Optical fiber, and optical-fiber production method

A method of producing an optical fiber, the optical fiber comprising:

• a core;
• a cladding that is formed on a periphery of the core and has a refractive index lower than that of the core;
• a resin coating that is formed on a periphery of the cladding;
• and
• a colored portion that is provided on a part of an outer surface of the resin coating in a circumferential direction thereof, the method including:
• a light introducing step which introduces light into a core of the fiber;
• a light leaking step which leaks the light introduced into the core to the outside of the optical fiber;
• a light detecting step which detects the light leaked in the light leaking step;
• an optical-fiber rotating step which rotates the optical fiber in a circumferential direction thereof so as to maintain the leaked light detected in the light detecting step to be substantially constant;
• and
• a resin applying step which applies a colored resin on a part of an outer surface of the resin coating in a circumferential direction thereof so that a positional relation between a position of the colored resin and a position of the core is substantially uniform over the longitudinal direction on a cross section perpendicular to the longitudinal direction of the optical fiber.