Evaluation of star couplers for application to FOAM experiments

The light-splitting properties of several commercial 8 × 8 transmission- type fiber optic star couplers were investigated for use under abnormal launch conditions. A severe modal selection process was observed. The results of this selection process were first observed in the variation of the throughput for each output fiber depending upon the input fiber used. Subsequently the effect on the emitted radiative profile was measured under a variety of launch conditions. Modal selection was maximized when the launch into the coupler underfilled the input fibers of the coupler, and the effect was minimized when the input was overfilled.