Optical fibers a drawn from a preform (large glass bar 30 or 40 mm). To test the quality of the glass before the optical fibers are drawn this accessory can be used in combination with a Agilent Cary 5000.
Mostly 2 bars of different lengths (short and long) are used to determine the ratio of the transmittance. From this the internal transmittance can be determined. So accurate measurements for low absorbance values.