Hologram recording/reproducing apparatus and light source apparatus

A hologram recording/reproducing apparatus that records data as a hologram by applying a signal light beam and a reference light beam to a hologram-recording medium, that obtains a diffracted light beam by applying a reproduction light beam to the hologram recorded in the hologram-recording medium, and that reproduces the recorded data using the diffracted light beam, the hologram recording/reproducing apparatus comprising:

• an external-cavity light source;
• a polarization-control element configured to change a polarization angle of a light beam emitted from the external-cavity light source;
• a polarizing-beam-splitting element configured to split the light beam polarized by the polarization-control element in two directions to obtain two light beams, and configured to change a ratio between amounts of the two light beams on the basis of the polarization angle of the light beam that is determined by the polarization-control element or on the basis of a polarization state of the light beam that is determined by the polarization-control element;
• a photoreceptor configured to receive one of the two light beams obtained by splitting the light beam in the two directions;
• a spatial light modulator configured to receive the other of the two light beams obtained by splitting the light beam in the two directions, and configured to generate a signal light beam, a reference light beam, and a reproduction light beam;
• and
• a control unit configured to perform a control operation of changing, on the basis of a light amount detected by the photoreceptor, the polarization angle or polarization state of the light beam that is determined by the polarization-control element.