Fig. 8.

Relative signal gain among the different fiber geometries. Spatial distribution of the collection gain for (A) axicon-lensed and (B) hemispherical fibers as compared to the bare fiber. White contours represents the collection gain of 1; improved photon collection over the bare fiber shown by the warmer color region. (C) Relative signal gain between axicon and hemispherical fibers. The figure clearly demonstrates that the axicon lensed fiber provides enhanced photon collection over a much wider range than the hemispherical counterpart, except very near the region of the fiber tip.