One of the problems in the design a magneto-optic read-write head is determining the light level needed at the data detectors. Figure 1 is a schematic of a typical M-O head in which PBS1 and PBS2 are actually leaky beam-splitters that divert from the main optical path (laser to disk and back) some fraction of the p-polarized (unrotated) light. On the outward path this diverted light reduces the efficiency of the head and, especially from the point of view of writing on the disk, the goal would be to minimize this loss. On the return path the light diverted by PBS 1 goes to the servo detectors to provide focus and track-error signals, and that by PBS2 goes to the data detectors.