Optical spectrum analyzer

An optical spectrum analyzer having a light incident portion that is inputted measurement target light, a collimator that converts the measurement target light incident on the light incident portion into parallel light, a diffraction grating that diffracts the parallel light, and a condenser that condenses diffracted light from the diffraction grating, the optical spectrum analyzer comprising:

• a polarization separation portion that separates the parallel light emitted from the collimator into light of two polarization components and outputs the light to the diffraction grating;
• a fixed slit that is disposed at a position at which diffracted light of each polarization component is condensed by the condenser;
• a 2-core ferrule that separately takes in the diffracted light of each polarization component that has passed through the fixed slit;
• two light receiving portions that each photoelectrically convert the diffracted light of each polarization component taken into the 2-core ferrule;
• and
• a signal processing portion that processes an electric signal output by each of the two light receiving portions to obtain an optical spectrum, wherein
• each polarization plane of the two polarization components separated by the polarization separation portion is incident on the diffraction grating in a state of being shifted by 45 degrees in opposite directions from each other with respect to an engraved line of the diffraction grating, and
• the fixed slit is fixed to an end portion of the 2-core ferrule in a state where the diffracted light of each of the two polarization components can pass therethrough.