Increasing semiconductor laser-optical fiber coupling efficiency by introducing microlens

The efficiency of coupling between semiconductor lasers and single-mode optical fibers can be greatly increased by a microlens of an appropriate focal length being fabricated at the end of the fiber. The reason for this is that the lens can effectively improve the mode matching of the laser and fiber fields. Theoretical work has been carried out to predict this improvement of coupling efficiency as a function of the focal length and spot size associated with the laser and fiber. A simple method was then used to fabricate the microlenses whose focal lengths required a radius of curvature ranging from about 10 mm to 15 mm for maximum coupling. The method comprised in tapering of the fiber to the required radius using a grinder and then with an electric arc and heating the end which next forms into a hemisphere due to surface tension forces. Another way is to dip the tapered end into molten optical glass picking up a droplet of glass.