Determining optical fiber types

A device for determining the type of an optical fiber, the device comprising:

• heating means for heating a region of the optical fiber to such a temperature that an observable amount of light is emitted,
• an optical system for imaging the region of the optical fiber,
• light sensitive means for recording light emitted when heating the region and imaged by the optical system as a first picture,
• determining means connected to the light sensitive means for determining from the first picture a first light intensity profile comprising values of the intensity of light emitted from all points in a line substantially perpendicular to the longitudinal direction of the fiber, as viewed in an observation direction, as a function of the position along the line, and
• analyzing means connected to the determining means for analyzing the determined light intensity profile,
• characterized in that the analyzing means comprise:
• calculating means for calculating the derivative of the determined first light intensity profile,
• comparing means connected to the calculating means for comparing derivatives of light intensity profiles previously determined for a plurality of optical fibers of known different types to the calculated derivative of the first light intensity profile, and
• decision means connected to the comparing means for deciding, in the case where a signal provided by the comparing means indicates that for one of the optical fibers of known different types, the calculated derivative deviates least from the derivative of the light intensity profile of said one of the optical fibers, that the optical fiber is the same type as said one of the optical fibers.

A method of automatically setting an optical system for imaging an optical fiber, characterized by the steps of:

• varying the distance between the optical fiber and the optical system to give pictures,
• determining from each of the pictures a light intensity profile comprising values of the intensity of light emitted from all points in a line substantially perpendicular to the longitudinal direction of the fiber, as viewed in an observation direction, as a function of the position along the line, and
• analyzing the determined light intensity profile to find in the picture a measure of the apparent diameter of the optical fiber and a measure of the width of a central peak,
• calculating the ratio of the measures and comparing it to a predetermined value, and
• setting the distance for a correct imaging so that the ratio substantially agrees with the predetermined value.