Optical performance evaluation results and an interferance fringe pattern analysis of alignment errors for an optical head of a near field recording(NFR) system are presented. The focusing unit is an optical head of a NFR system and is composed of a solid immersion lens and an objective lens. Generally, the size of the focusing unit is smaller than that of the conventional optical recording head. Hence there are difficulties to assemble the small focusing unit precisely. We composed an evaluation system with an interferometer and evaluated some focusing unit samples aligned and assembled by manual and present the obtained results. Using the conventional optical tool, CodeV, a tolerance analysis of the alignment error between the SIL and the objective lens and an interference pattern analysis for the assembly error are executed. Then, through an analysis of the simulation results, the conceptual auto-alignment methodology using a neural network approach is considered.