according to the magnetic field applied by said electromagnet, and the direction of Faraday rotation of said basic film Faraday elements and the direction of Faraday rotation of said compensating film Faraday element are opposite to each other;
• and
• wherein light that comes in from said input port makes a round trip in said main attenuator unit and goes out through said output port.