Abstract: A single mode fiber is provided which is suitable for high-speed, large-capacity optical communication and for optical wiring. The single mode fiber has a first cladding region with a uniform refractive index, a core region with a refractive index higher than that of the first cladding region, and a second cladding region including at least four air hole regions placed in the first cladding region. Optimization can be achieved by making the distance from the center of the core region to the air hole regions equal to 2–4.5 times the core radius, and the air hole radius equal to or greater than 0.2 times the core radius. It is preferable the core radius be 3.7–4.8 ?m, the relative index difference of the core region from the first cladding region be 0.3–0.55 %.

Abstract: A single mode fiber is provided which is suitable for high-speed, large-capacity optical communication and for optical wiring. The single mode fiber has a first cladding region with a uniform refractive index, a core region with a refractive index higher than that of the first cladding region, and a second cladding region including at least four air hole regions placed in the first cladding region. Optimization can be achieved by making the distance from the center of the core region to the air hole regions equal to 2-4.5 times the core radius, and the air hole radius equal to or greater than 0.2 times the core radius. It is preferable the core radius be 3.2-4.8 ?m, the relative index difference of the core region from the first cladding region be 0.3-0.55%.

Abstract: In a method for manufacturing an optical fiber having a core portion for waveguiding lights, and a plurality of holes arranged around the core portion, the optical fiber is manufactured by puncturing the holes in a glass rod that is to become the optical fiber, by using an ultrasonic drill, and then drawing the glass rod with the holes to form the optical fiber.

Abstract: A high-power acceptable optical fiber comprises a core and cladding provided on the outer peripheral surface of the core. The dopant concentrations in the core and cladding each change in the axial direction of the optical fiber. The core has a same relative refractive index profile in any cross section thereof taken in a direction perpendicular to the axial direction thereof. The relative refractive index profile is normalized by a maximum refractive index of the core.

Abstract: A single-polarization optical fiber comprising a core, an inner cladding surrounding the core, an outer cladding surrounding the inner cladding and at least one pair of stress-applying portions each of which are partially extended into both the inner and outer claddings and which are symmetrical about the axis of the core and having thermal expansion coefficient higher than those of both the inner and outer claddings. When the refractive index of the stress-applying portions is lower than that of the core and higher than that of the inner cladding and further not higher than that of the outer cladding, one of orthogonally polarized mode is cutoff and only one polarized mode can propagate in the optical fiber.