The size and weight of the pickup head will influence the form factor and the bandwidth of DVD. A MEMS-type DVD pickup was proposed, in which the objective lens will be manipulated with a micro actuator for focusing. A high order diffractive objective lens has been designed specially for meeting the request on reduced weight by optimizing the surface relief profile of each zone one by one. The simulation by ray tracing tool shows a well corrected geometrical aberration and a near diffraction limit focal spot. The lens is expected to be produced with gray scale mask photolithography, and the weight will have only one third of that of its refractive counterpart.
The majority of the beam splitters for three beam tracking in commercial DVD pickup employ lamellar phase gratings, which already provides sufficient efficiency. However, for a pickup with all diffractive elements, the power budget becomes more critical, and a higher efficiency of the beam splitter is required. In this paper, we have investigated and will present the influence of the desired energy ratio between the zeroth order central beam to the first order side beam on the total efficiency of the beam splitter. The simulation based on scalar diffraction theory shows that the total efficiency of a lamellar phase grating will drop as the ratio decrease, which can be improved by employing a more sophisticated surface relief. The equal-side triangular profile has been investigated as a solution and the geometrical size of the profile has been optimized for several desired energy ratio. For a low cost fabrication process with photolithography, the total efficiency loss due to quantization with different quantization levels of the triangular surface relief has been estimated with scalar diffraction theory. This paper is concluded with a table of optimal phase level for a given energy ratio and desired minimum total efficiency with the consideration of fabrication cost.