Measurement of loss and output numerical aperture of optical fiber splices

An ensemble of optical fiber splices has been evaluated to determine how source launching conditions and length of fiber between the source, splice, and detector affect the splice loss and far field output NA. The loss of a splice is strongly dependent upon the energy distribution and NA of the beam at the input of the splice. For the range of NA's considered, the splice loss varied by 0.5 dB. The average NA at the output of the ensemble of splices was greater than its corresponding input NA by as much as 12%. The splice appears to act as a transformer converting the input energy distribution into one at the output that contains a greater amount of its energy in higher order modes. As a consequence of this, the loss of a fiber following the splice in a long transmission path is greater than the loss the fiber would exhibit if measured with steady state excitation conditions.