Optical loss measurement in graded-index fiber using a dummy fiber

The utility of an auxiliary fiber, called a dummy fiber, is investigated for optical fiber loss measurements. The dummy fiber is spliced and used to excite the test fiber. Excess loss caused by undesirable modes is found to be reduced to less than 0.05 dB by using a 500-m dummy fiber and choosing the test fiber cut length to be 2 m for reference. Loss linearity to the fiber length is examined on 6-km spliced fibers, and satisfactory agreement is obtained between the total loss and the sum of the individual fiber and splice losses.