摘要:
One or more parts of an optical fiber is(are) exposed to a high temperature of gas flame for about 30 minutes so as to form one or more radially expanded core part(s) where a diameter of a core of the optical fiber is increased greater than its original size at a center and moderately decreased back to its original size as departing from the center. A part of the transmitting light leaks to the clad at the radially expanded core part. Leaked light hardly travels through the clad from the radially expanded core part to the output end of the optical fiber. This provides a function of an optical attenuator. Also, the attenuation is precisely adjusted to a desired level by controlling a size of the radially expanded core part. Furthermore, as an incident angle of the transmitting light from the core to the clad at the radially expanded core part becomes greater than conventional one, reflecting back the transmitting light to input side is prevented and the reflectance is minimized.