Rotary joint and optical measurement device using the same

An optical measurement device comprising the rotary joint including:

• a first fiber holding portion that holds a plurality of optical fibers included in a first optical cable such that a first end face of a first inner optical fiber included in the first optical cable is disposed in a first circular area and a second end face of a group of first outer optical fibers included in the first optical cable is disposed in a first annular area that is concentric with the first circular area and has an inner diameter larger than a diameter of the first circular area;
• a second fiber holding portion that holds a plurality of optical fibers included in a second optical cable such that a first end face of a second inner optical fiber included in the second optical cable is disposed in a second circular area and a second end face of a group of second outer optical fibers included in a second annular area that is concentric with the second circular area and has an inner diameter larger than a diameter of the second circular area;
• a rotation support portion that relatively and rotatably supports the first fiber holding portion and the second fiber holding portion such that the first circular area and the second circular area are separated from and opposed to each other and the first annular area and the second annular area are separated from and opposed to each other;
• and
• a light separating portion that is provided between the first fiber holding portion and the second fiber holding portion and inhibits passage of light between a columnar space and a cylindrical space, the columnar space being provided between the first circular area and the second circular area, the cylindrical space being provided between the first annular area and the second annular area.