Measurement of launching efficiency into multimode optical fibers using semiconductor laser diodes

The launching efficiency of light from semiconductor laser diodes into graded-index multimode optical fiber waveguides has been systematically studied. Four different terminations of the fibers were investigated: plane ends (PE), hemispherical ends (HE), taper-with-hemisphere ends (TE) and roof-top (RT) ends. Besides launching efficiency, the parameters of interest are the various misalignments, such as axial, lateral and angular, between laser and fiber, and the effect of these to produce a reduction in the launching efficiency. For the RT end, this reduction with angular rotation of the fiber about its axis has also been investigated. It has been found that RT fibers increase the launching efficiency from semiconductor lasers considerably, but rotational optimization of the fiber about its axial is essential. This is a considerable disc advantage as most of the other techniques do not require this optimization.