Optical fiber bending loss measuring method

A method for measuring a bending loss of an optical fiber coated with resin, the method comprising:

• determining a reference number of turns by which a wavelength dependency of a bending loss value of the optical fiber in a region of a predetermined transmission wavelength or less when the optical fiber is wrapped around a mandrel with a predetermined diameter has an exponential function shape with respect to a transmission wavelength;
• causing light with a predetermined power at the predetermined transmission wavelength to be incident on a first end of the optical fiber in a state in which the optical fiber is wrapped around the mandrel by the reference number of turns, and measuring a power of light emitted from a second end of the optical fiber to obtain a first power of light;
• causing light with the predetermined power at the predetermined transmission wavelength to be incident on the first end of the optical fiber in a state in which the optical fiber is wrapped around the mandrel by a number of turns larger than the reference number of turns, and measuring a power of light emitted from the second end of the optical fiber to obtain a second power of light;
• and
• obtaining, based on the first power of light and the second power of light, a bending loss value of the-optical fiber at the predetermined transmission wavelength when the optical fiber is bent with the predetermined diameter.