A consideration on a design for optical collimating system using rod lens

Optical circuits with low loss and stable operation are needed for developing optical communications systems with single‐mode optical fibers and laser diodes. The Gaussian beam field is analyzed by means of the beam expansion method and the Hermite generating function when the beam is incident on a rod lens off‐axis and obliquely. The coupling loss of the optical collimating system is obtained both experimentally and theoretically and the optimum design method is found. With rod lenses which have a radius of curvature of 2.5 mm and thickness of 5.5 mm, the insertion loss is as low as 0.4 dB for lens intervals larger than 100 mm. It is also shown that there is an optimum configuration which minimizes the increase in coupling loss when two connecting single‐mode fibers are displaced in opposite directions perpendicular to the optical axis.