Patent ID: 7693377

Claim:
An optical fiber module comprising: an optical fiber that transmits a light, the optical fiber including a first core region formed at a center of the optical fiber, a second core region formed around the first core region and having a refractive index lower than a refractive index of the first core region, and a cladding region formed around the second core region and having a refractive index higher than the refractive index of the second core region and lower than the refractive index of the first core region, a ratio of diameter of the first core region to outer diameter of the second core region from 0.3 to 0.85, a relative refractive index difference between the first core region and the second core region from 1.6% to 3.0%, and a relative refractive index difference between the second core region and the cladding region from −1.2% to −0.2%; and a holding unit that holds the optical fiber in a state in which the optical fiber is stretched in its longitudinal direction to change optical characteristics of the optical fiber.