“…These coupling methods can generally be divided into two groups. One group is to use discrete components as coupling optics, such as ball lenses [ 13, [2], GRIN lenses [3], cylindrical lenses [4], [5], and so on. The other is to integrate a len,s with a single-mode fiber such as hemispherical lensed fibers l [6]-[8], hyperbolic lensed fibers [9], [lo], etc.…”