PM fiber alignment

A device for aligning the polarization axes of fiber ends of two optical polarization maintaining fibers with each other, the device comprising:

• two retainer means, each one arranged to hold an end of an optical fiber and adapted to displace and rotate the end a full turn about the longitudinal axis of the end;
• control means connected to the two retainer means for controlling them to align the longitudinal axes of ends of optical fibers held by the retainer means and to move the ends into a close relationship at a splice position and then to rotate the ends;
• a light source for illuminating by parallel light the ends at the splice position from a side of the ends;
• a TV camera having a light sensitive surface and providing video signals;
• a lens assembly having an optical axis for imaging the splice position taken in an observation plane onto the light sensitive surface, the TV camera thereby capturing images of the splice position;
• processing and analysis means connected to the control means and to the TV camera for processing and analyzing video signals received from the TV camera;
• the control means adapted to control the retainer means to rotate the fiber end in repeated angular steps around the longitudinal axis of the fiber end to take successive angular positions, and then for each angular position to control the processing and analyzing means to determine from the image captured in each angular position a light intensity distribution along a line perpendicular to the longitudinal direction of the fiber end and to determine from the determined light intensity distribution a contrast value h, this resulting for each fiber end in a light contrast profile of h-values determined as a function of the angular position;
• the control means further adapted to control the processing and analyzing means to determine from the determined light contrast profiles the angular positions of the principal polarization axes of the fiber ends;
• and
• the control means further adapted to control the retainer means to rotate the fibers ends in relation to each other by an angle equal to the difference between the determined angular positions of the principals axes of the fiber ends, the control means are arranged to control the retainer means to move the fiber ends so to make the observation plane take a position so that the variation ranges of the determined light contrast profiles obtain largest possible values.