PHASE-SHIFTING APODIZER OF 3 OR MORE PORTIONS

This paper is aimed at the problem of attaining increased recording density in optical disks. One way of achieving this is to decrease the size of the optical disk drive's "beam waist spot" (the narrowest portion of the focused area). The author is presently developing a new type of apodizer structure designed for decreasing the sidelobe intensity and raising the center peak intensity ratio accompanying reduced beam waist spots. The apodizer incorporates a new optical structure and is currently undergoing evaluation. In developing designs for the new apodizer, the author first used algebraic approximate formulas to obtain a general understanding of the relationship between the intensity distribution at the beam waist spot and each of the relevant parameters. Computer simulation was then used to obtain a detailed performance evalution. The evaluation results indicated the following: (1) The beam waist spot's sidelobe intensity can be reduced by using an optimized apodizer consisting of three or more portions; (2) Phase-shifting apodizers serve to increase the center peak intensity ratio.