Magnetic disc unit has optical arrangement for detecting track following information beneath magnetic head emitting laser beam onto recording medium and receiving reflected beam

摘要

The unit has an optical arrangement mounted beneath the magnetic head (34) to emit a laser beam onto the recording medium (20) over a light path in the magnetic head and receive the reflected beam. The optical arrangement has a laser source (21), diffraction grid (23), aperture (3), telecentric objective lens (1), beam divider (27) and light reception element (28). An Independent claim is also included for a method of manufacturing a magnetic disc unit.