Tolerance analysis of aligning an astigmatic laser diode with a single-mode optical fiber

A general method of analyzing misalignment tolerance of coupling light from an astigmatic laser diode to a single-mode fiber is described. We apply the method to derive the 3 dB tolerances caused by longitudinal, lateral, and angular misalignments in the optimal conditions for two kinds of coupling schemes. One is by the use of a rotationally symmetric optical system, and the other by a rod which is a special case of utilizing a rotationally asymmetric optical system. In the latter coupling case, the misalignment caused by a laser is found to have a much less 3 dB tolerance in the vertical direction than that caused by a fiber.