Optical fiber unit for optical fiber sensor

An optical fiber unit for an optical fiber sensor, the optical fiber unit comprising:

• an optical fiber cable;
• a shaft including a peripheral surface having a male thread, and a through-hole in which the optical fiber cable is inserted;
• and
• a head shaped as a polygonal prism including a plurality of sides and a bottom connected to the shaft, the plurality of sides including a first side and a second side adjacent to each other, the head includes a space that communicates with the through-hole, the space exposed at an opening formed in at least the first side and the second side among the plurality of sides, the opening including a first opening portion formed in the first side and a second opening portion formed in the second side, the first opening portion and the second opening portion communicating with each other to allow the optical fiber cable free movement across the two openings, wherein
• the optical fiber cable is positioned through the space and extends from the opening.