Influence Of Optical Disk And Laser Diode Imperfections On 3-D Intensity Distribution Near Focus Of The Memory Pick-Up Objective Lens

The basic functions of the optical memory pick-up are: (1) to focus sufficient light energy for writing, reading or erasure to a spot of roughly 1 pm diameter located on a track of a rotating optical data storage disk, (2) to provide focus and tracking error signals and (3) to provide read signal. Disk tilt, variation of optical thickness of the disk cover layer, laser diode astigmatism and defocusing due to focus servo loop offsets caused by initial misalignment, material thermal expansion, laser diode thermal wavelength drift, age, etc. result in changes of the intensity distribution projected onto the disk surface and affect information spot forming, the amplitude of read signal, or erasure efficiency. The extent to which these imperfections affect the focused beam and consequently, the size of a written spot and the read signal is numerically investigated.